COLUMBIA LIBRARIES OFFSITE

HEALTH SCIENCES STANDARD

HX64098478
QP40.B831902 Acompendofhumanp

RECAP

UIZCOMPENDS

Physiology

DR. BRU BAKER.

>

Q.
O
O

z
o

<

X

id

Q

z
m

D
X
I-

MORRIS' ANATOMY.

SECOND EDITION.

79 i Illustrations, of which 2*4 are Colored*

Human Anatomy. A Complete Systematic Treatise by Vari-
ous Authors, Including Special Sections on Surgical and
Topographical Anatomy, the Skin, and Vestigial and
Abnormal Structures. Edited by Henry Morris, m.a. and

qp4-n

M.

Pi

b(

in
R
W
ir
i

ft

have i
been t
has de
many
editioi
the t>
partia
r\
of exc
systen
anatc

From
ti

graphic
great c
teachei
mended to all interested.

£#J

/0O£

Columbia Stotomitp

tntteCitpofjRntigutk

College of $jjps;iaan* anb burgeon*
Htbrarp

ex Hos-
; Mem-
Exam-
idition.
ughout.
re Orig-
Octavo.
t, $7.00

iblishers
text has
e editor
1 whole ;
:he first
•s, while
several

:cellence
e text is
00k on

and topo-
ented with
book with
be recom-

From The Philadelphia Medical Journal.

" Of all the text-books of moderate size on human anatomy in the English
language, Morris' is undoubtedly the most up-to-date and accurate. . . .
For the student, the surgeon, or for the general practitioner who
desires to review his anatomy, Morris' is decidedly the book to buy."

A Descriptive Circular of Morris' "Anatomy," with Sample Pages
and Colored Illustrations, will be sent free to any address.

Tyson's Practice of Medicine

SECOND EDITION,
J 27 Illustrations, Several of which are i) Colors,

The Practice of Medicine. A Text-Book for Jhysicians and
Students, with Special Reference to Diagnoss and Treat-
ment. By James Tyson, m.d., Professor of Medicine in
the University of Pennsylvania'; Physician lib the Uni-
versity and to the Philadelphia Hospitals; Ffllow of the
College of Physicians of Philadelphia ; Meriber of the
Association of American Physicians, etc. Second F^ition.
Octavo. 1222 pages. 127 Illustrations.

Cloth, net, $5.50; Sheep, tif/, £6.50

jg^- This, edition has been entirely reset from new type.
The author has revised it carefully and thoroughly, and added
much new material and 37 new illustrations.

From The Therapeutic Gazette.

" From the first to the last of this large volume of nearly 1200 pages we
find much to commend, almost nothing to criticise, and certainly nothing to
contradict.

" It is in the writing and preparation of a work of this character that Dr.
Tyson stands pre-eminent. Those of the profession — and t>~rc are many at
this time — who have been fortunate enough to have been his pupils during
their medical student days, will remember that he brought to his lectures and
to his writings an amount of industry and care which many other teachers
failed to bring ; and those who know him best as an author and teacher have
expected that his book on the Practice of Medicine, when it appeared, would
be a credit to himself and would increase his reputation as a medical author.
This belief has proved correct. . . . We look forward to using this vol-
ume upon the ' Practice of Medicine ' more than any of the others which grace
our library shelves, and they are many and all of them good."

From The North American Practitioner, Chicago.

" The individuality of the writer is clearly manifest in the clear and
practical manner in which diseases are described and their treatment expressed.
. . . The succeeding sections upon Diseases of the Digestive, Respiratory,
Circulatory, and Nervous Systems, together with those of the Blood, Urinary
Organs, Constitutional Diseases, etc., are so full as to well serve, in each
instance, the needs of the specialist, while their grouping in one complete
volume renders it a valuable text-book for students, and the one above any
other now at command most suited to the present needs of the active practi-
tioner. It is the best representative of the practical application of
modern research and discovery to the treatment of diseases now at
the command of the medical profession."

SYBASE' ON RECENT MEDICAL LITERATURE.

QOUid'S The Standard

M/t *• « Medical

iVlCCflCfl.] Reference Books.

Dictionaries.

130,000 HAVE
BEEN SOLD.

BY GEORGE M. GOULD, A.M., M.D.,

Editor of American Medicine.

THE ILLUSTRATED DICTIONARY OF MEDICINE, BI-
OLOGY, AND ALLIED SCIENCES, including the pro-
nunciation, ACCENTUATION, DERIVATION, AND DEFINITION OF THE
TERMS USED IN MEDICINE AND THOSE SCIENCES COLLATERAL TO IT:
BIOj.OGY (ZOOLOGY AND BOTANY), CHEMISTRY, DENTISTRY, PHARMA-
COLOGY, microscopy, etc. With many Useful Tables and numerous
Fine Illustrations. Large Square Octavo. 1 633 pages. Fifth Edition
row ready. Full Sheep," or Half Dark-Green Leather, net, $10.00 ;

With Thumb Index, net, $11.00; Half Russia, Thumb Index, net, $12.00

THE STUDENT'S MEDICAL DICTIONARY, including all

THE WORDS AND PHRASES GENERALLY USED IN MEDICINE, WITH
THEIR PROPER PRONUNCIATION AND DEFINITIONS, BASED ON RECENT

MEDICAL literature. With Tables of the Bacilli, Micrococci, Leuko-
mains, Ptomains, etc., of the Arteries, Muscles, Nerves, Ganglia, and
Plexuses ; Mineral Springs of the U. S., etc. Eleventh Edition,
Illustrated. Revised, Enlarged by over 150 pages. Small Square
Octavo. Half Dark Leather, net, $2.50; with Thumb Index, net, $3.00

( THE POCKET PRONOUNCING MEDICAL LEXICON. 30,000
words pronounced and denned. Containing all the Words, their
Definition and Pronunciation that the Student generally comes in contact
<4 with ; also elaborate Tables of the Arteries, Muscles, Nerves, Bacilli,

etc., etc.; a Dose List in both English and Metric Systems, etc., arranged
in a most convenient form for reference and memorizing. Fourth Edition,
837 pages. 64U10.

Full Limp Leather, Gilt Edges, net, $1.00; Thumb Index, net, $1.25

THE POCKET CYCLOPEDIA OF MEDICINE AND SUR-
GERY. Edited by Drs. George M. Gould and W. L. Pyle. A
Concise Practical Handbook containing a vast amount of Information Sys-
tematically Arranged so as to be of the Greatest Service to the Student.
Uniform with "Gould's Pocket Dictionary." 64mo.

Full Limp Leather, Round Corners, Gilt Edges, net, $1.00

Thumb Index, net, $1.25

Full descriptive circulars and sample pages sent free upon application.

HUMAN PHYSIOLOGY

ELEVENTH EDITION

BRUBAKER

From The Southern Clinic.

" We know of no series of books issued by any house that so fully meets our
approval as these ?Quiz-Compends?. They are well arranged, full, and con-
cise, and are really the best line of text-books that could be found for either
student or practitioner."

BLAKISTON'S ?QUIZ=COMPENDS?

The Best Series of Manuals for the Use of Students.

Price of each, Cloth, $0.80 net. Interleaved, for taking Notes, $1.00 net.

4®=-These Compends are based on the most popular text-books and the lectures of
prominent professors, and are kept constantly revised, so that they may thoroughly repre-
sent the present state of the subjects upon which they treat.

*3-The authors have had large experience as Quiz-Masters and attacnes of colleges,
and are well acquainted with the wants of students. '_ .

*5-They are arranged in the most approved form, thorough and concise, containing
over 600 fine illustrations, inserted wherever they could be used to advantage.

4^»Can be used by students of any college.

Ji&> They contain information nowhere else collected in such a condensed, practical

shape.

Illustrated Circular Free. *<- *

No 1 POTTER'S ANATOMY. Sixth Revised and Enlarged Edition. Including
Visceral Anatomy. Can be used with either Morris' or Gray's Anatomy. _ii7 Illus-
trations and 16 Lithographic Plates of Nerves and Arteries, with Explanatory Tables, etc.

No. 2. HUGHES. PRACTICE OF MEDICINE. Parti. Sixth Edition, Revised,
Enlarged, and Improved.

No 3 HUGHES. PRACTICE OF MEDICINE. Part II. Sixth Edition, Revised,
Enlarged, and Improved. These two books furnish a complete set of notes on the
Practice of Medicine, including Nervous and Mental Diseases.

No. 4. BRUBAKER. PHYSIOLOGY. nth Edition, with new Illustrations and
a Table of Physiological Constants. Enlarged and Revised.

Xo «; LANDIS. OBSTETRICS. Sixth Edition. Revised and Edited by Wm. H
Wells, m.d., Instructor Jefferson Medical College, Philadelphia. 47 Illustrations.

No. 6. POTTER. MATERIA MEDICA, THERAPEUTICS, AND PRESCRIP-
TION WRITING. Sixth Revised Edition.

No 7 WELLS. GYNAECOLOGY. Second Edition. With many Illustrations.

No. 8*. GOULD and PYLE. DISEASES OF THE EYE AND REFRACTION.
Including Treatment and Operations and a Section on Local Therapeutics. With
Formula: and 109 Illustrations, several of which are in Colors. Second Edition.

No Q HORWITZ'S SURGERY, Minor Surgery, and Bandaging. Fifth Edition,
Enlarged and Improved. With 98 Formulae and 167 Illustrations.

No. 10. LEFFMANN. CHEMISTRY. Inorganic and Organic. Fourth Edition.
Including Urinalysis, Animal Chemistry, Chemistry of Milk, Blood, 1 issues, the Se-
cretions, etc. t

No. 11. STEWART. PHARMACY. Fifth Edition. Based upon Prof. Remington s
Text-Book of Pharmacy.

No. 12. BALLOU. VETERINARY ANATOMY AND PHYSIOLOGY. With
29 graphic Illustrations.

No 13 WARREN. DENTAL PATHOLOGY AND DENTAL MEDICINE.
'Third Edition, Illustrated. Containing all the most noteworthy points of interest to
the Dental Student, and a Section on Emergencies.

No. 14. HATFIELD. DISEASES OF CHILDREN. Colored Plate. Third Edi-
tion, Revised and Enlarged.

No 15. THAYER. GENERAL PATHOLOGY. With 78 Illustrations.

No. 16. SCHAMBERG. DISEASES OF THE SKIN. Second Edition. Illus.

No*. 17. CUSHING. HISTOLOGY. With many Illustrations.

No. 18. THAYER. SPECIAL PATHOLOGY. With 34 Illustrations.

Price, each, $0.80 net. Interleaved, for taking Notes, $1.00 net.

P. BLAKISTON'S SON & CO., PUBLISHERS,

PHILADELPHIA.

?QUIZ-COIVlF>ENDS? NO. 4.

A COMPEND

OF

HUMAN PHYSIOLOGY

ESPECIALLY ADAPTED FOR THE USE OF
MEDICAL STUDENTS

BY

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

ADJUNCT PROFESSOR OF PHYSIOLOGY AND HYGIENE IN THE JEFFERSON MEDICAL COL-
LEGE ; PROFESSOR OF PHYSIOLOGY IN THE PENNSYLVANIA COLLEGE OF DENTAL
SURGERY; LECTURER ON ANATOMY AND PHYSIOLOGY IN THE DREXEL '
INSTITUTE OF ART, SCIENCE, AND INDUSTRY ; FELLOW OF
THE COLLEGE OF PHYSICIANS OF PHILADELPHIA.

ELEVENTH EDITION, REVISED AND ENLARGED
WITH ILLUSTRATIONS

AND

A TABLE OF PHYSIOLOGIC CONSTANTS

PHILADELPHIA

P. BLAKISTON'S SON & CO.

1012 WALNUT STREET
1902

Entered according to Act of Congress, in the year 1902, by

P. BLAKISTON'S SON & CO.

In the Office of the Librarian of Congress, at Washington, D. C.

T>£3

PREFACE TO THE ELEVENTH EDITION.

A new edition of the Corapend of Physiology having been called for the
opportunity has again been taken to revise some of the old, and to insert
some new paragraphs to various parts of the text, changes which it is
believed will be of value to the student during his attendance on the
lectures. It is hoped the Compend will continue to meet the needs of
the medical student.

Albert P. Brubaker.

September I, 1902.

TABLE OF CONTENTS.

PAGE,

Introduction, 9

General Structure of the Animal Body, u

Chemic Composition of the Human Body, 15

Physiology of the Cell, S3

Histology Of the Epithelial and Connective Tissues, .... 39

Mechanism of the Skeleton, 46

General Physiology of Muscular Tissue, 50

Special Physiology of Muscles, 63

Physiology of Nerve Tissue, 69

Foods and Dietetics, 86

Digestion, 95

Absorption, in

Blood, 119

Circulation of the Blood, -. 125

Respiration, ' 135

Animal Heat, 143

Secretion, 145

Mammary Glands, 148

Vascular Glands, 150

Excretion, 155

Kidneys, .... 155

Liver, 163

Skin, 168

Cerebro-Spinal Axis, 171

Spinal Cord, 172

Spinal Nerves, .174

vii

vill TABLE OF CONTENTS.

PAGE.

Cranial Nerves, 183

Medulla Oblongata, 197

Pons Varolii, 201

Crura Cerebri, 202

Corpora Quadrigemina, 203

Corpora Striata and Optic Thalami, 204

Cerebellum, . . ...... 205

Cerebrum, 207

Cerebral Localization of Function, 214

Sympathetic Nervous System, 218

Sense of Touch, 222

.Sense of Taste, 223

Sense of Smell, 225

Sense of Sight, 226

Sense of Hearing, . . . 237

Voice and Speech, 245

Embryology, 248

Generative Organs of the Female, 248

Generative Organs of the Male, 251

Development of Accessory Structures, 252

Development of the Embryo, 257

Table of Physiologic Constants, 263

Table Showing Relation of Weights and Measures, 266

Index, .... 267

A COMPEND

OF

HUMAN PHYSIOLOGY.

Introduction. — An animal organism in the living condition exhibits a
series of phenomena which relate to growth, movement, mentality, and
reproduction. During the period preceding birth, as well as during the
period included between birth and adult life, the individual grows in size
and complexity from the introduction and assimilation of material from
without. Throughout its life 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 position in space. 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 work. The result of normal growth is the attainment
of a physical development that will enable the animal, and, more espe-
cially, man, to perform the work necessitated by the nature of its environ-
ment and the character of its organization. In man, and probably in lower
animals as well, mentality manifests itself as intellect, feeling, and volition.
At a definite period in the life of the animal it reproduces itself, in conse-
quence of which the species to which it belongs is perpetuated.

The study of the phenomena of growth, movement, mentality, and re-
production 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, Physi-
ology 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,

10 HUMAN PHYSIOLOGY.

This may naturally be divided into :

1. Special physiology, the object of which is a study of the vital phe-
nomena or functions exhibited by the organs of any individual animal.

2. Comparative physiology, the object of which is a comparison of the
vital phenomena or functions exhibited by the organs of two or more
animals, with a view to unfolding their points of resemblance or dissimi-
larity.

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 with 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 familiar structures just mentioned, it is equally applicable 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 or-
ganized structure 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 rela-
tions 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 con-
struction 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, with a view to determining their points
of resemblance or dissimilarity.

If the organs, however, are 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

GENERAL STRUCTURE OF THE ANIMAL BODY. 11

simpler elements, termed cells and fibers. The investigation of the in-
ternal 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, constitutes a department of anatomic science known as His-
tology, 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 body.

GENERAL STRUCTURE OF THE ANIMAL BODY.

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

1. An axial and

2. An appendicular portion. The axial portion consists of the bead, neck,
and trunk ; the appendicular portion consists of the anterior and pos-
terior limbs or extremities.

The axial portion of all mammals, to which class man zoologically be-
longs, as well as of all birds, reptiles, amphibians, and fish, is character-
ized by the presence of a bony, segmented axis, which extends in a longi-
tudinal 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, the Vertebrata.

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

1. A solid 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 vertebne 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.

12

HUMAN PHYSIOLOGY.

Fig.

—Diagrammatic Longitudinal
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,/'. The ab-
"* dominal and thoracic divisions of the ven-
tral cavity, separated from each other by
a transverse muscular partition, the dia-
phragm 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 posterior portion
of the body. /. The liver. /. The pan-
creas, k. The kidney, o. The bladder.
/'. The lungs, h. The heart.

The dorsal cavity is found
not only in the trunk, but also in
the head. It walls are formed
partly by the arches which arise
from the posterior or dorsal sur-
face of the vertebrae and partly
by the bones of the skull. If a
longitudinal section be made
through the center of the verte-
bral column, and including the
head, the dorsal cavity will be
observed running through its
entire extent. (See Fig. i.)
Though for the most part it is
quite narrow, at the anterior ex-
tremity it is enlarged and forms
the cavity of the skull. This
cavity is lined by a membranous
canal, the neural canal, in which
is contained the brain and the
neural or spinal cord. Through
openings in the sides of the dor-
sal cavity nerves pass out which
connect the brain and spinal cord
with all the structures of the
body.

The ventral cavity is con-
fined 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 contained a rnus-
culo-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

GENERAL STRUCTURE OF THE ANIMAL BODY. 13

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 alimentary canal — that is, the stomach and intestines —
and the glands in connection with it, the liver and pancreas. In the pos-
terior portion of the abdominal cavity are found the kidneys, ureters, and
bladder, and in the female the organs of reproduction. The thoracic and
abdominal cavities are each lined by a thin serous membrane, known, re-
spectively, as the pleural and peritoneal membranes, which, in addition, are
reflected over the surfaces of the organs contained within them. The ali-
mentary canal and the various cavities connected with it are lined throughout
by a mucous membrane. The surface of the body is covered by the skin.
This is composed of an inner portion, the derma, and an outer portion, the
epidermis. 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 sym-
metric limbs, which project from the sides of the trunk, and which bear a
determinate relation to the vertebral column. They consist 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
peculiarities of structure in common are classified by anatomists into systems
— e. g., the bones, collectively, constitute the bony or osseous system ; the
muscles, the nerves, the skin, constitute, respectively, the muscular, the
nervous, 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 applied. While in the community of organs which

f

14 HUMAN PHYSIOLOGY.

together constitute the animal body each one performs some definite func-
tion, and the harmonious cooperation of all is necessary to the life of the
individual, everywhere it is found that two or more organs, though per-
forming totally distinct 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 func-
tion of which is the complete digestion of the food. The capillary blood-
vessels and lymphatic vessels of the body, and especially 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 constitute the circulatory apparatus, the function
of which is the distribution of blood to all portions of the body. The
lungs and trachea, together with the diaphragm and the walls of the chest,
constitute the respiratory apparatus, the function of which is the introduc-
tion of oxygen into the blood and the elimination from it of carbon dioxid
and other injurious products. The kidneys, the ureters, and the bladder con-
stitute 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 indi-
. vidual. 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 functions, 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 func-
tion of which, as a whole, is the reception of impressions and the trans-
mission 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 apparatus
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 apparatus, by means of which voice
and articulate speech are produced. The functions exhibited by the
apparatus just mentioned — viz., motion, sensation, language, mental and

CHEMIC COMPOSITION OF THE HUMAN BODY. 15

moral manifestations — are classified as Junctions 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 for-
mer producing the germ-cell, the latter the spermatic 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 reproduc-
tive apparatus characteristic of the two sexes. Their cooperation results in
the union of the germ-cell and spermatic element and the consequent de-
velopment of a new being. The function of reproduction serves to per-
petuate the species to which the individual belongs.

The animal body is therefore not a homogeneous organism, but one com-
posed of a large number of widely dissimilar but related organs. But as
all vertebrate animals have the same general plan of organization, there is
a marked similarity both in form and structure among corresponding parts
of different animals. Hence it is that in the study of human anatomy a
knowledge of the form, construction, and arrangement of the organs in
different types of animal life is essential to its correct interpretation ; also
it is that in the investigation and comprehension of the complex problems
of human physiology a knowledge of the functions 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 complex, but
the organs exhibiting them are practically inaccessible to investigation, we
must supplement our knowledge and judge of their functions by analogy,
by attributing to them, within certain limits, the functions revealed by ex-
perimentation upon the corresponding but simpler organs of lower animals.
This experimental knowledge, corrected by a study of the clinical phe-
nomena of disease and the results of post-mortem investigations, forms the
basis of modern human physiology.

CHEMIC COMPOSITION OF THE HUMAN

BODY.

Since it has been demonstrated that everv_exhihition_of functional activ-
ity 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 determina-

16 HUMAN PHYSIOLOGY.

tion of the successive changes in composition of the living 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 living bioplasm undergoes during functional activity.

A chemic analysis of the dead body, with a view to disclosing the sub-
stances 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 material and of the successive
changes it undergoes in the performance of its functions constitutes what
has been termed Chemic Physiology 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. That 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 carbo-
hydrate, fatty, and proteid groups of organic bodies ; the inorganic com-
pounds 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 elements which are thus
obtained, and the percentage in which they exist in the body, are as
follows— viz., oxygen, 72 per cent.; hydrogen, 9.10 ;»nitrogen, 2.5 ; carbon,
I3-5°» phosphorus, 1.15; calcium, 1.30; sulphur, o. 147 ; sodium, o. 10;
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, consisting
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 appro-
priate means are readily converted into one another. In composition

CHEMIC COMPOSITION OF THE HUMAN BODY. 17

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 proportion to form water, or as 2 : I. JThe molecule of
the carbohydrates 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) Amy-
loses, including starch, dextrin, glycogen, and cellulose; (2) dextroses,
including dextrose, levulose, galactose; (3) saccharoses, including saccha-
rose, lactose, and maltose. According to the number of carbon atoms
entering into the second group (six), they are frequently termed mono-
saccharids ; 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 con-
stituents 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.

1. AMYLOSES, (C6H10OB)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
some 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 light and dark. The
granule consists of an envelope and stroma of cellulose, containing in its
meshes the true starch material — granulose. Starch is insoluble in cold
water and alcohol. When heated with water up to 700 C, the granules
swell, rupture, and liberate the granulose, which forms an apparent solu-
tion ; if present in sufficient quantity, it forms a gelatinous mass termed
starch paste. On the addition of iodin, starch strikes a characteristic deep
blue color ; the compound formed — iodid of starch — is weak, and the color
disappears on heating, but reappears on cooling.

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

Dextrin is a substance formed as an intermediate product in the trans-
formation of starch into sugar. There are at least two principal varieties —
erythrodextrin, which strikes a red color with iodin, and achro'odextrin,

18 HUMAN PHYSIOLOGY.

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
animal ferments erythrodextrin 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 espe-
cially 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 (maltose).

Cellulose is the basis material of the more or less solid framework of
plants. It is soluble only in an 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, C6H1206.

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 crystallizes 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 ;
less so, however, than cane sugar. It is dextro-rotatory, turning the plane
of polarized light to the right. In alkaline solutions dextrose absorbs
oxygen, and hence in the presence of metallic salts, copper, bismuth,
silver, etc., it acts as a reducing agent. On this property the various tests
for dextrose, as well as other sugars which have the same property, are
based.

Fehling's Test. — The solution usually employed for both qualitative and
quantitative purposes is a solution of cupric hydroxid made alkaline by an
excess of sodium or potassium hydroxid, with the addition of sodium and
potassium tartrate. This solution, originally suggested by Fehling, bears
his name. It is made by dissolving cupric sulphate 34.64 grams, potas-
sium hydroxid 125 grams, sodium and potassium tartrate 1 73 grams in
I liter of distilled water.

The reaction is expressed by the following equation :

CuSOi + 2KOH = Cu(OH)2 + K2S04.

CHEMIC COMPOSITION OF THE HUMAN BODY. 19

The object of the sodium and potassium tartrate is to hold the Cu(OH)2
in solution. If a few cubic centimeters of this deep blue solution be
boiled and dextrose then added and the solution again heated to the boil-
ing-point, the cupric hydroxid is reduced to the condition of a cuprous oxid,
which 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 delicacy of this
test is shown by the fact that a few minims of this solution will detect in
one c.c. of water the y1^ of a milligram of sugar.

For quantitative analysis, ten c.c. of Fehling's solution, diluted with
forty c.c. of water, are heated in a porcelain capsule, to which the dextrose
solution is cautiously added from a buret until the blue color entirely
disappears. The strength of this solution is such that one c.c. is decolor-
ized by five milligrams of sugar, from which the percentage of sugar in
any solution can be determined.

Fermentation Test. — If to a solution of dextrose a small quantity of the
yeast plant be added, and the solution kept at a temperature of 250 C, it
will gradually undergo fermentation ; that is, will be reduced to simpler
compounds and especially to alcohol and carbon dioxid. The change
expressed in the following equation :

C6H1206 = 2C2H60 + 2C02

Dextrose. Alcohol. Carbon

Dioxid.

About ninety-five per cent, of the dextrose is so changed, the remaining
five per cent, yielding secondary products — succinic acid, glycerin, etc.

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 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, how-
ever, varies with the temperature and concentration of the solution.

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

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

20 HUMAN PHYSIOLOGY.

3. SACCHAROSES, CxaHnOxa.

Saccharose, or cane-sugar, is widely distributed throughout the vege-
table world, but is especially abundant in sugar-cane, sorghum 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 oxid, and hence its presence can not be detected by Fehling's
solution. It is dextro-rotatory. Boiled with dilute mineral, as well as
organic acids, saccharose combines with water, and undergoes some change
in virtue of which it rotates the plane of polarized light to the left, and hence
the product is 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 by the follow-
ing equation :

C12H22011 + H20 = C6H1206 + C6H1206
Saccharose. Water. Levulose. 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 undergoes inversion, as pre-
viously 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 mam-
malia, 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, insol-
uble in alcohol and ether. It is dextro-rotatory. It reduces cupric oxid,
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 lactic acid bacillus it is decomposed into
lactic acid, and finally into butyric acid, as follows :
C12H22Ou + H20=4C3H603

Lactose. Water. Lactic Acid.

2C,H603 = C4H802 + 2C02 -f 2H2

Lactic Acid. Butyric Acid. Carbon Free

Dioxid. Hydrogen.

Maltose is a transformation product of starch, and arises whenever the
latter is acted on by malt extract or the diastatic ferments in saliva and
pancreatic juice. It can also be produced by the action of dilute sulphuric
acid on starch. The change is expressed by the following equation :

2C6H10O6-f H20 = C12H22On

Starch. Water. Maltose.

CHEMIC COMPOSITION OF THE HUMAN BODY. 21

Maltose crystallizes 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 hydration and decomposition,
giving rise to two molecules of dextrose. It has a reducing action on
cupric oxid. 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
oxid 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 solubility
and optic properties, all of which serve to detect the various sugars and
to distinguish one from the other. Of the different osazones, phenyl -gluco-
sazone is the most characteristic, and occurs in the form of long, yellow
needles. It may be obtained from dextrose by the following method : To
fifty c.c. of a dextrose solution add two gm. of phenyl-hydrazin and two
gm. of sodium acetate, and boil for an hour. On cooling, the osazone
crystallizes 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 after death it soon solidifies from the loss of heat.

The fats are compounds consisting of carbon, hydrogen, and oxygen, of
which the first is the chief ingredient, forming by weight about seventy-five
per cent., while the last is present only in small quantity. The fat, as
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 :

C3H5(HO)3 + (HC18H3502)3 = C3H5(C18H3502)3 + 3H20.
Glycerin. Stearic Acid. Stearin, Water,

22 HUMAN PHYSIOLOGY.

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, C3H5(C18H3502)3, is the chief constituent of the more solid
fats. It is solid at ordinary temperatures, melting at 55 ° C, then solidify-
ing again as the temperature rises, until at Jl° C. it melts permanently.
It crystallizes in square tables.

Palmitin, C3H5(C16H3102)3, is a semifluid fat, solid at 450 C. and melt-
ing at 620 C. It crystallizes in fine needles, and is soluble in ether.

Olein, C3H5(C]8H3302)3, is a colorless, transparent fluid, liquid at ordi-
nary temperatures, only solidifying at o° 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 — i. e., decomposed into glycerin and the particu-
lar acid indicated by the name of the fat used : e. g., stearic, palmitic, or
oleic. The reaction is expressed as follows :

C3H5(C18H3302)3 + 3H20 = C3H5( HO)3 + 3( C18H3,Oa)

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 690 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 620 C.

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

If this saponification take place in the presence of an alkali, — e. g.,
potassium hydroxid, 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 + (C18H3402)3 - 3(KC18HSS02) + C3H5(HO)3

Potassium. Oleic Acid. Potassium Oleate. Glycerin.

All soaps are, therefore, salts formed by the union of alkalies and fatty
acids. The sodium soaps are generally hard, while the potassium 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.

CHEMIC COMPOSITION OF THE HUMAN BODY. 23

Emulcification. — 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
liquid. The most permanent emulsions are those made with soap solu-
tions. The process of emulsiflcation and the part played by soap, can be
readily observed by placing on a few cubic centimeters of a solution of
sodium carbonate o. 25 per cent, of a small quantity of a perfectly neutral
oil to which has been added 2 or 3 per cent, of a fatty acid. The combi-
nation 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, CwH90N.PO9, is found in blood, lymph, red and white cor-
puscles, nerve tissue, yolk of eggs, etc. When pure, it presents itself
generally under the form of a white, crystalline powder, though some-
times as a white, waxy mass. Lecithin is easily decomposed, yielding,
with various reagents, glycero-phosphoric acid, cholin and stearic acid.

Protagon, C1G0H308N5PO35, is found most abundantly in the brain tissue,
especially in the white portion. It crystallizes from warm alcoholic solu-
tions, on cooling, in the form of white needles, generally arranged in groups.
It melts at 2000 C, and forms a syrupy liquid.

Cerebrin, C17H33N.03, is found largely in the brain, in nerves, and in
pus-corpuscles. It is a soft, white, amorphous powder, insoluble in water,
but swelling up like starch in boiling water. When boiled with dilute
acids, it is decomposed, yielding a fermentable dextro-rotatory sugar, iden-
tical 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 bones, where they constitute
twenty per cent, and thirty per cent, respectively. Though genetically re-
lated, and possessing many features in common, the different members of
the proteid group are distinguished by characteristic physical and chemic
properties.

24 HUMAN PHYSIOLOGY.

The average percentage composition of several proteids is shown in the
following analyses :

C. H. N. O. S.

Egg-albumin, . 52.9 7.2 15. 6 23.9 0.4 ( Wurtz).

Serum-albumin, 53.0 6.8 16.0 22.29 1-77 (Hammersten).

Casein,. . . .53.3 7.07 15.91 22.03 0.82 (Chittenden and Painter).

Myosin, . . .52.82 7. II 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 C72HU2N18022S, while Schutzen-
berger raises the numbers to C240H392N65O75S3, 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 diffusing through parchment or
an animal membrane. Peptone, a product of the digestion of proteids, is
an exception as regards its diffusibility. 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 sepa-
ration and purification from crystalloid diffusible compounds oy the proc-
ess of dialysis.

2. Solubility. — Some of the proteids are soluble in water, others in solu-
tions of the neutral salts of varying degrees of concentration, 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 solid 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 tempera-
tures, but with different chemic reagents — distinctive features which
permit not only of their detection, but separation. Proteids are capable
of precipitation without losing their solubility by ammonium sulphate,
sodium chlorid and magnesium sulphate.

4. Fermentability. — In the presence of specific microorganisms — bac-
teria— the proteids, owing to their complexity and instability, 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— Mz. , a temperature
varying from 250 C. to 4QP C, moisture and oxygen. The intermediate

CHEMIC COMPOSITION OF THE HUMAN BODY. 25

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 ingestion of foods in various stages of putre-
faction 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 solution,
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 pro-
teid turns a purple -red color.

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

The proteids found in the animal body, though possessing many features
in common, are nevertheless characterized by certain special features
which not only serve for their identification, but for their classification into
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 magnesium 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 am-
monium 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 730 C, as well as
by various acids — e. g., citric, picric, nitric, etc. It has a rotatory
power of — 62. 6°.
3

26 HUMAN PHYSIOLOGY.

(£) Egg -albumin. — Though not a constituent of the human body,
egg- albumin resembles the foregoing in many respects. When ob-
tained 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 540 C. , and
in having a lower rotatory power, — 35 .5°.

2. GLOBULINS.

The rhembers of this group are insoluble in water and in saturated solu-
tions of sodium chlorid and magnesium sulphate and ammonium sulphate.
They are soluble, however, in dilute saline solutions — e. g., sodium chlorid
(one 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, solu-
ble in dilute acids and alkalies, and coagulating at 750 C.
(3) Fibrinogen. — This proteid is found in blood plasma in association
with serum-globulin 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 previously treated with
magnesium sulphate on the addition of a saturated solution of sodium
chlorid. It is soluble in dilute acids and alkalies, 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 i-eadily 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 560 C.
(</) 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.
(<?) Crystallin or Globulin. — This is obtained by passing a stream
of CO.; 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
globulins by the gradual action of dilute acids and alkalies, and may be
regarded as compounds of a proteid with an acid or an alkali.

CHEMIC COMPOSITION OF THE HUMAN BODY. 27

(a) Acid-albumin. — This is formed when a native albumin is
digested with dilute hydrochloric acid (0.2 per cent.) or dilute sul-
phuric acid for some minutes. It is precipitated by neutralization
with sodium hydroxid (0. 1 per cent, solution). After the precipi-
tate 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.

(6) Alkali-albumin. — This is formed when a native albumin is treated
with a dilute alkali — e. g., 0. 1 per cent, of sodium hydroxid — for
five or ten minutes. On careful neutralization with dilute hydro-
chloric acid, it is precipitated. It is also insoluble in distilled water
and in alkaline solutions ; it is not coagulable by heat.

(<r) Caseinogen. — This is the principal proteid of milk, in which it ex-
ists 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 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 relation to prepared
foods and to the digestive process. They are produced when solutions of
egg-albumin, serum-albumin, or globulins are subjected to a temperature of
1000 C. or to the prolonged action of alcohol. They are insoluble in water,
in dilute acids, and in neutral saline solutions. In this same group may be
included also those coagulated proteid's which are produced by the action
of animal ferments on soluble proteids - <?. 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 cir-
cumstances in the circulating blood, but makes its appearance after
the blood is withdrawn from the vessels and at the time of coagu-
lation. It can also be obtained by whipping the blood with a
bundle of twigs, on which it accumulates. 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

28 HUMAN PHYSIOLOGY.

converted into acid-albumin. In dilute alkalies a similar change takes
place, but the resulting product is an alkali-albumin. Fibrin possesses
the property of decomposing hydrogen dioxid, H202 — i. <?., liberat-
ing oxygen, which accumulates in the form of bubbles on the fibrin.
On incineration fibrin yields an ash which contains calcium phos-
phate 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 sub-
stances 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 differing 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 decomposed yield products similar to those
of the true proteids. The principal members of this group are as follows :

(«) 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 connective tissue
and in bone. When the tendons of muscles, the ligaments, or de-
calcified bone are boiled for several hours, the collagen and ossein
are converted into soluble gelatin, which, when the solution cools,
becomes solid.

(c) Chondrinigen. — 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.

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

(<?) 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.

CHEMIC COMPOSITION OF THE HUMAN BODY. 29

{/) Nuclein. — This is an amorphous substance obtained from the
nuclei of both animal and vegetable cells. The chief constituent
appears to be nucleic acid. Chemic analysis shows that nuclein
contains not less than three per cent, of phosphorus. On boiling
with strong alkalies, nuclein is partially decomposed, yielding a
proteid resembling globulin and phosphoric acid. A nucleo-
proteid is a compound of nuclein and a proteid.

INORGANIC CONSTITUENTS.

The inorganic compounds and mineral constituents obtained from the
solids and fluids of the body are very numerous, and, in some instances,
quite abundant. Though many of trie compounds thus obtained are un-
doubtedly 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 com-
pounds, the following are the most important :

WATER.

Water is the most important of the inorganic constituents, as it is indis-
pensable to life. It is present in all the tissues and fluids without exception,
varying from 99 per cent, in the saliva 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 mate-
rials 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 trans-
fers waste products from the tissues to the blood, from which they are
finally eliminated, along with the water in which they are dissolved. A
portion of the water is chemically combined with other tissue constituents,
and gives to the tissues their characteristic physical properties. The con-
sistency, elasticity, and pliability are, to a large extent, conditioned by the
amount of water they contain. The total quantity of water eliminated by
the kidneys, lungs, and skin amounts to about three kilograms (6}4
pounds).

30 HUMAN PHYSIOLOGY.

CALCIUM COMPOUNDS.

Calcium phosphate, Ca3(P04)2, has a very extensive distribution
throughout the body. It exists largely in the bones, teeth, and to a slight
extent in cartilage, blood, and other tissues. Milk contains 0.27 per cent.
The solidity 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 by the acid
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 eliminated 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, CaC03, 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 insolable, it is
held in solution by the carbonic acid diffused through the fluids.

Calcium fiuorid, 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,
o. 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 deter-
mines 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, increasing
the disintegration of the proteids, as shown by the increased amount of
urea excreted. During its existence in the body it undergoes some chemic

CHEMIC COMPOSITION OF THE HUMAN BODY. 31

transformations or decompositions, yielding its chlorid to form potassium
chlorid of the blood-corpuscles and muscles and to form the hydrochloric
acid of the gastric juice.

Sodium phosphate, Na2IIP04, is found in all solids and fluids of the
body, to which, with but few exceptions, it imparts an alkaline 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 alkaline medium.

Sodium carbonate, Na2C03, is generally found in association with the
preceding salt. As it is also an alkaline compound, it assists in giving to
the blood and lymph their characteristic alkalinity. In carnivorous ani-
mals the sodium phosphate is the more abundant, while in the herbivorous
animals the reverse is true.

Sodium sulphate, Na2S04, is present in many of the tissues and fluids,
especially the urine. Though introduced in the food, it is also, in all
probability, formed in the body from the decomposition and oxidation of
the proteids.

POTASSIUM COMPOUNDS.

Potassium chlorid, KC1, is met with in association with sodium chlorid
in almost all situations in the body. It preponderates, however, in the
tissue elements, especially in the muscle tissue, nerve tissue, and red cor-
puscles. The plasma with which these structures are bathed contains but
a very small amount of this salt, but, as previously stated, a relatively large
quantity 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, K2HP04, is found in association with sodium
phosphate in all the fluids and solids. As it has similar chemic properties,
its functions are practically the same.

Potassium carbonate, K2C03, is generally found with the preceding
salt.

MAGNESIUM COMPOUNDS.

Magnesium phosphate, Mg3(P04)2, is found in all tissues, in associa-
tion with calcium phosphate, though in much smaller quantity.

Magnesium carbonate, MgC03, occurs only in traces in the blood.
Both of these compounds have functions similar to the calcium com-
pounds, and exist, in all probability, under similar conditions.

32 HUMAN PHYSIOLOGY.

IRON COMPOUNDS.

Iron is a constituent of the coloring matter of the blood. Traces, how-
ever, 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
seventy-five kilograms is about three gm. It exists under various forms —
e. g., ferric oxid, ferrous oxid, and in combination with organic com-
pounds.

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 characteristic proportions,
to form compounds whose properties are the resultant of those of the ele-
ments. Of the four principal elements which make up ninety-seven 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 chemic inertia. C possesses the great atomic co-
hesion. 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 fol-
lows that the ternary compounds, starches, sugars, and fats must possess
more or less inertia, and at the same time instability ; while in the more
complex proteids, in which sulphur and phosphorus are frequently com-
bined with the four principal elements, molecular instability 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 un-
ceasingly 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., carbo-
hydrates, 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, pro-
pionic, 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. Crystal lizable nitrogenized bodies, such as urea, uric acid, xanthin, hip-
puric acid, creatin, creatinin, etc.

PHYSIOLOGY OF THE CELL. 33

While some few of these compounds may possibly be regarded as neces-
sary 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 body.

PHYSIOLOGY OF THE CELL.

A microscopic analysis of the tissues shows 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
line 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 g^Vo °f an mcn» the diameter of a red
blood- corpuscle, to ^jjo °^ an mcn> 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 entirely different character — e. g., small globules
of fat, granules of glycogen, mucigen, pigments, digestive ferments, etc.

34

HUMAN PHYSIOLOGY.

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.
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 protoplasm undergoes chemic changes and is
transformed into a thin, transparent, homogeneous membrane, — the cell
membrane, — which completely incloses the cell substance. The cell mem-

Nuclear mem-
brane.

Linin.

Nuclear fluid
(matrix).

Nucleolus.

Chromatin

cords (nuclear

network ) .

Nodal enlarge-
ments of the
chromatin.

Cell membrane.
Exoplasm.

Microsomes.
Centrosome

Spongioplasm.
Hyaloplasm.

Foreign inclo-
sures.

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

brane 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 protoplasm near
the center of the cell. In the resting condition of the cell it consists of a
distinct membrane, composed of amphipyrenin^ inclosing the nuclear con-
tents. 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

PHYSIOLOGY OF THE CELL. 35

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 are composed of granules of chromatin, — so called because of its
affinity for certain staining materials, — held together by an achromatin sub-
stance known as linin. Besides the nuclear network, there are embedded
in the nuclear matrix one or more small bodies composed of py renin ,
known as nucleoli. At the pole of the nucleus, either within or just
without in the protoplasm, is a small body, the centrosome, or pole corpuscle.
Chemic Composition of the Cell. — The composition of living pro-
toplasm is difficult of determination, for the reason that all chemic and
physical methods employed for its analysis destroy its vitality, and the prod-
ucts obtained are peculiar 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 con-
stituents or cleavage or disintegration products. Nevertheless, chemic in-
vestigations 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 seventy-five per cent, of protoplasm consists
of water and twenty-five per cent, of solids, of which the more important
compounds are various nucleo-proteids (characterized by their large per-
centage of phosphorus), globulins, traces of lecithin, cholesterin, and fre-
quently 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 repro-
duced 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 pos-
sesses 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 anabolism, 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 assimilative processes, a
series of disintegrative processes is constantly taking place, whereby the
living material is reduced, through a series of downward chemic changes, to

36 HUMAN PHYSIOLOGY.

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 dis-
similative, are embraced under the general term nutrition, or 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 living protoplasm pos-
sesses properties which serve to distinguish and characterize it — viz., irrita-
bility, conductivity, and motility.

Irritability, or the power of reacting in a definite manner to some form
of external excitation, whether mechanical, chemic, or electric, is a funda-
mental 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 will be a contraction ; if it be gland, the response will be secre-
tion ; 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 aris-
ing at one point to all portions of the irritable material, is also a character-
istic 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 periphery to the
brain, as well as in the reverse direction. Muscle protoplasm also pos-
sesses 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 molec-
ular 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 waving of cilia, the ameboid movements and migrations of
white blood -corpuscles, the activities of spermatozooids, the projections of
pseudopodia, etc. These movements, arising without any recognizable
cause, are frequently spoken of as spontaneous. Strictly speaking, how-
ever, all protoplasmic movement is the resultant of natural causes, the true
nature of which is beyond the reach of present methods of investigation.

Reproduction. — Cells reproduce themselves in the higher animals in
two ways — by direct division and by indirect division, or karyokinesis. In

THYSIOLOGY OF THE CELL.

37

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 divi-
sion by karyokinesis (Fig. 3) there is a progressive rearranging and
definite grouping of the nucleus, the result of which changes is the division
of the centrosome, the chromatin, and the rest of the nucleus into two
equal portions, which form the nuclei. Following the division of the nuclei,
the protoplasm divides. The process may be divided into three phases :

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

Loose Skein (viewed

from above — i. e., from

the pole).

Mother Stars (viewed from the side).

Mother Star (viewed Daughter Star. Beginning. Completed,

from above). Division of the Protoplasm.

Fig. 3. — Karyokinetic Figures Observed in the Epithelium of the Oral
Cavity of a Salamander.

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 develop-
ment of the spindle can be seen by this magnification. X 560-

Prophase. — The centrosoma, at first small and lying within the nucleus,
increases in size and moves into the protoplasm, where it lies near the
nucleus, surrounded by a clear zone, from which 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

38 HUMAN PHYSIOLOGY.

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 seg-
ments or loops, chromosomes, having their closed ends directed toward
a common center, the polar field, while the other ends interdigitate on the
opposite side of the nucleus — the anti-pole. The polar field corre-
sponds to the area occupied 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 cone, the apices of which correspond in position
to the centrosoma. This is known as the nuclear spindle. During the
prophase the nuclear membrane and the nucleoli disappear.

2. The Metaphase. — The two centrosomata 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 lie 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 earlier, 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 chromosomes. This separation of the daughter chromosomes,
and their movement toward the daughter centrosomata, is called meta-
kinesis. 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, disap-
pears, 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

HISTOLOGY OF THE EPITHELIAL AND CONNECTIVE TISSUES. 39

deepens until the original cell is divided, with the formation of two com-
plete cells.

HISTOLOGY OF THE EPITHELIAL AND
CONNECTIVE TISSUES.

i. EPITHELIAL TISSUE.

The epithelial tissue consists of one or more layers of cells resting
on a homogeneous membrane, the other side of which is abundantly sup-
plied with blood-vessels and nerves. The form of the epithelial cell varies
in different situations, and may be flattened, cuboid, spheroid, or columnar.
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 — mucin.

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 lines the entire alimentary canal and its associ-
ated body cavities) are both formed, in all situations, by the homogeneous
basement membrane, covered with one or more layers of cells. All ma-
terials, therefore, whether nutritive, secretory, or excretory, 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 (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 consistency of epithe-
lium 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 alimentary canal, in the lungs, and in other cavi-
ties, 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 cooperate with other mechanisms
in maintaining the normal temperature. The physiologic activity of all
epithelial tissue depends on a due supply of nutritive material derived from

40 HUMAN PHYSIOLOGY.

the blood, which not only maintains its own 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 epithelial tissues are :

i . To serve on the surface of the body as a protective covering to the under-
lying structures v which collectively form the true skin, thus protecting
them from the injurious influences of moisture, air, dust, microorgan-
isms, etc. , which would otherwise impair their vitality. Wherever con-
tinuous pressure is applied 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 influences
of acids, alkalies, and poisons.

2. To promote absorption. Inasmuch as the skin and mucous membranes
cover the surfaces of the body, it is obvious that all nutritive material
entering the body must first traverse the epithelial tissue. Owing to their
density, however, the epithelial 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 epithelium lining 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 connected
with the surfaces of the body is lined by epithelial cells, which are
actively concerned in the formation of the secretion peculiar to the gland.
Each excretory organ is similarly provided with epithelial 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 frame-
work 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

HISTOLOGY OF THE EPITHELIAL AND CONNECTIVE TISSUES. 41

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 diver-
sity, they possess many points of similarity. They have a common origin,
developing from the same embryonic material ; they have much the same
structure, 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 membrane to the struc-
tures on which they rest ; to fomi sheaths for the support of blood-vessels,
nerves, and lymphatics ; to unite into compact masses the muscular tissue
of the body, etc. Examined with the naked eye, it presents the appear-
ance 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 intercom-
municating 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 cor-
puscles, connective- tissue corpuscles, plasma cells, and granule cells.

Adipose Tissue. — This tissue, which exists very generally throughout
the body, though found most abundantly beneath the skin, around the kid-
neys, 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. Microscopic examination shows that these masses consist of small
vesicles or cells, round, oval, or polyhedral in shape, depending somewhat
on pressure. Each vesicle consists of a thin, colorless, protoplasmic mem-
brane, thickened at one point, in which a nucleus can usually be detected.
This membrane incloses a globule of fat, which during life is in the liquid
state. It is composed of olein, stearin, and palmitin. The origin of the
4

42 HUMAN PHYSIOLOGY.

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 drops 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 transference 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 membranes 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, homo-
geneous fibers, which pursue an independent course, neither branching nor
uniting with adjoining fibers. A small amount of ground substance serves
to hold them together. Fibrous tissue is tough and inextensible, and in
consequence is admirably adapted to fulfil various mechanical functions in
the body. It is, however, quite pliant, bending easily in all directions.
When boiled, fibrous tissue yields gelatin, a derivative of collagen.

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 nuchoe, 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 adjoin-
ing branches to form a more or less close network. As the name implies,

HISTOLOGY OF THE EPITHELIAL AND CONNECTIVE TISSUES. 43

these fibers are highly elastic, and are capable of being extended as much
as sixty per cent, before breaking.

Cartilaginous Tissue. — This form of connective tissue differs from the
preceding varieties chiefly in its density. As a rule, it is 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 solid ground substance. According to the amount and tex-
ture of the ground substance, three principal varieties may be distinguished :

1 . Hyaline cartilage, in which the cells, relatively few in number, are em-
bedded in an abundant quantity of ground substance. The body of the
cells is in many instances distinctly marked off from the surrounding sub-
stance by concentric lines or fibers, which form a capsule for the cell.
Repeated division of the cell substance takes place, until the whole
capsule is completely occupied by daughter cells. The ground sub-
stance 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 surrounding the cartilage. By means of these chan-
nels, nutritive fluid can permeate the entire structure. Hyaline cartilage
is found on the ends of the long bones, where it enters into the forma-
tion of the joints ; between the ribs and sternum, forming the costal
cartilage, as well as in the nose and larynx.

2. White fibro-cartilage, the ground substance of which is pervaded by
white fibers, arranged in bundles or layers, between which are scattered
the usual encapsulated cells. White fibro-cartilage is tough, resistant,
but flexible, and is found in joints where strength and fixedness are re-
quired. Hence it is present between the vertebrae, forming the inter-
vertebral 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.

3. Yellow fibro-cartilage, 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 corpuscles. ' As these fibers are elastic, they impart to the car-
tilage a very considerable degree of elasticity. Yellow fibro-cartilage is
well adapted, therefore, for entering into the formation of the external
ear, epiglottis, Eustachian tube, etc. — structures which require for their
functional activity a certain degree of flexibility and elasticity.

44 HUMAN PHYSIOLOGY.

Osseous Tissue. — Osseous tissue, 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 car-
bonate are the most abundant. Immersed in dilute solutions of hydro-
chloric acid, they can be converted into soluble salts and dissolved out.
The osseous matrix left behind is soft and pliable. When boiled, it yields
gelatin.

A thin, transverse section of a decalcified bone, when examined micro-
scopically, reveals a number of small, round or oval openings, which repre-
sent transverse sections of canals which run through the bone, for the
most part in a longitudinal direction, though frequently anastomosing
with one another. These so-called Haversian canals in the living state
contain blood-vessels and lymphatics.

Around each Haversian canal is a series of concentric laminae, composed
of white fibers. Between every two laminae are found small cavities
(lacunae), 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 intercommuni-
cating passages, through which lymph circulates destined for the nourish-
ment of bone. Each lacuna contains the bone corpuscle, which bears
a close resemblance to the 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 recent state is invested with a fibrous
membrane, the periosteum, except where it is covered with 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 concerned 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, resembling 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 abundance 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 can-
cellated 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 osteo-
blasts, the function of which is supposed to be the formation of bone. In

HISTOLOGY OF THE EPITHELIAL AND CONNECTIVE TISSUES. 45

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 believed
to give birth indirectly to the red blood-corpuscles.

Physical and Physiologic Properties of Connective Tissues. —
Among the physical properties may be mentioned consistency, cohesion,
and elasticity. Their consistency varies from the semiliquid to the solid
state, and depends on the quantity of water which enters into their compo-
sition. Their cohesion, except in the softer varieties, is very considerable,
and offers great resistance to traction, pressure, torsion, etc. In all the
movements of the body, in the contraction 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 composition 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 direc-
tion. If pressure be exerted in all directions, as upon membranes, 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. Extensibility is not a characteristic feature,
except in those forms containing an abundance of yellow elastic fibers.
The elasticity is an essential factor in many physiologic actions. It not
only opposes and limits 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 constitute 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 viscera and affording support for the epi-
thelial, muscle, and nerve tissues.

46 HUMAN PHYSIOLOGY.

THE PHYSIOLOGY OF THE SKELETON.

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 position of the indi-
vidual in space, as in the various acts of locomotion. If in the execution
of these movements the different parts are applied or directed to the over-
coming 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 accom-
plishment of work the skeleton, the muscle and nerve tissues constitute the
three primary mechanisms, all of which bear certain definite relations one
to another.

The Skeleton is the passive framework, the axial portion of which (the
vertebral column, head, ribs, and sternum) impart more or less fixity and
rigidity, while the appendicular portions (the bones of the arms and legs)
impart extreme mobility. 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 accomplishment 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 connected with the environment, e. g.,
gravity, cohesion, friction, elasticity, 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 movements, 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 mechan-
ical 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.t 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 peculiarities of
the skeleton, especially in its relation to joints, will be referred to
which underlie and determine both the static and dynamic states of the
body.

MECHANISM OF THE SKELETON. 47

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

1. Bones, the articulating surfaces of which are often more or less ex-
panded, especially in the case of long bones, and at the same time vari-
ously modified and adapted to one another in accordance with the char-
acter and extent of the movements which there take place.

2. Hyaline cartilage, which is closely applied to the articulating end of each
bone. The smoothness of this form of cartilage facilitates the move-
ments 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- cartilage 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 membrane is
composed largely of connective tissue, the inner surface of which is lined
by endothelial cells, which secrete a clear, colorless, viscid fluid— the
synovia. This fluid not only fills 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 inextensible but pliant, ligaments
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 con-
cave. 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 :

1. 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, practically 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,

48 HUMAN PHYSIOLOGY.

knee, ankle, the phalangeal joints of the fingers and toes — are, therefore,
termed ginglymi, or hinge-joints. Owing to the obliquity of their articu-
lating 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, left-handed screws. In the
knee-joint the form and arrangement of the articulating surfaces are
such as to produce that modification 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 sur-
face, 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 position with the point of contact.

In some few instances the long axis of the articulating surface is par-
allel rather than transverse to the long axis, and as the movement then
takes place around a more or less conic surface, the joint is termed a
trochoid or pulley — e. g.y 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 unequally
curved, though intersecting each other. When the surfaces 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 permitted by the former joint are flexion, ex-
tension, 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, extension, adduction,
abduction, and circumduction.

MECHANISM OF THE SKELETON. 49

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 oppos-
ing articulating surface. In such a joint, termed an enarlhrodial or
ball-and-socket joint, — e. ^the shoulder-joint, hip-joint, — the distal
bone revolves around an indefinite number of axes, all of which inter-
sect 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 circumduc-
tion.

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-iliac 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 ligaments.

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 in 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 vertebrae, 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 support 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, con-
stitute about one quarter of the length of the vertebral column. The ver-
tebrae 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.

50 HUMAN PHYSIOLOGY.

The amphiarthrodial character of the intervertebral joints endows the
entire column with certain forms of movement which are necessary to
the performance of many body activities. While the range of movement
between any two vertebrae is slight, the sum total of movement of the entire
series of vertebrae is considerable. In different regions of the column the
character, as well as the range of movement, varies in accordance with the
form of the vertebrae and the inclination of their articular processes. In
the cervical and lumbar 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 frame-
work, 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 complicated movements.

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 contra-
distinction to the bones and joints, which are but passive agents in the per-
formance of ihe corresponding 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,

GENERAL PHYSIOLOGY OF MUSCLE TISSUE. 51

shortening or contracting under the influence of a stimulus transmitted to
them from the nervous system. Muscles are therefore divided into :

1. Voluntary muscles, comprising those whose activity is called forth by
stimuli of the nerves as the result of an act or effort of volition.

2. Involuntary muscles, comprising those whose activity is entirely inde-
pendent of the volition.

The voluntary muscles are also known from their attachment to the
skeleton as skeletal, and from their microscopic appearance as striped
muscles. The involuntary muscles, from their relation to the viscera of
the body, are known also as visceral, and from their microscopic appear-
ance as plain or smooth muscles.

General Structure of Muscles. — All skeletal muscles consist of a
central fleshy portion, the body or belly, which is provided at either ex-
tremity with a tendon in the form of a cord or membrane by which it is
attached to the bones. The body is the contractile region, the source of
activity ; the tendon is a passive region, and merely transmits the activity
to the bones.

A skeletal muscle is a complex organ consisting of muscular fibers, con-
nective tissue, blood-vessels, and lymphatics. The general body of the
muscle is surrounded by a dense layer of connective tissue, the epimysium,
which blends with and partly forms the tendon ; from its inner surface
septa of connective tissue pass inward and group the muscle-fibers into
larger and smaller bundles, termed fasciculi. The fasciculi, invested by
this special sheath, the perimysium, are irregular in shape, and vary con-
siderably in size. The fibers of the fasciculi are separated from one an-
other and supported by a delicate connective tissue, the endomysium. The
connective tissue thus surrounding and penetrating the muscle binds its
fibers into a distinct organ, and affords support to blood-vessels, nerves,
and lymphatics. The muscle-fibers are arranged parallel to one another,
and their direction is that of the long axis of the muscle. In length they
vary from thirty to forty millimeters, and in diameter from twenty to thirty
micromillimeters.

The vascular supply to the muscles is very great, and the disposition
of the capillary vessels, with reference to muscle-fiber, is very charac-
teristic. The arterial vessels, after entering the muscle, are supported by
the perimysium ; 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 inti-
mate relation with the capillary is bathed with lymph derived from it. Its

52 HUMAN PHYSIOLOGY.

contractile substance, however, is separated from the lymph by its own
investing membrane, through which all interchange of nutritive and waste
materials must take place. Lymphatics are present in muscle, but are con-
fined to the connective tissue, in the spaces of which they have their origin.
The nerves which carry the stimuli to a muscle enter near its geomet-
ric 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 so many fibers as
the muscle. In such cases the nerve-fibers divide, until the number of
branches equals the number of muscle-fibers. The individual muscle-
fiber is penetrated near its center by the nerve, the ends being practically
free from nerve influence. The stimulus that comes to the muscle-fiber
acts primarily upon its center, and then travels in both directions to the ends.

Histology of the Skeletal Muscle-fiber. — A muscle-fiber consists of a
transparent elastic membrane, the sarcolemma, in which is contained the
true muscle element. Examined microscopically, the fiber presents a series
of alternate dim and bright bands, giving to it a striated appearance.

When the bright band is examined with high magnifying powers, a fine,
dark line is seen crossing it transversely. It was supposed by Krause to
be the optic expression of a membrane which divides the cavity of the
sarcolemma into a series of compartments, each of which contains a dim
band of sarcous or muscle substance, bounded at either extremity with the
half of a bright band. This membrane has since been resolved into a row
of granules.

The muscle-fiber also exhibits a longitudinal striation, indicating that it
is composed of fibrillae, placed side by side and embedded in some inter-
fibrillar substance, to which the name sarcoplasm has been given. The
fibrillae, which are arranged longitudinally to the long axis of the fiber, are
grouped by the intervening material into bundles of varying size, the
muscle columns. The fibrillse which extend throughout the length of the
fiber are not of uniform thickness, but present at regular intervals well-
marked constrictions.

In the region of the dim band the fibrilla presents itself in the form of
a homogeneous prismatic rod, termed sarcostyle, separated from neighbor-
ing rods by a slight amount of sarcoplasm. Between two successive rods
is found a dark granule, united by a thin band of similar ma erial to the
ends of the rods. The transverse row of granules corresponds to Krause' s
membrane.

GENERAL PHYSIOLOGY OF MUSCLE TISSUE. 53

In the region of the granules there is a diminution of the sarcous sub-
stance, but an increase in the amount of sarcoplasm, and as the latter is
more transparent than the former, the fiber presents at this point a con-
spicuous bright band. Rollet considers the sarcostyles to be preexistent,
not the result of post-mortem or chemic changes, and the seat of the con-
tractile elements. The sarcoplasm is a passive material similar in its
properties to protoplasm.

Briicke has shown that when the muscle-fiber is examined under
crossed Nichol prisms the dim band appears bright and the bright band
appears dim against a dark background, indicating that the former is
doubly refractile, or anisotropic, the latter singly refractile, or isotropic.
The fiber, therefore, appears to be composed of alternate discs of aniso-
tropic and isotropic substance.

Structure of Non-striated Muscle-fiber. — As the name implies,
the involuntary fiber is non-striated, being apparently uniform and homo-
geneous in appearance. When isolated, the fiber presents itself in the
form of an elongated fusiform cell, varying from y1^ to g^ of an inch
in length. In some animals the fiber exhibits a longitudinal striation,
as if it were composed of fibers. The cell is surrounded by a thin,
elastic membrane, and contains a distinct oval nucleus. The fibers are
usually arranged in bundles and lamellae, and held together by a cement
substance and connective tissue. This non-striated muscle tissue is found
in the muscularis mucosse of the alimentary canal as well as in the
muscular walls of the stomach and intestines, in the posterior part of the
trachea, in the bronchial tubes, in the walls of the blood-vessels, and in
many other situations.

Chemic Composition of Muscle. — The chemic composition of muscle
is imperfectly understood, owing to the fact that some of its constituents
undergo a spontaneous coagulation after death, and that the chemic
methods employed also tend to alter its normal composition. When fresh
muscle is freed from fat and connective tissue, frozen, rubbed up in a mor-
.tar, and expressed through linen, a slightly yellow, syrupy, alkaline, or
neutral fluid is obtained, known as mtiscle plasjna. This fluid at normal
temperature coagulates spontaneously, and resembles in many respects the
coagulation of blood plasma. The coagulum subsequently contracts and
squeezes out an acid muscle serum. The coagulated mass is termed myosin.
This proteid belongs to the class of globulins. Inasmuch as it is not
present in living muscle, and makes its appearance only in the as yet living
muscle plasma, it is probable that it is derived from some preexisting sub-

54 HUMAN PHYSIOLOGY.

stance, which is supposed to be myosinogen. Myosin is digested by pepsin
and trypsin. According to Halliburton, muscle plasma contains the follow-
ing proteid bodies : Myosinogen, paramyosinogen, albumin, myoalbumose,
all of which differ in chemic composition and respond to various chemic
and physical reagents.

Ferment bodies, such as pepsin and diastase ; non-nitrogenized bodies,
such as glycogen, lactic and sarcolactic acids, fatty bodies, and inosite ;
nitrogenized extractives — e. g. , urea, uric acid, kreatinin, as well as inor-
ganic salts, have been obtained from the muscle serum.

Metabolism in Muscles. — The chemic changes which underlie the
transformation of energy in living muscles are very active and complex.

As shown by an analysis of the blood flowing to and from the resting
muscle, it has, while passing through the capillaries, lost oxygen and
gained carbon dioxid. The amount of oxygen absorbed by the muscle
(nine per cent. ) is greater than the amount of C02 given off (6.7 per cent. ).
There is no parallelism between these two processes, as C02 will be given
off in the absence of oxygen, or in an atmosphere of nitrogen.

In the active or contracting muscle both the absorption of oxygen and
the production of C02 are largely increased, but the ratio existing between
them differs considerably from that of the resting muscle, for the quantity
of oxygen absorbed amounts to 1 1. 26 per cent., the quantity of C02 to 10.8
per cent. (Ludwig). Moreover, in a tetanized muscle the quantity of CO.,
given off may be largely in excess of the oxygen absorbed. From these
facts it is evident that the energy of the contraction does not depend upon
the direct oxidation of certain substances, but upon the decomposition of
some unstable compound of high potential energy, rich in carbon and
oxygen. When the muscle is active, its tissue changes from a neutral to an
acid reaction, from the development of sarcolactic and possibly phosphoric
acids. The amount of glycogen present in muscle (0.43 per cent.)
diminishes, but muscles wanting in glycogen, nevertheless, retain their
power of contraction. Water is absorbed. The amount of urea is not
materially increased by muscular activity, unless it is excessive and pro-
longed, and then only in the absence of a sufficient quantity of non-
nitrogenized material. Coincident with muscle contraction, the blood-
vessels become widely dilated, leading to a large increase in the blood-supply
and a rapid removal of products of decomposition.

Rigor Mortis. — A short time after death the muscles pass into a con-
dition of extreme rigidity or contraction, which lasts from one to five days.
In this state they offer great resistance to extension, their tonicity disap-

GENERAL PHYSIOLOGY OF MUSCLE TISSUE. 55

pears, their cohesion diminishes, their irritability ceases. The time of the
appearance of this post-mortem or cadaveric rigidity varies from a quarter
of an hour to seven hours. Its onset and duration are influenced by the
condition of the muscular irritability at the time of death. When the
irritability is impaired from any cause, such as 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 to continue for a longer period.

The rigidity appears first 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 practically the same order.

Chemic changes of a marked character accompany this rigidity. The
muscle becomes acid in reaction from the development of sarcolactic acid ;
it gives off a large quantity of carbonic acid, and is shortened and dimin-
ished in volume.

The immediate cause of the rigidity appears to be a coagulation of the
myosinogen within the sarcolemma, with the subsequent formation of
myosin and muscle serum. In the early stages of coagulation restitution is
possible by the circulation of arterial blood through the vessels. The final
disappearance of this contraction is due to the action of acids dissolving
the myosin, and possibly to putrefactive changes.

Source of Muscular Energy. — According to most experimenters, it
is certain that normal muscle activity is not dependent on the metabolism
of nitrogenous materials, inasmuch as its chief end product, urea, is not
increased. The marked production of C02 points to the combustion of
some non -nitrogenous matter, — e. g., glycogen, — especially as this substance
disappears during muscular activity. Muscles wanting in glycogen are,
nevertheless, capable of contracting for some time. Moreover, there is no
proof of the direct combustion of glycogen or any other carbohydrate. It
has been suggested by Hermann that the energy of a muscular contraction
may be due to the splitting and subsequent re-formation of a complex body
belonging neither to the carbohydrates nor to the fats, but to the albumins.
To this body the term inogen has been applied. This complex molecule,
the product of the metabolic activity of the muscle cell, in undergoing de-
composition would yield C02, sarcolactic acid, and a proteid residue resem-
bling myosin. With the cessation of the contraction, the muscle protoplasm
recombines the proteid residue with oxygen, carbohydrates, and fats, and
again forms inogen.

The phenomena of rigor mortis support such a view. At the moment
of this contraction the muscle gives off C02 in large amqunts, the muscle
becomes acid, and myosin is formed, There is thus a close analogy

56 HUMAN PHYSIOLOGY.

between the two processes ; in other words, a contraction is a partial death
of the muscle. As to what becomes of the myosin formed during a contrac-
tion, nothing is known. It may be used in the formation of new inogen.

The Physical Properties of Muscle Tissue. — The consistency c'
muscle tissue varies considerably, according to the different states of the
muscle. In a state of tension it is hard and resistant ; when free from
tension, it is soft and fluctuating, whether the muscle is contracting or rest-
ing. Tension alone produces hardness. The cohesion of muscle tissue
is less than that of connective tissue, and is broken more readily. Cohesion
resists traction and pressure, and lasts as long as irritability remains.

The elasticity of a muscle, though not great is almost perfect. After
being extended by a weight, it returns to its natural form. The limit of
elasticity, however, is soon passed. A weight of 50 or 100 grams will
overcome the elasticity so that it will not return to its natural length. In
inorganic bodies the extension is directly proportional to the extending
weight, and the line of extension is straight. With muscles, the extension
is not proportional to the weight. While at first it is marked, the elonga-
tion diminishes as the weight increases by equal increments, so that the
line of extension becomes a curve. In other words, the elasticity of a
passive muscle augments with increased extension. On the contrary, the
elasticity of an active is less than that of a passive muscle, for it is elongated
more by the same weight, as shown by experiment.

Tonicity is a property of all muscles in the body, in consequence of
being normally stretched to a slight extent beyond their natural length.
This may be due to the action of antagonistic muscles, or to the elasticity
of the parts of the skeleton to which they are attached. This is shown by
the shortening of the muscle which takes place when it is divided. Mus-
cular tonus plays an important role in muscular contraction. Being always
on the stretch, the muscle loses no time in acquiring that degree of tension
necessary to its immediate action on the bones. Again, the working power
of a muscle is increased by the presence of some resistance to the act of
contraction. According to Marey, the amount of work is considerably
increased when the muscular energy is transmitted by an elastic body to
the mass to be moved, while at the same time, the shock of the contraction
is lessened. The position of a passive limb is the resultant also of the
elastic tension of antagonistic groups of muscles.

Muscle excitability or contractility are terms employed to denote
that property of muscle tissue in virtue of which it contracts or shortens
in response to various excitants or stimuli. Though usually associated with

GENERAL PHYSIOLOGY OF MUSCLE TISSUE. 57

the activity of the nervous system, it is, nevertheless, an independent en-
dowment, and persists after all nervous connections are destroyed. If the
nerve terminals be destroyed, as they can be by the introduction of curara
into the system, the muscles become completely relaxed and quiescent.
The strongest stimuli applied to the nerves fail to produce a contraction.
Various external stimuli applied directly to the muscle substance produce
at once the characteristic contraction. The excitability of muscle is there-
fore an inherent property, dependent on its nutrition, and persisting as long
as it is supplied with proper nutritive materials and surrounded by those
external conditions which maintain its chemic or physical integrity.

Muscle Contractions. — All muscle contractions occurring in the body
under normal physiologic conditions are either voluntary, caused by a
volitional effort and the transmission of a nerve impulse from the brain
through the spinal cord and nerves to the muscles, or reflex, caused by
a peripheral stimulation and the transmission of a nerve impulse to the
spinal cord, to be reflected outward through the same nerves to the muscles.
In either case the resulting contraction is essentially the same. The normal
or physiologic sti7nulus which provokes the muscular contraction is a
nerve impulse the nature of which is unknown, but is perhaps allied to a
molecular disturbance. After removal from the body, muscles remain
in a state of rest, inasmuch as they possess no spontaneity of action.
Though consisting of a highly irritable tissue, they can not pass from
the passive to the active state except upon the application of some form of
stimulation.

The stimuli which are capable of calling forth a contraction may be
divided into —

1. Mechaniqal.

2. Chemic.

3. Physical.

4. Electric.

Every mechanical stimulus of a muscle, — e. g., pick, cut, or tap, — provid-
ing it has sufficient intensity, and is repeated with sufficient rapidity, will
cause not only a single contraction, but a series of contractions.

All chemic agents which impair the chemic composition of the muscle
with sufficient rapidity — e. g., hydrochloric acid, acetic and oxalic acids, dis-
tilled water injected into the vessels, etc. — act as stimuli, and produce
single and multiple contractions. Physical agents, as heat and electricity,
also act as stimuli. A muscle heated rapidly to 300 C. contracts vig-
orously, and reaches its maximum at 450 C. Of all forms of stimuli, the
5

58 HUMAN PHYSIOLOGY.

electric is the most generally used. Two forms are used — the induced
current and the make-and-break of a constant current.

Changes in a Muscle During Contraction. — When a muscle is
stimulated, either indirectly through the nerve or directly by any external
agent, it undergoes a series of changes, which relate to its form, volume,
optic, physical, chemic, and electric properties. These changes, in their
totality, constitute the muscular contraction.

i. Form. — The most obvious change is that of form. The fibers become
shorter in their longitudinal and wider in their transverse diameters, and
the muscle as a whole becomes shorter and thicker. The degree of
shortening may amount to thirty per cent, of the original length.

2. Volume. — The increase in transverse diameter does not fully compen-
sate for the diminution in length, for there is at the moment of contrac-
tion a slight shrinkage in volume, which has been attributed to a com-
pression of air in its interstices.

3. Optic Changes. — If a muscle-fiber be examined microscopically during
its contraction, it will be observed that when the contraction wave
begins, both bright and dim bands diminish in height and become
broader, though this change is more noticeable in the region of the bright
band. This Englemann attributes to a 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 fiber assumes its original shape and volume.
As the contraction wave reaches its maximum, the optic properties of
both the isotropic and anisotropic bands change. The former, which
was originally clear, now becomes darker and less transparent, until at
the crest of the wave it assumes the appearance of a distinct dark band.
The latter, the anisotropic, which was originally dim,jiow becomes, in
comparison, clear and light. This change in optic appearance is due
to an increase in refrangibility of the isotropic and a decrease in the
anisotropic bands coincident with the passage of 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 there is an intermediate point, at
which the strix almost entirely disappear, giving to the fiber an appear-
ance of homogeneity. There is, however, no change in refractive power,
as shown by the polarizing apparatus. After the contraction wave has
reached the stage of greatest intensity, there is a reversal of the foregoing
phenomena, and the fiber returns to its original condition, which is one
of relaxation.

GENERAL PHYSIOLOGY OF MUSCLE TISSUE.

59

/

Physical Changes. — The extensibility of muscle is increased during the
contraction, the same weight elongating the fibers to a greater extent than
during rest. The elasticity, or its power of returning to its original form
is correspondingly diminished.

Chemic Changes. — The metabolism of muscle during the contraction is
very active. There is an increase in the production of carbon dioxid and in
the absorption of oxygen. The muscle changes from an alkaline or neutral
to an acid reaction, from the development of sarcolactic acid. The muscle
also becomes warmer. The electric changes will be treated of in connec-
tion with nerves.

Transmission of the Contraction Wave. — Normally, when a muscle
is stimulated by the nerve impulse, the shortening and thickening of the
fibers begin at the end organ and travel in opposite directions to the ends
of the muscle. This change propagates itself in a wave-like manner, and
has been termed the contraction wave. If a stimulus be applied directly
to the end of a long muscle, the contraction wave passes along its entire
length to the opposite extremity, in virtue of the conductivity of muscular
tissue. The rapidity of the propagation varies in different animals — in the
frog, from three to four meters a second ; in man, from ten to thirteen
meters. The length of the wave varies from 200 to 400 millimeters.

Graphic Record of a Muscle Contraction. — The changes in the
form of a muscle during contraction and relaxation have been carefully

Fig. 4. — Muscle Curve Produced by a Single Induction Shock Applied to

a Muscle. — {Landois.)

a-f. Abscissa, a-c. Ordinate, a-b. Period of latent stimulation, b-d. Period of
increasing energy, d-e. Period of decreasing energy, e-f. Elastic after-vibrations.

studied by recording the muscle movement by means of an attached lever,
the end of which is allowed to rest upon a moving surface. The time rela-
tions of all phases of the muscular movement are obtained by placing be-
neath the lever a pen attached to an electromagnet thrown into action by a

60 HUMAN PHYSIOLOGY.

tuning-fork vibrating in hundredths of a second. A marking lever records
simultaneously the moment of stimulation.

Single Contraction. — When a single electric induction shock is applied
to a nerve close to the muscle, the latter undergoes a quick pulsation,
speedily returning to its former condition. As shown by the muscle
curve (see Fig. 4), there is between the moment of stimulation and the
beginning of the contraction a short but measurable period, known as the
latent period, during which certain chemic changes are taking place pre-
paratory to the exhibition of the muscle movement. Even when the
electric stimulus is applied directly to the muscle, a latent period, though
shorter, is observable. The duration of this period in the skeletal muscles
of the frog has been estimated at 0.01 of a second ; but it has been shown
by the employment of more accurate methods and the elimination of various
external influences to be much less — not more than 0.0033 to 0.0025 °f a
second.

The contraction follows the latent period. This begins slowly, rapidly
reaches its maximum, and ceases. This has been termed the stage of ris-
ing or increasing energy. The time occupied in the stage of shortening is
about 0.04 of a second, though this will depend on the strength of the
stimulus, the load with which the muscle is weighted, and the condition of
the muscle irritability.

The relaxation immediately follows the contraction. This takes place at
first slowly, after which the muscle rapidly returns to its original length.
This is the period of falling or decreasing energy, and occupies about 0.05
of a second. The whole duration of a muscle contraction occupies, there-
fore, about 0.1 of a second.

Residual or after-vibrations are frequently seen which are due to changes
in the elasticity of the muscle. The amplitude of the contraction depends
upon the condition of the muscle, the load, the strength of stimulus, etc.

Contraction of Non-striated Muscle. — The curve obtained by regis-
tration of the contraction of non-striated muscle shows that it is similar in
many respects to that of the striated muscle, except that the duration of the
former is considerably longer than that of the latter.

Action of Successive Stimuli. — If a series of successive stimuli be
applied to a muscle, the effect will be different according to the rapidity
with which they follow one another. If the second stimulus be applied at
the termination of the contraction clue to the first stimulus, a second con-
traction follows, similar in all respects to the first. A third stimulus pro-

GENERAL PHYSIOLOGY OF MUSCLE TISSUE. 61

duces a third contraction, and so on until the muscle becomes exhausted.
If the second stimulus be applied during either of the two periods of the
first contraction, the effects of the two stimuli will be added together and
the second contraction will add itself to the first. The maximum contrac-
tion is obtained when the second stimulus is applied 2xff of a second after
the first.

Tetanus. — When a series of stimuli are applied to a muscle, following
one another with median rapidity, the muscle does not get time to relax in
ihe intervals of stimulation, but remains in a state of vibratory contraction,
which may be regarded as incipient tetanus, or clonus. As the stimulation
increases in frequency, the vibrations become invisible, being completely
fused together. There is, nevertheless, during the tetanic condition a
series of continuous contractions and relaxations taking place. After a
varying length of time the muscle becomes fatigued, and notwithstanding
the stimulation, begins slowly to elongate. The number of stimuli neces-
sary a second for the production of tetanus varies in different animals — e.g.,
2 to 3 for muscles of the tortoise ; io for muscles of the rabbit; 15 to 20
for the frog; 70 to 80 for birds ; 330 to 340 for insects.

A voluntary contraction in man may be regarded as a state of
tetanus, for if the curve of a voluntary movement be examined, it will be
found to consist of intermittent vibrations. The simplest voluntary move-
ment of a muscle, however rapidly it may take place, lasts longer than a
single muscular contraction due to an induction shock. The most rapid
voluntary contraction is the result of from 2.5 to 4 stimulations a second,
and has a duration of from 0.041 to 0.064 of a second. A continuous
voluntary contraction is an incomplete tetanus. The number of stimuli
sent to the muscle is, on the average, 16 to 18 for rapid contractions, 8 to
12 for slow contractions.

The Production of Heat and Its Relation to Mechanical Work.

— The transformation of energy which takes' place during a muscle con-
traction, and which is dependent upon chemic changes occurring at that
time, manifests itself as heat and mechanical work. While heat is being
evolved continuously during the passive condition of muscles, the amount
of heat is largely increased during general muscle contraction. A skeletal
muscle of a frog, — e. g., the gastrocnemius, — when removed from the body,
shows, after tetanization, an increase in its temperature of from o. 140 to
0.180 C, and after a single contraction of from 0.0010 to 0.0050 C. While
every muscular contraction is attended by an increase in heat production,

62 HUMAN PHYSIOLOGY.

the amount so produced will vary in accordance with certain conditions —
e. g.t tension, work done, fatigue, circulation of blood, etc.

Tension. — The greater the tension of a muscle, the greater, other con-
ditions being equal, is the amount of heat evolved. When the ends of a
muscle are fastened so that no shortening is possible during stimulation, the
maximum of heat production is reached. In the tetanic state the great in-
crease in temperature is due to the tension of antagonistic and strongly
contracted muscles. The evolution of heat, therefore, bears a relation to
the resistance against which the muscle is acting.

Mechanical Work. — If a muscle contracts, loaded by a weight just suffi-
cient to elongate it to its original length, heat is evolved, but no mechanical
work is done, all the energy liberated manifesting itself as heat. When
the weight which has been lifted is removed from the muscle at the height
of contraction, external work is done. In this case the amount of heat
liberated is less, owing to the work done, for some of the heat generated is
transformed into mechanical motion. According to the law of the con-
servation of energy, the amount of heat disappearing should correspond in
heat units to the number of foot-pounds produced by muscular contraction.

Muscle Sound. — Providing a muscle be kept in a state of tension
during its contraction, the intermittent variations of its tension cause the
muscle to emit an audible sound. If the muscle be tetanized by induction
shocks, the pitch of the sound corresponds with the number of stimuli a
second. A voluntary contraction is attended by a tone having a vibration
frequency of about thirty -six a second, which is, however, the first overtone
of the true muscle tone, which is caused by a contraction frequency of
about eighteen a second. This low tone is inaudible, from the small
number of vibrations a second.

Muscle Fatigue. — Prolonged or excessive muscular activity is followed
by a diminution in the power of producing work and by" an increase in
the duration of the muscular contractions. Fatigue is accompanied by a
feeling of stiffness, soreness, and lassitude, referable to the muscles them-
selves. In the early stages of muscular fatigue the contractions increase
in height and duration, to be followed by a progressive decrease in height,
but an increase in duration, until the muscle becomes exhausted. The
cause of the fatigue is the production and accumulation of decomposition
products, such as phosphoric acid and phosphate of potassium, C02, etc.
A fatigued muscle is rapidly restored by the injection of arterial blood.

Work Done. — Muscles are machines capable of doing a certain amount
\ of work, by which is meant the raising of a weight against gravity or the

SPECIAL PHYSIOLOGY OF MUSCLES. 63

overcoming of some resistance. The work done is calculated by multiply-
ing the weight by the distance through which it is raised. Thus, if a
muscle shortens four millimeters and raises 250 grams, it does work equal
to 1,000 milligram-meters, or one gram-meter. If a muscle contracts with-
out being weighted, no work is done. Equally, when the muscle is over-
weighted so that it is unable to contract, no work is done. The amount of
work a muscle can do will depend upon the area of its transverse section,
the length of its fibers, and the amount of the weight. The amount of
work a laborer of 70 kilograms weight performs in eight hours averages
105,605 kilogram-meters, or 340.2 foot-tons.

SPECIAL PHYSIOLOGY OF MUSCLES.

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 gives rise to — e. g., groups of muscles which alternately bend
or straighten a joint, or alternately diminish or increase the angular distance
between two bones, are known respectively as flexors and extensors ; such
muscle groups are in association with ginglymus joints. Muscles which
turn the bone to which they are attached around its own axis without pro-
ducing any great change of position are known as rotators, and are in as-
sociation with the enarthrodial or ball-and-socket joints. Muscles which
impart an angular movement of the extremities to and from the median
line of the body are termed abductors and adductors.

In addition to the actions of individual groups of muscles in causing
special movements in some regions, several groups of muscles are coordi-
nated for the accomplishment of certain definite functions — e. g., muscles
of respiration, mastication, expression. The coordination of axial and
appendicular muscles enables the individual to assume certain postures,
such as standing and sitting ; to perform various acts of locomotion, as
walking, running, swimming, etc.

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 when the muscles are considered as sources of
power for imparting movement to the levers, with the object of overcoming
resistance or raising weights.

64 HUMAN PHYSIOLOGY.

In mechanics, levers of three kinds or orders are recognized, according
to the relative positions of the fulcrum or axis of motion, the applied
power, and the weight to be moved. ( See Fig. 5. )

In levers of the first order the fulcrum, F, lies between the weight or
resistance, W, and the power of moving force, P. The distance P-F is
known as the power arm, the distance W-F as the weight arm. As an
example of this form of lever in the human body may be mentioned :

1. The elevation of the trunk from the flexed position. The axis of move-
ment, the fulcrum, lies in the hip-joint ; the weight, that of the trunk,
acting as if concentrated at its center of gravity, lies between the
shoulders ; the power, the contracting 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 skull in its movements backward and forward upon the atlas.

In levers of the second order the weight

-j. ¥ lies between the power and the fulcrum.

W a ,r> (l) -^s an illustration of this form of lever may

» be mentioned :

p ^ 1 I. The depression ot the lower jaw, in

/\ W p ' / which movement the fulcrum is the

_ t temporomaxillary articulation ; the resis-

w r* (3) tance, the tension of the elevator mus-

cles ; the power, the contraction of the
Fig. 5. — The Three Orders . ,

T depressor muscles.

of Levers. r

2. The raising of the body on the toes —
F being the toes, W the weight of the body acting through the ankle,
P the gastrocnemius muscle acting upon 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 — F being the elbow-joint, P the contracting
biceps and brachialis anticus muscles applied at their insertion, W the
weight of the forearm and hand.

2. The extension of the leg on the thigh.

When levers are employed in mechanics, the object aimed at is the over-
coming of a great resistance by the application of a small force acting
through a great space, so as to obtain a mechanical advantage. In the
mechanism of the human body the reverse generally obtains — viz., the
overcoming of a small resistance by the application of a great force acting
through a small space. As a result, there is a gain in the extent and

SPECIAL PHYSIOLOGY OF MUSCLES. 65

rapidity of movement of the lever. The power, however, owing to its
point of application, acts at a great mechanical 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 name 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 the 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 falls within the area of both feet placed on the ground.
This position is maintained :

1. By firmly fixing the head on the top of the vertebral column by the
action of the muscles on the back of the neck.

2. By making the vertebral column rigid, which is accomplished by the
longissimus dorsi and the quadratus lumborum muscles. This having
been accomplished, the center of gravity falls in front of the tenth dorsal
vertebra ; the vertical line passing through this point falls behind the
line connecting both hip-joints. In consequence, the trunk is not balanced
on the hip-joints, and would fall backward were it not prevented by the
contraction of the rectus femoris muscle and ligaments. At the knees
and ankles a similar balancing of the parts above is brought about by
the action of various muscles. When the entire body is in the erect or
military position, the arms by the sides, the center of gravity lies between
the sacrum and the last lumbar vertebra, and the vertical line touches the
ground between the feet and within the base of support.

Sitting erect is a condition of equilibrium in which the body is balanced
on the tubera ischii, when the trunk and head together form a rigid column.
The vertical line passes between the tubera.

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 complicated act, involving almost all the voluntary muscles
of the body, either for purposes of progression or for balancing the head and
trunk, and may be defined as a progression in a forward horizontal direc-
tion, due to the alternate acdon 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 progressive leg, to become in turn the
active leg when the foot touches the ground. Each leg, therefore, is
alternately in an active and a passive state.

66 HUMAN PHYSIOLOGY.

Running is distinguished from walking by the fact that, at a given mo-
ment, both feet are off the ground and the body is raised in the air.

While the limits of a compend do not permit of a description of the origin,
insertion, and mode of action of the individual muscles of the body, it has
been thought desirable to call attention to a few of the principal muscles
whose function it is to produce special forms of movement, as well as loco-
motion. (See Fig. 6.) The erect position is largely maintained by the
fixation of the spinal column and the balancing of the head upon its upper
extremity ; the former is accompanied by the erector spina muscle, named
from its function and its fleshy continuations, situated on each side of the
vertebral column. Arising from the pelvis and lumbar vertebrae, this muscle
passes upward, and is attached by its continuations to all the vertebrae. Its
action is to extend the vertebral column and to maintain the erect position.
The head is balanced upon the top of the vertebral column by the com-
bined action of the trapezius and suboccipital muscles forming the nape of
the neck, and by the sterno-deido-mastoid muscle. This latter muscle
arises from the inner third of the clavicle and upper border of the sternum.
It is inserted into the temporal bone just behind the ear. Its action is to flex
the head laterally and to rotate the face to the opposite side. When both
muscles act simultaneously, the head and neck are flexed upon the thorax.

The temporal and masseter muscles, situated at the side of the head,
arise respectively from the temporal fossa and the zygomatic arch, and are
inserted into the ramus of the lower jaw. Their action is to close the
mouth and to assist in mastication. The occipito frontalis, the orbicularis
palpebrarum, and orbicularis oris muscles are largely concerned in wrink-
ling the forehead, closing the eyes and mouth, and in giving various ex-
pressions to the face.

The deltoid is a thick, triangular muscle covering the shoulder-joint.
Arising from the outer third of the clavicle, the acromial process, and the
spine of the scapula, its fibers converge to be inserted into the humerus
just above its middle point. Its action is to elevate the arm through a right
angle. Owing to its point of insertion it acts as a lever of the third order,
but, notwithstanding the advantageous point of insertion, it acts at a con-
siderable disadvantage, owing to the obliquity of its direction.

The biceps muscle, situated on the anterior aspect of the arm, arises from
the upper border of the glenoid fossa and the coracoid process, and is
inserted into the radius just beyond the elbow-joint. Its action is to flex
and supinate the forearm and to place it in the most favorable position for
striking a blow. When the forearm is fixed, it assists in flexing the arm,
as in climbing.

Fig. 6. — Superficial Muscles of the Body.
67

68 HUMAN PHYSIOLOGY.

The triceps muscle, situated on the back of the arm, arises from the
scapula and the posterior surface of the humerus, and is inserted in the
olecranon process of the ulna. In its action it directly antogonizes the
biceps, namely, extending the forearm. In so doing it acts as a lever of
the first order. The short distance between the muscular insertion and
the fulcrum causes it to act at a great mechanical disadvantage, but there is
a corresponding gain in both speed and range of movement. The muscles
of the forearm are very numerous. Their action is to impart to the fore-
arm and hand a variety of movements, such as pronation, supination,
flexion, extension, rotation, etc.

The pectoralis major and pectoralis minor muscles form the fleshy masses
of the breast. Arising from the inner half of the clavicle, the side of the
sternum, and the outer surfaces of the third, fourth, and fifth ribs anteriorly,
the muscle-fibers converge to be inserted into the humerus and coracoid
process. Their combined action is to adduct, flex, and rotate the arm in-
ward, and to draw the scapula downward and forward, movements neces-
sary to the folding of the arms across the chest.

The rectus abdominis and the obliquus externus assist in forming the
abdominal walls.

The glutei muscles are three in number, are arranged in layers, and form
the fleshy masses known as the buttocks. They arise from the side of the
pelvis and are attached to the femur in the neighborhood of the great tro-
chanter. Their action is to extend the hips, to raise the body from the
stooping position, and to assist in walking by firmly holding the pelvis on
the thigh while the opposite leg is advanced in the forward direction.

The rectus femoris, with its associates, the rectus internus and rectus
externus and the crureus, forms the fleshy mass on the anterior surface of the
thigh. The former arises from the anterior part of the ilium, the latter from
the femur. Their common tendon, which is united to the patella, is con-
tinued as the ligamentum patellae, which is attached to the upper part of
the tibia. The action of this muscular group is to extend the leg, to flex
the thigh, and to raise the entire weight of the body, as in changing from
the sitting to the erect position.

The biceps femoris muscle, situated on the outer and posterior aspect of
the thigh, arises from the tuber ischii, and is inserted into the head of the
fibula.

The semimembranosus and the semitendinosus muscles, situated on the
inner and posterior aspect of the thigh, are inserted into the head of the
tibia. Their combined action is to extend the hips and to flex the knee.
Acting from below, they assist in raising the body from the stooping position.

PHYSIOLOGY OF NERVE TISSUE. 69

The gastrocnemius muscle forms the enlargement known as the calf of
the leg. It arises by two heads from the condyles of the femur. Its ten-
don, the tendo Achillis, is inserted into the posterior surface of the heel
bone. Its action is to extend the foot and to raise the weight of the body
in walking and running. On the front of the leg are numerous muscles —
e. g., tibialis anticus, peroneus longus, etc., the action of which is to flex
the foot and to antagonize the gastrocnemius.

PHYSIOLOGY OF NERVE TISSUE.

The nerve tissue, which unites and coSrdinates the various organs and
tissues of the body and brings the individual into relationship with the
external world, is arranged anatomically into two systems, termed the
cerebro-spinal and the sympathetic.

The cerebro-spinal 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, abdo-
men, and pelvis. All these ganglia are united by an elaborate system
of intercommunicating nerves, many of which are connected with the
cerebro-spinal system.

HISTOLOGY OF NERVE TISSUE.

The Neuron. — The nerve tissue has been resolved by the investigations
of modern histologists into a single morphologic unit, to which the term
neuron has been applied. 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 investigations, 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 histo-
logic 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.

70 HUMAN PHYSIOLOGY.

The neuron, or neurologic unit, is histologically a nerve-cell, the sur-
face of which presents a greater or less number of processes in varying
degrees of differentiation. As represented in figure 7, 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 everywhere recognizable, they exhibit
a variety of secondary features in 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 development, pecu-
liarities 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 j-^q of an inch, the largest not more
than ¥^q of an inch. Each cell consists of granular, striated protoplasm,
containing a distinct vesicular 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, which por-
tions, 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 gem-
mules, which impart to the branches a feathery appearance. This charac-
teristic is common to the cells of the cortex, of the cerebrum, and of the
cerebellum. The ultimate branches of the dendrites, though forming an
intricate feltwork, never anastomose with one another, nor unite with den-
drites 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 ganglia
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. 7.) 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

PHYSIOLOGY OF NERVE TISSUE.

71

the surface of the cell, and is the first outgrowth from its protoplasm. 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 hyaline appearance. In struc-
ture, the axon appears to consist of fine fibrillce embedded in a clear, pro-
toplasmic substance. Shafer advocates the view that the fibrillse are

Dendrites.

Nerve-cell.

Nerve process
or axon.

Neurilemma. —••—••■*•

Medulla.

Terminal
branches.

Terminal
branches.

Neurilemma.

p Nerve-cell.

Fig. 7.
A. Efferent neuron. B. Afferent neuron.

exceedingly fine tubes filled with fluid. The axon varies in length from
a few millimeters to 100 cm. 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 structure.
In its course, however, especially in the central nervous system, it gives
off a number of collateral branches, which possess all its histologic features.

72 HUMAN PHYSIOLOGY.

The long axons seem to bring the body of the cell into direct relation with
peripheral organs, or with more or less remote 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 subsequently
become modified and constitute a medullary or myelin sheath. This is in-
vested by a thin, cellular membrane — the neurilemma. These three struc-
tures thus constitute what is known as a medullated nerve-fiber. In the
central nervous system the outer sheath is frequently absent. In the sym-
pathetic system the myelin is frequently absent, though the axon is inclosed
by the neurilemma, 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 peculiarities of
the terminal organs vary in different situations, and in many instances are
quite complex and characteristic. In peripheral organs, as muscles,
glands, blood-vessels, skin, mucous membrane, the tufts are in direct or-
ganic 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., medul-
lated 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 neurilemma.

2. An intermediate semifluid substance — the medulla or myelin.

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 the recent condition. When treated with various
reagents, it becomes distinct. Physically, it is quite resistant and elastic.
Its function is doubtless that of a protective agent to the structures
within.

The medulla, myelin, or white substance of Schwann completely fills
the neurilemma and closely invests the axis-cylinder. In the recent con-
dition the medulla is clear, homogeneous, semifluid, and highly refracting.
In composition it is oleaginous. When the nerve is treated with various

PHYSIOLOGY OF NERVE TISSUE. 73

reagents which alter its composition, the medulla becomes opaque and im-
parts to the nerve a white, glistening appearance. The function of the
medulla is quite unknown.

At intervals of about seventy-five times its diameter the medullated
nerve-fiber undergoes a remarkable diminution in size, due to an interrup-
tion 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 uniformly continuous
throughout. In the natural condition it is transparent 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 high magnification the axis presents a longitudinal
striation, indicating a fibrillar structure. The fibrillar appear to be united
by an intervening cement substance.

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 system. 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 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 tech-
nically known as nerve trunks or nerves. Each nerve is invested by a
thick layer of lamellated connective tissue, known as the epineurhim.
A transverse section of a nerve shows (see Fig. 8) 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 very freely with neighboring branches, forming plexuses,

74

HUMAN PHYSIOLOGY.

the fibers of which are distributed to associated organs and regions of the
body. From their origin to their termination, however, nerve-fibers retain
their individuality, and never become blended with 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 throughout all the branch-
ings down to the ultimate nerve-fibers, each of which is surrounded by a

Fig. 8. — Transverse Section of a Nerve (Median).
ep Epineurium. pe. Perineurium, ed. Endoneurium.

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 the parent axis-
cylinder and myelin.

PHYSIOLOGY OF NERVE TISSUE. 75

CLASSIFICATION OF NERVES.

Nerves are channels of communication 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 or nerve impulses 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 sensa-
tions or other modes of nerve activity. The former are termed efferent or
centrifugal nerves ; the latter are termed afferent or centripetal nerves.

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

1. Muscular ox motor nerves, those which convey nerve energy or nerve
impulses to muscles and give rise to muscular contraction.

2. Glandular or secretory nerves, those which convey nerve impulses to
glands, and cause the formation 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 the mech-
anism 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 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 subdivided into —
[a) Nerves of special sense — e.g., olfactory, optic, auditory, gusta-
tory, tactile, thermal, sensory, muscle — those which give rise to
olfactory, optic, auditory, gustatory, tactile, thermic, painful, and
muscle sensations.
(£) Nerves of general sense — e. g., the visceral afferent nerves — those
which give rise normally to vague and scarcely perceptible sensa-
tions, such as the general sensations of well-being or discomfort,
hunger, thirst, fatigue, sex, want of air, etc.

76 HUMAN PHYSIOLOGY.

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 sensational and reflex action, owing to the col-
lateral branches which are given off from the posterior roots as they
ascend the posterior column of the cord.

3. Inhibitory nerves, those which are capable reflexly of retarding or in-
hibiting the activity of either nerve centers or peripheral organs.

The Terminal Endings of Nerves. — The efferent nerves, as they
approach their ultimate terminations, lose both the neurilemma and medul-
lary sheath. The axis-cylinder then divides into a number of tufts or
branches, which become directly and intimately connected with the tissue
cells. The particular mode of termination varies in different situations.
These terminations are generally spoken of as " end organs"

In the skeletal muscles the nerve-fiber loses both neurilemma and myelin
sheath at the point where it comes into contact with the muscle-fiber.
After penetrating the sarcolemma, the axis- cylinder breaks up into small
branches with bulbous extremities, forming the so-called "motor plate,"
which rests directly on a, disc of granular material containing oval, vesic-
ular nuclei. Each muscle-fiber possesses an individual end-plate.

In the visceral muscles the terminal nerve-fibers form a plexus around the
muscle-fibers, and become organically connected with them. In the
glands the nerve-fibers have been traced directly to their secreting cells.
The exact mode of their termination and connection with the cells has not
been clearly determined.

The afferent nerves, as they approach their peripheral terminations, be-
come connected in like manner with end organs, which, in some instances,
are extremely complex, such as those found in the eye (retina), the internal
ear, the nose, and the tongue. (A consideration of these end organs will
be found in the chapters devoted to the organs of which they form a part. )
The end organs of the skin and mucous membranes present a variety of
forms, and may be classified as follows :

1 . Free endings in the epithelium of the skin, mucous membrane, and cornea.

2. Tactile cells of Merkel in the epidermis.

2. Tactile corpuscles in the papillae of the true skin.

4. Pacinian corpuscles found attached to the nerves of the hands and feet,
to the intercostal nerves, and to nerves in other situations.

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

PHYSIOLOGY OF NERVE TISSUE. 77

The end organs of the afferent nerves are specialized, highly irritable
structures placed between the nerve-fibers and the surface of the body.
They are especially adapted for the reception of those external forces tech-
nically known as stimuli, and for the liberation of energy capable of excit-
ing the nerve-fiber to activity.

Relation of Peripheral Nerves to the Central Nervous System. —
The nerves in connection with the spinal cord are thirty-one in number on
each side and have two roots of origin, an anterior and a posterior, which
arise from the anterior and posterior surfaces of the cord respectively.
They are more properly termed ventral and dorsal roots. The dorsal
roots present, near their entrance into the cord, an enlargement termed a
ganglion. Beyond the spinal canal these two roots unite to form the
ordinary spinal nerve. Some of the nerves in connection with the base
of the brain also present a ganglionic enlargement, and may, therefore, be
regarded physiologically as dorsal nerves, while others may be regarded as
ventral nerves. .

Experimentally, it has been determined that the anterior or ventral 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 formation of a secretion in glands.

3. Changes in the caliber of blood-vessels.

4. Inhibition of the rhythmic activity of certain organs.
Divisions of these roots is -followed by :

1. Loss of muscular movement (paralysis of motion).

2. Cessation of secretion.

3. Cessation of 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.

78

HUMAN PHYSIOLOGY.

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 Sylvius, beneath the floor of the fourth ventricle
and in the anterior horns of the gray matter of the spinal cord. These
cells are the modified descendants of independent, oval, pear-shaped cells
— the neuroblasts — 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,

Posterior
Jloot

Gcuuflian,

rrierwr
£oot

Fig. 9. — Diagram Showing the Mode of Origin of the Ventral and

Dorsal Roots.

the axions 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 of the central
nervous system and only subsequently become connected with it. ( See Fig.
9. ) At the time of the closure of the medullary tube a band or ridge of
epithelial tissue develops near the dorsal surface, which, becoming seg-
mented, moves outward and forms the rudimentary spinal ganglia. The cells
in this situation develop two axons, one from each end of the cell, which

PHYSIOLOGY OF NERVE TISSUE. 79

pass in opposite directions, one toward the spinal cord, the other toward
the periphery. In the adult condition the two axons shift their position,
unite, and form a T-shaped process, after which a division into two branches
again takes place. In the ganglia of all the sensoricranial and sensori-
spinal nerves the cells have this histologic peculiarity.

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 applied. The portion in connection with the brain or
cord retains its normal condition. The degenerative process begins simul-
taneously throughout the entire course of the nerve, and consists in a disin-
tegration and reduction of the medulla and axis-cylinder into nuclei, drops
of myelin, and fat, which in time disappear through absorption, leaving the
neurilemma intact. Coincident with these structural changes there is a
progressive alteration and diminution in the excitability 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 nutri-
tive or a trophic influence. This idea has been greatly strengthened since
the discovery that the axis-cylinder, 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 of itself of maintaining its nutrition.

The relation of the nerve-cells to the nerve-fibers, 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 posterior root be
divided on the peripheral side of the ganglion, degeneration takes place
only in the peripheral portion of the nerve. If the root be divided between
the ganglion 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
ganglia, 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
process is usually spoken of, after its discoverer, as the Wallerian degen-
eration.

When the degeneration of the efferent nerves is completed, the structures
to which they are distributed, especially the muscles, undergo an atrophic
or fatty degeneration, with a change or loss of their irritability. This is,

80 HUMAN PHYSIOLOGY.

apparently, not to be attributed merely to inactivity, but rather to a loss of
nerve influences, inasmuch as inactivity merely leads to atrophy and not to
degeneration.

Reactions of Degeneration. — In consequence of the degeneration
and changes in irritability which occur in nerves and muscles when sepa-
rated, either experimentally or as the result of disease, the response of
these structures to the induced and the make -and- break of the constant
currents differs from that observed in the physiologic condition. The facts
observed under the application of these two forms of electricity are of the
greatest importance in the diagnosis and therapeutics of the precedent
lesions. The principal difference of behavior is observed in the muscles,
which exhibit a 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 peculiarity of
the muscle response is termed the reaction of degeneration. The syn-
chronous diminished excitability of the nerves is the same for either cur-
rent. 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 stimulations of the terminal
organs of afferent nerves, they are termed, for convenience, reflex actions,
and, as they take place independently of the brain or of volitional impulses,
they are also termed involuntary 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 figure io, the necessary struc-
tures are as follows :

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

2. An afferent nerve.

3. An emissive cell, from which arises

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,

PHYSIOLOGY OK NERVE TISSUE. 81

the nerve portion of which is composed of but two neurons — an afferent
and an efferent. An arc of this simplicity would of necessity subserve
but a simple movement. The majority of reflex activities, 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 implies that a number of neurons are associated
in function. The afferent neurons are brought into relation with the den-
drites of the efferent neurons by the end tufts of the collateral branches,

/

Fig. io. — Diagram Illustrating Reflex Action. — {Kirke.)
S. Sentient surface from which proceeds the afferent nerve. M. C. Motor or emissive
cell giving origin to efferent nerve which terminates in M. 31. Motor organ. G.
Ganglion cell on afferent nerve

which may extend for some distance up and down the cord before passing
into the various segments.

For the excitation of a reflex action it is essential that the stimulus
applied to the sentient surface be of an intensity sufficient to develop in the
terminals of the afferent nerve a series of nerve impulses, which, traveling
inward, will be distributed to and received by the dendrites of the emissive
or motor cell. With the reception of these impulses there is apparently a
disturbance of the equilibrium of its molecules, a liberation of energy,
and, in consequence, a transmission outward of impulses through the

82 HUMAN PHYSIOLOGY.

efferent nerve to muscle, gland, or blood-vessel, separately or collectively,
with the production of muscular contraction, glandular secretion, vascular
dilatation 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 mastication ;
the secretion of saliva ; the muscular, glandular, and vascular phenomena
of gastric and intestinal digestion ; the vascular and respiratory movements ;
the mechanism of micturition, etc., are illustrations of reflex activity.

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 de-
velop and to conduct nerve impulses from the center to the periphery, from
the periphery to the center, in response to the action of stimuli. A nerve
is said to be excitable or irtritable as 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 composition. 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 stimulated.
The irritability of nerves continues for a certain period of time after separa-
tion from the nerve centers and even after the death of the animal, 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. 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 irritability, that is, the property of re-
sponding 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 irritability 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 his-
tologic connections have been impaired or destroyed by the introduction of
various chemic agents into the circulation. Curara, for example, induces a

PHYSIOLOGY OF NERVE TISSUE. 83

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 irritability 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
with the gland-cells, without destroying the irritability of either gland or
nerve.

Stimuli of Nerves. — 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 extraneural stimulus. In the living condition
the stimuli capable of throwing the nerve 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 con-/
nection with them. In the case of sensory or afferent nerves the stimuli act;
upon the peculiar end organs with which the sensory nerves are in connec-
tion, which in turn excite the nerve-fibers. Experimentally, it can be
demonstrated that nerves can be excited by a sufficiently powerful stimulus
applied in any part of their extent.

Nerves respond to stimulation according to their habitual function ; thus,
stimulation of a sensory nerve, if sufficiently strong, results in the sensation
of pain ; of the optic nerve, in the sensation of light ; of a motor nerve, in
conti action 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 pecu-
liarity of nervous function depends neither upon any special construction
or activity of the nerve itself, nor upon the nature of the stimulus, but
entirely upon the peculiarities of its central and peripheral end organs.

Nerve 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.

General stimuli :

1. Mechanical : as from a blow, pressure, tension, puncture, etc.

2. Thermal : heating a nerve at first increases and then decreases its
excitability.

3. Chemic : sensory nerves respond somewhat less promptly than motor
nerves to this form of irritation.

4. Electric : either the constant or interrupted current.

84 HUMAN PHYSIOLOGY.

5. The normal physiologic stimulus :

(a) Centrifugal or efferent, if proceeding from the center toward the

periphery.
(6) Centripetal or afferent, if in the reverse direction.
Special stimuli :

1. Light or ethereal vibrations acting upon the end organs of the optic
nerve in the retina.

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

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

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

Nature of the Nerve Impulse. — As to the nature of the nerve im-
pulse generated by any of the foregoing stimuli either general or special,
but little is known. It has been supposed to partake of the nature of a
molecular disturbance, a combination of physical and chemical processes
attended by the liberation of energy, which propagates itself from molecule
to molecule. Judging from the deflections of the galvanometer needle it is
probable that when the nerve impulse 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 graph-
ically represented as a wave-like movement with a definite length and time
duration. Under strictly physiological 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, how
ever, it can be demonstrated that when a nerve impulse is aroused in the
course of a nerve by an adequate 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 Transmission of Nerve Force. — The passage of a ner-
vous impulse, either from the brain to the periphery or in the reverse direc-
tion, requires an appreciable period of time. The velocity with which the
impulse travels in human sensory nerves has been estimated at about 190
feet a second, and for motor nerves at from 1 00 to 200 feet a second.
The rate of movement is, however, somewhat modified by temperature,
cold lessening and heat increasing the rapidity ; it is also modified by elec-
tric conditions, by the action of drugs, the strength of the stimulus, etc.
The rate of transmission through the spinal cord is considerably slower

PHYSIOLOGY OF NERVE TISSUE. 85

than in nerves, the average velocity for voluntary motor impulses being
only 33 feet a second, for sensitive impressions 40 feet, and for tactile
impressions 140 feet a second.

Electric Currents in Muscles and Nerves. — If a muscle or nerve
be divided and non-polarizable electrodes be placed upon the natural longi-
tudinal surface at the equator, and upon the transverse section, electric
currents are observed with the aid of a delicate galvanometer. The direc-
tion of the current is always from the positive equatorial surface to the
negative transverse surface. The strength of the current increases or di-
minishes according as the positive electrode is moved toward or from the
equator. When the electrodes are placed on the two transverse ends of a
nerve, an axial current will be observed the direction of which is opposite to
that of the normal impulse of the nerve.

The electromotive force of the strongest nerve-current has been estimated
to be equal to the 0.026 of a Daniell battery ; the force of the current of
the frog muscle, about 0.05 to 0.08 of a Daniell. *-

Negative Variation of Currents in Muscles and Nerves. — If a
muscle or nerve be thrown into a condition of tetanus, it will be observed
that the currents undergo a diminution or negative variation, a change
which passes along the nerve in the form of a wave and with a velocity
equal to the rate of transmission of the nerve impulse. The wave-length
of a single negative variation has been estimated to be eighteen millimeters,
the period of its duration being from 0.0005 to 0.0008 of a second.

It is asserted by Hermann that perfectly fresh, uninjured muscles and
nerves are devoid of currents, and that the currents observed are the
result of molecular death at the point of section, this point becoming
negative to the equatorial point. He applies the term " action currents "
to the currents obtained when a muscle is thrown into a state of activity.

Electric Properties of Nerves. — When a galvanic current is made to
flow along a motor nerve from the center to the periphery, from the posi-
tive to the negative pole, it is known as the direct, descending, or centrif-
ugal current. When it is made to flow in the reverse direction, it is known
as the inverse, ascending, or centripetal current.

The passage of a direct current enfeebles the excitability of a nerve ;
the passage of the inverse current increases it. The excitability of a nerve
may be exhausted by the repeated applications of electricity ; when thus
exhausted, it may be restored by repose, or by the passage of the inverse
current if the nerve has been exhausted by the direct current, or vice versa. /

86 HUMAN PHYSIOLOGY.

During the actual passage of a feeble constant current, in either direction,
neither pain nor muscular contraction is ordinarily manifested ; if the
current be very intense, the nerve may be disorganized and its excitability
destroyed.

Electrotonus. — The passage of a direct galvanic current through a por-
tion of a nerve excites in the parts beyond the electrodes a condition of
electric tension, or electrotonus , during which the excitability of the nerve
is decreased near the anode or positive pole, and increased near the cathode
or negative pole ; the increase of excitability in the catelectrotonic area —
that nearest the muscle — being manifested by a more marked contraction of
the muscle than the normal when the nerve is irritated in this region. The
passage of an inverse galvanic current excites the same condition of elec-
trotonus ; the diminution of excitability near the anode, the anelec-
trotonic area, — that now nearest the muscle, — being manifested by a less
marked contraction than the normal when the nerve is stimulated in this
region. Between the electrodes is a neutral point, where the catelectrotonic
area emerges into the anelectrotonic area. If the current be a strong one,
the neutral point approaches the cathode ; if weak, it approaches the anode.

When a nervous impulse passes along a nerve, the only appreciable effect
is a change in its electric condition, there being no change in its tempera-
ture, chemic composition, or physical condition. The natural nerve- cur-
rents, which are always present in a living nerve as a result of its nutritive
activity, in great part disappear during the passage of an impulse, under-
going a negative variation.

Law of Contraction. — If a feeble galvanic current be applied to a
recent and excitable nerve, contraction is produced in the muscles only
upon the making of the circuit with both the direct and inverse currents.

If the current be moderate in intensity, the contraction is produced in
the muscle, both upon the making and breaking of the circuit, with both
the direct and inverse currents.

If the current be inte?ise, contraction is produced only when the circuit
is made with the direct current, and only when it is broken with the inverse
current.

FOODS AND DIETETICS.

During the functional activity of every organ and tissue of the body the
living material of which it is composed — the protoplasm — undergoes more
or less disintegration. Through a series of descending chemic stages it is
reduced to a number of simpler compounds, which are of no further value
to the body, and which are in consequence eliminated by the various elim-

FOODS AND DIETETICS. 87

inating or excretory organs — the lungs, kidneys, skin, liver. Among these
compounds the more important are carbon dioxid, urea, and uric acid.
Many other compounds, inorganic as well as organic, are also eliminated
in the water discharged from the body, in which they are held in solution.
Coincident with this disintegration of the tissues there is an evolution or
disengagement of energy, particularly in the form of heat.

In order that the tissues may regain their normal composition and thus
be enabled to continue in the performance of their functions, they must be
supplied with the same nutritive materials of which their protoplasm orig-
inally consisted — viz., water, inorganic salts, proteids, sugar, fat. These
materials are furnished by the blood during its passage through the capillary
blood-vessels. The blood is a reservoir of nutritive material in a condition
to be absorbed, organized, and transformed into new living tissue.

Inasmuch as the loss of material from the body daily, which is very
great, is compensated for under other forms by the blood, it is evident that
this fluid would rapidly diminish in volume were it not restored by the intro-
duction of new and corresponding materials. As soon as the blood vol-
ume falls to a certain point, the sensations of hunger and thirst arise,
which in a short time lead to the necessity of taking food.

In addition to the direct appropriation of food by the tissues it is highly
probable that an indefinite amount undergoes oxidation and disintegration
without ever becoming an integral part of the tissues, and thus directly
contributes to the production of heat.

Inanition or Starvation. — If these nutritive principles be not supplied
in sufficient quantity, or if they are withheld entirely, a condition of physio-
logic decay is established, to which the term inanition or starvation is
applied. The phenomena which characterizes this pathologic process are
as follows — viz., hunger, intense thirst, gastric and intestinal uneasiness
and pain, muscle weakness and emaciation, a diminution in the quantity
of carbon dioxid exhaled, a lessening in the amount of urine and its con-
stituents excreted, a diminution in the volume of the blood, an exhalation
of a fetid odor from the body, vertigo, stupor, delirium, and at times con-
vulsions, a fall of bodily temperature, and, finally, death from exhaustion.

During starvation the loss of different tissues, before death occurs, aver-
ages T^, or 40 per cent., of their weight.

Those tissues which lose more than 40 per cent, are : Fat, 93.3 ; blood,
75 ; spleen, 71.4; pancreas, 64.1 ; liver, 52; heart, 44.8; intestines,
42.4 ; muscle, 42.3. Those which lose less than 40 per cent, are : The
muscular coat of the stomach, 39.7 ; pharynx and esophagus, 34.2 ; skin,
33.3 ; kidneys, 31. 9; respiratory apparatus, 22.2 ; bones, 16.7 ; eyes, IO ;
nervous system, 1.9.

The fat entirely disappears, with the exception of a small quantity which

88 HUMAN PHYSIOLOGY.

remains in the posterior portion of the orbits and arountl the kidneys.
The blood diminishes in volume and loses its nutritive properties. The
7nuscles undergo a marked diminution in volume and become soft and
flabby. The nervous system is last to suffer, not more than two per cent,
disappearing before death occurs.

The appearances presented by the body after death from starvation are
those of anemia and great emaciation ; almost total absence of fat ; blood-
lessness ; a diminution in the volume of the organs ; an empty condition
of the stomach and bowels, the coats of which are thin and transparent.
There is a marked disposition of the body to .undergo decomposition,
giving rise to a very fetid odor.

The duration of life after a complete deprivation of food varies from eight
to thirteen days, though life can be maintained much longer if a quantity of
water be obtained. The water is more essential under these circumstances
than the solid matters, which can be supplied by the organism itself.

The different alimentary or nutritive principles which are appropriated
by the tissues, and which are contained within the various articles of food,
belong to both the organic and inorganic groups and chemic compounds,
and may be classified according to their composition as follows :

CLASSIFICATION OF ALIMENTARY PRINCIPLES.
i. Proteid Group. — Nitrogenized, C, O, H, N, S, P.

Principle. Where Found.

Myosin, Flesh of animals.

Vitellin, albumin, . Yolk of egg, white of egg.

Fibrin, globulin* . Blood contained in meat.

7 & 7 ■ " " ■ ■ ^

Casein, Mdk, cheese.

Gluten, ... Grain of wheat and other cereals.

Vegetable albumin, Soft, growing vegetables.

Legumin, Peas, beans, lentils, etc.

Gelatin, Bones.

2. Oleaginous Group. — C, O, H.

Animal fats and oils, ) Found in the adipose tissue of ani-

Stearin, olein, . . . . > mals, seeds, grains, nuts, fruits,

Paltnitin, fatty acids, j and other vegetable tissues.

3. Carbohydrate Group. — C, O, H.
Saccharose, or cane-sugar, .... Sugar-cane.

Dextrose, ox glucose, \ Fruits>

Levulose, or fruit-sugar, .... J

Lactose, or milk-sugar, Milk.

Maltose, Malt, malt foods.

Starch, Cereals, tuberous roots, and legu-
minous plants.
Glycogen, Liver, muscles.

FOODS AND DIETETICS. 89

4. Inorganic Group. — Water; sodium and potassium chlorids ; sodium
calcium, magnesium, and potassium phosphates ; calcium carbonate ;
and iron.

5. Vegetable Acid Group. — Malic, citric, tartaric, and other acids,
found principally in fruits.

6. Accessory Foods. — Tea, coffee, alcohol, cocoa, etc.

The proteid principlts of the food, after undergoing digestion and con-
version into peptones, are absorbed and transformed into the form of pro-
teids characteristic of the blood plasma and the lymph. Of the proteids
thus brought into relation with the living protoplasm, a small percentage
only is utilized in the repair of its substance. This is known as tissue pro-
teid. A large percentage circulating among and permeating the tissues is
acted upon by them directly, and reduced to simpler compounds without
ever becoming a part of the tissue itself. This is known as circulating
proteid. In the process of tissue metabolism all the proteids suffer disin-
tegration, and give rise to the production of some carbon-holding com-
pound, probably fat, and some nitrogen-holding compounds which event-
ually produce urea. The intermediate stages are possibly represented by
glycin, creatin, uric acid, etc. An excess of proteids in the food is followed
by their decomposition, by the pancreatic juice, into leucin and tyrosin,
which, by the agency of the liver, are converted into urea. The disinte-
gration of the proteids is attended by the disengagement of heat : they thus
contribute to the energy of the body.

The oleaginous principles, after digestion, are absorbed into the blood,
from which they rapidly disappear. It is probable that a portion of the
fat enters directly into the composition of living protoplasm, out of which
it again emerges at some subsequent stage in the form of small drops which
make their appearance in the protoplasmic cells of the connective areolar
tissue, thus giving rise to the adipose tissue. Another portion probably
undergoes direct oxidation.

The carbohydrate principles, after digestion, are absorbed as dextrose
and temporarily stored up in the liver as glycogen. The intermediate
stages which sugar passes through and the combinations into which it
enters between its absorption and its elimination are but imperfectly under-
stood. That it contributes to the accumulation of fat is probable, though
it is doubtful if it is ever converted into fat. A large percentage of the
sugar absorbed is at once oxidized. The reduction of fat and sugar to
carbon dioxid and water, under which forms they are eliminated from the
body, is accompanied by the disengagement of a large quantity of heat.
7

90 HUMAN PHYSIOLOGY.

Water is present in all the fluids and solids of the body. It promotes
the absorption of new material from the alimentary canal ; it holds the
various ingredients of the blood, lymph, and other fluids in solution ; it
hastens the absorption of waste products from the tissues, and promotes their
speedy elimination from the body.

Sodiiwi chlorid is present in all parts of the body to the extent of no
gm. The average amount eliminated daily is 15 gm. Its necessity as an
article of diet is at once apparent. Taken as a condiment, it imparts
sapidity to the food, excites the flow of the digestive fluids, promotes the
absorption and assimilation of the albumins, influences the passage of
nutritive material through animal membranes, and furnishes the chlorin for
the free hydrochloric acid of the gastric juice. In some unknown way it
favorably promotes the activity of the general nutritive process.

The potassium salts are also essential to the normal activity of the nutri-
tive process. When deprived of these salts, animals become weak and
emaciated. When given in small doses, they increase the force of the
heart-beat, raise the arterial pressure, and thus increase the action of the
circulation of the blood.

The calcium phosphate and carbonate are utilized in imparting solidity
to the tissues, more especially the bones and teeth. Many articles of food
contain these salts in quantities sufficient to restore the amount lost daily.

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

The accessory foods, coffee and tea, when taken in moderation, overcome
the sense of fatigue and mental unrest consequent on excessive physical
and mental exertion. Coffee increases the action of the intestinal glands
and acts as a laxative. After absorption, its active principle, caffein,
stimulates the- action of the heart, raises the arterial pressure, and excites
the action of the brain. Tea acts as an astringent, owing to the tannic
acid it contains. One effect of the tannic acid is to coagulate the digestive
ferments and to interfere with the activity of the digestive process.

Alcohol, when introduced into the system in small quantities, undergoes
oxidation and contributes to the production of force, and is thus far a food.
It excites the gastric glands to increased secretion, improves the digestion,
accelerates the action of the heart, and stimulates the activities of the
nerve centers. In zymotic diseases, and in all cases of depression of the

FOODS AND DIETETICS. 91

vital powers, it is most useful as a restorative agent. When taken in
excessive quantities, it is eliminated by the lungs and kidneys. The meta-
morphosis of the tissue is retarded, the elimination of urea and carbonic acid
is lessened, the temperature is lowered, the muscular powers are impaired,
and the resistance to depressing external influences is diminished. When
taken throughout a long period of time, alcohol impairs digestion, produces
gastric catarrh, and disorders the secreting power of the hepatic cells. It
also diminishes the muscular power and destroys the structure and compo-
sition of the cells of the brain and spinal cord. The connective tissue of
the body increases in amount, and, subsequently contracting, gives rise to
sclerosis.

A proper combination of various alimentary principles is essential for
healthy nutrition, no one class being capable of maintaining life for any
definite length of time.

The albuminous food in excess promotes the arthritic diathesis, mani-
festing itself as gout, gravel, etc.

The oleaginous food in excess gives rise to the bilious diathesis, while a
deficiency of it promotes the scrofulous.

The farinaceous food when long continued in excess, favors the rheu-
matic diathesis by the development of lactic acid.

The quantities of the different nutritive materials which are required
daily for the growth and repair of the tissues and for the evolution of heat
have been variously estimated by different observers. The following table
shows the average diet scale of Vierordt, and the amount of waste products
to which it would give rise :

Comparison of the Ingesta and Egesta.

Ingest a. Egesta.

Proteids, .... 1 20 grams. Urea, .... 40 grams.

Fat, 90 " Inorganic salts, 32 "

Starch, . . . . 330 " Feces, .... 104 "

Inorganic salts, . 32 " Carbon dioxid, 800 "

Water, ..... 2,800 " Water, .... 3,096 "

Oxygen, .... 700 " Total, . . 4,072 "

Total, . . . 4,072 "

Other estimates as to the amount of the organic substances required
daily are as follows :

Ranke.

Voit.

Moleschott.

Proteid, . .100

118

130 grams.

Fat, ... 100

50

84 "

Starch, . . 240

500

404 "

92 HUMAN PHYSIOLOGY.

The Energy of the Animal Body. — The food consumed daily not
only repairs the loss of material from the body, but also furnishes the
energy to replace that which is expended daily in the shape of heat and
motion. All the energy of the body can be traced to the chemic changes
going on in the tissues, and more particularly to those changes involved in
the oxidation of the foods.

The amount of heat yielded by any given food principle can be deter-
mined by burning it to carbon dioxid and water, and ascertaining the
extent to which it will, when so liberated, raise the temperature of a given
volume of water. This amount of heat may be expressed in gram degrees
of heat — i. e. , calories or kilogrammeters of work. A calorie is the amount
of heat required to raise the temperature of one gram of water one degree
Centigrade, or one kilograiti of water one degree Centigrade. A kilogram-
meter of work is the amount of heat energy required to raise a weight of
one kilogram a distance of one meter.

The following estimates give, approximately, the number of calories pro-
duced when the food is reduced within the body to urea, carbon dioxid,
and water :

I gram of proteid yields 4,124 kilogram calories.
I " fat " 9,353 " "

1 " starch " 4,116 " "

The total number of kilogram calories yielded by any given diet scale
can be readily determined by multiplying the preceding factors by the
quantities of material consumed. The diet scale of Ranke, for example,
yields the following amount :

100 grams of proteid yield 412.4 calories.
100 " fat " 935.3 "

240 " starch " 987.8 "

Total, 2,335.5 "

It has also been determined experimentally that one gram of proteid, one
gram of fat, and one gram of starch, when completely oxidized, will yield
energy sufficient to perform 1,850, 3,841, and 1,567 kilogrammeters of
work, respectively.

The total energy of the Ranke diet scale can be easily calculated — e. g. :

100 grams of proteid yield 185,000 kilogrammeters.
100 " fat " 384,100 "

240 " starch " 397,680 "

Total, .... 9667780 "

FOODS AND DIETETICS. 93

It will be thus seen that the food consumed daily yields 2,335,000 gmm
calories, or 2,335 kilogram calories, which can be translated into its me-
chanical equivalent, 966,780 kilogrammeters of work.

The amount of food required in twenty-four hours is estimated from
the total quantity of carbon and nitrogen excreted from the body in
twenty -four hours, these two elements representing the waste or destruction
of the carbonaceous and nitrogenized compounds. It has been determined
by experimentation that about 4,600 grains of carbon and about 300 grains
of nitrogen are eliminated from the body daily, the ratio being about 15
to I. That the body may be kept in its normal condition, a proper pro-
portion of carbonaceous (bread) to nitrogenized (meat) food should be ob-
served in the diet.

The method of determining the proper amounts of both kinds of food is
as follows :

1,000 grs. of bread (2 oz. ) contain 300 grs. C and 10 grs. N.

To obtain the requisite amount of nitrogen from bread, 30,000 grains, or
about four pounds, containing 9,000 grains of carbon and 300 of nitrogen,
would have to be consumed. On such a diet there would be a large
excess of carbon, which would be undesirable. On a meat diet the reverse
obtains :

1,000 grs. of meat (2 oz. ) contain 100 grs. C and 30 grs. N.

To obtain the requisite amount of carbon from meat, 45,000 grains, or
about 6*4 pounds, containing 4,500 grains of carbon and 1,350 grains of
nitrogen would have to be consumed. Under such circumstances there
would arise an excess of nitrogen in the system, which would be equally
undesirable and injurious. By combining these two articles, however, in
proper proportion, the requisite amounts of carbon and nitrogen can be ob-
tained without any excess of either — e. g. :

2 pounds of bread contain 4,630 grs. C and 154 grs. N.
% " meat " 463 " " " 154 " "

5,093 C. 308 N.

The amount of carbon and nitrogen necessary to compensate for the loss
to the system daily would be contained in the foregoing amount of food.
As about 3^ ounces of oil or butter are. consumed daily, the quantity of
bread can be reduced to 19 ounces. In the quantities of bread and meat
just mentioned there are 4.2 ounces albumin, 9.3 sugar and starch.

94

HUMAN PHYSIOLOGY.

The alimentary principles are not introduced into the body as such,
but are combined in proper proportions to form compound substances,
termed foods, — e. g., bread, milk, eggs, meat, etc., — the nutritive value of
each depending upon the extent to which these principles exist.

The following tables show the average composition of various articles
of food :

COMPOSITION OF ANIMAL FOODS.

In ioo Parts.

Beef.

Veal.

Mutton.

Pork.

Fowl.

Fish.

Water, ....

76.25

77.82

75-59

72.57

70.80

79-30

Proteid, ....

20.24

I9.86

17. 11

19-31

22.70

18.30

Fat,

1.68

O.82

5-47

5.82

4.IO

O.70

Carbohydrates,

0.50

O.80

0.60

O 60

I.20

O.90

1-38

O.70

1 23

I.70

I.20

o.So

COMPOSITION OF VEGETABLE FOODS.

In ioo Parts.

Beans.

Peas.

Pota-
toes

Turnips.

Cabbage.

Aspara-
gus.

Water, ....

13-74

14.99

75-47

89.42

89.97

93-75

Proteid, ....

23.21

22.85

1-95

1-35

I.89

1.79

Fat,

2.14

I.79

0.15

O.18

0.20

0.25

Carbohydrates,

53-67

52-36

20.69

7.36

4.87

2.63

Cellulose, .

3- 69

5-43

0.76

O.94

. I.84

1.04

Salts, ...

3-55

2.58

0.98

0.75

I.23

o.54

DIGESTION.

ICOMPOSITION OF CEREAL FOODS.

95

In ioo Parts.

Whf.at.

Rye.

12.65

Barley.

13-77

Oats.
12.37

Corn.
I3.IO

Rice.

Water, . . .

I3-56

13.12

Proteid, . .

12.35

12-55

11. 14

IO.4I

9.85

7.88

Fat,

i-75

I.97

2.16

5-23

4-57

O.85

Carbohydrates.

67.90

67.95

64-93

57-78

68.42

76.55

Cellulose, . . .

2.63

3.00

5-3i

1 1 . 1 9

2.50

0.55

Salts,

1. 81

1.88

2.69

3.02

1.56

I.05

DIGESTION.

Digestion is a physical and chemic process by which the food intro-
duced into the alimentary canal is liquefied and its nutritive principles are
transformed by the digestive fluids into new substances capable of being
absorbed into the blood.

The digestive apparatus consists of the alimentary canal and its
appendages — viz. , teeth ; salivary, gastric, and intestinal glands ; liver ; and
pancreas.

Digestion maybe divided into seven stages: prehension, mastication,
insalivation, deglutition, gastric and intestinal digestion, and defecation.

Prehension, the act of conveying food into the mouth, is accomplished
by the hands, lips, and teeth.

MASTICATION.

Mastication is the trituration of the food, and is accomplished by the

teeth and lower jaw under the influence of muscular contraction. When

thoroughly divided, the food presents a larger surface for the solvent

action of the digestive fluids, thus aiding the general process of digestion.

The teeth are thirty -two in number, sixteen in each jaw, and divided
into four incisors or cutting teeth, two canines, four bicuspids, and six

96 HUMAN PHYSIOLOGY.

molars or grinding teeth ; each tooth consists of a crown covered by
enamel, a neck, and a root surrounded by the crusta petrosa and embedded
in the alveolar process ; a section through a tooth shows that its substance
is made of dentine, in the center of which is the pulp cavity containing
blood-vessels and nerves.

The lower Jaw is capable of making a downward and an upward, a
lateral and an anteroposterior movement, dependent upon the construction
of the temporomaxillary articulation.

The jaw is depressed by the contraction of the digastric ', geniohyoid, mylo-
hyoid, and platysma myoides muscles; elevated by the temporal, masseter,
and internal pterygoid muscles ; moved laterally by the alternate contrac-
tion of the external pterygoid muscles ; moved anteriorly by the pterygoid,
and posteriorly by the united actions of the geniohyoid, mylohyoid, and
posterior fibers of the temporal muscles.

The food is kept between the teeth by the intrinsic and extrinsic muscles
of the tongue from within, and the orbicularis oris and buccinator muscles
from without.

The movements of mastication, though originating in an effort of
the will and under its control, are, for the most part, of an automatic or
reflex character, taking place through the medulla oblongata and induced
by the presence of food within ihe mouth. The nerves and nerve- centers
involved in this mechanism are shown in the following table :

NERVOUS CIRCLE OF MASTICATION.

Afferent or Excitor Nerves. Efferent or Motor Nerves.

1. Lingual branch of 5th pair. 1. 3d branch of 5th pair.

2. Glossopharyngeal. 2. Hypoglossal.

3. Facial.

The impressions made upon the terminal filaments of the sensory nerves
are transmitted to the medulla ; motor impulses are here generated which
are transmitted through motor nerves to the muscles involved in the move-
ments of the lower jaw. The medulla not only generates motor impulses,
but coordinates them in such a manner that the movements of mastication
may be directed toward the accomplishment of a definite purpose.

INSALIVATION.

Insalivation is the incorporation of the food with the saliva secreted
by the parotid, submaxillary, and sublingual glands ; the parotid saliva,
thin and watery, is poured into the mouth through Steno's duct ; the sub-

DIGESTION.

97

maxillary and sublingual salivas, thick and viscid, are poured into the
mouth through Wharton's and Bartholin's ducts.

In their minute structure the salivary glands resemble one another. They
belong to the racemose variety, and consist of small sacs or vesicles, which
are the terminal expansions of the smallest salivary ducts. Each vesicle or
acinus consists of a basement membrane surrounded by blood-vessels and
lined with epithelial cells. In the parotid gland the lining cells are
granular and nucleated ; in the submaxillary and sublingual glands the
cells are large, clear, and contain a quantity of mucigen. During and
after secretion very remarkeble changes take place in the cells lining the
acini, which are in some way connected with the essential constituents
of the salivary fluids.

In a living serous gland, — e. g., parotid, — during rest, the secretory cells
lining the acini of the gland are seen to be filled with fine granules, which
are often so abundant as to obscure the nucleus and enlarge the cells until
the lumen of the acinus is almost obliterated. (See P'ig. II.) When the
gland begins to secrete the saliva, the granules disappear from the outer

Fig. ii.— Cells of the Alveoli of a Serous or Watery Salivary Gland. —
( Yeo's " Text-Book of Physiology.")

A. After rest. B. After a short period of activity. C. After a prolonged period of

activity.

boundary of the cells, which then become clear and distinct. At the end
of the secretory activity the cells have been freed of granules and have
become smaller and more distinct in outline. It would seem that the
granular matter is formed in the cells during the period of rest and dis-
charged into the ducts during the activity of the gland.

In the mucous glands — e. g., submaxillary and sublingual — the changes
that occur in the cells are somewhat different. (See Fig. 12.) During
the intervals of digestion the cells lining the gland are large, clear, and
highly refractive, and contain a large quantity of mucigen. After secretion
has taken place the cells exhibit a marked change. The mucigen cells
have disappeared, and in their place are cells which are small, dark, and

98

HUMAN PHYSIOLOGY.

Fig. 12. — Section of a Mucous Gland. — (Lavdowsky.)
A. In a state rest. B. After it has been for some time actively secreting.

composed of protoplasm. It would appear that the cells, during rest,
elaborate the mucigen, which is discharged into the tubules during secretory
activity, to become part of the secretion.

Saliva is an opalescent, slightly viscid, alkaline fluid, having a specific
gravity of 1. 005. Microscopic examination reveals the pfesence of
salivary corpuscles and epithelial cells. Chemically it is composed of
water, proteid matter, a ferment (ptyalin), and inorganic salts. The
amount secreted in twenty-four hours is about 2.l/2 lbs. Its function is
twofold :

1. Physical. — Softens and moistens the food, agglutinates it, and facili-
tates swallowing.

2. Chemic. — Converts starch into sugar. This action is due to the pres-
ence of the organic ferment, ptyalin. Ptyalin is an amorphous nitrog-
enized substance, which can be precipitated from the saliva by calcium
phosphate. Its power of converting starch into sugar is manifested most
decidedly at the temperature of the living body and in a slightly alkaline
medium. The conversion of starch into sugar takes place through
several stages, the nature of which depends upon the structure of the
starch granule. This consists of two portions, a stroma of cellulose and
a contained material, granulose, which is the more abundant and impor-
tant of the two. When subjected to the action of boiling water, the
starch granule swells up and bursts, forming a viscid, opalescent mass
of starch paste. If saliva be now added to this paste and kept at a
temperature of IO40 F. for a few minutes, the paste becomes clear and
limpid. The first stage in the digestion is now complete, with the

DIGESTION. 99

formation of soluble starch. If the action of saliva be continued, a
number of substances intermediate between starch and sugar are formed,
to which the name dextrin has been given. Among these may be
mentioned :

a. Erythrodextrin, which gives the reddish-brown color with iodin.
As the digestion continues and sugar is formed, the erythrodextrin
disappears, giving way to —

b. Achroodextrin, which yields no coloration with iodin, but which may
be precipitated by alcohol.

The sugar formed by the action of saliva is maltose, the formula for
which is C12H22On. A small quantity of dextrose is also formed.

NERVOUS CIRCULATION OF INSALIVATION.

Afferent or Excitor Nerves. Efferent or Secretory Nerves.

1. Lingual branch of 5th pair. I. Auriculotemporal branch of 5th

2. Glossopharyngeal. pair, for parotid gland.

2. Chorda tympani, for submaxil-
lary and sublingual glands.

The centers regulating the secretion are two — viz., the medulla oblon-
gata and the submaxillary ganglion of the sympathetic, the latter acting
antagonistically to the former. Impressions excited by the food in the
mouth reach the medulla oblongata through the afferent nerves ; motor
impulses are there generated which pass outward through the efferent nerves.

Stimulation of the auriculotemporal branch increases the flow of saliva
from the parotid gland ; division arrests it.

Stimulation of the chorda tympani is followed by a dilatation of the
blood-vessels of the submaxillary gland, increased flow of blood (thus
acting as a vaso-dilator nerve), and an abundant discharge of a thin saliva ;
division of the nerve arrests the secretion.

Stimulation of the cervical sympathetic is followed by a contraction of
the blood-vessels, diminishing the flow of blood (thus acting as a vaso-con-
strictor nerve), and a diminution of the secretion, which now becomes thick
and viscid ; division of the sympathetic does not, however, completely
dilate the vessels. There is evidence of the existence of a local vaso-
motor mechanism, which is inhibited by the chorda tympani, exalted by
the sympathetic.

DEGLUTITION.

Deglutition is the act of transferring food from the mouth into the
stomach, and may be divided into three stages :
I. The passage of the bolus from the mouth into the pharynx.

100 HUMAN PHYSIOLOGY.

2. From the pharynx into the esophagus.

3. From the esophagus into the stomach.

In the first stage, which is entirely voluntary, the mouth is closed and
respiration momentarily suspended ; the tongue, placed against the roof of
the mouth, arches upward and backward, and forces the bolus in tothe fauces.

In the second stage, which is entirely reflex, the palate is made tense and
directed upward and backward by the levatores palati and tensores palati
muscles ; the bolus is grasped by the superior constrictor muscle of the
pharynx and rapidly forced into the esophagus.

The food is prevented from entering the posterior nares by the uvula and
the closure of the posterior half-arches (the palatopharyngeal muscles) ;
from entering the larynx by its ascent under the base of the tongue and
the action of the epiglottis.

In the third stage the longitudinal and circular muscle-fibers, contract-
ing from above downward, strip the bolus into the stomach. ( For Nervous
Mechanism of Deglutition, see Medulla Oblongata. )

GASTRIC DIGESTION.

The Stomach. — Immediately beyond the termination of the esophagus
the alimentary canal expands and forms a receptacle for the temporary
retention of the food. To this dilatation the term stomach has been
applied. This organ is somewhat pyriform in outline, and occupies the
upper part of the abdominal cavity. It is about 13 inches long, 5 deep,
and 3^ wide, and has a capacity of about five pints. It presents two
orifices, the cardiac or esophageal, and the pyloric ; two curvatures, the
lesser and the greater.

The left or cardiac end of the stomach is enlarged, and forms the fundus ;
the right end is much narrower, and forms the pylorus. The stomach
possesses three coats :

1. The serous, or reflection of the peritoneum.

2. The muscular, the fibers of which are arranged in a longitudinal, a cir-
cular, and an oblique direction. At the pyloric end the circular fibers
increase in number and form a thick ring or band, which is known as
the sphincter of the pylorus.

3. The mucous, which is somewhat larger than the muscular coat, and in
consequence is thrown into folds or rugre. The surface of the mucous
coat is covered by tall, narrow, columnar epithelium.

Gastric Juice. — During the period of time the food remains in the
stomach it is subjected to the disintegrating action of an acid fluid, the

DIGESTION. 101

gastric juice. This fluid, secreted from glands in the mucous membrane, is
thoroughly incorporated with the food in consequence of the contractions
of the muscular coat. The food is gradually liquefied and reduced to a
form which partly fits it for passage into the small intestine and for absorp
tion into the blood. Gastric juice, when obtained in a pure state, is a
clear, colorless fluid, decidedly acid in reaction, with a specific gravity of
1005. It is composed of the following ingredients :

COMPOSITION OF GASTRIC JUICE.

Water, . . 994.404

Hydrochloric acid, 0.200

Organic matter, 3-!95

Inorganic salts, 2.201

1000.000

The water forms by far the largest part of this fluid, and serves the
purpose of holding the other ingredients in solution, and by its saturating
power brings them into relation with the constituents of the food. Of the
inorganic salts the sodium and potassium chlorids are the most abundant
and important.

The hydrochloric acid, which exists in a free state, is present in variable
amounts. In the foregoing table the number of part a thousand is much
smaller than is usually stated. According to most observers, hydrochloric
acid is present to the extent of from 0.2 to 0.3 part a hundred. Though
secreted as soon as the food enters the stomach, the acid can not be
detected in the free state until after the lapse of from thirty to forty minutes.
It acidulates the food and prevents fermentative changes.

TYlg. pepsin, which is present in gastric juice associated with the organic
matter, is a hydrolytic ferment or enzyme. When freed from its associa-
tions and obtained in a pure state, pepsin presents the characteristics of a
colloid body, and resembles in its reactions the albuminoids. It has the
power, when brought into relation with acidulated proteids, of transform-
ing them into new forms capable of absorption into the blood.

Rennin. — In addition to pepsin a second ferment exists in the gastric
juice, to which the term rennin has been given. It possesses the power of
coagulating the caseinogen of milk. It exists in the mucous membrane,
from which it can be extracted by appropriate means. When rennin acts
on caseinogen, the latter is split into insoluble casein and a soluble albumin.
Calcium phosphate is essential to the action of this enzyme.

Gastric Glands. — Embedded within the mucous membrane are to be
found enormous numbers of tubular glands, which, though resembling one

102

HUMAN PHYSIOLOGY.

another in general form, differ in their histologic details in various por-
tions of the stomach.

In the cardiac end or fundus the glands consist of several long tubules,
opening into a short, common duct, which opens by a wide mouth on
the surface of the mucous membrane. Each gland consists primarily of a
basement membrane lined by epithelial cells. In the duct the epithelium
is of the columnar variety, resembling that covering the surface of the
mucous membrane. The secretory portion of the tubule is lined by a layer
of short, polyhedral, granular, and nucleated cells, which, as they border
the lumen of the tubule, and thus occupy the central portion of the gland,
are termed central cells. At irregular intervals, between the central cells

Fig. 13.
Diagram showing the relation of the ultimate twigs of the blood-vessels, V and A, and
of the absorbent radicles to the glands of the stomach and the different kinds of
- epithelium — viz., above cyiindric cells ; small, pale eel sin the lumen, outside which
are the dark ovoid cells. — ( Yeo's" Text-book 0/ Physiology.'")

and the wall of the tubule, are found large, oval, reticulated cells, which,
on account of their position, are termed parietal cells. (See Fig. 13.)

Each parietal cell is in relation with a system of fine canals, which open
directly into the lumen of the gland. It is estimated that the fundus con-

DIGESTION. 103

tains about five million glands. In the pyloric end of the stomach the
glands are generally branched at their lower extremities, and the common
duct is long and wide. The duct is lined by columnar epithelium, while
the secreting part is lined by short, slightly columnar, granular cells. The
parietal cells are entirely wanting. The epithelium covering the surface
of the mucous membrane is tall, narrow and cylindric in shape, and con-
sists of mucus-secreting goblet cells. The outer half of the cell contains a
substance, mucinogen, which produces mucin. The gastric glands in both
situations are surrounded by a fine connective tissue, which supports
blood-vessels, nerves, and lymphatics.

Changes in the Cells During Secretion. — During the periods of rest
and secretory activity the cells of the glands undergo changes in structure
which are supposed to be connected with the production of the pepsin and
hydrochloric acid. During rest, the protoplasm of the central cells becomes
filled with granular matter ; during the time of secretion this disappears,
presumably passing into the lumen of the tubule, and as a result the proto-
plasm becomes clear and hyaline in appearance. The granular material
is probably the mother substance, pepsinogen, which, inactive in itself,
yields the active ferment, pepsin. The parietal cells during digestion in-
crease in size, but do not become granular. It is at this period that they
secrete the hydrochloric acid. After digestion they rapidly diminish in
size and return to their former condition. The pyloric glands secrete
pepsin only.

Mechanism of Secretion. — In the intervals of digestion the mucous
membrane of the stomach is covered with a layer of mucus. As soon as
the food passes from the esophagus into the stomach, the blood-vessels
dilate, the circulation becomes more active, and the membrane assumes a
bright red appearance. Coinciden tally, small drops of gastric juice begin
to exude from the glands, which, as they increase in number, run together
and trickle down the sides of the stomach. This pouring out of fluid con-
tinues during the presence of food in the stomach.

The secretion of gastric juice is a reflex act, taking place through the
central nervous system and called forth in response to the stimulus of food
in the stomach. That the central nervous system also directly influences
the production of the secretion is shown by the fact that emotion, such
as fear or anger, will arrest or vitiate the normal secretion. The reflex
nature of the process can be shown by experimentation upon the pneu-
mogastric nerve. If during digestion, when the peristaltic movements are
active and the gastric mucous membrane is flushed and covered with gas-

104 HUMAN PHYSIOLOGY.

trie juice, the pneumogastric nerves are divided on both sides, the mucous
membrane becomes pale, the secretion is arrested, and the peristaltic move-
ments become less marked. Stimulation of the peripheral end produces
no constant effects ; stimulation of the central end, however, is at once
followed by dilatation of the vessels, flushing of the mucous membrane,
and reestablishment of the secretion. It is evident, therefore, that during
digestion afferent impulses are passing up the pneumogastrics to the med-
ulla ; efferent impulses, in all probability, pass through the fibers of the
sympathetic nervous system to the blood-vessels and glands concerned in
the elaboration of the gastric juice. After all the nerve connections of
the stomach are divided, the secretion of a small quantity of juice continues
for several days. This has been attributed to the action of a local nervous
mechanism and to the direct action of the food upon the protoplasm of the
secreting cells.

Chemic Action of the Gastric Juice. — By the combined influence of
the contraction of the muscular walls, the action of the gastric juice, and
the temperature, the food is reduced to a semiliquid condition and acquires
a distinct acid odor. This semifluid mass will vary in composition and
appearance according to the nature of the food. To this matter the term
chyme has been given.

Meat is rapidly disintegrated by the solution of its connective tissue.
The fibers thus separated are readily broken up into particles by solution
of the sarcolemma. Well-cooked meat is more easily digested, owing to
the conversion of the connective tissue into gelatin.

Connective tissues in the raw or imperfectly gelatinized condition are
very slowly dissolved. Cartilage, tendons, and even bones will in time be
corroded and liquefied.

Vegetables are not easily digested unless thoroughly prepared by sufficient
cooking. The nutritive principles are inclosed by cellulose walls, which
are not affected by gastric juice. The influence of heat and moisture
softens and ruptures the cellulose walls so as to permit the introduction of
gastric juice and the solution of its nutritive principles.

The principal action of the gastric juice, however, is the transforma-
tion of the different proteid principles of the food into peptones, the inter-
mediate stages of which are due to the influence of the acid and pepsin re-
spectively. As soon as any one of the albumins is penetrated by the acid
it is converted into acid-albumin, a fact which indicates that the first step
in gastric digestion is the acidification of the proteids. This having been
accomplished, the pepsin becomes operative and In a varying length gf

DIGESTION. 105

time transforms the acid- albumin into a new form of proteid' termed pep-
tone, of which, as indicated by chemic tests, there are probably two forms,
hemi- and anti-peptone. In this transformation it is possible to isolate inter-
mediate bodies by the addition of ammonium sulphate, to which the term
albumose or proteose has been given. 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, hemi- and anti-. This supposed change is represented
in the following scheme :

Albumin.

I
Acid-albumin.

/\
Hemi- albumose. Anti-albumose.

I
Hemi-peptone. Anti-peptone.

From the fact that one form of peptone — hemi — under the influence of
the pancreatic ferment trypsin can be decomposed into leucin, tyrosin,
aspartic acid, etc., it is believed that all the simple proteids contain two
distinct groups or radicles termed hemi- and anti-radicles, and that it is
this fact that determines the line of cleavage and the characteristics of the
cleavage products.

Peptones. — Peptones are the final products of the digestion of proteid
bodies, and differ from the bodies from which they are derived in the
following particulars :

1. They are diffusible, — i. e., capable of passing readily through animal
membranes, — a condition essential for their absorption.

2. They are soluble in water and in saline solution.

3. They are non-coagulable by heat and nitric or acetic acids. They
can be readily precipitated, however, by tannic acid, by bile acids, and
by mercuric chlorid.

4. They are absorbable and assimilab 'e, soon becoming transformed into
serum -album in.

The duration of gastric digestion will depend largely upon the quantity
and quality of the food. The digestion of the average meal occupies from
three to five hours.

Movements of the Stomach. — As soon as digestion commences the

cardiac and pyloric orifices are closed ; the walls of the stomach contract

upon the food, and a peristaltic action begins, which carries the food along

the greater and lesser curvatures, and thoroughly incorporates it with the

8

106 HUMAN PHYSIOLOGY.

gastric juice. As soon as any portion of the food is digested, it passes
through the pylorus into the intestine.

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, " . \ 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 30

Turnips, " 3 30

Beets, " ... 3 45

Parsnips, " • . . . 2 30

INTESTJNAL DIGESTION.

The process of digestion as it takes place in the small intestine is ex-
ceedingly important and complex, and is brought about by the action of
the pancreatic juice, the bile, and the intestinal juice.

The contents of the stomach at the close of gastric digestion consist of
water, inorganic salts, peptones, undigested albumins and starches, maltose,
cane-sugar, liquefied fats, cellulose, and the indigestible portions of meats,
cereals, fruits, etc. This so-called chyme is quite acid in reaction, and upon
its passage through the now open pylorus into the intestine it excites a reflex
stimulation and secretion of the intestinal fluids, which are decidedly
alkaline in reaction, and which have a neutralizing action on the chyme.
As soon as the latter becomes alkaline and gastric digestion is arrested, the

DIGESTION. 107

various phases of intestinal digestion begin which eventuate in the trans-
formation of all the remaining undigested nutritive materials into absorb-
able and assimilable compounds.

The small intestine is about 22 feet in length and about 1^ inches
in diameter. Like the stomach, it possesses three coats, as follows :

1. The serous, or peritoneal.

2. The muscular, the fibers of which are arranged for the most part cir-
cularly. Some of the fibers are so arranged as to form longitudinal
bands.

3. The mucous, which presents a series of transverse folds, known as the
valvulcc conniventes.

Intestinal Glands. — In that portion of the small intestine known as
the duodenum are to be found a number of small, branched, tubular glands
(Brunner's), the acini of which are lined by short, cylindric cells, similar
to those lining the pyloric glands. From the duodenum to the termination
of the intestine the mucous membrane contains an enormous number of
tubular glands (Lieberkiihn's), formed by an inversion of the basement
membrane and lined by epithelial cells. The common secretion of these
intestinal glands forms the intestinal juice. This is a thin, opalescent,
slightly yellowish fluid, alkaline in reaction, and contains water, salts, and
proteid matter.

The function of the intestinal juice is but incompletely known. It ap-
pears to have the power of converting starch into dextrose ; it is doubtful
whether it is capable of digesting either albumins or fats. Its most dis-
tinctive action is the inversion of cane-sugar, maltose, and lactose into
dextrose, thus preparing them for absorption. This change is dependent
on the presence of a ferment body known as invertin.

The pancreatic juice is secreted by the pancreas, a flattened gland,
about six inches long, running transversely across the posterior wall of the
abdomen behind the stomach ; its duct opens into the duodenum.

The pancreas is similar in structure to the salivary glands, and consists
of a system of ducts terminating in acini. The acini are tubular or flask-
shaped, and consist of a basement membrane lined by a layer of cylindric,
conic cells, which encroach upon the lumen of the acini. The cells
exhibit a difference in their structure (Fig. 14), and may be said to consist
of two zones — viz., an outer parietal zone, which is transparent and appar-
ently homogeneous, staining rapidly with carmin ; an inner zone, which
borders the lumen, and is distinctly granular and stains but slightly with
carmin. These cells undergo changes similar to those exhibited by the

108

HUMAN PHYSIOLOGY.

cells of the salivary glands during and after active secretion. As soon as
the secretory activity of the pancreas is established, the granules disappear,
and the inner granular layer becomes reduced to a, very narrow border,
while the outer zone increases in size and occupies nearly the entire cell.
During the intervals of secretion, however, the granular layer reappears
and increases in size until the outer zone is reduced to a minimum. It
would seem that the granular matter is formed by the nutritive processes
occurring in the gland during rest, and is discharged during secretory
activity into the ducts, and takes part in the formation of the pancreatic
secretion.

The pancreatic juice is transparent, colorless, strongly alkaline, and
viscid, and has a specific gravity of 1040. It is one of the most im-

■*'

A B

Fig. 14. — One Saccule of the Pancreas of the Rabbit in Different States
of Activity. — ( Yeo's " Text-book of Physiology ," after Kilhne and Lea.)

A. After a period of rest, in which case the outlines of ihe cells are indistinct and the
inner zone — i. 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
outlines (d) are clearer, the granular zone (a) is smaller, and the clear outer zone is
wider.

portant of the digestive fluids, as it exerts a transforming influence upon
all classes of alimentary principles, and has been shown to contain at least
three distinct ferments. It has the following composition :

COMPOSITION OF PANCREATIC JUICE.

Water, 900.76

Albuminoid substances, . 90.44 *

Inorganic salts, 8.80

1,000.00
The pancreatic juice is characterized by its action :
I. Upon starch. When starch is subjected to the action of the juice, it
is at once transformed into maltose ; the change takes place more rapidly

DIGESTION. 109

than when saliva is added. This action is caused by the presence of a
special ferment, amylopsin.

2. Upon albumin. The proteid bodies which escape digestion in the
stomach are converted into peptones by the action of the alkali and fer-
ment. The first effect of the alkali is to change the proteid into an
alkali-albumin, a fact which indicates that in the digestion of albumin
by pancreatic juice, the first stage is alkalinization. This having been
accomplished, the ferment trypsin transforms the alkali-albumin into
peptone, of which, as in gastric digestion, there are two forms, hemi- and
a7iti -peptone. For the same reason it is believed that here also these
bodies are preceded in their development by albumoses, of which there
are probably two forms. Long-continued action of the pancreatic juice
as previously stated, decomposes the hemi-peptone intoleucin, tyrosin, etc.

3. Xlpoxi fats. The most striking action of the pancreatic juice is the emul-
sification of the fats or their subdivision into minute particles of micro-
scopic size. This change takes place rapidly, and depends upon the
alkalinity of the fluid and the quantity of albumin present, combined with
the intestinal movements. The neutral fats are also decomposed into
their corresponding fatty acids and glycerin ; the acids thus set free unite
with the alkaline bases present in the intestine and form soaps. This
decomposition of the neutral fats is caused by the ferment, sleapsin.

The bile has an important function in the elaboration of the food and in
its preparation for absorption. It is a golden-brown, viscid fluid, having a
neutral or alkaline reaction and a specific gravity of 1 020.

COMPOSITION OF BILE.

Water, 859.2

Sodium glycocholate, 1 or .4

Sodium taurocholate, J

Fat, 9.2

Cholesterin, .... 2.6

Mucus and coloring-matter, 29 8

Salts, 7-8

1,000.0

The biliary salts, sodium glycocholate and taurocholate, are characteristic
ingredients, and by the process of secretion are formed in the liver from
materials furnished by the blood. It is probable that they are derived from
the nitrogenized compounds, though the stages in the process are unknown.
They are reabsorbed from the small intestine to play some ulterior part
in nutrition.

Cholesterin is a product of waste taken up by the blood from the nerve
tissues and excreted by the liver. It crystallizes in the form of rhombic

110 HUMAN PHYSIOLOGY.

plates, which are quite transparent. When retained within the blood, it
gives rise to the condition of cholesteremia, attended with severe nervous
symptoms. It is given off in the feces under the form of stercorin.

The coloring-matters which give the tints to the bile are biliverdin and
bilirubin, and are probably derived from the coloring-matter of the blood.
Their presence in any fluid can be recognized by adding to it nitric acid
containing nitrous acid, when a play of colors is observed, beginning with
green, blue, violet, red, and yellow.

The bile is both a secretion and an excretion ; it is constantly being
formed and discharged by the hepatic ducts into the gall-bladder, in which
it is stored up during the intervals of digestion. As soon as food enters the
intestines it is poured out abundantly by the contraction of the walls of the
gall-bladder.

The amount secreted in twenty-four hours is about 2j^ pounds.

Functions of the Bile :

1. It assists in the enmhification of the fats and promotes their absorption.

2. It tends to prevent putrefactive changes in the food.

3. It stimulates the secretion of the intestinal glands, and excites the
normal peristaltic movement of the bowels.

The digested food, the chyme, is a grayish, pultaceous mass, but as it
passes through the intestines it becomes yellow from admixture with the
bile. It is propelled onward by vermicular motion — by the contraction of
the circular and longitudinal muscle-fibers.

During the passage of the digesting food through the intestinal canal the
nutritive products — the peptones, the dextrose and levulose, the fatty emul-
sions, the fatty acids and their soaps — are absorbed into the blood, while
the undigested residue is carried onward by the peristaltic movements
through the ileo-cecal valve into the large intestine.

Intestinal Fermentation. — Owing to the favorable conditions for
fermentative and putrefactive processes — e.g., heat, moisture, oxygen, micro-
organisms — the food, when consumed in excessive quantity or when acted
upen by defective secretions, undergoes a series of decomposition changes
which are attended by the production of gases and various chemic com-
pounds. Grape-sugar and maltose are partially split into lactic acid, this
into butyric acid, carbon dioxid, and hydrogen. Fats are reduced to
glycerol and fatty acids ; the glycerol, according to the organisms present,
yields succinic and other fatty acids, carbon dioxid, and hydrogen.

The proteids, under the prolonged action of the pancreatic juice, are
decomposed, and yield leucin and tyrosin ; the former is split into valerianic

ABSORPTION. HI

acid, ammonia, and carbon dioxid ; the latter is split into indol, which is
the antecedent of indican in the urine. Skatol is another proteid deriva-
tive constantly present in the fecal substance.

The large intestine extends from the ileo-cecal valve to the anus, and
is about five feet in length. Like the stomach it consists of three coats :
the serous, the muscular, and mucous. The mucous membrane contains a
number of mucous glands, the secretion from which lubricates the surface
of the canal. The ascending portion of the large intestine possesses the
power of absorption, and hence its contents become less liquid and more
consistent. As the residue passes toward the sigmoid flexure it acquires
the characteristics of fecal matter. This residue consists of the undigested
portions of the food, decomposition products, mucus, and inorganic salts.

Defecation is the voluntary act of extruding the feces from the rectum,
and is accomplished by a relaxation of the sphincter ani muscle and by
the contraction of the muscular walls of the rectum, aided by the contrac-
tion of the abdominal muscles.

ABSORPTION.

The term absorption is applied to the passage gr transference of material
into the blood from the tissues, from the serous cavities, and from the
mucous surfaces of the body. The most important of these surfaces,
especially in its relation to the formation of the blood, is the mucous sur-
face of the alimentary canal ; for it is from this organ that new materials
are derived which maintain the quality and quantity of the blood. The
absorption of materials from the interstices of the tissues is to be regarded
rather as a return to the blood of liquid nutritive material which has
escaped from the blood-vessels for nutritive purposes, and which, if not
returned, would lead to an accumulation of such fluid and the develop-
ment of dropsical conditions.

The anatomic mechanisms involved in the absorptive process are, pri-
marily, the lymph-spaces, the lymph- capillaries, and the blood-capillaries ;
secondarily, the lymphatic vessels and larger blood-vessels.

Lymph-spaces, Lymph-capillaries, Blood-capillaries. — Every-
where throughout the body, in the intervals between connective-tissue bun-
dles and in the interstices of the several structures of which an organ is
composed, are found spaces of irregular shape and size, determined largely
by the nature of the organ in which they are found, which have been termed

112 HUMAN THYSIOLOGY.

lymph-spaces or lacuna, from the fact that during the living condition they
are continually receiving the lymph which has escaped from the blood-
vessels throughout the body. In addition to the connective-tissue lymph-
spaces, various observers have described special lymph-spaces in the
testicle, kidney, liver, thymus gland, and spleen; in all secreting glands
between the basement membrane and blood-vessels ; around blood-vessels
(perivascular spaces), and around nerves. The se>ous cavities of the body
— peritoneal, pleural, pericardial, etc. — may also be regarded as lymph-
spaces, which are in direct communication by open mouths or stomata with
the lymphatic capillaries. This method of communication is not only true
of serous membranes, but to some extent also of mucous membranes.
The cylindric sheaths and endothelial cells surrounding the brain, spinal
cord, and nerves can also be looked upon as lymph-spaces in connection
with lymph- capillaries.

The lymphatic capillaries, in which the lymphatic vessels proper take
their origin, are arranged in the form of plexuses of quite irregular shape.
In most situations they are intimately interwoven with the blood-vessels,
from which, however, 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 epithelioid cells, with sinuous outlines, and
which accurately dovetail with one another. In no instance are valves
found. In the villus of the small intestine the beginning of the lymphatic
is to be regarded as a lymph-capillary, generally club-shaped, which at the
base of the villus enters a true lymphatic ; at this point a valve is situated,
which prevents regurgitation. The lymphatic capillaries anastomose freely
with one another, and communicate on the one hand with the lymph- spaces,
and on the other with the lymphatic vessels proper.

As the shape, size, etc., of both lymph-spaces and capillaries are deter-
mined largely by the nature of the tissues in which they are contained, it
is not always possible to separate the one from the other. Their function,
however, may be regarded as similar — viz., the collection of the lymph
which has escaped from the blood-vessels, and its transmission onward into
the regular lymphatic vessels.

The blood-capillaries not only permit the escape of the liquid nutritive
portions of the blood through their delicate walls, but are also engaged in
the reabsorption of this transudate, as well as in the absorption of new
materials from the alimentary canal. The extensive capillary network
which is formed by the ultimate subdivision of the arterioles in the sub-
mucous tissue and villi of the small intestine forms an anatomic arrange-
ment well adapted for absorption. It is now well known that in the

ABSORPTION. 113

absorption of the products of digestion the blood-capillaries are more active
than the lymphatic capillaries.

Lymphatic Vessels. — These constitute a system of minute, delicate
transparent vessels, found in nearly all the organs and tissues of the
body. Having their origin at the periphery in the lymphatic capillaries
and spaces, they rapidly converge toward the trunk of the body and
empty into the thoracic duct. In their course they pass through numerous
small ovoid bodies, the lymphatic glands.

The lymphatic vessels of the small intestines — the lacteah — arise within
the villous processes which project from the inner surface of the intestine
throughout its entire extent. The wall of the villus is formed by an eleva-
tion of the basement membrane, and is covered by a layer of columnar
epithelial cells. The basis of the villus consists of adenoid tissue, a fine
plexus of blood-vessels, unstriped muscle-fibers, and the lacteal vessel.
The adenoid tissue consists of a number of intercommunicating spaces,
containing leukocytes. The lacteal vessel possesses a thin but distinct
wall composed of endothelial plates, with here and there openings which
bring the interior of the villus into communication with the spaces of the
adenoid tissue.

The structure of the larger vessels resembles that of the veins, consisting
of three coats :

1. External, composed of fibrous tissue and muscle-fibers, arranged longi-
tudinally.

2. Middle, consisting of white fibers and yellow elastic tissue, non-striated
muscle-fibers, arranged transversely.

3. Internal, composed of an elastic membrane, lined by endothelial cells.
Throughout their course are found numerous semilunar valves, opening

toward the larger vessels, formed by a folding of the inner coat and
strengthened by connective tissue.

Lymphatic Glands. — The lymphatic glands consist of an external
capsule composed of fibrous tissue which contains non striped muscle-
fibers ; from its inner surface septa of fibrous tissue pass inward and sub-
divide the gland-substance into a series of compartments, which communi-
cate with one another. The blood-vessels which penetrate the gland are
surrounded by fine threads, forming a follicular arrangement, the meshes of
which contain numerous lymph-corpuscles. Between the follicular threads
and the wall of the gland lies a lymph-channel traversed by a reticulum of
adenoid tissue. The lymphatic vessels, after penetrating this capsule, pour
their lymph into this channel, through which it passes ; it is then collected

114

HUMAN PHYSIOLOGY.

Fig.

-Diagram Showing the Course of the Main Trunks of the
Absorbent System.— ( Yeo's " Text-Book of Physiology.")

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).

ABSORPTION. 115

by the efferent vessels and transmitted onward. The lymph- corpuscles
which are washed out of the gland into the lymph-stream are formed, most
probably, by division of preexisting cells.

The thoracic duct is the general trunk of the lymphatic system ; into
it the vessels of the lower extremities, of the abdominal organs, of the left
side of the head, and of the left arm empty their contents. It is about twenty
inches in length, arises in the abdomen, opposite the third lumbar vertebra,
by a dilatation (the receptaculum chyli), ascends along the vertebral column
to the seventh cervical vertebra, and terminates in the venous system at
the junction of the internal jugular and subclavian veins on the left side.
The lymphatics of the right side of the head, of the right arm, and of the
right side of the thorax terminate in the right thoracic duct, about one
inch in length, which joins the venous system at the junction of the internal
jugular and subclavian on the right side.

The general arrangement of the lymphatic vessels is show in figure 15.

The blood-vessels which are concerned in the conduction of fresh
nutritive material from the alimentary canal have their origin in the elabo-
rate capillary network in the mucous membrane. The small veins which
emerge from the network gradually unite, forming larger and larger trunks,
which are known as the gastric, superior, and inferior mesenteric veins.
These finally unite to form the portal vein, a short trunk about three inches
in length. The portal vein enters the liver at the transverse fissure, after
which it forms a fine capillary plexus ramifying throughout the substance
of the liver ; from this plexus the hepatic veins take their origin, and
finally empty the blood into the vena cava inferior. (See Fig. 16. )

Absorption of Food. — Physiological experiments have demonstrated
that the agents concerned in the absorption of new materials from the ali-
mentary canal are :

1. The blood-vessels of the entire canal, but more particularly those uniting
to form the portal vein.

2. The lymphatics coming from the small intestine, which converge to
empty into the thoracic duct.

As a result of the action of the digestive fluids upon the different classes
of food principles — albumins, sugars, starches, and fats — there are formed
peptones, glucose, and fatty emulsion, which differ from the former in being
highly diffusible — a condition essential to their absorption. In order that
these substances may get into the blood, they must pass through the layer
of cylindric epithelial cells and the underlying basement membrane, and
into the lymph-spaces of the villi and submucous tissue. The mechanism

116

HUMAN PHYSIOLOGY.

by which the cells effect this passage of the food is but imperfectly under-
stood. Osmosis and nitration are conditions, however, made use of by the
cells in the absorptive process.

The products of digestion find their way into the general circulation by
two routes :
I. The water, peptones, glucose, and soluble salts, after passing into the

Fig. 16.

Diagram of the portal vein [fiv) arising in the alimentary tract and spleen (s),
and carrying the blood from these organs to the liver. — ( Yeo's " Text-book oj
Physiology.")

lymph-spaces of the villi, pass through the wall of the capillary blood-
vessel ; entering the blood, they are carried to the liver by the vessels
uniting to form the portal vein ; emerging from the liver, they are
empted into the inferior vena cava by the hepatic vein.
2. The emulsified fat enters the lymph-capillary in the interior of the
villus ; by the contraction of the layer of muscle-fibers surrounding

ABSORPTION. 117

it its contents are forced onward into the lymphatic vessels or lacteal,
thence into the thoracic duct, and finally into the circulation at the
junction of the internal jugular and subclavian veins on the left side.

Absorption of Lymph. — Similar to the absorption of food from the
alimentary canal is the absorption of lymph from the lymph -spaces of the
organs and tissues. During the passage of the blood through the capillary
blood-vessels a portion of the liquor sanguinis, or plasma, or lymph, passes
through the capillary wall out into the lymph-spaces. The tissue-cells are
thus bathed with this new materal ; from it those substances are selected
which are necessary for their growth, repair, and all purposes of nutrition.
An excess of nutritive material, far beyond the needs of the tissues,
transudes from the blood-vessels, and it is this excess which is absorbed
by the lymphatics and returned to the blood by the thoracic duct. It is
quite probable, also, that a portion of this transudate is reabsorbed by the
blood-vessels.

Properties and Composition of Lymph and Chyle. — Lymph, as
found in the lymphatic vessels of animals, is a clear, colorless, or opalescent
fluid, having an alkaline reaction, a saline taste, and a specific gravity of
about 1040. It holds in suspension a number of corpuscles resembling
in their general appearance the white corpuscles of the blood. Their
number has been estimated at 8,200 per cubic millimeter, though the num-
ber varies in different portions of the lymphatic system. As the lymph
flows through the lymphatic gland it receives a large addition of corpuscles.
Lymph- corpuscles are granular in structure, and measure ^ttVo °f an inch
in diameter. When withdrawn from the vessels, lymph undergoes a spon-
taneous coagulation similar to that of the blood, after which it separates in
serum and clot.

COMPOSITION OF LYMPH.

Water, 95-536

Proteids (serum-albumin, fibrin-globulin), .... 1.320

Extractives (urea, sugar, cholesterin), 1.559

Fatty matters, a trace

Salts, 0.585

100.000

Chyle. — Chyle is the fluid found in the lymphatic vessels, coming from
the small intestine after the digestion of a meal containing fat. In the
intervals of digestion the fluid of these lymphatics is identical in all re-
spects with the lymph found in all other regions of the body. As soon

118 HUMAN PHYSIOLOGY.

as the emulsified fat passes into the lymphatic vessels and mingles with the
lymph it becomes milky white in color, and the vessels which previously
were invisible become visible, and resemble white threads running between
the layers of the mesentery. Chyle has a composition similar to that of
lymph, but it contains, in addition, numerous fatty granules, each surrounded
by an albuminous envelope. When examined microscopically, the chyle
presents a fine molecular basis, made up of the finely divided granules of
fat.

COMPOSITION OF CHYLE.

Water, 902.37

Albumin, 35. 16

Fibrin, 3.70

Extractives, 15.65

Fatty matters, . 36.01

Salts, 7. 1 1

1,000.00

Forces Aiding the Movement of Lymph and Chyle. — The lymph
and chyle are continually moving in a progressive manner from the periph-
ery or beginning of the lymphatic system to the final termination of the
thoracic duct. The force which primarily determines the movement of the
lymph has its origin in the beginnings of the lymphatic vessels, and depends
upon the difference in pressure here and the pressure in the thoracic duct.
The greater the quantity of fluid poured into the lymph-spaces, the greater
will be the pressure and, consequently, the movement. The first move-
ment of chyle is the result of a contraction of the muscle-fibers within the
walls of the villus. At the time of contraction the lymphatic capillary is
compressed and shortened, and its contents are forced onward into the true
lymphatic. When the muscle-fibers relax, regurgitation is prevented by
the closure of the valve in the lymphatic at the base of the villus.

As the walls of the lymphatic vessels contain muscle-fibers, when they
become distended these fibers contract and assist materially in the onward
movement of the fluid.

The contraction of the general muscular masses in all parts of the body,
by exerting an intermittent pressure upon the lymphatics, also hastens the
current onward ; regurgitation is prevented by the closure of valves which
everywhere line the interior of the vessels.

The respiratory movements aid the general flow of both lymph and chyle
from the thoracic duct into the venous blood. During the time of an in-
spiratory movement the pressure within the_thorax, but outside the lungs,

BLOOD. 119

undergoes a diminution in proportion to the extent of the movement ; as a
result, the fluid in the thoracic duct outside of the thorax, being under a
higher pressure, flows more rapidly into the venous system. At the time
of an expiration, the pressure rises and the flow is temporarily impeded,
only to begin again at the next inspiration.

BLOOD.

The blood is a nutritive fluid containing all the elements necessary for
the repair of the tissues ; it also contains principles of waste absorbed from
the tissues, which are conveyed to the various excretory organs and by them
eliminated from the body.

The total amount of blood in the body is estimated to be about one eighth
of the body-weight ; from sixteen to eighteen pounds in an individual of
average physical development. The quantity varies during the twenty-four
hours, the maximum being reached in the afternoon, the minimum in the
early morning hours.

Blood is an opaque, red fluid, having an alkaline reaction, a saline taste,
and a specific gravity of 1055.

The opacity is due to the refraction of the rays of light by the elements
of which the blood is composed. The color varies in hue, from a bright
scarlet in the arteries to a deep purple in the veins, due to the presence of
a coloring-matter — hemoglobin — in different degrees of oxidation.

The alkalinity is constant, and depends upon the presence of the alka-
line sodium phosphate, Na2HPOr

The saline taste is due to the amount of sodium chlorid present.

Within the limits of health the specific gravity ranges from 1045 to 1075.

The odor of the blood is characteristic, and varies with the animal from
which it is drawn ; it is due to the presence of caproic acid.

The temperature of the blood ranges from 9S0 F. at the surface to 1070
F. in the hepatic vein ; it loses heat by radiation and evaporation as it
approaches the extremities and as it passes through the lungs.

Blood Consists of Two Portions :

1. The liquor sanguinis ox plasma, a transparent, colorless fluid, in which
are floating —

2. Red and white corpuscles, these constituting by weight less than one
half (40 per cent. ) of the entire amount of blood.

120 HUMAN PHYSIOLOGY.

COMPOSITION OF PLASMA.

Dalton.

Water, 902.00

Albumin, 53°°

Paraglobulin, 22.00

Fibrinogen, 3-00

Fatty matters 2.50

Crystallizable nitrogenous matters, 4.00

Other organic matter, 5-°°

Mineral salts, 8.50

1,000.00

Water acts as a solvent for the inorganic matters and holds in suspension
the corpuscular elements.

Albumin is the nutritive principle of the blood ; it is absorbed by the
tissues to repair their waste and is transformed into the organic basis char-
acteristic of each structure.

Paraglobulin or fibrinoplastin is a soft, amorphous substance precipitated
by sodium chlorid in excess, or by passing a stream of carbonic acid
through dilute serum.

Fibrinogen also can be obtained by strongly diluting the serum and
passing carbonic acid through it for a long time, when it is precipitated as
a viscous deposit.

Fatty matter exists in small proportion, except in pathologic conditions
and after the ingestion of food rich in oleaginous matters ; it soon disap-
pears, undergoing oxidation, generating heat and force, or is deposited as
adipose tissue.

Sugar is represented by glucose, a product of the digestion of saccharine
matter and starches in the alimentary canal ; glycogenic matter is derived
from the liver.

The saline constituents aid the process of osmosis, give alkalinity to
the blood, promote the absorption of carbonic acid from the tissues into
the blood, and hold other substances in solution ; the most important
are the sodium and potassium chlorids and the calcium and magnesium
phosphates.

Excrementitious matters are represented by carbonic acid, urea, creatin,
creatinin, urates, oxalates, etc.; they are absorbed from the tissues by the
blood and conveyed to the excretory organs, lungs, kidneys, etc.

Gases. — Oxygen, nitrogen, and carbonic acid exist in varying propor-
tions.

BLOOD.

121

BLOOD-CORPUSCLES.

The corpuscular elements of the blood occur under two distinct forms,
which, from their color, are known as the red and white corpuscles.

The red corpuscles as they float in a thin layer of the liquor sanguinis
are of a pale straw-color ; it is only when aggregated in masses that they
assume the bright red color. In form they are circular and biconcave ;
they have an average diameter of 3^00 of an inch.

In -mammals, birds, reptiles, amphibia, and fish the corpuscles vary in
size and number, gradually becoming larger and less numerous as the scale
of animal life is descended, e. g. :

TABLE SHOWING COMPARATIVE DIAMETER OF RED CORPUSCLES.

Mammals.

Birds.

Reptiles.

Amphibia.

Fish

Man,

Chimpanzee,
Orang,
Dog,

32(55
34 15
3355
3BS3

Eagle, rs»T2
Owl, T7l63
Sparrow, *^
SwalioWj^j'jj

Turtle, j^'sx
Tortoise, j^g^
Lizard, ^s
Viper, 15V5

Frog,
Toad,
Proteus,
Siren,

ires

T543

■tun
1

?35

Perch,
Carp,
Pike,
Eel,

553 5
5T?T
JOJS5
175 K

Cat,
Hog,

4"?U4
4530

Pigeon, TgV.3
Turkey, ^Vo

Amphiuma,

3C3

Horse,

4"B(J(J

Goose, I5!Bg

Ox,

5357

Swan, T^5e

In man and the mammals the red corpuscles present neither a nucleus
nor a cell wall, and are universally of a small size. They can be readily
distinguished from the corpuscles of birds, reptiles, and fish, in which
animals they are larger, oval in shape, and possess a well-defined nucleus.

The red corpuscles are exceedingly numerous, amounting to about
5,000,000 in a cubic millimeter of blood. In structure they consist of a
firm, elastic, colorless framework, — the stroma, — in the meshes of which
is entangled the coloring-matter — the hemoglobin.

CHEMIC COMPOSITION OF RED CORPUSCLES.

Water, 68S.00

Globulin, 282.22

Hemoglobin, .... 16.75

Fatty matter, ... ....... 2. 3 1

Extractives, 2.60

Mineral salts, , 5.12

1,000.00

Hemoglobin, the coloring matter of the corpuscles, is an albuminous
compound, composed of C, O, H, N, S, and iron. It may exist in either
an amorphous or a crystalline form. When deprived of all its oxygen, ex-
cept the quantity entering into its intimate composition, the hemoglobin
9

122 HUMAN PHYSIOLOGY.

becomes purplish in color, and is known as reduced hemoglobin. When
exposed to the action of oxygen, it again absorbs a definite amount and
becomes scarlet in color, and is known as oxyhemoglobin. The amount of
oxygen absorbed is 1. 76 c. c. (y^of a cubic inch) for I mg. (^ of a
grain) of hemoglobin.

It is this substance which gives the color to the venous and arterial
blood. As the venous blood passes through the capillaries of the lungs
the reduced hemoglobin absorbs the oxygen from the pulmonary air and
becomes oxyhemoglobin, scarlet in color ; the blood becomes arterial.
When the arterial blood passes into the systemic capillaries, the oxygen is
absorbed by the tissues ; the hemoglobin becomes reduced, purple in color,
and the blood becomes venous. A dilute solution of oxyhemoglobin gives
two absorption bands between the lines D and E of the solar spectrum.
Reduced hemoglobin gives but one absorption band, occupying the space
existing between the two bands of the oxyhemoglobin spectrum.

The function of the red corpuscle is, therefore, to absorb oxygen and
carry it to the tissues ; the smaller the corpuscles and the greater the num-
ber, the greater is the quantity of oxygen absorbed, and, consequently, all
the vital functions of the body become more active.

The white corpuscles are far less numerous than the red, the proportion
being, on an average, about I white to from 350 to 400 red ; they are
globular in shape, and are ^Vc °^ an incn m diameter, and consist of a
soft, granular, colorless substance, containing several nuclei.

The white corpuscles possess the power of spontaneous movement, alter-
nately contracting and expanding, throwing out processes of their substance
and quickly withdrawing them, thus changing their shape from moment to
moment. These movements resemble those of the ameba, and for this
reason are termed ameboid. The white corpuscles also possess the capa-
bility of moving from place to place. In the interior of the vessels they
adhere to the inner surface, while the red corpuscles move through the
center of the stream.

The white corpuscles are identical with the leukocytes, and are found in
milk, lymph, chyle, and other fluids.

Origin of Corpuscles. — The red corpuscles take their origin from the
mesoblastic cells in the vascular area of the developing embryo.

In the adult they are produced from colorless, nucleated corpuscles re-
sembling the white corpuscles. The spleen is the organ in which they are
finally destroyed.

The white corpuscles originate from the leukocytes of the adenoid tissue,

BLOOD. 123

and subsequently give rise to the red corpuscles ; they assist in the forma-
tion of the new tissues that result from inflammatory action.

COAGULATION OF THE BLOOD.

When blood is withdrawn from the body and allowed to remain at rest,
it becomes somewhat thick and viscid in from three to five minutes ; this
viscidity gradually increases until the entire volume of blood assumes a
jelly- like consistence, which process occupies from five to fifteen minutes.

As soon as coagulation is completed, a second process begins, which
consists in the contraction of the coagulum and the oozing of a clear,
straw-colored liquid, — the serum, — which gradually increases in quantity
as the clot diminishes in size, by contraction, until the separation is com-
pleted, which occupies from twelve to twenty-four hours.

The changes in the blood are as follows :

Before coagulation.

{Liq. Sanguinis, ~\ C Water.

> consisting of J Albumin.
J ) Fibrinogen.

Plasma, v. Salts.

Corpuscles, red and white.
After coagulation.

{Crassamentum, > . . f Fibrin.

Clot or coagulum, J I Corpuscles,

r Water.
Serum, containing -J Albumin.

I Salts.

The serum, therefore, differs from the liquor sanguinis in not containing
fibrin.

In from twelve to twenty-four hours the upper surface of the clot
presents a grayish appearance, — the buffy coat, — owing to the rapid sink-
ing of the red corpuscles beneath the surface, permitting the fibrin to coagu-
late without them ; this substance then assumes a grayish-yellow tint. In-
asmuch as the white corpuscles possess a lighter specific gravity than the
red, they do not sink so rapidly, and, becoming entangled in the fibrin,
assist in forming the buffy coat. Continued contraction gives a cupped
appearance to the surface of the clot.

Inflammatory states of the blood produce a marked increase in the buffed
and cupped condition, on account of the aggregation of the corpuscles
and their tendency to rapid sinking.

124 HUMAN PHYSIOLOGY.

Nature of Coagulation. — Coagulated fibrin does not preexist in the
blood, but is formed at the moment blood is withdrawn from the vessels.
According to Denis, a liquid substance — plasmin — exists in the blood,
which, when withdrawn from the circulation, decomposes into fibrin and
metalbnmin.

According to Schmidt, fibrin results from the union of fibrinoplastin
(paraglobulin) and fibrinogen, brought about by the presence of a third
substance, the fibrin-ferment.

According to Hammersten and others, the fibrin obtained from the blood
after coagulation comes from the fibrinogen alone, the conversion being
brought about by the presence of a ferment substance, paraglobulin in this
case having nothing to do with the change. This view is supported by the
fact that the quantity of fibrin obtained from the blood is never greater than
the quantity of fibrinogen previously present. The origin of the ferment is
obscure, but there is reason to believe that it comes from the injured vascu-
lar coats or from the breaking of the white corpuscles.

Conditions Influencing Coagulation. — The process is retarded by
cold, retention within living vessels, neutral salts in excess, inflammatory
conditions of the system, imperfect aeration, exclusion from air, etc.

It is accelerated by a temperature of ioo° F., contact with air, rough
surfaces, and rest.

Blood coagulates in the body after the arrest of the circulation in the
course of twelve to twenty-four hours ; local arrest of the circulation, from
compression or a ligature, will cause coagulation, thus preventing hemor-
rhages from wounded vessels.

The composition of the blood varies in different portions of the body.
The arterial differs from the venous, in being more coagulable ; in contain-
ing more oxygen and less carbonic acid ; in having a bright scarlet color,
from the union of oxygen with hemoglobin. The purple hue of venous
blood results from the deoxidation of the coloring-matter.

The blood of the portal vein differs in constitution, according to different
stages of the digestive process ; during digestion it is richer in water, albu-
minous matter, and sugar ; occasionally it contains fat ; corpuscles are
diminished, and there is an absence of biliary substances.

The blood of the hepatic vein contains a larger proportion of red and
white corpuscles ; the sugar is augmented, while albumin, fat, and fibrin
are diminished.

CIRCULATION OF THE BLOOD. 125

CIRCULATION OF THE BLOOD.

The circulatory apparatus by which the blood is distributed to all
portions of the body consists of a central organ, — the heart, — with which
is connected a system of closed vessels known as arteries, capillaries, and
veins. Within this system the blood is kept, by the action of the heart, in
continual movement, distributing nutritive matter to all portions of the
body and carrying waste matters from the tissues to the various eliminating
organs.

The heart is a hollow, muscular organ, pyramidal in shape, measuring
about $}4 inches in length and about 3j4 in breadth, weighing from 10 to
12 ounces in the male and from 8 to io in the female. Situated in the
thoracic cavity, between the lungs, its base is directed upward, backward,
and to the right ; its apex is directed downward and to the left.

Pericardium. — The heart is surrounded by a closed fibrous membrane
called the pericardium. The inner surface of this membrane is lined by a
serous membrane, which is also reflected over the surface of the heart ;
between the two surfaces of the serous membrane is found a small quantity
of fluid (the pericardial fluid), which lubricates the surfaces and prevents
friction during the movements of the heart. The interior of the heart is
also lined by a serous membrane, called the endocardium.

Cavities of the Heart. — The general cavity of the heart is subdivided
by a longitudinal septum into a right and left half; each of these cavities
is in turn subdivided by a transverse constriction into two smaller cavities,
which communicate with each other and are known as the auricles and
ventricles, the orifice between the auricle and ventricle being known as the
auriculoventricular orifice. The heart, therefore, consists of four cavities
— a right auricle and ventricle and a left auricle and ventricle.

Into the right auricle the two terminal trunks of the venous system — the
superior and inferior vence cava: — empty the venous blood which has been
collected from all parts of the system ; from the right ventricle arises the
pulmonary artery, which, passing into the lungs, distributes the blood to
the walls of the air-cells of the lungs ; into the left auricle empty four
pulmonary veins, which have collected the blood from the lung capil-
laries ; from the left ventricle springs the aorta, the general trunk of the
arterial system, the branches of wh'ch distribute the blood to the entire
system.

126

HUMAN PHYSIOLOGY.

Fig. 17. — Scheme of the Cir-
culation.— {Landois.)

a Right, b. left, auricle. A. Right,
B, left ventricle. 1. Pulmon-
ary artery. 2. Aorta. 1. Area
of pulmonary, K, area of sys-
temic, circulation. o. The
superior vena cava. G Area
supplying the inferior vena
cava, u. d, d. Intestine, m.
Mesenteric artery, q. Portal
vein. L. Liver, h. Hepatic
vein.

The Valves of the Heart.— The
valves of the heart are formed by a redup-
lication of the endocardium strengthened
by connective tissue. At the auriculo-
ventricular openings on the right and
left sides of the heart, respectively, are
found the tricuspid and mitral valves.
The tricuspid valve consists of three, the
mitral of two, cusps or segments, which
project into the interior of the ventricle
when it does not contain blood. At their
bases the segments are united so as to
form an annular membrane attached to
the margin of the orifice. To the free
edges of the valves are attached numer-
ous fine threads, — the chorda tendinece, —
which are the tendons of the small papil-
lary muscles springing from the walls of
the ventricles.

The Semilunar Valves. — At the open-
ings of the pulmonary artery and the
aorta are found three cup shaped or sem-
ilunar valves, the free edges of which are
directed away from the interior of the
heart. The anatomic arrangement of the
valves is such that upon their closure
regurgitation of the blood is prevented.

The Course of the Blood through
the Heart. — Reference to figure 17 will
make it clear that there is a pathway for
the blood between the venae cavae 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 towards the heart is emptied by the superior and
inferior venae cavae into the right auricle from which it passes through the
auriculoventricular opening into the right ventricle ; thence into and through
the pulmonary artery and its branches to the pulmonary capillaries where it

CIRCULATION OF THE BLOOD. 127

is arterialized, i. e., yields up its carbon dioxid and takes on a fresh supply
of oxygen — and is changed in color from dark blue to scarlet red. The
arterialized blood flowing towards the heart is emptied by the pulmonary
veins into the left auricle from which it passes through the auriculoventric-
ular opening into the left ventricle ; thence into the aorta and its branches
to the systemic capillaries where it is de-arterialized by an opposite exchange
of gases, i. e., yields up a portion of its oxygen to, and absorbs carbon
dioxid from the tissues, and changes in color from scarlet to dark blue. The
venous blood is again returned by the systemic veins to the venae cavae.

While there is but one circulation, physiologists frequently divide the
circulatory apparatus into —

1 . The systemic circulation, which includes the movement 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.

2. The pulmonary circulation, which includes the course of the blood from
the right side through the pulmonary artery, through the capillaries of
the lungs and pulmonary veins, to the left side of the heart.

3. The portal circulation, which includes the portal vein. This vein is
formed by the union of the radicles of the gastric, mesenteric, and splenic
veins, and carries the blood directly into the liver, where the vein divides
into a fine capillary plexus, from which the hepatic veins arise ; these
empty into the ascending vena cava.

The Mechanism of the Heart. — The immediate cause of the move-
ment of the blood through the blood-vessels is the alternate contraction
and relaxation of the muscular walls of the heart, and more especially 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 fur-
nished by the heart itself. 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 are in the same physiologic relation they contract
and relax in the same periods of time.

Movements of the Heart. — At each beat, during the systole,
the heart hardens and becomes shortened in its long diameter ; its apex is
raised up, rotated on its axis from left to right, and thrown forward against
the walls of the chest. The impulse of the heart, observed about two
inches below the nipple and one inch to the sternal side, between the fifth
and sixth ribs, is caused mainly by the apex of the heart striking against

128 HUMAN PHYSIOLOGY.

the chest walls, assisted by the distention of the great vessels about the base
of the heart.

The Cardiac Cycle. — The entire period of the heart's pulsation may be
divided into three stages, viz. :

1. The auricular contraction and relaxation.

2. The ventricular contraction and relaxation.

3. The pause or period of repose during which both auricles and ventricles
are at rest. These three stages constitute collectively a cardiac cycle or
a cardiac revolution.

L The duration of a cycle, as well as the duration of its three stages, varies
in different animals in accordance with the number of cycles which recur
in a minute. In human beings in adult life there are about 72 cycles to
the minute; the average duration is, therefore, 0.80 sec. From this it
follows that the time occupied by any one of the three stages must be
extremely short and difficult of determination. From experiments on
animals and from observations made on human beings, the following esti-
mates have been made and accepted as approximately correct for human
beings :

1. The auricular systole — 0.16 sec. ; the auricular diastole, 0.64 sec.

2. The ventricular systole — 0.32 sec. ; the ventricular diastole, 0.48 sec.

3. The period of rest for both auricles and venticles — 0.32 sec.

The Action of the Valves. — The forward movement of the blood is
permitted and regurgitation prevented by the alternate action of the auriculo-
ventricular and semilunar valves as a point of departure for a consideration
of the action of these valves and their relation to the systole and diastole
of the heart, the close of the ventricular systole may be selected. At this
moment, the semilunar valves, which during the systole, are directed
outward by the blood current are now suddenly and completely closed by
the pressure of the blood in the aorta and pulmonary artery. Regurgitation
into the ventricles is thus prevented.

During the ventricular systole, the relaxed auricles are filling with blood.
With the ventricular diastole this blood or its equivalent flows into the
relaxed and easily distensible ventricles until both auricles and ventricles
are nearly filled. The tricuspid and mitral valves which are hanging down
into the ventricular cavities, are now floated up by currents of blood welling
up behind them until they are nearly closed. The auricles now suddenly
contract, forcing their contained volumes into the ventricles which become
fully distended.

With-the cessation of the auricular systole, the ventricular systole begins.

CIRCULATION OK THE BLOOD. 129

If the blood is not to be returned to the auricles the tricuspid and mitral
valves must be instantly and completely closed. This is accomplished by
the upward pressure of the blood which brings their free edges in close
apposition. Reversal of these valves is prevented by the contraction of the
papillary muscles which exert a traction on their under surfaces and edges
and hold them steady.

The blood now confined in the ventricles between the closed auriculo-
ventricular and semilunar valves is subjected to pressure on 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 ; at once the semilunar valves are thrown open and
the blood discharged. Both contraction and outflow continue until the
ventricles are practically empty, when relaxation sets in attended by a rapid
fall of pressure, under the influence of the positive pressure of the blood in
the aorta and pulmonary artery, the semilunar valves are again closed. The
accumulation of blood in the auricles, attended by a rise in pressure, again
•forces the tricuspid and mitral valves open. With these events the cardiac
cycle is again completed.

Sounds of the Heart. — If the ear be placed over the cardiac region,
two distinct sounds are heard during each revolution of the heart, closely
following each other, and which differ in character.

The sound coinciding with the systole in point of time — the first sound —
is prolonged and dull, and caused by the closure and vibration of the auricu-
loventricular valves, the contraction of the walls of the ventricles, and the
apex-beat ; the second sound, occurring during the diastole, is short and
sharp, and caused by the closure of the semilunar valves.

The frequency of the heart's action varies at different periods of life,
but in the adult male it beats about seventy-two times a minute. It is
influenced by age, exercise, posture, digestion, etc.

Age. — Before birth, the number of pulsations a minute averages . . 140

During the first year it diminishes to 128

During the third year diminishes to . 95

From the eighth to the fourteenth year averages 84

In adult life the average is . . . . 72

Exercise and digestion increase the frequency of the heart's action.

Posture influences the number of pulsations a minute ; in the male,
standing, the average is 81 ; sitting, 71 ; lying, 66 — independent, for the
most part, of muscular effort.

The rhythmic movements of the heart are dependent upon —

130 HUMAN PHYSIOLOGY.

1. An inherent irritability of the muscle-fiber, which manifests itself as
long as the nutrition is maintained.

2. The continuous flow of blood through its cavities, distending them and
stimulating the endocardium.

The force exerted by the left ventricle at each contraction has been
estimated at fifty-two pounds. If a tube be inserted into the aorta, the
pressure there will be sufficient to support a column of blood nine feet, or
a column of mercury six inches, in height, the weight in either case being
about four pounds. The estimation of the force which the heart is required
to exert to support this column of blood is arrived at by multiplying the
pressure in the aorta (four pounds) by the area of the internal surface of
the left ventricle (about thirteen inches), each inch of the ventricle being
capable of supporting a downward pressure of four pounds.

Work Done by the Heart. —The work done by the heart is estimated
by multiplying the amount of blood sent out from the right and left ven-
tricles at each contraction by the pressure of the pulmonary artery and
aorta, respectively — e. g., when the right ventricle contracts, it forces out
^ of a pound of blood, and in so doing must overcome a pressure in the
pulmonary artery sufficient to support a column of blood three feet in
height ; that is, must exert energy sufficient to raise ^ of a pound 3 feet,
or ^ X 3> or % °f a pound I foot. When the left ventricle contracts, it
sends out }( of a pound of blood, and in so doing the left ventricle must
overcome a pressure in the aorta sufficient to support a column of blood 9
feet in height ; that is, must exert energy sufficient to raise % of a pound
9 feet, or ^ X 9> or 2X pounds I foot. Work done is estimated by the
amount of energy required to raise a definite weight a definite height ; the
unit, the foot-pound, being that required to raise I pound I foot.

The heart, therefore, at each systole exerts energy sufficient to raise 3
foot-pounds, and as it contracts 72 times a minute, it would raise in that
time 3 X 72j or 2I6 foot-pounds; and in one hour 216X60, or 12,960
foot-pounds; and in twenty-four hours 12,960 X 24> or 3ll>°4° foot-
pounds, or 138.5 foot-tons.

Influence of the Nervous System upon the Heart. — When the
heart of a frog is removed from the body, it continues to beat for a variable
length of time, depending upon the nature of the conditions surrounding
it. The heart of a warm-blooded animal continues to beat but for a very
short time. The cause of the continued pulsations of the frog-heart is the
presence of nerve-ganglia in its substance. These ganglia^ have riot been

CIRCULATION OF THE BLOOD. 131

shown to exist in the mammalian heart, but there is reason to believe that
the nervous mechanism is fundamentally the same.

The ganglia of the heart are three in number : one situated at the open-
ing of the inferior vena cava (the ganglion of Remak), a second situated
in the auriculoventricular septum (the ganglion of Biddle), and a third
situated in the interauricular septum (the ganglion of Ludwig). The first
two are motor in function and excite the pulsations of the heart ; the third
is inhibitory in function and retards the action of the heart. The actions
of these ganglia, though for the most part automatic, are modified by impres-
sions coming through nerves from the medulla oblongata. When the
inhibitory center is stimulated by muscarin, the heart is arrested in dias-
tole ; when atropin is applied, the heart recommences to beat, because
atropin paralyzes the inhibitory center.

The nerves modifying the action of the heart are the pneumogastric
(vagus) and the accelerator nerves.

The pneumogastric nerve, after emerging from the medulla, receives
motor fibers from the spinal accessory nerve. It then passes downward,
giving off branches, some of which terminate in the inhibitory ganglion.
Stimulation of the vagus, by increasing the activity of the inhibitory center,
arrests the heart in diastole with its cavities full of blood ; but as the stim-
ulation is only temporary, after a few seconds the heart recommences to
beat ; at first the pulsations are weak and feeble, but they soon regain their
original vigor. After the administration of atropin in sufficient doses to
destroy the termination of the pneumogastric, stimulation of its trunk has
no effect upon the heart'. The inhibitory fibers in the vagus are constantly
in action, for division of the nerve on both sides is always followed by an
increase in the frequency of the heart's pulsations.

The accelerator fibers arise in the medulla, pass down the cord, emerge
in the cervical region, pass to the last cervical and first dorsal ganglia of
the sympathetic, and thence to the heart. Stimulation of these fibers
causes an increased frequency of the heart's pulsations, but they are dimin-
ished in force.

ARTERIES.

The arteries are a series of branching tubes conveying blood to all
portions of the body. They are composed of three coats :

1. External, formed of areolar and elastic tissue.

2. Middle, contains both elastic and muscle fibers, arranged transversely
to the long axis of the artery. The elastic tissue is more abundant in
the larger vessels, the muscular in the smaller.

132 HUMAN PHYSIOLOGY.

3. Internal, composed of a thin, homogeneous membrane, covered with a

layer of elongated endothelial cells.

The arteries possess both elasticity and contractility.

The property of elasticity allows the arteries already full to accommodate
themselves to the incoming amount of blood, and to convert the intermit-
tent acceleration of blood in the large vessels into a steady and continuous
stream in the capillaries.

The contractility of the smaller vessels equalizes the current of blood,
regulates the amount going to each part, and promotes the onward flow of
blood.

Blood-pressure. — Under the influence of the ventricular systole, the
recoil of the elastic walls of the arteries, and the resistance offered by the
capillaries, the blood is constantly being subjected to a certain amount of
pressure. If a large artery of an animal be divided, and a glass tube of
the same caliber be inserted into its lumen, the blood will rise to a height
of about nine feet ; or if it be connected with a mercurial manometer, the
mercury will rise to a height of six inches. This height will be a measure,
of the pressure in the vessel. The absolute quantity of mercury sustained
by an artery can be ascertained by multiplying the height of the column
by the area of a transverse section of that artery.

The pressure of the blood is greatest in the large arteries, but gradually
decreases toward the capillaries.

The blood-pressure is increased or diminished by influences acting upon
the heart or upon the peripheral resistance of the capillaries, viz. :

If, while the force of the heart remains the same, the number of pulsa-
tions a minute increases, thus increasing the volume of blood in the arteries,
the pressure rises. If the rate remains the same, but the force increases,
the pressure again rises. Causes that increase the peripheral resistance
by contracting the arterioles — e. g., irritation of the vasomotor nerves, cold,
etc. — produce an increase of the pressure.

On the other hand, influences which diminish either the volume of the
blood, or the number of pulsations, or the force of the heart, or the pe-
ripheral resistance, lower the pressure.

The pulse is the sudden distention of the artery in a transverse and
longitudinal direction, due to the injection of a volume of blood into the
arteries at the time of the ventricular systole. As the vessels are already
full of blood, they must expand in order to accommodate themselves to the
incoming volume of blood. The blood-pressure is thus increased, and the
pressure originating at the ventricle excites a pulse-wave, which passes from

CIRCULATION OF THE BLOOD. 133

the heart toward the capillaries at the rate of about twenty-nine feet a
second. It is this wave that is recognized by the finger.

The velocity with which the blood flows in the arteries diminishes from
the heart to the capillaries, owing to an enlargement in the united sectional
area of the vessels ; the velocity increases from the capillaries toward the
heart. The blood moves most rapidly in the large vessels, and especially
under the influence of the ventricular systole. From experiments on animals,
it has been estimated to move in the carotid of man at the rate of sixteen
inches a second, and in the large veins at the rate of four inches a second.

The caliber of the blood-vessels is regulated by the vasomotor
nerves, which have their origin in the gray matter of the medulla oblongata.
They issue from the spinal cord through the anterior roots of spinal nerves,
pass through the sympathetic ganglia, and ultimately are distributed to the
coats of the blood-vessels. They exert at different times a constricting and
a dilating action upon the vessels, thus keeping up the arterial tonus.

Capillaries. — The capillaries constitute a network of vessels of micro-
scopic size, which distribute the blood to the inmost recesses of the tissues,
inosculating with the arteries on the one hand and the veins on the other ;
they branch and communicate in every possible direction.

The diameter of a capillary vessel varies from -$-50^ to j-^q ^ of an inch ;
the walls of these consist of a delicate, homogeneous membrane, ^oiyoo °f
an inch in thickness, lined by flattened, elongated, endothelial cells, be-
tween which, here and there, are observed stomata.

It is through the agency of the capillary vessels that the phenomena of
nutrition and secretion take place, for here the blood flows in an equable
and continuous current, and is brought into intimate relationship with the
tissues — two of the essential conditions for proper nutrition.

The rate of movement in the capillary vessels is estimated at one inch in
thirty seconds.

In the capillary current the red corpuscles may be seen hurrying down
the center of the stream, while the white corpuscles in the still layer adhere
to the walls of the vessel, and at times can be seen to pass through the
walls of the vessel by ameboid movements.

The passage of the blood through the capillaries is mainly due to the
force of the ventricular systole and the elasticity of the arteries ; but it is
probably also aided by a power resident in the capillaries themselves, the
result of a vital relation between the blood and the tissues.

The veins are the vessels which return the blood to the heart ; they

134 HUMAN PHYSIOLOGY.

have their origin in the venous radicles, and as they approach the heart
converge to form larger trunks, and terminate finally in the venae cavae.
They possess three coats —

1. External, made up of areolar tissue.

2. Middle, composed of non -striated muscle -fibers ; yellow, elastic, and
fibrous tissue.

3. Internal, an endothelial membrane similar to that of the arteries.
Veins are distinguished by the possession of valves throughout their

course, which are arranged in pairs, and formed by a reflection of the in-
ternal coat, strengthened by fibrous tissues ; they always look toward the
heart, and when closed prevent a reflux of blood in the veins. Valves are
most numerous in the veins of the extremities, but are entirely absent in
many others.

The onward flow of blood in the veins is mainly due to the action
of the heart, but is assisted by the contraction of the voluntary muscles and
the force of respiration.

Muscular contraction, which is intermittent, aids the flow of blood in the
veins by compressing them. As regurgitation is prevented by the closure
of the valves, the blood is forced onward toward the heart.

Rhythmic movements of veins have been observed in some of the lower
animals, aiding the onward current of blood.

During the movement of inspiration the thorax is enlarged in all its
diameters, and the pressure on its contents at once diminishes. Under
these circumstances a suction force is exerted upon the great venous trunks,
which causes the blood to flow with increased rapidity and volume toward
the heart.

Venous Pressure. — As the force of the heart-beat is nearly expended
in driving the blood through the capillaries, the pressure in the venous sys-
tem is not very marked, not amounting in the jugular vein of. a dog to
more than ^ that of the carotid artery.

The time required for a complete circulation of the blood throughout the
vascular system has been estimated to be from twenty to thirty seconds,
while for the entire mass of blood to pass through the heart fifty-eight
pulsations would be required, occupying forty-eight seconds.

The forces keeping the blood in circulation are :

1. Action of the heart.

2. Elasticity of the arteries.

3. Capillary force.

4. Contraction of the voluntary muscles upon the veins.

5. Respiratory movements.

RESPIRATION. 135

RESPIRATION.

Respiration is the function by which oxygen is absorbed into the
blood and carbonic acid exhaled. The assimilation of the oxygen and
the evolution of carbonic acid takes place in the tissues as a part of the
general nutritive process, the blood and respiratory apparatus constituting
the media by means of which the interchange of gases is accomplished.

The respiratory apparatus consists of a larynx, trachea, and lungs.

The larynx is composed of firm cartilages, united by ligaments and
muscles. Running anteroposteriorly across the upper opening are four
ligamentous bands, — the two superior or false vocal cords, and the two
inferior or true vocal cords, — formed by folds of the mucous membrane.
They are attached anteriorly to the thyroid cartilages and posteriorly to the
arytenoid cartilages, and are capable of being separated by the contraction
of the posterior crico-arytenoid muscles, so as to admit the passage of air
into and from the lungs.

The trachea is a tube from four to five inches in length, f of an
inch in diameter, extending from the cricoid cartilage of the larynx to
the third dorsal vertebra, where it divides into the right and left bronchi.
It is composed of a series of cartilaginous rings, which extend about two
thirds around its circumference, the posterior third being occupied by fibrous
tissue and non-striated muscle-fibers; which are capable of diminishing its
caliber.

The trachea is covered externally by a tough, fibro-elastic membrane,
and internally by mucous membrane, lined by columnar, ciliated, epithelial
cells. The cilia are always waving from within outward. When the two
bronchi enter the lungs, they divide and subdivide into numerous smaller
branches, which penetrate the lungs in every direction until they finally
terminate in the pulmonary lobules.

As the bronchial tubes become smaller their walls become thinner ; the
cartilaginous rings disappear, but are replaced by irregular angular plates
of cartilage ; when the tube becomes less than J^ of an inch in diameter,
they wholly disappear, and the fibrous and mucous coats blend, forming
a delicate elastic membrane, with circular muscle- fibers.

The lungs occupy the cavity of the thorax, are conic in shape, of a
pink color and a spongy texture. They are composed of a great number of
distinct lobules (the pulmonary lobules), connected by interlobular con-
nective tissue. These lobules vary in size, are of an oblong shape, and

136 HUMAN PHYSIOLOGY.

are composed of the ultimate ramifications of the bronchial tubes, within
which are contained the air-vesicles or cells. The walls of the air- vesicles,
exceedingly thin and delicate, are lined internally by a layer of tessellated
epithelium, externally covered by elastic fibers, which give the lungs their
elasticity and distensibility.

The venous blood is distributed to the lungs for aeration by the pulmo-
nary artery, the terminal branches of which form a rich plexus of capillary
vessels surrounding the air-cells ; the air and blood are thus brought into
intimate relationship, being separated only by the delicate walls of the air-
cells and capillaries.

The thoracic cavity, in which the respiratory organs are lodged, is of a
conic shape, having its apex directed upward, its base downward. Its
framework is formed posteriorly by the spinal column, anteriorly by the
sternum, and laterally by the ribs and costal cartilages. Between and over
the ribs lie muscles, fascia, and skin, above, the thorax is completely closed
by the structures passing into it and by the cervical fascia and skin ; below,
it is closed by the diaphragm. It is, therefore, an air-tight cavity.

The Pleura. — Each lung is surrounded by a closed serous membrane
(the pleura), one layer of which (the visceral} is reflected over the lung ;
the other (the parietal ) , reflected over the wall of the thorax; between the
two layers is a small amount of fluid, which prevents friction during the
play of the lungs in respiration.

Owing to the elastic tissue which is present in the lungs, they are very
readily distensible, ; so much so, indeed, that the pressure of the air inside
the trachea and lungs is sufficient to distend them until they completely fill
all parts of the thoracic cavity not occupied by the heart and great vessels.
The elastic tissue endows them not only with distensibility, but also with
the power of elastic recoil, by which they are enabled to accommodate
themselves to all variations in the size of the thoracic cavity.

When the chest- walls recede, the air within the lungs expands and presses
them against the ribs ; when the chest-walls contract, the air being driven
out, the elastic tissue recoils and the lungs return to their original condi-
tion. The movements of the lungs are, therefore, entirely passive.

As the capacity of the chest in a state of rest is greater than the volume
of the lungs after they are collapsed, it is quite evident that in the living
condition the lungs are distended and in a state of elastic tension, which
is greater or less in proportion as the thoracic cavity is increased or dimin-
ished in size. The elastic tissue, always on the stretch, is endeavoring to
pull the visceral layer of the pleura away from the parietal layer, but is

RESPIRATION.

137

antagonized by the pressure of the air within the air-passages. This con-
dition of things persists as long as the thoracic cavity remains air-tight ; but
if an opening be made in the thoracic wall, the pressure of the external air,
which was previously supported by the practically rigid walls of the thorax,
now presses upon the lung with as much force as the air within the lung.
The two pressures being neutralized, there is nothing to prevent the elastic
tissue from recoiling, driving the air out, and collapsing. The elastic tension
of the lungs can be readily measured
in man after death by inserting a man-
ometer into the trachea. Upon opening
the thorax and allowing the tissue to
recoil, the air passes upon the mercury
and elevates it, the extent to which it
is raised being the index of the pres-
sure. Hutchinson calculated the pres-
sure to be one half pound to the square
inch of lung surface.

Respiratory Movements. — The
movements of respiration are two, and
consist of an alternate dilatation and
contraction of the chest, known as in-
spiration and expiration.

1. Inspiration is an active process, the
result of the expansion of the thorax,
whereby air is introduced into the
lungs.

2. Expiration is a partially passive pro-
cess, the result of the recoil of the
elastic walls of the thorax, and the
recoil of the elastic tissue of the
lungs, whereby the carbonic acid is expelled

Fig. 18. — Diagram of the Respi-
ratory Organs.

The windpipe, leading down from the
larynx, is seen to branch into two
large bronchi, which subdivide
after they enter their respective
lungs.

In inspiration the chest is enlarged by an increase in all its diameters —

1. The vertical is increased by the contraction and descent of the dia-
phragm when it approximates a straight line.

2. The anteroposterior and t>ansver:e diameters are increased by the
elevation and rotation of the ribs upon their axes.

In ordinary tranquil inspiration the muscles which elevate the ribs and
IO

138 HUMAN PHYSIOLOGY.

thrust the sternum forward, and so increase the diameters of the chest, are
the external inter costals, running from above downward and forward, the
sternal portion of the internal intercostals, and the levatores costarum.

In the extraordinary efforts of inspiration certain auxiliary muscles are
brought into play, — viz. , the sternomastoid ', perforates, serratus magnus, —
which increase the capacity of the thorax to its utmost limit.

In expiration the diameters of the chest are all diminished — viz. :

1. The vertical, by the ascent of the diaphragm.

2. The anteroposterior, by a depression of the ribs and sternum.

In ordinary tranquil expiration the diameters of the thorax are dimin-
ished by the recoil of the elastic tissue of the lungs and the ribs ; but in
forcible expiration the muscles which depress the ribs and sternum, and
thus further diminish the diameter of the chest, are the internal inlercostals,
the infracostals, and the triangularis sterni.

In the extraordinary efforts of expiration certain auxiliary muscles are
brought into play, — viz., the abdominal and sacrohimbalis muscles, — which
diminish the capacity of the thorax to its utmost limit.

Expiration is aided by the recoil of the elastic tissue of the lungs and
ribs and by the pressure of the air.

Movements of the Glottis. — At each inspiration the rima glottidis is
dilated by a separation of the vocal cords, produced by the contraction of
the crico-arytenoid muscles, so as freely to admit the passage of air into
the lungs ; in expiration they fall passively together, but do not interfere
with the exit of air from the chest.

Nervous Mechanism of Respiration. — The movements of respira-
tory muscles, though capable of being modified to a certain extent by
efforts of the will, are of an automatic character, and called forth by ner-
vous impulses emanating from the medulla oblongata. The respiratory
center, the so-called vital point, generates the nerve impulses, which, travel-
ing outward through the phrenic and intercostal nerves, excite contractions
of the diaphragm and intercostal muscles, respectively. This center is for
the most part automatic in its action, though it is capable of being modi-
fied by impulses reflected to it through various sensory nerves.

This center may be stimulated :
I. Directly, by the condition of the blood. An increase of carbonic acid
or a diminution of oxygen in the blood causes an acceleration of the
respiratory movements ; the reverse of these conditions causes a dimin-
ution of the respiratory movements.

RESPIRATION. 139

2. Indirectly, by reflex action. The medulla may be excited to action
through the pneumogastric nerve, by the presence of carbonic acid in the
lungs irritating its terminal filaments ; through the fifth nerve, by irrita-
tion of the terminal branches; and through the nerves of general sensi-
bility. In either case this center reflects motor impulses to the respira-
tory muscles through the phrenic, intercostah, inferior laryngeal, and
other nerves.

Types of Respiration. — The abdominal type is most marked in young
children, irrespective of sex, the respiratory movements being effected by
the diaphragm and abdominal muscles.

In the superior costal type, exhibited by the adult female, the respiratory
movements are more marked in the upper part of the chest, from the first to
the seventh ribs, permitting the uterus to ascend in the abdomen during
pregnancy without interfering with respiration.

In the inferior costal type, manifested by the male, the movements are
largely produced by the muscles of the lower portions of the chest, from
the seventh rib downward, assisted by the diaphragm.

The respiratory movements vary according to age, sleep, and exercise,
being most frequent in early life, but averaging twenty a minute in adult
life. They are diminished by sleep and increased by exercise. There are
about four pulsations of the heart to each respiratory act.

During inspiration two sounds are produced : the one, heard in the
thorax, in the trachea, and larger bronchial tubes, is tubular in character ;
the other, heard in the substance of the lungs, is vesicular in character.

AMOUNT OF AIR EXCHANGED IN RESPIRATION, AND CAPACITY

OF LUNGS.

The tidal or breathing volume of air, that which passes in and out of the
lungs at each inspiration and expiration, is estimated at from twenty to
thirty cubic inches.

The complemental air is that amount which can be taken into the lungs
by a forced inspiration, in addition to the ordinary tidal volume, and
amounts to about I io cubic inches.

The reserve air is that which usually remains in the chest after the ordi-
nary efforts of expiration, but which can be expelled by forcible expiration.
The volume of reserve air is about ioo cubic inches.

The residual air is that portion which remains in the chest and cannot
be expelled after the most forcible expiratory efforts, and which amounts,
according to Dr. Hutchinson, to about ioo cubic inches.

140 HUMAN PHYSIOLOGY.

The vital capacity of the chest indicates the amount of air that can
be forcibly expelled from the lungs after the deepest possible inspiration,
and is an index of an individual's power of breathing in disease and during
prolonged severe exercise. The combined amount of the tidal, the com-
plemental, and the reserve air, 230 cubic inches, represents the vital
capacity of an individual five feet seven inches in height. The vital
capacity varies chiefly with stature. It is increased eight cubic inches for
every inch in height above this standard, and diminishes eight cubic inches
for each inch below it.

The tidal volume of air is carried only into the trachea and large
bronchial tubes by the inspiratory movements. It reaches the deeper por-
tions of the lungs in obedience to the law of diffusion of gases, which is
inversely proportionate to the square root of their densities.

The ciliary action of the columnar cells lining the bronchial tubes also
assists in the interchange of air and carbonic acid.

The entire volume of air passing in and out of the thorax in twenty-four
hours is subject to great variation, but can be readily estimated from the
tidal volume and the number of respirations a minute. Assuming that an
individual takes into the chest twenty cubic inches at each inspiration, and
breathes eighteen times a minute, in twenty-four hours there would pass in
and out of the lungs 518,400 cubic inches, or 300 cubic feet.

Chemistry of Respiration. — As the inspired air undergoes a change
in composition during its stay in the lungs which renders it unfit for further
respiration, it becomes requisite, for the correct understanding of respira-
tion, to ascertain the composition of both inspired and expired air.

Composition of Air. — Chemic analysis has shown that every 100
volumes of air contain 20.81 volumes of oxygen, 70.19 volumes of nitro-
gen, and 0.03 volume of carbonic acid. Aqueous vapor is also present,
though the quantity is variable. The higher the temperature, the greater
the amount.

The changes in the air effected by respiration are :
Loss of oxygen, to the extent of five cubic inches per 100 of air, or one in

twenty.
Gain of carbonic acid, to the extent of 4.66 cubic inches per 100 of air, or

0.93 inch in twenty.
Increase of water- vapor and organic matter.
Elevation of temperature.
Increase, and at times decrease, of nitrogen.
Gain of ammonia.

RESPIRATION. 141

The total quantity of oxygen withdrawn from the air and consumed by
the body in twenty-four hours amounts to fifteen cubic feet, and can be
readily estimated from the amount consumed at each respiration. Assum-
ing that one cubic inch of oxygen remains in the lungs at each respiration,
in one hour there are consumed 1080 cubic inches, and in twenty four
hours 25,920 cubic inches, or fifteen cubic feet, weighing eighteen ounces.
To obtain this quantity, 300 cubic feet of air are necessary.

The quantity of oxygen consumed daily is subject to considerable varia-
tions. It is increased by exercise, digestion, and lowered temperature, and
decreased by the opposite conditions.

The quantity of carbonic acid exhaled in twenty-four hours varies greatly.
It can be estimated in the same way. Assuming that an individual exhales
0.93 -f- cubic inch at each respiration, in one hour there are eliminated 1008
cubic inches, and in twenty-four hours 24,192 cubic inches, or fourteen
cubic feet, containing seven ounces of pure carbon.

The exhalation of carbonic acid is increased by muscular exercise, nitrog-
enous food, tea, coffee, and rice, age, and by muscular development ; de-
creased by a lowering of temperature, repose, gin and brandy, and a dry
condition of the air.

As there is always more oxygen consumed than carbonic acid exhaled,
and as oxygen unites with carbon to form an equal volume of carbonic acid,
it is evident that a certain quantity of oxygen disappears within the body. In
all probability it unites with the sulphur hydrogen of the food to form water.

The amount of watery vapor which passes out of the body with the ex-
pired air is estimated at from one to two pounds.

The organic matter, though slight in amount, gives the odor to the breath.
In a room with defective ventilation the organic matter accumulates and
gives rise to headache, nausea, drowsiness, etc. Long-continued breathing
of such air produces general ill health. It is not so much the presence of
C02 in increased amount as the presence of organic matter which necessi-
tates thorough ventilation.

Condition of the Gases in the Blood.

Oxygen is absorbed from the lungs into the arterial blood by the coloring-
matter, hemoglobin, with which it exists in a state of loose combination,
and is disengaged during the process of nutrition.

Carbonic acid, arising in the tissues, is absorbed into the blood in con-
sequence of its alkalinity, where it exists in a state of simple solution and
also in a state of feeble combination with the carbonates, soda and potassa,
forming the bicarbonates.

142 HUMAN PHYSIOLOGY*

Nitrogen is simply held in solution in the plasma.

Exchange of Gases in the Air-cells. — From the difference in ten-
sion of the oxygen in the air-cells (27.44 mm of Hg) and of the oxygen
in the venous blood (22 mm. Hg), and from the difference of the carbonic
acid tension in the venous blood (41 mm. Hg) and in the air-cells (27 mm.
Hg), it might be concluded that the passage of the gases is due solely
to pressure. The absorption of oxygen, however, does not follow abso-
lutely the law of pressure; that chemic processes are involved is shown
by the union of oxygen with the hemoglobin of the blood corpuscles.
The exhalation of C02 is also partly a chemic process, as it has been
shown that the quantity excreted is greatly increased when oxygen is simul-
taneously absorbed. Oxygen not only favors the exhalation of loosely
combined C02, but favors the expulsion of that which can be excreted only
by the addition of acids to the blood.

Changes in the Blood during Respiration.

As the blood passes through the lungs it is changed in color, from the
dark purple of venous blood to the bright red of arterial blood.

The heterogeneous composition of venous blood is exchanged for the
uniform composition of the arterial.

It gains oxygen and loses carbonic acid.

Its coagulability is increased. Temperature is diminished.

Asphyxia. — If the supply of oxygen to the lungs be diminished and the
carbonic acid retained in the blood, the normal respiratory movements cease
and the condition of asphyxia ensues, which soon terminates in death.

The phenomena of asphyxia are violent spasmodic action of the respi-
ratory muscles attended by convulsions of the muscles of the extremities,
engorgement of the venous system, lividity of the skin, abolition of sensi-
bility and reflex action, and death.

The cause of death is a paralysis of the heart from overdistention by
blood. The passage of the blood through the capillaries is prevented by
contraction of the smaller arteries, from irritation of the vasomotor center.
The heart is enfeebled by a want of oxygen and inhibited in its action by
the inhibitory centers.

ANIMAL HEAT. 143

ANIMAL HEAT.

The functional activity of all the organs and tissues of the body is
attended by the evolution of heat, which is independent, for the most part,
of external conditions. Heat is a necessary condition for the due perform-
ance of all vital actions ; although the body constantly loses heat by radia-
tion and evaporation, it possesses the capability of renewing it and of main-
taining it at a fixed standard. The normal temperattcre of the body in the
adult, as shown by means of a delicate thermometer placed in the axilla,
ranges from 97. 250 F. to 99. 50 F., though the mean normal temperature
is estimated by Wunderlich at 98 6° F.

The temperature varies in different portions of the body according to
the extent to which oxidation takes place, being highest in the muscles, in
the brain, blood, liver, etc.

The conditions which produce variations in the normal temperature
of the body are : age, period of the day, exercise, food and drink, climate,
season, and disease.

Age. — At birth the temperature of the infant is about 1° F. above that of
the adult, but in a few hours falls to 95. 50 F. , to be followed in the course
of twenty-four hours by a rise to the normal or a degree beyond. During
childhood the temperature approaches that of the adult ; in aged persons
the temperature remains about the same, though they are not so capable of
resisting the depressing effects of external cold as adults. A diurnal
variation of the temperature occurs from 1.8° F. to 3.70 F. (Jiirgensen) ;
the maximum occurring late in the afternoon, from 4 to 9 P. M. ; the mini-
mum, early in the morning, from I to 7 A. M.

Exercise. — The temperature is raised from i° to 2° F. during active
contractions of the muscular masses, and is probably due to the increased
activity of chemic changes ; a rise beyond this point being prevented by its
diffusion to the surface, consequent on a more rapid circulation, radiation,
more rapid breathing, etc.

Food and Drink. — The ingestion of a hearty meal increases the tem-
perature but slightly ; an absence of food, as in starvation, produces a
marked decrease. Alcoholic drinks, in large amounts, in persons unac-
customed to their use, cause a depression of the temperature amounting to
from 1° to 2° F. Tea causes a slight elevation.

External Temperattire. — Long-continued exposure to cold, especially if
the body is at rest, diminishes the temperajture from 1° to 2° F., while
exposure to a great heat slightly increases it.

144 HUMAN PHYSIOLOGY.

Disease frequently causes a marked variation in the normal temperature
of the body, which rises as high as 1070 F. in typhoid fever and 105 ° F.
in pneumonia ; in cholera it falls as low as 8o° F. Death usually occurs
when the heat remains high and persistent, from 1060 to HO° F. ; the in-
crease of heat in disease is due to excessive production rather than to
diminished elimination.

The source of heat is to be sought for in the chemic decompositions and
hydrations taking place during the general process of nutrition, and in the
combustion of the carbonaceous compounds by the oxygen of, the inspired
air ; the amount of its production is in proportion to the activity of the in-
ternal changes.

Every contraction of a muscle, every act of secretion, each exhibition of
nerve force, is accompanied by a change in the chemic composition of the
tissues and an evolution of heat. The reduction of the disintegrated
tissues to their simplest form by oxidation, and the combination of the oxy-
gen of the inspired air with the carbon and hydrogen of the blood and tis-
sues, results in the formation of carbonic acid and water and the generation
of a great amount of heat.

Certain elements of the food, particularly the non-nitrogenized sub-
stances, undergo oxidation without taking part in the formation of the tis-
sues, being transformed into carbonic acid and water, and thus increase
the sum of heat in the body.

Heat-producing Tissues. — All the tissues of the body add to the
general amount of heat, according to the degree of their activity. But
special structures, on account of their mass and the large amount of
blood they receive, are particularly to be regarded as heat producers, e. g.:

1. During mental activity the brain receives nearly one fifth of the entire
volume of blood, and the venous blood returning from it is charged with
waste matters, and its temperature is increased.

2. The muscular tissue, on account of the many chemic changes occurring
during active contractions, must be regarded as the chief heat-producing
tissue.

3. The secreting glands, during their functional activity, add largely to the
amount of heat.

The entire quantity of heat generated within the body has been demon-
strated experimentally to be about 2,300 calories, a calory, or heat unit,
being that amount of heat required to raise the temperature of one kilogram
of water (2.2 pounds) 1° C. This quantity of heat, if not utilized and re-

SECRETION. 145

tained within ths body, would elevate its temperature in twenty-four hours
about 6o° F. That this volume of heat depends very largely upon the
oxidation of the food -stuffs can be shown experimentally.

The normal temperature of the body is maintained by a constant expen-
diture of the heat in several directions :

1. In warming the food, drink, and air that are consumed in twenty-four
hours. For this purpose about 157 heat units are required.

2. In evaporating water from the skin and lungs, 619 heat units being
utilized for this purpose.

3. In radiation and conduction. By these processes the body loses at
least fifty per cent, of its heat, or 1,156 heat units.

4. In the production of work ; the work of the circulatory, respiratory,
muscidar, and nervous apparatus being performed by the transformation
of 369 heat units into units of work.

The nervous system influences the production of heat in a part by increas-
ing the amount of blood passing through it by its action upon the vasomotor
nerves. Whether there exists a special heat-center has not been satisfac-
torily determined, though this is probable.

SECRETION.

The process of secretion consists in the separation of materials from
the blood which are either to be again utilized to fulfil some special pur-
pose in the economy, or are to be removed from the body as excrementi-
tious matter ; in the former case they constitute the secretions, in the latter,
the excretions.

The materials which enter into the composition of the secretions are
derived from the nutritive principles of the blood, and require special
organs — e. g., gastric glands, mammary glands, etc. — for their proper
elaboration.

The materials which compose the excretions preexist in the blood, and
are the results of the activities of the nutritive process ; if retained within
the body, they exert a deleterious influence upon the composition of the
blood.

Destruction of a secreting gland abolishes the secretion peculiar to it,
and it can not be formed by any other gland ; but among the excreting
organs there exists a complementary relation, so that if the function of one
organ be interfered with, another performs it to a certain extent.

146 HUMAN PHYSIOLOGY.

CLASSIFICATION OF THE SECRETIONS.

PERMANENT FLUIDS.

Serous fluids. Vitreous humor of the eye.

Synovial fluid. Fluid of the labyrinth of the internal

Aqueous humor of the eye. ear.

Cerebro-spinal fluid.

TRANSITORY FLUIDS.

Mucus. Gastric juice.

Sebaceous matter. Pancreatic juice.

Cerumen (external meatus). Secretion from B runner's glands.

Meibomian fluid. Secretion from Lieberkiihn's glands.

Milk and colostrum. Secretions from follicles of the large

Tears. intestine.

Saliva. Bile (also an excretion).

EXCRETIONS.

Perspiration and the secretion of Urine.

the axillary glands. Bile (also a secretion).

FLUIDS CONTAINING FORMED ANATOMIC ELEMENTS.

Seminal fluid, containing sperma- Fluid of the Graafian follicles,
tozoids.

The essential apparatus for secretion is a delicate, homogeneous,
structureless membrane, on one side of which, in close contact, is a capil-
lary plexus of blood-vessels, and on the other side a layer of cells the
physiologic function of which varies in different situations.

Secreting organs may be divided into membranes and glands.

Serous membranes usually exist as closed sacs, the inner surfaces of which
are covered by pale, nucleated epithelium, containing a small amount of
secretion.

The serous membranes are the pleura, peritoneum, pei'icardium, synovial
sacs, etc.

The serous fluids are of a pale amber color, somewhat viscid, alkaline,
coagulable by heat, and resemble the serum of the blood ; their amount
is but small. The pleural fluid varies from four to seven drams ; the peri-
toneal from one to four ounces ; the pericardial from one to three drams.

The synovial fluid 'is colorless, alkaline, and extremely viscid, from the
presence of synovin.

SECRETION. 147

The function of serous fluids is to moisten the opposing surfaces, so as
to prevent friction during the play of the viscera.

The mucous membranes are soft and velvety in character, and line the
cavities and passages leading to the exterior of the body — e. g., the gastro-
intestinal, pulmonary and genito-urinary. They consist of a primary
basement membrane covered with epithelial cells, which in some situations
are tessellated, in others, columnar.

Mucus is a pale, semitransparent, alkaline fluid, containing epithelial
cells and leukocytes. It is composed, chemically, of water, an albuminous
principle (mucosin), and mineral salts ; the principal varieties are nasal,
bronchial, vaginal, and urinary.

Secreting glands are formed of the same elements as the secreting
membranes, but instead of presenting flat surfaces, are involuted, forming
tubules, which may be simple follicles — e. g., mucous, uterine, or intestinal ;
or compound follicles — e.g., gastric glands, mammary glands, or racemose
glands — e. g., salivary glands and pancreas. They are composed of a
basement membrane, enveloped by a plexus of blood-vessels, and are lined
by epithelial and true secreting cells, which in different glands possess the
capability of elaborating elements characteristic of their secretions.

In the production of the secretion two essentially different processes
are concerned.

1. Chemic. — The formation and elaboration of the characteristic organic
ingredients of the secreted fluids — e. g., pepsin, pancreatin — take place
during the intervals of glandular activity, as a part of the general func-
tion of nutrition. They are formed by the cells lining the glands, and
can often be seen in their interior with the aid of the microscope — e. g.,
bile in the liver cells, fat in the cells of the mammary gland.

2. Physical. — Consisting of a transudation of water and mineral salts from
the blood into the interior of the gland.

During the intervals of glandular activity only that amount of blood
passes through the gland sufficient for proper nutrition ; when the gland
begins to secrete, under the influence of an appropriate stimulus, the blood-
vessels dilate and the quantity of blood becomes greatly increased beyond
that flowing to the gland during its repose.

Under these conditions a transudation of water and salt takes place,
washing out the characteristic ingredients, which are discharged by the
gland ducts. The discharge of the secretions is intermittent ; they are
retained in the glands until they receive the appropriate stimulus, when

148 HUMAN PHYSIOLOGY.

they pass into the larger ducts by the vis a tergo, and are then discharged
by the contraction of the muscular walls of the ducts.

The activity of grandular secretion is hastened by an increase in the
blood-pressure and retarded by a diminution.

The nei~vous centers in the medulla oblongata influence secretion :

1. By increasing or diminishing the amount of blood entering a gland.

2. By exerting a direct influence upon the secreting cells themselves, the
centers being excited by reflex irritation, mental emotion, etc.

MAMMARY GLANDS.

The mammary glands, which secrete the milk, are two more or less
hemispheric organs, situated in the human female on the anterior surface
of the chest. Though rudimentary in childhood, they gradually increase
in size as the young female approaches puberty.

The gland presents at its convexity a small prominence of skin (the nip-
ple), which is 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 meshwork of fibrous tissue.
During utero- gestation the mammary glands become larger, firmer, and
more lobulated ; the areola darkens and the veins become 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 the glands diminish in size, undergo involution, and gradually
return to their original non-secreting condition.

Structure of the Mammary Glands. — Each mammary gland consists
of an aggregation of some fifteen or twenty lobes, each of which is sur-
rounded by a framework of fibrous tissue. The lobe is provided with an
excretory duct, which, as it approaches the base of the nipple, expands
to form a sinus or reservoir, beyond which it opens by a narrowed orifice
on the surface of the nipple. On tracing the duct into a lobe, it is found to
divide and subdivide, and finally to terminate in lobules or acini. Each
acinus consists of a basement membrane, lined by low polyhedral cells.
Externally it is surrounded by connective tissue, supporting blood-vessels,
lymphatics, and nerves.

MILK.
Milk is an opaque, bluish-white fluid, almost inodorous, of a sweet taste,
an alkaline reaction, and a specific gravity of 1025 to 1040. When exam-

MAMMARY GLANDS.

149

ined microscopically it 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 an average, y<ny^ °^ an lnc^ m diameter,
Each globule is supposed by some observers to be surrounded by a thin,
albuminous envelope, which enables it to maintain the discrete form. The
quantity of milk secreted daily by the human female averages about two
and a half pints. The milk of all the mammalia consists of all the differ-
ent classes of nutritive principles, though in varying proportions. The
relative proportions in which these constituents exist are shown in the fol-
lowing table of analyses :

COMPOSITION OF MILK.

In ioo Parts.

Human.

Cow.

Goat.

Ass.

Sheep.

Mare.

Water.

88.OO

86.87

87-54

91-57

82.27

88.80

Caseinogen.

2.40

3-98

3.00

1.09

6.IO

2.I9

Lactalbumin.

0.57

O.77

O.62

0.70

I. OO

O.42

Fat.

2.90

3-50

4.20

1.02

5-30

2.50

Lactose.

5.87

4.00

4.00

5-5o

4.20

5-5°

Salts.

O.16

O.17

O.56

0.42

1.00

O.50

Caseinogen is the chief proteid constituent of milk, and is held in so-
lution by the presence of calcic phosphate. On the addition of acetic acid
or of sodic chlorid up to the point of saturation, the caseinogen is precipi-
tated 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. The fer-
ment which induces this change is known as rennin. The presence of
calcic phosphate is necessary for this coagulation.

The fat of milk is more or less solid at ordinary temperatures. It is a
composition of olein, palmitin, and stearin, with a small quantity of butyrin
and caproin. When milk is allowed to stand for some time the fat-glob-
ules rise to the surface and form a thick layer, known as cream. When

150 HUMAN PHYSIOLOGY.

subjected to the churning process, the fat globules run together and form a
cohesive mass — the butter.

Lactose is the particular form of sugar characteristic of milk. It be-
longs to the saccharose group and has the following composition : C12H22-
On. In the presence of the bacillus acidi lactici the lactose is decomposed
into lactic acid and carbon dioxid, the former of which will cause a coagu-
lation of the caseinogen.

Mechanism of Secretion. — During the time of lactation the mam-
mary gland exhibits periods of secretory activity which alternate with pe-
riods of rest. Coincidentally with these periods, certain histologic changes
take place in the secreting structures of the gland. At the close of a period
of active secretion each acinus presents the following features : the epi-
thelial cells are short, cubic, nucleated, and border a relatively wide
lumen in which is to be found a variable quantity of non-discharged milk.
After the gland has rested for some time, active metabolism again begins.
The epithelial cells grow and elongate ; the nucleus divides into two or
three new nuclei, and at the same time the cell becomes constricted ; the
inner portion is detached and is discharged into the lumen. Coincidentally
with these changes oil-globules make their appearance in the cell proto-
plasm, some of which are discharged separately into the lumen, while others
remain for a time associated with the detached cell. From these histo-
logic changes it would appear that the caseinogen and the fat-globules are
metabolic products of the cell protoplasm, and not derived directly from the
blood. That lactose has a similar origin appears certain from the fact that
it is formed independently of carbohydrate food. The water and inorganic
salts are doubtless secreted by a mechanism similar to that of all other
secreting glands.

VASCULAR OR DUCTLESS GLANDS.

INTERNAL SECRETIONS.

The metabolism of the body generally, as well as that of individual
organs, has been shown to be related not only to the physiologic activity
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 liver in the maintenance of the general metabolism through the pro-

VASCULAR OR DUCTLESS GLANDS. 151

duction 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 maintenance of physiologic pro-
cesses, appears certain from the results of animal experimentation. The
explanation given, and generally accepted at the present time, for the influ-
ence 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 declines and in a short time a fatal termination
ensues.

Inasmuch as these partly unknown substances are formed by cell activity
and are poured into the interstices of the tissues, they have been termed
"internal secretions." Though the term internal secretions is applicable
to all substances which arise in consequence of tissue metabolism, and
which, after being poured into the blood, influence in varying degrees and
ways physiological 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, the lobes are
united by a narrow band or isthmus of the same tissue. In color the
gland is reddish, and it is 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 meas
uring more than o. I mm. in diameter. Each sac is composed of a thin
homogeneous membrane lined by cuboid epithelium. The interior of the
sac in adult life 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 supported by connective tissue, which forms, in addition, a
covering for the entire gland.

Function of the Thyroid. — The knowledge at present possessed as to
the function of the thyroid gland, especially in mammals, is the outcome of
a study of the effects which follow its arrest of development in the child,
its degeneration in the adult, its extirpation in the human being as well as

152 HUMAN PHYSIOLOGY.

in animals. The results, however, which follow its extirpation are not
always uniform in all animals ; sufficient reasons for which lack of uni-
formity 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 or an arrested development of the thyroid, either at the time of
birth or during 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 generally re-
garded 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 expression. 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.

Extirpation of the thyroid, for relief from symptoms due to grave patho-
logic 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 followed
surgical removal of the thyroid, Schiff, in 1 887, repeated his earlier experi-
ments on dogs, and found again that removal of the thyroid was speedily fol-
lowed 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 ; fibrillar
contractions of muscles ; tremors ; spasms ; mucinoid degeneration of the
skin, giving rise to puffiness of the eyelids and face and to a swollen con-
dition of the abdomen ; hebetude of mind, frequently terminating in idiocy ;
fall of blood-pressure ; dyspnea ; albuminuria ; atrophy 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: vix., 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 certain toxic bodies, rendering them innocuous, and
thus preserving the body from a species of auto-intoxication, is gvadually
yielding to the more probable view that the epithelium is engaged to the

VASCULAR OR DUCTLESS GLANDS. 153

secretion of a specific material, which finds its way into the blood or
lymph and in some unknown way influences favorably tissue metabolism.
This view of the function of the thyroid is supported by the fact that suc-
cessful grafting of a portion of the thyroid beneath the skin or in the
abdominal cavity will prevent the usual symptoms which follow thyroidec-
tomy. 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 benefited, and even cured, by feed-
ing them with fresh thyroids or even 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 containing
iodin, which, under the influence of various reagents, undergoes 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
milligram for each gram of tissue. To this compound the term thyro-
iodin 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 diminution of all myxedematous symptoms.
In normal states of the body, thyroiodin influences very actively the gen-
eral 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 symp-
toms : e. g,, increased cardiac action, vertigo, and glycosuria.

The Hypophysis Cerebri. — 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. 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 hypophysis has been found in connection with a hy-
pertrophic condition of the bones of the face and extremities, to which the
term acromegalia has been given.

Intravenous injection of an extract of the hypophysis increases the
II

154 HUMAN PHYSIOLOGY.

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
Oliver). The material secreted by the hypophysis has not been isolated,
hence its chemic features are unknown. After its formation it probably
passes through a system of ducts into the cerebrospinal fluid, after which
it influences the metabolism of the nervous and osseous tissues as well as
the force of the heart muscle.

An extract of the hypophysis itself exerts no appreciable effect on the
blood-pressure or on the rate of the heart-beat, nor does it influence the
circulatory and respiratory organs (Howell). An extract of the infundib-
ular body intravenously injected, however, gives rise to increased blood-
pressure and to a slowing of the heart-beat.

Adrenal Bodies, or Suprarenal Capsules. — These are two flattened
bodies, somewhat crescentic or triangular in shape, situated each upon the
upper extremity of the corresponding kidney, and held in place by con-
nective 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 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 prog-
ress 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 essential 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 charac-
teristic of Addison's disease. Their development, however, was more
acute. From the fact that animals so promptly die from extirpation of
these bodies, and the further fact that the blood of such animals is toxic to
those the subjects of recent extirpation, but not to normal animals, the
conclusion was drawn that the function of the adrenal bodies was to
remove from the blood some toxic material the product of muscle metab-
olism. Its accumulation after extirpation gives rise to death through
auto-intoxication.

On the supposition that the adrenals might secrete and pour into the
blood a specific material which favorably influences general ^metabolism,

KIDNEYS. 155

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 than in the latter instance.
This is attributed to a direct stimulation and contraction of the muscle-
fibers of the arterioles themselves, and not to vaso-motor 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, the adrenal extract produces contraction 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 stimu-
lates to increased activity the muscle-fibers of the heart and arteries, and
thus assists in maintaining the normal blood-pressure as well as the tonicity
of the skeletal muscles. The active principle of this gland has been iso-
lated by Abel and termed epinephrin.

EXCRETION.

The principal excrementitious fluids discharged from the body are
the urine, perspiration, and bile ; they hold in solution principles of waste
which are generated during the activity of the nutritive process and are
the ultimate forms to which the organic constituents are reduced in the
body. They also contain inorganic salts.

The urinary apparatus consists of the kidneys, ureters, and bladder.

KIDNEYS.

The kidneys are the organs for the secretion of urine ; they resemble
a bean in shape, are from four to five inches in length, two in breadth,
and weigh from four to six ounces.

156

HUMAN PHYSIOLOGY.

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

Fig. 19. — Longitudinal Section through the Kidney, the Pelvis of the
Kidney, and a number of Renal Calyces. — {Tyson, after Henle.)

A. Branch of the renal artery. U. Ureter. C. Renal calyx. 1. Cortex. 1'. Medul-
lary rays. 1". Labyrinth, or cortex proper. 2. Medulla. 2'. Papillary portion 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.

of the ilium ; the anterior surface is convex, the posterior surface concave,
the latter presenting a deep notch, the hilus.

The kidney is surrounded by a thin, smooth membrane composed of

KIDNEYS.

157

white fibrous and yellow elastic tissue ; though it is attached to the surface
of the kidney by minute processes of connective tissue, it can be readily
torn away. The substance of the kidney is dense, but friable.

Upon making a longitudinal section of the kidney it will be observed
that the hilus extends into the interior of the organ and expands to form
a cavity known as the sinus. This cavity is occupied by the upper, dilated
portion of the ureter, the interior of which forms the pelvis. The ureter
subdivides into several portions, which ultimately give origin to a number
of smaller tubes, termed 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. They present a dis-
tinctly striated appearance, a condition due
to the straight direction of the tubules and
blood-vessels.

2. An external or cortical portion, consisting of a
delicate matrix containing an immense number
of tubules having a markedly convoluted ap-
pearance. Throughout its structure are found
numerous small ovoid bodies, termed Mal-
pighian corpuscles.

The Uriniferous Tubules. — The kidney is a
compound, tubular gland composed of micro-
scopic tubules whose function it is to secrete
from the blood those waste products which col-
lectively constitute the urine. If the apex of
each pyramid be examined with a lens, it will
present a number of small orifices, which are the
beginnings of the uriniferous tubules. From
this point the tubules pass outward in a straight
but somewhat divergent manner toward the cortex, giving off at acute
angles a number of branches (Fig. 20). From the apex to the base of the
pyramids they are known as the tubules of Bellini. In the cortical portion
of the kidney each tubule becomes enlarged and twisted, and after pur-
suing an extremely convoluted course, turns backward into the medullary
portion for some distance, forming the descending limb of Henle's loop :

Fig. 20. — Diagrammatic
Exposition of the
Method in which
the Uriniferous
Tubes Unite to
Form Primitive
Cones. — ( Tyson,
after Ludnvig.)

158 HUMAN PHYSIOLOGY.

it then turns upon itself, forming the ascending limb of the loop, reenters
the cortex, again expands, and finally terminates in a spheric enlargement
known as Midler'' s or Boivmari 's capsule. Within this capsule is contained
a small tuft of blood-vessels, constituting the glomerulus, or Malpighian
corpuscle.

Structure of the Tubules. — Each tubule consists of a basement mem-
brane lined by epithelial cells throughout its entire extent. The tubule
and its contained epithelium vary in shape and size in different parts of
its course. The termination of the convoluted tube consists of a little sac
or capsule, which is ovoid in shape and measures about ^i^ of an inch.
This capsule is lined by a layer of flattened epithelial cells, which is
also reflected over the surface of the glomerulus. During the periods of
secretory activity the blood-vessels of the glomerulus become filled with
blood, so that the cavity of the sac is almost obliterated ; after secretory
activity the blood-vessels contract and the sac- cavity becomes enlarged.
In that portion of the tubule lying between the capsule and Henle's loop
the epithelial cells are cuboid in shape; in Henle's loop they are flat-
tened, while in the remainder of the tubule they are cuboid and
columnar.

Blood-vessels of the Kidney. — The renal artery is of large size and
enters the organ at the hilum ; it divides into several large branches, which
penetrate the substance of the kidney between the pyramids, at the base
of which they form an anastomosing plexus, which completely surrounds
them. From this plexus vessels follow the straight tubes toward the apex,
while others, entering the cortical portion, divide into small twigs, which
enter the Malpighian body and form a mass of convoluted vessels, the
glomerulus. After circulating through the Malpighian tuft, the blood is
gathered together by two or three small veins, which again subdivide and
form a fine capillary plexus, which envelops the convoluted tubules ; from
this plexus the veins converge to form the emulgent vein, which empties
into the vena cava.

The nerves of the kidney follow the course of the blood-vessels and
are derived from the renal plexus.

The ureter is a membranous tube, situated behind the peritoneum,
about the diameter of a goose-quill, eighteen inches in length, and extends
from the pelvis of the kidney to the base of the bladder, which it perforates
in an oblique direction. It is composed of three coats : fibrous, muscular,
and mucous.

The bladder is a reservoir for the temporary reception of the urine

URINE. 159

prior to its expulsion from the body; when fully distended it is ovoid in
shape, and holds about one pint. It is composed of four coats : serous,
muscular (the fibers of which are arranged longitudinally and circularly),
areolar, and mucous. The orifice of the bladder is controlled by the
sphincter vesit a i a muscular band about x/, of an inch in width.

As soon as the urine is formed it passes through the tubuli uriniferi
into the pelvis and thence through the ureters into the bladder, which it
enters at an irregular rate. Shortly after a meal, after the ingestion of
large quantities of fluid, and after exercise, the urine flows into the bladder
quite rapidly, while it is reduced to a few drops during the intervals of
digestion. It is prevented from regurgitating into the ureters by the
oblique direction they take between the mucous and muscular coats.

Nervous Mechanism of Urination. — "When the urine has passed into
the bladder, it is there retained by the sphincter vesicas muscle, kept in a
state of chronic contraction by the action of a nerve center in the lumbar
region of the spinal cord. This center can be inhibited and the sphincter
relaxed, either reflexly, by impressions coming through sensory nerves from
the mucous membrane of the bladder, or directly, by a voluntary impulse
descending the spinal cord. When the desire to urinate is experienced,
impressions made upon the vesical sensory nerves are carried to the centers
governing the sphincter and detrusor urince muscles and to the brain. If
now the act of urination is to take place, a voluntary impulse originating in
the brain passes down the spinal cord and still further inhibits the sphincter
vesicae center, with the effect of relaxing the muscle and of stimulating
the center governing the detrusor muscle, with the effect of contracting the
muscle and expelling the urine. If the act is to be suppressed, voluntary
impulses inhibit the detrusor center and possibly stimulate the sphincter
center.

The genitospinal center controlling these movements is situated in that
portion of the spinal cord corresponding to the origin of the third, fourth,
and fifth sacral nerves.

URINE.

Normal urine is of a pale yellow or amber color, perfectly transparent,
with an aromatic" odor, an acid reaction, a specific gravity of 1020, and a
temperature when first discharged of loo° F.

The color varies considerably in health, from a pale yellow to a brown
hue, owing to the presence of the coloring-matter, urobilin or urochrome.

160

HUMAN PHYSIOLOGY.

The transparency is diminished by the presence of mucus, the calcium
and magnesium phosphates, and the mixed urates.

The reaction of the urine is acid, owing to the presence of acid phos-
phate of sodium. 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, especially if the food is largely
vegetable in character, is either neutral or alkaline.

The specific gravity varies from 1 015 to 1 025.

The quantity of urine excreted in twenty-four hours is between forty and
fifty fluidounces, but ranges above and below this standard.

The odor is characteristic, and caused by the presence of taurylic and
phenylic acids, but is influenced by vegetable foods and other substances
eliminated by the kidneys.

COMPOSITION OF URINE.

Water, 967.0

Urea,

Other nitrogenized crystalline bodies, uric acid, prin-'

cipally in the form of alkaline urates,
Creatin, creatinin, xanthin, hypoxanthin,
Hippuric acid, leucin, tyrosin, taurin, cystin, all in

small amounts, and not constant,
Mucus and pigment,

14.230

10.635

Salts

Inorganic : principally sodium and potassium sul-
phates, phosphates, and chlorids, with magnesium
and calcium phosphates, traces of silicates and
chlorids,

Organic : lactates, hippurates, acetates, formates,
which appear only occasionally,

Sugar

Gases (nitrogen and carbonic acid principally).

8.I3S

a trace

1,000.000

The average quantity of the principal constituents excreted in twenty-
four hours is as follows :

Water, 52.0 fluidounces.

Urea, 512-4 grains.

Uric acid, ... 8.5 "

Phosphoric acid, 45-° "

Sulphuric acid, 3I-H "

Inorganic salts, 323. 25 "

Lime and magnesia, 6.5 "

URINE. 161

To determine the amount of solid matters in, any given amount of
urine, multiply the last two figures of the specific gravity by the coefficient
of Haeser, 2.33 — e. g., in 1,000 grains of urine having a specific gravity
1022, there are contained 22 X 2-33 = 51.26 grains of solid matter.

Organic Constituents of Urine. — Urea is one of the most important
of the organic constituents of the urine, and is present to the extent of
from 2.5 to 3.2 per cent. Urea is a colorless, neutral substance, crystalliz-
ing in four-sided prisms terminated by oblique surfaces. When crystalliza-
tion is caused to take place rapidly, the crystals take the form of long,
silky needles. Urea is soluble in water and alcohol ; when subjected to
prolonged boiling, it is decomposed, giving rise to carbonate of ammonia.
In the alkaline fermentation of urine, urea takes up two molecules of
water with the production of carbonate of ammonia.

The average amount of urea excreted daily has been estimated at about
500 grains. As urea is one of the principal products of the breaking up of
the albuminous compounds within the body, it is quite evident that the
quantity produced and eliminated in twenty-four hours will be increased by
any increase in the amount of albuminous food consumed, or by a rapid
destruction of albuminous tissues, as is observed in various pathologic
states, inanition, febrile conditions, fevers, etc. A farinaceous or vegetable
diet will diminish the urea production nearly one half.

Muscular exercise when the nutrition of the body is in a state of equi-
librium does not seem to increase the quantity of urea.

Seat of Urea Formation. — As to the seat of urea formation, little
is positively known. It is quite certain that it preexists in the blood and is
merely excreted by the kidneys. It is not produced in muscles, as even
after prolonged exercise hardly a trace of urea is to be found in them.
Experimental and pathologic facts point to the liver as the probable organ
engaged in urea formation. Acute yellow atrophy of the liver, suppura-
tive diseases of the liver, diminish almost entirely the production of urea.

Uric acid is also a constant ingredient of the urine and is closely allied
to urea. It is a nitrogenized substance, carrying out of the body a large
quantity of nitrogen. The amount eliminated daily varies from five to ten
grains. Uric acid is a colorless crystal belonging to the rhombic system.
It is insoluble in water, and if eliminated in excessive amounts, it is de-
posited as a " brick -red" sediment in the urine. It is doubtful if uric acid
exists in a free state, being combined for the most part with sodium and
potassium bases forming urates. It is to be regarded as one of the termi-

162 HUMAN PHYSIOLOGY.

nal products of the disassimilation of albuminous compounds, and is prob-
ably produced in the liver.

Hippuric acid is found very generally in urine, though it is present
only in small amounts. It is increased by a diet of asparagus, cranberries,
plums, and by the administration of benzoic and cinnamic acids. It is
probably formed in the kidney.

Kreatinin resembles the kreatin derived from muscles. It is a color-
less crystal, belonging to the rhombic system. Its origin is unknown,
though it is largely increased in amount by albuminous food. About
fifteen grains are excreted daily.

Xanthin, sarkin, oxaluric acid, and allantoin are also constituents
of urine. They are nitrogenized compounds and are also terminal products
of albuminous compounds.

Urobilin, the coloring- matter of the urine, is a derivative of the bile
pigments. It is particularly abundant in febrile conditions, giving to the
urine its reddish -yellow color.

Inorganic Constituents of Urine. — Earthy Phosphate. Phos-
phoric acid in- combination with magnesium and calcium is excreted daily
to the extent of from fifteen to thirty grains. The phosphates are insol-
uble in water, but are held in solution in the urine by its acid ingredients,
alkalinity of the urine being attended with a copious precipitation of the
phosphates. Mental work increases the amount of phosphoric acid ex-
creted, a condition caused by increased metabolism of the nervous tissue.

Sulphuric acid in combination with sodium and potassium constitutes the
sulphates, of which about thirty grains are excreted daily. Sulphuric acid
results largely from the decomposition of albuminous food and from in-
creased destruction of animal tissues.

The gases of urine are carbonic acid and nitrogen.

Mechanism of Urinary Secretion. — As the kidney anatomically pre-
sents an apparatus for filtration (the Malpighian bodies) and an apparatus
for secretion (the epithelial cells of the urinary tubules), it might be inferred
that the elimination of the constituents of the urine is accomplished by
the twofold process of filtration and secretion ; that the water and highly
diffusible inorganic salts simply pass by diffusion through the walls of the
blood-vessels of the glomerulus into the capsule of Miiller, while the urea
and remaining organic constituents are removed by true secretory action of
the renal epithelium. Modern experimentation supports this view of renal
action.

LIVER. 163

The secretion of urine is, therefore, partly physical and partly vital.

The filtration of urinary constituents from the glomerulus into Midler's
capsule depends largely upon the blood -pressure and the rapidity of blood
flow in the renal artery and glomerulus. Among the influences which
increase the pressure and velocity may be mentioned increased frequency
and force of the heart's action, contraction of the capillary vessels of the
body generally, dilatation of the renal artery, and increase in the volume
of the blood.

The reverse conditions lower the blood -pressure and diminish the secre-
tion of urine.

The fact that organic matters are eliminated by the secretory activity of the
renal epithelium seems to be well established by modern experiments.
These substances, removed from the blood in the secondary capillary plexus
of blood-vessels, by a true selective action of the epithelium, are dissolved
and washed toward the pelves by the liquid coming from the capsules.

The blood-supply to the kidney is regulated by the nervous system. If
the renal nerves be divided, the renal artery dilates and a copious flow of
urine takes place. If the peripheral ends of the same nerves be stimulated,
the artery contracts and the urinary flow ceases. The same is true of the
splanchnic nerves, through which the vaso-motor nerves coming from the
medulla oblongata and spinal cord pass to the renal plexus.

LIVER.

The liver is a highly vascular, conglomerate gland, appended to the
alimentary canal. It is the largest gland in the body, weighing about four
and one half pounds ; it is situated in the right hypochondriac region, and
is retained in position by five ligaments, four of which are formed by dupli-
catures of the peritoneal investment.

The proper coat of the liver is a thin but firm fibrous membrane, closely
adherent to the surface of the organ, which it penetrates at the transverse
fissure, and follows the vessels in their ramifications through its substance,
constituting Glisson 's capsule.

Structure of the Liver. — The liver is made up of a large number of
small bodies (the lobmes), rounded or ovoid in shape, measuring ^ of an
inch in diameter, separated by a space in which are situated blood-vessels,
nerves, hepatic ducts, and lymphatics.

164 HUMAN PHYSIOLOGY.

The lobules are composed of cells, which, when examined microscop-
ically, exhibit a rounded or polygonal shape, and measure, on the average,
toVtt °f an *ncn m diameter ; they possess one, and sometimes two, nuclei ;
they also contain globules of fat, pigment matter, and animal starch. The
cells constitute the secreting structure of the liver, and are the true hepatic
cells.

The blood-vessels which enter the liver are :

1. The portal vein, made up of the gastric, splenic, and superior and infe-
rior mesenteric veins.

2. The hepatic artery, a branch of the celiac axis.

Both the portal vein and the hepatic artery are invested by a sheath of
areolar tissue.

The vessels which leave the liver are the hepatic veins, originating in its
interior, collecting the blood distributed by the portal vein and hepatic
artery, and conducting it to the ascending vena cava.

Distribution of Vessels. — The portal 'vein and the hepatic artery, upon
entering the liver, penetrate its substance,, divide into smaller and smaller
branches, occupy the spaces between the lobules, completely surrounding
and limiting them, and constitute the interlobular vessels. The hepatic
artery, in its course, gives off branches to the walls of the portal vein and
Glisson's capsule, and finally empties into the small branches of the portal
vein in the interlobular spaces.

The interlobular vessels form a rich plexus around the lobules, from
which branches pass to neighboring lobules and enter their substance,
where they form a very fine network of capillary vessels, ramifying over
the hepatic cells, in which the various functions of the liver are performed.
The blood is then collected by small veins, converging toward the center
of the lobule, to form the intralobular vein, which runs through its long
axis and empties into the sublobular vein. The hepatic veins are formed
by the union of the sublobular veins, and carry the blood to the ascending
vena cava ; their walls are thin and adherent to the substance of the hepatic
tissue.

The hepatic ducts or bile capillaries originate within the lobules,
in a very fine plexus lying between the hepatic cells ; whether the smallest
vessels have distinct membranous walls, or whether they originate in the
spaces between the cells by open orifices, has not been satisfactorily deter-
mined.

The bile-channels empty into the interlobular ducts, which measure about
Wfftf °f an mcn *n diameter, and are composed of a thin, homogeneous
membrane lined by flattened epithelial cells.

LIVER. 165

As the interlobular bile-ducts unite to form large trunks, they receive
an external coat of fibrous tissue, which strengthens their walls; they
finally unite to form one large duct (the hepatic duct), which joins the
cystic duct ; the union of the two forms the ductus communis choledochus,
which is about three inches in length, the size of a goose-quill, and opens
into the duodenum.

The gall-bladder is a pear-shaped sac, about four inches in length,
situated in a fossa on the under surface of the liver. It is a reservoir for
the bile, and is capable of holding about one ounce and a half of fluid. It
is composed of three coats :

1. Serous, a reflection of the peritoneum.

2. Fibrous and muscular. •

3. Mucous.

Functions of the Liver. — The liver is a complex organ having a
variety of relations to the general processes of the body. While its physio-
logic actions are not yet wholly understood, it may be said that it —

1. Secretes bile.

2. Forms glycogen.

3. Assists in the formation of urea and allied products.

4. Modifies the composition of the blood as it passes through it.

The Secretion of Bile. — The characteristic constituents of the bile do
not preexist in the blood, but are formed in the interior of the liver
cells of materials derived from the venous and arterial blood. The
hepatic cells, absorbing these materials, elaborate them into bile- elements,
and in so doing undergo histologic changes similar to those exhibited by
other secretory glands. The bile once formed, it passes into the mouths
of the bile capillaries, near the periphery of the lobules. Under the influ-
ence of the vis a tergo of the new-formed bile it flows from the smaller
into the larger bile-ducts, and finally empties into the intestine, or is regur-
gitated into the gall-bladder, where it is stored up until it is required for
the digestive process in the small intestine. The study of the secretion of
bile by means of biliary fistulse reveals the fact that the secretion is contin-
uous and not intermittent ; that the hepatic cells are constantly pouring
bile into the ducts, which convey it into the gall-bladder. As this fluid is
required only during intestinal digestion, it is only then that the walls of
the gall-bladder contract and discharge it into the intestine.

The flow of bile from the liver cells into the gall-bladder is accomplished
by the inspiratory movements of the diaphragm, and by the contraction of
the muscle-fibers of the biliary ducts, as well as the vis a tergo of new-

166 HUMAN PHYSIOLOGY. '

formed bile. Any obstacle to the outflow of bile into the intestine leaps
to an accumulation within the bile-ducts. The pressure within the ducts
increasing beyond that of the blood within the capillaries, a reabsorption
of biliary matters by the lymphatics takes place, giving rise to the phe-
nomena of jaundice.

The bile is both a secretion and an excretion ; it contains new constit-
uents, which are formed only in the substance of the liver, and are destined
to play an important part ultimately in nutrition ; it contains also waste
ingredients, which are discharged into the intestinal canal and eliminated
from the body.

Glycogenic Function. — In addition to the preceding function, Ber-
nard, in 1848, demonstrated the fact that the liver, during life, normally
produces a sugar-forming substance, analogous in its chemic composition to
starch, which he terms glycogen ; also that, when the liver is removed from
the body, and its blood-vessels are thoroughly washed out, after a few hours
sugar again makes its appearance in abundance.

It can be shown to exist in the blood of the hepatic vein as well as in a
decoction of the liver substance by means of either Trommer's or Fehling's
test, even when the blood of the portal vein does not contain a trace of
sugar.

Origin and Destination of Glycogen. — Glycogen appears to be
formed de novo in the liver cells, from materials derived from the food,
whether the diet be animal or vegetable, though a larger percentage is formed
when the animal is fed on starchy and saccharin than when fed on animal
food. The glucose, which is one of the products of digestion, is absorbed
by the blood-vessels and carried directly into the liver ; as it does not
appear in the urine, as it would if injected at once into the general circu-
lation, it is probable that it is detained in the liver, dehydrated, and stored
up as glycogen. The change is shown by the following formula :

C6H12°6 — H2° = C6H10°5-
Glucose. Water. Glycogen.

The glycogen thus formed is stored up in the hepatic cells for the future
requirements of the system. When it is carried from the liver, it is again
transformed into glucose by the agency of a ferment. Glycogen does not
undergo oxidation in the blood ; this process takes place in the tissues,
particularly in the muscles, where it generates heat and contributes to the
development of muscular force.

LIVER. 167

Glycogen, when obtained from the liver, is an amorphous, starch-like
substance, of a white color, tasteless and colorless, and soluble in water ;
by boiling with dilute acids, or subjected to the action of an animal ferment,
it is easily converted into dextrose. When an excess of sugar is generated
by the liver, dextrose can be found not only in the blood of the hepatic vein,
but also in other portions of the body ; under these circumstances it is elimi-
nated by the kidneys, appearing in the urine, constituting the condition of
glycosuria .

Formation of Urea. — The liver is now regarded by many physiolo-
gists as the principal organ concerned in urea formation. The liver
normally contains a certain amount of urea ; and if blood be passed
through the excised liver of an animal which has been in full digestion
when killed, a large amount of urea is obtained. The clinical evidence
proves that in destructive diseases of the liver substance there is at once a
falling-off in urea elimination. Various drugs which stimulate liver action
increase the urea in the urine.

Elaboration of Blood. — Besides the capability of secreting bile, the liver
possesses the property of so acting upon and modifying the chemic compo-
sition of the products of digestion as they traverse its substance that they are
readily assimilated by the blood, and are transformed into materials capa-
ble of being converted into the elements of the blood and into solid tissues.

The albuminous principles particularly require the modifying influence of
the liver ; for if they are removed from the portal vein and introduced into
the jugular vein, they are at once removed from the blood by the action of
the kidneys.

The blood of the hepatic vein differs from the blood of the portal vein
in being richer in blood-corpuscles, both red and white ; its plasma is more
dense, containing a smaller percentage of water and a greater amount of
solid constituents, but no fibrin ; its serum contains less albumin, fats, and
salts, but its sugar is increased.

Influence of the Nervous System. — The nervous system directly
controls the functional activity of the liver, and more especially its glyco-
genic function. It was discovered by Bernard that puncture of the medulla
oblongata is followed by so enormous a production of sugar that it is at
once excreted by the kidneys, giving rise to diabetic or saccharine urine.
This part of the medulla is, however, the vaso-motor center for the blood-
vessels of the liver. Destruction of this center, or injury to the vaso-motor
nerves emanating from it in any part of their course, is followed at once by
dilatation of the hepatic blood-vessels, slowing of the blood- current, a pro-

168 HUMAN FHYSIOLOGY.

found disturbance of the normal relation existing between the blood and
liver-cells, and a production of sugar. Many of the hepatic vaso-motor
nerves may be traced down the cord as far as the lumbar region, while
others leave the cord high up in the neck and enter the cervical ganglia of
the sympathetic, and so reach the liver. Injury to the sympathetic ganglia
is often followed by diabetes. Peripheral stimulation of various nerves, —
e. g., sciatic, pneumogastric, depressor nerve, — as well as the direct action
of many drugs, impair or depress the hepatic vaso-motor center and so give
rise to diabetes.

SKIN.

The skin, the external investment of the body, is a most complex and
important structure, serving —

1. As a. protective covering.

2. As an organ for tactile sensibility.

3. As an organ for the elimination of excre??ientitious matters.

The amount of skin investing the body of a man of average size is
about twenty feet, and varies in thickness, in different situations, from \ to
Ti^ of an inch.

The skin consists of two principal layers — viz., a deeper portion, the
corium, and a superficial portion, the epider?nis.

The corium, or cutis vera, may be subdivided into a reticulated and a
papillary layer. The former is composed of white fibrous tissue, non-
striated muscle-fibers, and elastic tissue, interwoven in every direction,
forming an areolar network, in the meshes of which are deposited masses
of fat, and a structureless, amorphous matter ; the latter is formed mainly
of club-shaped elevations or projections of the amorphous matter, consti-
tuting the papillce ; they are most abundant and well developed upon the
palms of the hands and upon the soles of the feet ; they average T^ of an
inch in length, and may be simple or compound ; they are well supplied
with nerves, blood-vessels, and lymphatics.

The epidermis, or scarf skin, is an extravascular structure, a product
of the true skin, and is composed of several layers of cells. It may be
divided into two layers : the rete mucosum, or the Malpighian layer, and
the horny or corneous.

The former is closely adherent to the papillary layer of the true skin,

SKIN. 169

and is composed of large, nucleated cells, the lowest layer of which, the
"prickle cells," contains pigment-granules, which give to the skin its
varying tints in different individuals and in different races of men ; the
more superficial cells are large, colorless, and semi-transparent. The latter,
the corneous layer, is composed of flattened cells, which, from their
exposure to the atmosphere, are hard and horny in texture ; it varies in
thickness from \ of an inch on the palms of the hands and soles of the feet
to j^-q of an inch in the external auditory canal.

APPENDAGES OF THE SKIN.

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.

They consist of a root and a shaft. The latter is oval in shape and
about ¥^-j5- of an inch in diameter ; 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 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 hair protects the head from the heat of the sun and from the cold,
retains the heat of the body, prevents the entrance of foreign matter into
the lungs, nose, ears, etc. The color is due to pigment matter. In old
age the hair becomes more or less whitened.

The sebaceous glands, embedded in the true skin, are simple and
compound racemose glands, opening, by a common excretory duct, upon
the surface of the epidermis or into the hair-follicle. They are found in
all portions of the body, most abundantly in the face, and are formed by
a delicate, structureless membrane, lined by flattened polyhedral cells. The
sebaceous glands secrete a peculiar oily matter (the sebum), by which the
12

170 HUMAN PHYSIOLOGY.

skin is lubricated and the hairs are softened ; it is quite abundant in the
region of the nose and forehead, which often presents a greasy, glistening
appearance ; it consists of water, mineral salts, fatty globules, and epithe-
lial cells.

The vernix caseosa, which frequently covers the surface of the fetus at
birth, consists of the residue of the sebaceous matter, containing epithelial
cells and fatty matters ; it seems to keep the skin soft and supple, and
guards it from the effects of the long- continued action of the amniotic water.

The sudoriparous glands excrete the sweat. They consist of a mass
or coil of a tubular gland duct, situated in the derma and in the subcutane-
ous tissue, average y1^ of an inch in diameter, and are surrounded by
a rich plexus of capillary blood-vessels. From this coil the duct passes
in a straight direction up through the skin to the epidermis, where it
makes a few spiral turns and opens obliquely upon the surface. The
sweat-glands consist of a delicate homogeneous membrane lined by epi-
thelial cells, whose function is to extract from the blood the elements
existing in the perspiration.

The glands are very abundant all over the cutaneous surface — as many at
3528 to the square inch, according to Erasmus Wilson.

The perspiration is an excrementitious fluid, clear, colorless, almost
odorless, slightly acid in reaction, with a specific gravity of 1003 to 1004.

The total quantity of perspiration excreted daily has been estimated at
about two pounds, though the amount varies with the nature of the food
and drink, exercise, external temperature, season, etc.

The elimination of the sweat is not intermittent, but continuous ; it
takes place so gradually that as fast as it is formed it passes off by
evaporation as insensible perspiration. Under exposure to great heat and
exercise the evaporation is not sufficiently rapid, and it appears as sensible
perspiration.

COMPOSITION OF SWEAT.

Water, 995-573

Urea, 0.043

Fatty matters, 0.014

Alkaline lactates, °-3l7

Alkaline sudorates, 1. 562

Inorganic salts, 2-49l

1,000.000
Urea is a constant ingredient.

Carbonic acid is also exhaled from the skin, the amount being about ^^
of that from the lungs.

CEREBROSPINAL AXIS. 171

Perspiration regulates the temperature and removes waste matters from
the blood ; it is so important that if elimination be prevented, death occurs
in a short time.

Influence of the Nervous System. — The secretion of sweat is regu-
lated by the nervous system. Here, as in the secreting glands, the fluid is
formed from material in the lymph-spaces surrounding the gland. Two
sets of nerves are concerned — viz. , vaso-motor, regulating the blood-supply ;
and secretory, stimulating the activities of the gland cells. Generally the
two conditions, increased blood flow and increased glandular action, coexist.
At times profuse clammy perspiration occurs, with diminished blood flow.

The dominating sweat-center is located in the medulla, though subordi-
nate centers are present in the cord. The secretory fibers reach the perspi-
ratory glands of the head and face through the cervical sympathetic ; of
the arms, through the thoracic sympathetic, ulnar, and radial nerves ; of the
leg, through the abdominal sympathetic and sciatic nerves.

The sweat-center is excited to action by mental emotions, increased tem-
perature of blood circulating in the medulla and cord, increased venosity
of blood, many drugs, rise of external temperature, exercise, etc.

CEREBRO-SPINAL AXIS.

The cerebro-spinal axis consists of the spinal cord, medulla oblongata,
pons Varolii, cerebellum, and cerebrum, exclusive of the spinal and
cranial nerves. It is contained within the cavities of the cranium and
spinal column, and surrounded by three membranes, — the dura mater,
arachnoid, and pia mater, — which protect it from injury and supply it with
blood-vessels.

MEMBRANES.

The dura mater, the outermost of the three, is a tough membrane,
composed of white fibrous tissue arranged in bundles, which interlace in
every direction. In the cranial cavity it lines the inner surface of the
bones, and is attached to the edge of the foramen magnum ; it sends proc-
esses inward, forming the falx cerebri, falx cerebelli, and tentorium cere-
belli, supporting and protecting parts of the brain. In the spinal canal it
loosely invests the cord, and is separated from the walls of the canal by
areolar tissue.

172 HUMAN PHYSIOLOGY.

The arachnoid, the middle membrane, is a delicate serous structure
which envelops the brain and cord, forming the visceral layer, and is then
reflected to the inner surface of the dura mater, forming the parietal layer.
Between the two layers there is a small quantity of fluid, which prevents
friction by lubricating the two surfaces.

The pia mater, the innermost of the three, composed of areolar
tissue and blood-vessels, covers the entire surface of the brain and cord,
to which it is closely adherent, dipping down between the convolutions
and fissures. It is exceedingly vascular, sending small blood-vessels some
distance into the brain and cord.

The cerebro- spinal fluid occupies the subarachnoid space and the
general ventricular cavities of the brain, which communicate by an opening
(the foramen of Magendie) in the pia mater, at the lower portion of the
fourth ventricle. This fluid is clear, transparent, alkaline, possesses a salty
taste, and has a low specific gravity ; it is composed largely of water, and
there are traces of albumin, glucose, and mineral salts. It is secreted by
the pia mater ; the quantity is estimated at from two to four fluidounces.

The function of the cerebro- spinal fluid is to protect the brain and cord
by preventing concussion from without ; as it is easily displaced into the
spinal canal, it prevents undue pressure and insufficiency of blood to the
brain.

SPINAL CORD.

The spinal cord varies from sixteen to eighteen inches in length ; it is
]/z of an inch in thickness, weighs \y2 ounces, and extends from the atlas
to the second lumbar vertebra, terminating in the filum terminate. It is
cylindric in shape, and presents an enlargement in the lower cervical and
lower dorsal regions, corresponding to the origin of those nerves which are
distributed to the upper and lower extremities. The cord is divided into
two lateral halves by the anterior and posterior fissures. It is composed of
both white or fibrous and gray or vesicular matter, the former occupying
the exterior of the cord, the latter the interior, where it is arranged in the
form of two crescents, one in each lateral half, united by the central mass,
the gray commissure ; the white matter being united in front by the white
commissure.

Structure of the Gray Matter. — The gray matter is arranged in the
form of two crescents, united by a commissural band, forming a figure

SPINAL CORD.

173

a

resembling the letter H. Each crescent presents an anterior and a posterior
horn. The center of the commissure presents a canal which extends from
the fourth ventricle downward to the filum terminale. The anterior horn
is short and broad and does not extend to the surface. The posterior horn
is narrow and elongated and extends quite to the surface. It is covered
and capped by the substantia gelatinosa. The gray matter consists pri-
marily of a framework of fine connective tissue, supporting blood-vessels,
lymphatics, medullated and non-medullated nerve-fibers, and groups of
nerve-cells.

The nerve-cells are arranged in groups, which extend for some distance
throughout the cord, forming
columns more or less continu-
ous. The first group is situ-
ated in the anterior horn, the
cells of which are large, multi-
polar, and connected with the
anterior roots of the spinal
nerves. The second group is
situated in the posterior horn,
the cells of which are spindle-
shaped, and from their relation
to the posterior roots are sup-
posed to be sensory in function.
The third group is situated in
the lateral aspect of the gray
matter, and is quite separate
and distinct, except in the lum-
bar and cervical enlargements,
where it blends with those of
the anterior horn. A fourth
group is situated at the inner

base of the posterior horn ; it begins about the seventh or eighth cervical
nerve and extends downward to the second or third lumbar, being most
prominent in the dorsal region. This column is known as Clark's vesicular
column.

Structure of the White Matter. — The white matter surrounding each
lateral half of the cord is made up of nerve-fibers, some of which are
continuations of the nerves which enter the cord, while others are derived
from different sources. It is subdivided into —

Fig. 21. — Scheme of the Conducting
Path in the Spinal Cord at the
Third Dorsal Nerve. — {Landois )

The black part is the gray matter, v. Ante-
rior, hw, posterior, root. a. Direct, and
g, g, crossed, pyramidal tracts. b. An-
terior column, ground bundle. c. Goll's
column, d. Postero-external column, e, e,
and f, f. Mixed lateral paths, h, h. Direct
cerebellar tracts.

174 HUMAN PHYSIOLOGY.

1. An anterior column, comprising that portion between the anterior roots
and the anterior fissure, which is again subdivided into two parts :

(a) An inner portion, bordering the anterior median fissure, the direct
pyramidal tract, or column of Tiirck ; it contains motor fibers which
do not decussate, and which extend as far down as the middle of
the dorsal region.

(b) An otder portion, surrounding the anterior cornua, known as the
a?iterior root zone, composed of short, longitudinal fibers which
serve to connect different segments of the spinal cord.

2. A lateral column, the portion between the anterior and posterior roots,
which is divisible into —

(a) The crossed pyramidal tract, occupying the posterior portion of
the lateral column, and containing all those fibers of the motor tract
which have decussated at the medulla oblongata ; it is composed of
longitudinally running fibers, which are connected with the multi-
polar nerve-cells of the anterior cornua.

(b) The direct cerebellar tract, situated upon the surface of the lat-
eral column, consisting of longitudinal fibers which terminate in the
cerebellum ; it first appears in the lumbar region, and increases in
thickness as it passes upward.

(c) The anterior tract, lying just posterior to the anterior cornua.

3. A posterior column, the portion included between the posterior roots and
the posterior fissure, also divisible into two portions :

(a) An inner portion, the poster o-internal column, or the column of
Goll, bordering the posterior median fissure, and

(b) An external portion, the postero-extemal column, the column of
Burdach, lying just behind the posterior roots.

The two portions of the posterior column are composed of long and short
commissural fibers, which connect different segments of the spinal cord.

SPINAL NERVES.

Origin. — The spinal nerves are thirty-one in number on each side of the
spinal cord, and arise by two roots, an anterior and a posterior, from the
anterior and posterior aspect of the cord, respectively. The. posterior roots
present, near their emergence from the cord, a small ganglionic enlarge-
ment. Outside of the spinal canal the two roots unite to form a main trunk,
which is ultimately distributed to the skin, muscles, and viscera.

For the functions of the roots of the spinal nerves, see page 77.

SPINAL CORD. 175

COURSE OF THE ANTERIOR AND POSTERIOR ROOTS.

The anterior roots pass through the anterior columns, horizontally, in
straight and distinct bundles, and enter the anterior cornua, where they
diverge in four directions :

1. Many become connected with the prolongations of the multipolar nerve-
cells.

2. Others leave the gray matter, pass through the anterior white commis-
sure, and enter the anterior columns of the opposite side.

3. A considerable number enter the lateral columns of the same side,
through which they pass to the medulla oblongata, where they decussate
and finally terminate in the corf -us striatum of the opposite side.

4. Others traverse the gray matter horizontally, and come into relation with
the cells of the intermediary lateral column.

The posterior roots enter the posterior horns of the gray matter —

1. Through the substantia gelatinosa.

2. Through the posterior columns.

Of the former some bend upward and downward, and become connected
with the anterior cornua ; others pass through the posterior commissure to
the opposite side ; of the latter, fibers pass into the gray matter to the poste-
rior vesicular columns, passing obliquely through the posterior white col-
umns upward and downward for some distance, and enter the gray matter
at different heights.

Decussation of Motor and Sensory Fibers. — The motor fibers,
which conduct volitional impulses from the brain outward to the anterior
cornua, arise in the motor centers of the cerebrum ; they then pass down-
ward through the corona radiata, the internal capsule, the inferior portions
of the crura cerebri, the pons Varolii, to the medulla oblongata, where the
motor tract of each side divides into two portions, viz. :

1. The larger, containing ninety-one to ninety-seven per cent, of the fibers,
which decussates at the lower border of the medulla and passes down in
the lateral column of the opposite side, and constitutes the crossed pyra-
midal tract.

2. The smaller, containing three to nine per cent, of the fibers, does not
decussate, but passes down the anterior column of the same side, and
constitutes the direct pyramidal tract, or the column of Turck.

Some of the motor fibers of these two tracts, after entering the anterior
cornua of the gray matter, become connected with the large multipolar

176 HUMAN PHYSIOLOGY.

nerve- cells, while others pass directly into the anterior roots. Through this
decussation each half of the brain governs the muscular movements of
the opposite side of the body.

The sensory fibers, which convey to the cord and brain the impression
made upon the periphery, pass into the cord through the posterior roots
of spinal nerves ; they then diverge and enter the gray matter at differen
levels, and at once decussate, passing to the opposite side of the gray
matter. The sensory tract passes upward, through the cord, the medulla,
pons Varolii, the superior portion of the cruri cerebri, the posterior third
of the internal capsule, to the sensory perceptive center, located in the
hippocampus major and uncinate convolution (Ferrier). Through this de-
cussation each half of the brain governs the sensibility of the opposite half
of the body.

Properties of the Spinal Cord. — Irritation applied directly to the
anterolateral white columns produces muscular movements, but no pain ;
they are, therefore, excitable, but insensible.

The surface of the posterior columns is not sensitive to direct irritation,
except near the origin of the posterior roots. The sensibility is due, how-
ever, not to its own proper fibers, but to the fibers of' the posterior root,
which traverse it.

Division of the anterolateral columns abolishes all power of voluntary
movement in the lower extremities.

Division of the posterior column impairs the power of muscular coordi-
nation, such as is witnessed in locomotor ataxia.

The gray matter is probably both insensible and inexcitable under the
influence of direct stimulation.

A transverse section of one lateral half of the cord produces —

1. On the same side, paralysis of voluntary motion, a relative or abso-
lute elevation of temperature, and an increased flow of blood in the
paralyzed parts ; hyperesthesia, for the sense of contact, tickling ,pain,
and temperature.

2. On the opposite side, complete anesthesia as regards contact, tickling,
and temperature in the parts corresponding to those which are paralyzed
in the opposite side, with a complete preservation of voluntary power
and of the muscular sense.

A vertical section through the middle of the gray matter results in the
loss of sensation on both sid^s of the body below the section, but no loss
of voluntary power.

SPINAL CORD.

177

Fig. 22. — Diagram showing the Course, through the Spinal Cord, of the
Motor and Sensory Nerve-fibers.

B and B' represent the right and left hemispheres of the brain, from which the motor
fibers take their origin, and in which the sensory fibers terminate. The viotor tract
from the right side, i, passes down through the crus, through the pons to the medulla
oblongata, where it divides into two portions : (i) The larger portion, ninety-seven
per cent., crosses over to the opposite side of the cord and passes down through the
lateral column. It gives off fibers at different levels, which pass into the gray matter
and become connected with the muscles, M, through the multipolar cells. (2) The
smaller portion, three per cent., does not cross over, but descends on the same side
of the cord in the anterior column and supplies the muscles, m. The same is true
for the motor tract for the left hemisphere.

The sensory fibers from the left side of the body enter the gray matter through the pos-
terior roots. They then cross over at once to the opposite side of the cord and ascend
to the hemisphere, partly in the gray matter, partly in the posterior column. The
same is true for the sensory nerves of the right side of the body.

178 HUMAN PHYSIOLOGY.

FUNCTIONS OF THE SPINAL CORD.

i. As an Independent Nerve Center.

The spinal cord, in virtue of its contained nerve-cells, is capable of
transforming afferent nerve impulses arriving through the afferent nerves
into efferent impulses, which are reflected outward through efferent nerves
to muscles, producing motion ; to glands, exciting secretion ; to blood-
vessels, changing their caliber. All such actions taking place independent
of either sensation or volition are termed reflex actions. The mechanism
involved in every reflex action consists of a sentient surface, an afferent
nerve, an emissive center, an efferent nerve, and a responsive organ,
muscle, gland, or blood-vessel (see p. 81).

The reflex excitability of the cord may be —

1. Increased by disease of the lateral columns, by the administration of
strychnin, and, in frogs, by a separation of cord from the brain, the
latter apparently exerting an inhibitory influence over the former and
depressing its reflex activity.

2. Inhibited by destructive lesion of the cord — e. g., locomotor ataxia,
atrophy of the anterior cornua — the administration of various drugs, and,
in the frog, by irritation of certain regions of the brain. When the
cerebrum alone is removed and the optic lobes are stimulated, the time
elapsing between the application of an irritant to a sensory surface and
the resulting movement will be considerably prolonged, the optic lobes
(Setschenow's center) apparently generating impulses which, descend-
ing the cord, retard its reflex movement.

All movements taking place through the nervous system" are of this reflex
character, and may be divided into excito-motor, sensori-motor, and ideo-
motor.

Classification of Reflex Movements (Kiiss). — They may be divided
into four groups, according to the route through which the centripetal and
centrifugal impulses pass :

1. Those normal reflex acts {e.g. , deglutition, coughing, sneezing, walking,
etc.) and pathologic reflex acts (e.g., tetanus, vomiting, epilepsy) which
take place both centripetally and centrifugally through spinal nerves.

2. Reflex acts which take place in a centripetal direction through a cere-
brospinal sensory nerve, and in a centrifugal direction through a sym-
pathetic motor nerve, usually a vaso-motor nerve — e. g., the normal reflex
acts, which give rise to most of the secretions, pallor of the skin and
blushing, certain movements of the iris, certain modifications in the beat

SPINAL CORD. 179

of the^heart ; the pathologic reflexes, which, on account of the difficulty
in explaining their production, are termed metastatic — e. g., ophthalmia,
coryza, orchitis, which depend on a reflex hyperemia ; amaurosis, par-
alysis, paraplegia, etc., due to a reflex anemia.

3. Reflex movements in which the centripetal impulse passes through a
sympathetic nerve, and the centrifugal through a cerebro-spinal nerve ;
most of these phenomena are pathologic — e. g., convulsions from intes-
tinal irritation produced by the presence of worms, eclampsia, hysteria,
etc.

4. Reflex actions in which both the centripetal and centrifugal impulses
pass through filaments of the sympathetic nervous system — e. g., those
obscure reflex actions which preside over the secretions of the intestinal
fluids, which unite the phenomena of the generative organs, the dilata-
tion of the pupils from intestinal irritation (worms), and many path-
ologic phenomena.

Laws of Reflex Action (Pfliiger).

1. Law of 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 oppo-
site side of the body.

3. Law of Intensity. — Reflex movements are usually more intense on the
side of the 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 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 act-
ing as a focus whence radiate all reflex movements.

Special Reflex Movements.

There are a number of reflex movements taking place through the spinal
cord, a study of which enables the physician to determine the condition of
its different segments. They may be divided into —

1. Skin or superficial, and

2. Tendon or deep reflexes.

180 HUMAN PHYSIOLOGY.

The skin reflexes are induced by irritation of the skin and mucous mem-
branes— 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 integ-
rity 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 slight 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 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, leading to arrest of their normal functions. The tendon
or deep reflexes are also of great value in diagnosing the condition of the
spinal segments. They are induced by a sharp blow upon a tendon. The
following are the principal forms :

1. Patellar reflex, or knee-jerk, consisting of a contraction of the extensor
muscles of the thigh when the ligamentum patella is struck between the
patella and tibia. This reflex is best observed when the legs are
freely hanging over the edge of a table. The patellar reflex is generally
present in health, being absent in only two per cent.; it is greatly exag-
gerated in lateral sclerosis and in descending degeneration of the cord ;
it is absent in locomotor ataxia and in atrophic lesions of the anterior
gray corn u x.

2. Ankle-jerk or Reflex. — If the extensor muscles of the leg be placed

SPINAL CORD. 181

upon the stretch and the tendo Achillis be sharply struck, a quick exten-
sion of the foot will take place.
3. Ankle-clonus. — This consists of a series of rhythmic reflex contractions
of the gastrocnemius muscle, varying in frequency from six to ten a
second. To elicit this reflex, pressure is made upon the sole so as sud-
denly and energetically to flex the foot at the ankle, thus putting the
tendo Achillis upon the stretch. The rhythmic movements thus pro-
duced continue as 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 zvrist reflex are also present in scle-
rosis of the lateral columns and in the late rigidity of hemiplegia.

Special Nerve Centers in Spinal Cord. — Throughout the spinal
cord there are a number of special nerve centers, capable of being excited
reflexly and of producing complex coordinated movements. Though for
the most part independent in action, they are subject to the controlling
influences of the medulla and brain.

1. Ciliospinal center, situated in the cord between the lower cervical and
the third dorsal vertebra. It is connected with the dilatation of the
pupil through fibers which emerge in this region and enter the cervical
sympathetic. Stimulation of the cord in this locality causes dilatation
of the pupil on the same side ; destruction of the cord is followed by
contraction of the pupil.

2. Genitospinal center, situated in the lower part of the cord. This is a
complex center, and comprises a series of subordinate centers for the
control of the muscular movements involved in the acts of defecation,
micturition, and ejaculation of semen, and of the movements of the
uterus during parturition, etc.

3. Vaso-?nolor centers, giving origin to both vaso-constrictor and vaso-
dilator fibers, which are distributed throughout the cord. Though acting
reflexly, they are under the dominating influence of the center in the
medulla.

4. Sweat-centers are also present in various parts of the cord.

2. As a Conductor.

The lateral columns, particularly the posterior portions, the "pyramidal
tracts," and the columns of Tiirck, are the channels through which pass
the voluntary motor impulses from the brain to the large multipolar nerve-
cells, in the anterior cornua of gray matter, and through them become

182 HUMAN PHYSIOLOGY.

connected with the anterior roots which transmit the motor stimuli to the
muscles.

The anterior columns, especially the portion surrounding the anterior
cornua, the " anterior radicular zones," are composed of short, longitudi-
nal commissural fibers, which serve to connect different segments of the
spinal cord, a condition required for the coordination of muscular move-
ments.

The posterior columns are composed of short and long commissural
fibers which connect different segments of the cord. They are insensible
to direct irritation, but aid in the coordination of muscular movements in
walking, standing, running, etc. Degeneration of the posterior columns
gives rise to the lack of muscular coordination observed in locomotor
ataxia.

The gray matter, and especially that portion immediately surrounding the
central canal, transmits the sensory nerve-fibers from the posterior roots up
to the brain. Decussation of the sensory fibers takes place throughout the
whole length of the gray matter.

The multipolar cells of the anterior cornua are connected with the
generation and transmission of motor impulses outward ; are centers for
reflex movements ; are the trophic centers for the motor nerves and
muscle-fibers to which they are distributed. The anterior roots give pas-
sage to the vaso-constrictor and vaso-dilator fibers, which exert an influ-
ence upon the caliber of the blood-vessels. Complete destruction of the
anterior horns is followed by paralysis of motion, degeneration of the an-
terior roots, atrophy of muscles and bones, and abolition of reflex move-
ments.

Paralysis from Injuries of the Spinal Cord.

Seat of Lesion. — If it be in the lower part of the sacral canal, there is
paralysis of the compressor urethra;, accelerator urinse, and sphincter ani
muscles ; no paralysis of the muscles of the leg.

At the Upper Limit of the Sacral Region. — Paralysis of the muscles of
the bladder, rectum, and anus ; loss of sensation and motion in the muscles
of the legs, except those supplied by the anterior crural and obturator —
viz., psoas iliacus, Sartorius, pectineus, adductores longus, magnus, and
brevis, obturator, vasti externus and internus, etc.

At the Upper Limit of \the Lumbar Region. — Sensation and motion
paralyzed in both legs ; loss of power over the rectum and bladder ; paraly-
sis of the muscular walls of the abdomen, interfering with expiratory
movements.

CRANIAL NERVES. 183

At the Lower Portion of the Cervical Region. — Paralysis of the legs,
etc., as in the foregoing ; in addition, paralysis of all the intercostal muscles
and consequent interference with respiratory movements ; paralysis of mus-
cles of the upper extremities, except those of the shoulders.

Above the Middle of the Cervical Region. — In addition to the preceding,
difficulty of deglutition and vocalization, contraction of the pupils, paraly-
sis of the diaphragm, scalene muscles, intercostals, and many of the acces-
sory respiratory muscles ; death resulting immediately from arrest of res-
piratory movements.

CRANIAL NERVES.

The cranial nerves come off from the base of the brain, pass through
the foramina in the walls of the cranium, and are distributed to the skin,
muscles, and organs of sense in the face and head.

According to the classification of Soemmering, there are twelve pairs of
nerves, enumerating them from before backward, as follows — viz. :

First pair, or olfactory. Seventh pair, or facial (portio dura).

Second pair, or optic. Eighth pair, or auditory ( portio mol-
Third pair, or motor oculi communis. lis) .

Fourth pair, or patheticus ( tro- Ninth pair, or glosso-pharyngeal.

chlearis). Tenth pair, or pneumogastric.

Fifth pair, or trifacial (trigeminus). Eleventh pair, or spinal accessory.

Sixth pair, or abducens. Twelfth pair, or hypoglossal.

The cranial nerves may also be classified physiologically, according to
their function, into three groups :

1 . Nerves of special sense.

2. Nerves of motion.

3. Nerves of general sensibility.

First Pair. Olfactory.
Apparent Origin. — From the inferior and internal portion of the ante-
rior lobes of the cerebrum by three roots — viz., an external white root,
which passes across the fissure of Sylvius to the middle lobe of the cere-
brum ; an internal white root, from the most posterior part of the anterior
lobe ; a. gray root, from the gray matter in the posterior and inner portion
of the inferior surface of the anterior lobe.

Deep Origin, — Not satisfactorily determined.

184 HUMAN PHYSIOLOGY.

Distribution. — The olfactory nerve, formed by the union of the three
roots, passes forward along the under surface of the anterior lobe to the
ethmoid bone, where it expands into the olfactory bulb. This bulb con-
tains ganglionic cells and is grayish in color and soft in consistency ; it gives
off from its under surface from fifteen to twenty nerve filaments, the true
olfactory nerves, which pass through the cribriform plate of the ethmoid
bone and are distributed to the Schneiderian mucous membrane. This
membrane extends from the cribriform plate of the ethmoid bone down-
ward, about one inch.

Properties. — The olfactory nerves give rise to neither motor nor sensory
phenomena when stimulated. They carry simply the special impressions
of odorous substances. Destruction or injury of the olfactory bulbs is
attended by a loss of the sense of smell.

Function. — Governs the sense of smell. Conducts the impressions
which give rise to odorous sensations.

Second Pair. Optic.

Apparent Origin. — From the anterior portion of the optic commissure.

Deep Origin. — The origins and connections of the optic tract are very
complex. The immediate origins are bands of fibers from the thalamus
opticus and anterior corpora quadrigemina. The corpora geniculata are
interposed ganglia. The ultimate roots are traced —

1. By a broad band of fibers — " the optic radiation of Gratiolet " — to the
psycho-optic centers in the occipital lobes.

2. To the gyrus hippocampi and sphenoid lobes.

3. Through the corpus callosum to the motor areas of the opposite cerebral
hemispheres.

4. To the frontal region by " Meynert's commissure."

5. To the spinal cord.

6. To the corpora geniculata, pulvinar, and anterior corpula geniculata by
ganglionic roots.

Distribution. — The two roots unite to form a flattened band, the optic
tract, which winds around the crus cerebri to decussate with the nerve of
the opposite side, forming the optic chiasm. The decussation of fibers is
not complete ; some of the fibers of the left optic tract going to the outer
half of the eye of the same side and to the inner half of (he eye^ of the
opposite side ; the same holds true for the right optic tract.

CRANIAL NERVES. 185

The optic nerves proper arise from the commissure, pass forward through
the optic foramina, and are finally distributed in the retina.

Properties. — They are insensible to ordinary impressions, and convey
only the special impressions of light. Division of one of the nerves is
attended by complete blindness in the eye of the corresponding side. '

Hemiopia and Hemianopsia. — Owing to the decussation of the fibers
in the optic chiasm, division of the optic tract produces loss of sight in the
outer half oi the eye of the same side, and in the inner half 'of the eye of
the opposite side, the blind part being separated from the normal part by a
vertical line. The term hemiopia is applied to the loss of function or
paralysis of the one half of the retina ; hemianopsia is applied to the
blindness in the field of vision. If, for example, the right optic tract be
divided, there will be hemiopia in the outer half of the right eye and inner
half of the left eye, thus causing left lateral hemianopsia, and as the two
halves are affected which correspond in normal vision, the condition is
known as homonymous hemianopsia. Lesion of the anterior part of the
optic chiasm causes blindness in the inner half of the two eyes.

Functions. — Governs the sense of sight. Receives and conveys to the
brain the luminous impressions which give rise to the sensation of sight.

The reflex movements of the iris are called forth by the optic nerve.
When an excess of light falls upon the retina, the impression is carried
back to the tubercula quadrigemina, where it is transformed into a motor
impulse, which then passes outward through the motor oculi nerve to the
contractile fibers of the iris and diminishes the size of the pupil. The
absence of light is followed by a dilatation of the pupil.

Third Pair. Motor Oculi Communis.

Apparent Origin. — From the inner surface of the crura cerebri.

Deep Origin. — By three sets of filaments coming from the oculomo-
torius nucleus, which lies under the aqueduct of Sylvius ; these three
groups of filaments are destined for the innervation of the muscles of the
eyeball, the sphincter pupillse, and the ciliary muscle. By filaments com-
ing from the lenticular nucleus, corpora quadrigemina, optic thalamus ;
these filaments converge to form a main trunk, which winds around the
eras cerebri, in front of the pons Varolii.

Distribution. — The nerve then passes forward, and enters the orbit
through the sphenoid fissure, where it divides into a superior branch dis-

l3

186 HUMAN PHYSIOLOGY.

tributed to the superior rectus and levator palpebrce muscles ; an inferior
branch, sending branches to the internal and inferior recti and the inferior
oblique muscles ; filaments also pass into the ciliary or ophthalmic ganglion ;
from this ganglion the ciliary nerves arise, which enter the eyeball and are
distributed to the circular fibers of the iris and the ciliary muscle. The
third nerve also receives filaments from the cavernous plexus of the sym-
pathetic and from the fifth nerve.

Properties. — Irritation of the root of the nerve produces contraction of
the pupil, internal strabismus, and muscular movements of the eye, but no
pain. Division of the nerve is followed by ptosis (falling of the upper eye-
lid) ; external strabismus, due to the unopposed action of the external
rectus muscle ; paralysis of the accommodation of the eye ; dilatation of the
pupil from paralysis of the circular fibers of the iris and ciliary muscle ; and
inability to rotate the eye, slight protrusion, and double vision. The images
are crossed ; that of the paralyzed eye is a little above that of the sound,
and its upper end inclined toward it.

Function. — Governs movements of the eyeball by animating all the
muscles except the external rectus and superior oblique, influences the
movements of the iris, elevates the upper lid, influences the accommodation
of the eye for distances. Can be called into action by ( I ) voluntary stimuli,
(2) by reflex action through irritation of the optic nerve.

Fourth Pair. Patheticus.

Apparent Origin. — From the superior peduncles of the cerebellum.

Deep Origin. — By fibers terminating in the corpora quadrigemina,

lenticular nucleus, valve of Vieussens, and substance of the cerebellar

peduncles ; some filaments pass over the median line and decussate with
fibers of the opposite side.

Distribution. — The nerve enters the orbital cavity through the sphenoid
fissure, and is distributed to the superior oblique muscle ; in its course it
receives filaments from the ophthalmic branch of the fifth pair and the
sympathetic.

Properties. — When the nerve is irritated, muscular movements are pro-
duced in the superior oblique muscle, and the pupil of the eye is turned
downzvard and outward. Division or paralysis lessens the movements and
rotation of the globe downward and outward. The diplopia consequent
upon this paralysis is homonymous, one image appearing above the other.

CRANIAL NERVES. 187

The image of the paralyzed eye is below, its upper end inclined toward
that of the sound eye.

Function. — Governs the movements of the eyeball produced by the
action of the superior oblique muscles.

Sixth Pair.* Abducens. Motor Oculi Externus.
Apparent Origin. — From the groove between the anterior pyramidal
body and the pons Varolii, where it arises by two roots.

Deep Origin. — From the gray matter of the medulla oblongata.

Distribution. — The nerve then passes into the orbit through the sphe-
noid fissure, and is distributed to the external rectus muscle. Receives
filaments from the cervical portion of the sympathetic, through the carotid
plexus, and spheno -palatine ganglion.

Properties. — When irritated, the external rectus muscle is thrown into
convulsive movements and the eyeball is turned outward. When divided
ox paralyzed, this muscle is paralyzed, motion of the eyeball outward past
the median line is impossible, and the homonymous diplopia increases as
the object is moved outward past this line. The images are upon the same
plane and parallel. Internal strabismus results because of the unopposed
action of the internal rectus.

Function. — To turn the eyeball outward.

Fifth Pair. Trifacial. Trigeminal.
Apparent Origin. — By two roots from the side of the pons Varolii.

Deep Origin. — The deep origin of the two roots is the upper part of
the floor and anterior wall of the fourth ventricle, by three bundles of Ali-
ments, one of which anastomoses with the auditory nerve ; another passes
to the lateral tract of the medulla ; while a third, grayish in color, goes to
the restiform bodies, and may be traced to the point of the calamus scrip-
torius.

Filaments of origin have been traced to the " trigeminal sensory nu-
cleus," located on a level with the point of exit of the nerve, and to the
posterior gray horns of the cord, as low down as the middle of the neck.

*The sixth nerve is considered in connection with the third and fourth nerves, since
they together constitute the motor apparatus by which the ocular muscles are excited to
action.

188 HUMAN PHYSIOLOGY.

Distribution. — The large root of the nerve passes obliquely upward and
forward to the ganglion of Gasser, which receives filaments of communi-
cation from the carotid plexus of the sympathetic. It then divides into
three branches :

1. Ophthalmic branch, which receives communicating filaments from the
sympathetic, and sends sensitive fibers to all the motor nerves of the
eyeball. It is distributed to the ciliary ganglion, to the lacrymal gland,
sac, and caruncle, to the conjunctiva, integument of the upper eyelid,
forehead, side of head and nose, anterior portion of the scalp, ciliary
muscle, and iris.

2. Superior maxillary branch, sends branches to the sphenopalatine
ganglion, integument of the temple and lower eyelid, side of the forehead
nose, cheek, upper lip, teeth of the upper jaw, and alveolar processes.

3. Inferior maxillary branch, which, after receiving in its course filaments
from the small root and from the facial, is distributed to the submaxil-
lary ganglion, the parotid and sublingual glands, external auditory
meatus, mucous membrane of the mouth, anterior two thirds of the
tongue (lingual branch), gums, arches of the palate, teeth of the lower
jaw, and integument of the lower part of the face, and to the muscles of
mastication.

The small root passes forward beneath the ganglion of Gasser, through
the foramen ovale, and joins the inferior maxillary division of the large
root, which then divides into an anterior and a posterior branch, the former
of which is distributed to the muscles of mastication — viz., temporal, mas-
seter, and internal and external pterygoid muscles.

Properties. — It is the most acutely sensitive nerve in the body, and
endows all the parts to which it is distributed with general sensibility.

Irritation of the large root, or of any of its branches, will give rise to
marked evidence of pain ; the various forms of neuralgia of the head and
face being occasioned by compression, disease, or exposure of some of its
terminal branches.

Division of the large root within the cranium is followed at once by a
complete abolition of all sensibility in the head and face, but is not attended
by any loss of motion. The integument, the mucous membranes, and the
eye may be lacerated, cut, or bruised, without the animal exhibiting any
evidence of pain. At the same time the lacrymal secretion is diminished,
the pupil becomes contracted, the eyeball is protruded, and the sensibility
of the tongue is abolished.

The reflex movements of deglutition are also somewhat impaired, the

CRANIAL NERVES. 189

impression of the food being unable to reach and excite the nerve center
in the medulla oblongata.

Galvanization of the small root produces movements of the muscles of
mastication ; section of the root causes paralysis of these muscles, and the
jaw is drawn to the opposite side by the action of the opposing muscles.

Influences of the Special Senses. — After division of the large root
within the cranium, a disturbance in the nutrition of the special senses
sooner or later manifests itself.

Sight. — In the course of twenty-four hours the eye becomes very vascular
and inflamed, the cornea becomes opaque and ulcerates, the humors are
discharged, and the eye is totally destroyed.

Smell. — The nasal mucous membrane swells up, becomes fungous, and
is liable to bleed on the slightest irritation. The mucous is increased in
amount, so as to obstruct the nasal passages ; the sense of smell is finally
abolished.

Hearing. — At times the hearing is impaired from disorders of nutrition
in the middle ear and external auditory meatus.

Alteration in the nutrition of the special senses is not marked if the sec-
tion is made posterior to the ganglion of Gasser and to the anastomos-
ing filaments of the sympathetic, which join the nerves at this point ;
but if the ganglion be divided, these effects are very noticeable, owing
to the section of the sympathetic filaments.

Function. — Gives sensibility to all parts of the head and face to which
it is distributed ; through the small root, endows the masticatory muscles
with motion ; through fibers from the sympathetic, governs the nutrition of
the special senses.

Seventh Pair. Portio Dura. Facial Nerve.

Apparent Origin. — From the groove between the olivary and restiform
bodies at the lateral portion of the medulla oblongata and below the margin
of the pons Varolii.

Deep Origin. — From a nucleus of large cells in the floor of the fourth
ventricle, below the nucleus of origin of the sixth pair, with which it is
connected. Some filaments are traceable to the lenticular nucleus of the
opposite side. Some of the fibers cross the median line and decussate. It
is intimately associated with the nerve of Wrisberg at its origin.

Distribution. — From its origin the facial nerve passes into the internal
auditory meatus, and then, in company with the nerve of Wrisberg, enters

190 HUMAN PHYSIOLOGY.

the aqueduct of Fallopius. The filaments of the nerve of Wrisberg are
supplied with a ganglion, of a reddish color, having nerve-cells. These
filaments unite with those of the root of the facial to form a common trunk,
which emerges at the stylomastoid foramen.

In the aqueduct the facial gives off the following branches — viz. :

1. Large petrosal nerve, which passes forward to the spheno-palatine, or
Meckel's ganglion, and through this to the levator palati and azygos
uvulae muscles, which receive motor influence from this source.

2. Small petrosal nerve, passing to the otic ganglion and thence to the
tensor tympani muscle, endowing it with motion.

3. Ty?npanic branch, giving motion to the stapedius muscle.

4. Chorda tympani nerve, which, after entering the posterior part of the
tympanic cavity, passes forward between the malleus and incus, through
the Glaserian fissure, and joins the lingual branch of the fifth nerve.
It is then distributed to the mucous membrane of the anterior two thirds
of the tongue and the submaxillary glands.

After emerging from the stylomastoid foramen, the facial nerve sends
branches to the muscles of the ear, the occipitofrontalis, the digastric, the
palatoglossi, and palatopharyngei ; after which it passes through the paro-
tid gland and divides into the temporofacial and cervicofacial branches,
which are distributed to the superficial muscles of the face— viz., occi-
pitofrontalis, corrugator supercilii, orbicularis palpebrarum, levator labii
superioris et alseque nasi, buccinator, levator anguli oris, orbicularis oris,
zygomatici, depressor anguli oris, platysma myoides, etc.

Properties. — Undoubtedly a motor nerve at its origin, but in its course
receives sensitive filaments from the fifth pair and the pneumogastric.

Irritation of the nerve, after its emergence from the stylomastoid fora-
men, produces convulsive movements in all the superficial muscles of the
face. Division of the nerve at this point causes paralysis of these muscles
on the side of the section, constituting facial paralysis, the phenomena
of which are a relaxed and immobile condition of the same side of the
face ; the eyelids remain open, from paralysis of the orbicularis palpe-
brarum ; the act of winking is abolished ; the angle of the mouth droops,
and saliva constantly drains away ; the face is drawn over to the second
side ; the face becomes distorted upon talking or laughing ; mastication
is interfered with, the food accumulating between the gums and cheek,
from paralysis of the buccinator muscle ; fluids escape from the mouth in
drinking ; articulation is impaired, the labial sounds being imperfectly
pronounced.

CRANIAL NERVES. 191

Properties of the Branches givin off in the Aqueduct oj Fullupius. — 'lhe
large petrosal, when irritated, throws the levator palati and azygos uvulae
muscles into contraction. Paralysis of this nerve, from deep-seated lesions,
produces a deviation of the uvula to the sound side, a drooping of the
palate, and an inability to elevate it.

The small petrosal influences hearing by animating the tensor tympani
muscles ; when paralyzed, there occurs partial deafness and an increased
sensibility to sonorous impressions.

The tympanitic branch animates the stapedius muscle and influences
audition.

The chorda tympani influences the circulation and the secretion of
saliva in the submaxillary glands, and governs the sense of taste in the
anterior two thirds of the tongue. Galvanization of the chorda tympani
dilates the blood-vessels, increases the quantity and rapidity of the stream
of blood, and increases the secretion of saliva. Division of the nerve is
followed by contraction of the vessels, an arrest of the secretion, and a
diminution of the sense of taste on the same side.

Function. — The facial is the nerve of expression, and coordinates the
muscles employed to delineate the various emotions, influences the sense
of taste, deglutition, movements of the uvula and soft palate, the tension of
the membrana tympani, and the secretions of the submaxillary and parotid
glands. Indirectly influences smell, hearing, and vision.

Eighth Pair. Portio Mollis. Auditory Nerve.

Apparent Origin. — From the upper and lateral portion of the medulla
oblongata, just below the margin of the pons Variolii.

Deep Origin. — By two roots from the floor of the fourth ventricle, each
root consisting of a number of gray filaments, some of which decussate in
the median line ; the external root has a gangliform enlargement containing
fusiform nerve-cells.

Distribution. — The two roots wind around the restiform bodies and
enter the internal auditory meatus, and divide into an anterior branch, dis-
tributed to the cochlea, and a posterior branch, distributed to the vestibule
and semicircular canals.

Properties. — They are soft in consistence, grayish in color, consisting
of axis-cylinders with a medullary sheath only ; they are not sensible to
ordinary impressions, but convey the impression of sound.

192 HUMAN PHYSIOLOGY.

Function. — Governs the sense of hearing. Receives and conducts to
the brain the impression of sound, which gives rise to the sensations of
hearing.

Ninth Pair. Glossopharyngeal.

Apparent Origin. — Partly from the medulla oblongata and the inferior
peduncles of the cerebellum.

Deep Origin. — From the lower portion of the gray substance in the
floor of the fourth venticle.

This nerve has two ganglia : The jugular ganglion includes only a por-
tion of the root-filaments ; the ganglion of Andersch includes all the
fibers of the trunk.

Distribution. — The trunk of the nerve passes downward and forward,
receiving near the ganglion of Andersch fibers from the facial and pneu-
mogastric nerves. It divides into two large branches, one of which is
distributed to the base of the tongue, the other to the pharynx. In its
course it sends filaments to the otic ganglion ; a tympanic branch which
gives sensibility to the mucous membrane of the fenestra rotunda, fenestra
ovalis, and Eustachian tube ; lingual branches to the base of the tongue ;
palatal branches to the soft palate, uvula, and tonsils ; pharyngeal branches
to the mucous membrane of the pharynx.

Properties. — Irritation of the roots at their origin calls forth evidences
of pain ; it is, therefore, a sensory nerve, but its sensibility is not so acute
as that of the trifacial. Irritation of the trunk after its exist from the
cranium produces contraction of the muscles of the palate and pharynx,
owing to the presence of anastomosing motor fibers.

Division of the nerve abolishes sensibility in the structures to which it is
distributed and impairs the sense of taste in the posterior third of the
tongue (see Sense of Taste).

Function. — Governs sensibility of pharynx, presides partly over the
sense of taste, and controls reflex movements of deglutition and vomiting.

Tenth Pair. Pneumogastric. Par Vagum.

Apparent Origin. — From the lateral side of the medulla oblongata,
just behind the olivary body.

Deep Origin. — In the gray nuclei in the lower half of the floor of the
fourth ventricle and in the substance of the restiform body. Some fila-
ments are traced along the restiform tract, toward the cerebellum, and

CRANIAL NERVES. 193

others to the median line of the floor of the fourth ventricle, where many
of them decussate.

This nerve has two ganglia : one in the jugular foramen, called the
ganglion of the root, and another outside of the cranial cavity on the
trunk, the ganglion of the trunk.

Distribution. — The filaments from the roots unite to form a single trunk,
which leaves the cavity of the cranium, through the jugular foramen, in
company with the spinal accessory and glossopharyngeal. It soon receives
an anastomotic branch from the spinal accessory, and afterward branches
from the facial, the hypoglossal, and the anterior branches of the two upper
cervical nerves.

As the nerve passes down the neck it sends off the following main
branches :

1. Pharyngeal newes, which assist in forming the pharyngeal plexus,
which is distributed to the mucous membrane and to the muscles of the
pharynx.

2. Superior laryngeal nerve, which enters the larynx through the thyro-
hyoid membrane, and is distributed to the mucous membrane lining the
interior of the larynx, and to the cricothyroid muscle and the inferior
constrictor of the pharynx. The " depressor nerve" found in the rabbit,
is formed by the union of two branches, one from the superior laryngeal,
the other from the main trunk ; it passes downward to be distributed to
the heart.

3. Inferior laryngeal, which sends its ultimate branches to all the intrinsic
muscles of the larynx except the cricothyroid, and to the inferior con-
strictor of the pharynx.

4. Cardiac branches given off from the nerve throughout its course, which
unite with the sympathetic fibers to form the cardiac plexus, to be dis-
tributed to the heart.

5. Pulmonary branches, which form a plexus of nerves, and are distributed
to the bronchi and their ultimate terminations, the lobules and air-cells.
From the right pneumogastric nerve branches are distributed to the mu-
cous membrane and muscular coats of the stomach and intestines, and to
the liver, spleen, kidneys, and suprarenal capsules.

Properties. — At its origin the pneumogastric nerve is sensory, as shown
by direct irritation or galvanization, though its sensibility is not very marked.
In its course it exhibits motor properties, from anastomosis with motor
nerves.

The pharyngeal branches assist in giving sensibility to the mucous

194 HUMAN PHYSIOLOGY.

membrane of the pharynx, and influence reflex phenomena of deglutition
through motor fibers which they contain, derived from the spinal accessory.

The superior laryngeal nerve endows the upper portion of the larynx
with sensibility ; protects it from the entrance of foreign bodies ; by con-
ducting impressions to the medulla, excites the reflex movements of deglu-
tition and respiration ; through the motor filaments it contains, produces
contraction of the cricothyroid muscle.

Division of the ' ' depressor nerve ' ' and galvanization of the central
end retard and even arrest the pulsations of the heart, and by depressing
the vaso-motor center, diminish the pressure of blood in the large vessels,
by causing dilatation of the intestinal vessels through the splanchnic
nerves.

The inferior laryngeal contains, for the most part, motor fibers from
the spinal accessory. When irritated, produces movement in the laryngeal
muscles. When divided, is followed by paralysis of these muscles, except
the cricothyroid, impairment of phonation, and an embarrassment of the
respiratory movements of the larynx, and, finally, death from suffocation.

The cardiac branches, through filaments derived from the spinal acces-
sory, exert a direct inhibitory action upon the heart. Division of the
pneumogastrics in the neck increases the frequency of the heart's action.
Galvanization of the peripheral ends diminishes the heart's pulsations, and,
if sufficiently powerful, paralyzes it in diastole.

The pulmonary branches give sensibility to the bronchial mucous
membrane and govern the movements of respiration. Division of both
pneumogastrics in the neck diminishes the frequency of the respiratory
movements, which may fall as low as four to six a minute ; death usually
occurs in from five to eight days. Feeble galvanization of the central ends
of the divided nerves accelerates respiration ; powerful galvanization
retards, and may even arrest, the respiratory movements.

The gastric branches give sensibility to the mucous coat, and through
sympathetic filaments, which join the pneumogastrics high up in the neck,
give motion to the muscular coat of the stomach. They influence the
secretion of gastric juice, aid the process of digestion and absorption from
the stomach.

The hepatic branches, probably through anastomosing sympathetic fila-
ments, influence the secretion of bile and the glycogenic function of the
liver ; division of the pneumogastrics in the neck produces congestion of
the liver, diminishes the density of the bile, and arrests the glycogenic
function ; galvanization of the central ends exaggerates the glycogenic
function and makes the animal diabetic.

CRANIAL NERVES. 195

The intestinal branches give sensibility and motion to the small intestines,
and when divided, purgative generally fail to produce evacuation.

Function. — A great sensitive nerve, which, through anastomotic fila-
ments from motor sources, influences deglutition, the action of the heart,
the circulatory and respiratory systems, voice, the secretions of the stomach,
intestines, and various glandular organs.

Eleventh Pair. Spinal Accessory.

Apparent Origin. — By two sets of filaments :

1 . A bulbar or medullary set, four or five in number, from the lateral or
motor tract of the lower half of the medulla oblongata, below the origin
of the pneumogastric.

2. A spinal set, from six to eight in number, from the lateral portion of the
spinal cord, between the anterior and posterior roots of the upper four
or five cervical nerves.

Deep Origin. — The medullary portion arises in a nucleus in the lower
half of the floor of the fourth ventricle, common to the pneumogastric and
glossopharyngeal nerves. The spinal portion has its origin in an elongated
nucleus lying along the external surface of the anterior cornua of the spinal
cord, extending down to the fifth cervical vertebra.

Distribution. — From this origin the fibers unite to form a main trunk,
which enters the cranial cavity through the foramen magnum, where it is
at times joined by fibers from the posterior roots of the two upper cervical
nerves, and sends filaments to the ganglion of the root of the pneumo-
gastric. After emerging from the cranial cavity through the jugular for-
amen, it sends a branch to the pneumogastric and receives others in return,
and also from the second, third, and fourth cervical nerves. It divides
into two branches :

1. An internal or anastomotic branch, made up of filaments coming prin-
cipally from the medulla oblongata ; it is distributed to the muscles of
the pharynx through the pharyngeal nerves coming from the pneumo-
gastric ; to all the muscles of the larynx, except the cricothyroid, through
the inferior laryngeal nerve ; to the heart, by filaments which reach it
through the pneumogastric nerve.

2. An external branch, which is distributed to the sterno-cleido-mastoid
and trapezius muscles ; these muscles also receive filaments from the
cervical nerves.

196 HUMAN PHYSIOLOGY.

Properties. — At its origin it is 5 purely motor nerve, but in its course it
exhibits some sensibility, which it received from anastomosing fibers.

Destruction of the medullary root, by tearing it from its attachment by
means of forceps, impairs the action of the muscles of deglutition and
destroys the power of producing vocal sounds by paralysis of the laryngeal
muscles, without, however, interfering with the respiratory movements of
the larynx, these being controlled by other motor nerves. The normal
rate of movement of the heart is also impaired by destruction of the medul-
lary root.

Irritation of the external branch throws the trapezius and sternomastoid
muscles into convulsive movements, though section of the nerve does not
produce complete paralysis, as they are also supplied with motor influence
from the cervical nerves. The sternomastoid and trapezius muscles per-
form movements antagonistic to those of respiration, fixing the head, neck,
and upper part of the thorax, and delaying the expiratory movement during
the acts of pushing, pulling, straining, etc. , and in the production of a pro-
longed vocal sound, as in singing. When the external branch alone is
divided, in animals, they experience shortness in breath during exercise,
from a want of coordination of the muscles of the limbs and respiration ;
and while they can make a vocal sound, it can not be prolonged.

Function. — Governs phonation by its influence upon the vocal move-
ments of the glottis ; influences the movements of deglutition, inhibits the
action of the heart, and controls certain respiratory movements associated
with sustained or prolonged muscular efforts and phonation.

Twelfth Pair. Hypoglossal or Sublingual.

Apparent Origin. — By two groups of filaments from the medulla ob-
longata, in the grooves between the olivary body and the anterior pyramid.

Deep Origin. — From the hypoglossal nucleus, situated deep in the
substance of the medulla, on a level with the lowest portion of the floor of
the fourth ventricle ; some decussating filaments have been traced to a
higher encephalic center.

Distribution. — The trunk formed by a union of the root filament passes
out of the cranial cavity through the anterior condyloid foramen, occa-
sionally receiving a filament from the lateral and posterior portion of the
medulla oblongata. After emerging from the cranium, it sends filaments
to the sympathetic and pneumogastric ; it anastomoses with the lingual
branch of the fifth pair, and receives and sends filaments to the upper cer-

MEDULLA OBLONGATA. 197

vical nerves. The nerve is finally distributed to the sternohyoid, sterno-
thyroid, omohyoid, thyrohyoid, styloglossi, hyoglossi, geniohyoid, genio-
hyoglossi, and the intrinsic muscles of the tongue.

Properties. — A purely motor nerve at its origin, but derives sensibility
outside the cranial cavity from anastomosis with the cervical, pneumogas-
tric, and fifth nerves.

Irritation of the nerve gives rise to convulsive movements of the tongue
and slight evidences of sensibility.

Division of the nerve abolishes all movements of the tongue and inter-
feres considerably with the act of deglutition.

When the hypoglossal nerve is involved in hemiplegia, the tip of the
tongue is directed to the paralyzed side when the tongue is protruded,
owing to the unopposed action of the geniohyoglossus on the sound side.

Articulation is considerably impaired in paralysis of this nerve, great
difficulty being experienced in the pronunciation of the consonantal sounds.

Mastication is performed with difficulty, from inability to retain the food
between the teeth until it is completely triturated.

Function. — Governs all the movements of the tongue and influences
the functions of mastication, deglutition, and articulaton.

MEDULLA OBLONGATA.

The medulla oblongata is the expanded portion of the upper part of
the spinal cord. It is pyramidal in form and measures 1*4 inches in length,
^ of an inch in breadth, y^ of an inch in thickness, and is divided into two
lateral halves by the anterior and posterior median fissures, which are con-
tinuous with those of the cord. Each half is again subdivided by minor
grooves into four columns — viz;, anterior pyramid, lateral and tract olivary
body, resliform body, and posterior pyramid.

1. The anterior pyramid is composed partly of fibers continuous with those
of the anterior column of the spinal cord, but mainly of fibers derived
from the lateral tract of the opposite side by decussation. The united
fibers then pass upward through the pons Varolii and crura cerebri, and
for the most part terminate in the corpus striatum and cerebrum.

2. The lateral tract is continuous with the lateral columns of the cord ; its
fibers in passing upward take three directions — viz., an external bundle
joins the restiform body, and passes into the cerebellum ; an internal

198

HUMAN PHYSIOLOGY.

bundle decussates at the median line and joins the opposite anterior pyra-
mid ; a middle bundle ascends beneath the olivary body, behind the
pons, to the cerebrum, as the fasciculus teres. The olivary body of each
side is an oval mass, situated between the anterior pyramid and restiform
body ; it is composed of white matter externally and gray matter inter-
nally, forming the corpus dentatum.

Fig. 23. — View of Cerebellum in Section, and of Fourth Ventricle, with
the Neighboring Parts. — {From Sappey.)

1. Median groove fourth ventricle, ending below in the calamus scriptorius , with the
longitudinal eminences formed by the fasciculi teretes, one on each side. 2. The
same groove, at the place where the white streaks of the auditory nerve emerge from
it to cross the floor of the ventricle. 3. Inferior 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 processus 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 Leveille.')

3. The restiform body, continuous with the posterior column of the cord,
also receives fibers from the lateral column. As the restiform bodies
pass upward they diverge and form a space (the fourth ventricle), the
floor of which is formed by gray matter, and then turn backward and
enter the cerebellum.

4. The posterior pyramid is a narrow white cord bordering the posterior
median fissure ; it is continued upward, in connection with the fasciculus
teres, to the cerebrum.

MEDULLA OBLONGATA. 199

The gray matter of the medulla is continuous with that of the cord.
It is arranged with much less regularity, becoming blended with the white
matter of the different columns, with the exception of the anterior. By the
separation of the posterior columns the transverse commissure is exposed,
forming part of the floor of the fourth ventricle ; special collections of gray
matter are found in the posterior portions of the medulla, connected with
the roots of origin of different cranial nerves.

Properties and Functions. — The medulla is excitable anteriorly and
sensitive posteriorly to direct irritation. It serves —

1. As a conductor of sensitive impressions upward from the cord, through
the gray matter to the cerebrum.

2. As a conductor of voluntary impulses from the brain to the spinal cord
and nerves, through its anterior pyramids.

3. As a conductor of coordinating impulses from the cerebellum, through
the restiform bodies to the spinal cord.

As an Independent Reflex Center. — The medulla oblongata contains
special collections of gray matter, constituting independent nerve centers
presiding over different functions, some of which are as follows — viz. :

1 . A center which controls the movements of mastication, through afferent
and efferent nerves. (See p. 96. )

2. A center reflecting impressions which influence the secretion of saliva.
(See p. 99.)

3. A center for sucking, mastication, and deglutition, whence are derived
motor stimuli exciting to action and coordinating the muscles of the
palate, pharynx, and esophagus, necessary for the swallowing of the
food.

The secretion of saliva is also controlled by a center in the medulla.

NERVOUS CIRCLE OF DEGLUTITION.
Second and Third Stages.
Palatal branch of the fifth pair.
Pharyngeal branches of the glossopharyngeal.
Superior laryngeal branches of the pneumogastric.
Esophageal branches of the pneumogastric.

Pharyngeal branches of the pneumogastric, derived from

the spinal accessory.
Hypoglossal and branches of the cervical plexus.
Inferior or recurrent laryngeal.

Motor filaments of the third division of the fifth pair.
Portio dura.

Excitor

or

centripetal

nerves.

Motor

or

centrifugal

nerves.

200 HUMAN PHYSIOLOGY.

4. A center which coordinates the muscles concerned in the act of vomit-
ing.

5. A speech center, coordinating the various muscles necessary for the ac-
complishment of articulation through the hypoglossal, facial nerves, and
the second division of the fifth pair.

6. A center for the harmonization of muscles concerned in expression, re-
flecting its impulses through the facial nerve.

7. A cardiac center, which exerts (i) an accelerating influence over the
heart's pulsations through accelerating nerve-fibers emerging from the
cervical portion of the cord, entering the inferior cervical ganglion, and
thence passing to the heart; (2) an inhibitory ox retarding influence
upon the action of the heart, through fibers of the spinal accessory nerve
running in the trunk of the pneumogastric. The cardio-inhibitory center
is in a state of tonic excitement and continuously sends impulses to the
heart which exert an inhibitory influence upon its action. It may be
stimulated directly by anemia as well as by venous hyperemia of the
blood-vessels of the medulla and increased venosity of the blood. It is
excited reflexly by the stimulation of the central end of the vagus, sciatic,
and splanchnic nerves.

8. A vaso-motor center, which, by alternately contracting and dilating the
blood-vessels through nerves distributed in their walls, regulates the
quantity of blood distributed to an organ or tissue, and thus influences
nutrition, secretion, and calorification. The vaso-motor center is situated
in the medulla oblongata and pons Varolii, between the corpora quadri-
gemina and the calamus scriptorius. The vaso-motor fibers having their
origin in this center descend through the interior of the cord, emerge
through the anterior roots of spinal nerves, enter the ganglia of the sym-
pathetic, and thence pass to the walls of the blood-vessels, and maintain
an arterial tonus; they may be divided into two classes — viz., vaso-
dilators (<?. g., chorda tympani) and vaso-constrictors {e.g., sympathetic
fibers).

Division of the cord at the lower border of the medulla is followed by a
dilatation of the entire vascular system and a marked fall of the blood pres-
sure. Galvanic stimulation of the divided surface of the cord is followed
by a contraction of the blood-vessels and a rise in the blood pressure.

The vaso-motor center is stimulated directly by the condition of the
blood in the medulla oblongata. When the blood is highly venous this
center becomes very active, the blood-vessels throughout the body are con-
tracted, and the blood current becomes swifter ; sudden anemia of the
medulla has a similar effect. The action of the vaso-motor center may be

IONS VAROLII. 201

accelerated, with attendent rise of blood pressure, by irritation of certain
afferent nerve-fibers. These are known as pressor fibers. On the other
hand, its action may be depressed by other fibers, with attendant fall of
blood pressure. These are known as depressor fibers.

9. A diabetic center, irritation of which causes an increase in the amount
of urine secreted and the appearance of a considerable quantity of sugar
in the urine.

10. Respiratory center, situated near the origin of the pneumogastric
nerves, presides over the movements of respiration and its modifications,
laughing, singing, sobbing, sneezing, etc. It may be excited rcjlexly by
the presence of carbonic acid in the lungs irritating the terminal pneu-
mogastric filaments ; or automatically, according to the character of the
blood circulating through it ; an excess of carbonic acid or a diminution
of oxygen increasing the number of respiratory movements ; a reverse
condition diminishing the respiratory movements.

11. A spasm center, stimulation of which gives rise to convulsive phe-
nomena, such as coughing, sneezing, etc.

12. A center for certain ocular functions, governing the^ closure of the eye-
lids and dilatation of the pupil.

13. A sweat center is also localized in the medulla.

NERVOUS CIRCLE OF RESPIRATION.

Entirely Reflex.

P • r Pulmonary branches of the pneumogastric.

I Superior laryngeal.
. • , J Trifacial, or fifth pair.

_ I Nerves of general sensibility.

I Sympathetic nerve.

yt r Phrenic, distributed to the diaphragm.

Intercostals, distributed to the intercostal muscles.
■ r 1 -! Facial nerve, or portio dura, to the facial muscles.

External branch of spinal accessory, to the trapezius and
I sterno-cleido-mastoid muscles.

nerves.

PONS VAROLII.

The pons Varolii unites the cerebrum above, the cerebellum behind,
and the medulla oblongata below. It consists of transverse and longi-
tudinal fibers, amidst which are irregularly scattered collections of gray or
vesicular nervous matter.
14

202 HUMAN PHYSIOLOGY.

The transverse fibers unite the two lateral halves of the cerebellum.
The longitudinal fibers are continuous —

1. With the anterior pyramids of the medulla oblongata, which, interlacing
with the deep layers of the transverse fibers, ascend to the crura cerebri,
forming their superficial or fasciculated portions.

2. With fibers derived from the olivary fasciculus, some of which pass to
the tubercula quadrigemina, while others, uniting with fibers from the
lateral and posterior columns of the medulla, ascend in the deep or
posterior portions of the crura cerebri.

Properties and Functions. — The superficial portion is insensible and
inexcitable to direct irritation ; the deeper portion appears to be excitable,
consisting of descending motor fibers ; the posterior portions are sensible,
but inexcitable to irritation.

Transmits motor impulses and sensory impressions from and to the
cerebrum.

The gray ganglionic matter consists of centers which convert impressions
into conscious sensations and originate motor impulses, these taking place
independent of any intellectual process ; they are the seat of instinctive
reflex acts, the centers which assist in the coordination of the automatic
movements of station and progression.

CRURA CEREBRI.

The crura cerebri are largely composed of the longitudinal fibers of the
pons (anterior pyramids, fasciculi teretes) ; after emerging from the pons
they increase in size, and become separated into two portions by a layer
of dark-gray matter, the locus niger.

The superfii ial portion, the crusta, composed of the anterior pyramids,
constitutes the motor tract, which terminates, for the most part, in the cor-
pus striatum, but to some extent, also, in the cerebrum ; the deep portion,
made up of the fasciculi teretes and posterior pyramids and accessory fibers
from the cerebellum, constitutes the sensory tract (the tegmentum), which
terminates in the optic thalamus and cerebrum.

Function. — The crura are conductors of motor impulses and sensory
impressions ; the gray matter, the locus niger, assists in the coordination of

CORPORA QUADRIGEMINA. 203

the complicated movements of the eyeball and iris, through the motor oculi
communis nerve. They also assist in the harmonization of general mus-
cular movements, section of one crus giving rise to peculiar movements of
rotation and somersaults forward and backward.

CORPORA QUADRIGEMINA.

The corpora quadrigemina are four small, rounded eminences, two
on *each side of the median line, situated immediately behind the third
ventricle, and beneath the posterior border of the corpus callosum.

The anterior tubercles are oblong from before backward, and larger than
the posterior, which are hemispheric in shape ; they are grayish in color,
but consist of white matter externally and gray matter internally.

Both the anterior and posterior tubercles are connected with the optic
thalami by commissural bands, named the anterior and posterior brachia,
respectively. They receive fibers from the olivary fasciculus and fibers
from the cerebellum, which press upward to enter the optic thalami.

The corpora geniculata are situated, one on the inner side and one on
the outer side of each optic tract, behind and beneath the optic thalamus,
and from their position are named the corpora geniculate interna and ex-
terna ; they give origin to fibers of the optic nerve.

Functions. — The corpora quadrigemina are centers associated with the
visual centers. Destruction of these tubercles is immediately followed by
a loss of the sense of sight ; moreover, their action in vision is crossed,
owing to the decussation of the optic tracts, so that if the tubercle of the
right side be destroyed by disease or extirpated, in a pigeon, the sight is
lost in the eye of the opposite side, and the iris loses its mobility.

The tubercula quadrigemina as nerve centers preside over the reflex
movements which cause a dilatation or contraction of the iris, irritation of
the tubercles causing contraction, destruction causing dilatation. Removal
of the tubercles on one side produces a temporary loss of power of the
opposite side of the body, and a tendency to move around an axis is mani-
fested, as after a section of one crus cerebri, which, however, may be due
to giddiness and loss of sight.

They also assist in the coordination of the complex movements of the
eye, and regulate the changes of the iris during the movements of accom-
modation for distance.

204 HtfMAN PHYSIOLOGY.

CORPORA STRIATA AND OPTIC THALAMI.

The corpora striata are two large ovoid collections of gray matter,
situated at the base of the cerebrum, the larger portions of which are
embedded in the white matter, the smaller portions projecting into the
anterior part of the lateral ventricle. Each striated body is divided, by a
narrow band of white matter, into two portions — viz. :

1. The caudate nucleus, the intraventricular portion, which is conic in
shape, having its apex directed backward, as a narrow, tail-like process.

2. The lenticular nucleus, embedded in the white matter, and for the most
part external to the ventricle. On the outer side of the lenticular nucleus
is found a narrow band of white matter, the external capsule ; and
between it and the convolutions of the island of Reil, a thin band of gray
matter, the claustrum.

The corpora striata are grayish in color, and when divided, present trans-
verse striations, from the intermingling of white fibers and gray cells.

The optic thalami are two oblong masses situated in the ventricles
posterior to the corpora striata, and resting upon the posterior portion of the
crura cerebri. The internal surface, projecting into the lateral ventricles, is
white, but the interior is grayish, from a commingling of both white fibers
and gray cells. Separating the lenticular nucleus from the caudate nucleus
and the optic thalamus is a band of white tissue, the internal capsule .

The internal capsule is a narrow, curved tract of white matter, and is, for
the most part, an expansion of the motor tract of the crura cerebri. It
consists of two segments — an anterior, situated between the caudate nucleus
and the anterior surface of the lenticular nucleus, and a posterior ', situated
between the optic thalamus and the posterior surface of the lenticular
nucleus. These two segments unite at an obtuse angle, which is directed
toward the median line. Pathologic observation has shown that the nerve-
fibers of the direct and crossed pyramidal tracts can be traced upward
through the anterior two thirds of the posterior segment into the centrum
ovale, where, for the most part, they are lost ; a portion, however, remain-
ing united, ascend higher and terminate in the paracentral lobule, the
superior extremity of the ascending frontal and parietal convolutions.
Those of the sensory trad can be traced upward, through the posterior
third, into the cerebrum, where they probably terminate in the hippocam-
pus major and uncinate convolution.

Functions. — The corpora striata are the centers in which terminate
some of the fibers of the superficial or ?notor tract of the crura cerebri ;

CEREBELLUM. 205

others pass upward through the internal capsule, to be distributed to the
cerebrum. It might be inferred, from their anatomic relations, that the cor-
pora striata are motor centers. Irritation by a weak galvanic current pro-
duces muscular movements of the opposite side of the body ; destructio?i of
their substance by a hemorrhage, as in apoplexy, is followed by a paralysis
of motion of the opposite side of the body, but there is no loss of sensation.
When the hemorrhagic destruction involves the fibers of the anterior two
thirds of the posterior segment of the internal capsule, and thus separates
them from their trophic centers in the cortical motor region, a descending
degeneration is established, which involves the direct pyramidal tract of
the same side and the crossed pyramidal tract of the opposite side.

Destruction of the posterior one third of the posterior segment of the
internal capsule is followed by a loss of sensation on the opposite side of
the body and a loss of the senses of smell and vision on the same side
(Charcot). The precise function of the corpora striata is unknown, but
they are in some way connected with motion.

The optic thalami receives the fibers of the tegmentum, the posterior
portion of the crura cerebri. They are insensible and inexcitable to direct
irritation. Removal of one optic thalamus, or destruction of its substance
by disease or hemorrhage, is followed by a loss of sensibility of the oppo-
site side of the body, but there is no loss of motion ; their precise function
is also unknown, but they are in some way connected with sensation. In
both cases their action is crossed.

CEREBELLUM.

The cerebellum is situated in the inferior fossae of the occipital bone,
beneath the posterior lobes of the cerebrum. It attains its maximum
weight, which is about five ounces, between the twenty-fifth and fortieth
years, the proportion between the cerebellum and cerebrum being as I to 8^.

It is composed of two lateral he?nispheres and a central elongated lobe,
the verjniform process ; the two hemispheres are connected with each other
by the fibers of the middle peduncle, forming the superficial portion of the
pons Varolii. The cerebellum is brought into connection with the medulla
oblongata and spinal cord through the prolongation of the restiform bodies ;
with the cerebrum, by fibers passing upward beneath the corpora quadri-
gemina and the optic thalami, and then forming part of the diverging
cerebral fibers.

206 HUMAN PHYSIOLOGY.

Structure. — It is composed of both white and gray matter, the former
being internal, the latter external, and is convoluted, for economy of space.

The white matter consists of a central stem, the interior of which is a
dentated capsule of gray matter, the corpus dentatuni. From the external
surface of the stem of white matter processes are given off, forming the
lamina, which are covered with gray matter.

The gray ??iatter is convoluted and covers externally the laminated pro-
cesses ; a vertical section through the gray matter reveals the following
<t uetures :

1. A delicate connective-tissue layer, just beneath the pia mater, containing
rounded corpuscles, and with branching fibers passing toward the ex-
ternal surface.

2. The cells of Purkinje, forming a layer of large, nucleated, branched
nerve-cells sending off processes to the external layer.

3. A granular layer of small but numerous corpuscles.

4. A nerve-fiber layer, formed by a portion of the white matter.

Properties and Functions. — Irritation of the cerebellum is not fol-
lowed by any evidences either of pain or convulsive movements ; it is,
therefore, insensible and inexcitable.

Coordination of Movements. — Removal of the superficial portions of
the cerebellum in pigeons produces feebleness and want of harmony in the
muscular movements ; as successive slices are removed, the movements
become more irregular, and the pigeon becomes restless ; when the last
portions are removed, all power of flying, walking, standing, etc., is en-
tirely gone, and the equilibrium can not be maintained, the power of coor-
dinating muscular movements being wholly lost. The same results have
been obtained by operating on all classes of animals.

The following symptoms were noticed by Wagner, after removing the
whole or a large part of the cerebellum :

1. A tendency on the part of the animal to throw itself on one side, and to
extend the legs as far as possible.

2. Torsion of the head on the neck.

3. Trembling of the muscles of the body, which was general.

4. Vomiting and occasional liquid evacuations.

Forced Movements. — Division of one crus cerebelli causes the animal
to fall on one side and roll rapidly on its longitudinal axis. According to
Schiff, if the peduncle be divided from behind, the animal falls on the same
side as the injury ; if the section be made in front, the animal turns to the
opposite side.

CEREBRUM. 207

Disease of the cerebellum partially corroborates the result of experi-
ments ; in many cases symptoms of unsteadiness of gait, from a want of
coordination, have been noticed.

Comparative anatomy reveals a remarkable correspondence between the
development of the cerebellum and the increase in complexity of muscular
actions. It attains a much greater development, relatively to the rest of the
brain, in those animals whose movements are very complex and varied in
character, such as the kangaroo, shark, and swallow.

The cerebellum may possibly exert some influence over the sexual func-
tions, but physiologic and pathologic facts are opposed to the idea of its
being the seat of the sexual instinct. It appears to be simply a center
for the coordination and equilibration of muscular movements.

CEREBRUM.

The cerebrum is the largest portion of the encephalic mass, constituting
about four fifths of its weight ; the average weight of the adult male brain
is from forty-eight to fifty ounces, or about three pounds, while that of the
adult female is about five ounces less. After the age of forty the weight
of the cerebrum gradually diminishes at the rate of one ounce every ten
years. In idiots the brain weight is often below the normal, at times not
amounting to more than twenty ounces.

The blood-supply to the cerebrum is unusually large, considering its
comparative bulk, nearly one fifth of the entire volume of blood in the body
being distributed to it by the carotid and vertebral arteries. These vessels
anastomose so freely, and are so arranged within the cavity of the cranium,
that an obstruction in one vessel will not interfere with the regular supply of
blood to the parts to which its branches are distributed. A diminished
amount, or complete cessation, of the supply of blood is at once followed
by a suspension of its functional activity.

The cerebrum is connected with the pons Varolii and medulla oblongata
through the crura cerebri, and with the cerebellum through the superior
peduncles. It is divided into two lateral halves, or hemispheres, by the
longitudinal fissure running from before backward in the median line ; each
hemisphere is composed of both white and gray matter, the former being
internal, the latter external ; it covers the surfaces of the hemisphere which
are infolded, forming convolutions, for economy of space.

208 HUMAN PHYSIOLOGY.

Fissures.

i. The fissure of Sylvius is one of the most important; it is the first to
appear in the development of the fetal brain, being visible at about the
third month ; in the adult it is quite deep and well marked, running from
the under surface of the brain upward, outward, and backward, and
forms a boundary between the frontal and temporosphenoid lobes.

2. The fissure of Rolando is second in importance, and runs from a point
on the convexity near the median line transversely outward and down-
ward toward the fissure of Sylvius, but does not enter it. It separates
the frontal from the parietal lobe.

3. The parietal 'fissure, arising a short distance hehind the fissure of Ro-
lando, upon the convexity of the hemisphere, runs downward and back-
ward to its posterior extremity.

4. The parietooccipital fissure separates the occipital from the parietal
lobe. Beginning upon the outer surface of the cerebrum, it is continued
on the mesial aspect downward and forward until it terminates in the
calcarine fissure.

5. The callosomarginal fissure lies upon the mesial surface, where it runs
parallel with the corpus callosum.

Secondary fissures of importance are found in different lobes of the
cerebrum, separating the various convolutions. In the anterior lobe are
found the precentral, superior frontal, and inferior frontal fissures ; in
the temporosphenoid lobes are found the first and second temporo-
sphenoid fissure ; in the occipital lobe, the calcarine and hippocampal
fissures.

Convolutions. Frontal Lobe.

The ascending frontal convolution, situated in front of the fissure of
Rolando, runs downward- and forward ; it is continuous above with the
anterior frontal, and below with the inferior frontal, convolution.

The superior frontal convolution is bounded internally by the longitu-
dinal fissure, and externally by the superior frontal fissure ; it is connected
with the superior end of the frontal convolution, and runs downward and
forward to the anterior extremity of the frontal lobe, where it turns back-
ward, and rests upon the orbital plate of the frontal bone.

The middle frontal convolution, the largest of the three, runs from be-
hind forward, along the sides of the lobe, to its anterior part ; it is
bounded above by the superior and below by the inferior frontal fissures.

The inferior frontal convolution winds around the ascending branch of
the fissure of Sylvius, in the anterior and inferior portion of the cerebrum.

CEREBRUM.

209

Parietal Lobe. — The ascending parietal convolution is situated just
behind the fissure of Rolando, running downward and forward ; above, it

Fig. 24. — Diagram showing Fissures and Convolutions of the Left Side
of the Human Brain. — (Lanctois' "Physiology.")

F. Frontal. P. Parietal. O. Occipital. T. Temporosphenoid lobe. S. Fissure
of Sylvius. S'. Hirizontal. S". Ascending ramus of S. c. Sulcus centralis, or
fissure of Rolando. A. Ascending frontal, and B. Ascending parietal convolutions.
Fj. Superior, F2. Middle, and F3. Inferior frontal convolutions. fx. Superior, f„.
Inferior frontal fissures. f3. Sulcus prsecentralis. Px. Superior paretial lobule.
P2. Inferior parietal lobule, consisting of P9. Supramarginal gyrus, and P2'. Angu-
lar gyrus, ip. Sulcus interpari' talN. cm. Terminat on of callosomarginal fissure.
O,. First, (32. Second, 03. Third occipital convolutions, po. Parieto-occipi'al
fissure, o. Transverse occipital fissure. o2. Inferior longitudinal occipital fissure.
T1. First, T2. Second, T3. Temporospheno d, convolutions. tx, tx. First, t2-
Second, temporosphenoid fissures.

becomes continuous with the upper parietal convolution, and below, winds
around to be united with the ascending frontal.

210 HUMAN PHYSIOLOGY.

The upper parietal convolution is situated between the parietal and
longitudinal fissures.

The supramarginal convolution winds around the superior extremity of
the fissure of Sylvius.

The angular convolution, a continuation of the preceding, follows the
parietal fissure to its posterior extremity, and then makes a sharp angle
downward and forward.

Temporosphenoid Lobe. — Contains three well-marked convolutions,
the superior, middle and inferior, separated by well-defined fissures, and
continuous posteriorly with the convolutions of the parietal lobe.

The occipital lobe lies behind the parieto-occipital fissure, and contains
the superior, middle and inferior convolutions, not well marked.

The central lobe, or island of Reil, situated at the bifurcation of the
fissure of Sylvius, is a triangular- shaped cluster of six convolutions, the
gyri operti, which are connected with those of the frontal, parietal, and
temporosphenoid lobes.

Upon the inner or mesial aspect of the hemisphere are found (Fig. 25) —

1. The paracentral lobule, lying in the region of the upper extremity of
the fissure of Rolando ; it contains the large giant cells of Betz. Injury
to this convolution is followed by degeneration of the motor tract.

2. The gyrus fornicatus, lying below the callosomarginal fissure. Run-
ning parallel with the corpus callosum, it terminates at its posterior border
in the hippocampal gyrus.

3. The gyrus hippocampus (H) is formed by the union of the preceding
convolution with the occipitotemporal. It runs forward and terminates
in a hooked extremity — uncus.

4. The quadrate lobule, or precuneus, lies between the upper extremity of
the callosomarginal fissure and the parieto-occipital.

5. The cuneus lies posteriorly to the quadrate lobule. It is a wedge-
shaped mass inclosed by the calcarine and parieto-occipital fissures.

Structure. — The gray matter of the cerebrum, about y$ of an inch
thick, is composed of five layers of nerve-cells :

1. A superficial layer, containing a few small multipolar ganglion cells.

2. Small ganglion cells, pyramidal in shape.

3. A layer of large pyramidal ganglion cells with processes running off
superiorly and laterally.

4. The granular formation containing nerve-cells.

5. Spindle-shaped and branching nerve-cells of a moderate size.

CEREBRUM.

211

The white matter consists of three distinct sets of fibers.
The diverging ox peduncular fibers are mainly derived from the columns
of the cord and medulla oblongata ; passing upward through the crura
cerebri, they receive accessory fibers from the olivary fasciculus, corpora
quadrigemina, and cerebellum. Some of the fibers terminate in the optic

Fig. 25.

-Diagram showing Fissures and Convolutions on Mesial Aspect of
the Right Hemisphere.

Median aspect of the right hemisphere. CC. Corpus callosum divided longitudinallyi
Gf. Gyrus fornicatus. H. Gyrus hippocampi, h. Sulcus hippocampi. U. Unc,-
nate gyrus, cm. Callosomarginal fissure. Fx. First frontal convolution, c. Ter-
minal portion of fissure of Rolando. A. Ascending frontal, B. Ascending parietal,
convolution and paracentral lobule. P/. Prsecuneus or quadrate lobule. Oz.
Cuneus. Po. Parieto-occipital fissure, o. Transverse occipital fissure, oc. Cal-
carine fissure, oc' . Superior, oc" . Inferior, rami of the same. D. Gyrus descen-
dens. T4. Gyrus occipitotemporalis lateralis (lobulus fusiformis). T5. Gyrus
occipitotemporalis medialis (lobulus lingualis).

thalami and corpora striata, while others radiate into the anterior, mid-
dle, and posterior lobes of the cerebrum.

2. The transverse commissural fibers connect the two hemispheres, through
the corpus callosum and anterior and posterior commissures.

3. The longitudinal commissural fibers connect different parts of the same
hemisphere.

Functions. — The cerebral hemispheres are the centers of the nervous
system through which are manifested all the phenomena of the mind ; they

212

HUMAN PHYSIOLOGY.

are the centers in which impressions are registered and reproduced subse-
quently as ideas ; they are the seat of intelligence, reason, and will.

Fig. 26. — Side View of the Brain of Man, with the Areas of the Cerebral
Convolutions according to Ferrier.

The figures are constructed by marking on the brain of man, in their respective
situations , the areas of the brain of the monkey as determined by experiment, and
the description of the effects of stimu'ating the various areas refers to the brain
of the monkey.

1. Advance of the opposite hind limb, as in walking. 2, 3, 4. Complex movements of
the opposite leg and arm, and of the trunk, as in swimming, a, b, c, d. Individual
and combined movements of the fingers and wrists of the opposite hand. Prehensile
movements. 5. Extension forward of the opposite arm and hand. 6. Supination
and flexion of the opposite forearm. 7. Retraction and elevation of the opposite
angle of the mouth, by means of the zygomatic muscles. 8. Elevation of the alae
nasi and upper lip, with depression of the lower lip on the opposite side. 9, 10.
Opening of the mouth, with (9) protrusion and (10) retraction of the tongue; region
of aphasia, bilateral action. 11. Retraction of the opposite angle of the mouth, the
head turned slightly to one side. 12. The eyes open widely, the pupils dilate, and
the head and eyes turn toward the opposite side. 13, 13'. The eyes moved toward
the opposite side with an upward (13) or downward (13') deviation. The pupils are
generally contracted. 14. PricKing of the opposite ear, the head and eyes turn to
the opposite side, and the pupils dilate widely.

CEREBRUM. 213

However important a center the cerebrum may be for the exhibition of
this highest form of nervous action, it is not directly essential for the con-
tinuance of life, for it does not exert any control over those automatic reflex
acts, such as respiration, circulation, etc., which regulate the functions of
organic life.

From the study of comparative anatomy, pathology, vivisection, etc.,
evidence has been obtained which throws some light upon the physiology
of the cerebral hemispheres.

1. Comparative anatomy shows 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, the 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 anthropoids. The most culti-
vated races of men have the greatest cranial capacity ; that of the edu-
cated European being about Il6 cubic inches, that of the Australian
being about 60 cubic inches, a difference of 56 cubic inches. Men dis-
tinguished for great mental power usually have large and well-developed
brains ; that of Cuvier weighed 64 ounces ; that of Abercrombie, 63
ounces ; the average being about 48 to 50 ounces. Not only the size, but,
above all, the texture, of the brain must be taken into consideration.

2. Pathology. — Any severe injury or disease disorganizing the hemispheres
is at once attended by a disturbance or an entire suspension of mental
activity. A blow on the head, producing concussion, or undue pressure
from cerebral hemorrhage, destroys consciousness ; physical and chemic
alterations in the gray matter have been shown to coexist with insanity,
and with loss of memory, speech, etc. Congenital defects of organization
from imperfect development are usually accompanied by a corresponding
deficiency of intellectual power and of the higher instincts. Under these
circumstances no great advance in mental development can be possible,
and the intelligence remains of a low grade. In congenital idiocy not
only is the brain of small size, but it is wanting in proper chemic com-
position, phosphorus, a characteristic ingredient of the nervous tissue,
being largely diminished in amount.

3. Experimentation upon the lower animals by removing the cerebral
hemispheres is attended by results similar to those observed in disease
and injury. Removal of the cerebrum in pigeons produces complete
abolition of intelligence, and destroys the capability of performing spon-
taneous movements. The pigeon remains in a condition of profound
stupor, which is not accompanied, however, by a loss of sensation or of

214 HUMAN PHYSIOLOGY.

the power of producing reflex or instinctive movements. The pigeon
can be temporarily aroused by pinching the feet, loud noises, lights placed
before the eyes, etc., but soon relapses into a state of quietude, being
unable to remember impressions and connect them with any train of
ideas, the faculties of memory, reason, and judgment being completely
abolished.

CEREBRAL LOCALIZATION OF FUNCTION.

From experiments made upon animals, and from the results of clinical and
post-mortem observations upon men, it has been shown that the phenomena
of organic and psychic life are presided over by anatomically localized
centers in the brain. A knowledge of the position of these centers becomes
of the highest importance in localizing the seat of lesions, thrombi, hemor-
rhages, new growths, etc. , which show themselves in paralyses, epilepsies,
etc. It has not been possible to thus localize all functions, and to many
parts of the brain no special use can be assigned. The following are the
centers most definitely mapped out and that are of paramount importance.

Motor Centers. — These are in the cortical gray matter, and are ar-
ranged along either side of the fissure of Rolando. This area is known
as the motor area or motor zone, stimulation of which is followed by con-
vulsive movements of the muscles of the opposite side of the body, while
destruction of the gray matter of this area is followed by permanent paral-
ysis of the muscles of the opposite side. From experiments made upon
monkeys, Ferrier has mapped out a number of motor centers which he has
transferred to corresponding localities on the human brain. (See Fig. 26. )
The descriptive text of the illustration renders his results intelligible.
Pathologic studies have largely confirmed his deductions. In a general
way it maybe said that the upper third of the ascending frontal and parietal
convolutions about this fissure preside over the movements of the leg of
the opposite side of the body ; the middle third controls the movements of
the arm ; the upper part of the inferior third is the facial area. The lowest
part of the inferior third governs the motility of the lips and tongue, and
this space, with the posterior extremity of the third frontal convolution,
constitutes the speech center.

The experiments of Horsley and Schafer have enabled them to furnish
a new diagrammatic representation of the motor area and more accurately

CEREBRAL LOCALIZATION OF FUNCTION.

215

to 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 deter-
mined by these observers, will be readily understood by an examination of
Figures 27 and 28.

Fig. 27. — Diagram of the Motor Areas on the Outer Surface of a Monkey's
Brain. — (Horsley and Schafer.)

Fig. 28. — Diagram of the Motor Areas on the Marginal Convolution of a
Monkey's Brain. — {Horsley and Schafer.)

For diagnostic purposes the motor areas for the face and limbs have been

subdivided as follows :

I. The /ace 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 centers governing the movements of the muscles of the

216 HUMAN PHYSIOLOGY.

opposite angle of the mouth and of the lower face. The anterior portion
of the lower two thirds controls the movements of the vocal cords, and
may be regarded as a laryngeal center ; the posterior portion governs the
opening and shutting of the mouth and the protrusion and retraction of
the tongue.

2. The upper limb area may be subdivided as follows : The upper part
controls the movements of the shoulder ; posteriorly and below this point
are centers for the elbow ; below and anteriorly, centers for the wrist
and finger movements, while lowest and posteriorly, centers governing the
thumb.

3. The leg area may be subdivided as follows : The anterior part, both on
the mesial and lateral surfaces, contains centers governing the hip and
thigh movements ; in the posterior part are centers for the movements of
the leg and toes. The center for the great toe has been located in the
paracentral lobule.

4. The trunk area, situated largely on the mesial surface, contains ante-
riorly centers governing the rotation and arching of the spine, while
posteriorly are found centers governing movements of the tail and pelvis.

5. The head area, or area for visual direction, contains centers excitation
of which causes " opening of the eyes, dilatation of the pupils, and turn-
ing of the head to the opposite side, with conjugate deviation of the eyes
to that side."

The centers of origin of the nerves for the ocular muscles lie in the gray
matter of the aqueduct of Sylvius. Destruction of the gray matter at these
points is followed by paralysis of the muscles of the opposite side of the
body, and morbid growths, hemorrhages, or thrombi of the vessels of the
part result in abnormal stimulation or in interference with the functions cor-
responding to the nature and extent of the lesion. Cerebral or Jacksonian
epilepsy is a result of local cortical disease.

Center for Speech. — Pathologic investigations have demonstrated that
the left third frontal convolution is of essential importance for speech.
Adjoining this convolution are the centers controlling the motility of the
lips, tongue, etc. In the majority of cases the speech centers are on the
left side of the brain, though in exceptional cases they are on the right
side, especially in left-handed persons. In deaf mutes this convolution is
very imperfectly developed, while in monkeys it is quite rudimentary.

Lesions of the third frontal convolution on the left side, if the patient be
right-handed, produce the various forms of aphasia^ or the partial or com-
plete loss of the power of articulate speech.

CEREBRAL LOCALIZATION OF FUNCTION.

217

Aphasia is of many degrees and kinds. In ataxic aphasia the patient is
unable to communicate his thoughts by words, there being an inability to
execute the movements of the mouth, etc., necessary for speech. In
agraphic aphasia there is an inability to execute the movements necessary
for writing, though the mental processes are retained. In the ataxic form
the lesion is in the third
frontal convolution, and in
the agraphic form it is in the
arm center.

In amnesic aphasia there
is a loss of the memory of
words, the purest examples
of which consist of the affec-
tions known as word-deaf-
ness and word-blindness. In
word -deafness the patient can
not understand vocal speech,
though he is capable of hear-
ing other sounds. This con-
dition is associated with le-
sion of the first temporal con-
volution. In ivord-blindness
the patient can not name a
letter or a word when printed
or written, though he can see
all other objects. This con-
dition is associated with im-
pairment of the visual cen-
ters.

Figure 29 will illustrate
the conditions in the various
forms of aphasia. Impres-
sions are constantiy passing

from eye and ear to the visual and auditory centers and are there being regis-
tered. Commissural fibers connect these centers with the arm and speech
centers, which in turn are connected by efferent fibers with the muscles of
the hand and of the vocal apparatus. Muscular movements of the eyes, hand,
and mouth are also registered by means of the afferent fibers, s, s7, s".

Sensory Centers. — These are the centers in which the sensory impres-
15

Fig. 29.

218 HUMAN PHYSIOLOGY.

sions are coordinated, and in which they probably become parts of our
consciousness. The most important are :

The visual center, located in the occipital lobe and especially in the
cuneus. Unilateral destruction of this area results in hemianopsia, or
blindness of the corresponding halves of the two retinae. Destruction of
both occipital lobes in man results in total blindness. Stimulation or irri-
tation of the visual center causes photopsia, or hallucinations of sight, in
corresponding halves of the retinae. There have been instances of injury
of these parts when sensations of color were abolished with preservation of
those of space and light, thus showing a special localization of the color
center. Recent experiments show that the centers of the two hemispheres
are united, as ocular fatigue of an unused eye was found to be proportional
to the fatigue of the exercised one.

The auditory centers are located in the temporosphenoid lobes. Word-
deafness is associated with softening of these parts, and their complete
removal results in deafness.

The gustatory and olfactojy centers are located in the uncinate gyrus, on
the inner side of the temporosphenoid lobes. There does not seem to be
any differentiation, up to this time, of these two centers.

The center for tactile impressions was located by Ferrier in the hippo-
campal region. Horsley and Schafer found that destructive lesions of the
gyrus fornicatus were followed by hemianesthesia of the opposite side of the
body, which was more or less marked and persistent. These observers
conclude that the limbic lobe "is largely, if not exclusively, concerned in
the appreciation of sensations, painful and tactile."

The superior and middle frontal convolutions appear to be the seats of
the reason, intelligence, and will. Destruction of these parts is followed
by proportional hebetude, without any impairment of sensation or motion.

SYMPATHETIC NERVOUS SYSTEM.

The sympathetic nervous system consists of a chain of ganglia
connected by longitudinal nerve filaments, situated on each side of the
spinal column, running from above downward. The two ganglionic cords
are connected in the interior of the cranium by the ganglion of Ribes, on
the anterior communicating artery, and terminate in the ganglion impar,
situated at the top of the coccyx.

The chain of ganglia is divided into groups, and named according to the

SYMPATHETIC NERVOUS SYSTEM. 219

location in which they are found — viz., cranial, four in number; cervical,
three ; thoracic, twelve ; lumbar, five ; sacral, five ; coccygeal, one. Each
ganglion consisis of a collection of vesicular nervous matter, bundles of
non-medullated nerve-fibers, embedded in a capsule of connective tissue.
The ganglia are reinforced by motor and sensory fibers from the cerebro-
spinal nervous system.

The ganglia have distinct nerve-fibers, from which branches are dis-
tributed to the glands, arteries, and muscles, and to the cerebral and spinal
nerves ; many pass, also, to the visceral ganglia — e. g., cardiac, semilunar,
pelvic, etc.

Cephalic Ganglia.

1. The ophthalmic or ciliary ganglion is situated in the orbital cavity, pos-
terior to the eyeball ; it is of small size and of a reddish-gray color ;
receives filaments of communication from the motor oculi, ophthalmic
branch of the fifth pair, and the carotid plexus. Its filaments of distri-
bution are the ciliary nerves, which consist of —

(a) Motor fibers for the circular fibers of the iris and ciliary muscle.
(3) Sensory fibers for the cornea, iris, and associated parts.

(c) Vaso-motor fibers for the blood-vessels of the choroid, iris, and
retina.

(d) Motor fibers for the dilator fibers of the iris.

2. The sphenopalatine or Meckel's ganglion, triangular in shape, is
situated in the sphenomaxillary fossa ; receives filaments from the facial
(Vidian nerve) and the superior maxillary branch of the fifth nerve. Its
filaments of distribution pass to the gums, the soft palate, and the levator
palati and azygos uvulse muscles.

3. The otic or Arnold's ganglion is of small size, oval in shape, and situ-
ated beneath the foramen ovale ; receives a motor filament from the facial
and sensory filaments from the glossopharyngeal and fifth nerves ; sends
filaments to the mucous membrane of the tympanic cavity and to the
tensor tympani muscle.

4. The submaxillary ganglion, situated in the submaxillary gland, receives
filaments from the chorda tympani, sensory filaments from the lingual
branch of the fifth nerve, and filaments from the sympathetic. The
chorda tympani nerve supplies vaso-dilator and secretoiy fibers to the sub-
maxillary and sublingual glands. The fifth nerve endows the glands with
sensibility, while the sympathetic supplies secretory or trophic fibers.

Cervical Ganglia.

The stcperior cervical ganglion is fusiform in shape, of a grayish-red

220 HUMAN PHYSIOLOGY.

color, and situated opposite the second and third cervical vertebrae ; it sends
branches to form the carotid and cavernous plexuses, which branches follow
the course of the carotid arteries to their distribution ; also sends branches
to join the glossopharyngeal and pneumogastric, to form the pharyngeal
plexus.

The middle cervical ganglion, the smallest of the three, is occasionally
absent ; it is situated opposite the fifth cervical vertebra ; sends branches
to the superior and inferior cervical ganglia and to the thyroid artery.

The inferior cervical ganglion, irregular in form, is situated opposite the
last cervical vertebra ; it is frequently united with the first thoracic ganglion.

The superior, middle, and inferior cardiac nerves, arising from these cer-
vical ganglia, pass downward and forward to form the deep and superficial
cardiac plexuses located at the bifurcation of the trachea, from which
branches are distributed to the heart, coronary arteries, etc.

The thoracic ganglia are usually twelve in number, and are placed
against the heads of the ribs behind the pleura ; they are small in size
and gray in color ; they communicate with the cerebro-spinal nerves by
two filaments, one of which is white, the other gray.

The great splanchnic nerve is formed by the union of branches from the
sixth, seventh, eighth, and ninth ganglia ; it passes through the diaphragm
to the semilunar ganglion.

The lesser splanchnic nerve is formed by the union of filaments from the
tenth and eleventh ganglia, and is distributed to the celiac plexus.

The renal splanchnic nerve arises from the last thoracic ganglion and
terminates in the renal plexus.

The semilunar ganglia , the largest of the sympathetic system, are situated
by the side of the celiac axis ; they send radiating branches to form the solar
plexus ; from the various plexuses, nerves follow the gastric, splenic, he-
patic, renal, etc., arteries, into the different abdominal viscera.

The lumbar ganglia, four in number, are placed upon the bodies of
the vertebra ; they give off branches, which unite to form the aortic lumbar
plexus and the hypogastric plexus, and follow the blood-vessels to their
terminations.

The sacral and coccygeal ganglia send filaments of distribution to
all the blood-vessels of the pelvic viscera.

Properties and Functions.— The sympathetic nerve possesses both
sensibility and the power of exciting motion, but these properties are much
less decided than in the cerebro-spinal system. Irritation of the ganglia

SYMPATHETIC NERVOUS SYSTEM. 221

does not produce any evidence of pain until some time has elapsed. If
caustic soda be applied to the semilunar ganglia, or a galvanic current be
passed through the splanchnic nerve, no instantaneous effect is noticed, as
in the case of the cerebro-spinal nerves ; but in the course of a few seconds
a slow, progressive contraction of the muscular coat of the intestines is
established, which continues for some time after the irritation has been
removed. Division of the sympathetic nerve in the neck is followed by a
vascular congestion of the parts above the section on the corresponding side,
attended by an increase in the temperature ; not only is there an increase in
the amount of blood, but the rapidity of the blood current is very much
accelerated and the blood in the veins becomes of a brighter color. Gal-
vanization of the upper end of the divided nerve causes all the preceding
phenomena to disappear ; the congestion decreases, the temperature falls,
and the venous blood becomes dark again.

The sympathetic exerts a similar influence upon the circulation of the
limbs and the glandular organs ; destruction of the first thoracic ganglion
and division of the nerves forming the lumbar and sacral plexuses are fol-
lowed by a dilatation of the vessels, an increased rapidity of the circula-
tion, and an elevation of temperature in the anterior and posterior limbs ;
galvanization of the peripheral ends of these nerves causes all of these phe-
nomena to disappear. Division of the splanchnic nerve causes a dilatation
of the blood-vessels of the intestine.

These phenomena of the sympathetic nervous system are dependent upon
the presence of vaso-motor nerves, which, under normal circumstances,
exert a tonic influence upon the blood-vessels. These nerves, derived
from the cerebro-spinal system and the medulla oblongata, leave the spinal
cord by the rami comtnunicantes, enter the sympathetic ganglia, and finally
terminate in the muscular walls of the blood-vessels.

Sleep is a periodic condition of the nervous system in which there is a
partial or complete cessation of the activities of the higher nerve centers.
The cause of sleep is a diminution in the quantity of blood, occasioned by
a contraction of the smaller arteries under the influence of the vaso-motor
nerves.

During the waking state the brain undergoes a physiologic waste, as a
result of the exercise of its functions ; after a certain length of time its
activities become enfeebled, and a period of repose ensues, during which a
regeneration of its substance takes place.

When the brain becomes enfeebled, there is a diminished molecular
activity and an accumulation of waste products ; under these circumstances

222 HUMAN PHYSIOLOGY.

it ceases to dominate the medulla oblongata and the spinal cord. These
centers then act more vigorously, and diminish the caliber of the cerebral
blood-vessels through the action of the vaso-motor nerves, producing a
condition of physiologic anemia and sleep ; during this state waste products
are removed, force is stored up, nutrition is restored, and waking finally
occurs.

THE SENSE OF TOUCH.

The sense of touch is a modification of general sensibility, and is located
in the skin, which is especially adapted for this purpose on account of the
number of nerves and papillary elevations it possesses. The structures of
the skin and the modes of termination of the sensory nerves have already
been considered.

The tactile sensibility varies in acuteness in different" portions of the
body, being most marked in those regions in which the tactile corpuscles
are most abundant — e. g., the palmar surface of the third phalanges of
the fingers and thumb.

The relative sensibility of different portions of the body has been ascer-
tained by means of a pair of compasses : the points of the instrument being
guarded by cork, it was then determined how closely they could be brought
together, and yet be felt at two different points. The following are some
of the measurements :

Point of tongue, ^ of a line.

Palmar surface of third phalanx, I line.

Red surface of lips, 2 lines.

Palmar surface of metacarpus, 3 "

Tip of the nose, 3 "

Part of lips covered by skin, 4 "

Palm of hand, . . 5 "

Lower part of forehead, . . 10 "

Back of hand, 14 "

Dorsum of foot, 1 8 "

Middle of the thigh, . . . 30 "

The sense of touch communicates to the mind the idea of resistance only,
and the varying degrees of resistance offered to the sensory nerves enable
us to estimate, with the aid of the muscular sense, the qualities of hardness
or softness of external objects. The idea of space or extension is obtained
when the sensory surface or the external object changes its place in regard

THE SENSE OF TASTE. 223

to the other ; the character of the surface, its roughness or smoothness, is
estimated by the impressions made upon the tactile papilke.

Appreciation of Temperature. — The general surface of the body is more
or less sensitive to differences of temperature, though this sensation is
separate from that of touch ; whether there are nerves especially adapted
for the conduction of this sensation has not been fully determined. Under
pathologic conditions, however, the sense of touch may be abolished, while
the appreciation of changes in temperature may remain normal.

The cutaneous surface varies in its sensibility to temperature in different
parts of the body, and depends, to some extent, upon the thickness of the
skin, exposure, habit, etc. ; the inner surface of the elbow is more sensitive
to changes in temperature than the outer portion of the arm ; the left hand
is more sensitive than the right, the mucous membrane less so than the
skin.

Excessive heat or cold has the same effect upon the sensibility ; the tem-
peratures most readily appreciated are those between 500 F. and 115° F.

The sensations of pain and tickling appear to be conducted to the brain,
also, by nerves different from those of touch ; in abnormal conditions the
appreciation of pain may be entirely lost while touch remains unimpaired.

THE SENSE OF TASTE.

The sense of taste is localized mainly in the mucous membrane cover-
ing the superior surface of the tongue.

The tongue is situated in the floor of the mouth ; its base is directed
backward and is connected with the hyoid bone and by numerous muscles
with the epiglottis and soft palate ; its apex is directed forward against the
posterior surface of the teeth.

The substance of the tongue is made up of intrinsic muscle-fibers, the
linguales ; it is attached to surrounding parts, and its various movements are
performed by the extrinsic muscles — e. g., styloglossus, geniohyoglossus, etc.

The mucous membrane covering the tongue is continuous with that lining
the commencement of the alimentary canal, and is furnished with vascular
and nervous papillae.

The papillce are analogous in their structure to those of the skin, and are
distributed over the dorsum of the tongue, giving it its characteristic
roughness.

224 HUMAN PHYSIOLOGY.

There are three principal varieties —

1 . The filiform papillae are most numerous, and cover the anterior two
thirds of the tongue ; they are conic or filiform in shape, often pro-
longed into filamentous tufts, of a whitish color, and covered by horny
epithelium.

2. The. fungiform papilla are found chiefly at the tip and sides of the
tongue ; they are larger than the preceding, and may be recognized by
their deep red color.

3. The circumvallate papillce are rounded eminences, from eight to ten in
number, situated at the base of the tongue, where they form a V-shaped
figure. They are quite large, and consist of a central projection of
mucous membrane, surrounded by a wall, or circumvallation, from which
they derive their name.

The taste-beakers, supposed to be the true organs of taste, are flask-
like-bodies, ovoid in form, about j^ of an inch in length, situated in the
epithelial covering of the mucous membrane, on the circumvallate papillae.
They consist of a number of fusiform, narrow cells, which are curved so as to
form the walls of this flask-like body ; in the interior are elongated cells,
with large, clear nuclei, the taste-cells.

Nerves of Taste. — The chorda tympani nerve, a branch of the facial,
after leaving the cavity of the tympanum, joins the third division of the fifth
nerve between the two pterygoid muscles, and then passes forward in the
lingual branches, to be distributed to the mucous membrane of the anterior
two thirds of the tongue. Division or disease of this nerve is followed by
a loss of taste in the part to which it is distributed.

The glossopharyngeal enters the tongue at the posterior border of the
hyoglossus muscle, and is distributed to the mucous membrane of the base
and sides of the tongue, fauces, etc.

The lingual branch of the trifacial nerve endows the tongue with gen-
eral sensibility ; the hypoglossal endows it with motion.

The nerves of taste in the superficial layer of the mucous membrane form
a fine plexus, from which branches pass to the epithelium and penetrate
it ; others enter the taste-beakers, and are directly connected with the
taste -cells.

The seat of the sense of taste has been shown by experiment to be the
whole of the mucous membrane over the dorsum of the tongue, soft palate,
fauces, and upper part of the pharynx.

The sense of taste enables us to distinguish the savor of substances

THE SENSE OF SMELL. 225

introduced into the mouth, which faculty is different from tactile sensibility,
The sapid qualities of substances appreciated by the tongue are designated
as bitter, sweet, alkaline, sour, salt, etc.

The essential conditions for the production of the impressions of taste
are :

1. A state of solubility of the food.

2. A free secretion of the saliva, and

3. Active movements on the part of the tongue, exciting pressure against
the roof of the mouth, gums, etc., thus aiding the solution of various
articles and their osmosis into the lingual papillae.

Sapid substances, when in a state of solution, pass into the interior of
the taste-beakers, and come into contact, through the medium of the taste-
cells, with the terminal filaments of the gustatory nerves.

THE SENSE OF SMELL.

The sense of smell is located in the mucous membrane lining the upper
part of the nasal cavity, in which the olfactory nerves are distributed.

The nasal fossae are two cavities, irregular in shape, separated by the
vomer, the perpendicular plate of the ethmoid bone, and the triangular car-
tilage. They open anteriorly and posteriorly by the anterior and posterior
nares, the latter communicating with the pharynx. They are lined by
mucous membrane, of which the only portion capable of receiving odorous
impressions is the part lining the upper one third of the fossse.

The olfactory nerves, arising by three roots from the posterior and
inferior surface of the anterior lobes, pass forward to the cribriform plate
of the ethmoid bone, where they each expand into an oblong body, the
olfactory bulb. From its under surface from fifteen to twenty filaments
pass downward through the foramina, to be distributed to the olfactory
mucous membrane, where they terminate in long, delicate, spindle-shaped
cells, the olfactory cells, situated between the ordinary epithelial cells.

The olfactory bulbs are the centers in which odorous impressions are
perceived as sensations, destruction of these bulbs being attended by an
abolition of the sense of smell.

In animals which possess an acute sense of smell there is a correspond-
ing increase in the development of the olfactory bulbs.

226 HUMAN PHYSIOLOGY.

The essential conditions for the sense of smell are —

1. A special nerve center capable of receiving impressions and transform-
ing them into odorous sensations.

2. Emanations from bodies which are in a gaseous or vaporous condition.

3. The odorous emanations must be drawn freely through the nasal fossae ;
if the odor be very faint, a peculiar inspiratory movement is made, by
which the air is forcibly brought into contact with the olfactory filaments.
The secretions of the nasal fossae probably dissolve the odorous particles.
Various substances, as ammonia, horseradish, etc. , excite the sensibility

of the mucous membrane ; this must be distinguished from the perception
of true odors.

THE SENSE OF SIGHT.

The Eyeball. — The eyeball, or organ of vision, is situated at the fore
part of the orbital cavity and is supported by a cushion of fat ; it is protected
from injury by the bony walls of the cavity, the lids, and the lashes, and is so
situated as to permit of an extensive range of vision. The eyeball is loosely
held in position by a fibrous membrane, the capstde of Tenon, which is
attached on the one hand to the eyeball itself and on the other to the walls
of the cavity. Thus suspended, the eyeball is capable of being moved in
any direction by the contraction of the muscles attached to it.

Structure. — The eyeball is spheroid in shape and measures about T9^ of
an inch in its anteroposterior diameter, and a little less in its transverse
diameter. When viewed in profile, it is seen to consist of the segments of
two spheres, of which the posterior is the larger, occupying five sixths, and
the anterior the smaller, occupying one sixth, of the ball.

The eye is made up of several membranes, concentrically arranged,
within which are inclosed the refracting media essential to vision. These
membranes, enumerated from without inward, are —

1 . The sclerotic and cornea.

2. The choroid and iris.

3. The retina.

The refracting media are the aqueous humor, the crystalline lens, and
the vitreous humor.

The Sclerotic and Cornea. — The sclerotic is the opaque fibrous mem-
brane covering the posterior five sixths of the ball. It is composed of
connective tissue arranged in layers, which run both transversely and
longitudinally ; it is pierced posteriorly by the optic nerve about Txff of an

THE SENSE OF SIGHT. 227

inch internal to the optic axis. The sclerotic, by its density, gives form to
the eye and protects the delicate structures within it, and serves for the
attachment of the muscles by which the ball is moved.

The cornea is a transparent non-vascular membrane covering the anterior
one sixth of the eyeball. It is nearly circular in shape and is continuous
at the circumference with the sclerotic, from which it can not be separated.
The substance of the cornea is made up of thin layers of delicate, trans-
parent fibrils of connective tissue, more or less united ; between these layers
are found a number of intercommunicating lymph-spaces, lined by endothe-
lium, which are in connection with lymphatics. Leukocytes or lymph-
corpuscles are often found in these spaces. The anterior surface of the
cornea is covered by several layers of nucleated epithelium, which rest
upon a structureless membrane known as the anterior elastic lamina.
The posterior surface is covered by a similar membrane, the membrane of
Descemet, which at its periphery becomes continuous with the iris ; it is
also covered by a layer of epithelial cells. At the junction of the cornea
and sclerotic is found a circular groove, the canal of Schlemm.

The choroid, the iris, the ciliary muscle, and the ciliary processes
together constitute the second or middle coat of the eyeball.

The choroid is a dark brown membrane which extends forward nearly
to the cornea, where it terminates in a series of folds, the ciliary processes.
In its structure the choroid is highly vascular, consisting of both arteries
and veins. Externally it is connected with the sclerotic by connective
tissue ; internally it is lined by a layer of hexagonal pigment cells, which,
though usually classed as belonging to the choroid, is now known to belong,
embryologically and physiologically, to the retina. From without inward
may be distinguished the following layers :

1. The lamina suprachoroidea.

2. The elastic layer of Sattler, consisting of two endothelial layers.

3. The chorio-capillaris, choroid proper, or membrane of Ruysch — a thick,
elastic network of arterioles and capillaries lying within the outer layer
of veins and arteries called the vense vorticosse.

4. The lamina vitrea, or internal limiting membrane.

The choroid with its contained blood-vessels bears an important relation
to the nutrition of the eye ; it provides for the blood-supply and for drain-
age from the body of the eye, and presents a uniform and high temperature
to the retina.

The iris is the circular, variously colored membrane placed in the
anterior portion of the eye just behind the cornea. It is perforated a little

228

HUMAN PHYSIOLOGY.

to the nasal side of the center by a circular opening, the pupil. The outer
or circumferential border is connected with the cornea, ciliary muscle, and
ciliary processes ; the free inner edge forms the boundary of the pupil, the
size of which is constantly changing. The framework of the iris is com-
posed of connective tissue blood-vessels, muscle-fibers and pigmented
connective-tissue corpuscles. The anterior surface is covered with a layer
of ephithelial cells continuous with those covering the posterior surface of
the cornea ; the posterior surface is lined by a limiting membrane bearing
pigment epithelial cells continuous with those of the choroid. The various

- f

Fig. 30. — Sclerotic Coat removed to show Choroid Ciliary Muscle, and
Nerves. — {Frojn Holden's "Anatomy.")

a. Sclerotic coat.

b. Veins of the choroid. c. Ciliary nerves, d. Veins of the
choroid, e. Ciliary muscle, f. Iris.

colors which the iris assumes in different individuals depend upon the
quantity and disposition of the pigment granules.

The muscle-fibers of the iris, which are of the non-striated variety, are
arranged in two sets — the sphincter and dilator.

The sphincter pupillce is a circular, flat band of muscle-fibers surrounding
the pupil close to its posterior surface ; by its contraction and relaxation
the pupil is diminished or increased in size. The dilatator pupillce consists
of a thin layer of fibers arranged in a radiate manner ; at the margin of the
pupil they blend with those of the sphincter muscle, while at the outer
border they arch to form a circular muscular layer.

The ciliary muscle is a gray, circular band, consisting of unstriped

THE SENSE OF SIGHT. 229

muscle-fibers about y1^ of an inch long running from before backward.
It is attached anteriorly to the inner surface of the sclerotic and cornea, and
posteriorly to the choroid coat opposite the ciliary processes. At the an-
terior border of the radiating fibers and internally are found bundles of
circular muscle-fibers, constituting the anntdar muscle of Miiller. The
ciliary muscle thus consists of two sets of fibers, a radiating and a circular,
both of which are concerned in effecting a change in the convexity of the
lens in the accommodation of the eye to near vision.

The retina forms the internal coat of the eye. In the fresh state it is a
delicate, transparent membrane of a pink color, but after death soon
becomes opaque ; it extends forward almost to the ciliary processes, where
it terminates in an indented border, the ora serrata. In the posterior part
of the retina, at a point corresponding to the axis of vision, is a yellow spot,
the macula lulea, which is somewhat oval in shape and tinged with yellow
pigment. It presents in its center a depression, the fovea centralis, cor-
responding to a decrease in thickness of the retina ; about y1^ of an inch to
the inner side of the macula is the point of entrance of the optic nerves
The arteria centralis retince pierces the optic nerve near the sclerotic, runs
forward in its substance, and is distributed in the retina as far forward as
the ciliary processes.

The retina is remarkably complex, consisting of ten distinct layers, from
within outward, supported by connective tissue. These are as follows —
viz. :

1. Membrana limitans interna.

2. Fibers of optic nerve.

3. Layers of ganglionic corpuscles.

4. Molecular layer.

5. Internal granular layer.

6. Molecular layer.

7. External granular layer.

8. Membrana limitans externa.

9. Jacobson's membrane, or layer of rods and cones.
10. The layer of pigment cells.

The most important of these, however, is the layer of rods and cones in
the external portion of the retina. The rods are straight, elongated cylin-
ders extending through the entire thickness of Jacobson' s membrane. They
consist of an external portion, which is clear, homogeneous, and highly
refracting, and of an internal portion, which is slightly granular and less
refractive ; the outer end of each rod is in direct contact with the pig-

230 HUMAN PHYSIOLOGY.

ment epithelium lining the choroid, while the inner end, tapering to a
fine thread, pierces the external limiting membrane and passes into the
external granular layer. The cones consist also of two portions, the inner
of which is somewhat thicker than the rod and rests upon the limiting
membrane ; the outer portion tapers to a fine point, which is known as the
cone-style. The cones, as a rule, are somewhat shorter than the rods.
The proportion of rods to cones varies in different parts of the retina, though
there are on an average about fourteen rods to one cone. In the macula
lutea, where vision is most acute, the rods are almost entirely absent, cones
alone being present. All the retinal elements at this point are changed.
The nerve-fiber layer is absent, the axis-cylinders radiating in such a man-
ner as to leave the spot free from their covering. The remaining layers are
all thinned and the stroma is reduced to a minimum. The optic nerve,
after passing forward from the brain, penetrates in succession the sclerotic,
choroid, and retina ; the nerve-fibers then spread out over the anterior sur-
face of the retina and become connected with the large ganglionic cells,
the third layer of the retina.

The number of optic nerve-fibers in the retina is estimated to be about
800,000, and for each fiber there are about seven cones, one hundred rods,
and seven pigment cells. The points of the rods and cones are directed
toward the choroid, or away from the entering light, and dip into the pig-
ment layer. They, with the pigment layer, are the intermediating ele-
ments in the change of the ethereal vibrations into nerve force ; out of
these nerve vibrations the brain fashions the sensations of light, form, and
color.

The vitreous humor, which supports the retina, is the largest of the re-
fracting media ; it is globular in form and constitutes about four fifths of
the ball ; it is hollowed out anteriorly for the reception of the crystalline
lens. The outer surface of the vitreous is covered by a delicate, transparent
membrane, termed the hyaloid membrane, which serves to maintain its
globular form.

The aqueous humor, found in the anterior chamber of the eye, is a clear
alkaline fluid, having a specific gravity of 1003-1009. It is secreted most
probably by the blood-vessels of the iris and ciliary processes. It passes
from the interior of the eye, through the canal of Schlemm and the meshes
at the base of the iris, into the anterior circular vein.

The crystalline lens, inclosed within its capsule, is a transparent bicon-
vex body, situated just behind the iris and resting in the depression in the
anterior part of the vitreous. The two convexities are not quite alike, the

0

curvature of the posterior surface being slightly greater than that of the an-

THE SENSE OF SIGHT. 231

terior. The lens measures about \ of an inch in the transverse diameter
and £ of an inch in the anteroposterior diameter.

The suspensory ligament, by which the lens is held in position, is a firm,
transparent membrane, united to the ciliary processes. A short distance
beyond its origin it splits into two layers, the anterior of which is inserted
into the capsule of the lens and blends with it ; the posterior, passing inward
behind the lens, becomes united to its capsule. The anterior layer pre-
sents a series of foldings, zone of Zinn, which are inserted into the inter-
vals of the folds of the ciliary processes. The triangular space between the
two layers is the canal of Petit.

Blood-vessels and Nerves. — The structures composing the eyeball
are supplied with blood by the long and short ciliary arteries, branches of
the ophthalmic ; they pierce the sclerotic at various points and are ulti-
mately distributed to all tissues within the ball.

The nerve-supply comes largely from the ophthalmic or ciliary ganglion.
This is a small body, situated in the posterior part of the orbit ; it receives
motor fibers from a branch of the motor oculi, or third nerve ; a sensory
branch from the ophthalmic division of the fifth nerve, and fibers from the
cavernous plexus of the sympathetic. From the anterior border of the
ganglion proceed the ciliary nerves, which, entering the eyeball, endow its
structures with motion and sensation.

The Eyeball a Living Camera Obscura. — The eyeball may be com-
pared in a general way to a camera obscura. The anatomic arrangement
of its structures reveals many points of similarity. The sclerotic and choroid
\nay be compared with the walls of the chamber ; the combined refractive
media, cornea, aqueous } -mor, lens, and vitreous humor, to the lens for
focusing the rays of light ; the retina, to the sensitive plate receiving the
image formed at the focal point ; the iris, to the diaphragm, which, by
cutting off the marginal rays, prevents spheric aberration and at the same
time regulates the amount of light entering the eye ; the ciliary muscle, to
the adjusting screw, by which distinct images are thrown upon the retina in
spite of varying distances of the object from which the light rays emanate.
The structures just enumerated are those essential for normal vision.

The relationship of the various structures composing the eyeball is shown
in Figure 31.

The dioptric or refracting apparatus, by which the rays of light enter-
ing the eye are so manipulated as to produce an image on the retina, con-
sists of the cornea, aqueous humor, crystalline lens, and vitreous humor. A
ray of light in passing through each of these media will undergo refraction

232

HUMAN PHYSIOLOGY.

at their surfaces and ultimately be brought to a focus at the retina. Inas-
much as the two surfaces of the cornea are parallel and its refractive power
practically the same as the aqueous humor, the media may be reduced to
three — viz. :

1. Cornea and aqueous humor.

2. The lens.

3. The vitreous humor.

Fig. 31. — Diagram of a Vertical Section of the Eye. — {From Holdens,

" Anatomy.")

1. Anterior chamber filled with aqueous humor. 2. Posterior chamber. 3 Canal of
Petit, a. Hyaloid membrane, b. Retina (dotted line), c. Choroid coat (black
line), d. Sclerotic coat. e. Cornea, f. Iris. g. Ciliary processes, h. Canal of
Schlemm or Fontana. z. Ciliary muscle.

The refracting surfaces may also be reduced to three — viz. :

1. Anterior surface of the cornea.

2. Anterior surface of lens.

3. Posterior surface of lens.

The refraction effected by the cornea is very great, owing to the passage
of the light from the air into a comparatively dense medium, and is sufficient
of itself to bring parallel rays of light to a focus about ten millimeters behind
the retina. This would be the condition in an eye in which the lens was
congenitally absent. Perfect vision requires, however, that the convergence
of the light shall be great enough to allow the image to fall upon the retina.

THE SENSE OF SIGHT.

233

This is accomplished by the crystalline lens, a body denser than the cornea
and possessing a higher refractive power. The manner in which a bicon-
vex lens focuses both parallel and divergent rays is shown in figures 32
and 33.

The function of the crystalline lens, therefore, is to focus the rays of light
with the formation of an image on the retina.

The retinal image corresponds in all respects to the object from which
the light proceeds. The existence of this image can be demonstrated by
removing from the eye of a recently killed animal a circular portion of the
sclerotic and choroid posteriorly, and then placing at the proper distance in

Fig. 32. — Diagram showing the Course of Parallel Rays of Light from
A, in their Passage through a Biconvex Lens, L, in which they are
so Refrated as to Bind Toward and Come in a Focus at a Point, F.
— {Fro?)i Yeo's " Te.xf-book of Physiology."")

Fig. 33. — Diagram showing the Course of Diverging Rays which are Bent
to a Point Further from the Lens than the Parallel Rays in Pre-
ceding Figure. — ( Yeo's " Text-book of Physiology.")

front of the cornea a lighted candle ; an inverted image of the candle will
be seen upon the retina. The size of the retinal image depends upon the
visual angle, which in turn depends upon the size of the object and its dis-
tance from the eye. At a distance of 15.2596 meters the image of an object
one meter high would be one millimeter, or a thousand times smaller than
the object.

Accommodation. — By accommodation is understood the power which
the eye possesses of adjusting itself to vision at different distances. In a
normal or emmetropic eye parallel rays of light are brought to a focus on
16

234 HUMAN PHYSIOLOGY.

the retina ; but divergent rays — that is, rays coming from a near luminous
point — will be brought to a focus behind the retina, provided the refractive
media remain the same ; as a result, vision would be indistinct, from the
formation of diffusion circles. It is impossible to see distinctly, therefore,
a near and a distant object at the same time. We must alternately direct
the vision from one to the other. A normal eye does not require adjusting
for parallel rays ; but for divergent rays a change in the eye is necessitated ;
this is termed accommodation. In the accommodation for near vision the
lens becomes more convex, particularly on its anterior surface. The in-
crease in convexity augments its refractive power ; the greater the degree
of divergence of the rays previous to entering the eye, the greater the in-
crease of convexity of the lens and convergence of the rays after passing
through it. By this alteration in the shape of the lens we are enabled to
focus light rays coming from, and to see distinctly, near as well as distant
objects.

Function of the Ciliary Muscle. — Though it is admitted that the
change in the convexity of the lens is caused by the contraction of the
ciliary muscle and the relaxation of the suspensory ligament, the exact
manner in which it does so is not understood. When the eye is in repose,
as in distant vision, the suspensory ligament is tense, and the lens possesses
that degree of curvature necessary for focusing parallel rays. In the volun-
tary efforts to accommodate the eye for near vision, the ciliary muscle con-
tracts, the suspensory ligament relaxes, and the lens, inherently elastic,
bulges forward and once again focuses the rays upon the retina. It is?
therefore, termed the muscle of accommodation, and by its alternate con-
traction and relaxation the lens is rendered more or less convex, according
to the requirements for near and distant vision.

Range of Accommodation. — Parallel rays coming from a luminous
point distant not less than 200 feet do not require adjustment ; from this
point up to infinity no accommodation is required for perfect vision. This
is termed the punctum remoium, and indicates the distance to which an
object may be removed and yet distinctly seen. If the object be brought
nearer to the eye than 200 feet, the accommodative power must come into
play ; the nearer the object, the more energetic must be the contraction of
the ciliary muscle and the consequent increase in the convexity of the lens.
At a distance of five inches, however, the power of accommodation reaches
its maximum ; this is termed the punctum proximum, and indicates the
nearest point at which an object may be seen distinctly. The distance be-
tween these two points is the range of accommodation.

THE SENSE OF SIGHT. 235

Optic Defects. — Astigmatism is a condition of the eye which prevents
vertical and horizontal lines from being focused at the same time, and is
due to a greater curvature of the cornea in one meridian than in another.

Spheric aberration is a condition in which there is an indistinctness of
an image from the unequal refraction of the rays of light passing through
the circumference and the center of the lens ; it is corrected mainly by the
iris, which cuts off the marginal rays, and transmits only those passing
through the center.

Chromatic aberration is a condition in which the image is surrounded by
a colored margin, from the decomposition of the rays of light into their
elementary parts.

Myopia, or shortsightness, is caused by an abnormal increase in the
anteroposterior diameter of the eyeball, or by a hypernormal refracting
power of the lens. It is generally due to the first cause ; the lens, being
too far removed from the retina, forms the image in front of it, and the
perception becomes dim and blurred. Concave glasses correct this defect
by preventing the rays from converging too soon.

Hypermetropia, or longsightness, is caused by a shortening of the
anteroposterior diameter or by a subnormal refractive power of the lens ;
the focus of the rays of light would, therefore, be behind the retina. Con-
vex glasses correct this defect by converging the rays of light more
anteriorly.

Presbyopia is a loss of the power of accommodation of the eye to near
objects, and usually occurs between the ages of forty and sixty ; it is reme-
died by the use of convex glasses.

The Iris. — The iris plays the part of a diaphragm, and by means of its
central aperture the pupil regulates the quantity of light entering the
interior of the eye ; by preventing rays from passing through the margin
of the lens it diminishes spheric aberration. The size of the pupil depends
upon the relative degree of contraction of the circular and radiating fibers ;
the variations in size of the pupil from variations in the degree of contrac-
tion depend upon different intensities of light. If the light be intense, the
circular fibers contract, and diminish the size of the pupil ; if the light
diminishes in intensity, the circular fibers relax and the pupil enlarges.

Point of Most Distinct Vision. — While all portions of the retina are
sensitive to light, their sensibility varies within wide limits. At the
macula lutea, and more especially in its most central depression, the fovea,
where the retinal elements are reduced practically to the layer of rods and

236 HUMAN PHYSIOLOGY.

cones, the sensibility reaches its maximum. It is at this point that the
image is found when vision is most distinct. The macula and fovea are
always in the line of direct vision. From the macula toward the periphery
of the retina there is a gradual diminution in sensibility, and a correspond-
ing decline in the distinctness of vision. In those portions of the retina
lying outside the macula, the indistinctness of vision depends not only on
diminished sensibility, but also upon inaccurate focusing of the rays.

Blind Spot. — Although the optic nerve transmits the impulses excited
in the retina by the ethereal vibration, the nerve-fibers themselves are in-
sensitive to light. At the point of entrance of the optic nerve, owing to
the absence of the rods and cones, the rays of light make no impression.
This is the blind spot. As this spot is not in the line of vision, no dark
point is ordinarily observed in the field of vision — the circular space before
a fixed eye within which reflections of objects are perceptible.

The rods and cones are the most sensitive portions of the retina. 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 probable that the ethereal vibrations
are transformed into heat, which excites the rods and cones. These, act-
ing 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 differences in the intensity of light, while the cones, in addition, are
impressed by qualitative differences or color.

Accessory Structures. — The muscles which move the eyeball are six
in number — the superior and inferior recti, the external and internal recti,
the superior and inferior oblique muscles. The four recti muscles, arising
from the apex of the orbit, pass forward and are inserted into the sides of
the sclerotic coat ; the superior and inferior muscles rotate the eye around
a horizontal axis ; the external and internal rotate it around a vertical
axis.

The superior oblique muscle, having the same origin, passes forward to
the inner and upper angle of the orbital cavity, where its tendon passes
through a cartilaginous pulley ; it is then reflected backward and inserted
into the sclerotic just behind the transverse diameter. Its function is to

THE SENSE OF HEARING. 237

rotate the eyeball in such a manner as to direct the pupil dowmvard and
outward.

The inferior oblique muscle arises at the inner angle of the orbit, and
then passes outward and backward, to be inserted into the sclerotic. Its
function is to rotate the eyeball and to direct the pupil upward and out-
ward.

By the associated action of all these muscles, the eyeball is capable of
performing all the varied and complex movements necessary for distinct
vision.

The eyelids, bordered with short, stiff hairs, shade the eye and protect it
from injury. On the posterior surface, just beneath the conjunctiva, are
the Meibomian glands, which secrete an oily fluid ; this covers the edge of
the lids, and prevents the tears from flowing over the cheek.

The lacrymal glands are ovoid in shape, and are situated at the upper
and outer part of the orbital cavity ; they open by from six to eight ducts at
the outer portion of the upper lids.

The tears, secreted by the lacrymal glands, are distributed over the cor-
nea by the lids during the act of winking, and keep it moist and free from
dust. The excess of tears passes into the lacrymal ducts, which begin by
two minute orifices, one on each lid, at the inner canthus. They conduct
the tears into the nasal duct, and so into the nose.

THE SENSE OF HEARING.

The ear, or organ of hearing, is lodged within the petrous portion of
the temporal bone. It may be, for convenience of description, divided
into three portions — viz :

1. The external ear.

2. The middle ear.

3. The internal ear or labyrinth.

The external ear consists of the pinna, or auricle, and the external
auditory canal. 'Wit pinna consists of a thin layer of cartilage, presenting
a series of elevations and depressions ; it is attached by fibrous tissue to the
outer bony edge of the auditory canal ; it is covered by a layer of integu-
ment continuous with that covering the side of the head. The general
shape of the pinna is concave, and presents, % little below the center, a deep
depression — the concha. The external aziditory canal extends from the
concha inward for a distance of about 1% inches. It is directed some-

238 HUMAN PHYSIOLOGY.

what forward and upward, passing over a convexity of bone, and then dips
downward to its termination ; it is composed of both bone and cartilage,
and is 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
ceruminous glands, — which in their conformation resemble the perspiratory
glands. They secrete the cerumen, or ear-wax.

The middle ear, or tympanum, is an irregularly shaped cavity hol-
lowed out of the temporal bone and situated between the external ear and
the labyrinth. It is narrow from side to side, but relatively long in its
vertical and anteroposterior diameters ; it is separated from the external
auditory canal by a membrane — the membrana tympani ; from the internal
ear it is separated by an osseomembranous partition, which forms a common
wall for both cavities. The middle ear communicates posteriorly with the
mastoid cells ; anteriorly with the nasopharynx, by means of the Eustachian
tube. The interior of this cavity is lined by mucous membrane continuous
with that lining the pharynx.

The membrana tympani is a thin, translucent, nearly circular membrane,
measuring about ■§ of an inch in diameter, placed at the inner termination
of the external auditory canal. The membrane is inclosed within a ring
of bone, which in the fetal condition can be easily removed, but in the
adult condition becomes consolidated with the surrounding bone. The
membrana tympani consists primarily of a layer of fibrous tissue, arranged
both circularly and radially, and forms the membrana propria ; externally
it is covered by a thin layer of skin continuous with that lining the auditory
canal ; internally it is covered by a thin mucous membrane. The tympanic
membrane is placed obliquely at the bottom of the auditory canal, inclining
at an angle of forty-five degrees, being directed from behind and above
downward and inward. On its external surface this membrane presents
a funnel-shaped depression, the sides of which are somewhat convex.

The Ear Bones. — Running across the tympanic cavity and forming an
irregular line of joined levers is a chain of bones which articulate with
one another at their extremities. They are known as the malleus, incus,
and stapes.

The form and position of these bones are shown in figure 34.

The malleus 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 surface, which receives the head of the
malleus ; the stapes, or stirrup bone, articulates externally with the long

THE SENSE OF HEARING.

239

process of the incus, and internally, by its oval base, with the edges of the
foramen ovale.

The tensor tympani muscle consists of a fleshy, tapering portion, %
of an inch in length, which terminates in a slender tendon ; it arises from
the cartilaginous portion of the Eustachian tube and the adjacent surface of
the sphenoid bone. From this origin the muscle passes nearly horizontally

Fig. 34. — Tympanum and Auditory Ossicles (Left) Magnified.
A.G. External meatus. M. Membrana tympani, which is attached to the handle of the
malleus, n, and near it the short process, p. h. Head of the malleus, a. Incus;
K, its short process, with its ligament; 1, long process, s. Sylvian ossicle. S.
Stapes. Ax, Ax, is the axis of rotation of the ossicles ; it is shown in perspective,
and must be imagined to penetrate the plane of the paper, t. Line of traction of the
tensor tympani. The other arrows indicate the movement of the ossicles when the
tensor contracts.

backward to the tympanic cavity ; just opposite to the" fenestra ovalis its
tendon bends at a right angle over the processus cochleariformis, and then
passes outward across the cavity, to be inserted into the angle of the mal-
leus near the neck.

The stapedius muscle emerges from the cavity of a pyramid of bone
projecting from the posterior wall of the tympanum ; the tendon passes

240 HUMAN PHYSIOLOGY.

forward, and is inserted into the neck of the stapes bone, posteriorly, near
its point of articulation with the incus.

The laxator tympani muscle, so called, is now generally regarded as
being ligamentous in nature, and not muscular.

The Eustachian tube, by means of which a free communication is
established between the middle ear and the pharynx, is partly bony and
partly cartilaginous in structure. It measures about l^£ inches in length ;
commencing at its opening into the nasopharynx, it passes upward and
outward to the spine of the sphenoid bone, at which point it becomes some-
what contracted ; the tube then dilates as it passes backward into the
middle-ear cavity ; it is lined by mucous membrane, which is continued
into the middle ear and mastoid cells.

The function of the ear, as a whole, is the reception and transmis-
sion of aerial vibrations to the terminal organs concealed within the in-
ternal ear, and which are connected with the auditory nerve-fibers. The
excitation of these end organs caused by the impact of the vibrations
arouses in the auditory nerve impulses which are then transmitted to the
brain, where the hearing process takes place. In order to appreciate the
functions of the individual parts of the ear, a few of the characteristics of
sound waves must be kept in mind.

Sound Waves. — All sounds are caused by vibrations in the atmosphere
which have been communicated to it by vibrating elastic bodies, such as
membranes, strings, rods, etc. These vibrating bodies produce in the air
a to-and-fro movement of its particles, resulting in a series of alternate
condensations and rarefactions, which are propagated in all directions. A
complete oscillation of a particle of air forward and backward constitutes a
sound wave. Musical sounds are caused by a succession of regular waves,
which follow one another with a certain rapidity. Noises are caused by
the impact of a series of irregular waves.

All sound waves possess intensity, pitch, and quality. The intensity, or
loudness, of a sound depends upon the amplitude of its vibrations or the
extent of its excursion. The pitch depends upon the number of vibra-
tions which affect the auditory nerve in a second of time ; the pitch of the
note C, the first below the leger line of the musical scale, is caused by
256 vibrations a second; the pitch of the same note an octave higher is
caused by 512 vibrations a second. If the vibrations are too few a second,
they fail to be perceived as a continuous sound ; the minimum number
of vibrations capable of producing a sound has been fixed at sixteen a

THE SENSE OF HEARING. 241

second ; the highest pitched musical note capable of being heard has been
shown to be due to 38,000 vibrations a second. In the ascent of the
musical scales there is, therefore, a gradual increase in the number of
vibrations and a gradual increase in the pitch of the sounds. Between the
two extreme limits lies the range of audibility, which embraces eleven
octaves, of which seven are employed in the musical scale.

The quality of sound depends upon a combination of the fundamental
vibration with certain secondary vibrations of subdivisions of the vibrating
body. These so-called over-tones vary in intensity and pitch, and by
modifying the form of the primary wave produce that which is termed the
quality of sound.

Function of the Pinna and External Auditory Canal. — In those
animals possessing movable ears the pinna plays an important part in the
collection of sound waves. In man, in whom the capability of moving the
pinna has been lost, it is doubtful if it is at all necessary for hearing.
Nevertheless an individual with dull hearing may have the perception of
sound increased by placing the pinna at an angle of 45 degrees to the side
of the head. The external auditory canal transmits the sonorous vibra-
tions to the tympanic membrane. Owing to the obliquity of this canal it
has been supposed that the waves, concentrated at the concha, undergo a
series of reflections on their way to the tympanic membrane, and, owing to
the position of this membrane, strike it almost perpendicularly.

Function of the Tympanic Membrane. — The function of the tym-
panic membrane appears to be the reception of sound vibrations by being
thrown by them into reciprocal vibrations which correspond in intensity and
amplitude. That this membrane actually reproduces all vibrations within
the range of audibility has been experimentally demonstrated. The mem-
brane not being fixed, so far as its tension is concerned, does not possess a
fixed fundamental note, like a stationary fixed membrane, and is, therefore,
just as well adapted for the reception of one set of vibrations as for another.
This is made possible by variations in its tension in accordance with the
pitch of the sounds. In the absence of all sound the membrane is in 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 ten-
sion of the tympanic membrane is gradually increased until its maximum
tension 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 indistinct and inaudible.

Function of the Tensor Tympani Muscle. — The function of this

242 HUMAN PHYSIOLOGY.

muscle is, as its name indicates, to increase the tension of the membrane in
accordance with the pitch of the sound wave. The tension of this muscle
playing over the processus cochleariformis and attached at almost a right
angle to the handle of the malleus will, when the muscle contracts, pull the
handle inward, increase the convexity of the membrane, and at the same
time increase its tension ; with the relaxation of this muscle, the handle of
the malleus passes outward and the tension is diminished. The contrac-
tions of the tensor muscle are reflex in character and excited by nerve-
impulses reaching it through the small petrosal nerve and otic ganglion.
The number of nerve stimuli passing to the muscle and determining the
degree of contraction will depend upon the pitch of the sound wave and the
subsequent excitation of the auditory nerve. The tensor tympani muscle
may be regarded as an accommodative apparatus by which the tympanic
membrane is so adjusted as to enable it to receive vibrations of varying de-
grees of pitch.

Function of the Ossicles. — The function of the chain of bones is to
transmit the sound wave across the tympanic cavity to the internal ear.
The first of these bones, the malleus, being attached to the tympanic mem-
brane, will take up the vibrations much more readily than if no membrane
intervened. Owing to the character of the articulations, when the handle
of the malleus is drawn inward, the position of the bones is so changed
that they form practically a solid rod, and are therefore much better adapted
for the transmission of molecular vibrations than if the articulations re-
mained loose. As the stapes bone is somewhat shorter than the malleus,
its vibrations are slighter than those of the tympanic membrane, and by this
arrangement the amplitude of the vibrations is diminished, but their force
increased.

The function of the stapedius muscle is, according to Henle, to fix
the stapes bone so as to prevent too great a movement from being commu-
nicated to it from the incus and transmitted to the perilymph. It may be
looked upon, therefore, as a protective muscle.

The function of the Eustachian tube is to maintain a free communi-
cation between the cavity of the middle ear and the nasopharynx. The pres-
sure of air within and without the ear is thus equalized, and the vibrations
of the tympanic membrane are permitted to attain their maximum, one of
the conditions essential for the reception of sound waves. The impairment
in the acuteness of hearing which is caused by an unequal pressure of the
air in the middle ear can be shown —

THE SENSE OF HEARING. 243

1. By closing the mouth and nose and forcing air from the lungs through
the Eustachian tube into the ear, producing an increase in pressure.

2. By closing the nose and mouth, and making efforts at deglutition, which
withdraws the air from the ear and diminishes its pressure.

In both instances the free vibrations of the tympanic membrane are in-
terfered with. The pharyngeal orifice of the Eustachian tube is opened
by the action of certain of the muscles of deglutition — viz., the levator
palati, the tensor palati, and the palato-pharyngei muscles.

The internal ear, or labyrinth, is located in the petrous portion of the
temporal bone, and consists of an osseous and a membranous portion.

The osseous labyrinth is divisible into three parts — viz., the vestibule,
the semicircular canals, and the cochlea.

The vestibule is a small, triangular cavity, which communicates with the
middle ear by the foramen ovule ; in the natural condition it is closed by
the base of the stapes bone. The filaments of the auditory nerve enter the
vestibule through small foramina in the inner wall, at the fovea hemi-
spherica.

The semicircular canals are three in number, the superior vertical, the
inferior vertical, and the horizontal, each of which opens into the cavity of
the vestibule by two openings, with the exception of the two vertical, which
at one extremity open by a common orifice.

The cochlea forms the anterior part of the internal ear. It is a gradually
tapering canal, about \)/2 inches in length, which winds spirally around a
central axis, the modiolus, two and one half times. The interior of the coch-
lea is partly divided into two passages by a thin plate of bone, the lamina
osseous spiralis, which projects from the central axis two thirds of the way
across the canal. These passages are termed the scala vestibuli and the srala
tympani, from their communication with the vestibule and tympanum. The
scala tympani communicates with the middle ear through the foramen
rotundum, which, in the natural condition, is closed by the second mem-
bran a tympani ; superiorly they are united by an opening, the helicotrema.

The whole interior of the labyrinth, the vestibule, the semicircular canals,
and the scala of the cochlea, contains a clear, limpid fluid, the perilymph
secreted by the periosteum lining the osseous walls.

The membranous labyrinth corresponds to the osseous labyrinth with
respect to form, though it is somewhat smaller in size.

The vestibular portion consists of two small sacs, the utricle and
the saccule.

244 HUMAN PHYSIOLOGY.

The semicircular canals communicate with the utricle in the same man-
ner as the bony canals communicate with the vestibule. The saccule com-
municates with the membranous cochlea by the canalis reuniens. In the
interior of the utricle and saccule, at the entrance of the auditory nerve,
are small masses of carbonate of lime crystals, constituting the otoliths.
Their function is unknown.

The membranous cochlea is a closed tube, commencing by a blind ex-
tremity at the first turn of the cochlea, and terminating at its apex by a
blind extremity also. It is situated between the edge of the osseous lamina
spiralis and the outer wall of the bony cochlea, and follows it in its turns
around the modiolus.

A transverse section of the cochlea shows that it is divided into two
portions by the osseous lamina and the basilar membrane :

1. The scala vestibuli, bounded by the periosteum and membrane of
Reissner.

2. The scala tympani, occupying the inferior portion, and bounded above
by the septum, composed of the osseous lamina and the membrana
basilaris.

The true membranous canal is situated between the membrane of Reiss-
ner and the basilar membrane. It is triangular in shape, but is partly
divided into a triangular portion and a quadrilateral portion by the tectorial
membrane.

The organ of Corti is situated in the quadrilateral portion of the canal,
and consists of pillars of rods of the consistence of cartilage. They are
arranged in two rows — the one internal, the other external ; these rods rest
upon the basilar membrane ; their bases are separated from one another,
but their upper extremities are united, forming an arcade. In the internal
row it is estimated there are about 3,500 and in the external row about 5j2°°
of these rods.

On the inner side of the internal row is a single layer of elongated hair-
cells ; on the outer surface of the external row are three such layers of hair-
cells. Nothing definite is known as to their function.

The endolymph occupies the interior of the utricle, saccule, and mem-
branous canals, and bathes the structures in the interior of the membranous
cochlea throughout its entire extent.

The auditory nerve at the bottom of the internal auditory meatus

divides into —

I. A vestibular branch, which is distributed to the utricle and to the semi-
circular canals.

VOICE AND SPEECH. 245

2. A cochlear branch, which passes into the central axis at its base and
ascends to its apex ; as it ascends, fibers are given off, which pass be-
tween the plates of the osseous lamina, to be ultimately connected with
the organ of Corti.

The function of the semicircular canals appears to be to assist in main-
taining the equilibrium of the body ; destruction of the vertical canal is fol-
lowed by an oscillation of the head upward and downward ; destruction of
the horizontal canal is followed by oscillations from left to right. "When
the canals are injured on both sides, the animal loses the power of main-
taining equilibrium upon making muscular movements.

Function of the Cochlea. — It is regarded as possessing the power of ap-
preciating the quality of pitch and the shades of different musical tones.
The elements of the organ of Corti are analogous, in some respects, to a
musical instrument, and are supposed, by Helmholtz, to be tuned so as to
vibrate in unison with the different tones conveyed to the internal ear.

Summary. — The waves of sound are gathered together by the pinna and
external auditory meatus, and conveyed to the membrana tympani. This
membrane, made tense or lax by the action of the tensor tympani and laxa-
tor tympani muscles, is enabled to receive sound waves of either high or
low pitch. The vibrations are conducted across the middle ear by a chain
of bones to the foramen ovale, and by the column of air of the tympanum
to the foramen rotundum, which is closed by the second membrana tym-
pani, the pressure of the air in the tympanum being regulated by the Eu-
stachian tube.

The internal ear finally receives the vibrations, which excite vibrations
successively in the perilymph, the walls of the membranous labyrinth, the
endolymph, and, lastly, the terminal filaments of the auditory nerve, by
which they are conveyed to the brain.

VOICE AND SPEECH.

The larynx is the organ of voice. Speech is a modification of voice, and
is produced by the teeth and the muscles of the lips and tongue, coordi-
nated in their action by stimuli derived from the cerebrum.

The structures entering into the formation of the larynx are mainly the
thyroid, cricoid, and arytenoid cartilages ; they are so situated and united

246 HUMAN PHYSIOLOGY.

by means of ligaments and muscles as to form a firm cartilaginous box.
The larynx is covered externally by fibrous tissue, and lined internally with
mucous membrane.

The vocal cords are four ligamentous bands, running anteroposteriorly
across the upper portion of the larynx, and are divided into the two superior
or false vocal cords, and the two inferior or true vocal cords ; they are
attached anteriorly to the receding angle of the thyroid cartilages, and pos-
teriorly to the anterior part of the base of the arytenoid cartilages. The
space between the true vocal cords is the rima glottidis.

The muscles which have a direct action upon the movements of the
vocal cords are nine in number, and take their names from their points of
origin and insertion — viz., the two crico-thyroid, two thyro -arytenoid, two
posterior crico-arytenoid, two lateral crico- arytenoid, and one arytenoid
muscles.

The crico-thyroid muscles, by their contraction, render the vocal cords
more tense by drawing down the anterior portion of the thyroid cartilage
and approximating it to the cricoid, and at the same time tilting the poste-
rior portion of the cricoid and arytenoid cartilages backward.

The thyro-aryteitoid, by their contraction, relax the vocal cords by draw-
ing the arytenoid cartilage forward and the thyroid backward.

The posterior crico-arytenoid muscles, by their contraction, rotate the
arytenoid cartilages outward and thus separate the vocal cords and enlarge
the aperture of the glottis. They principally aid the respiratory move-
ments during inspiration.

The lateral cj'ico-arytenoid muscles are antagonistic to the former, and
by their contraction rotate the arytenoid cartilages so as to approximate the
vocal cords and constrict the glottis.

The arytenoid muscle assists in the closure of the aperture of the glottis.

The inferior laryngeal nerve animates all the muscles of the larynx, with
the exception of the cricothyroid.

Movements of the Vocal Cords. — During respiration the movements
of the vocal cords differ from those occurring during the production of voice.

At each inspiration the true vocal cords are widely separated, and the
aperture of the glottis is enlarged by the action of the crico-arytenoid mus-
cles, which rotate outward the anterior angle of the base of the arytenoid
cartilages ; at each expiration the larynx becomes passive ; the elasticity of
the vocal cords returns them to their original position, and the air is forced
out by the elasticity of the lungs and the walls of the thorax.

VOICE AND SPEECH. 247

Phonation. — As soon as phonation is about to be accomplished, a marked
change in the glottis is noticed with the aid of the laryngoscope. The true
vocal cords suddenly become approximated and are made parallel, giving
to the glottis the appearance of a narrow slit, the edges of which are capa-
ble of vibrating accurately and rapidly ; at the same time their tension is
much increased.

With the vocal cords thus prepared, the expiratory muscles force the
column of air into the lungs and trachea through the glottis, throwing the
edges of the cords into vibration.

The pitch of sounds depends upon the extent to which the vocal cords
are made tense and the length of the aperture through which the air passes.
In the production of sounds of a high pitch, the tension of the vocal
cords becomes very marked and the glottis diminished in length. When
sounds having a low pitch are emitted from the larynx, the vocal cords are
less tense and their vibrations are large and loose.

The quality of voice depends upon the length, size, and thickness of the
cords, and upon the size, form, and construction of the trachea, the larynx,
and the resonant cavities of the pharynx, nose, and mouth.

The compass of the voice comprehends from two to three octaves. The
range is different in the two sexes, the lowest note of the male being about
one octave lower than the lowest note of the female ; while the highest
note of the male is an octave less than the highest note of the female.

The varieties of voice — e. g., bass, baritone, tenor, contralto, mezzo-
soprano, and soprano — are due to the length of the vocal cords, being
longer when the voice has a low pitch, and shorter when it has a high
pitch.

Speech is the faculty of expressing ideas by means of combinations of
sounds, in obedience to the dictates ot the cerebrum.

Articulate saunds may be divided into vowels and consonants. The vowe
sounds, a, e, i, o, u, are produced in the larynx by the vocal cords. The
consonant sounds are produced in the air-passages above the larynx by an
interruption of the current of air by the lips, tongue, and teeth ; the conso-
nants may be divided into :

1. Mutes, b, d, k,p, t,'c,g.

2. Dentals, d,J, s, t, z.

3. Nasals, m, n, ng.

4. Labials, b,p,f, v, m.

5. Gutturals, k, g, c, and g hard

6. Liquids, /, m, n, r.

EMBRYOLOGY.

Reproduction is the function by which the species is preserved ; it is
accomplished by the organs of generation in the two sexes. Embryology
is the science which investigates the successive stages in the development
of the embryo.

GENERATIVE ORGANS OF THE FEMALE.

The generative organs of the female consist of the ovaries, Fallo-
pian tubes, uterus, and vagina.

The ovaries are two small, ovoid, flattened bodies, measuring \yz inches
in length and ^f of an inch in width ; they are situated in the cavity of the
pelvis, and are imbedded in the posterior layer of the broad ligament ; at-
tached to the uterus by a round ligament, and to the extremities of the Fal-
lopian tubes by the fimbriae. The ovary consists of an external membrane
o fibrous tissue, the cortical portion, in which are embedded the Graafian
vesicles, and an internal portion, the stroma, containing blood-vessels.

The Graafian vesicles are exceedingly numerous, but are situated only
in the cortical portion. Although the ovary contains the vesicles from the
period of birth, it is only at puberty that they attain their full development.
From this time onward to the catamenial period there is a constant growth
and maturation of the Graafian vesicles. They consist of an external in-
vestment, composed of fibrous tissues and blood-vessels, in the interior of
which is a layer of cells forming the membrana granulosa ; at its lower
portion there is an accumulation of cells, the proligerous disc, in which the
ovum is contained. The cavity of the vesicle contains a slightly yellowish
alkaline, albuminous fluid.

The ovum is a globular body, measuring about T|^ of an inch in
diameter : it consists of an external investing membrane, the vitelline mem-
brane ; a central granular substance, the vitellus, or yolk ; a nucleus, the
germinal vesicle, in the interior of which is imbedded the nucleolus, or
germinal spot.

The Fallopian tubes are about four inches in length, and extend out-
ward from the upper angles of the uterus, between the folds of the broad

248

EMBRYOLOGY. 249

ligaments, and terminate in a fringed extremity which is attached by one
of the fringes to the ovary. They consist of three coats :

1. The external, or peritoneal.

2. Middle, or muscular, the fibers of which are arranged in a circular or
longitudinal direction.

3. Internal, or mucous, covered with ciliated epithelial cells, which are
always waving from the ovary toward the uterus.

The uterus is pyriform in shape, and may be divided into a body and
neck ; it measures about three inches in length and two inches in breadth
in the unimpregnated state. At the lower extremity of the neck is the os
externum ; at the junction of the neck with the body is a constriction, the
os internum. The cavity of the uterus is triangular in shape, the walls of
the triangle being almost in contact.

The walls of the uterus are made up of several layers of non-striated
muscle-fibers, covered externally by peritoneum, and lined internally by
mucous membrane, containing numerous tubular glands, and covered by
ciliated epithelial cells.

The vagina is a membranous canal, from five to six inches in length,
situated between the rectum and bladder. It extends obliquely upward
from the surface, almost to the brim of the pelvis, and embraces at its upper
extremity the neck of the uterus.

Discharge of the Ovum. — As the Graafian vesicle matures it increases
in size, from an augmentation of its liquid contents, and approaches the
surface of the ovary, where it forms a projection, measuring from %
to % of an inch. The maturation of the vesicle occurs periodically,
about every twenty-eight days, and is attended by the phenomena of men-
struation. During this period of active congestion of the reproductive
organs the Graafian vesicle ruptures, the ovum and liquid contents escape,
and are caught by the fimbriated extremity of the Fallopian tube, which
has adapted itself to the posterior surface of the ovary. The passage of
the ovum through the Fallopian tube into the uterus occupies from ten to
fourteen days, and is accomplished by muscular contraction and by the
action of the ciliated epithelium.

Menstruation is a periodic discharge of blood from the mucous mem-
brane of the uterus, due to a fatty degeneration of the small blood-vessels.
Under the pressure of an increased amount of blood in the reproductive
organs, attending the process of ovulation, the blood-vessels rupture, and a
hemorrhage takes place into the uterine cavity ; thence it passes into the
17

250

HUMAN PHYSIOLOGY.

vagina. Menstruation lasts from five to six days, and the amount of blood
discharged averages about five ounces.

Corpus Luteum. — For some time previous to the rupture of a Graafian
vesicle it increases in size and becomes vascular ; its walls become thick-
ened from the deposition of a reddish-yellow, glutinous substance, a prod-
uct of cell growth from the proper coat of the follicle and the membrana
granulosa. After the ovum escapes there is usually a small effusion of
blood into the cavity of the follicle, which soon coagulates, loses its color-
ing-matter, and acquires the characteristics of fibrin, but it takes no part in
the formation of the corpus luteum. The walls of the follicle become con-
voluted and vascular, and undergo hypertrophy, until they occupy the whole
of the follicular cavity. At its period of fullest development the corpus
luteum measures 3^ of an inch in length and ]/?, of an inch in depth. In a
few weeks the mass loses its red color and becomes yellow, constituting
the corpus luteum, or yellow body. It then begins to retract and becomes
pale ; and at the end of two months nothing remains but a small cicatrix
upon the surface of the ovary. Such are the changes in the follicle if the
ovum has not been impregnated.

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 unimpreg-
nated and pregnant condition is expressed in the following table by Dalton :

Corpus Luteum of Menstruation. Corpus Luteum of Pregnancy.

At the end of
three weeks.
One month.

Two months.

Four months.

Six months.

Nine months.

Three quarters of an inch in diameter ; central qlot red-
dish ; convoluted wall pale.

Smaller ; convoluted
wall bright yellow ; clot
still reddish.

Reduced to the condi-
tion of an insignificant
cicatrix.

Absent
able.

Absent.

Absent.

or unnotice-

Larger ; convoluted wall
bright yellow ; clot still reddish.

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 radiat-
ing cicatrix ; external wall toler-
ably thick and convoluted, but
without any bright yellow color.

EMBRYOLOGY. 251

GENERATIVE ORGANS OF THE MALE.

The generative organs of the male consist of the testicles, vasa
deferentia, vesiculce seminales, and penis.

The testicles, the essential organs of reproduction in the male, are two
oblong glands, about 1]/, inches in length, compressed from side to side,
and situated in the cavity of the scrotum.

The proper coat of the testicle, the tunica albuginea, is a white, fibrous
structure, about ^ of an inch in thickness ; after enveloping the testicle,
it is reflected into its interior at the posterior border, and forms a vertical
process, the mediastinum testis, from which septa are given off, dividing
the testicle into lobules.

The substance of the testicle is made up of the seminiferous tubules, which
exist to the number of 840 ; they are exceedingly convoluted, and when
unravelled are about thirty inches in length. As they pass toward the apices
of the lobules, they become less convoluted, and terminate in from twenty
to thirty straight ducts, the vasa recta, which pass upward through the
mediastinum and constitute the rete testis. At the upper part of the medi-
astinum the lobules unite to form from nine to thirty small ducts, the vasa
efferentia, which become convoluted and form the globus major of the
epididymis ; the continuation of the tubes downward behind the testicle
and a second convolution constitutes the body and globus niinor.

The seminal tubule consists of a basement membrane lined by granular
nucleated epithelium.

The vas deferens, the excretory duct of the testicle, is about two feet in
length, and may be traced upward from the epididymis 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 two
inches in length, situated on the inner surface of the bladder.

They have an external fibrous coat, a middle muscular coat, and an in-
ternal mucous coat, covered by epithelium, which secretes a mucous fluid.
The vesiculae seminales serve as reservoirs, in which the seminal fluid is
temporarily stored up.

The ejaculatory duct, about ^ of an inch in length, opens into the
urethra, and is formed by the union of the vasa deferentia and the ducts of
the vesiculae seminales.

The prostate gland surrounds the posterior extremity of the urethra,

252 HUMAN PHYSIOLOGY.

and opens into it by from twenty to thirty openings, the orifices of Xhz pros-
tatic tubules. The gland secretes a fluid which forms part of the semen and
assists in maintaining the vitality of the spermatozoa.

Semen is a complex fluid, made up of the secretions from the testicles,
the vesiculse seminales, the prostatic and urethral glands. It is grayish-
white in color, mucilaginous in consistence, of a characteristic odor, and
somewhat heavier than water. From half a dram to a dram is ejaculated
at each orgasm.

The spermatozoa are peculiar anatomic elements, developed within
the seminal tubules, and possess the power of spontaneous movement.
The spermatozoa consist of a conoid head and a long, filamentous tail,
which is in continuous and active motion ; so long as they remain in the
vas deferens they are cpiiescent, but when free to move in the fluid of the
vesicula; seminales, they become very active.

Origin. — The spermatozoa appear at the age of puberty, and are then
constantly formed until an advanced age. They are developed from the
nuclei of large, round cells contained in the anterior of the seminal tubules,
as many as fifteen to twenty developing in a single cell.

When the spermatozoa are introduced into the vagina, they pass readily
into the uterus and through the Fallopian tubes toward the ovaries, where
they remain and retain their vitality for a period of from eight to ten days.

Fecundation is the union of the spermatozoa with the ovum during its
passage toward the uterus, and usually takes place in the Fallopian tube,
just outside of the womb. After floating around the ovum in an active
manner, they penetrate the vitelline membrane, pass into the interior of the
vitellus, where they lose their vitality, and, along with the germinal vesicle,
entirely disappear.

DEVELOPMENT OF ACCESSORY STRUCTURES.

Segmentation of the Vitellus. — After the disappearance of the sper-
matozoa and the germinal vesicle there remains a transparent, granular,
albuminous substance, in the center of which a new nucleus soon appears ;
this constitutes the parent cells, and is the first stage in the development of
the new being.

Following this, the vitellus undergoes segmentation ; a constriction ap-
pears on the opposite side of the vitellus, which gradually deepens, until the
yolk is divided into two segments, each of which has a distinct nucleus and

EMBRYOLOGY. 253

nucleolus ; these two segments undergo a further division into four, the
four into eight, the eight into others, and so on, until the entire vitellus is
divided into a great number of cells, each of which contains a nucleus and
a nucleolus.

The peripheral cells of this "mulberry mass" then arrange themselves
so as to form a membrane, and, as they are subjected to mutual pressure,
assume a polyhedral shape, which gives to the membrane a mosaic appear-
ance. The central part of the vitellus becomes filled with a clear fluid. A
second membrane shortly appears within the first, and the two together
constitute the external and internal blastodermic membranes.

Germinal Area. — At about this period there is an accumulation of cells
at a certain spot upon the surface of the blastodermic membranes, which
marks the position of the future embryo. This spot, at first circular, soon
becomes elongated, and forms the primitive trace, around which is a clear
space, the area pellucida, which is itself surrounded by a darker region,
the area opaca.

The primitive trace soon disappears, and the area pellucida becomes
guitar-shaped ; a new groove, the medullary groove, is now formed, which
develops from before backward, and becomes the neural canal.

Blastodermic Membranes. — The embryo, at this period, consists of
three layers — viz., the external and the internal blastodermic membranes
and a middle membrane formed by a genesis of cells from their internal
surfaces. These layers are known as the epiblast, mesoblast, and hypoblast.

The epiblast gives rise to the central nervous system, the epidermis of the
skin and its appendages, and the primitive kidneys.

The mesoblast gives rise to the dermis, muscles, bones, nerves, blood-
vessels, sympathetic nervous system, connective tissue, the urinary and re-
productive 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 epithelium
of the respiratory tract.

Dorsal Laminae. — As development advances, the true medullary
groove deepens, and there arise two longitudinal elevations of the epiblast,
— the dorsal lamina, one on either side of the groove, — which grow up,
arch over, and unite so as to form a closed tube, the primitive central
nervous system.

The chorda dorsalis is a cylindric rod running almost throughout the
entire length of the embryo. It is formed by an aggregation of mesoblastic
cells, and is situated immediately beneath the medullary groove.

254 HUMAN PHYSIOLOGY.

Primitive Vertebrae. — On either side of the neural canal the cells of
the mesoblast undergo a longitudinal thickening, which develops and ex-
tends around the neural canal and the chorda dorsalis, and forms the arches
and bodies of the vertebrae. They become divided transversely into four-
sided segments.

The mesoblast now separates into two layers : the external, joining with
the epiblast, forms the somatopleura ; the internal, joining with the hypo-
blast, forms the splanchnapleura ; the space between them constitutes the
pleuro-fieritoneal cavity.

Visceral Laminae. — The walls of the pleuro-peritoneal cavity are
formed by a downward prolongation of the somatopleura (the visceral
I a mince), which, as they extend around in front, pinch off a portion of the
yolk-sac (formed by the splanchnopleura), which becomes the primitive
alimentary canal ; the lower portion, remaining outside of the body cavity,
forms the umbilical vesicle, which after a time disappears.

Formation of Fetal Membranes. — The amnion appears shortly after
the embryo begins to develop, and is formed by folds of the epiblast and
external layer of the mesoblast, rising up in front and behind and on each
side ; these amniotic folds gradually extend over the back of the embryo
to a certain point, where they coalesce and inclose a cavity — the amniotic
cavity. The membranous partition between the folds disappears, and the
outer layer recedes and becomes blended with the vitelline membrane, con-
stituting the chorion — the external covering of the embryo.

The Allantois. — As the amnion develops, there grows out from the
posterior portion of the alimentary canal a pouch, or diverticulum (the
allantois), which carries blood-vessels derived from the intestinal circula-
tion. As it gradually enlarges it becomes more vascular, and inserts itself
between the two layers of the amnion, coming into intimate contact with
the external layer. Finally, from increased growth, it completely surrounds
the embryo, and its edges become fused together.

In the bird the allantois is a respiratory organ, absorbing oxygen and
exhaling carbonic acid ; it also absorbs nutritive matter from the interior of
the egg.

Amniotic Fluid. — The amnion, when first formed, is in close contact
with the surface of the ovum ; but it soon enlarges, and becomes filled
with a clear, transparent fluid, containing albumin, glucose, fatty matters,
urea, and inorganic salts. It increases in amount up to the latter period
of gestation, when it amounts to about two pints. In the space between

EMBRYOLOGY. 255

the amnion and allantois is a gelatinous material, which is encroached
upon and finally disappears as the amnion and allantois come in contact, at
about the fifth month.

The chorion, the external investment of the embryo, is formed by a
fusion of the original vitelline membrane, the external layer of the amnion,
and the allantois. The external surface now becomes covered with villous
processes, which increase in number and size by the continual budding
and growth of club-shaped processes from the main stem, and give to the
chorion a shaggy appearance. They consist of a homogeneous granular
matter, and are penetrated by branches of the blood-vessels derived from
the aorta.

The presence of villous processes in the uterine cavity is proof positive
of the previous existence of a fetus. They are characteristic of the chorion,
and are found under no other circumstances.

At about the end of the second month the villosities begin to atrophy
and disappear from the surface of the chorion, with the exception of those
situated at the points of entrance of the fetal blood-vessels, which occupy
about one third of its surface, where they continue to grow longer, become
more vascular, and ultimately assist in the formation of the placenta ; the
remaining two thirds of the surface loses its villi and blood-vessels and
becomes a simple membrane.

The umbilical cord connects the fetus with that portion of the chorion
which forms the fetal side of the placenta. It is a process of the allantois,
and contains two arteries and a vein, which have a more or less spiral
direction. It appears at the end of the first month, and gradually increases
in length until, at the end of gestation, it measures about twenty inches.
The cord is also surrounded by a process of the amnion.

Development of the Decidual Membrane. — The interior of the
uterus is lined by a thin, delicate mucous membrane, in which are embedded
immense numbers of tubules, terminating in blind extremities — the uterine
tubules. At each period of menstruation the mucous membrane becomes
thickened and vascular, which condition, however, disappears after the
usual menstrual discharge. When the ovum becomes fecundated, the
mucous membrane takes on an increased growth, becomes more hypertro-
phied and vascular, sends up little processes or elevations from its surface,
and constitutes the decidtia vera.

As the ovum passes from the Fallopian tube into the interior of the
uterus, the primitive vitelline membrane, covered with villosities, becomes
entangled with the processes of the mucous membrane. A portion of the

256 HUMAN PHYSIOLOGY.

decidua vera then grows up on all sides and incloses the ovum, forming the
decidua refiexa, while the villous processes of the chorion insert themselves
into the uterine tubules and in the mucous membrane between them.

As development advances, the decidua refiexa increases in size, and at
about the end of the fourth month comes in contact with the decidua vera,
with which it is ultimately fused.

The Placenta. — Of all the embryonic structures, the placenta is the
most important. It is formed in the third month, and then increases in
size until the seventh month, when a retrogressive metamorphosis takes
place until its separation during labor, at which time it is of an oval or
rounded shape, and measures from seven to nine inches in length, six to
eight inches in breadth, and weighs from fifteen to twenty ounces. It is
most frequently situated at the upper and posterior part of the inner surface
of the uterus.

The placenta consists of two portions, a fetal and a maternal.

The fetal portion is formed by the villi of the chorion, which, by devel-
oping, rapidly increase in size and number. They become branched and
penetrate the uterine tubules, which enlarge and receive their many rami-
fications. The capillary blood-vessels in the anterior of the villi also
enlarge and freely anastomose with one another.

The maternal portion is formed from that part of the hypertrophied and
vascular decidual membrane between the ovum and the uterus, the decidua
serotina. As the placenta increases in size, the maternal blood-vessels
around the tubules become more and more numerous, and gradually fuse
together, forming great lakes, which constitute sinuses in the walls of the
uterus.

As the terminal period of gestation approaches, the villi extend deeper
into the decidua, while the sinuses in the maternal portion become larger
and extend further into the chorion. Finally, from excessive development of
the blood-vessels, the structures between them disappear, and as their walls
come in contact they fuse together, so that, ultimately, the maternal and
fetal blood are separated only by a thin layer of a homogeneous substance.
When fully formed, the placenta consists principally of blood-vessels inter-
lacing in every direction. The blood of the mother passes from the uterine
vessels into the lake surrounding the villi ; the blood from the fetus flows
from the umbilical arteries into the interior of the villi ; but there is not at
any time an intermingling of blood, the two being separated by a delicate
membrane formed by a fusion of the walls of the blood-vessels and the
walls of the villi and uterine sinuses.

EMBRYOLOGY. 257

The function of the placenta, besides nutrition, is that of a respiratory
organ, permitting the oxygen of the maternal blood to pass by osmosis
through the delicate placental membrane into the blood of the fetus ; at
the same time permitting the carbonic acid and other waste products, the
result of nutritive changes in the fetus, to pass into the maternal blood, and
so to be carried to the various eliminating organs.

Through the placenta also passes all the nutritious materials of the
maternal blood which are essential to the development of the embryo.

At about the middle of gestation there develops beneath the decidual
membrane a new mucous membrane, destined to perform the functions of
the old when it is extruded from the womb, along with the other embryonic
structures, during parturition.

DEVELOPMENT OF THE EMBRYO.

Nervous System. — The cerebro-spinal axis is formed within the
medullary canal by the development of cells from its inner surfaces, which,
as they increase, fill up the canal, and there remains only the central canal
of the cord. The external surface gives rise to the dura mater and pia
mater. The neural canal thus formed is a tubular membrane ; it terminates
posteriorly in an oval dilatation, and anteriorly in a bulbous extremity,
which soon becomes partially contracted, and forms the anterior, middle,
and posterior cerebral vesicles, from which are ultimately developed the cere-
brum, the corpora quadrigemina, and the medulla oblongata, respectively.

The anterior vesicle soon subdivides into two secondary vesicles, the
larger of which becomes the hemispheres, the smaller the optic thalami;
the posterior vesicle also divides into two, the anterior becoming the cere-
bellum, the posterior the pons Varolii and medulla oblongata.

About the seventh week the straight chain of cerebral vesicles becomes
curved from behind forward and forms three prominent angles. As devel-
opment advances, the relative size of the encephalic masses changes. The
cerebrum, developing more rapidly than the posterior portion of the brain,
soon grows backward and arches over the optic thalami and the tubercula
quadrigemina ; the cerebellum overlaps the medulla oblongata.

The surface of the cerebral hemispheres is at first smooth, but at about
the fourth month begins to be marked by the future fissures and convolu-
tions.

The eye is formed by a little bud projecting from the side of the anterior
vesicle. It is at first hollow, but becomes lined with nervous matter, form-

258 HUMAN PHYSIOLOGY.

ing the optic nerve and retina ; the remainder of the cavity is occupied by
the vitreous body. The anterior portion of the pouch becomes invaginated
and receives the crystalline lens, which is a product of the epiblast, as is
also the cornea. The iris appears as a circular membrane without a cen-
tral aperture, about the seventh week ; the eyelids are formed between the
second and third months.

The internal ear is developed from the auditory vesicle, budding from
the third cerebral vesicle ; the membranous vestibule appears first, and
from it diverticula are given off, which become the semicircular canals and
the cochlea.

The cavity of the tympanum, the Eustachian tube, and the external
auditory canal are the remains of the first branchial cleft, the cavity of this
cleft being subdivided into the tympanum and external auditory meatus by
the membrana tympani.

The Skeleton. — The chorda dorsalis, the primitive part of the vertebral
column, is a cartilaginous rod situated beneath the medullary groove. It
is a temporary structure, and disappears as the true bony vertebrae develop.
On either side are the quadrate masses of the mesoblast, the primitive ver-
tebrae, which send processes upward and around the medullary groove, and
downward and around the chorda dorsalis, forming in these situations the
arches and bodies of the future vertebrae.

More externally the outer layers of the mesoblast and epiblast arch down-
ward and forward, forming the ventral laminae, in which develop the
muscles and bones of the abdominal walls.

The trtie cranium is an anterior development of the vertebral column,
and consists of the occipital, parietal, and frontal segments, which corre-
spond to the three cerebral vesicles. The base of the cranium consists, at
this period, of a cartilaginous rod on either side of the anterior extremity
of the chorda dorsalis, in which three centers of ossification appear, the
basi-occipital, the basisphenoid, and the presphenoid. They ultimately
develop into the basilar process of the occipital bone and the body of the
sphenoid.

The entire skeleton is at first either membranous or cartilaginous. At
the beginning of the second month centers of ossification appear in the jaws
and clavicle ; as development advances the ossific points in all the future
bones extend, until ossification is completed.

The limbs develop from four little buds projecting from the sides of the
embryo, which, as they increase in length, separate into the thigh, leg, and

EMBRYOLOGY. 259

foot, and the arm, forearm, and hand ; the extremities of the limbs undergo
subdivision, to form the fingers and toes.

Face and Visceral Arches. — In the facial and cervical regions the
visceral laminae send up three processes, the visceral arches, separated by
clefts, the visceral clefts.

The first, or the mandibular arches, unite in the median line to form
the lower jaw, and superiorly form the malleus. A process jutting from
its base grows forward, unites with the frontonasal process growing from
above, and forms the upper jaw. When the superior maxillary processes
fail to unite there results the cleft-palate deformity ; if the integument also
fails to unite, there results the hare-lip deformity. The space above the
mandibular arch becomes the mouth.

The second arch develops the incus and stapes bones, the styloid process
and ligament, and the lesser cornu of the hyoid bone. The cleft between
the first and second arches partially closes up, but there remains an opening
at the side, which becomes the Eustachian tube, tympanic cavity, and ex-
ternal auditory meatus.

The third arch develops the body and greater cornu of the hyoid bone.

Alimentary Canal and Its Appendages. — The alimentary canal is
formed by a pinching-off of the yolk-sac by the visceral plates as they grow
downward and forward. It consists of three distinct portions — the fore gut,
the hind gut, and the central part, which communicates for some time with
the yolk-sac. It is at first a straight tube, closed at both extremities, lying
just beneath the vertebral column. The canal gradually increases in length
and becomes more or less convoluted ; at its anterior portion two pouches
appear, which become the cardiac and pyloric extremities of the stomach,
At about the seventh week the inferior extremity of the intestine is brought
into communication with the exterior by an opening, the anus. Anteriorly
the mouth and pharynx are formed by an involution of epiblast, which
deepens until it communicates with the fore gut.

Th liver appears as a slight protrusion from the sides of the alimentary
canal, about the end of the first month ; it grows very rapidly, attains a
large size, and almost fills up the abdominal cavity. The hepatic cells are
derived from the intestinal epithelium, the vessels and connective tissue
from the mesoblast.

The pancreas is formed by the hypoblastic membrane. It originates in
two small ducts budding from the duodenum, which divide and subdivide,
and develop the glandular structure.

The lungs are developed from the anterior part of the esophagus. At

260 HUMAN PHYSIOLOGY.

first a small bud appears, which, as it lengthens, divides into two branches ;
secondary and tertiary processes are given off from these, which form the
bronchial tubes and air-cells. The lungs originally extended into the ab-
dominal cavity, but became confined to the thorax by the development of
the diaphragm.

The bladder is formed by a dilatation of that portion of the allantois
remaining within the abdominal cavity. It is at first pear-shaped and
communicates with the intestine, but later becomes separated and opens
exteriorly by the urethra. It is attached to the abdominal walls by a
rounded cord — the urachus, the remains of a portion of the allantois.

Genito-urinary Apparatus. — The Wolffian bodies appear about the
thirteenth day, as long, hollow tubes running along each side of the primi-
tive vertebral column. They are temporary structures, and are sometimes
called the primordial kidneys. The Wolffian bodies consist of tubules
which run transversely and are lined with epithelium ; internally they be-
come invaginated to receive tufts of blood-vessels ; externally they open
into a common excretory duct, the dud of the Wolffian body, which unites
with the duct of the opposite body and empties into the intestinal canal
at a point opposite the allantois. On the outer side of the Wolffian body
there appears another duct, the duct of Miiller, which also opens into the
intestine.

Behind the Wolffian bodies are developed the structures which become
either the ovaries or testicles. In the development of the female the
Wolffian bodies and their ducts disappear ; the extremities of the Mullerian
ducts dilate and form the fimbriated extremity of the Fallopian tubes, while
the lower portions coalesce to form the body of the uterus and vagina,
which now separate themselves from the intestine.

In the development of the male the Mullerian ducts atrophy, and the
ducts of the Wolffian body ultimately form the epididymis and vas defer-
ens. About the seventh month the testicles begin to descend, and by the
ninth month have passed through the abdominal ring into the scrotum.

The kidneys are developed out of the Wolffian bodies. They consist of
little pyramidal lobules, composed of tubules which open at the apex into
the pelvis. As they pass outward they become convoluted and cup-shaped
at their extremities, receive a tuft of blood-vessels, and form the Malpig-
hian bodies.

The ureters are developed from the kidneys and pass downward to be
connected with the bladder.

The circulatory apparatus assumes three forms at different periods of

EMBRYOLOGY. 261

life, all having reference to the manner in which the embryo receives
nutritive matter and is freed of waste products.

The vitelline circulation appears first and absorbs nutritive material
from the vitellus. It is formed by blood-vessels which emerge from the
body and ramify over a portion of the vitelline membrane, constituting the
area vasculosa. The heart, lying in the median line, gives off two arches,
which unite to form the abdominal aorta, from which two large arteries
are given off, passing into the vascular area ; the venous blood is returned
by veins which enter the heart. These vessels are known as the omphalo-
mesenteric arteries and veins. The vitelline circulation is of short dura-
tion in mammals, as the supply of nutritive matter in the vitellus soon be-
comes exhausted.

The placental circulation becomes established when the blood-vessels in
the allantois enter the villous processes of the chorion and come into close
relationship with the maternal blood-vessels. The circulation lasts during
the whole of intra-uterine life, but gives way at birth to the adult circula-
tion, the change being made possible by the development of the circulatory
apparatus.

The heart appears as a mass of cells coming off from the anterior por-
tion of the intestine ; its central part liquefies, and pulsations soon begin.
The heart is at first tubular, receiving posteriorly the venous trunks and
giving off anteriorly the arterial trunks. It soon becomes twisted upon
itself, so that the two extremities lie upon the same plane.

The heart now consists of a single auricle and a single ventricle. A
septum, growing from the apex of the ventricle, divides into two cavities,
a right and a left. The auricles also become partly separated by a septum,
which is perforated by the foramen ovale. The arterial trunk becomes
separated, by a partition, into two canals, which become, ultimately, the
aorta and the pulmonary artery. The auricles are separated from the ven-
tricles by incomplete septa, through which the blood passes into the
ventricles.

Arteries. — The aorta arises from the cephalic extremity of the heart and
divides into two branches, which ascend, one on each side of the intestine,
and unite posteriorly to form the main aorta ; posteriorly to these first aortic
arches four others are developed, so that there are five altogether running
along the visceral arches. The two anterior soon disappear. The third
arch becomes the internal carotid and the external carotid ; a part of the
fourth arch, on the right side, becomes the subclavian artery, and the
remainder atrophies and disappears, but on the left side it enlarges and
becomes the permanent aorta ; theji/th arch becomes the pulmonary artery

262 HUMAN PHYSIOLOGY.

on the left side. The communication between the pulmonary artery and
the aorta, the ductus arteriosus, disappears at an early period.

Veins. — The venous system appears first as two short, transverse veins,
the canals of Cuvier, formed by the union of the vertebral veins and the
cardinal veins, which empty into the auricle. The inferior vena cava is
formed, as the kidneys develop, by the union of the renal veins, which, in
a short time, receive branches from the lower extremities. The subclavian
veins join the jugular as the upper extremities develop. The heart descends
in the thorax, and the canals of Cuvier become oblique ; they shortly com-
municate by a transverse duct, which ultimately becomes the left innominate
vein. The left canal of Cuvier atrophies and becomes a fibrous cord. A
transverse branch now appears, which carries the blood from the left cardiac
vein into the right, and becomes the vena azygos minor ; the right cardiac
vein becomes the vena azygos major.

Circulation of Blood in the Fetus. — The blood returning from the
placenta, after having received oxygen and being freed from carbonic acid,
is carried by the umbilical vein to the under surface of the liver ; here a
portion of it passes through the ductus venosus into the ascending vena cava,
while the remainder flows through the liver and passes into the vena cava
by the hepatic veins. When the blood is emptied into the right auricle, it
is directed by the Eustachian valve through the foramen ovale, into the left
auricle, thence into the left ventricle, and so into the aorta and to all parts of
the system. The venous blood returning from the head and upper extremities
is emptied, by the superior vena cava, into the right auricle, from which it
passes into the right ventricle, and thence into the pulmonary artery. Owing
to the condition of the lung only a small portion flows through the pulmo-
nary capillaries, the greater part passing through the ductus arteriosus, which
opens into the aorta at a point below the origin of the carotid and subclavian
arteries. The mixed blood now passes down the aorta to supply the lower
extremities, but a portion of it is directed, by the hypogastric arteries, to
the placenta, to be again oxygenated.

At birth, the placental circulation gives way to the circulation of the
adult. As soon as the child begins to breathe, the lungs expand, blood
flows freely through the pulmonary capillaries, and the ductus arteriosus
begins to contract. The foramen ovale closes about the tenth day. The
umbilical vein, the ductus venosus, and the hypogastric arteries become
impervious in several days, and ultimately form rounded cords.

TABLE OF PHYSIOLOGIC CONSTANTS.

Mean height of male, 5 feet d% inches ; of female, 5 feet 2 inches.
Mean weight of male, 145 pounds ; of female, 121 pounds.
Number of chemic elements in the human body : from 16 to 18.
Number of proximate principles in the human body : about 100.
Amount of water in the body weighing 145 pounds : 109 pounds.
Amount of solids in the body weighing 145 pounds : 36 pounds.
Amount of saliva secreted in 24 hours : about 3}^ pounds.

Function of saliva : converts starch into maltose.

Active principle of saliva : ptyalin.
Amount of gastric juice secreted in 24 hours : from 8 to 14 pounds.

Function of gastric juice : converts albumin into peptone.

Active principles of gastric juice : pepsin and hydrochloric acid.
Duration of digestion : from 3 to 5 hours.
Amount of intestinal juice secreted in 24 hours : about I pound.

Function of intestinal juice : converts cane sugar into dextrose and
levulose ; maltose into dextrose.
Amount of pancreatic juice secreted in 24 hours : about 1% pounds.

Active principles of pancreatic juice : trypsin, amylopsin, and
steapsin.

{I. Splits the neutral fats into fatty acids and glycerin.
2. Converts albumin into peptone.
3. Converts starch into maltose.
Amount of bile poured into the intestines daily : about 2]A pounds.
I. Assists in the emulsification of fats.

t- 2. Stimulates the peristaltic movements.

r unctions : \ r

I 3. Prevents putrefactive changes in the food.

I 4. Promotes the absorption of fat.
Amount of blood in the body : from 16 to 18 pounds.
Size of red corpuscles : -^V 0 °f an inch.
Size of white corpuscles : ^jqtt °f an inch.
Shape of red corpuscles : circular biconcave discs.
Shape of white corpuscles : globular.

Number of red corpuscles in a cubic millimeter of blood (the cubic 03 of
an inch) : 5,000,000.

263

264 "human physiology.

Function of red corpuscles : to carry oxygen from the lungs to the tissues.
Frequency of the heart's pulsation a minute : 72 on the average.
Velocity of the blood movement in the arteries : about 12 inches a

second.
Length of time required for the blood to make an entire circuit of the vas-
cular system : about 20 seconds.
Amount of air passing in and out of the lungs at each respiratory act :

from 20 to 30 cubic inches.
Amount of air that can be taken into the lungs on a forced inspiration :

no cubic inches.
Amount of reserve air in the lungs after an ordinary expiration : 100 cubic

inches.
Amount of residual air always remaining in the lungs : about 100 cubic

inches.
Vital capacity of the lungs : 230 cubic inches.
Entire volume of air passing in and out of the lungs in 24 hours : about

400 cubic feet.
Composition of the air: nitrogen, 79.19 : oxygen, 20.81, in 100 parts.
Amount of oxygen absorbed in 24 hours : 18 cubic feet.
Amount of carbonic acid exhaled in 24 hours : 14 cubic feet.
Temperature of the human body at the surface : 98^° F.
Amount of urine excreted daily : from 40 to 50 ounces.
Amount of urea excreted daily : 512 grains.
Specific gravity of urine : from 1015 to 1025.
Number of spinal nerves : 31 pairs.
Number of roots of origin : two ; 1st, anterior, efferent ; 2d, posterior,

afferent.
Rate of transmission of nerve force : about 100 feet a second.
Number of cranial nerves : 12 pairs.

1. Olfactory, or first pair.

2. Optic, or second pair.

3. Auditory, or eighth pair.

4. Chorda tympani for anterior two thirds
of tongue.

5. Branches of glasso-pharyngeal, or eighth
pair, for posterior one third of tongue.

Motor nerves to eyeball and accessory structures : motor oculi, or

third pair ; pathetic, or fourth pair ; abducens, or sixth pair.
Motor nerves to facial muscles : portio dura, facial, or seventh pair.
Motor nerve to tongue : hypoglossal, or twelfth pair.

Nerves of special sense :

TABLE OF PHYSIOLOGIC CONSTANTS. 265

Motor nerve to laryngeal muscles : spinal accessor)', or eleventh pair.
Sensory nerve of the face : trifacial, or fifth pair.
Sensor}' nerve of the pharynx : glossopharyngeal, or ninth pair.
Sensory nerves of the lungs, stomach, etc.: pneumogastric, or tenth pair.
Length of spinal cord : 16 to 18 inches ; weight, \yz ounces.
Point of decussation of motor fibers : at the medulla oblongata.
Point of decussation of sensory fibers : throughout the spinal cord.
Function of anterolateral column of spinal cord : transmit motor im-
pulses from' the brain to the muscles.
Function of the posterior columns : assist in the coordination of mus-
cular movements.
Function of the medulla oblongata : controls the functions of insaliva-

tion, mastication, deglutition, respiration, circulation, etc.
Function of the cerebellum : center for the coordination of muscular

movement.
Function of the cerebrum : center for intelligence, reason, and will.
Center for articulate language : third frontal convolution on the left side

of cerebrum.
Number of coats to the eye : three : 1st, cornea and sclerotic ; 2d, choroid ;

3d, retina.
Function of iris : regulates the amount of light entering the eye.
Function of crystalline lens : refracts the rays of light so as to form an

image on the retina.
Function of retina : receives the impressions of light.
Function of membrana tympani : receives and transmits waves of sound

to internal ear.
Function of Eustachian tube : regulates the passage of air into and from

the middle ear.
Function of semicircular canals : assist in maintaining the equipoise of

the body.
Function of the cochlea : appreciates the shades and combinations of

musical tones.
Size of human ovum : j^ of an inch in diameter.
Size of spermatozoa : j-^jq of an inch in length.
Function of the placenta : acts as a respiratory and digestive organ for

the fetus.
Duration of pregnancy : 280 days.

18

TABLE SHOWING RELATION OF WEIGHTS AND
MEASURES OF THE METRIC SYSTEM TO APPROX-
IMATE WEIGHTS AND MEASURES OF THE U. S.

One Myriameter
One Kilometer
One Hectometer
One Decameter

One Meter

One Decimeter
One Centimeter

One Millimeter =

One Myriagram
One Kilogram
One Hectogram
One Decagram

One Gram

One Decigram

One Centigram

One Milligram

One Myrialiter
One Kiloliter
One Hectoliter

One Decaliter

One Liter

One Deciliter

One Centiliter

One Milliliter

MEASURES OF LENGTH.
=: 10,000 meters =

= 1,000 "

= IOO '; :

= IO " :

{the ten-millionth part of a \
quarter of the Meridian of > ■
the Earth J

= the tenth part of one meter
_ j the one-hundredth part oO
_ \ one meter J '

f the one- thousandth part)
\ of one meter J

WEIGHTS.
= 10,000 grams
= 1,000 ".
= 100 "

= 10

_ ( the weight of a cubic cen
_ \ timeter of water at 40 C
== the tenth part of a gram
_ f the hundredth part of one
~\gram

_ f the thousandth part of one ")
~ \ gram j

MEASURES OF CAPACITY

{10 cubic Meters or the^
measures of I o Milliers of j- =
water J

32,800 feet.
: 3,280 "
328 "
32.80 "

: 39-368 inches.

: 3.936

: °-393 (I) inch.
: 0-039 (25) "

z 26^ pounds Troy.

(« <<

2%

2)% ounces "

2X/Z drams "

J5.434 grains.

1-543 (iK) "■
0.154(1^) grain.

j I cubic Meter or the meas- ")
\ ure of I Miller of water j

{100 cubic Decimeters or \
the measure of I Quintal >-
of water J

{io cubic Decimeters or
the measure of 1 Myria-
gram of water
1 cubic Decimeter or the ^
measure of I Kilogram >
of water

{100 cubic Centimeters or
the measure of I Hecto-
gram of water
!io cubic Centimeters or
the measure of 1 Deca-
gram of water
{I cubic Centimeter or the
measure of I Gram of
water

: O.OI5 (^) «

2,600 gallons.
260
26 "

2.6 "
2.1 pints.
3.3 ounces.

2.7 drams.
16.2 minims.

INDEX.

A BDUCENS NERVE,
•**■ Aberration, chromatic,

-, spheric,

Absorption,

by lacteals,

by blood-vessels

of oxygen in respiration, . . .

Accommodation of the eye, . .
Adipose tissue, uses of, in the body, .
Adrenal bodies, . . ....

Adult circulation, establishment of, at
birth, ... ......

Air, atmospheric, composition of, . .
, amount exchanged in respira-

changes in, during respiration,

Albumin, uses of, in the body, . .

Albuminoid substances,

Alcohol, action of, . . ....

Alimentary canal, development of, .

principles, classification of, . .

, albuminous principles, . . .

, saccharine principles, ....

, oleaginous principles, . . .

, inorganic principles . . .

Allantois, development and function

of,

Amnion, formation of,

Animal heat,

Anterior columns of spinal cord, . . .

Area, germinal,

Areo'ar tissue,

Arteries, properties of,

Articulations,

-, classification of,

>AGE

187
235
235
in

115
"5
141

233

4i

154

262
140

Asphyxia,
Astigmatism . . .
Axis, cerebro-spinal, . .
cylinder of nerves.

139
140

90
259

254
254
143
182

253

41

131

46

47
142

234
171

73

PAGE

Blood pressure, 132

Bone, structure of, 44

Burdach, column of, 174

CANALS OF CUVIER, ....
Capillary blood-vessels,, . . .

Capsule, internal,

, external,

Cardiac cycle,

Cartilage,

Caudate nucleus,

Cells, structure of,

, manifestation of life by,.

of anterior horns of gray matter,

Center for articulate language, ....

Cerebellum,

-, forced movements of,

"DILE, no

■^ Bladder, urinary-, 155

Blastodermic membranes, 253

Blood, 119

, composition of, plasma, . . . 120

, coagulation of. 123

, coloring matter of,. . . 121

, changes in, during respiration 142

, circulation of, 125

, rapidity of flow in arteries, . . 133

, rapidity of flow in capillaries, 133

, corpuscles, 121

, origin of, 122

Cerebral vesicles of embryo,

Cerebrum,

, fissures and convolutions, . .

, functions of,

, localization of functions, . . .

, motor area of,

, special centers of, . .

Chemic composition of human body, .

Chorda dorsalis, ...

tympani nerve, course and func-
tion of,

Chorion,

Chyle, . .

Ciliary muscle,

Circulation of blood,

Claustrum,

Cochlea,

Columns of spinal cord, . . . .

Connective tissues, physiologic prop-
erties of, . .

Corium,

Corpora Wolffiana,

quadrigemina, . .

Corpus luteum,

striatum, .

Corti, organ of,

Cranial nerves,

Crura cerebri,

Crystalline lens,

262

133
204
204
128
43
204

33
35
173
216
205
206

257
207
208
213
214
214
215
15
258

191

255
117

234
125
204
243

174

45
167
260
203
250
204
244
183
202
230

T-\ECIDUAL MEMBRANE, .

Decussation of motor and sen-
sory fibers, 175

Deglutition, ... _ 99

, nervous circle of, 199

267

268

INDEX.

PAGE

Development of accessory structures

of embryo 252

Digestion, . 95

Ductuslarteriosus, 262

venosus, . . 262

fTAR, 237

■*-' Electrotonus, 85

Embryo, development of, 257

Embryology, 248

Endolymph, 244

Epididymis, , . 251

Eustachian tube, 239

Excretion, 155

Eye, 225

, refracting apparatus of, . 231

, blind spot of, 236

"FACIAL NERVE, 189

■*■ paralysis, symptoms of, . 190

Fallopian tubes, 24^

Fat, uses of, in the body, 89

Feces,' 111

Female organs of generation, .... 247

Fissures and convolutions of brain, . 208

Foods and dietetics, 86

, animal, 93

, vegetable, 94

, cereal, 94

, percentage, composition of, . 94

, daily amount required, . 91

, albuminous principles of, . . 88

, saccharine principles of, ... 89

, oleaginous principles of, . . 89

, inorganic principles of, . . . 89

Fovea centralis, 234

f*ALVANIC CURRENTS,

^-* effect on nerves, 85

Ganglia, .... 219

, ophthalmic, 219

, Gasserian, .... 219

, spheno-palatine, 219

. otic, 219

, submaxillary, 219

, semilunar, ... . 220

Gases of the intestine in

Gastric digestion, 101

juice, 101

, action of, . . 105

Generation, male organs of, 251

, female organs of, 248

Globules of the blood, 121

of the lymph 119

Glomeruli of the kidneys, 155

Glosso-pharyngeal nerve, . . . 192

Glottis, respiratory movements of, . . 138

Glycogen, . . .... 165

Glycogenic function of the liver, . 166

Goll, column of, . . . .... 174

Graafian follicles, 247

HAIR' l69

■*■■*■ Hearing, sense of, .... 237

Heart, 125

PAGE

Heart, valves of, 128

, sounds of, 129

— — — , influence of pneumogastric

nerve upon, 131

, ganglia of, . . . .... 130

, force exerted by left ventricle, 130

, work done by, 130

, course of blood through, . . . 126

, influence of nervous system

upon, 131

Hemoglobin, 121

Hyaloid membrane, 230

Hypermetropia, 235

Hypoglossal nerve, 196

Hypophysis cerebri, 153

TNCUS BONE, 238

■*■ Insalivation, . 96

, nervous circle of, 99

Inspiration, movements of thorax in, . 137

Internal capsule, . . . . . . 204

, results of injury to, . . 204

secretions, 150

Intestinaljuice, 107

Iris, . . 227

, action of, 235

K

IDNEYS,

, excretion of urine by,

155
J59

T ABYRINTH OF INTERNAL

"L/ ear, 243

, function of cochlea, 244

, function of semicircular canals, 244

Language, articulate, center for, . . . 216

Larynx, ... 245

Lateral columns of spinal cord, . . . 174

Laws of muscular contraction, ... 85

Lens, crystalline, 230

Lime phosphate, 29

Liver, 163

, secretion of bile by, 165

, glycogenic function of, ... 166

, elaboration of blood, .... 165

cells, 161

Localization of functions in cerebrum, 214

Lungs, • 135

, changes in blood while passing

through, 142

Lymph, .... 117

Lymphatic glands, 113

vessels, origin and course of, . 113

TWTALLEUS BONE, 258

■"•*■ Mammary glands, 148

Mastication, 95

, nervous circle of, 96

, muscles of, 95

Medulla oblongata, . . . 197

, properties and functions of, . 199

Membrana tympani, ... . . 238

Menstruation, 240

Middle ear, . 2^8

INDEX.

•269

PAGE

Milk, 149

Motor centers of cerebrum 214

Muscles, properties of, 51

, changes in, during contraction, 57

, special physiology of, ... . 63

Muscle-fiber, histology of, . . . . 52

Myopia, 235

TSJERVE, OLFACTORY, . . 183

* ' , optic, 184

, motor oculi 185

, pathetic, 186

, trigeminal, 187

, abducens, 187

, facial, 189

, auditory, 191

, glosso-pharyngeal, 192

, pneumogastric, 192

, spinal accessory, igo

, hypoglossal, 196

cells, structure of, .... 70

fibers, structure of 72

, terminations of, ... 76

force, rate of transmission of, . 83

roots, function of anterior and

posterior, 77

tissue, histology of, 69

trunks, structure of, . . . . 73

Nerves, centrifugal and centripetal. . 77

, classification of, . . . . 75

, relation of, to central nervous

system, 77

, development and nutrition of, 78

, cranial, . . 183

, decussation of motor and sen-
sory, 175

, vaso-motor, . . .... 200

, properties and functions of, . 75

, spinal, 174

Nervous tissue, physiology of, ... 69

, cerebrospinal 171

, sympathetic, 220

Neurone, 70

Nucleus caudatus, 204

, lenticularis, 204

QLFACTORY NERVES, ... 183

^•^ Ophthalmic ganglion, 181

Optic nerves, 184

, thalamus, 204

, functions of, . . . , . . . 205

Organs of Corti, 244

Otic ganglion, 219

Ovaries, 248

Ovum, 248

, discharge of, from the ovary, • 248

Oxygen, absorption of, by hemo-
globin, 122

OANCREATIC JUICE 107

■*■ Patheticus nerve, 186

Peptones, 105

Perilymph, 243

Perspiration, 170

PAGE

Petrosal nerves, large and small. . . 190

Phonation, . . 247

Physiology, definition of, 9

Placenta, formation and function of, . 256

Pleura, . . ... .... 136

Pneumogastric nerve, 192

Pons Varolii, 201

Portal vein, . . . . 161

Posterior columns of spinal cord, . . 182

, functions of, 182

Prehension, 95

Presbyopia, . 235

Pressure of blood in arteries, .... 132

Proximate principles, . . .... 16

, inorganic, . 29

, organic, non-nitrogenized, . . 16

, organic, nitrogenized, .... 23

, of waste, 32

, quantity of chemic elements in

body, 16

Ptyalin, 98

Pulse, 132

Pyramidal tracts, 174

DED CORPUSCLES OF

■*^" blood, 121

Reflex movements of spinal cord, . . 188

action, laws of, 177-181

Reproduction, 248

Respiration, 135

, movements of, 137

, types of, 139

, nervous circle of, 138

Retina, 229

Rigor mortis, ..'... 54

OALIVA, . 98

*** Sebaceous glands, 169

Secretion, . . . 155

Semen, 252

Semicircular canals 243

Sight, sense of, 226

Skeleton, 46

Skin 168

Smell, sense of, 225

Sounds of heart 129

Spermatozoa, 252

Spheno-palatine ganglion, 2x9

Spinal accessory nerve, 195

cord 171

cord, membranes of, 171

, structure of white matter, . . 173

, structure of gray matter, . . 173

, properties of, 174

, function of, as a conductor, . . 181

, as an independent center, . . 176

, decussation of motor and sen-
sory fibers, 175

, reflex action of, 178

, special centers of, 181

, paralysis from injuries of, . . 182

, nerves, origin of 174

, course of anterior and posterior

roots of, 175

270

INDEX.

PAGE

Spleen, 151

Starvation, phenomena of, 86

Stomach, . . 100

Submaxillary ganglion 219

Sudoriparous glands, 170

Sugar, uses of, in the body, 89

Supra-renal capsules, 154

Sympathetic nervous system, .... 218
, properties and functions of, . 219

npASTE, SENSE OF, ..... 223

■*• , nerve of, . 224

Teeth, 95

Tensor tympani muscle, 241

Testicles, . . 251

Thoracic duct, 115

Thorax, enlargement of, in inspiration, 137

Thyroid gland 151

Tissues, physiology of, 39

Tongue, 223

, motor nerve of, 224

, sensory nerve of, 224

Touch, sense of, 292

Tiirck, column of, 174

PAGE

TTMBILICAL CORD 254

*"*' Urea, . . 167

Uric acid, . . 161

Urination, nervous mechanism of, . . 159

Urine, 159

. , composition of, ...... . 160

, average quantity of constitu-
ents secreted daily, 160

Uterus, . 249

TT-APOR, WATERY, OF

" breath, 150

Vascular glands, . 150

system, development of, 260

Vaso-motor nerves, origin of, ... 200

Veins, . . 133

Vertebral column, 49

Vesiculse seminalesj 251

Vision, psychic center for, 21S

Vital capacity of lungs, 140

Vocal cords, 246

Voice, 245

TX7ATER, AMOUNT OF, IN

vv body, 29

I Wolffian bodies, 260

MEDICAL
BOOKS

There have been sold more than
140,000 copies of Gould's Dictionaries

See Pas:e 12

P. Blakiston's Son & Company

PUBLISHERS OF MEDICAL AND SCIENTIFIC BOOKS
1012 WALNUT STREET, PHILADELPHIA

Montgomery's Gynecology

A PRACTICAL TEXT-BOOK

A modern comprehensive Text-Book. By Edward E.
Montgomery, m.d., Professor of Gynecology in Jefferson
Medical College, Philadelphia ; Gynecologist to the Jefferson
and St. Joseph's Hospitals, etc. 527 Illustrations, many of
which are from original sources. 800 pages. Octavo.

Cloth, $5.00; Leather, $6.00

*.£* This is a systematic modern treatise on Diseases of
Women. The author's aim has been to produce a book
that will be thorough and practical in every particular. The
illustrations, nearly all of which are from original sources,
have for the most part been drawn by special artists who,
for a number of months, devoted their sole attention to this
work.

" The book is one that can be recommended to the student, to
the general practitioner — who must sometimes be a gynecologist to
a certain extent whether he will or not — and to the specialist, as an
ideal and in every way complete work on the gynecology of
to-day— a practical work for practical workers." — The Jour-
nal of the American Medical Association.

Byford's Gynecology

Third Revised Edition
A MANVAL FOR. STUDENTS AND PHYSICIANS

By Henry T. Byford, m.d., Professor of Gynecology and
Clinical Gynecology in the College of Physicians and Sur-
geons of Chicago ; Professor of Clinical Gynecology,
Women's Medical School of Northwestern University, and
in Post-Graduate Medical School, etc. Third Edition, En-
larged. 363 Illustrations, many of which are from original
drawings and several of which are Colored. l2mo.

Cloth, #3.00

" As a book to help the student to quickly review what ought
to be gotten up, so as to be prepared for the early examination, it is of
great service. Such a book would also make a most excellent text-
book for the college classroom.."— Virginia Medical Semi-Monthly,
Richmond.

2

By JAMES TYSON, M.D.,

Professor of Medicine, University of Pennsylvania,
Physician to the Philadelphia Hospital, etc.

The Practice of Medicine. Second Edition.

A Text-Book for Physicians and Students, with Special Ref-
erence to Diagnosis and Treatment. With Colored Plates
and many other Illustrations. Second Edition, Revised and
Enlarged. 127 Illustrations. 8vo. 1222 pages.

Cloth, $5.50; Leather, $6.50; Half Russia, $7.50

*V* This edition has been entirely reset from new type.
The author has revised it carefully and thoroughly, and
added much new material and 37 new illustrations.

"We are firmly convinced that at the present time Dr. Tyson's
hook on Practice can be most heartily commended to both the practi-
tioner and student as a safe, reliable, and thoroughly up-to-date guide
in the practice of medicine." — The Therapeutic Gazette.

" The clinical descriptions are clear and full, and the methods of
treatment described are those generally recognized as being the most
modern and satisfactory." — The London Lancet.

Guide to the Examination of Urine. Tenth
Edition.

For the Use of Physicians and Students. With Colored
Plate and Numerous Illustrations Engraved on Wood.
Tenth Edition, Revised, Enlarged, and in many parts entirely
rewritten. Cloth, $1.50

*£* A French translation of this book has been pub-
lished in Paris.

" The book is probably more widely and generally known and ap-
preciated than any of its similars in subject and scope." — New York
Medical Journal.

" The book is a reliable one, and should find a place in the library
of every practitioner and student cf medicine." — B-jston Medical and
Surgical Journal.

Handbook of PhysicaJ Diagnosis. Fourth
Edition.

Revised and Enlarged. With two Colored Plates and 55
other Illustrations. 298 pages. i2mo. Cloth, $1.50

" Like everything else emanating from this distinguished author
this little book is replete with practical information from beginning to
end." — The Chicago Medical Recorder.

" The author approaches his subject from a practical point of
view and the little work will prove a good friend to the student." —
The American Journal 0/ the Medical Sciences.

3

Morris' Anatomy

Rewritten — Revised — Improved
WITH MANY NEW ILLUSTRATIONS

Out of 102 of the leading medical schools 60 recommend
" Morris." It contains many features of special advantage
to students. It is modern, up-to-date in every respect. It
has been carefully revised, the articles on Osteology and
Nervous System having been rewritten. Each copy con-
tains the colored illustrations and a Thumb Index.

Octavo. With 838 Illustrations, of which a large number
are printed in colors

CLOTH, $6.00; LEATHER, $7.00

" The ever-growing popularity of the book with teachers and stu-
dents is an index of its value, and it may safely be recommended to all
interested." — From The Medical Record, New York.

" Of all the text-books of moderate size on human anatomy in the
English language, Morris is undoubtedly the most up to-date and accu-
rate."— From The Philadelphia Medical Journal.

McMurrich — Embryology

Nearly Ready. 276 Illustrations

A Text-Book for Medical Students. By J. PlAYFAIR
McMurrich, Professor of Anatomy, Medical Department,
University of Michigan. Ready October 1st.

NINTH EDITION

POTTER'S MATERIA MEDICA,
PHARMACY, and THERAPEUTICS

An Exhaustive Handbook

Including the Action of Medicines, Special Therapeutics of
Disease, Official and Practical Pharmacy, and Minute Direc-
tions for Prescription Writing, etc. Including over 650
Prescriptions and Formulas. By Samuel 0. L. Potter,
M.A., M.D., M.R.C.P. (Lond.), formerly Professor of the
Principles and Practice of Medicine, Cooper Medical Col-
lege, San Francisco ; Major and Brigade Surgeon, U. S.
Vol. Ninth Edition, Revised and Enlarged. 8vo.
With Thumb Index in each copy.

Cloth, $5.00 ; Leather, $6.00
*.£* This is the most complete and trustworthy book
for the use of students and physicians. Students who pur-
chase it will find it to contain a vast deal of information not
in the usual text-books arranged in the most practical man-
ner for facilitating study and reference. It cannot be sur-
passed as a physician's working book.

WHITE AND WILCOX. Materia Medica,
Pharmacy ♦ Pharmacology, and Thera-
peutics* Fifth Edition*

A Handbook for Students. By W. Hale White, m.d.,
F.R.C.P., etc., Physician to, and Lecturer on Materia
Medica and Therapeutics at, Guy's Hospital, etc. Fifth
American Edition, Revised by Reynold W. Wilcox,
m A , m. d. , ll.d. , Professor of Clinical Medicine and Thera-
peutics at the New York Post-Graduate Medical School and
Hospital ; Visiting Physician, St. Mark's Hospital ; Assist-
ant Visiting Physician, Bellevue Hospital. l2mo.

Cloth, $3.00 ; Leather, $3. 50
5

SUBJECT [INDEX.

Gould's Medical Dictionaries,
Morris' Anatomy, New Edition,
Compends for Students,

Page 12
Page 4
Page 26

SUBJECT PAGE

Alimentary Canal (see Surgeiy) 23

Anatomy 7

Anesthetics 18

Autopsies (see Pathology) 20

Bacteriology (see Pathology).. 20

Bandaging (see Surgery) 23

Blood, Examination of 20

Brain 8

Chemistry. Physics 8

Children, Diseases of 10

Climatology 18

Clinical Charts 24

Compends 26

Consumption (see Lungs) 15

Cyclopedia of Medicine 12

Dentistry 11

Diabetes (see Urin. Organs).. 24

Diagnosis 10

Diagrams (see Anatomy) 7

Dictionaries, Cyclopedias 12

Diet and Food 18

Disinfection • 15

Dissectors 7

Ear 13

Electricity 13

Embryology 7

Emergencies 23

Eye 13

Fevers 14

Food 18

Formularies 21

Gynecology 25

Hay Fever 24

Heart 14

Histology 14

Hydrotherapy 18

Hygiene 15

Hypnotism 8

Insanity 8

Intestines 22

Latin, Medical (see Miscella-
neous and Pharmacy) 18,20

Life Insurance 18

Lungs 75

Massage 16

Materia Medica 16

SUBJECT. PAGE

Mechanotherapy 16

Medical Jurisprudence 17

Mental Therapeutics 8

Microscopy 17

M ilk Analysis (see Chemistry) 8

Miscellaneous 18

Nervous Diseases 18

Nose 24

Nursing 19

Obstetrics 20

Ophthalmology *3

Organotherapy 18

Osteology (see Anatomy) 7

Pathology 20

Pharmacy 20

Physical Diagnosis n

Physical Training 16

Physiology 21

Pneumotherapy 18

Poisons (see Toxicology) 17

Practice of Medicine 22

Prescription Books (Pharm'y), 21

Refraction (see Eye) 13

Rest 18

Sanitary Science 15

Skin 23

Spectacles (see Eye) 13

Spine (see Nervous Diseases) 18

Stomach 22

Students' Compends 26

Surgery and Surg'l Diseases, 23

Technological Books 8

Temperature Charts 24

Therapeutics 16

Throat 24

Toxicology 17

Tumors (see Surgery) 23

U. S. Pharmacopoeia 21

Urinary Organs 24

Urine 24

Venereal Diseases 25

Veterinary Medicine 25

Visiting Lists, Physicians'.
(Send for Special Circular.)

Water Analysis.. 15

Women, Diseases of. 25

Self-Examination for Medical Students. 3500 Questions on
Medical Subjects, with References to Standard Works in which the
correct replies will be found. Together with Questions from State
Examining Boards. 3d Edition. Paper Cover, 10 cts.

SUBJECT CATALOGUE OF MEDICAL BOOKS. 7

SPMCIAI, NOTE.— -The prices given in this catalogue are
net, no discount can be allowed retail purchasers under any considera-
tion. This rule has been established in order that everyone will be
treated alike, a general reduction in former prices having been made to
meet previous retad discounts. Upon receipt of the advertised price any
book will be forwarded by mail or express, all charges prepaid.

ANATOMY. EMBRYOLOGY.

MORRIS. Text-Book of Anatomy. Revised and Enlarged Edi-
tion. 838 Illustrations, 269 of which are printed in colors. Thumb
Index in Each Copy. Cloth, $6.00; Leather, $7.00

" The ever-growing popularity of the book with teachers and students

is an index of its value." — Medical Record, New Y%rk.

BROOMELL. Anatomy and Histology of the Human Mouth
and Teeth. 2d Edition, Enlarged. 337 Illustrations. $4 50

CAMPBELL. Dissection Outlines. Based on Morris' Anatomy.
2d Edition. .50

DEAVER. Surgical Anatomy. A Treatise on Anatomy in its
Application to Medicine and Surgery. With 450 very Handsome full-
page Illustrations Engraved from Original Drawings made by special
Artists from dissections prepared for the purpose. Three Volumes.
Cloth, $2 1. 00; Half Morocco or Sheep, £24.00; Half Russia, $27.00

GORDINIER. Anatomy of the Central Nervous System.
With 271 Illustrations, many of which are original. Cloth, $6.00

HEATH. Practical Anatomy. 8th Edition. 300 Illus. $4.25

HOLDEN. Anatomy. A Manual of Dissections. Revised by A.
Hbwson, m.d., Demonstrator of Anatomy, Jefferson Medical College,
Philadelphia. 320 handsome Illustrations. 7th Edition. In two
compact i2mo Volumes. 850 Pages. Large New Type.
Vol. I. Scalp— Face— Orbit— Neck— Throat— Thorax— Upper Ex-
tremity. $1-50
Vol. II. Abdomen — Perineum — Lower Extremity — Brain — Eye —
Ear — Mammary Gland — Scrotum — Testes. $1.50

HOLDEN. Human Osteology. Comprising a Description of the
Bones, with Colored Delineations of the Attachments of the Muscles.
The General and Microscopical Structure of Bone and its Develop-
ment. With Lithographic Plates and numerous Illus. 8th Ed. $5.25

HOLDEN. Landmarks. Medical and Surgical. 4th Ed. .75

HUGHES AND KEITH. Dissections. With 527 Colored Plates
and other Illustrations. In three Parts. Just Ready.

I, Upper and Lower Extremity. $3 .00

II, Abdomen — Thorax. $3.00

III, Head — Neck — Central Nervous System. $3°°

MACALISTER. Human Anatomy. Systematic and Topograph-
ical. 816 Illustrations. Cloth, $5.00 ; Leather, $6.00

McMURRICH. Embryology. 270 Illustrations. Nearly Ready.

MARSHALL. Physiological Diagrams. Eleven Life-Size
Colored Diagrams (each seven feet by three feet seven inches).
Designed for Demonstration before the Class.

In Sheets, Unmounted, $40.00 ; Backed with Muslin and Mounted
on Rollers, $60.00 ; Ditto, Spring Rollers, in Handsome Walnut Wall
Map Case, $100.00; Single Plates — Sheets, $5.00 ; Mounted, $7.50
Explanatory Key, .50. Purchaser must pay freight charges.

MI NOT. Embryology. Illustrated. In Press.

POTTER. Compend of Anatomy, Including Visceral Anatomy.
6th Ed. 16 Lith. Plates and 117 other Illus. .80 ; Interleaved, $1.00

WILSON. Anatomy, nth Edition. 429 Illus., 26 Plates. $5.00

8-1-02.

SUBJECT CATALOGUE.

BRAIN AND INSANITY (see also
Nervous Diseases).

BLACKBURN. A Manual of Autopsies. Designed for the Use
of Hospitals for the Insane and other Public Institutions. Ten full-
page Plates and other Illustrations. $i-*5

CHASE. General Paresis. Illustrated. Just Ready. $i 75

DERCUM. Mental Therapeutics, Rest, Suggestion. See

Cohen, Physio. ogic Therapeutics , page id.

GORDINIER. The Gross and Minute Anatomy of the Central
Nervous System. With full-page and other Illustrations. $6.00

HORSLEY. The Brain and Spinal Cord. The Structure and
Functions of. Numerous Illustrations. $2.50

IRELAND. The Mental Affections of Children. 2d Ed. $4.00

LEWIS (BEVAN). Mental Diseases. A Text-Book Having
Special Reference to the Pathological Aspects of Insanity. 26 Litho-
graphic Plates and other Illustrations. 2d Ed. $7-oo

MANN. Manual of Psychological Medicine. $3.00

PERSHING. Diagnosis of Nervous and Mental Disease.
Illustrated $*-25

REGIS. Mental Medicine. Authorized Translation by H. M.
Bannister, m.d. $2.00

SCHOFIELD. The Force of Mind. Just Ready. $200

STEARNS. Mental Diseases. With a Digest of Laws Relating
to Care of Insane. Illustrated. Cloth, $2. 75 ; Sheep, $3.25

TUKE. Dictionary of Psychological Medicine. Giving the
Definition, Etymology, and Symptoms of the Terms used in Medical
Psychology, with the Symptoms, Pathology, and Treatment of the
Recognized Forms of Mental Disorders. Two volumes. £10.00

WOOD, H. C. Brain and Overwork. .40

CHEMISTRY AND TECHNOLOGY.

Special Catalogue of Chemical Books sent free upon application.

ALLEN. Commercial Organic Analysis. A Treatise on the

Modes of Assaying the Various Organic Chemicals and Products

Employed in the Arts, Manufactures, Medicine, etc., with concise

methods for the Detection of Impurities, Adulterations, etc. .8vo.

Vol. I. Alcohols, Neutral Alcoholic Derivatives, etc., Ethers, Veg-
etable Acids, Starch, Sugars, etc. 3d Edition. $4.50

Vol. II, Part I. Fixed Oils and Fats, Glycerol, Explosives, etc.
3d Edition. $3-5°

Vol. II, Part II. Hydrocarbons, Mineral Oils, Lubricants, Benzenes,
Naphthalenes and Derivatives, Creosote, Phenols, etc. 3d Ed. $3.50

Vol. II, Part III. Terpenes, Essential Oils, Resins, Camphors, etc.
3d Edition. Preparing.

Vol. Ill, Part I. Tannins, Dyes and Coloring Matters. 3d Edition.
Enlarged and Rewritten. Illustrated. $4-5°

Vol. Ill, Part II. The Amines, Hydrazines and Derivatives,
Pyridine Bases. The Antipyretics, etc. Vegetable Alkaloids, Tea,
Coffee, Cocoa, etc. 8vo. 2d Edition. ^4-5°

Vol. Ill, Part III. Vegetable Alkaloids, Non-Basic Vegetable Bitter
Principles. Animal Bases, Animal Acids, Cyanogen Compounds,
etc. 2d Edition, 8vo. $4-5°

Vol. IV. The Proteids and Albuminous Principles. 2d Ed. $4.50

BAILEY AND CADY. Qualitative Chemical Analysis. $1.25

MEDICAL BOOKS. 9

BARTLEY. Medical and Pharmaceutical Chemistry. A
Text-Book for Medical, Dental, and Pharmaceutical Students. With
Illustrations, Glossary, and Complete Index. 5th Edition. $3-oo

BARTLEY. Clinical Chemistry. The Examination of Feces,
Saliva, Gastric Juice, Milk, and Urine. $1.00

BLOXAM. Chemistry, Inorganic and Organic. With Experi-
ments. 9th Ed.. Revised. 381 Engravings. Preparing.

BUNGE. Physiologic and Pathologic Chemistry. From the
Fourth German Enlarged Edition. Just Ready. J3.C0

CALDWELL. Elements of Qualitative and Quantitative
Chemical Analysis. 3d Edition, Revised. $1.00

CAMERON. Oils and Varnishes. With Illustrations. $2.25

CAMERON. Soap and Candles. 54 Illustrations. $2.00

CLOWES AND COLEMAN. Quantitative Analysis. 5th

Edition. 122 Illustrations. $3-5o

COBLENTZ. Volumetric Analysis. Illustrated. $r.a5

CONGDON. Laboratory Instructions in Chemistry. With

Numerous Tables and 56 Illustrations. $1.0°

GARDNER. The Brewer, Distiller, and Wine Manufac-
turer. Illustrated. $1.50

GRAY. Physics. Volume I. Dynamics and Properties of Matter.
350 Illustrations. $4-5o

GROVES AND THORP. Chemical Technology. The Appli-
cation of Chemistry to the Arts and Manufactures.
Vol. I. Fuel and Its Applications. 607 Illustrations and 4 Plates.

Cloth, $5.00; Yz Mor., $6.50
Vol. II. Lighting. Illustrated. Cloth, $4.00; J^ Mor., $5.50

Vol. III. Gas Lighting. Cloth, £3.50; % Mor., $4.50

Vol. IV. Electric Lighting. Photometry. In Press.

HEUSLER. TheTerpenes. Just Ready. $400

HOLLAND. The Urine, the Gastric Contents, the Common
Poisons, and the Milk. Memoranda, Chemical and Microscopi-
cal, for Laboratory Use. 6th Ed. Illustrated and interleaved, $1.00

LEFFMANN. Compend of Medical Chemistry, Inorganic
and Organic. 4th Edition, Revised. .80; Interleaved, $1.00

LEFFMANN. Analysis of Milk and Milk Products. 2d

Edition, Enlarged. Illustrated. $1 .25

LEFFMANN. Water Analysis. For Sanitary and Technic Pur-
poses. Illustrated. 4th Edition. $1.25

LEFFMANN. Structural Formulae. Including 180 Structural
and Stereo-Chemical Formulae, ismo. Interleaved. $1.00

LEFFMANN AND BEAM. Select Methods in Food Analy-
sis. Illustrated. $2.50

MUTER. Practical and Analytical Chemistry. 2d American
from the Eighth English Edition. Revised to meet the requirements
of American Students. 56 Illustrations. $**5

OETTEL. Exercises in Electro-Chemistry. Illustrated. .75

OETTEL. Electro-Chemical Experiments. Illustrated. .75

RICHTER. Inorganic Chemistry. 5th American from 10th Ger-
man Edition. Authorized translation by Edgar F. Smith, m.a.,
ph.d. 89 Illustrations and a Colored Plate. ^I-75

RICHTER. Organic Chemistry. 3d American Edition. Trans,
from the 8th German by Edgar F. Smith. Illustrated. 2 Volumes.
Vol. I. Aliphatic Series. 625 Pages. $3-°o

Vol. II. Carbocyclic Series. 671 Pages. $3-°°

10 SUBJECT CATALOGUE.

ROCKWOOD. Chemical Analysis for Students of Medicine,
Dentistry, and Pharmacy. Illustrated. $1-50

SMITH. Electro-Chemical Analysis. 2d Ed. 28 Illus. $1.25

SMITH AND KELLER. Experiments. Arranged for Students
in General Chemistry. 4th Edition. Illustrated .60

SUTTON. Volumetric Analysis. A Systematic Handbook for
the Quantitative Estimation of Chemical Substances by Measure,
Applied to Liquids, Solids, and Gases. 8th Edition, Revised. 112
Illustrations. #5.00

SYMONDS. Manual of Chemistry. 2d Edition. #2.00

TRAUBE. Physico-Chemical Methods. Translated by Hardin.

97 Illustrations. $1.50

THRESH. "Water and Water Supplies. 3d Edition. $2.00

ULZER AND FRAENKEL. Chemical Technical Analysis.

Translated by Fleck. Illustrated. $1-25

WOODY. Essentials of Chemistry and Urinalysis. 4th

Edition. Illustrated. $1-50

*** Special Catalogue of Books on Chemistry free upon application.

CHILDREN.

HATFIELD. Compend of Diseases of Children. With a
Colored Plate. 3d Edition. In Press. .80; Interleaved. $1.00

IRELAND. The Mental Affections of Children. Idiocy,
Imbecility, Insanity, etc. 2d Edition. #4.00

POWER. Surgical Diseases of Children and their Treat-
ment by Modern Methods. Illustrated. $2.50

STARR. The Digestive Organs in Childhood. The Diseases of
the Digestive Organs in Infancy and Childhood. 3d Edition, Rewrit-
ten and Enlarged. Illustrated. ftj.oo

STARR. Hygiene of the Nursery. Including the General Regi-
men and Feeding of Infants and Children, and the Domestic Manage-
ment of the Ordinary Emergencies of Early Life, Massage, etc. 6th
Edition. 25 Illustrations. $1.00

SMITH. Wasting Diseases of Children. 6th Edition. $2.00

TAYLOR AND WELLS. The Diseases of Children. 2d Edi-
tion, Revised and Enlarged. Illustrated. 8vo. #4.5°

" It is well worthy the careful study of both student and practitioner,
and can not fail to prove of great value to both. We do not hesitate
to recommend it." — Boston Medical and Surgical Journal.

DIAGNOSIS.

BROWN. Medical Diagnosis. A Manual of Clinical Methods.
4th Edition. 112 Illustrations. Cloth, #2.25

DA COSTA. Clinical Hematology. A Practical Guide to Exam-
ination of Blood. 6 Colored Plates. 48 other Illustrations. Just
Ready. Cloth, $5.00; Sheep, $6.00

EMERY. Bacteriological Diagnosis. 2 Colored Plates and 32
other Illustrations. Just Ready. $1.50

MEMMINGER. Diagnosis by the Urine. 2d Ed. 24 Illus. $1.00

MEDICAL BOOKS. 11

PERSHING. Diagnosis of Nervous and Mental Diseases.
Illustrated. 5I25

STEELL. Physical Signs of Pulmonary Disease. $1-25

TYSON. Hand-Book of Physical Diagnosis. For Students and
Physicians. By the Professor of Clinical Medicine in the University
of Pennsylvania. Illus. 4th Ed., Improved and Enlarged. With
Two Colored and 55 other illustrations. $1.50

DENTISTRY.

Special Catalogue of Dental Books sent free upon application.

BARRETT. Dental Surgery for General Practitioners and
Students of Medicine and Dentistry. Extraction of Teeth,
etc. 3d Edition. Illustrated. #1.00

BROOMELL. Anatomy and Histology of the Human Mouth
and Teeth. Second Edition, Revised and Enlarged. 337 Hand-
some Illustrations. $4-5°

FILLEBROWN. A Text-Book of Operative Dentistry.

Written by invitation of the National Association of Dental Facul-
ties. Illustrated. #2.35

GORGAS. Dental Medicine. A Manual of Materia Medica and
Therapeutics. 7th Edition. Cloth, $4.00; Sheep, #5.00

GORGAS. Questions and Answers for the Dental Student.
Embracing all the subjects in the Curriculum of the Dental Student.
Octavo. #6.00

HARRIS. Principles and Practice of Dentistry. Including
Anatomy, Physiology, Pathology, Therapeutics, Dental Surgery,
and Mechanism. 13th Edition. Revised by F. J. S. Gorgas, m.d.,
d.d.s. 1250 Illustrations. Cloth, $6.00; Leather, $7.00

HARRIS. Dictionary of Dentistry. Including Definitions of Such
Words and Phrases of the Collateral Sciences as Pertain to the Art and
Practice of Dentistry. 6th Edition. Revised and Enlarged by Fer-
dinand F. S. Gorgas, m.d., d.d.s. Cloth, #5.00; Leather, $6.00

RICHARDSON. Mechanical Dentistry. 7th Edition. Thor-
oughly Revised and Enlarged by Dr. Geo. W. Warren. 691 Illus-
trations. Cloth, $5. 00; Leather, #6.00

SMITH. Dental Metallurgy, ad Edition. Illustrated. In Press.

TAFT. Index of Dental Periodical Literature. #2.00

TOMES. Dental Anatomy. Human and Comparative. 263 Illus-
trations. 5th Edition. #4.00
TOMES. Dental Surgery. 4th Edition. 289 Illustrations. $4.00

WARREN. Compend of Dental Pathology and Dental Medi-
cine. With a Chapter on Emergencies. 3d Edition. Illustrated.

.80; Interleaved, $1.25

WARREN. Dental Prosthesis and Metallurgy. 129 Ills. £1.25
WHITE. The Mouth and Teeth. Illustrated. .40

12 SUBJECT CATALOGUE.

DICTIONARIES AND CYCLOPEDIAS

GOULD. The Illustrated Dictionary ot Medicine, Biology
and Allied Sciences. Being an Exhaustive Lexicon of Medicine
and those Sciences Collateral to it: Biology (Zoology and Botany),
Chemistry, Dentistry, Parmacology, Microscopy, etc., with many
useful Tables and numerous fine Illustrations. 1633 pages. 5th Ed.
Sheep or Half Morocco, $10.00 ; with Thumb Index, $11.00
Half Russia, Thumb Index, $12. co

GOULD. The Medical Student's Dictionary, nth Edition.
Illustrated. Including all the Words and Phrases Generally Used
inMedicine, with their Proper Pronunciation and Definition, Based
on Recent Medical Literature. With Table of Eponymic Terms and
Tests and Tables of the Bacilli, Micrococci, Mineral Springs, etc.,
of the Arteries, Muscles, Nerves, Ganglia, Plexuses, etc. nth Edi-
tion. Enlarged and illustrated with a large number of Engravings.
840 pages. Half Morocco, $2.30; with Thumb Index, $3 00

GOULD. The Pocket Pronouncing Medical Lexicon. 4th Edi-
tion. (30,000 Medical Words Pronounced and Defined.) Containing
all the Words, their Definition and Pronunciation, that the Medical,
Dental, or Pharmaceutical Student Generally Comes in Contact
With; also Elaborate Tables of Eponymic Terms. Arteries, Muscles,
Nerves, Bacilli, etc., etc., a Dose List in both English and Metric
Systems, etc., Arranged in a Most Convenient Form for Reference and
Memorizing. Fourth Edition, Revised and Enlarged. 838
pages. Full Limp Leather, Gilt Edges, $1.00 ; Thumb Index, $1.25
140,000 Copies of Gould's Dictionaries Have Been Sold.

GOULD AND PYLE. Cyclopedia of Practical Medicine and
Surgery. Seventy-two Special Contributors. Illustrated.
One Volume. A Concise Reference Handbook of Medicine,
Surgery, Obstetrics, Materia Medica, Therapeutics, and the Various
Specialties, with Particular Reference to Diagnosis and Treatment.
Compiled under the Editorial Supervision of George M. Gould,
m.d., Author of " An Illustrated Dictionary of Medicine," etc.;
and Walter L. Pyle, m.d., Assistant Surgeon Wills Eye
Hospital ; formerly Editor "International Medical Magazine," etc.,
and Seventy-two Special Contributors. With many Illustrations.
Large Square 8vo, to correspond with Gould's " Illustrated Dic-
tionary." Full Sheep or Half Mor ,$10.00; with Thumb Index, $11.00
Half Russia, Thumb Index, $12.00 net.

GOULD AND PYLE. Pocket Cyclopedia of Medicine and
Surgery. Based upon above book and uniform in size with " Gould's
Pocket Dictionary."

Full Limp Leather, Gilt Edges, $1.00, with Thumb Index, $1.25

HARRIS. Dictionary of Dentistry. Including Definitions of Such
Words and Phrases of the Collateral Sciences as Pertain to the Art
and Practice of Dentistry. 6th Edition. Revised and Enlarged by
Ferdinand J. S. Gorgas, m.d., d.d.s. Cloth, $5.00; Leather, $6.00

LONGLEY. Pocket Medical Dictionary. Cloth, .75

MAXWELL. Terminologia Medica Polyglotta. By Dr.
Theodore Maxwell, Assisted by Others. $3.00

The object of this work is to assist the medical men ot any nationality

In reading medical literature written in a language not their own.

Each term is usually given in seven languages, viz. : English, French,

German, Italian, Spanish, Russian, and Latin.

TREVES AND LANG. German-English Medical Dictionary.

Half Calf, $3.25

MEDICAL BOOKS. 13

EAR (see also Throat and Nose).

BURNETT. Hearing and How to Keep It. Illustrated. .46

DALBY. Diseases and Injuries of the Ear. 4th Edition. 38

Wood Engravings and 8 Colored Plates. $2.50

HOVELL. Diseases ot the Ear and Naso-Pharynx. Includ-
ing Anatomy and Physiology of the Organ, together with the Treat-
ment of the Affections of the Nose and Pharynx which Conduce to
Aural Disease. 128 Illustrations. 2d Edition. f, 5.50

PRITCHARD. Diseases of the Ear. 3d Edition, Enlarged.
Many Illustrations and Formulae. $1.50

ELECTRICITY.

BIGELOW. Plain Talks on Medical Electricity and Bat-
teries. With a Therapeutic Index and a Glossary. 43 Illustra-
tions. 2d Edition. $1.00

HEDLEY. Therapeutic Electricity and Practical Muscle
Testing, qq Illustrations. $2.50

JACOBY. Electrotherapy. 2 Vols. Illustrated. See Cohen,
Physiologic Therapeutics , page lb.

JONES. Medical Electricity. 3d Edition. 117 Illus. I3.00

EYE.

A Special Circular 0/ Books on the Eye sent free upon application.

DONDERS. The Nature and Consequences of Anomalies of
Refraction. With Portrait and Illustrations. Half Morocco, $1. 25

FICK. Diseases of the Eye and Ophthalmoscopy. Trans-
lated by A. B. Hale, m. d. 157 Illustrations, many of which are in
colors, and a glossary. Cloth, $4.50 ; Sheep, $5.50

GOULD AND PYLE. Compend of Diseases of the Eye and
Refraction. Including Treatment and Operations, and a Section
on Local Therapeutics. With Formulae, Useful Tables, a Glossary,
and m Illus., several of which are in colors. 2d Edition, Revised.

Cloth, .80; Interleaved, $1. 00

GREEFF. The Microscopic Examination of the Eye. Illus-
trated. |I<25

HARLAN. Eyesight, and How to Care for It. Illus. .40

HARTRIDGE. Refraction. 104 Illustrations and Test Types,
nth Edition, Enlarged. t1-5°

HARTRIDGE. On the Ophthalmoscope. 4th Edition. With
4 Colored Plates and 68 Wood-cuts. £1.50

HANSELL AND REBER. Muscular Anomalies ot the Eye.
Illustrated. $1.50

HANSELL AND BELL. Clinical Ophthalmology. Colored
Plate of Normal Fundus and 120 Illustrations. #1.50

JENNINGS. Manual of Ophthalmoscopy. 95 Illustrations and
1 Colored Plate. #1.50

14 SUBJECT CATALOGUE.

MORTON. Refraction of the Eye. Its Diagnosis and the Cor-
rection of its Errors. 6th Edition. $1.00

OH LE MANN. Ocular Therapeutics. Authorized Translation,
and Edited by Dr. Charles A. Oliver. $r-75

PARSONS. Elementary Ophthalmic Optics. With Diagram-
matic Illustrations. $2.00

PHILLIPS. Spectacles and Eyeglasses. Their Prescription
and Adjustment, ad Edition. 49 Illustrations. $1.00

SWANZY. Diseases of the Eye and Their Treatment. 7th
Edition, Revised and Enlarged. 164 Illustrations, 1 Plain Plate,
and a Zephyr Test Card. $2.50

From The Medical News.

" Swanzy has succeeded in producing the most intellectually con-
ceived and thoroughly executed resume of the science within the
limits he has assigned himself. As a ' students' handbook,' small
in size and of moderate price, it can hardly be equaled."

THORINGTON. Retinoscopy. 4th Edition. Carefully Revised.
Illustrated. $1.00

THORINGTON. Refraction and How to Refract. 200 Illustra-
tions, 13 of which are Colored. 2d Edition. $1.50

WALKER. Students' Aid in Ophthalmology. Colored Plate
and 40 other Illustrations and Glossary. $i-5°

WRIGHT. Ophthalmology. 2d Edition, Revised and Enlarged.
117 Illustrations and a Glossary. $3.00

FEVERS.

GOODALL AND WASHBOURN. Fevers and Their Treat-
ment. Illustrated. $3-°°

HEART.

THORNE. The Schott Methods of the Treatment of Chronic
Heart Disease. Fourth Edition. Illustrated. Just Ready. $2.00

HISTOLOGY.

CUSHING. Compend of Histology. By H. H. Cushing, m.d.,
Demonstrator of Histology, Jefferson Medical College, Philadelphia.
Illustrated. Nearly Ready. .80; Interleaved, $1. 00

STIRLING. Outlines of Practical Histology. 368 Illustrations.
2d Edition, Revised and Enlarged. With new illustrations. $2.00

STOHR. Histology and Microscopical Anatomy. Edited by
A. Schaper, m.d., University of Breslau, formerly Demonstrator of
Histology, Harvard Medical School. Fourth American from 9th Ger-
man Edition, Revised and Enlarged. 379 Illustrations. #3 00

MEDICAL BOOKS. 15

HYGIENE AND WATER ANALYSIS.

Special Catalogue of Books on Hygiene sent free upon application.

CANFIELD. Hygiene of the Sick-Room. A Book for Nurses
and Others. Being a Brief Consideration of Asepsis, Antisepsis, Dis-
infection, Bacteriology, Immunity, Heating, Ventilation, etc. $1.25
CONN. Agricultural Bacteriology. Illustrated. £2.50

COPLIN. Practical Hygiene. A Complete American Text-Book.
138 Illustrations. New Edition. Preparing.

HARTSHORNE. Our Homes. Illustrated. .40

KENWOOD. Public Health Laboratory Work. 116 Illustra-
tions and 3 Plates. $2.00

LEFFMANN. Select Methods in Food Analysis. 53 Illustra-
tions and 4 Plates. #2.50

LEFFMANN. Examination ot Water for Sanitary and
Technical Purposes. 4th Edition. Illustrated. $1.25

LEFFMANN. Analysis of Milk and Milk Products. Illus-
trated. Second Edition. . $1.25
'LINCOLN. School and Industrial Hygiene. .40

McFARLAND. Prophylaxis and Personal Hygiene. Care of
the Sick. See Cohen. Physiologic Therapeutics, page lb.

OTTER. The Theory and Practice of Hygiene. 15 Plates
nd 138 other Illustrations. 8vo. 2d Edition. $7.00

PA^RKES. Hygiene and Public Health. By Louis C. Parkes,
M.p. 6th Edition. Enlarged. Illustrated. $3.00

PARKES. Popular Hygiene. The Elements of Health. A Book
for Lay Readers. Illustrated. $*-25

ROSENAU. Disinfection and Disinfectants. Illustrated. $2.00
STARR. The Hygiene of the Nursery. Including the General
Regimen and Feeding of Infants and Children, and the Domestic
Management of the Ordinary Emergencies of Early Life, Massage,
etc. 6th Edition. 25 Illustrations. $1.00

STEVENSON AND MURPHY. A Treatise on Hygiene. By

Various Authors. In Three Octave Volumes. Illustrated.

Vol. I, $6.00; Vol. II, J6.00; Vol. Ill, $5.00
%* Each Volume sold separately. Special Circular upon application.

THRESH. Water and Water Supplies. 3d Edition. $2.00

WILSON. Hand-Book of Hygiene and Sanitary Science.

With Illustrations. 8th Edition. $3°o

WEYL. Sanitary Relations of the Coal-Tar Colors. Author-
ized Translation by Henry Leffmann, m.d., ph.d. #1-25

LUNGS AND PLEURAE.

KNOPF. Pulmonary Tuberculosis. Its Modern Prophylaxis
and Treatment in Special Institutions and at Home. Illus. $3.00

STEELL. Physical Signs of Pulmonary Disease. Illus. $1.25

16 SUBJECT CATALOGUE.

MASSAGE— PHYSICAL EXERCISE.

OSTROM. Massage and the Original Swedish Move-
ments. Their Application to Various Diseases of the Body. A
Manual for Students, Nurses, and Physicians. Fifth Edition, En-
larged. 115 Illustrations, many of which are original. #1.00

MITCHELL AND GULICK. Mechanotherapy, Physical
Education, etc. Illustrated. See Cohen, Physiologic Therapeu-
tics, below.

TREVES. Physical Education. Its Value, Methods, etc. .75

MATERIA MEDICA AND THERA-
PEUTICS.

BIDDLE. Materia Medica and Therapeutics. Including Dose
List, Dietary for the Sick, Table of Parasites, and Memoranda of
New Remedies. 13th Edition, Revised. 64 Illustrations and a
Clinical Index. Cloth, $4.00 ; Sheep, $5.00

BRACKEN. Outlines of Materia Medica and Pharmacology. #2.75

COBLENTZ. The Newer Remedies. Including their Synonyms,
Sources, Methods of Preparation, Tests, Solubilities, Doses, etc.
3d Edition, Enlarged and Revised. #1.00

COHEN. Physiologic Therapeutics. Methods other than Drug-
Giving useful in the Prevention of Disease a/nd in the Treatment of
the Sick. Mechanotherapy, Mental Therapeutics, Suggestion,
Electrotherapy. Climatology, Hydrotherapy, Pneumatotherapy,
Prophylaxis, Dietetics, Organotherapy, Phototherapy, Mineral
Waters, Baths, etc. 11 Volumes, Octavo. Illustrated. {Subscrip-
tion.) Cloth, $27.50 ; % mor., $38.50
Special Descriptive Circular will be sent upon application.

DAVIS. Materia Medica and Prescription Writing. $1.50

GORGAS. Dental Medicine. A Manual of Materia Medica and
Therapeutics. 7th Edition, Revised. $4.00

GROFF. Materia Medica for Nurses, with questions for Self Exam-
ination. 2d Edition, Revised and Improved. In Press.

HELLER. Essentials of Materia Medica, Pharmacy, and
Prescription Writing. $1.50

MAYS. Theine in the Treatment of Neuralgia. J6 bound, .50

POTTER. Hand-Book of Materia Medica, Pharmacy, and
Therapeutics, including the Action of Medicines, Special Therapeu-
tics, Pharmacology, etc., including over 600 Prescriptions and For-
mulae. 9th Edition, Revised and Enlarged. With Thumb Index in
each copy. Just Ready. Cloth, $5.00; Sheep, $6.00

POTTER. Compend of Materia Medica, Therapeutics, and
Prescription Writing, with Special Reference to the Physiologi-
cal Action of Drugs. 6th Edition. .80; Interleaved, $1.00

MURRAY. Rough Notes on Remedies. 4th Edition. $135

MEDICAL BOOKS. 17

SAYRE. Organic Materia Medica and Pharmacognosy. An
Introduction to the Study of the Vegetable Kingdom and the Vege-
table and Animal Drugs. Comprising the Botanical and Physical
Characteristics, Source, Constituents, and Pharmacopeial Prepara-
tions, Insects Injurious to Drugs, and Pharmacal Botany. With
sections on Histology and Microtechnique, by W. C. Stevens.
374 Illustrations, many of which are original. 2d Edition.

Cloth, $4.50

TAVERA. Medicinal Plants of the Philippines. $2.00

WHITE AND WILCOX. Materia Medica, Pharmacy, Phar-
macology, and Therapeutics. 5th American Edition, Revised by
Reynold W. Wilcox, m.a., m.d., ll.d., Professor of Clinical
Medicine and Therapeutics at the New York Post-Graduate Medical
School. Cloth, $3.00; Leather, $3.50

" The care with which Dr. Wilcox has performed his work is con-
spicuous on every page, and it is evident that no recent drug possess-
ing any merit has escaped his eye. We believe, on the whole, this is
the best book on Materia Medica and Therapeutics to place in the
hands of students, and the practitioner will find it a most satisfactory
work for daily use." — The Cleveland Medical Gazette.

MEDICAL JURISPRUDENCE AND
TOXICOLOGY.

REESE. Medical Jurisprudence and Toxicology. A Text-Book
for Medical and Legal Practitioners and Students. 5th Edition.
Revised by Henry Leffmann, m.d. C1o.,$3.oo; Leather, $3.50

" To the student of medical jurisprudence and toxicology it is in-
valuable, as it is concise, clear, and thorough in every respect." — The
American Journal of the Medical Sciences.

MANN. Forensic Medicine and Toxicology. Illus. £6.50

TANNER. Memoranda of Poisons. Their Antidotes and Tests.
8th Edition, by Dr. Henry Leffmann. .75

MICROSCOPY.

CARPENTER. The Microscope and Its Revelations. 8th
Edition, Revised and Enlarged. 817 Illustrations and 23 Plates.

Cloth, |8.oo ; Half Morocco, $9.00

LEE. The Microtomist's Vade Mecum. A Hand-Book of
Methods of Microscopical Anatomy. 887 Articles. 5th Edition,
Enlarged. $4.00

OERTEL. Medical Microscopy. A Guide to Diagnosis, Ele-
mentary Laboratory Methods and Microscopic Technic. 120 Illus-
trations. Nearly Ready.

REEVES. Medical Microscopy, including Chapters on Bacteri-
ology, Neoplasms, Urinary Examination, etc. Numerous Illus-
trations, some of which are printed in colors. $2 .50

WETHER ED. Medical Microscopy. A Guide to the Use of the
Microscope in Practical Medicine. 100 Illustrations. $2.00

18 SUBJECT CATALOGUE.

MISCELLANEOUS.

BERRY. Diseases of Thyroid Gland. Illustrated. $4.00

BURNETT. Foods and Dietaries. A Manual of Clinical Diet-
etics. 2d Edition. #1.50

BUXTON. Anesthetics. Illustrated. 3d Edition. $1.50

COHEN. Organotherapy. See Cohen, Physiologic Therapeutics
page ib.

DAVIS. Dietotherapy. Food in Health and Disease. With
Tables of Dietaries, Relative Value of Foods, etc. See Cohen,
Physiologic Therapeutics, page ib.

GOULD. Borderland Studies. Miscellaneous Addresses and
Essays. i2mo. $2.00

GREENE. Medical Examination for Life Insurance. Illus-
trated. With Colored and other Engravings. #4.00

HAIG. Causation of Disease by Uric Acid. The Pathology of
High Arterial Tension, Headache, Epilepsy, Gout, Rheumatism,
Diabetes, Bright's Disease, etc. 5thEdition. $3.00

HAIG. Diet and Food. Considered in Relation to Strength and
Power of Endurance. 3d Edition. $1.00

HENRY. A Practical Treatise on Anemia. Half Cloth, .50

LEFFMANN. Food Analysis. Illustrated. $2.50

NEW SYDENHAM SOCIETY'S PUBLICATIONS. Circulars
upon application. Per Annum, $8.00

OSGOOD. The Winter and Its Dangers. .40

PACKARD. Sea Air and Sea Bathing. .40

RICHARDSON. Long Life and How to Reach It. ^- .40

ST. CLAIR. Medical Latin. $1.00

TISSIER. Pneumatotherapy. See Cohen, Physiologic Therapeu-
tics, page ib.
TURNBULL. Artificial Anesthesia. 4th Edition. Illus. $2.50

WEBER AND HINSDALE. Climatology and Health
Resorts. Including Mineral Springs. 2 Vols. Illus'rated with
Colored Maps. See Cohen, Physiologic Therapeutics , page ib.

WILSON. The Summer and Its Diseases. .40

WINTERNITZ. Hydrotherapy, Thermotherapy, Photo-
therapy, Mineral Waters, Baths, etc. Illustrated. See Cohen,
Physiologic Therapeutics , page lb.

NERVOUS DISEASES.

DERCUM. Rest, Suggestion, Mental Therapeutics. See
Cohen, Physiologic Therapeutics, page lb.

GORDINIER. The Gross and Minute Anatomy of the Cen-
tral Nervous System. With 271 original Colored and other
Illustrations. Cloth, $6.00; Sheep, $7.00

GOWERS. Syphilis and the Nervous System. $1.00

MEDICAL BOOKS. 19

GOWERS. Manual of Diseases of the Nervous System. A
Complete Text-Book. Revised, Enlarged, and in many parts Re-
written. With many new Illustrations. Two volumes.
Vol. I. Diseases of the Nerves and Spinal Cord. 3d Edition, En-
larged. Cloth, $4.00; Sheep, $5.00
Vol. II. Diseases of the Brain and Cranial Nerves ; General and
Functional Disease. 2d Edition. Cloth, $4.00; Sheep, $5.00

GOWERS. Epilepsy and Other Chronic Convulsive Diseases.
2d Edition. $3.00

HORSLEY. The Brain and Spinal Cord. The Structure and
Functions of. Numerous Illustrations. $2.50

ORMEROD. Diseases of the Nervous System. 66 Wood En-
gravings. $1.00

PERSHING. Diagnosis of Nervous and Mental Diseases.

Illustrated. $1.25

PRESTON. Hysteria and Certain Allied Conditions. Their

Nature and Treatment. Illustrated. $2.00

WOOD. Brain Work and Overwork. .40

NURSING (see also Massage).

Special Catalogue of Books for Nurses sent free upon application.

CANFIELD. Hygiene of the Sick-Room. A Book for Nurses and
Others. Being a Brief Consideration of Asepsis, Antisepsis, Disinfec-
tion, Bacteriology, Immunity, Heating and Ventilation, and Kindred
Subjects for the Use of Nurses and Other Intelligent Women. $1.25

CUFF. Lectures to Nurses on Medicine. Third Edition. $1.25

DAVIS. Bandaging. Its Principles and Practice. 163 Original
Illustrations. Just Ready. $1.50

DOMVILLE. Manual for Nurses and Others Engaged in At-
tending the Sick. 9th Edition. With Recipes for Sick-room Cook-
ery, etc. In Press.

FULLERTON. Obstetric Nursing. 41 Ills. 5th Ed. $1.00

FULLERTON. Surgical Nursing. 3d Ed. 69 Ills. $1.00

GROFF. Materia Medica for Nurses. With Questions for Self-Ex-
amination. 2d Edition, Revised and Improved. Just Ready. $1.25

HADLEY. General, Medical, and Surgical Nursing. A very
Complete Manual, Including Sick-Room Cookery. Just Ready. $1.25

HUMPHREY. A Manual for Nurses. Including General
Anatomy and Physiology, Management of the Sick Room, etc.
23d Edition. 79 Illustration^. $1.00

STARR. The Hygiene of the Nursery. Including the General
Regimen and Feeding of Infants and Children, and the Domestic Man-
agement of the Ordinary Emergencies of Early Life, Massage, etc. 6th
Edition. 25 Illustrations. $1.00

TEMPERATURE AND CLINICAL CHARTS. See page 24.

VOSWINKEL. Surgical Nursing. Second Edition, Enlarged.
1x2 Illustrations. $1.00

20 SUBJECT CATALOGUE.

OBSTETRICS.

CAZEAUX AND TARNIER. Midwifery. With Appendix by
Mundb. The Theory and Practice of Obstetrics, including the Dis-
eases ot Pregnancy and Parturition, Obstetrical Operations, etc.
8th Edition. Illustrated by Colored and other full-page Plates, and
numerous Wood Engravings. Cloth, #4.50 ; Full Leather, $5.50

EDGAR. Text-Book of Obstetrics. By J. Clifton Edgar,
m.d., Professor of Obstetrics, Medical Department of Cornell
University, New York City. Elaborately Illustrated. In Press.

FULLERTON. Obstetric Nursing. 5th Ed. Illustrated. $1.00

LANDIS. Compend of Obstetrics. 7th Edition, Revised by Wm.

H. Wells, Demonstrator of Clinical Obstetrics, Jefferson Medical

College. 52 Illustrations. .80; Interleaved, $1.00

WINCKEL. Text-Book of Obstetrics, Including the Pathol-
ogy and Therapeutics of the Puerperal State. Illus. $5.00

PATHOLOGY— BACTERIOLOGY.

BARLOW. General Pathology. 795 pages. 8vo. $5.00

BLACK. Micro-Organisms. The Formation of Poisons. .75

BLACKBURN. Autopsies. A Manual of Autopsies Designed for

the Use of Hospitals for the Insane and other Public Institutions.

Ten full-page Plates and other Illustrations. $1.25

CONN. Agricultural Bacteriology. Illustrated. $2.50

CONN. Bacteria in Milk Products. Illustrated. In Press.

COPLIN. Manual of Pathology. Including Bacteriology, Technic
of Post-Mortems, Methods of Pathologic Research, etc. 330 Illus-
trations, 7 Colored Plates. 3d Edition. fr}-50

DA COSTA. Clinical Hematology. A Practical Guide -tcsthe
Examination of the Blood. Six Colored Plates and 48 Illustrations.
Just Ready. Cloth, $5.00 ; Sheep, $6.00

EMERY. Bacteriological Diagnosis. 2 Colored Plates and 32
other Illustrations. Just Ready. $1.50

HEWLETT. Manual of Bacteriology. 75 Illustrations. Second
Edition, Revised and Enlarged. Just Ready. $4.00

ROBERTS. Gynecological Pathology. Illustrated. $6.00

THAYER. Compend of General Pathology. Illustrated.

Just Ready. .80 ; Interleaved, $1.00

THAYER. Compend of Special Pathology. Illustrated.

Just Ready. .80 ; Interleaved, $1.00

VIRCHOW. Post-Mortem Examinations. 3d Edition. .75

WHITACRE. Laboratory Text-Book of Pathology. With
121 Illustrations. $i-5o

WILLIAMS. Bacteriology. A Manual for Students. 90 Illus-
trations. 2d Edition, Revised. $1.50

PHARMACY.

Special Catalogue of Books on Pharmacy sent free upon application.

COBLENTZ. Manual of Pharmacy. A Complete Text-Book
by the Professor in the New York College of Pharmacy. 2d Edition,
Revised and Enlarged. 437 Illus. Cloth, $3.50; Sheep, $4.50

COBLENTZ. Volumetric Analysis. Illustrated. $1.25

MEDICAL BOOKS. 21

BEASLEY. Book of 3100 Prescriptions. Collected from the
Practice of the Most Eminent Physicians and Surgeons — English,
French, and American. A Compendious History ot the Materia
Medica, Lists of the Doses of all the Officinal and Established Pre-
parations, an Index of Diseases and their Remedies. 7th Ed. $2.00

BEASLEY. Druggists' General Receipt Book. Comprising
a Copious Veterinary Formulary, Recipes in Patent and Proprietary
Medicines, Druggists' Nostrums, etc. ; Perfumery and Cosmetics,
Beverages, Dietetic Articles and Condiments, Trade Chemicals,
Scientific Processes, and many Useful Tables. 10th Ed. $2.00

BEASLEY. Pharmaceutical Formulary. A Synopsis of the
British, French, German, and United States Pharmacopoeias. Com-
prising Standard and Approved Formulae for the Preparations and
Compounds Employed in Medicine. 12th Edition. $2.00

PROCTOR. Practical Pharmacy. 3d Edition, with Illustrations
and Elaborate Tables of Chemical Solubilities, etc. $3-°°

ROBINSON. Latin Grammar of Pharmacy and Medicine.

3d Edition. With elaborate Vocabularies. $I-75

SAYRE. Organic Materia Medica and Pharmacognosy. An

Introduction to the Study of the Vegetable Kingdom and the Vege-
table and Animal Drugs. Comprising the Botanical and Physical
Characteristics, Source, Constituents, and Pharmacopeial Prepar-
ations, Insects Injurious to Drugs, and Parmacal Botany. With
sections on Histology and Microtechnique, by W. C. Stevens.
374 Illustrations. Second Edition. Cloth, $4.50

SCOVILLE. The Art of Compounding. Second Edition, Re-
vised and Enlarged. Cloth, #2.50

STEWART. Compend of Pharmacy. Based upon " Reming-
ton's Text-Book of Pharmacy." 5th Edition, Revised in Accord-
ance with the U. S. Pharmacopoeia, 1890. Complete Tables ot
Metric and English Weights and Measures. .80 ; Interleaved, $1.00

TAVERA. Medicinal Plants of the Philippines. $2.00

UNITED STATES PHARMACOPOEIA. 7th Decennial Revision.
Cloth, $2.50 (postpaid, #2.77) ; Sheep, $3.00 (postpaid, $3.27) ; Inter-
leaved, $4.00 (postpaid, $4.50); Printed on one side of page only,
unbound, $3.50 (postpaid, #3.90).

Select Tables from the U. S. P. Being Nine of the Most Impor-
tant and Useful Tables, Printed on Separate Sheets. .25
POTTER. Hand-Book of Materia Medica, Pharmacy, and
Therapeutics. 600 Prescriptions. 8th Ed. Clo., $5.00; Sh., $6.00

PHYSIOLOGY.

BIRCH. Practical Physiology. An Elementary Class Book.

62 Illustrations. $i-75

BRUBAKER. Compend ot Physiology. 10th Edition, Revised

and Enlarged. Illustrated. .80; Interleaved, $1. 00

JONES. Outlines of Physiology. 96 Illustrations. $*-5<>

KIRKES. Handbook of Physiology. 17th Authorized Edition.
Revised, Rearranged, and Enlarged. By Prof. W. D. Hallibur-
ton, of Kings College, London. 681 Illustrations, some of which
are in colors. Cloth, $3.00; Leather, $3.75

22 SUBJECT CATALOGUE.

LANDOIS. A Text-Book of Human Physiology, Including
Histology and Microscopical Anatomy, with Special Reference to
the Requirements of Practical Medicine. 5th American, translated
from the last German Edition, with Additions by Wm, Stirling,
m.d.,d.sc. 845 Illus., many of which are printed in colors. In Press.

STARLING. Elements of Human Physiology. 100 Ills. $1.00

STIRLING. Outlines of Practical Physiology. Including
Chemical and Experimental Physiology, with Special Reference to
Practical Medicine. 3d Edition. 289 Illustrations. $2.00

TYSON. Cell Doctrine. Its History and Present State. fci.50

PRACTICE.

BEALE. On Slight Ailments; their Nature and Treatment.

2d Edition, Enlarged and Illustrated. $}-*S

FAGGE. Practice of Medicine. 4th Edition, by P. H. Pye-
Smith, m d. 2 Volumes. Vol. I, $6 00 ; Vol. II, In Press.

FOWLER. Dictionary of Practical Medicine. By various
writers. An Encyclopaedia of Medicine. Clo.,$3.oo; Half Mor. $4.00
GOULD AND PYLE. Cyclopedia of Practical Medicine and
Surgery. A Concise Reference Handbook, with particular Refer-
ence to Diagnosis and Treatment. Edited by Drs. Gould and
Pyle, Assisted by 72 Special Contributors. Illustrated, one volume.
Large Square Octavo, Uniform with "Gould's Illustrated Diction-
ary." Sheep or Half Mor., $10 00 ; with Thumb Index, $11.00

Half Russia, Thumb Index, $12 00
j8SP* Complete descriptive circular free upon application.
GOULD AND PYLE'S Pocket Cyclopedia of Medicine and
Surgery. Based upon the above and Uniform with " Gould's
Pocket Dictionary."

Full Limp Leather, Gilt Edges, Round Corners, $1.00
With Thumb Index, $1.25
HUGHES. Compend of the Practice of Medicine. 6th Edition,
Revised and Enlarged.

Part I. Continued, Eruptive, and Periodical Fevers, Diseases of the
Stomach, Intestines, Peritoneum, Biliary Passages, Liver, Kid-
neys, etc., and General Diseases, etc.
Part II. Diseases of the Respiratory System, Circulatory System,
and Nervous System; Diseases of the Blood, etc.

Price of each part, .80; Interleaved, $1.00

Physician's Edition. In one volume, including the above two

parts, a Section on Skin Diseases, and an Index. 6th Revised

Edition. 625 pp. Full Morocco, Gilt Edge, $2.25

MURRAY. Rough Notes on Remedies. 4th Ed. $1.25

TAYLOR. Practice of Medicine. 6th Edition. $4.00

TYSON. The Practice of Medicine. By James Tyson, m.d.,
Professor of Medicine in the University of Pennsylvania. A Com-
plete Systematic Text-book with Special Reference to Diagnosis and
Treatment. 2d Edition, Enlarged and Revised. Colored Plates and
125 other Illustrations. 1222 Pages. Cloth, $5.50 ; Leather, $6.50

STOMACH. INTESTINES.

HEMMETER. Diseases of the Stomach. Their Special Path-
ology, Diagnosis, and Treatment. With Sections on Anatomy,
Analysis of Stomach Contents, Dietetics, Surgery of the Stomach,
etc. 3d Edition, Revised. With 15 Plates and 41 other Illustrations,
a number of which are in Colors. Just Ready

Cloth, $6.00; Sheep, $7.00

MEDICAL BOOKS. 23

HEMMETER. Diseases of the Intestines. Their Special Path-
ology, Diagnosis, and Treatment. With Sections on Anatomy and
Physiology, Microscopic and Chemic Examination of Intestinal
Contents, Secretions, Feces and Urine, Intestinal Bacteria and
Parasites, Surgery of the Intestines, Dietetics, Diseases of the
Rectum, etc. With Full-page Colored Plates and many other
Original Illustrations. 2 Volumes. Octavo. Just Ready.

Price of each Volume, Cloth, $5.00; Sheep, $6.00

SKIN.

BULKLEY. The Skin in Health and Disease. Illustrated. .40

CROCKER. Diseases of the Skin. Their Description, Pathol-
ogy, Diagnosis, and Treatment, with Special Reference to the Skin
Eruptions of Children. 3d Edition, Thoroughly Revised. With
New Illustrations. Nearly Ready. $5.00

SCHAMBERG. Diseases of the Skin. 2d Edition, Revised and
Enlarged. 105 Illustrations. Being No. 16 ? Quiz-Compend ? Series.

Cloth, .80; Interleaved, $1.00

VAN HARLINGEN. On Skin Diseases. A Practical Manual
of Diagnosis and Treatment, with special reference to Differential
Diagnosis. 3d Edition, Revised and Enlarged. With Formulae
and 60 Illustrations, some of which are printed in colors. $2.75

SURGERY AND SURGICAL DIS-
EASES (see also Urinary Organs).

BERRY. Diseases of the Thyroid Gland and Their Surgical
Treatment. Illustrated. $4.00

BUTLIN. Operative Surgery of Malignant Disease. 2d Edi-
tion. Illustrated. Octavo. $4-5Q

DAVIS. Bandaging. Its Principles and Practice. 163 Original
Illustrations. $1.50

DEAVER. Surgical Anatomy. A Treatise on Human Anatomy
in its Application to Medicine and Surgery. With about 450 very
Handsome full-page Illustrations Engraved from Original Drawings
made by special Artists from Dissections prepared for the purpose.
Three Volumes. Royal Square Octavo.
Cloth, $21.00; Half Morocco or Sheep, $24.00 ; Half Russia, $27.00

Complete descriptive circular and special terms upon application.

DEAVER. Appendicitis, Its Symptoms, Diagnosis, Pathol-
ogy. Treatment, and Complications. Elaborately Illustrated
with Colored Plates and other Illustrations. 3d Edition. Preparing.

DULLES. What to Do First in Accidents and Poisoning.

5th Edition. New Illustrations. $1.00

FULLERTON. Surgical Nursing. 3d Edition. 69 Illus. $1.00

HAMILTON. Lectures on Tumors. 3d Edition. $1.25

HEATH. Minor Surgery and Bandaging. 12th Edition, Revised
and Enlarged. 195 Illus., Formulae, Diet List, etc. $150

HEATH. Clinical Lectures on Surgical Subjects. Second
Series. Just Ready. $2.00

HORWITZ. Compend of Surgery and Bandaging, including
Minor Surgery, Amputations, Fractures, Dislocations, Surgical Dis-
eases, etc., with Differential Diagnosis and Treatment. 5th Edition,
very much Enlarged and Rearranged. 167 Illustrations, c-8 Formulae.

Cloth, .80; Interleaved, $1.00

24 SUBJECT CATALOGUE.

JACOBSON. Operations of Surgery. 4th Edition, Enlarged.
550 Illustrations. Two Volumes. Cloth, $10.00 ; Leather, $12.00

KEAY. Medical Treatment of Gall Stones. Just Ready. $1.25

KEHR. Gall-Stone Disease. Translated by William Wotkvns
Seymour, m.d. #2.50

MAK1NS. Surgical Experiences in South Africa. 1899-1900.
Illustrated. $4.00

MAYLARD. Surgery of the Alimentary Canal. 97 Illustrations.
2d Edition, Revised. J3.00

MOULLIN. Text-Book of Surgery. With Special Reference to
Treatment. 3d American Edition. Revised and edited by John B.
Hamilton, m.d., ll.d., Professor of the Principles of Surgery and
Clinical Surgery, Rush Medical College, Chicago. 623 Illustrations,
many of which are printed in colors. Cloth, $6.00; Leather, $7.00

SMITH. Abdominal Surgery. Being a Systematic Description of
all the Principal Operations. 224 Illus. 6th Ed. 2 Vols. Clo., $10.00

VOSWINKEL. Surgical Nursing. Second Edition, Revised and
Enlarged. 11 1 Illustrations. $1.00

WALSHAM. Manual of Practical Surgery. 7th Ed., Re-
vised and Enlarged. 483 Engravings. 950 pages. #3-5°

TEMPERATURE CHARTS, ETC. I

GRIFFITH. Graphic Clinical Chart for Recording Temper-
ature, Respiration, Pulse, Day of Disease, Date, Age, Sex,
Occupation, Name, etc. Printed in three colors. Sample copies
free. Put up in loose packages of fifty, .50. Price to Hospitals, 500
copies, $4.00 ; 1000 copies, $7. so.

KEEN'S CLINICAL CHARTS. Seven Outline Drawings of the
Body, on which may be marked the Course of Disease, Fractures,
Operations, etc. Each Drawing may be had separately, twenty-five
to pad, 25 cents.

SCHREINER. Diet Lists. Arranged in the form of a chart.
With Pamphlets of Specimen Dietaries. Pads of 50. .75

THROAT AND NOSE (see also Ear).

COHEN. The Throat and Voice. Illustrated. .40

HALL. Diseases of the Nose and Throat. 2d Edition, Enlarged.
Two Colored Plates and 80 Illustrations. $2-75

HOLLOPETER. Hay Fever. Its Successful Treatment. $1.00

KNIGHT. Diseases of the Throat. A Manual for Students.
Illustrated. Nearly Ready.

LAKE. Laryngeal Phthisis, or Consumption of the Throat.
Colored Illustrations. $2.00

McBRIDE. Diseases of the Throat, Nose, and Ear. With col-
ored Illustrations from original drawings. 3d Edition. $7-°°

POTTER. Speech and its Defects. Considered Physiologically,
Pathologically, and Remedially. $1.00

SHEILD. Nasal Obstructions. Illustrated. $1.50

URINE AND URINARY ORGANS.

ACTON. The Functions and Disorders of the Reproductive
Organs in Childhood, Youth, Adult Age, and Advanced Life,
Considered in their Physiological, Social, and Moral Relations.
8th Edition. $1-75

MEDICAL BOOKS. 25

HOLLAND. The Urine, the Gastric Contents, the Common
Poisons, and the Milk. Memoranda, Chemical and Microscopi-
cal, for Laboratory Use. Illustrated and Interleaved. 6th Ed. $1.00
KLEEN. Diabetes and Glycosuria. $2.50

MEMMINGER. Diagnosis by the Urine. 2d Ed. 24 Illus. $1.00
MORRIS. Renal Surgery, with Special Reference to Stone in the
Kidney and Ureter and to the Surgical Treatment of Calculous
Anuria. Illustrated. $2.00.

MOULLIN. Enlargement of the Prostate. Its Treatment and
Radical Cure. 2d Edition. Illustrated. $i-75

MOULLIN. Inflammation of the Bladder and Urinary Fever.
Octavo. $1.50

SCOTT. The Urine. Its Clinical and Microscopical Examination.
41 Lithographic Plates and other Illustrations. Quarto. Cloth, $5.00

TYSON. Guide to Examination of the Urine. For the Use of
Physicians and Students. With Colored Plate and Numerous Illus-
trations engraved on wood. 10th Edition, Revised, Enlarged, and
partly Rewritten. With New Illustrations. Just Ready. $i.\o

VAN NUYS. Chemical Analysis of Urine. 39 Illus. $1.00

VENEREAL DISEASES.

GOWERS. Syphilis and the Nervous System. $1.00

STURGIS AND CABOT. Student's Manual of Venereal

Diseases. 7th Revised and Enlarged Ed. 12010. $1-25

VETERINARY.

BALLOU. Veterinary Anatomy and Physiology. 29 Graphic
Illustrations. .80; Interleaved, $1. 00

WOMEN, DISEASES OF.

BISHOP. Uterine Fibromyomata. Their Pathology, Diagnosis,
and Treatment. Illustrated. Cloth, $3.50

BYFORD (H. T.). Manual of Gynecology. Third Edition,
Revised and Enlarged. 363 Illustrations. Just Ready. $3.00

DUHRSSEN. A Manual of Gynecological Practice. 105
Illustrations. $1.50

FULLERTON. Surgical Nursing. 3d Edition, Revised and
Enlarged. 69 Illustrations. $1.00

LEWERS. Diseases of Women. 146 Illus. 5th Ed. $2.50

MONTGOMERY. Practical Gynecology. A Complete Sys-
tematic Text-Book. 527 Illustrations. Cloth, $5.00; Leather, $6.00

ROBERTS. Gynecological Pathology. With 127 Full-page
Plates containing 151 Figures. $6.00

WELLS. Compend of Gynecology. Illustrated. 2d Edition.

.80; Interleaved, % 1 .00

" We know of no series of books issued by any house that so fully
meets our approval as these ? Quiz-Compends ?. They are well ar-
ranged, full, and concise, and are really the best line of text-books that
could be found for either student or practitioner." — Southern Clinic.

BLAKISTON'S ? QUIZ-COMPENDS?

The Best Series of Manuals for the Use of Students.
Price of each, Cloth, .80. Interleaved, for taking Notes, $1.00.

These Compends are based on the most popular text-books and
the lectures of prominent professors, and are kept constantly re-
vised, so that they may thoroughlv represent the present state of the
subjects upon which they treat. The authors have had large experi-
ence as Quiz-Masters and attaches of colleges, and are well acquainted
with the wants of students. They are arranged in the most ap-
proved form, thorough and concise, containing nearly iooo illustra-
tions and lithograph plates, inserted wherever they could be used to
advantage. Can be used by students of any college. They contain
information nowhere else collected in such a condensed, practical shape.

No. i. POTTER. HUMAN ANATOMY. Sixth Edition. 117

Illustrations and 16 Plates of Nerves and Arteries.
No. 2. HUGHES. PRACTICE OF MEDICINE. Part I. Sixth

Edition, Enlarged and Improved.

No. 3. HUGHES. PRACTICE OF MEDICINE. Part II.

Sixth Edition, Revised and Improved.

No. 4. BRUBAKER. PHYSIOLOGY. Tenth Edition. Illus.

No. 5. LANDIS. OBSTETRICS. Seventh Edition. 52 Illus.

No. 6. POTTER. MATERIA MEDICA, THERAPEUTICS,

AND PRESCRIPTION WRITING. Sixth Revised EditioD.

No. 7. WELLS. GYNECOLOGY. Second Ed. 14c1 IUus.
No. 8. GOULD AND PYLE. DISEASES OF THE EYE.

Second Edition. Refraction, Treatment, Surgery, etc. 109 Illus.

No. 9. HORWITZ. SURGERY. Including Minor Surgery,
Bandaging, Surgical Diseases, Differential Diagnosis and Treat-*
ment. Fifth Edition. With 98 Formulae and 71 Illustrations.

No. 10. LEFFMANN. MEDICAL CHEMISTRY. Fourth

Edition. Including Urinalysis, Animal Chemistry, Chemistry of
Milk, Blood, Tissues, the Secretions, etc.

No. 11. STEWART. PHARMACY. Fifth Edition. Based upon
Prof. Remington's Text-Book of Pharmacy.

No. 12. BALLOU. VETERINARY ANATOMY AND PHY-
SIOLOGY. 29 graphic Illustrations.

No. 13. WARREN. DENTAL PATHOLOGY AND DEN-
TAL MEDICINE. Third Edition, Illustrated.

No. 14. HATFIELD. DISEASES OF CHILDREN. 3d Ed.

No. 15. THAYER. GENERAL PATHOLOGY. 78 Illus.

No. 16. SCHAMBERG. DISEASES OF THE SKIN. Second

Edition, Revised and Enlarged. 105 Illustrations.

No. 17. CUSHING. HISTOLOGY. Illustrated.
No. 18. THAYER. SPECIAL PATHOLOGY. 34 Illustrations.
Careful attention has been given to the construction of each sentence,
and while the books will be found to contain an immense amount of
knowledge in small space, they will likewise be found easy reading.

26

^

DA COSTA

Clinical Hematology

A Practical Guide to the Examination of the Blood by
Clinical Methods. With Reference to the Diagnosis of
Disease. With Colored Illustrations. Cloth, $5.00

*^* A new, thorough, systematic, and comprehensive
work, its purpose being, first, to show how to examine the
blood, and second, how to diagnose from such examination
diseases of the blood itself and general diseases. The
author's aim has been to cover not alone the field of original
research, but to supply a book for the student, the hospital
physician and the general practitioner. It will be found
wanting in none of these respects.

OERTEL

Medical Microscopy

NEARLY READY

A GUIDE TO DIAGNOSIS, ELEMEN-
TARY LABORATORY METHODS,
AND MICROSCOPIC TECHNIC

By T. E. Oertel, M.D.,

Professor of Pathology and Clinical Microscopy, Medical Depart-
ment, University of Georgia.

WITH 120 ILLUSTRATIONS

27

JACOBSON'S
Operations of Surgery

The Operations of Surgery. By W. H. A.
Jacobson, f.r.c.s., Surgeon to Guy's Hospital;
Consulting Surgeon Royal Hospital for Children
and Women; Member Court of Examiners Royal
College of Surgeons; Joint Editor Annals of Sur-
gery; and F. J. Steward, f.r.c.s., Assistant
Surgeon Guy's Hospital and to the Hospital for
Sick Children. Fourth Edition, Revised, En-
larged and Improved. 550 Illustrations. Two
Volumes, Octavo, 1524 pages. Cloth), $10.00

Sheep, $12.00

PRESS NOTICES OF FORMER EDITIONS

" The author proves himself a judicious operator, as
shown by his choice of methods and by the emphasis with
which he refers to the different dangers and complications
which may arise to mar success or jeopardize life." — New
York Medical Record.

" The important anatomical points are clearly set forth,
the conditions indicating or contraindicating operative inter-
ference are given, the details of the operations themselves
are brought forward prominently, and frequently the after-
treatment is considered. Herein is one of the strong points
of the book." — New York Medical Journal.

28

The Pocket Cyclopedia, of
Medicine and Surgery

Full Limp Leather, Round Corners, Gilt Edges, $1.00
With Thumb Index, $1.25

Uniform 'with "Gould's Pocket Dictionary"

A concise practical volume of nearly 600
pages, containing a vast amount of infor-
mation on all medical subjects, including
Diagnosis and Treatment of Disease,
with Formulas and Prescriptions, Emer-
gencies, Poisons, Drugs and Their Uses,
Nursing, Surgical Procedures, Dose List
in both English and Metric Systems, etc.

By Drs. Gould and Pyle

Based upon their large u Cyclopedia of
Medicine and Surgery/* J* <£ jt

*.£* This is a new book which will prove of the greatest
value to students. It is to the broad field of general medi-
cal information what "Gould's Pocket Dictionary" is to
the more special one of definition and pronunciation of
words. The articles are concise but thorough, and arranged
in shape for quick reference. In no other book can be
found so much exact detailed knowledge so conveniently
classified, so evenly distributed, so methodically grouped.
It is Multum in Parvo.

29

A NEW EDITION

Crocker on the Skin

The 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. , Physician to the Department of Skin Diseases, Uni-
versity College Hospital, London. With new Illustrations.

Third Edition, Rewritten and Enlarged

NEARLY READY j CLOTH, $5.00

*#* This new edition will easily hold the high position
given the previous printings. The author is a member of
American, English, French, German, and Italian Dermalo-
logical Societies, and a recognized authority the world over.

STURGIS— MANUAL OF
VENEREAL DISEASES

By F. R. Sturgis, m.d., Sometime Clinical Professor of
Venereal Diseases in the Medical Department of the Uni-
versity of the City of New York. Seventh Edition, Revised
and in Part Rewritten by the Author and FoLLEN Cabot,
M.D., Instructor in Genito-Urinary and Venereal Diseases
in the Cornell University Medical College. i2mo. 216
pages. Cloth, $1.25

*x* This manual was originally written for students'
use, and is as concise and as practical as possible. It pre-
sents a careful, condensed description of the commoner
forms of venereal diseases which occur in the practice of
the general physician, together with the most approved
remedies.

30

FOR THE DISSECTING ROOM

Holden's Anatomy — Seventh Edition
320 Illustrations

A Manual of the Dissections of the Human Body. By John
LANGTON, f.r.c.s. Carefully Revised by A. HKWSON, m.D.,
Demonstrator of Anatomy. Jefferson Medical College, Phila-
delphia, etc. 320 Illustrations. Two small compact vol-
umes. i2mo.

Vol. I. Scalp, Face, Orbit, Neck, Throat, Thorax, Upper
Extremity. 435 pages. 153 Illustrations.

Oil Cloth, $1.50

Vol. II. Abdomen, Perineum, Lower Extremity, Brain,
Eye, Ear, Mammary Gland, Scrotum, Testes.
445 pages. 167 Illustrations.

Oil Cloth, $1.50

Each volume sold separately.

Hughes a.nd Keith — Dissections
Illustrated

A Manual of Dissections by Alfred W. Hughes, m.b.,
m.R.C.s. (Edin. ), late Professor of Anatomy and Dean of
Medical Faculty, King's College, London, etc. , and Arthur
Keith, M.D., Joint Lecturer on Anatomy, London Hospital
Medical College, etc. In three parts. With 527 Colored
and other Illustrations.

I. Upper and Lower Extremity. 38 Plates, 116 other
Illustrations. Cloth, $3.00

II. Abdomen. Thorax. 4 Plates, 149 other Illus-
trations. Cloth, $3.00
III. Head, Neck, and Central Nervous System. 16
Plates, 204 other Illustrations. Cloth, S3. 00

Each volume sold separately.

*.£* The student will find it of great advantage to have
a "Dissector" to supplement his regular text-book on
anatomy. These books meet all requirements, and as they
can be purchased in parts as wanted, the outlay is small.

31

EDGAR'S

OBSTETRICS

A NEW TEXT -BOOK

The Illustrations in Edgar's Ob-
stetrics surpass in number, in artistic
beauty, and in practical worth those
in any book of similar character. They
are largely from original sources, are
made to a scale, and have been drawn
by artists of long experience in this
class of medical work.
The Text has been prepared with
great care. The author's extensive ex-
perience in hospital and private prac-
tice and as a teacher, his cosmopolitan
knowledge of literature and methods,
and an excellent judgment based upon
these particularly fit him to prepare
what must be a standard work.

/ N P R E s s

JUST READY

c/L Companion Volume to Gould's Tocket dictionary

A POCKET CYCLOPEDIA

OF

MEDICINE * SVRGERY

EDITED BY

GEORGE M. GOVLD, A.M., M.D.

Author of ** Gould's Medical Dictionaries % ** Editor of ** American Medicine "

AND

WALTER L. PYLE, A.M., M.D.

Assistant Surgeon Wills Eye Hospital, Philadelphia j formerly Editor
"International Medical Magazine," etc.

BEING BASED UPON GOULD AND PYLE'S LARGE " CYCLOPEDIA OF
PRACTICAL MEDICINE AND SURGERY"

Vniform with Gould's Pocket Dictionary. 64mo. Flexible Leather,
Gilt Edges, Round Comers, net $1.00; with Thumb Index. $1.25

T* HIS book bears to Gould and Pyle's large " Cyclopedia of Medicine
and Surgery ' ' a relation similar to that which the Pocket Dic-
tionary bears to Gould's complete "Illustrated Dictionary." As
the Dictionary gives the derivation, pronunciation, and definition
of medical words, the Cyclopedia is designed to furnish general
information concerning medical subjects. Every subject, concerning which
the student may desire a brief and thorough description, supplementing the
mention which may be given in lectures or a general text-book, is taken up
and treated thoroughly and concisely. To those desiring concise authoritative
information on medical or surgical themes or who wish to look up any new
term or matter of recent discovery and use, the book will prove invaluable.
It includes articles on Emergencies, Hygiene, Poisons, Nursing, etc.; describes
Drugs and their Uses ; gives Treatment of Diseases ; explains Surgical Oper-
ations ; contains many Prescriptions and Formulae, Tables of Differential
Diagnosis, Dose Table in both English and Metric Systems, etc.

P. BLAKISTON'S SON ©. CO., Publishers and Booksellers
1012 WALNUT STREET, PHILADELPHIA

FOR MEDICAL STUDENTS.

COLUMBIA UNIVERSITY

This book is due on the date indicated below, or at the
expiration of a definite period after the date of borrowing,
as provided by the rules of the Library or by special ar-

rangement with the Librarian in charge.

o
h

DATE BORROWED

DATE DUE

DATE BORROWED

DATE DUE ,e

ie
X

1

o

■>

bf

o

:y

>n

' fe

ie

»n

c.

'5

rv

id
>3

jo

1.

ot

13

s.

id

th

C28'638)M80

>y

ie

Npw ~Vnr]z TYi<;l

-drfulimtp Medical .

School and Hospita

I. Cloth, net. #roo

P. BLAKISTON'S SON & CO., Publishers and Booksellers,

1012 WALNUT STREET. PHILADELPHIA.

FOR MEDICAL STUDENTS.

KIRKES' PHYSIOLOGY. Seventeenth Edition. {The Authorized

Edition. i2»io. Dark Red Cloth.) Revised and Enlarged. By W.
D. Halliburton, m.d., f.r.s., Professor of Physiology. Kind's; Collate,

Londo1

AC. Til — ••

HA.

WI

TY!

TY

RE|

SW

BYI

BAB

QP40

Brubaker

B83
1902

rs.
oo

[E

;or

a,

■al

, . , — ~~ «■■« ^nittigcu. wun 92 illustrations,

Glossary, and Complete Index. i2mo. Cloth, net, #3.00

P. BLAKISTON'S SON & CO., Publishers and Booksellers,
1012 Walnut street, Philadelphia.