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COLLEGE OF

PHYSICIANS AND SURGEONS

LIBRARY

Digitized by tine Internet Arciiive

in 2010 with funding from
Columbia University Libraries

I

http://www.archive.org/details/physiologymanualOOmann

The Students' Quiz Series.

A series covering the essential subjects of a thorough medical
education, arranged in form of question and answer. By
qualified teachers and examiners in New York. Illustrations
wherever desirable. Priced at uniform low rate of $1.00,
except double numbers on Anatomy and Surgery, which are
-priced at f 1.75 each.

ANATOMY (BotibU Number)— ■Ry Fbec J.
Bkockway, M.D., Ass't Demonstrator
of Anatomy, College of Physicians and
Surgeons, New York, and A. O'Malley,
M. D., Instructor in Surgery, New York
Polyclinic. §1.75.

PHYSIOLOGY— By F. A. Manning, M. D.,
At tending Surgeon, Manhattan Hospital,
N.Yo $1.00.

CHEWiSTRY ANiJ PHYSICS— By Joseph
STEtrrHERS,PH.B.,Columbia Coll. School
of Mines, N. Y., D. W. Ward, Ph, B.,
Columbia College School of Mines, N. Y.,
and Chas, H. Willmarth, M. S., N. Y. 81 .

HISTOLOGY, PATHOLOGY AND BAC-
TEKIOLOGY— By Bknnett S. Beach,
M.D., Lecturer on Histology, Pathology
and Bacteriology, New York Polyclinic.
?1.00.

MATEHIA MEDICA AND THERAPEU-
TICS—By L. F.AVarnek, M.D., Attend-
ing Physician, St. Bartholomew's Dispen-
sary, N.Y. irl.OO.

PRACTICEOF MEDICINE, including Ner-
vous Diseases— By Edwin T. Double-
day, M.D., Member N.Y. Pathological
Society, and J. D. Naoel, M.D., Mem-
ber N . Y. County Medical Asso'n. 81.00.

SURGERY (Double Number)— ^y Bern B.
Gallaudet, M. D., Attending Surgeon
Bellevue Hospital, N. Y., and Charles
Dixon Jones, M.D., Surgeon to York-
ville Dispensary and Hospital, N. Y.
81.75.

GENITO-URINARY AND VENEREAL
DISEASES— By Chas. H. Chetwood,
M. D., Visiting Surgeon, Domilt Dispen-
sary, Department of Surgery and Genito-
urinary Diseases, New York. $1.00.

DISEASES OF THE SKIN-By Charles
C. Kansom, M. D., Assistant Dermatolo-
gist, Yanderbilt Clinic, N. Y. 81.00.

DISEASES OF THE EYE, EAR, THROAT

AND NOSE— By Frank E. Milleh,
M. D., Throat Surgeon, Vanderbil.t Clinic,
N. Y., James P. MacEvoy, M. D.,
Throat Surgeon, Bellevue Hospital, Out-
Pat lent Department, New York, and
J. E. Weeks, M.D., Lecturer on Oph-
thalmology and Otology, Bellevue Hos-
pital Medical College, New York. 81.00.

OBSTETRICS — By Charles W, Hayt,
M. D., House Physician, Nursery and
Child's Hospital, New York. 81.00,

GYNECOLOGY-By G. W. Bratenahl,
M. I>., Assistant in Gynecology, Yander-
bilt Clinic, New York, and Sinclair
TouSEY, M. D., Assistant Surgeon, Out-
Patient Department, Koosevelt Hospital,
New York. 81.00.

DISEASES OF CHILDREN — By C. A.

EnoDES, M.D., Instructor in Diseases of
Children, N. Y. Post-Graduate Medical
School 81.00.

LEA BROTHERS & CO.. PUBLISHERS, PHILADELPHIA.

Th? Students* Quiz Scries.

PHYSIOLOGY.

A MANUAL FOR STUDENTS AND PRACTITIONEUS.

BY

FREDERICK A. MANNING, M. D.,

Attending Surgeon, Manhattan Hospital, New York.

SERIES EDITED BY

BERN B. GALLAUDET, M.D,

Demonstrator of Anatomy, College of Physicians and Surgeons, New York; Visiting
Surgeon Bellevue Hospital, New York.

PHILADELPHIA :
LEA BROTHERS & CO.

Entered according to Act of Congress, in the year 1892, by

LEA BROTHERS & CO.,

In the Oflace of the Librarian of Congress, at Washington. All rights reserved.

Westcott 4 Thomson, William J. Dornan,

Stereotypers and Electrolypers, Philada. Printer, Philada.

PREFACE.

The present book is a brief summary of the salient features
of Human Physiology. It is not intended to compete with nor
to take the place of the more elaborate text-books. The idea
has been to present the subject in such a manner as to fix in
the memory facts already learned in less limited treatises.

There is no claim of originality for this book. It is practi-
cally and of necessity an abstract of standard works, and princi-
pally of those of Dalton, Foster, and Kirke. The arrangement
has in a general way, been made to conform with that of the
last-named authority. The cuts are many of them from Dal ton's
Physiology. Doubtful questions have often been referred to
Foster, whose Text-booh of Physiology is the reference-book of
a large proportion of the schools. Some of the histological
descriptions are derived from Prudden's Practical Normal His-
tology.

New York.

CONTENTS,

PAGE

General Considerations and Proximate Principles 17

The Blood 22

Circulation of the Blood 27

Kespiration 36

Digestion 42

Absorption 59

Animal Heat 62

Secretion: The Mammary Glands; The Skhi ; The Kidneys and

the Urine; The Vascular Glands 64

Muscle 82

Nutrition 89

Nervous System : The Nerves ; Sympathetic System ; Spinal Cord ;

The Medulla Oblongata; The Pons Varolii and Crura Cerebri;

The Cerebrum ; The Cerebellum ; The Cranial Nerves 93

The Senses : Touch ; Taste ; Smell ; Hearing ; Sight 145

Embryology : Eeproductiou ; Development ; Parturition 173

APPENDIX.

Table op the Development of an Eiwbryo 205

Chemical Tests used Commonly in Physiological Analysis . . 205

Metric System 207

5

PHYSIOLOGY.

GENERAL CONSIDERATIONS AND PROXIMATE
PRINCIPLES.

Define human physiology.

Human Physiology is that branch of biology which refers to
the functions and properties of the organs in the living human
body.

In entering upon the study of the functions of organs it becomes
desirable to understand something of the nature of the fundamental
elements of living tissue which we call cells.

What are cells?

Cells may be described as nucleated masses of protoplasm of
microscopic size, usually possessing limiting membranes known
as cell-walls, and capable of passing through the changes which
are characteristic of life and death. Some cells do not possess
a nucleus, but this is quite exceptional. More commonly each
cell has a nucleus or more than one, and in many instances there
is a nucleolus within the body of the nucleus.

What is protoplasm?

Protoplasm is an unstable albuminoid substance of more or less
gelatinous nature. Its reactions are those of albumin (coagulation
: by heat and mineral acids), and its chemical composition is of vary-
ing proportions of the elements C, H, N, 0, S. Protoplasm is living
albumin or proteid.

Illustrate the life of the cells by the amoeba.

The characteristic changes through which cells pass are well
illustrated by the amoeba : {a) The" power of spontaneous move-
ment, in . which a small portion of the cell is first advanced, and
2— Phy. 17

18 GENERAL CONSIDERATIONS.

then the whole cell seems to flow to and into its branch, (i)
Motion in response to various phj-sical and chemical stimuli.
(c) The power of taking food, absorbing portions and rejecting
the rest. ((^) Reproduction of its kind. This is accomplished by
splitting of the cell into two, each with it.s own nucleus and life-
history, (e) Death, in which the constituent elements undergo
chemical changes. All cells follow more or less clo.sely this cycle
of changes by which we differentiate living matter from unorgan-
ized substances.

Name some of the kinds of cells found in man.
Epithelial, connective-tissue, blood-, and nerve-cells.

What is epithelium ?

The name '• epithelium " is given t(t the cells which cover the skin,
mucous and serous membranes of the body, and also enter into the
formation of the glands. Its varieties are — (1) Simple, a layer
of flat (s(iuanious), cubical, (spheroidal), or cylindrical (columnar)
cells, as in the serous and mucous surfaces ; (2) sfra/ijicil, when it
occurs in layers, as in the skin ; (3) transldoiKil, wliere it has the
characteristics of both in situations where the other two forms
approach one another, as in the ureters. (4) In the glands are
found finicfiaiud n/ls, winch partake of the character of the epi-
thelium of the surface. They arc arranged in groups about the
ducts. Such cells are often known as secreting or glandular epi-
thelial cells.

What is ciliated epithelium ?

The simple epithelium posses.se.s hair-like proces.ses in certain
locations, and this is known as riliafrd ipithcUnm. The hairs are
endowed with motion, and wave in such manner as to throw for-
ward small particles wliidi f;i]] upon them.

Name the chief uses of epithelium.

Protection, as skin, serous surfaces; motion, ciliated epithelium
of air-passages and Fallopian tubes ; secretion, in glands — p. g.
gastric juice; .sen.sation, in the cones of the retina, olfactory cells
of nose, etc.

What is endothelium ?

It is a simple form of squamous or scale-like, flat epithelial cells
which line the serous membranes and the blood-vessels. The cells

PROXIMATE PRINCIPLES. 19

are very delicate, and are not stratified. They are of various forms,
usually irregularly polygonal, and are joined at tte edges so as to
form a sort of mosaic.

What are connective tissues?

They are the structures which form the frame and supports of
the body and of the organs of the body. The ligaments, tendons,
fascige, cartilage, and bones are examples of them. The fibrous
connective-tissue cells are found in all organs in greater or less
amount. In the organs whose use is the support of the body or
one of its members these cells predominate. In other organs the
fibrous cells serve to hold in place the functional cells and to
maintain the shape of the organs.

What are the proximate principles of the hody ?

They are the substances entering into the composition of the
body, and are inorganic and organic.

What are the inorganic elements ?

Chemically, C, H, 0, N make up a very large portion of the
body-weight, water alone (H2O) forming about three-fourths of
the total. Besides these, sodium, potassium, lime, and magnesium,
in chemical combinations with sulphur, phosphorus, chlorine, and
carbon (sulphates, phosphates, chlorides, and carbonates),_ are
found in considerable amounts, and less abundantly iron, silica,
and fluorine. Occasionally minute quantities of some of the other
metallic elements— arsenic, lead, copper, and manganese— are found.

How are the organic proximate principles classified ?

(1) Nitrogenous, and (2) non-nitrogenous.

(1) The former take the principal part in the formation of solid
constituents of the body, and occur in all the body tissues and
fluids. They make up the protoplasm of cells and essential in-
gredients of the fluids, both circulatory and excretory. Chemi-
cally, they are compounds of C, H, 0, N, sometimes with sulphur
or phosphorus.

(2) The latter (non-nitrogenous) class of bodies are made up of
the fats and carbohydrates.

What is the reaction of the fluids of the hody ?

Alkaline, with only four notable exceptions. These are — gas-
tric juice, perspiration, vaginal mucus, and acid urine.

20

PROXIMATE PRINCIPLES.

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PROXIMATE PRINCIPLES.

21

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22 THE BLOOD.

THE BLOOD.
What is blood ?

Blood, while circulating in the body, is a somewhat viscid, opaque
fluid, of a red color ; this color varies in different parts of the body
from a brilliant scarlet to a deep purple or nearly black color. It
consists of a nearly colorless liquid (plasma or liquor sanguinis), in
which swim the blood-corpuscles or globules.

What are the physical characteristics of blood ?

It has a specific gravity at 60° F. (15° C.) of 1055 (1045-1062) ;
a faintly alkaline (potassium phosphate) reaction ; temperature
about 100° F. (37.8° C.) ; a salty taste ; and an odor which is
characteristic, and often peculiar to the animal from which it is
taken. When taken from the body it tends to form a clot or
coagulum (crassamentum).

What is the quantity of the blood ?

About one-twelfth of the body-weight, and is distributed as fol-
lows in round numbers :

About one-fourth in heart, lungs, and large vessels ;

" " in liver ;

" " in muscles ;

" " in other organs.

Describe the formation of a clot.

If blood be drawn into a shallow vessel and exposed to the air, it
will become semisolid at the. surface in two or three minutes. This
jelly-like condition will extend to the sides of the vessel, and then
throughout the entire mass, so that if the vessel be inverted the
blood will not flow at the end of ten or fifteen minutes. Then
drops of pale fluid (serum) begin to appear at the surface, and
these unite to form an amount of fluid sufficient in an hour to float
the clot, which meanwhile is contracting from the sides of the
vessel. The serum continues to exude and the clot to contract for
twenty-four to thirty-six hours. The color of the clot remains red,
while the serum has a pale straw color.

Why does blood clot?

Clotting is due to the formation of a substance called fibrin^
which appears as a mesh of fine fibrils and soon entangles the
corpuscles. This mesh of fibrin contracts and squeezes out the

THE BLOOD.

23

watery elements of the blood to form serum, and holds the solid
components, as shown by diagram as follows :

Blood.

Plasma.

Corpuscles.

Serum.

I
Fibrin.

Clot.

I
Clotted blood.

What is the source of the fibrin ?

Largely, if not entirely, from the plasma. A substance known
s j)h(!<t)u'ite is obtained from plasma by saturation with salt, Avith-
c \t which there is no formation of fibrin : and this substance redis-
so-ved readily clots and forms fibrin. Plasmine may be imitated
by uniting solutions o^ fibrinogen and paragJohuJin, obtained from
plasma. A third element is considered probable, and this is known
as the fibrin ferment: it is probably derived from the colorless
blood-corpuscles. There is some reason for the belief that para-
globulin is not an active factor in forming fibrin, but that it may
unite with and render inert some substance (unknown) which pre-
vents the formation of fibrin in the conditions of life.

Mention some conditions which affect the coagulation of blood.

Retard or prevent.

Greater heat or extreme cold retard
or entirely check.

Contact with living tissues, espe-
cially blood-vessels.

Absence of air retards. After death
by asphyxia blood remains fluid ; also
when air is withheld from drawn
blood, as by film of oil.

Agitation of vessel retards.

More then twice the bulk of water.

Addition of viscid substances — e. 7.
glycerin, syrup.

Addition of neutral salts, about 2
per cent, solution.

Digestive ferments.

Strong acids or alkalies.

Hasten.
Moderate warmth, 100°-120° F.

Contact with foreign matters.

Access of air.

Eest.

Addition of moderate amounts of
water.

24 THE BLOOD.

Why does not blood clot in the living vessels?

The reason is not clearly understood, but it is supposed tbat the
living blood-vessels exert a restraining influence upon the formation
of the fibrin ferment. The formation of a clot may occur in a vessel
after injury of the lining by ligation, by the introduction of a for-
eign substance, or by disease of the vessel. This fact is made
apparent in the ligation of vessels, in the treatment of aneurism,
and in the formation of emboli.

What are the principal forms of blood-corpuscles ?

The red or colored, and white or colorless. They make up
nearly half (40-45 per cent.) of the total weight of fluid blood.
The proportion of the red to the white is about 500 to 1.

Describe the red blood-corpuscles.

Human colored blood-corpuscles are circular, biconcave disks
with rounded edges ; in diameter they are about -^jq-q in., in thick-
ness about Y2-Jo"¥ ^^- -'-^ water they swell and become flat or
convex. When seen singly they appear yellow, but their color is
red when seen in groups. Microscopic examination shows that
they have no nucleus and no limiting membrane (which defects
preclude the name "cell"); but they have an elastic framework
or stroma, which retains an individuality for each corpuscle, and
allows changes of shape to adapt them for capillary circulation,
and brings them back to the original form after such distortion.

Why are they red?

Because the stroma of each corpuscle is infiltrated with a red
coloring matter, hsemoglobm.

Mention some other peculiarities of red cells.

(1) Blood-corpuscles (sp. gr. 1088) are somewhat heavier than
plasma (sp. gr. 1030), and therefore tend to sink when drawn in
a vessel. In blood that coagulates slowly the corpuscles have an
opportunity to do this, and the result is a formation of fibrin at
the surface of the clot. This surface is of a light yellowish color,
and is known as the " bufi"y coat."

(2) The red corpuscles in the process of clot-formation form in
rolls or columns like piles of coins, the corpuscles adhering to one
another at the edges, and the columns so formed adhere to one
another by their ends, so as to make clusters.

THE BLOOD. 25

Are the red corpuscles the same in man as in the animals?

In inauiiuals the geiiuial eliaracttT ol' tlie curpu.scle.s is tlie .same
as in man, but the size of the corpuscles varies in different animals.
In reptiles, fishes, and birds the red corpuscles are oval, nucleated,
and usually are larger than those of mammals.

What are microcytes?

In many specimens oi" blood are observed some corpuscles which
are smaller than the rest : they are called microcytes, and are
probably immature corpuscles. One form is of especial interest.
They are of about one-third the size of ordinary corpuscles, not
deeply pigmented, round or oval. They are called the hlood-jilatoi
of Bizzozero, and have been affirmed to be broken up to form the
fibrin ferment.

What is the origin of the colored corpuscles ?

This is somewhat uncertain, but it is probable that red corpuscles
take their origin from colorless nucleated corpuscles similar to if
not identical with white corpuscles ; possibly also from the nuclei
of white globules, from the tissue of the spleen, and from the
marrow of the bones.

How are the red corpuscles destroyed?

Without doubt, the red corpuscles have a definite life, and when
their work is done die as do the other parts of the body, after a
tolerably definite existence. Neither the length of their life nor
the manner of their death is definitely understood. It is believed,
and partially demonstrated, that they undergo disintegration in the
spleen.
What is the number of the red blood-corpuscles ?

It is almost beyond estimate, but it is calculated that the aver-
age for normal human blood is about 5,000,000 in each cubic
millimetre. In practice it is customary to estimate the number
of red corpuscles by counting the corpuscles in a minute but
measured quantity of blood spread upon a ruled microscope slide.
Such an instrument is known as a hajmocytometer, and that of
Oowers is frecjuently used.

Describe the white or colorless blood-corpuscles.

They are spherical, granular masses of protoplasm, possessing
a nucleus, but no cell-wall. They are about YzaJi "'• ^" diameter,
though some appear smaller, and are probably undeveloped white
corpuscles.

26 THE BLOOD.

By what other name are they known ?

Leucocytes.
What is their proportion, numerically, to the red corpuscles ?

The proportion is 1 to 500 or 600, but this relation is varied by
conditions of health and disease, by age, etc.. being more abun-
dant in youth, in anaemic conditions, in pregnancy, and after a full
meal.

What power is peculiar to white corpuscles?

The power of amoeboid movement, by which they are able to
pass through the walls of capillaries into the surrounding tissues.
This we call diapedesis. The physiological value of this is not
known.

What is the source of the white corpuscles ?

Leucocytes come, no doubt, from the lymph-glands, in which
they may be seen in large numbers — "lymph-corpuscles" — and
from which they are poured into the blood. They also originate
by fission. Some also, probably, are derived from the spleen and
from the thymus gland, perhaps also from microcytes.

What is the ending .of the leucocytes ?

Many, probably, are decomposed in the blood-vessels, but more
end as colored cells ; still others take part in inflammatory pro-
cesses and are ended in this way.

What are the uses of the blood ?

(1) To receive and convey food and oxygen to all the parts of
the body.

(2) To receive from the organs and carry away the refuse mat-
ters to other organs whose function is to excrete them.

(3) To warm and moisten all parts of the body.

What is the active ingredient of the blood in its oxygen-carry-
ing function?

Haemoglobin. In the lungs the haemoglobin of the red corpus-
cles is combined in loose chemical union with oxygen, and this
union is broken down in the tissues of the body.

What is the difference between arterial and venous blood?

(1) Arterial blood is bright red (scarlet) from the combination
of haemoglobin with oxygen (oxy-haemoglobin) ; and venous blood
is purplish or blue from deoxidation of the oxy-haemoglobin.

(2) Arterial blood coagulates somewhat more quickly.

CIRCULATION OF THE BLOOD. 27

(3) Arterial blood contains more oxygon and less carbon dioxide
than venous.

What is the chemical basis of blood ?

Water is the principal constituent, and in it are dissolved salts
and proteid matters, and suspended in it are the corpuscles.
Roughly, the composition of blood may be tabulated as follows :

Seruvi. , Corpuscles.

- - Water . . ......... 69

Inorganic salts (chiefly sodium
chloride and potassium phos-
phate),
Organic matter,

(Haemoglobin 27

Proteids 2.7

Fats 0.3)

Water 90

Proteids 8

Salts 1

Fats, ]

Glucose, I ■•

Extractives, f

Pigment, J ^

100

30

100

What are the gases of the blood ?

Carbonic oxide, oxygen, and nitrogen. The proportion of gases
to the blood is about one-half the volume. Of these, carbonic oxide
is greatly in excess in both arterial and venous blood. The propor-
tion is shown in the tabular form, thus :

Arterial blood, per 100 volumes, CO^ 39, 0^ 20, N 1 + .
Venous blood, per 100 volumes, CO, 46, 0, 10, N 1 + .

CIRCULATION OF THE BLOOD.

What is meant by the circulation of the blood?

The course which the blood, as a transporting medium, follows
in taking food and air to the tissues and bringing away the used-up
material for excretion, returning when freshly charged with oxygen
and food.

Of what does the circulatory apparatus consist?

(1) The heart, which propels the blood ;

(2) The arteries, which convey it from the heart to the diiierent
parts of the body ;

(3) The capillaries, a network of inosculating tubules inter-
woven with the substance of the tissues and bringing the blood into
intimate contact with it ;

(4) The veins, which collect the blood from the capillaries and
return it the heart.

28

CIKCULATION OF THE BLOOD.

Fig. 1.

Describe the course of the blood in
circulation, beginning with its
entrance into the left auricle.

Into the left auricle from pul-
monary veins, thence passing the
open mitral valve into the left ven-
tricle (Fig. 1). Upon contraction
of the ventricle the mitral valve is
closed and the aortic valve thrown
open, so that the blood is thrown
into the aorta, and thence through
the systemic arterial circulation into
capillaries and on into veins, the
systemic veins finally joining to fill
the venas cavas, and from them the
right auricle. From the right auricle
past the tricuspid valve into the
right ventricle, whence it is thrown
through the pulmonary artery
(guarded by the pulmonary semi-
lunar valve) into the pulmonary
capillaries, and thence into the pul-
monary veins, whence it started.
Thus we have in reality two cir-
culations, the systemic and pul-
monary.

Describe the heart.

The heart is a muscular organ
situated in the thorax, where it lies
between the lungs within the peri-
cardial sac, and rests upon the dia-
phragm somewhat to the left of the
mid-line of the body. It is con-
ical in form, and is so suspended
by the great vessels that the apex
points to the left and downward.
Its size is about that of the closed
fist (weight, in adults, about 10
ounces).

Diagram of the Circulation: 1, heart; 2, lungs; 3, head
and upper extremities; 4, spleen; 5, intestine; 6, kid-
ney ; 7, lower extremities ; 8, liver.

CIRCULATION OF THE BLOOD.

29

What are its cavities?

It is divided by a septum into
two cavities, not connected, the
right and left (Fig. 2). Each
of tliese in turn is subdivided
into two parts, tlie auricle and
the ventricle. The auricU'S arc
thin-walled cavities, whose func-
tion is to receive tiie blood from
the veins and pour it into the
ventricles. The ventricles are
the most powerful portions of
the heart-muscle, the left being
much stronger and thicker than
the riaht ventricle.

Fio. 2.

Tran.svci'sc SfLiion ultlu' lUillDck's Heart in
the State of Cadaverie Kijiidity : a, cavity
of tlic left ventricle; b, cavity of the riglit
ventricle.

What is the capacity of these cavities ?
Auricles, about 4 oz. ; ventricles, about 6 oz.

Fk;. 3.

Course of lUooil tlirouf,'li the Heart : a, it, vena cava, superior and inferior ; h, right ven-
tricle ; c, luilnionary artery ; </, iniluionary vein ; e, left ventricle ; /, aorta.

What is the use of the valves?

To allow the blood to pass in one direction only through the
heart (Fig. 4).

30 CIRCULATIOK OF THE BLOOD.

Describe the structure of the arteries.

They are surrounded by a dense fibrous coat externally, and
lined internally by a smooth serous (endothelial) lining } between

Fig. 4.

Valves of the Heart.

these is an elastic layer of fibrous tissue, which has interlaced in
its structure muscle-cells. Each artery has its own vasa vasorum,
or nutrient vessels, and is usually enmeshed in a plexus of sympa-
thetic nerves, " vaso-motor nerves."

Describe the capillaries.

The capillary blood-vessels are channels of very small but
variable size, but usually of about sufficient calibre to just permit
the passage of the red and white corpuscles. They are usually
composed of a single layer of endothelial cells joined at the edges,
though near the arteries and veins there is sometimes an elastic
fibrous coat. A sympathetic nerve-plexus surrounds these vessels.
The capillaries form a complicated network in the tissues, and the
mesh of the net varies in shape and size greatly with the vascu-
larity and function of the tissue.

Describe the characteristics of the veins.

In structure the veins are similar to the arteries, but much less

CIRCULATION OF TlIK BLOOD.
Fw. 5.

31

Capillary Plexus in a Portion of the Web of a Frog's Foot (magnified 110 diameters) : 1,
trunk of vein ; 2, 2, 2, its branches; 3, 3, pigmeut-cells.

firm and elastic ; veins collapse, while arteries remain open when
not distended by blood. Valves occur in most of the veins ; these
are so placed as to prevent the blood from tending to flow back-
ward. The valves are so placed as to aid the onward progress of
the blood in the veins, the pressure of neighboring muscles forcing
forward the blood, which cannot regurgitate past the valves.

What is the relative area of arteries, capillaries, and veins ?

With the divisiuii of the arteries into branches the sectional
area of the branches is greater than of the stem. Of the veins
the same is true, while the total sectional area of the capillary
system is much greater than of either. For purpo.ses of simile the
comparison may be made of two funnels placed base to base. In
numbers one may consider the sectional area of aorta as 1 ; of
venae cavae, 2 or 3 ; of capillaries, (about) 800.

32 CIUCULATION OF THE BLOOD.

Describe the action of the auricles.

During the period of rest of the heart blood flows freely from
the veins into the ventricles, the auriculo-ventricular valves offer-
ing no resistance ; but the influx is so strong that by the time the
heart begins to contract the auricle is quite filled and the ventricle
partially. The contraction of the auricle is sudden and very quick,
comrriencing at the great veins and extending toward the ventricu-
lar opening. Both auricles contract simultaneously.

Why does not the auricle throw the blood back into veins ?

(1) The power of the auricular contraction is not sufficient to
cause a reflux.

(2) The muscular coat of the great veins near the heart con-
tracts, and helps to prevent this regurgitation.

(3) The weight of the incoming blood opposes.

(4) Valves in the veins oppose, and the Eustachian valve guards
the inferior vena cava.

Describe the action of the ventricles.

The ventricle is distended during its period of rest by the flow
of the blood from the veins and by the auricular contraction ; and
its contraction seems continuous with that of the auricle, so imme-
diately does it succeed. The ventricular contraction is slower, and
probably completely empties the cavity. The ventricles contract
simultaneously. The shape of the ventricles is changed : as the
heart-muscle becomes hard and rigid in contraction, the section of
its base becomes circular instead of elliptical, as it is during re-
pose ; the ventricles shorten and twist to the right, and the form is
conical. As the organ relaxes, it turns back to its former position
and shape, that of a cone with elliptical base. This shortening of
the ventricles in contraction is compensated by the lengthening of
the great vessels at the base as they become distended by the load
of blood.*

What are the functions of the valves of the heart ?

In considering the functions of the valves of the heart one
must bear in mind constantly that the organ is a pump whose
office is to force the blood in one direction. There are four
principal valves — two auriculo-ventricular. and two in the great
arteries, the aorta and the pulmonary artery. (1) As the ventricle
fills, the auriculo-ventricular valves are floated up from the sides of

* Some physiologists deny the shortening of the ventricles in systole.

CIRCULATION OF THE BLOOD. 33

tlie ventricle in sucli manner that tlieir edges are in contact, cusp
to cusp. As the ventricle contracts more violently, pressure is
hrouglit to bear upon the valve, so that not only is the edge in
contact, but also portions of the surfaces of the cusps. These
valves are of considerable area, and are guyed in position by the
chnrdse tetullnex, which spring from the papillary muscles, so that
evcrsion of the valve into the auricle is impossible. (2) The
semilunar ralrcs form a guard against the return of blood to the
ventricle at the pulmonary and aortic openings of the ventricles.
These valves are forced open by the ventricular contraction, and
through them the blood rushes to distend the elastic walls of the
large arteries. The pressure of the blood under this elastic grasp
is sufficient to throw the cusps of the valves into action. The
corpora Arantii are useful in making a perfect closure of the valve,
though not absolutely essential. A part of the weight of this
pressure is borne by the thick ventricular wall, from the outer
edge of which the artery springs, while the valves are attached to
the inner edge.

What is meant by the safety-valve action of the tricuspid valve ?

Under some circumstances the tricuspid valve does not entirely
close, but allows a certain amount of regurgitation of blood. This
is in conditions of disease or of violent exertion, in which the lung
capillaries are overcharged with blood. This leakage of the valve
is conservative, by relieving the pressure upon the delicate capilla-
ries of the alveolae. Pulsation in the jugular veins indicates this
regurgitation. The condition is not pathological, and with altered
conditions disappears.

What terms are used to describe the alternate contraction and
relaxation of the heart ?

Systole, a contraction ; diastole, a relaxation

What is meant by the period of repose ?

Between the contractions of the heart-muscle there is a percep-
tible pause, which has been called the period of repose. If the
time of a cycle be divided into five parts, the systole of auricles
will employ 1 part ; systole of ventricles, 2 parts ; period of repose,
2 parts. The accuracy of this division is not absolute, for, whatever
the pulse-rate, the ventricular systole consumes nearly four-tenths
of a second.

3— Phy.

34 CIRCULATION OF THE BLOOD.

Describe the heart-sounds.

The first sound is heard best over the apex of the heart. It is
of a dull, prolonged, booming character. The second sound is heard
immediately after the first, and is a sharp, quick, almost clicking
sound ; it is heard most clearly over the base. The sounds are said
to somewhat resemble that expressed by luhh-dup.

What is the cause of the heart-sounds ?

The origin of the first sound of the heart is not fully explained ;
but as it is synchronous with the ventricular systole and with the
closure of the auriculo-ventricular valves, it is supposed to be due
to muscular action and vibration of auriculo-ventricular valves and
chordae tendineae. The second sound is synchronous with the
closure of the semilunar valves, and is caused by this action.

What is the normal frequency of the heart's action ?

At birth, about 130 per minute.

At three years, " 100 " "

In adult life, " 75 " "

In old age, " 65 " "

This rate is varied from time to time by conditions of bodily
health and by environment. The heart in women is somewhat
more rapid than in men. After eating, during exercise, in a hot or
rarefied atmosphere the heart is more rapid. The relative frequency
of heart and respiratory action is about three or four heart-beats
to one respiratory act.

What force does the heart exert in systole?

The left ventricle exerts more than twice as much power as the
right. The exact intraventricular pressure in man has not been as-
certained. The expansion of the heart exerts a negative (or suc-
tion) pressure, which aids the onfiow of the blood, especially from
the lungs to the left ventricle. The intra-auricular pressure is very
much less than the intraventricular, and there is a negative pres-
sure during diastole in the auricles.

What is the estimated work of the heart in systole ?

Estimated' in foot-pounds, each ventricular contraction repre-
sents 3^ to 4j foot-pounds. In twenty-four hours this is estimated
to equal more than 120 foot-tons. In another light, if the blood is
one-twelfth of the body-weight, and if the amount of blood pumped
with each ventricular contraction is 6 oz., in an ordinary man an

CIRCULATION OF THE BLOOD. 35

amount of blood equal to the total blood of the body will pass
tliroutrli the heart in about half a luiuuto.

What are influences of the nervous system upon the heart's
action ?

This matter is somewhat undecided at tlie i)resent, fur the reason
that many of the results must be obtained from experiments upon
the hearts of cold-blooded animals. We do know that the mechan-
ism of rhythmical contraction is contained within the heart itself.
Nerve-ganglia are demonstrated in the frog's heart which are essen-
tial to its action ; presumably similar ganglia exist in the human
heart. These ganglia are connected with fibres from the pneumo-
gastric (or vagus) nerve and with the sympathetic system.

What is the effect of the pneumogastric nerve upon the heart?

It has an inhibitoiy or slowing effect upon the heart ; for if we
cut the nerve the heart becomes more rapid, and if we stimulate
the peripheral end of the nerve we slow the heart again. This
action may be traced to the medulla oblongata, where a cardio-inhib-
itory centre is located.

What is the relation of the heart to the sympathetic nervous

system ?
Certain fibres of the sympathetic from the cervical and upper
dorsal spinal cord pass to the heart. If these fibres are left after
all other nerve-connections of the heart are cut away, stimulation
of the spinal cord will cause the heart to become rapid. These are
known as accelerator nerves.

What is meant by the pulse?

The wave which is felt in an artery after the systole of the
ventricle.

What is a sphygmograph ?

An instrument used to trace mechanically a diagram of the

pulse-wave.

How is the heart nourished?

Hy the coronary arteries, which arise in the sinuses of Valsalva
behind the leaves of the semilunar valve. They do not receive blood
during systole, but during diastole from the pressure of blood in the
elastic arteries. The blood is returned to the right auricle through
the coronary vein.

36 EESPIRATIOlSr.

What causes unite to compel the return of the blood through
the veins?

(1) Vis a tergo, or the pressure remaining from the force of the
left ventricular systole and arterial elasticity.

(2) Muscular action in pressing upon the veins which have valves.

(3) Suction Poioer of the Heart. — During diastole the opening of
the heart-cavity is sufficiently strong to exert a rather strong " neg-
ative pressure " or suction power.

(4) Aspiration (or suction) power of the chest in respiration.

(5) The slight rhythmical contractions of the veins.

What is meant by vital capillary force ?

The capillaries are not unchanging blood-channels, but may be
seen to dilate and contract under the influence of stimuli. We
have seen that each capillary has its accompanying vaso-motor
sympathetic plexus ; and this it is which controls this force, seen
in blushing, pallor, etc.

What is arterial tension?

The walls of the arteries being very elastic, and the blood being
forced into them at considerable pressure, permits them to keep the
blood under elastic compression within the arteries, so that when
an artery is cut the blood spurts from it in a jet. The capillaries,
though collectively of much greater area than the arteries, by rea-
son of the friction they offer to the blood-stream maintain a less
degree of tension.

What causes modify the arterial tension ?

(1) The rate of the heart-beats, by keeping the arteries fuller or
less full, will modify the blood-pressure in the arteries.

(2) Vaso-motor changes, by increasing or decreasing the friction
offered the arterial blood, vary the tension in the arteries.

(3) The amount of blood in the system must to a great extent
determine the limits of arterial pressure. In great exsanguination
the arterial pressure is quite low.

(4) Motion of the thoracic walls in breathing necessarily changes
the arterial tension by the pumping force exerted by this motion.

RESPIRATION.
What constitutes respiration?

By respiration we mean the process by which oxygen is intro-
duced to the system and by which carbonic oxide is excreted.

RESPIRATION. 37

This function is performed in the lungs, and the transfer is
effected by the agency of the blood.

Describe the course of the air in entering the lungs.

Air is taken through the nose (ir mouth, and passes through the
l)liarynx to the larynx ; entering the rinia glottidis, it passes through
the larynx to the trachea and bronchi. The air is somewhat warmed
and moistened in its passage. The trachea and bronchi are lined
with ciliated epithelium, which serves to sweep particles of dust
and the like out of the air-passages.

Describe roughly the minute anatomy of the lung.

Each lobe of the lung is composed of numerous lobules, to each
of which a small bronchiole enters, and the minute terminal branches
of these bronchioles (^infundlhuhi) widen into a sort of ii'regular
funnel having pouched or saccuhited dilatations known as air-
cells. These air-cells are supported by numerous elastic fibres, and
are lined with a very thin layer of flat (not ciliated) epithelium.
Outside the epithelial lining is a very clo.se mesh of capillaries,
which are often exposed to air on both sides by lying in a partition
between two of the air-cells. The air-cells or vesicles are about gig-
in. in diameter, and the space between the capillaries is often less
than the diameter of a capillary.

What is the blood-supply of the lungs ?

There are two sources : (1) from the bronchial arteries (systemic)
for nutrition ; (2) from pulmonary artery for oxidation.

How is air introduced to the lungs?

The thoracic cavity in which the lungs lie being a closed cavity,
the expansions of its walls will tend to create a partial vacuum
in its interior. It is by this means that air is introduced. This
expansion of the chest-wall (and with it the lung) we call inspira-
tion. Contraction of the cavity of the thorax tends to cause com-
pression of its contents, and thus to expel the contained air: this
we call expirdtion. The complete act is called i-esjxirafioji.

Describe briefly the mechanism of respiration.

A. Jiispinitioii. — 'J'hc diameters of the thoracic cavity are all in-
creased— (1) the vertical by the action of the diaphragm ; (2) the
lateral and antero-posterior diameters by the elevation of the ribs.
Thus we may have a diaphragmatic or abdominal type of breath-

38 RESPIRATION.

ing and a costal or ctest type ; the former is characteristic of men,
the latter of women.

B. In expiration the natural elasticity of the lungs and the chest-
wall causes very little muscular action to be needed in natural
expiration. In forced expiratory efforts all muscles which depress
the ribs may be called into action here.

What is the force of the respiratory effort ?

The average man is able to elevate a column of mercury in a
manometer tube 2\ to 3 inches by an effort at inspiration. In
expiration, when forced, the mercury will range about an inch
higher, but it should be remembered that many muscles which are
ordinarily used for other purposes may be called into play in this
effort.

What is meant by the term " vesicular murmur " ?

It is the sound heard in listening over a normal lung during
respiration, and is described as a soft sighing sound heard at the
instant air enters the alveoli. Its cause is not fully understood,
but it is supposed to be due to the friction of the air against the
walls of the vesicles.

What is tidal air ?

The amount of air which is habitually changed in an ordinary
act of breathing. In forced inspiration the excess of air is known
as compleniental air.

What is reserve air?

The air left in the lung after ordinary expiration. After forced
expiration there always remains a certain amount of air, known as
residual air.

What is the respiratory capacity?

The greatest quantity of air which one can drive from the lungs
after forced inspiration : this is about 225 cubic in. in an average
adult man. The tidal air for the same man will be about 30 cubic
in. These figures are not constant, and vary with conditions of
health, figure, age, sex, and atmospheric conditions.

What is the normal rapidity of the respiration ?

In a healthy adult 14 to 18 per minute. In infants and invalids
the rate is often much more rapid. The ratio to the pulse-rate is
about 1 to 5 in the healthy individual.

RESPIRATION. 39

Describe the rhythm of respiration.

The respirator}' aet is rliytliiiiical, inspiration bcin,2j Rlifrbtly more
ra])i(l tliaii expiration, a slight pause occurring after expiration
het'orc a fresh breath is drawn.

Describe the movements of the nostrils and larynx in respira-
tion.

With every inspiration (especially if rapid) there is dilatation of
the nostrils and a partial closure during expiration. The rima glot-
tidis is in the same way opened for the ingress of air. This is like
the respiratory act, in that the opening is a muscular act during
inspiration, and the recoil elastic in ordinary breathing.

What is the composition of the atmosphere ?

It has a nearly unil'urm composition.

By Volume. By Weight.

Oxygen, 79 parts. 75 parts.

Nitrogen, 21 " 25 "

Carbonic acid, .04.
Ammonia and impurities, trace.

What is the temperature of expired air?

The expired air is at about the temperatui'c of the body, what-
ever its temperature when inspired.

How much carbonic acid does exhaled air contain?

While ordinary air contains only about •] a part of carbonic acid
])er 1000, expired air is found to contain about 43 parts per 1000
of COa- This is varied by conditions of health and disease, age,
atmospheric conditions, and a number of other causes.

How much oxygen is taken from the air in respiration?

The oxygen of the exhaled air is decreased in about the same
ratio that its carbonic acid is increased (roughly 5 per cent.). This
proportion is not exact, as there is some excess of oxygen which is
absorbed in the system and does not reappear as 00.^.

How much water appears in expired air?

The amount varies with the atmospheric conditions as well as
bodily changes, but ordinarily in a day about 10 ounces of water in
the form of vapor are found in expired air in excess of that normally
present. This may amount to 30 ounces, or fall as low as G
ounces.

40 RESPIRATION.

Mention some other changes in the respired air.

Small quantities of organic matter and of ammonia are found.

Has the nitrogen of the air a physiological bearing?

A small amount of this gas is found in the blood, but it is
mostly in simple solution, and is not supposed to be of physio-
logical value. In respired air it is of use as a diluent of the
oxygen.

Describe the respiratory changes of the air in the lungs.

In the blood oxygen is in loose chemical combination with the
haemoglobin (oxy-haemoglobin). The amount of the oxygen in the'
residual air of the pulmonary alveoli is estimated at about 10 per
cent., that of expired air being 16 per cent. It is found that unless
there is present about 4 per cent, of oxygen there is no tendency for
the blood of the pulmonary arteries (venous) to take up fresh oxygen,
or the tension of the oxygen in the reduced hasmoglobin of venous
blood is about 4 per cent., and unless the oxygen tension in the
lungs is greater, there is no absorption of oxygen. But, as we
have seen, the amount of oxygen amounts to at least 10 per cent.,
and therefore the excess is sufficient to exceed the demands, and
the exchange is readily made by diffusion through the thin capil-
lary walls in the alveoli.

On the other hand, the tension of the carbonic acid in the
pulmonary arteries is much higher than in the alveoli, and hence
the extrusion of this gas by diffusion is accomplished.

How is the blood changed by respiration ?

(1) Color, deep purple to bright scarlet by oxidation of the
reduced haemoglobin — i. e. from venous becomes arterial blood ;
(2) gains oxygen ; (3) loses carbonic acid ; (4) becomes cooler ;
(5) coagulates more readily.

Name some of the special actions of modified respiration.

There are a number of involuntary and voluntary special respi-
ratory acts, largely reflex, which are dependent upon modifications
of inspiration and expiration — e. g. sighing, hiccough, cough, sneez-
ing, speaking, singing, sniffing, sobbing, laughing, yawning.

What is the nervous mechanism of respiration ?

i In the medulla oblongata are centres for each half of the body,

)( from which arise automatically the rhythmical impulses for the

respiratory acts. While these are automatic, they may be stimu-

RESPIRATION. 41

lated by reflex influence. The nerves which convey to the muscles
of inspiration their impulse are tlie plirenics (to the diaphragm)
and tlie intercostals (to the intercostal muscles). The reflex stimuli
are conveyed l)y the pncuniogastric nerve, and are twofold : by the
main trunk of the nerve the inspiratory efforts are excited, and by
the superior laryngeal l)ranch expiratory reflexes are obtained.
Thus stimulation of the superior laryngeal nerve may be said to
inhibit the inspiratory centre and to excite the expiratory centre,
while the contrary may be said of the main trunk of the nerve.

How is the vagus excited to this reflex activity?

While the respiratory centres seem to act automatically, yet in
certain conditions, in which oxygen is wanting in the blood, the
absence of oxygen (not the presence of carbonic acid) stimulates
the respiratory centres, through the pneumogastric filaments in the
lungs, to increased activity. This reflex activity results in forcible
respirator}^ efforts which we call dijs^pnaa. It is not known whether
this reflex arises from the absence of oxygen from the air of the
alveoli or from the blood of the pulmonary capillaries.

What are the symptoms of lack of oxygen in the blood ?

If the need be only moderate, there will be increased effort of
both expiration and inspiration, and the respirations will be rapid —
a condition known as hyprrpnoea. As the oxygen becomes less and
less abundant the symptoms become moi'e severe, and the condition
is known as di/sjmo'a. The dyspnoea increasing, the respiratory
eff"orts become very violent, and the condition of nxpltijxia is seen.
In this the face is blue, eyes starting, face anxious, and respirations
very rapid and strident. Then follows a convulsive condition which
is brief, the convulsions being very violent and involving the entire
body. After this the patient lapses into a state of exhaustion, in
which the respirations are slow, very feeble, and the general con-
dition is one of collapse. Death ensues very soon.

How is air vitiated by lack of ventilation ?

In ill-ventilated rooms the air of the room is used repeatedly,
and, besides becoming partially deprived of its oxygen, is charged
with carbonic acid and with putrescible nitrogenous organic mat-
ters. This causes an atmosphere which is intolerable to one who
enters from fresh air. That such a condition is unsanitary needs
no argument.

42 DIGESTION.

What are the requirements for good ventilation?

It is generally accepted as a fact that about 1000 cubic feet of
air-space per head must be allowed in sleeping quarters, and suffi-
cient facilities for exchange of air to allow complete change in each
hour. This ventilation must be accomplished without exposure to
draughts.

What effect has respiration upon the circulation ?

Each inspiration causes a partial vacuum in the thoracic cavity,
and hence it, so to speak, sucks the blood to the heart from the
great veins. Each expiration does not, however, check the flow
of blood, for the expiration does not increase the air-pressure, but
simply returns to the normal. The inspiration, then, increases
arterial tension by facilitating the venous return.

DIGESTION.
What is digestion?

By this term we indicate the process by which food is introduced
to the body and prepared in such way that it becomes suitable for
absorption and tissue-nutrition. The process may be divided logi-
cally and conveniently into mastication, insalivation, deglutition,
stomach digestion, intestinal digestion, and defecation.

Describe mastication.

When a mass of food enters the mouth it is caught by the tongue
and moved to a position such that it may be crushed and ground
between the upper and lower teeth. This process is favored by
the action of the tongue and of the cheeks, which not only crush
the softer food-masses, but bring the less tractable portions re-
peatedly under the action of the teeth.

Describe the teeth.

There are during life two sets of teeth, temporary and permanent.
In the first set are 20 teeth, and in the second 32. The perma-
nent set are arranged as follows :

Molar. Bicuspid. Canine. Incisor. Canine. Bicuspid. Molar.

Upper. 3 2 1 4 1 2 3

Lower. 3 2 14 1 2 3 "

The tooth-structure resembles bone in anatomical as well as chemi-
cal view. The central portion, or cement^ is true bone, and about
it is a somewhat harder layer called dentine. Outside of all is a
very dense layer of enamel.

DIGESTION. 43

What muscles are involved in the act of eating ?

Biting nioveuioiits arc prodiu'cd by action of the temporal, nias-
sotcr, and internal pterygoid muscles, opposing the depressors of
the jaw ; grinding movements are produced by the alternate action
of the external pterygoids. The action is to some extent reflex,
though largely voluntary, and is controlled in the medulla through
branches of the cranial nerves, motor impulses coming through
branches of the trigeminus and (to the tongue) hypoglossal nerves.

What do we mean by the term " insalivation " ?

The mixing and thorough moistening of the food-mass with the
saliva and mucus in the mouth d.uring the act of chewing is called
insalivation.

What is the saliva?

The saliva is derived almost entirely from the parotid, submax-
illary, and sublingual glands, and is secreted most abundantly
during mastication of food. It is a transparent watery fluid, and
is somewhat viscid from the mixture of mucus. This viscidity
allows it to retain air-bubbles when churned by the action of the
tongue and cheeks. It has a sp. gr. of about 1006 and an alkaline
reaction. Chemically, it is mostly (99 2 per cent.) water, holding
in solution very small amounts of salts and proteids, with the addi-
tion of a ferment called ptyalin. The amount secreted in twenty-
four hours is estimated to be 1 to 2 quarts, most abundant secretion
occurring during mastication.

What is the use of saliva ?

It keeps the mouth in a moist condition, and so lubricates the
tongue in speaking and in chewing ; dissolves the soluble portions
of the food, and in this way brings them in contact with the organs
of taste ; mixes with the food, and forms a soft and slippery bolus
suitable for swallowing. Saliva from the front of the mouth, con-
taining more water, softens the bolus, while the tonsillar and
pharyngeal secretions, being mucous, coat it with a slippery sur-
face ; and the saliva has a special digestive function by the action
of its ferment, ptyalin.

What is the action of ptyalin ?

Ptyalin is a ferment (a non-nitrogenous body having an uncer-
tain chemical composition), with the s]»ecial property of converting
cooked starch into grape-sugar, ^\'hil(' the ferment it.self cannot

44 DIGESTION.

be isolated and analyzed, a glycerin solution may be obtained from
salivary glands which have been dehydrated by alcohol. This
ferment does not act upon any other body than starch. The action
of the ferment in changing starch to sugar is known as an amylo-
lytic action, and such a ferment is called an amylolytic ferment.
The kind of sugar resulting from the action of ptyalin is grape-
sugar or glucose, maltose being found as an intermediate step in
the ferment's action.

At what age do the salivary glands become active ?

At four to six months ; hence the reason for avoiding starchy
food for young infants.

What tests are used to determine the presence of sugar and of
starch ?

For starch an entirely reliable and simple test is that by iodine :
a blue color follows the reaction ; it is a very delicate test. For
sugar Moore's and Fehling's tests depend upon the reduction of a
copper solution, and are quite delicate. The fermentation test is of
value in accurate quantitative determination of sugar.

What is the action of the nervous system upon the salivary
glands ?

Saliva is secreted more abundantly upon the application of a
stimulus. It is therefore increased by reflex nerve-force. The
stimuli may be mechanical or chemical or mental ; thus the flow
of saliva is increased by taking food into the mouth or by irritat-
ing the inside of the mouth by scratching or burning, or by looking
at or smelling or even thinking about food.

In the submaxillary gland the chorda tympani nerve is said to
have a double function — to increase the vascularity of the gland
by one portion of its fibres, and to excite the secreting function by
another set of fibres, the sympathetic nerves of the gland acting as
the vaso-constrictors.

In the parotid the vaso-dilator impulse comes also from the facial
nerve through the fifth by the communication of the lesser petrosal
nerve. The vaso-constrictor impulse comes from the sympathetic.

There is found a medullary centre which controls this function.

Describe an act of deglutition.

Deglutition, or swallowing, is the process by which we convey
food from the mouth to the stomach, and may be divided for the
purpose of analysis into three actions : 1st. The food after masti-

45

Human Alimentary Canal: n, a?sophaf;us ; /), stomach ; c, cardiac orifice; d, pylorus; e,
small intestine; /, biliary duct ; ;;, pancreatic duct ; h, ascending colon; /, transverse
colon ; j, descending colon ; k, rectum.

46

DIGESTION.

cation is pushed by the tongue against the palate, and so forced on
toward the fauces. 2d. As soon as the bolus enters the pharynx it
is pushed on by the tongue and by the contraction of the pillars
of the fauces and the constrictors of the pharynx toward the
oesophageal opening. The pharyngeal vault is guarded from in-
vasion by solid or liquid food by the valve-action of the soft palate,
while the opening of the glottis is protected by the simulta-
neous intrinsic muscular closure of the rima glottidis and by the
valve-like cover of the epiglottis. When the muscles of the fauces
and tongue push on the food-mass, they also draw up the larynx
and dilate the oesophageal opening. 3d. The oesophagus grasps the
food, and a peristaltic wave-series carries it rapidly on to the cardiac
opening of the stomach. The beginning (1st) of the act of swallow-
ing is voluntary, the remainder reflex, and is governed by centres in
the medulla oblongata acting through the cranial nerves which sup-
ply the parts. The trigeminus, glosso-pharyngeus, and vagus by
their sensory and motor functions act both in the capacity of affer-
ent and efferent communication with the medullary centre.

Fig. 7.

Free Surface of the Gastric Mucous Membrane, viewed from above, from pig's stomach,
cardiac portion, moderately magnified.

Describe the structure and function of the stomach.

The stomach (Fig. 6) is an organ which resembles in structure

DIGESTION.

47

the rest of the intestinal tract ; it is liollow, having a peritoneal cov-
ering antl a mucous membrane lining, with a muscular layer between.
It is in this mucous membrane that tlie special function of the stom-
ach lies, for here are found glands which secrete the gastric juice.
The active peristaltic motion churns the food about after deglutition,
and exposes it thoroughly to the action of the digestive agents. The
function of the stomach is the digestion of proteids.

Describe the glands of the stomach.

If one looks closely at the mucous surface of the stomach, it
is seen to present a sort of reticulated (Fig. 7) appearance,
meshes being larger at the pyloric than at the cardiac end of
stomach. It is in the interstices

the
the

of this mesh that the glands
open. The openings are smaller
at the cardiac than at the pyloric
end, and the character of the
glands changes : we therefore
speak of two varieties of gastric
glands — 1, peptic; 2, pyloric.

1. The peptic glands are ar-
ranged in groups throughout the
stomach, but not so abundantly
at the pyloric end. They often
consist of a simple tube dipping
into the surface and lined with
columnar epithelium (Fig. 8), but
they may be branched — i. e. sev-
eral glands may empty into a
common duct. The columnar epi-
thelium in the deeper portion of
the gland contains large, almost
globular, cells, which are known
as peptic cells.

2. The pyloric glands, or mu-
cous glands, like tlie peptic, may
be simple or compound. The
ducts are larger, and the large
cells are wanting (Fig. 9). Dur-
ing digestion the cells of both
varieties of glands become swoU-

Fjg

Compound Gastric Follicle, I'roin the car-
diac portion of the liuniaii stomach: 1,
excretory tiihes leadin}; to the surface;
2, tubercular follicles containing sphe-
roidal cells (Kiilliker).

48

DIGESTION.

en, and in them are found granules wliicli are supposed to be pepsin
or that from which pepsin is formed.

Fig. 9

Tubular Follicles, from pyloric portion of pig's stomach, showing their caecal extremities
and epithelial lining : at a the torn end of a follicle, showing its cavity more highly
magnified.

What is the gastric juice ?

When the stomach is not at work it contain-s no gastric juice,
but is bathed in an alkaline mucus. As soon as food enters the
organ, however, it immediately begins to secrete considerable quan-
tities of an acid fluid which soaks into and mingles with the food.
The celebrated case of Alexis St. Martin, who had a gunshot wound
resulting in gastric fistula, enabled Beaumont, surgeon U. S. A., to
investigate accurately its composition. It is a limpid, colorless fluid
of sp. gr. 1001-1010 and acid reaction. It contains about i per cent,
solid matter. Its composition is nearly —

Water 99.50

Pepsin 25

Hydrochloric acid 05

Salts (alkaline chlorides and phosphates) . . .20

100.00

This composition is not constant, as the proportions vary consider-
ably, HCl, for example, being present much more abundantly in
some cases.

DIGESTION. 49

What is the daily secretion of gastric juice ?
I'min 10 to 20 pints.

What is the source of the hydrochloric acid?

It is probably secreted by tlie cubical parietal cells of the peptic
alamls. A^er}^ little seems to be formed liy tbe pyloric glands.

What other acids are found in the stomach?

Lactic, acetic, butyric, and some other fatty acids. They are
products of digestion or of abnormal processes due to decomposition
of food.

What is the source of pepsin?

The globular cells in the peptic glands. These cells are supposed
to form a substance called pejisinoc/en, from which pepsin is derived.
Pepsin is derived for commercial or for experimental purposes from
fresh stomachs by scraping the surface and dissolving out the fer-
ment with cold water, or by mincing the mucous membrane and
extracting the ferment with glycerin after dehydrating with
alcohol.

What is the function of gastric juice ?

The principal function of the gastric juice is the transforming
of proteids into peptones. This action depends upon the presence
of both pepsin and acid. The first change which occurs is the foi'-
mation of acid albumin, but as the action of the ferment continues
the acid albumin is transformed to peptone. The presence of acid
albumin is demonstrated by the addition of an alkali, which precip-
itates it.

What are the characteristics of peptone?

(1) They are diftusible— <'. c. have the property of osmosis, or
passing through an animal membrane. This is of great importance
in digestion, for if this property were absent no animal food could
be absorbed from the intestines. (2) They are very freely soluble
in water and neutral solutions. (3) They do not respond to the
chemical tests for other proteid substances. They are not precip-
itated by heat and the mineral acids, but arc precipitated by tannic
acid, picric acid, or by the bichloride of mercury.

What is the name given the food after digestion in the stomach ?
Chyme. The action of the pepsin in converting proteids to pep-
tones is called a protcolijtic action, and chemically its action is to
cause a hydration of the proteid molecules.
4— Phy.

50 DIGESTION.

What forms of peptones occur ?

(1) Parapeptone, — acid albumin, which results from incomplete
action of the gastric juice ; (2) antipeptone. — a form on which
pancreatic digestion has no effect; (3) hemipeptone, — a form in
which pancreatic digestion has the effect of producing leucin and
tyrosin.

What conditions favor gastric digestion?

The temperature of the body is most favorable, and the presence
of acid — preferably HCl — ^is essential. Digestive secretion does
not continue except during the presence of food.

What is the milk-curdling ferment?

Milk is curdled in the stomach by a ferment, aside from pepsin,
which is derived from the gastric juice. This action takes place in
the absence of hydrochloric acid. Rennet (derived from the fourth
stomach of calves) is used for this purpose in the cheese manu-
facture.

How are non-nitrogenous bodies affected by the gastric juice ?

Starches are unaffected. Sugar is dissolved and cane-sugar (sac-
charose) is changed to grape-sugar (glucose) by the aid of the mu-
cus present. Fats are unaffected, except that the albuminous cap-
sules of fat-cells in adipose tissues are digested and- the oil set free
in globules.

What is the time required for the stomach digestion?

The time varies, with the kind and amount of food, from one
to five or six hours. Digestion is favored by rest of the stomach
before eating, by gentle exercise of the mind or body, by an undis-
turbed mental condition, and by a healthy condition of the body.

Does absorption take place from the stomach?

No, except in a very slight degree.

How does the stomach empty itself?

The stomach is elastic, and is supplied with circular and longi-
tudinal muscles in its middle coat. These muscular fibres are
capable of producing peristaltic movements of the organ which turn
the food over and over during the process of digestion. This elas-
tic pouch is closed at each end by strong, sphincter-like circular
bands of muscle at the cardiac and pyloric openings, and until the
stomach digestion is well advanced none of the contents escapes;

DIGESTION. 51

but as the peptone-making advances tlic pyloric opening permits
the escape of chyme, and tlii.s is aided by strong peristaltic efforts
on the part of the stomach at its pyloric end. Toward the end of
digestion the pylorus permits the escape of undigested as well as
of digested matter. The circulation of the stomach contents is cir-
cnmferentially toward the pylorus, but centrally toward the cardiac
opening.

What is the capacity of the stomach ?

About a quart in the adult, but its muscular walls enable it to
contract so as to fit its contents if much or little.

What is the nervous mechanism of stomach digestion ?

The pneumogastric and sympathetic (splanchnic from solar
plexus) are the nerves which supply the stomach, and besides these
there are numerous ganglia in the stomach-walls. The ordinary
motion-stimulus of the organ lies in the intrinsic ganglia. Irri-
tation of the pneumogastric nerve causes contraction ; its division,
cessation of peristalsis. But, further than this, the vagus has con-
trol to considerable degree over secretion in the stomach.

Describe vomiting.

The regurgitation of food from the stomach through the cardiac
orifice, and thence through the mouth, may occur when the cardiac
opening is free and the pylorus is closed. This is usually a reflex
act, and is performed by the contraction of the stomach, aided by
the pressure of the abdominal muscles opposing the fixed diaphragm.
It may be described as a reversed peristalsis. The stimuli which
excite the reflex may be either local in the stomach or peripheral.
Violent irritation of the gastric mucous membrane will excite it ;
also mental impulses, from ocular, auditory, or olfactory sources ;
injury or irritation of the testis, ovary, kidney, etc.; unusual
motion, as swinging; certain diseases; and eff"ort of will in some
is sufficient.

How is this reflex controlled?

By a centre in the medulla oblongata acting through the pneu-
nuigastric nerve.

What is meant by rumination in man?

Some few persons have the ability to force half-digested food
back from the stomach into the mouth, remasticate it, and again
swallow it.

52 DIGESTION.

What do we mean by "intestinal digestion"?

Soon after passing the pylorus, food comes in contact with the
alkaline secretions of the small intestine and of the liver and pan-
creas. In the small intestine the food is still further prepared for
absorption, and from this part of the alimentary tract the digested
food is taken up for body nutrition.

Describe the process of digestion in the small intestine.

By the peristaltic action of the gut the food is carried on through
the length of the organ, but its progress is more or less impeded
by the valvulas conniventes. These folds of the mucous coat not
only retard the too rapid advance of food, but cause it to be thor-
oughly exposed to the action of the digestive fluids.

How is the peristaltic action regulated?

By the sympathetic system of nerves. Auerbach's plexus lies
between the circular and longitudinal muscular coats. It is also
known as the plexus mesentericus.

How is the blood-supply regulated?

Also by the sympathetic system. Meissner's plexus lies beneath
the mucous coat, and is regarded as the source of control of the
blood-supply and of the function of absorption.

What are the glands peculiar to the small intestine ?
Lieberkiihn's, Brunner's, and Peyer's glands.

Describe Lieberkiihn's glands.

These glands (or follicles or crypts) are thickly distributed over
the whole surface of the small and large intestine, being larger in
the large intestine. They are simply tubular depressions in the
mucous membrane, lined with columnar epithelium, which contains
occasional large " goblet "-cells.

What are Brunner's glands?

They are found in the duodenum alone, and are situated in the
submucous tissue. They resemble the pyloric glands of the stom-
ach, and, like them, are usually compound glands. The duct of
the gland passes up through the mucous membrane and opens at
its surface.

What are Peyer's glands?

These are of two varieties : (1) solitary ; (2) agminate.

DIGESTION. 53

(1) Solitary glands consist of a rounded mass of whitish adenoid
tissue about tj'- to y'^ in. in diameter, situated in the submucous
tissue, but often projeetinj^- to tlie surface of the intestine. Eacli
lymphoid mass is surrounded by Lieberkiilm's iullicles.

('Z) Afi'uiinate glands (Peyer's patches) consist of groups of these
adenoid masses, making "patches " in the mucous membrane 2 to 3
in. long and about 2 in. wide.

What is the function of the intestinal glands ?

Secretion of the intestinal juice (succus cntericus).

What is the function of the intestinal juice ?

Its etfect upon digestion is not fully understood, but it probably
has some effect upon saccharose, and possibly upon proteids, con-
verting the one into glucose and the other into peptones. However,
its chief function seems to be to supply the loss of fluid to take
the place of that which is absorbed as digestion progresses. At
any rate, the contents of the small intestine as they enter the colon
are about as fluid as when they leave the stomach.

What other glands discharge their secretions into the small in-
testine ?
The pancreas and the liver.

Describe the pancreas.

The pancreas is an organ lying in the upper part of the abdo-
men in contact with the duodenum : in length it is about 6 in., and
is thicker at its right or duodenal end. It is a conglomerate gland,
resembling in structure the salivary glands. During digestion it is
active, but is quiescent in the intervals. Its secretion, pancreatic
fluid, is discharged into a main duct which receives branches from
the lobes of the gland, and is emptied with the bile through a com-
mon opening about 2 or 3 in. beyond the pylorus. During digestion
the cells of the organ become granular, and the granules are thought
to consist of the substance from which the ferments of the pancreas
are derived, zijiuogcii, rather than of the ferments themselves.

What are the characteristics of pancreatic secretion ?

The pancreatic juice is a clear, colorless fluid, having an alkaline
reaction and a notably viscid consistency. It coagulates with heat,
and is made quite gelatinous by cold. Specific gravity, 1015. Its
composition varies, but in general is as follows :

9

54 DIGESTION.

Water 90

Organic matter :

Ferments,

Serum albumin

Alkali albumin

Fats, soaps, etc., j
Inorganic salts (chiefly sodium carbonate) ... 1

~100
What are the pancreatic ferments?

(1) Trypsin, a peptone-forming (proteolytic) ferment, which,
continues the digestion of proteids begun in the stomach. It
forms a peptone which resembles the stomach .peptone in its
reactions. This ferment, unlike pepsin, only acts in an alkaline
medium. It acts less vigorously upon gelatins and other nitrog-
enous bodies.

(2) Amylopsin, a starch-changing (amylolytic) ferment, by
which starch is converted to maltose, and finally glucose, as by
the ptyalin in the saliva.

(3) (unnamed), a rennet or milk-curdling ferment. This

ferment will act in the presence of an acid.

(4) Strypsin (?), a questionable ferment by which fats are
broken up from the large globules and emulsified or saponified
in alkaline media. It is claimed by some that this is not a fer-
ment action, but is the result of the action of the alkaline intes-
tinal contents upon the fat.

Of these processes the emulsification, or breaking the fat-glob-
ules into minute particles, is by far the more important, as it
allows this form of food to be absorbed from the gut. Milk is
an excellent example of a natural emulsion.

Saponification (or soap-making) results from the fatty acid
combining with an alkah, forming the corresponding salt and
glycerin — e. g. :

stearin + Potassium Hydrate = Potassium Stearate + Glycerin.

^ CsHf^^' j O3 + 3 1 1 0 =3 (g«H350 ) Q^ ^ C3H5 1 Q^

What is the function of the pancreatic juice ?

It is most active in the digestion, and is peculiar in having an
effect upon all forms of food which require preparation for absorp-
tion — upon proteids, starches, and fats, as well as upon milk.

DIGESTION. 55

What conditions favor the action of the pancreatic fluid ?

Moderate heat (1UU° ¥.), an alkaline medium, and the removal
of the products of the ferment-action as soon as the change is
completed.

What name is given to the intestinal contents of the pancreatic
digestion ?

Chyle.

Describe the liver.

The liver is the largest gland in the body, and is situated in the
upper part of the abdominal eavity. It secretes a fluid known as
the bile or gall, which is stored in a bladder lying attached to its
lower surface. The functions of the organ are — (1) secretion, and
(2) the elaboration of the blood.

What is the character of bile ?

It is a viscid, almost ropy fluid, of a yellow or red or greenish
color and bitter taste. It is fi\intly alkaline or neutral in reaction,
and has a specific gravity of about 1020. Its composition is,
approximately —

Water 86

r Bile salts, 9 ^

Organic matter, -j Fat and cholesterin, 1 v .... 13

( Mucus and pigments, 3 )
Inorganic salts 1

100
How is the flow of bile excited ?

The secretion of the liver is stored in the gall-bladder until its
flow is excited by the acid discharge of the stomach-contents into
the duodenum. It is an active secretion, and not a passive filtra-
tion from the blood, for if a manometer-tube be listened in the
duct it will indicate a pressure greater than that of the blood.
"While tlie gall-bladder acts as a storage reservoir, the bile does not
necessarily enter it, but may discharge directly from the hepatic
into the common duct. The opening of the common duct into the
duodenum is guai'ded by a sphincter-like aiTangement of the muscu-
lar fibres in the gut-wall. The gall-bladder and the gall-duct are
])rovided with unstriped muscular fibres, so that they may empty
themselves. Inspiration and expiration bring alternating pressure
upon the gall-bladder, and aid in emptying it.

56

DIGESTION.

What is the quantity of bile secreted daily ?

The quantity varies with the amount of food taken, but is esti-
mated to vary between 20 and 40 ounces, or, approximately, from
a pint to a quart, in twenty-four hours.

What is the resemblance between bile and meconium ?

There are strong similarities. Meconium contains considerable
proportions of bile salts and pigment, as well as cholesterin. It is
supposed that in the foetus the liver has the function of purifying
the circulating blood and excreting certain oflfensive matters in this
way.

What are some of the more important ingredients of bile ?

(1) Bile salts, sodium glycocholate and sodium taurocholate.
They may be isolated in crystalline form from bile, and are pres-

FiG. 10.

Cholesterin from the Contents of an Encysted Tumor.

ent in human bile in about equal proportions. They are soluble
and very deliquescent colorless crystals which have the bitter taste
of bile. Test by Pettenkofer's method : Add to a solution of bile
a small amount of a solution of cane-sugar. On treating this
solution with pure sulphuric acid drop by drop there is first a
precipitation of a turbid sediment (cholic acid). This is cleared

DIGESTION. 57

by a further addition of sulphuric acid, and the solution assumes
a bright cherry color, cluinging to violet, and, if much bile be
present, to deep purple.

(2) ('cy/o//y/r/ »/a^^'<- of the bilo, biliverdiii and bilirubin. Both
piirnients ure found in human bile, but the former is characteristic
of the bile of herbivora, and the latter, bilirubin, of the bile of
caniivora. The pitrments are crystallizablc, and are insoluble in
water. The crystals have the ureen and red colors of the pij^ments.
Test, " Gmelin's bile test:" Add fumini;; nitric (nitroso-nitric) acid,
and there results a play of colors which is best seen when the bile
solution is in thin layer on a white plate. The presence of the
bile-pigments is shown also by absorption-bands in the spectrum.
Bilirubin is probably derived from hivmoglobin, and biliverdin from
the bilirubin, as they are chemically closel}' allied.

(8) Choksfen'i), a crystallizablc. insoluble substance which belongs
to the alcohol group in chemical composition. Best recognized by
microscopic appearance of ci'ystals (Fig. 10), though it may be
tested chemically by the addition of sulphuric acid, which gives a
red reaction.

What are the functions of the liver ?

This must be considered to be still a somewhat unfinished prob-
lem, but we can safely assume three duties : (1) that of excretion,
(2) as an element in the process of digestion, (3) the elaboration of
absorbed food before passing it into the blood-circulation. Of the.se
uses, (1) and (2) are dependent upon the secretion of bile ; (3) is an
intrinsic property of the organ.

What excretory function has the liver?

The bile for the most part, in normal conditions, is a sort of circu-
lating fluid : it is secreted by the liver, poured into the intestines,
and reabsorbed from them, to be returned through the portal vein
to the liver for recirculation. There is, however, a small propor-
tion of biliary matter, about one-sixteenth, which is not absorbed,
and this consists chiefly of the pigments of the bile. The salts
are nearly all reabsorbed in the assimilation. Further than this,
the liver is found to, so to speak, filter materials which would
be poi.sonous if circulating in the general system, and either to
reject them at once or to store them up and reject them slowly-
back to the intestine. The excrementitious material from the liver
is known as stercobilin. Stercorin is found in the fjvces, and is
thought to be an excretion of the liver: it closely resembles cho-

58 DIGESTION.

lesterin, and is supposed to be a modification of cholesterin by
digestion. Whether or not the stercorin (cholesterin) is an excre-
tion of the liver corresponding to the urea of the kidney is some-
what uncertain.

What effect has bile upon the digestion?

(1) The alkaline reaction of the bile aids the pancreatic and checks
the pepsin digestion ; it aids in the emulsion of the fats, and is
probably very active in this process. (2) It moistens the mucous
membrane and favors the absorption of digested food. (3) It acts
as a natural purgative and as a natural antiseptic, and in this way
is very essential to the proper performance of the digestive process.
As a purgative bile acts by stimulating peristalsis.

What is the effect of the liver upon absorbed chyle ?

(1) Peptones resulting from the digestion of proteids undergo
some modification in the liver, for it is found that if injected into
the portal vein they do not appear in the urine, while if injected into
the general system they do appear. This matter is not fully under-
stood as yet, since the change the peptones undergo in the lym-
phatic vessels, to allow absorption without relation to the liver, is
still in the dark.

(2) The liver normally forms a substance resembling starch in its
chemical composition. This is known as glycogen, and is formed
from glucose taken up by the portal circulation. Its chemical for-
mula is that of starch (CgHigOs), and it is derived from glucose
(CgHijOe) by dehydration, and is rapidly changed by diastatic fer-
ments to glucose. This process is known as the glycogenic function
of the liver : its use is supposed to be the storage of a fund of
carbohydrate material (an " animal starch ") to maintain a steady
supply to the system.

What is the duty of the large intestine in digestion ?

The chyme which enters the large intestine still continues in the
influence of the ferments, and the process of digestion continues.
The food may undergo acid fermentation here, but there is no new
digestive action. That the large intestine may have the power of
acting upon food is shown by the absorption of fats, proteids, etc.
which are taken in nutrient enemata.

Describe defecation.

The expulsion of the refuse of digestion from the intestine is
partly a voluntary act, but more especially reflex. The voluntary

ABSORPTION. 59

act is the pressure of the abdoiuiiial muscles upon the contained
viscera, wliile the reflex is an increased j)eristalsis in the sigmoid
flexure and rectum and tlie rehixation of the spliincter. The centre
which governs tliis act, so far as it is reflex, lies in the lumbar
region of the spinal cord.

ABSORPTION.

What is absorption?

The digested food is taken from the intestines and carried into
the l)lood, whence it is taken to nourish the cells. This process
we know as absorption. The same term is applied to the removal
of worn-out material from the tissues.

By what channels is food absorbed from the intestines?

By the ]>loi id- vessels and lymphatics.

What property of chyle renders it fit for absorption ?

The property of passing through animal membranes. Chyle is
the name given to food after digestion. By digestion the proteids,
starches, and fats, which were not dialj'zable. have become pep-
tones, sugars, and emulsified fat. All these products of digestion
are readily capable of dialysis, and therefore ready for absorption.

What is dialysis?

By dialysis we mean the property of fluids which enables them
to pass through animal membranes — osmosis. This we have seen
is possessed in a high degree by the ingredients of chyle. The
reverse process may occur, and fluids (serum) from the blood may
similarly be drawn into the intestinal canal, as is seen when the
salines are used as purgatives.

What anatomical features of the gut favor absorption ?

(1) The valvulai conniventcs greatly increase the area of the
intestinal surface, and by their shelf-like formation delay the ad-
vance of ch3'le. (2) The villi of the intestine not only increase
the area, but are the .special organs of the function of absorption.
(3) The contraction of the intestine upon its fluid contents also
favors, mechanically, the filtration of the contents through its walls.

What are the villi?

The villi are almost innumerable, minute, teat-like projections
from the surface of the wall of the intestine. They are very
numerous in the small intestine, and none are found in the largo

60

ABSOEPTION.

gut. Each villus is covered by an epithelial layer, and within, sup-
ported by areolar tissue, is a delicate capillary network of blood-

FlG. 11.

Fig. 12.

I^

Fig. U. — An Intestinal Villus : a, layer of cylindrical epithelium, with its external trans-
parent striated portion; hb, blood-vessels entering and leaving the villus; c, lym-
phatic vessels, occupying its central axis (Leydig).

Fig. 12. — Patch of Peyer's Glands, from the lower part of the ileum, shovping villi (mag-
nified).

vessels, a muscular layer (muscularis mucosae), and a more or less
branched ending of a lacteal vessel (Figs. 11 and 12). The ileo-
caecal valve shows the absolute alteration which is apparent in the
mucous membrane of the small as compared with the large intes-
tine. On the side toward the ileum are found villi in great num-
bers, while its cgecal side shows none.

Where does the absorption occur in the intestine?

Probably throughout its length in some degree. In the stomach
and large intestine the absorption is very much less than in the
small intestine, but there is reason to think that there is consider-
able activity of absorption from the entire gut so long as digestion
continues.

ABSORPTION.

61

What becomes of the food absorbed by the blood-vessels ?

It is taken by the portal vein to tlic liver, and tiicrc further
elaborated for tissue-nutrition.

What becomes of the food absorbed by the lacteals ?

It is colK'clt'd rmni all llu; Ivnipli-spaces in tin; villi and about the
jzlandular structure of tlie intestines, and is taken thence into the
larger lacteals, whence it passes through the mesenteric lymphatic
glands and into the receptaculum chyli of the thoracic duct (Fig. 13).
Hence it passes on into the blood-vas-
cularsystem, which it joins at the root
of the neck at the union of the left in-
ternal jugular and subclavian veins.

Does chyle undergo change in the
lacteals ?

Yes. Peptones, as such, are not
found in the blood nor in the thoracic
duct, and in the same way sugar is
not more abundant in chyle after
absorption than in the blood ; nor
can we fully account for the fats
which are absorbed. The trace is
lost, to a great degree, after absorp-
tion of most substances, and we do
not know the exact history of the
metamorphoses which render them
fit for tissue-building.

What elements are chiefly taken
up by the portal system?
All elements to a greater or less
degree, but the crystallizable sub-
stances are taken up in greater pro-
portion by the blood-vessels than by
the lacteals. Thus we find that
sugars and salts seem to pass into
the portal system, and the proteids

and fats into the lacteal system in a I.acteals and Lymphatics during Di-

little greater proportion. ^^* ""*'

What is the appearance of chyle in the lacteals?

It is opacjue, whitish, milky from the minute fat-globules which

62 ANIMAL HEAT.

are suspended in it (emulsion). The basis of the fluid found in
the lacteals is lymph, and it is only during digestion that the lymph
in the visceral lacteals becomes chylous.

What is the character of lymph ?

It is a limpid, watery fluid, which differs from blood-plasma only
in that it is somewhat more watery. Like plasma, the lymph co-
agulates or clots on exposure to the air, but the clot is not so firm,
and the clotting is due to the presence of fibrinogen and globulin.
Chyle is lymph in which there is present an increased amount of
fatty and proteid material.

What conditions favor the absorption of food ?

To be absorbed by the blood-vessels or lacteals we must have
substances in (1) a fluid state, and the more dilute in solution the
more ready the absorption ; insoluble substances are not apprecia-
bly aff"ected by this process, nor are any dense solutions readily
taken up. (2) The rapid removal of the absorbed matter and the
renewal of fresh blood in the capillaries is of importance. Thus,
if the portal circulation is obstructed, so that the blood is circulat-
ing slowly or the capillaries are tense from intravascular pressure,
the absorption will be slow.

What is the quantity of chyle which is taken into the system
daily ?
This is somewhat problematical, but it is estimated to be about
one-half to two-thirds of the volume of the blood.

How is lymph propelled in the lymphatic vessels ?

In the villi are bands of unstriped muscle (musculi mucosae),
which act to propel it into the larger channels ; muscular pi-essure
upon the lymph-vessels and intrinsic contractile power of the vessel-
walls help it along ; while the pumping force of the respiratory
movements and the " negative pressure " in the great veins are of
great value in maintaining the circulation.

ANIMAL HEAT.
What is the normal temperature of the body ?

98.5° F. (37° C). This temperature is not invariable, but in
the superficial cavities, mouth, and axilla, which are convenient for
ascertaining the body-temperature, this is nearly exact. In the in-

ANIMAL HEAT. 03

ternal organs the theriiioinotcr may indicate as liigh as 100° F. in
normal conJitions. In the rectum the temperature is about 1° F.
liighcr than in mouth or armpit.

Is this normal temperature constantly maintained?

Yes, with very trifling variations. I nder all circumstances the
healthy body maintains about this temperature, varying very
slightly uiulcr torrid and frigid climates. There are also slight
variations from exercise, age, etc.

How is this heat maintained?

It is produced from union of the oxygen of the air, which is
taken up by the blood in the lungs, with carbon and hydrogen.
This is an exact analogy of combustion in the air.

What products result from this combustion in the body ?

Carbonic oxide and water.

What is metabolism?

It is a change constantly going on in the body by which the
protoplasm of cells is destroyed in doing work (destructive metab-
olism), and by which new protoplasm is built up by the assimi-
lation of food (constructive metabolism). When any group of
cells is in active use {<'.g. in a muscle) the destructive process
is rapid and the formation of carbonic oxide and water is active ;
in other words, there is active combustion of the cells with the
production of heat. Simultaneously, there is reconstruction of
the used protoplasm, but this process is not accompanied by the
creation of heat.

How is the loss of heat regulated ?

(1) The blood at the surface of the body is cooled by the colder
air or by evaporation of the sweat. This is automatically regulated
by the vaso-motor nerves, for upon exposure to a colder atmosphere
there is immediate contraction of the superficial capillaries, and upon
entering a warmer environment there is dilatation ; so that the quan-
tity of blood presented for cooling is an inconstant factor, depeiuling
upon external temperature. The sweat-production is similarly under
reflex control.

(2) Loss of heat is considerable by the lungs, though less than
that from the skin : the air is warmer, in usual conditions, after
leaving the lungs than before it has entered them.

64 SECRETION.

(3) Clothing and the protection aiforded by houses, and the ele-
vation of the temperature of air indoors by fire, are factors in the
regulation of the body-temperature.

What is meant by heat-centres in the brain?

There are reasons for believing that there are nervous centres
exciting the heat-production in the tissues (thermogenic centres),
and centres which check the metabolism of tissue, and thus con-
trol the temperature (inhibitory heat-centres). , This is not entirely
proven, nor can these centres be localized. We do know that the
innervation of a part is necessary for the maintenance of its
warmth, aside from vaso-motor causes for alteration of tempera-
ture.

What are the extreme limits of body-temperature found in life ?

In ordinary pathological conditions the temperature does not
remain long at a point below 95° P. or above 105° F. without
fatal results. Under extreme conditions of prolonged exposure to
cold and the algid stage of cholera recovery has occurred after a
bodily temperature as low as 75° F. On the other hand, in some
cases of extreme fever, as from sunstroke, recovery has been noted
after a temperature of 110°-112° F. has been observed.

SECRETION.

What are secretions?

Materials separated from the blood by the cells to serve some
further purpose in the animal- economy. These secretions are for
the most part elaborated by the glands, though the mucous and
serous membranes act in this capacity as well. Examples of
secretions are found in milk, bile, gastric juice, tears, etc.

What are excretions?

Materials which are separated from the blood by cell-activity
and discharged from the body, being either useless or harmful if
retained ; e. g. ui'ine, sweat.

What is the function of the serous secretions ?

Lubrication of surfaces in which friction is undesirable. Such
conditions are found in the pleural cavity, peritoneum, tunica
vaginalis, and in a similar way in the synovial cavities of joints,
tendon-sheaths, etc.

SECRETION.

65

What is the function of mucus ?

To lubricate and inoi.steii the soft and delicate cells of mucous
membrane. Mucous tracts which are so protected are the digestive,
respiratory, and genito-uriuary.

How are these processes of secretion and excretion carried on ?

r»y mean,- (if the activity of the cells. In most cases the cells
are grouped in organs which are known as glands. The serous
fluids are the only notable exception to this rule, the endothelial
cells secreting without the intervention of complex anatomical
groups.

What forms of secreting glands occur?

1. Si))ipir tit/ntivii, or tuhnlar (/hinih, which are pits or depres-
sions in epithelial surfaces lined with epithelial cells. The mucous
surfaces furnish the most numerous examples of this form of
gland, follicles of Lieberkiihn (Fig. 14), tubular (mucous) glands

Fig. 14.

Follicles of Lieberkiihu, lioiu small intestine of dog.

of the stomach ; but the skin, in the sweat-glands, shows a more
complicated form of tubular gland in that it is convoluted and
tortuous.

2. Compound tuhuhir glanih consist of a tubular gland which

5— Phy,

ee

SECRETION.

subdivides the main tubule,

Fig. 15.

Portion of one of Bruuner's Glands, from
human intestine.

SO as to have several branching
tubules leading into it. Often
these branches again subdivide
so as to form a group of ulti-
mate glandular elements grouped
about the main tubule, which acts
as a duct. This form of gland is
found in kidney, testis, salivary
and mammary glands, Brunner's
glands (Fig. 15), and in many of
the other glandular structures.

3. Racemose or aggregate glands^
in which the glandular structure
is divided into lobules or acini.
These glands may be regarded
as a refinement of the compound
tubular variety, and examples are
found in the salivary glands and
in the Meibomian follicles.

How is secretion effected by the glands ?

(1) By physical processes — viz. filtration and dialysis — the cells
are able to separate from the blood-plasma the ingredients which
make up the secretion. It is important to remember that the force
of dialysis may actually operate against pressure, and is, conse-
quently, not a mere negative process ; and, again, the fact that the
condition of the blood as to consistency and saline ingredients
makes filtration a sort of check-valve upon the permanency of the
blood-condition.

(2) By chemical processes the cells of glands manufacture new
substances not found in the blood-plasma and add them to the
secretions. These processes are peculiarly noticeable in the fer-
ment-producing glands, salivary, peptic, and pancreatic.

What circumstances affect glandular activity?

(a) If the amount of hlood passing through a gland be increased,
there will be increased activity of the function, and, conversely, as
a rule, during functional activity the gland will increase in vascu-
larity. The stomach, for example, during digestion is quite en-
gorged, and when idle is supplied with much less blood, as is seen
by the color deepening during its period of activity.

(J)) An increase in the material upon which the gland acts stimu-

THE MAMMARY GLANDS. 67

lates the gland to greater effort ami iiioreases the production of the
ghuid. Thus, the amount <tt' urea is increased by an increase of
nitroiicnous waste, as l)y exercise, or by an increase of nitrogenous
matter in tlie blood, as by a full meal of animal food.

(f) The iirrroiis s^sto)! cxois (Ui actirr Injlaence upon secretion.
This is usually reflex in character, and fre(juently is active through
the vaso-motor nerves, as when the salivary and gastric secretion.s
are increased by the sight or smell of food, as well as by its actual
administration. There is also a so-called tropldc influence of the
nervous system, which directly affects the secreting power of a
gland : this is especially well shown in the case of the chorda
tympani in its relation to the secretion of the submaxillary
gland.

Describe the correlation of the secretions.

There oi'ten seems to be a relation in the amount of one secre-
tion to that of some of the others ; thus in a diseased condition of
the intestinal mucous membrane, with increased secretion, there
will often be an increase of the bile secreted, and perhaps a
diminution of other secretions, as salivary or urinary. And, again,
unusual perspiration is followed by decrease in the activity of the
kidneys.

THE MAMMARY GLANDS.
Describe the mammary glands.

They are large glands which are made up of several distinct
lobes. f]ach lobe has its duct, which leads to the nipple, and
there are about twenty such lobes and ducts. The lobes are
subdivided, and the small lobes, lobules, or alveoli are made up
of the terminal tubules of the duct, which lie in a mesh of
fibrous alveolar tissue containing considerable fat in its reticu-
lum. The ultimate divisions of the duct (alveoli) are lined with
columnar epithelial cells, as are the ducts and their branches, but
the epithelium of the ducts becomes flat (squamous) near the nip-
ple. The main ducts (lactiferous duets) are sacculated, and during
lactation the secretion of the alveoli collects in them, and is drawn
from them through their small orifices in the nipple. The flow of
milk is also aided ])y the presence of a small amount of unstriped
muscular fibre in the wall of the ducts.

The mammae are abundantly supplied with blood-vessels, lym-

68 SECRETION.

phatics, and nerves, and during pregnancy and lactation tlie ves-
sels, as well as the gland, undergo considerable increase in size.

What is milk ?

The secretion of the mammary gland is a bluish-white fluid. It
is opaque, and this opacity is caused b}" the presence of minute fat-
globules which are held suspended — an emulsion. Besides the fat-
globules the microscope shows in milk from a newly-active gland
certain albuminous bodies which are known as colostrum-corpus-
cles. They are probably cells from the gland which are under-
going fatty degeneration. Milk is alkaline in reaction, and has a
sp. gr. of about 1030.

Describe the composition of milk.

The ingredients of milk are water, containing in suspension fats
and in solution casein, serum, albumin, milk-sugar, and salts. Hu-
man milk differs from cow's milk in containing less proteids and fats
and more sugar:

Human Milk. Cow's Milk.

Water 890 858

Proteids .... 35 68

Fats 25 38

Sugar 48 30

Salts 2 _6

1000 1000

What is cream?

The fat-globules rise to the top if milk is allowed to stand, and
are called cream. By agitating or '■ churning" the cream the albu-
minous envelopes of the fat-globules are broken, and they coalesce
to form a fat mass known as " butter."

Why does milk "turn sour" ?

The addition of an acid to milk causes the casein, which is held
in solution by the alkaline sodium phosphate present, to be precip-
itated. The precipitation of the casein leaves behind the watery
and soluble ingredients, but includes with it the fat-globules. The
precipitate is known as the " curd," and the watery residuum as
" whey." This process is imitated in nature by the breaking up
of milk-sugar (lactose) to form lactic acid through the action of a
micro-organism, hactermm lactis.

THE SKIN. 69

What is meant by milk-curdling ferments?

Certain feniieiits will act upon luilk tu cause its separation into
curd and whey. These arc called uiilkcurdling ferments. They
are found especially in the secretions of the stomach, pancreas, and
intestine.

How is a milk-curdling ferment utilized in the arts?

In cheese manufacture the fourth stomach of the calf (rennet)
is used to curdle milk.

What causes a scum to form upon boiled milk ?
The serum-albumin is solidified by heat.

What changes occur in milk at different periods of lactation ?

The milk of mothers prior to and just after parturition is known
as colostrum, and is deficient in casein and contains an excess of
serum-albumin, as well as colostrum-corpuscles. Toward the end
of lactation there is also said to be the same excess of serum-albu-
min and lack of casein.

How are the fat-globules of milk secreted?

It seems probable that two methods are possible : (1) The epithe-
lial cells of the gland seem capable of causing a metabolism of pro-
teids to form fat ; (2) the cells themselves may undergo a fatty
metamorphosis.

What is the value of milk as a food ?

As the food of all young animals it has to be considered of the
greatest importance ; besides this, as a direct food, both in the
natural state and in the derived forms of butter and cheese, it is
one of the most used articlesof adult diet. The causes which lead
to its choice in the dietary are easily seen : it contains all the ele-
ments necessary to sustain life — water, proteids. carbohydrates, and
salts. As an exclusive diet it will probably sustain life better than
any other substance.

THE SKIN.
Describe, roughly, the structure of the skin.

There are two layers of tissue which form the entire thickness
of the .skin. The superficial epithelial layer is known as the epiiJer-
mis or cuticle; the deeper stratum, in which lie the active functional
elements, is called the cutis vera, corium, or derma.

70 SECEETION.

What is the function of the epidermis ?

The epidermis is a stratification of epithelial cells of varying
thickness. The epithelium is flat and horny at the surface, in the
deeper portions are flattened and polyhedral cells, and it is closely
adapted to the surface of the corium beneath it. In its deeper
layer is found the pigment which characterizes the complexion of
individuals and of races. Its function is purely one of protection.
The growth to replace worn-out cells is very rapid, and in cases
of considerable use of a part, with interrupted pressure upon the
skin, the cuticle becomes very thick and horny, as is often seen
upon the hands and feet. The hair and nails are modifications of
the epidermal epithelium.

Describe the structure of the corium.

The true skin is a tough, elastic tissue composed of interlacing
bundles of connective-tissue cells containing spaces between the
fasciculi. These spaces are known as areolse. There are also num-
erous unstriped muscular fibres. This structure lies upon a more
or less thick layer of fatty or loose cellular tissue. In the cutis are
found the active organs of the skin — the papillae, sweat- and seba-
ceous glands, and the hairs (Fig. 16).

What are the papillae and their uses ?

Upon the superficial surface of the cutis vera are innumerable
minute elevations which project into the epithelium. They are
very vascular, and contain the nerve-endings which give to the skin
its sensibility, the sense of touch. The papillae are especially abun-
dant upon the parts in which this sense is most acute — palms, finger-
tips, soles.

Describe the sweat-glands.

Each gland lies in the subcutaneous fat, and consists of a con-
voluted mass of tubules which terminates in a duct leading up
through the derma and epidermis, discharging the secretion of the
gland through a minute opening. This secretion is known as per-
spiration or sweat.

What is meant by the term " insensible perspiration " ?

When the secretion of the sweat-glands forms in drops upon the
skin, we speak of this as sensible perspiration or sweat. However,
at all times the glands continue active and the fluid evaporates rap-

THE SKIN.

71

idly, so that no moisture is noticeable upon the surface ; and we call
this the insensible perspiration.

Fig. 16.

Sectional View of the Skin, magnified.

What is the sweat ?

Tt is a watiTY fluid, oolorless. sli<:htly turbid, slightly salty to the
taste, of acid reaction, and possessing a peculiar odor. It is an
excrement. Its composition is somewhat variable, but in general it

72 SECEETION.

may be said to contain about J per cent, of solids suspended and
dissolved in water. These solids are fats and fatty acids, sodium
chloride, epithelium, and a trace of urea. Besides these there is a
considerable amount of carbonic dioxide (CO2) excreted by the
skin.

What is the amount of sweat excreted in twenty-four hours ?

About one and a half to two pints, but this varies greatly with
the environment.

What factors affect the amount of the sweat ?

The condition of the atmosphere, the nature and quantity of the
food, the amount of fluids consumed, the exercise taken, and the
relative activity of the other glands, especially of the kidneys.
Certain mental conditions, some diseases, and drugs also interfere
with sweat-secretion.*

What ingredients produce the characteristic odor of perspiration ?

The fatty acids — formic, acetic, butyric, propionic, caproie, and
caprylic — have been found. The odor of sweat varies in diiferent
portions of the body.

Upon what nervous '^mechanism does the production of perspira-
tion depend?

It is probable that the sweat-glands are under the reflex control
of centres in the medulla and in the spinal cord, and that these
centres regulate this function of the skin through the vaso-motor
system.

Is sweat-excr.etion necessary to life ?

Yes, because of the disturbance of heat-regulation by absence of
evaporation, or, perhaps, by absorption or retention of poisonous
matter. The symptoms are those of an acute poisoning — pyrexia
and exhaustion.

What is the character of the sebaceous glands ?

The sebaceous glands occur everywhere over the entire skin sur-

* Under conditions which exaggerate the flow of the perspiration, as hard
work in hot air, with free consumption of fluids, the amount of the perspi-
ration is said to exceed twenty pints in a day.

THE KIDNEYS AND THE URINE. 73

face with the exception of the palms and soles, and most abun-
dantly in the hairy parts. They are intimately connected with
the hair-follicles, and their ducts, as a rule, open into the folli-
cles, though sometimes they discharge separately. The glands are
aggregate glands ; that is, are formed by the subdivision of the duct
to make up the lobules of the gland. There is a delicate plexus
of capillary vessels about the sacculi.

What do they secrete ?

The secretion of the sebaceous glands is a soft, oily, white mate-
rial, and has, besides other fats, stearin for basis. Its use seems to
be to lubricate the skin, keeping it soft and flexible, and at the same
time, by its oily nature, to prevent maceration of the skin by con-
tinued exposure to moisture, and to check the undue absorption
from the surface. Sebaceous matter is not excrementitious, but
is a secretion.

Has the skin power to absorb ?

It has. This function of the skin is utilized in the application
of medicines, of food, and of drink in appropriate cases.

What further function has the skin ?
That of regulation of body -temperature.

THE KIDNEYS AND THE URINE.
Describe the gross appearance of the kidneys.

The kidneys are glandular organs having somewhat the form of
a bean. In size they are somewhat more than 4 inches in length,
somewhat more than 2 inches wide, and about 1 inch thick. The
weight of each organ is about 4 to 6 ounces. A thin but rather
tough capsule invests the kidney (Fig. 17). This may be pulled
off readily, leaving the surface of the organ smooth and even and
of a deep-red color. If a vertical section of the organ be made,
the central cavity (sinus) will be noticed, and about it the kidney
tissue. Within the sinus are the apices of pyramidal projections.
about ten in number, and if the cut surface be examined closely it
may be noted that the outer (cortical) portion differs in appearance
from the more central (medullary) portion. The blood-supply is
from the renal artery, and the nerve-supply is from the sympathetic
system through the solar plexus.

74

SECEETION.

What is the function of the kidney ?

The secretion of the urine. The kidney is a compound tubular
gland. The medullary portion of the organ is almost entirely

Fig. 17.

Vertical Section of Kidney.

made up of tubules, which take origin in the cortex and empty
upon the apices of the pyramids of Malpighi of the medullary
portion.

What are the Malpighian bodies?

In the cortical portion of the kidneys are found minute tufts of

THE KIDNEYS AND THE URINE.

75

capillaries which are .surrouiuled by a capsule lined by epithelial

cells (Fig. IS), and here it it is that the urin-

iterous tubules arise, the tuft of capillary Fio. 18.

vessels being, as it were, built into the end

of the tubule.

What are the uriniferous tubules?

BoyiMning in the curti'X of the kidney at
one of the bodies of Malpighi, the minute
secreting ducts pursue a tortuous course to
the larger collecting tubules, which empty at
the apices of the pyramids of Malpighi into
the calyces of the kidney. Without entering
minutely upon the course of the tubules, it is
important to remember that they form a loop
(of Henle) which dips into the pyramid, and
that they pursue a somewhat tortuous course
both before entering into the loop of Henle
and upon returning to the cortical portion of
the kidney, where they empty into the straight collecting tubules.
The straight course of the arms of Henle's loop and of the collect-
ino- tubules gives to the pyramids a finely striated apppearauce.
(See Fig. 19.)

Malpighi.in Body.

Describe the blood-circulation in the kidney.

On entering the kidney the renal artery breaks up into several
])ranches, which pass into the tissue proper of the organ. Branches
from these arteries (arteria propria renales) have two determina-
tions— (1) into the cortex, and (2) into the pyramids.

(1) Those branches (interlobular) which pass into the cortex
divide to become the ajferent vessels to the jMalpighian bodies, and,
after there passing through the capillary tuft, the blood is re-col-
lected and goes out by an efferent vessel. This efferent vessel in
its turn is broken into a minute capillary plexus which surrounds
the uriniferous tubules in the cortex of the kidney, and these
capillaries unite to form the venous return circulation. Thus, //(**•
si/sfem hatf, it in to he noted, tiro capiflari/ divisions, in the Maljjighian
tii/t. and again about the tuhides of the cortex.

(2) Numerous minute branches (arterise rectae) are given off,
which pass into the pyramids, surround the portion of the urin-
iferous tubule (Henle's loop) which passes into the medullary

76

SECEETION.
Fig. 19.

Arterise rectse

Vense rectae.

Diagram of the Tubules and Vascular Supplj' of the Kidney. On the left is a tubule
alone ; in the middle is a tubule along with the blood-vessels ; on the right are blood-
vessels only.

region of the kidney, and return (venae rectge) to join the branches
from the cortex and form the ven^e propriae of the kidney.

How do the kidneys secrete urine ?

(1) By filtration, and (2) by real functional action of the epi-
thelium.

(1) In the circulation of the blood through the Malpighian tuft
there seems to be no active separation of the urinary ingredients

THE KIDNEYS AND THE URINE, 77

by cell-power, but the water and saline elements are given off here
by the bli)od by a pnjcess uf simple filtration. The amount of
fluid which passes here is governed by the blood-pressure in the
arteries of the kidney and by tlie fluidity of" the blood.

(2) The epitheliiini of the uriniferous tubules has secreting
fmictiun, and is able to firfxtra/e from the blood foreign substances
{<'■</■ indigo-carmine) and eject them into the tubules, and to man-
ii/'(icfi(rc from material taken from the blood new substances not
found there (('. ^. urea and pigments).

What is the course of the urine after leaving the kidney ?

The urine collected in the tubules of the kidney passes into
the pelvis, and is carried to the urinary bladder in irregular quan-
tities by the ureter. The ureters simply act as ducts, and do
not store up urine, nor do they usually actively eject it into the
bladder. As a few drops of urine collect in the pelvis of the kid-
ney, they run into the bladder, the action of the two kidneys not
being in alternation nor absolutely regular in point of time. Re-
gurgitation from the bladder is prevented by the oblique course
of the ureter through the muscular wall of the bladder.

Describe the act of micturition.

When the bladder is filled the act of emptying it is called mictu-
rition. It is a voluntary act, aided by the involuntary reflex con-
traction of the muscular coat of the organ itself. The voluntary
muscles involved are those of respiration — the diaphragm and the
abdominal muscles. So far as micturition is involuntary, it is a
reflex depending upon a centre in the lumbar spinal cord.

What are the physical characteristics of normal urine ?

It is a clear, amber-colored fluid of slightly acid reaction. It
may develop a flocculent precipitate of a light cloud of mucus upon
standing. It has a characteristic odor and a salty-bitter taste.

What is the normal specific gravity of the urine ?

About 1020, but under conditions of health it may vary from
1010 to lOP.O. or even beyond these limits.

What conditions afifect the acidity of the urine ?

The acidity of the urine is due to the presence of acid sodium
])hosphate. There is no free acid present, as is shown by the fact
that no precipitate is formed upon the addition of sodium hyposul-
l)hite. The degree of acidity varies, being less during active diges-

78

SECRETION.

tion and less after vegetable food. Herbivora have alkaline urine,
while carnivora have strongly acid urine ; but the herbivorous ani-
mal during fasting has acid urine, because it is then living from its
own tissues and is for the time a carnivore. After excretion, how-
ever, the urine soon becomes more acid (probably because of the
presence of some fermentation), and at this time uric acid and
urates may precipitate. Upon further exposure it is attacked by
micro-organisms, and the urea is changed to ammonium carbonate,
the reaction becoming alkaline, and there is a precipitation of triple
phosphates and alkaline urates. In the body these conditions do
not occur in conditions of health.

What is the chemical composition of urine ?

The urine is an excrementitious fluid, and may be considered as
a watery solution of the excrementitious products of the retrograde
metamorphosis of nitrogenous bodies, resulting from the processes
of life and action. Chemically, it is a solution of urea and urates
with a small percentage of organic salts.

Tahle of the Cliemical Composition of the Urine.

Water 967

Solids, crystallizable nitrogenous bodies :

Urea 14

Uric acid, free (trace),
Uric acid in form of alkaline urates,

Hippuric acid and hippurates, V . 11

Pigments, extractives, and mucus,
All in small and constant amounts.
Salts :

Inorganic —

Chlorides of sodium and potassium,

Sulphates and phosphates of sodium and potas-
sium.

Phosphates of magnesium and calcium,

Silicates (trace),
Organic —

Lactates, acetates, and formates, which only
appear occasionally,
Sugar (occasionally), a trace,
Gases, nitrogen, and carbonic acid.

Tooo

THE KIDNEYS AND THE URINE. 79

What is the daily quantity of urine secreted ?

One to two (jiiarts. The (juaiitity varies greatly in health with
the Amount of fluid taken, of food consumed, of the activity of the
skin evaporation, and somewhat with the character of the food. In
a more general way it may be said to depend upon the condition of
the blood, an excess of fluids demanding increase of functional ac-
tivity on the part of the kidneys. In conditions of disease or under
the stimulus of drugs the limits mentioned are by no means final,
for in certain pathological conditions the secretion may be almost
wholly suspended or very greatly increased.

What conditions increase the urinary secretion?

The conditions which favor filtration of water by the glomeruli
of Malpighi ; that is, the presentation of a larger amount of blood
to the action of these bodies. This is accomplished —

(1) By increasing the force of the heart.

(2) Through the nervous system by its action upon the vascular,
so as to produce local congestion. The effect of the nervous sys-
tem in increasing the urine by reflex vaso-motor impulses is felt
most in the glomeruli, and the urine is therefore very watery.

(o) Conditions which cause anaemia of other parts may produce
a greater determination of blood to the kidneys, and so increase
the urinary flow. So marked is this that the skin and kidneys
may almost be said to be complementai'y in their action in elimi-
nating water from the system ; and in this regard their relative
activity may be said to be inversely proportional to one another.

Kirke has the following table (modified from Foster), which is
useful for reference :

Table of the Relation of the Secretion of Urine to Arterial Pressure

(Kirke).

A. Secretion of urine may be increased —

a. Biy increasing the general hlood-pressure — by

1. Increase of the force or frequency of heart-beat.

2. Constriction of the small arteries of areas other than that

of the kidney.
h. By increasing the local blood-pressure by relaxation of the renal
artery ^ without compensating relaxation elsewhere — by

1. Division of the renal nerves (causing polyuria).

2. Division of the renal nerves and stimulation of the cord,

below the medulla (causing greater polyuria).

80 SECEETION.

3. Division of the splanchnic nerves ; but the polyuria pro-

duced is less than in 1 or 2, as these nerves are distrib-
uted to a wider area, and the dilatation of the renal
artery is accompanied by dilatation of other vessels, and
therefore with a somewhat diminished general blood-
supply.

4. Puncture of the floor of fourth ventricle or mechanical

irritation of the superior cervical ganglion of the sympa-
thetic, possibly from the production of dilatation of the
renal arteries.
B. Secretion of urine may be diminished —

a. By diminishing the general blood-p^'essiio'e — by

1. Diminution of the force or frequency of the heart-beats.

2. Dilatation of capillary areas other than that of the kidney.

3. Division of spinal cord below the medulla, which causes

dilatation of general abdominal area, and urine generally
ceases being secreted.

b. By increasing the hhod-pressure — by stimulation of the spinal

cord below the medulla, the constriction of the renal
artery which follows not being compensated for by the
increase of general blood-pressure.

c. By constriction of the renal artery — by stimulating the renal or

splanchnic nerves or the spinal cord.

What two methods of elimination, then, do we find in the
kidneys ?

(1) The process of filtration, depending upon blood-pressure and
acting almost solely upon the aqueous elements.

(2) Secretion proper, by which cell-activity performs the func-
tion of excreting the solid matters of the urine.

What is the source of the urea?

It is not fully known whether the urea is taken from the blood
as such by the kidneys, or if it is made up by the cells of the kid-
neys from elements taken from the blood. It is probable that the
former is for the most part the source of urea, and a less amount
is really composed in the cells of the kidney-tubules. At any rate,
the source of the urea is the nitrogenous matters of the body : 1,
those taken in as food, urea being greatly increased by a nitrog-
enous meal ; 2, by the metabolism of the tissues. The measure
of the amount of work done is, however, not found in the quantity

THE VASCULAR GLANDS. 81

of urea excreted. The secretion of urea continues if nitrogenous
food he absent from the diet ; and the elimination is increased by
increased cell-activity, and. consequently, of cell-degeneration, as
by muscular work.

What is the amount of urea excreted?

The amount varies, but it may be considered to be about one-
half the solid constituents of the urine. Koughly speaking, the
urinary solids may be regarded as 4 per cent, of the total, and
the urea (including the uric acid and urates) about 1.5 to 5 per
cent. This proportion is very variable, and there may be urea in
healthy urine to exceed 2h per cent., or in a much less ratio than
5 per cent.

Metliod of Estimating Solids. — A useful rule for approximately
estimating the total solids in any given specimen of healthy urine
is to multiply the last two figures representing the specific gravity
by 2.33. Thus, in urine of sp. gr. 1025, 25 X 2.33 = 58.25 gr. of
solids in 1000 gr. of urine. In using this method it must be re-
membered that the limits of error are much wider in diseased than
in healthy urine.

What abnormal matters are sometimes found in urine ?

In disease or after the introduction of certain foods we ma}' find
certain abnormal elements in urine — serum-albumin, globulin, fer-
ments, peptone, blood, sugar, bile acids and pigments, casts, fats,
micro-organisms, etc.

THE VASCULAR GLANDS.

What is meant by the term "vascular glands"?

Certain glandular organs which are made up largely of lym-
phatic tissues, but which do not seem to be connected, at least
directly, with secretion or excretion. Among those glands may be
mentioned, as the more noticeable, the spleen, the thymus gland,
the thyroid gland, the tonsils, the suprarenal capsules, the pineal
and the pituitary glands, and Peyer's glands.

What, in a general way, is the function of the vascular glands ?

This cannot be fully answered, as the subject is not understood
at all completely ; but it may be said that their work has probably
to do with the elaboration of the blood, and, further, that each of

6— Phy.

82 MUSCLE.

the glands has an unknown special office beyond the function of
maintaining a constant supply of red and white blood-corpuscles,
and of caring for them when past usefulness. Such an opinion is
based upon the disturbance of the special glands in certain diseases,
and upon the great activity of these glands during foetal and infant
life, when the elaboration of the blood is necessarily very rapid to
maintain rapid development. In function, as well as in structure,
these glands are similar to lymph-glands.

Has the spleen a special function?

The spleen becomes considerably increased in size during diges-
tion of food, and the tissue of the organ becomes filled with
albuminous particles which gradually disappear, and hence it is
inferred that there are special functions which have to do with the
elaboration of the nitrogenous foods. Besides this, the spleen may
be regarded as a prominent source of origin of both red and color-
less blood-corpuscles, and as the organ in which many of the red
corpuscles undergo degeneration when their usefulness is impaired.
Furthermore, it is a very vascular organ, and is capable of very
great iistension, and becomes, in a passive way, a sort of safety-
valve 'in relieving the portal system, more especially of the
stomach.

Can any special function be attributed to any other of the vascu-
lar glands?

No.

MUSCLE.

What kinds of muscular tissue are found ?

1, plain or unstriated muscle-fibres ; 2, striated muscle-fibres.

Describe the unstriped or plain muscles.

They are found in the tissues in which the will has no control,
and are known as involuntary muscles. These muscles are made up
of bundles of elongated, spindle-shaped cells. Each cell has an
oblong nucleus and is flattened (Fig. 20). In length they are about
-g-^g- to g-^Q- inch, and about -^-^-^-^ inch in width. The cells are
bound into bundles by an albuminous cement, and these again
into larger bundles by areolar tissue.

What is the appearance of the striated muscle ?

This form of muscle-tissue makes up the most of the bodily
tissue, for it is found in all of the voluntary muscles. All such

MUSCLE.

83

muscles arc made up of fasciculi of fibres of this striat
tissue, each bein^ enclosed in a sheath (surcolemma)
The arrangement of the elements of each
fibre is such that its microscopic appearance Fir;,

is as though there were alternate light and A. .

dark bands about it. the dark being the
wider. These are the elements of the muscle-
tissue, the dark bands representing disks of
contractile tissue, while the brighter bands
represent a disk of interstitial substance.

What are sarcous elements?

The fibres may be split up longitudinally
into minuter fibrils which have the micro-
scopic appearance of alternate light and
dark particles ; these particles are the sar-
cous elements (Fig. 21, B, d). and it is b}'
the fusion of these fibrils that the fibres are
made up.

How large are striped muscle-fibres?

They are about an inch in length and
■j^ inch in diameter. They join the con-
nective-tissue cells of a tendon or aponeu-
rosis or another muscle-fibre by adhesion of
the sareolemma at the ends, and thus unite
the muscle-bundles in a firm mass ; and this
union is further strengthened by the cohe-
sion of the fibres.

ed m

uscle-
. 21).

Non-striated Elementary
Fil)res, from the human
colon : a, treated with
acetic acid, showing the
corpuscles : b, fragment
of a detached fibre not
touched with acid.

What is peculiar in the heart-muscle?

It is an exception to the rule that involuntary muscles are un-
striped. The striation of the heart-muscle fibres is not so marked
as in ordinary muscle, and the form of the fibres is different, for
they are branched and more slender. Each fibre is nucleated, a
large oval nucleus occurring at the centre. The appearance of
the heart-fibres indicates that they occupy an intermediate position
between typical plain and striped fibres.

What is myosin?

Myosin is an albuminoid substance belonging to the class of

84

A, Portion of a Medium-sized Human Muscular Fibre (magnified nearly 800 diameters).

B, Separated Bundles of Fibrils, equally magnified : a, a, larger, and 6, 6, smaller collec-

tions; c, still smaller; d, d, the smallest which could be detached.

globulins, which may be derived from muscle. This substance
bears the same relation to living muscle that plasma does to living
blood. By pressing muscle kept at a temperature below the freez-
ing-point it is possible to obtain a viscid, opalescent fluid of alkaline
reaction, which soon presents the phenomenon of clotting, and one
has resulting a muscle-senim and mvscle-clot. This muscle-clot is
myosin. During the process the fluid becomes acid in reaction.
The clotting of muscle-plasma is caused (probably) by ferment
action, and the ferment (myosin-ferment) is derived from a com-
posite antecedent, similar to fibrinogen, called myosinogen.

What gives muscle its red color?

Haemoglobin of the blood in some degree ; but there is also a
distinct pigment known as myo]i8e,inaturin.

MUSCLE. 85

What is tlie chemical composition of muscle ?

Water is a cliict' intrredieut, and myosin the characteristic one.
Salts arc found, chiefly of potassium. A'arious proteids, such as
gehxtin, ehistic material, and al))uniins, are found, together with
fats and extractives. The extractives are mostly complex organic
compounds : among them may be mentioned kreatin, lactic acid,
and sugar. Urea is not found, except in minute quantities, though
it is regarded as origiiuiting from the waste products of muscular
action. The following table formulates the proportion of these con-
stituents :

Water 745

Solids :

Myosin and insoluble proteids 155

Soluble proteids 20

Gelatin 21

Fats 23

Organic and inorganic salts 36

1000
What is the reaction of live muscle ?

Alkaline, due to the presence of potassium phosphate.

What is the function of the muscles ?

They contract and cause motion in the parts to which they are
attached. During life the muscles are always tense, and this con-
dition favors a more powerful action when the muscles contract in
response to stimuli.

How do the muscles affect the blood passing through them ?

They abstract much of the oxygen and give oft' large amounts
of carbonic acid, so that blood after circulating through the mus-
cles, even when they are at rest, becomes very dark. It is prol)able
that an abundance of oxygen is especially essential to the healthy
condition of the muscles, and it is found that in an atmosphere of
oxygen muscles retain their power of contraction longer than in
one of hydrogen or carbonic acid.

What peculiar electrical condition is noticed in living muscle ?

When a living muscle is tested by means of the galvanometer
after removal from the body, it is found to develop certain electri-
cal currents known as muscle-currents or currents of rest. They are

86 MUSCLE.

strongest from the centre of the muscle toward the cut end, though
certain minor currents are developed with the electrodes in closer
proximity. The cut ends of a muscle are always electro-negative
to its equator. This phenomenon cannot be observed in uninjured
muscle when in the body, but any injury will render the injured
portion electro-negative to the rest of the muscle. This condition
ceases with the power of contraction, and cannot be demonstrated
in dead muscle.

What is the effect of contraction upon this "current of rest"?

When the muscle is made to contract, the galvanometer needle,
which has indicated the passage of an electrical current during rest,
flies quickly back toward the zero indicating the cessation of the
current of rest. This action is known as the negative variation of
the galvanometer, and as soon as the contraction of the muscle has
ceased the instrument again indicates the presence of the current
of rest.

What is the cause of these electrical currents ?

This is not yet fully determined, but they are probably due to
chemical changes resulting from the physiological degeneration. It
has been held that such currents occur naturally in muscle as the
result of certain of the cells exciting electro-motive forces, but the
former theory seems the more plausible.

What stimulus causes a muscle to contract?

The stimulus is supplied by the motor nerve which is distributed
to the muscle.

How do the motor impulses reach the fibres?

The nerve divides and subdivides in the muscle until only a
single axis-cylinder is supplied to a small group of muscle-fibres.
This axis-cylinder then forms a delicate plexus about the muscle-
fibres, and in the case of plain muscle-fibres ends in the nucleus of
the fibre. In the striped fibres there is a special termination in a
small granular mass called the motorial end-plate.

Is the property of contraction inherent in the muscle itself, or
does it depend upon the nerve?
It is a property of muscle.

What artificial stimuli may be used to cause muscular contrac-
tion?
Certain stimuli may be applied to a muscle or to the nerve sup-

MUSCLE. 87

plying it which excite it to action. It is mure usual to stimulate
the nerve, as this is more convenient and more effectual. There
are four kinds of excitants that may he used : 1, mechanical, as hy
a hlow or prick or pinch ; 2, heat, as hy a hot needle ; 8, chemical,
as dilute acids, etc. ; 4, electrical, as by the galvanic*or faradic cur-
rent. This is the most usual as well as most convenient kind of
stimulus for experiment.

How are the phenomena of a contraction observed ?

They are connnoiily observed in a tracing upon an instrument
called the myograph, and usually a large muscle of a frog and its
nerve are taken for the demonstration. The time of the observa-
tion is recorded by the vibrations of a tuning-fork. Such a pi'epa-
ratiou is known as " a nerve-muscle preparation," and the tracing
obtained is called a '' muscle-curve."

At what period of an electrical current do the muscles contract ?

Only at the making and breaking. If a nerve-muscle prepara-
tion be arranged for experiment and stimulus be applied by means
of a galvanic cell, it will be found that the muscle will contract
only at the instant the circuit is completed and at the instant it is
broken. During the time the current is pas.si}iff no contractions of
the muscle occur, unless the character of the current changes or
the strength of the current is considerable. The mere passage of
an electrical current does not cause a muscle to contract, but the
entrance or exit of the current is the stimulus. It does not matter
if the positive pole be applied to the nerve nearer the muscle, or if
the negative pole is the nearer : the contraction is the same with
an ascending as with a JcscenJuiff current.

Describe the phenomena observed in a single contraction fol-
lowing a stimulus.

There is a brief period during which no action occurs, the latent
period, during which the stimulus applied to the nerve is being
transmitted to the muscle. Then follows a sharp, sudden contrac-
tion of the muscle (stage of contraction), which is intensified
steadily to a maximum, and then the muscle more slowly relaxes
(stage of elongation), and the muscle returns to its former condi-
tion of rest. There are sometimes less violent contractions which
follow, and are due to the elasticity of the musi-le. The whole
time consumed is about one-tenth of one second, and of this time

»» MUSCLE.

the latent period and the stage of contraction consume only about
one-tenth each. •

What is tetanus ?

When the stimuli follow one another in rapid succession the con-
tractions are practically constant, and the stage of elongation does
not follow. This condition is known as tetanus. The stimuli may
be slow enough to allow perceptible quivering of the muscle (and
a wavy tracing of the myogram), or may be very rapid, so as to
keep the contraction constant.

What effect has fatigue upon the muscle ?

Its latent period is longer and the strength of the contractions
diminish.

Is the temperature of muscle elevated by action ?

Yes. It has been estimated that the temperature of the biceps
muscle may be elevated one to two degrees of the Fahrenheit scale
by exercise. It is not known whether this is due to chemical
action or to friction between the fibres.

How does the shape of the muscle change in contraction ?

The muscle becomes shorter, thicker, and harder, and seems to
bulge at the centre. This is not an actual increase in bulk, for
what is gained in thickness is made up in the loss by shortening.
Each fibre of the muscle contracts and becomes short and thick,
as does the whole muscle. This shortening is due to an approxi-
mation of the elements probably, and not to a change in the
arrangement of the elements.

What chemical changes occur in muscle with action?

The muscle (in rest alkaline) becomes acid from the develop-
ment of lactic acid, and there is found a kind of glucose known as
inosite, or " muscle-sugar." Besides this, the active metabolism
increases the production of carbonic acid and of extractives.

What is rigor mortis?

When a muscle is dead it will no longer respond to stimuli, but
remains in a contracted state, fixing the limbs and body in rigid
condition. This post-mortem rigidity constitutes rigor mortis.
The muscles of the neck and jaw are usually first afiected, and

NUTRITION. 89

then of the arms, gradually passing downward until the whole
body is stiff. This begins usually soon after death, but may be
delayed for several hours, and lasts until putrefactive changes have
set in, when the body relaxes. All muscles are affected, plain as
well as striped.

What is tlie cause of rigor mortis ?
Coagulation of the muscle-plasma.

What is the post-mortem rise of temperature ?

After death there is considerable rise of the temperature of the
body, which is very marked during the progress of rigor mortis. It
may amount to 5° or 10° ¥., or even more.

What changes occur in muscle after death?

The muscles become set in contraction, and their reaction becomes
acid from the development of lactic acid.

How do the voluntary muscles act?

They act as the power which moves the bones in their function
as levers. Each of the three classes of levers is illustrated in the
body : (1) Fulcrum between power and weight : ham-string mus-
cles acting upon the ischium to raise the body from a stooping
position ; hip-joint, fulcrum. (2) Weight between power and ful-
crum : depi'cssors of lower jaw acting against the tension of the
temporals, etc., with temporo-maxillary articulation for fulcrum.
(8) Power between weight and fulcrum : biceps of the arm in
raising the forearm, with elbow-joint as fulcrum.

How do the involuntary muscles act?

They do not have attachments to the hard parts, but enter into
the composition of the walls of hollow organs which require elas-
ticity and variation in size. The heart and arteries, as well the
digestive tract, furnish numberless examples of their action. They
are often rhythmical in their action (peristalsis), and the stimula-
tion of this class of muscles does not cause a tetanus (except the
heart), but a succession of alternate contractions and relaxations.

NUTRITION.
What is nutrition ?

By nutriliun we mean the ])liysioliigical principles which preserve
the normal couditions of the structure and fuuctiun ol' the body, so

90 NUTEITION.

far as refers to the balance between the income and outgo of mate-
rial. While it is almost an impossibility to study this subject ex-
actly, yet an idea of the modes of expense and income may be
gained by consideration of data which are tolerably fixed. In con-
sidering the income and expenditure of the body it is always neces-
sary to bear in mind that all the factors are variable and the results
inconstant, for the income often exceeds the expense, and vice versa,
in life.

What are the daily expenditures of the body ?

The more important are those by the ordinary excretory channels
— lungs, skin, kidneys, and intestines.

From the lungs there are exhaled every twenty-four hours —

Of carbonic acid, about 30 ounces.

Of water 10 " 40 ounces.

Traces of organic matter.
From the skin —

Water 23 "

Solid and gaseous matter 1 ounce. 24 "

From the kidneys —

Water 50 ounces.

Organic matter I2 "

Minerals and salines ■ . . 2 ounce. 52 "

From the intestines —

Water 4 ounces.

Various organic and mineral sub-
stances 2 " 6 "

Total, 122 ounces.

What are the sources of income ?

Food and drink and oxygen are the factors of the income, and
may be calculated about as follows for twenty-four hours :

Food (chemically dry) 16 ounces.

Water (as drink and as combined with solid food) . 80 " •
Oxygen (absorbed by lungs) 26 "

Total, 122 ounces.

Thus we may represent the schematic plan of income and ex-

NUTRITION. 91

pensc as about equal, but it must Ik- borm; in mind tbat thu iihiii
(iiily iv])ri'soiifs an average result i)f" botli.

How are variations in the rate of income and expenditure shown ?
By (.'lianues in tlie liodily weiglit.

What is the result of the expenditure ?

(1) The groicth of the body and secretion of its necessary mate-
rials, as well as the maintenance of the tissues, subjected as they
are to the wear incident to the continuance of life and function.

(2) The continuance of physical conditions suitable to life in the
form of heat and motion. Tbe actual cimibustion of carbon (/. e. oxi-
dation) must be sufficient to maintain the animal heat and the nour-
ishment of the muscles upon wliicli tbe continuance of Hie dej)end.

(8) Nervous energy, as in the regulation of all physiological pro-
cesses by the reflexes, as well as in voluntary mental and nervous
action.

What is the amount of energy resulting from the bodily expend-
iture?

The daily work of the body has been calculated to be about
3400 foot-tons. Of this about one-tenth has been considered to be
exhausted in involuntary muscular action (circulation, respiration,
etc.) and in voluntary motion, while the remainder (nine-tenths) is
expended in maintaining the body -heat. Another method of con-
sidering this enormous force may be of use : it is equivalent in
heat to that required to raise nearly 50 pounds of water from tbe
freezing to the boiling-point, or in mechanical force it is sufficient
to raise the body of a man weighing 150 pounds to a height of 82
miles.

Does this calculation include all the energy developed in the
body?

No. It takes no account of energy exerted in nervous manifes-
tations, nor does it take into consideration the utilization of the
heat absorbed by the body.

What is "nitrogenous equilibrium"?

Wlien an animal is fed exclusively upon a nitrogenous diet, it is
found that after a time the egested nitrogen approaches and finally
balances that taken in as food. Tliis is known as tbe " nitrogenous

92 NUTEITION.

equilibrium." But at the same time the animal may increase in
weight, and this occurs by the formation of fat which is stored up
in the tissues. The nitrogenous equilibrium is more easily main-
tained by the addition of carbohydrates to the food.

What is the eflfect of starvation upon the body ?

There is a loss of weight in all the tissues, but it is in the loss of
the fat that the change is most marked : the fat almost entirely
(93 per cent.) disappears after death from starvation. The sense
of hunger gives way to a sense of pain ; thirst is excessive ; sleep
is absent ; progressive weakness accompanies increasing emaciation ;
the exhalations of the skin and lungs are foetid ; and diarrhoea with
convulsions or delirium often precedes death. Death occurs with
absolute deprivation of both food and drink at the end of about a
week (six to ten days), though life may be considerably prolonged
by small quantities of food or water. The temperature of the body
falls before death very considerably (30° C.), and it has been con-
sidered that death resulted from cold, no fuel being furnished to
maintain animal heat. The body decays rapidly after death from
starvation.

What is the effect of an exclusive diet ?

The result of feeding animals exclusively on a single article of
diet (sugar, gum, oil, etc.) is practically the same as that of star-
vation, except that death does not occur until the end of four or
five weeks. In man the exclusive diet of isolated communities
often results in the breaking down of tissue and general malnu-
trition.

What is the effect of over-feeding ?

An excess of nitrogenous food, if digested, increases the meta-
bolic work of the glandular organs (especially of liver and kidneys),
and induces disease in those organs and faulty excretion of nitrog-
enous matter. This may be obviated or delayed by active physi-
cal exercise. Carbohydrate food in excess is stored up in the form
of fat, which may be excessive, with resulting fatty infiltration of
the viscera, or it may show as glycosuria.

An excess of any food is apt to pass undigested through the intes-
tines and undergo putrefactive changes, with resulting gaseous

NERVOUS SYSTEM. 93

distension : the carbohydrates are especially apt to give rise to this
disturbance.

What are the requirements of a normal diet ?

There should bo a general diet of well-cooked food, and it should
contain about the amount of carbon and nitrogen which is excreted;
tliat is, it should maintain an e(|uilibrium. This is. commonly,
about two pounds of solid food and two quarts of fluid. The pro-
])ortion of the various kinds of foods varies considerably, but in a
general way for a healthy man one may divide the solid food some-
what in this way : nitrogenous food (meat), about I pound ; hydro-
carbon and fiit-food (bread, vegetables, and butter), about lo
])ounds. Besides this, the food will contain from 1 to 2 ounces
of salts and a varying amount of sugar.

NERVOUS SYSTEM.

THE NERVES.

What are the elementary tissues of the nervous system ?

Nerve-fibres and nerve-cells. The fibres are of two kinds, and
are united in bundles to form nerve-trunks or nerves. The cells
are collected in groups and form the nerve-ganglia, but the nerve-
fibres are also found in the ganglia.

What varieties of nerve-fibres occur ?

1, The medullated or white fibres ; 2, the non-meduUated or gray
fibres.

Describe the medullated or white fibres.

1'liese fibres consist of an external nucleated sheath or Pjo. 22.
neurilemma which is made up of (1) a layer (Fig. 22)
of endothelial cells which surround and invest ; and (2)
an inner protective medidhiry sheath (the white matter
of Schwann). Within these is (3) the axis-cylinder,
which consists of a number of the primitive fibrillae
of the nervous tissue. In size these fibres vary con-
siderably, but the average may be said to be about
Tr,Vu ^"^^^ "1 diameter. Diagram of

Structure of

What are the nodes of Ranvier? Nerve-tibre.

They are constrictions which occur here and there in the course

94

JfEEVOUS SYSTEM.

of the white fibres. These constrictions (Fig. 23) are of the ex-
ternal sheath, and break the continuity of the
Fig. 23. medullary layer.

Is the axis-cylinder broken at the nodes of Ran-
vier?

No. The axis-cylinder is continuous from one
end of the nerve-fibre to the other.

Describe the non-meduUated fibres.

They consist of the axis-cylinder alone, with-
out the medullary layer. They do not differ in
any other regard from the white fibres. When
collected in bundles to form nerves they have a
yellowish or grayish color. They are found in
the olfactory and auditory nerves and in the
nerves of the sympathetic system, and they occur
in greater or less number in the nerves of the
cerebro-spinal system. In size these fibres are
about one-third to one-half the diameter of the
medullated. They are sometimes spoken of as
the fibres of Remah.

What change occurs to the white fibres near
their termination?

The medullary layer disappears and the axis-
cylinder continues with the neurilemma ; but this
too disappears before the final ending of the fibre
in the tissues. The fibre then splits into two or
more terminal branches ; that is, the white fibre
becomes a non-medullated fibre.

^r— -

Nerve-fibre from the
Sciatic Nerve of the
Rabbit, after the ac-
tion of nitrate of sil-
ver : a, ring formed
by thiclvened mem-
brane of Schwann ;
TO, wliite substance
of Schwann render-
ed transparent by
glycerin ; cy, cylin-
der-axis, which just
above and below the
level of the annular
constriction p r e -
sents the striae of
Frommann.

How are the fibres united to form nerves?

The fibres are joined in bundles which are
enclosed in a thin fibrous sheath (perineurium), and these bundles
of nerve-fibres are bound in a firm connective tissue which serves
to protect and to unite them strongly.

What are the characteristics of nerve-cells ?

Nerve-cells or ganglion-cells present a great variety of shapes,
and yet have common characteristics. The cell-body is granular
and contains a large nucleus which contains a prominent nucleolus.
The cells have at least one process, and often more (Fig. 24). and

THE NERVES. 95

the cells are classified as unipolar, bipolar, or multipolar. These
])rocesses are of two kinds — one kind dividing and subdividing
i^hninchiii(/ ju-ocL'sscs) until they become very delicate and seem to

Fig. 24.

Nerve-cells from the Anterior Horn of Gray Substance of the Spinal Cord.

join with the equally fine processes from other cells ; another class
(^(t.rii>-ci/h'niler processes') pass on without division, and become axis-
cylinders of medullated nerve-fibres.

The nerve-cells vary greatly in size, and arc very diverse in
form, but the presence of nucleus and nucleolus and of the pro-
cesses is characteristic of nerve-cells. They may be enclosed in a
delicate capsule which becomes continuous with the neurilemma
(Fig. 25).

What is the function of the nerve-fibres ?

The transmission of a stimulus. The axis-cylinder connects
the centre and periphery cells, and conveys between them the
stimuli. This transmission for any particular fibre is in one direc-
tion only.

How may the nerve-fibres be classified?

Into afferent (or centripefitf) and efferent (or centrifugal) fibres.

96

NERVOUS SYSTEM.
Fig. 25.

Nerve-cells, from Spinal and Sympathetic Ganglia of Man, enclosed in their Capsular
Sheaths — from hardened preparations (Key and Eetzius).

The former are those by which impressions are taken from the
periphery to the brain, and are commonly called sensory fibres.
The latter conduct the stimuli to the periphery, and are known
as motor fibres. Besides these, some of the fibres serve to connect
ganglia of the central system one with another, and these are
known as intereentral fibres.

What modifications of function belong to the afferent nerves ?

The direct function of the centripetal nerves is the conduction
of an impulse which gives rise to a sensation, as of pain or heat;
but beyond this we may have a reflex or an inhibitory impulse
conducted.

What modifications of function belong to the efferent nerves?
The centrifugal nerve-fibres may carry other than motor im-

THE NERVES. 97

pulses : they control nutrition (trophic nerves) and secretion
(secretory nerves), and they may also increase or check other
etlorent impulses.

What is the velocity of the transmission of impulses ?

Kftcreut impulses are somewhat slower than atlerent. the rate
for the former being about llU feet per second, for the latter
about 150 feet.

What are "personal error" and "personal equation"?

The time occupied in executing a voluntary movement at a given
signal — for instance, the recording the time of a transit in an astro-
nomical observation — is found to be sufficient to demand a correction
for an accurate result. This amounts to i to -^^ of one second with
different individuals. The time lost in this Avay is known as the
/x'rsoita/ error of the observer. When this has been ascertained
by experiment, the allowance to be made for the personal error is
his personal equation. This remains nearly constant for each
person.

How do the sensory nerves terminate at the periphery?

The sensory nerves ending in the skin find their way to certain
bodies (sense-organs) which are essential to the conduction of the
sensory impression to the central nerve-ending. These sense-
organs are of several kinds. In the fingers and toes are found
two kinds of sense-organs which may be especially mentioned :
1, touch-corpuscles; 2, Pacinian corpuscles. The anatomy and
physiological use of these bodies are still somewhat obscure ;
and, indeed, the whole subject of sensory nerve-terminations is
but illy understood. We may regard the fibres of sensory nerves,
as a majority, to form a minute plexus in the corium and to ter-
minate in sense-organs in a way not known. Some of the special
sense-organs are possessed of nerve-endings which are more clearly
observed.

What two sets or systems of nerves do we possess ?
The cerebro-spinal and sympathetic.

What constitutes the cerebro-spinal system?

The brain, tlu; niedulla oblongata, and the spinal cord, with the
nerves proceeding from them.

What constitutes the sympathetic system?

Primarily, the sympathetic system consists of a double chain of
7— Phy.

98 NERVOUS SYSTEM.

ganglia and communicating nerves whicli lie on either side of the
vertebral column and extend throughout its entire length. Other
ganglia occur in connection with some of the cranial nerves, more
especially the vagus and trigeminus. There are ganglia and plex-
uses connected with the various organs (e.g. cardiac and solar), and
still others in the substance of some of the organs (e. g. stomach and
intestines). The sympathetic system has numerous communications
with the cerebro-spinal system.

What is a reflex action?

An action which results from a centripetal nerve-impulse passing
to a nerve-centre in a ganglion, and there transforming to a centrifu-
gal impulse passing to a muscle. Such an action may be simple and
involve a single muscle, or complex and involve many : thus, a ray
of light falling upon the retina causes a simple reflex contraction of
a single muscle, and the iris contracts. As an illustration of a com-
plex reflex action, however, irritation of the larynx causes not only
a closing of the glottis, but a contraction of all the muscles involved
in forced expiration or coughing.

Are all reflex actions involuntary?

Yes, but many of them may be checked or prevented by a vol-
untary effort.

Do the reflexes depend upon the cerebro-spinal nervous system
or upon the sympathetic?

They are more noticeable in the cerebro-spinal system, but they
may belong to either, or may be mixed, the impulse going by the
one system and returning by the other. Examples : sneezing,
coughing, swallowing are cerebro-spinal reflexes ; the vaso-motor
reflexes are largely sympathetic, but the centripetal nerve is often
cerebro-spinal, as in the secretion of saliva or in blushing.

What relations exist between the stimulus and the resulting
reflex ?

A stimulus which is mild causes a reflex of the muscle of the
same side, but as the stimulus is increased the muscles of the op-
posite side may be involved, the reflex of the irritated side remain-
ing the stronger. As the irritation is increased the reflex involves
more muscles ; that is, the stimulus spreads to a greater number
of cells in the ganglion and more efferent fibres are involved.
These relations are obtained largely by experiments upon decap-
itated frogs.

SYMPATHETIC SYSTEM. 99

Wliat are acquired reflex actions ?

A reflex action which is as strong in an infant as in an adult
(the contraction of the pupil in the presence of light) is a prirnnry
reflex. Another class of reflex actions re(juirc frecjuent repetition
before they are automatically performed, and such actions arc called
acquired reflex actions, as walking, reading, etc.

What is automatic action of nerve-centres ?

There are certain actions which continue, and, while they are
closely related to reflex action, do not seem to be reflexes, but to
originate in the part. Thus, the peristaltic action of the alimentary
tract is not dependent upon the presence of food in the intestines,
but may be excited in the absence of food or checked when it is
present. The action has been referred to small ganglia and nerve-
plexuses found there (Auerbachs and Meissner's), and is consid-
ered to originate in the local nerve-centres. This is what is known
as automatism or automatic nerve-action.

What power of inhibition and augmentation of action has the
nerve-centres ?
In speaking of the action of the heart it was .shown that certain
fibres of the vagus nerve check the hearts action, and certain
other fibres increase it. This control of the action of organs is
not confined to the heart, but similar power of regulation belongs
to the nervous centres for many other organs.

SYMPATHETIC SYSTEM.
How is the sympathetic nervous system arranged?

It is arranged in ganglia and plexuses. It is intimately con-
nected with the cerebro-spinal system by communicating branches
from each spinal nerve and many of the ci'anial nerves.

What is a ganglion ?

It is a collection of gray and white nerve-substance, which is
usually oval in outline, and is frequently found in the course of a
nerve-trunk. In the sympathetic system the ganglia contain
numerous nerve-cells, smaller than those of the brain and spinal
cord, and from these cells arise nerve-fibres which distribute them-
selves in the plexuses.

What peculiarities have the fibres of the sympathetic nerve ?
They are often smaller than those of the cerebro-spinal .system,

100 NERVOUS SYSTEM.

and there are in the nerves a considerable number of non-medul-
lated fibres — more than in the spinal nerves.

Do the sympathetic nerves differ materially from the cerehro-
spinal ?

No. They are very similar. The occurrence of ganglia upon
the sensory branch of the spinal nerves and upon the sensory cra-
nial nerves (pneumogastric, glosso-pharyngeal, and trigeminus) adds
to the similarity. Then, too, the frequent communications be-
tween the two systems practically makes one system of them, and
the division is largely one for convenience.

Is the sympathetic system dependent upon its connection with
spinal axis?

Yes.

Where are the functions of the sympathetic system most shown ?
In the organs of nutrition and secretion and in the vascular
system.

What are the sympathetic ganglia in the head?

They are four in number — ophthalmic, spheno-palatine, submax-
illary, and otic ganglia. Each has communications from the gen-
eral sympathetic, and from the cranial nerves both motor and sen-
sory fibres.

Describe the ophthalmic ganglion.

It is a small ganglion situated in the orbit, and receives com-
munications' from the sympathetic and from the motor oculi
(third) nerve, a motor branch, and from the trigeminus (fifth)
nerve a sensory branch. Its branches pass into the eyeball (ciliary
nerves), and are distributed in the iris. Their function is the con-
trol of the pupil, of the apparatus of accommodation, and of the
vaso-motor function in the vessels of the eye.

Describe the spheno-palatine ganglion.

It is situated in the spheno-maxillary fossa, and receives branches
from the cervical sympathetic system and motor fibres from the
facial (seventh) nerve, and sensory from the fifth. Its branches are
distributed to the mucous membrane and muscles of the palate
and uvula, and to the naso-pharynx. They are both sensory and
motor.

SYMPATHETIC SYSTEM.

Fi<;. 2G.

101

Ganglia and Nerves of the Sympathetic System.

Describe the submaxillary ganglion.

It lies in close proximity to the submaxillary glaud. It receives

102 NERVOUS SYSTEM.

branches from the superior ganglion of the neck and a sensory
branch from the lingual branch of the fifth nerve. Its motor branch
is through the chorda tympani nerve from the seventh or facial
nerve. Its branches are distributed to the submaxillary gland and
control its function.

Describe the otic ganglion.

It is a small ganglion lying upon the third division of the fifth
nerve as it emerges from the foramen ovale. It has branches from
the sympathetic on the middle meningeal artery, and both a motor
and a sensory communication from the fifth, as well as a branch from
the glosso-pharyngeal through Jacobson's nerve. Its branches are
motor, to the tensor palati and tensor tympani muscles ; and sensory,
to the mucous membrane of the tympanum and Eustachian tube.

How does the sympathetic system in the trunk communicate
with the spinal nerves ?
From each spinal nerve is given off a communicating branch to
a neighboring ganglion. These branches contain both motor and
sensory fibres.

How are the ganglia classified?

Into cervical, thoracic, abdominal, and pelvic ganglia and
plexuses.

Describe the cervical ganglia.

There are two — a superior and inferior (with sometimes a third,
middle) — ganglia on each side (Fig. 26). These ganglia receive
communications from each of the cervical spinal nerves and from
each other. Their branches are given off to form (1) the carotid
plexus, which follows the carotid artery and its branches. It forms
by its inosculations the vaso-motor plexuses of the arterial system,
and furnishes branches for distribution to the thyroid gland, larynx,
trachea, pharynx, and oesophagus. (2) It furnishes the cardiac
nerves, which are distributed in the cardiac plexus.

"What is the distribution of the thoracic ganglia?

In the chest the ganglia are numerous (Fig. 26), and each gan-
glion receives two branches of communication from the intercostal
nerve above it, while the relationship of the ganglia is maintained
by the intercommunicating chain. The nerves originating here
are distributed to the plexuses on the thoracic aorta, and to those
of the lungs and oesophagus.

SYMPATHETIC SYSTEM. 103

Describe the abdominal sympathetic.

In the alxlunn'ii the sympathetic consists mainly of an aggrega-
tion of ganglionic enlargements situated upon the coeliac artery,
known as the semilunar or coeliac ganglion. It communicates with
the thoracic ganglia and with all the lumbar nerves. From this
centre proceed a multitude of diverging and inosculating fibres,
which, from their common origin and radiating course, are called
the aolar phwun. Its secondary plexuses, accompanying the branches
of the abdominal aorta, are distributed to the stomach, intestines,
spleen, pancreas, liver, kidney, and internal organs of generation.

How are the pelvic plexuses derived?

From four or tive pairs of ganglia situated on the anterior por-
tion of the sacrum and terminating in the gnnglioti I'mjxir, lying
upon the coccyx. Its fibres join those from the solar plexus, and
are distributed with them along the course of the branches of the
internal iliac arteries.

Describe the sensibility and motor influence of the sympathetic
nerves.

It will be remembered that the spinal nerves, both afferent and
efferent, act very quickly upon the tissues supplied by them ; the
sympathetic nerves act more slowly. Thus, if the afferent nerve
or a ganglion or its efferent nerve be stimulated, there is a slow
wave-like series of motions set up in the parts supplied, which con-
tinue for some time after the stimulus is withdrawn. This is par-
ticularly Avell seen in the intestinal peristalsis which may be excited
by stimulation of the intestine or of the semilunar ganglion or of
the branches of the solar plexus.

What is the effect of the sympathetic nerves upon special senses ?

The dilatation of the pupil is effected through it, and probably
the accommodation is acted xxpon by fibres other than the oculo-
motorius, which come through the lenticular ganglion. The tensor
tympani muscle is supplied from the otic ganglion.

What is the vaso-motor function of the sympathetic ?

The muscular coats of the lilood-vessels. especially' of the arteries,
are under the control of the sympathetic filaments and plexuses,
which accompany them throughout their entire system. These
fibres are of two kinds as regards their function : (1) vaso-con-
strictor and (2) vaso-dilator fibres.

104 NERVOUS SYSTEM.

How do the vaso-motor fibres arise?

They probably arise from spinal centres, and are controlled in
some way by the vertebral ganglia of the sympathetic system.
The vaso-dilator fibres are not to be distinguished as such, though
their presence is inferred from the action of special nerves. Eor
example, the stimulation of the chorda tympani nerve has a vaso-
dilator effect in the submaxillary gland. The inhibitory and aug-
mentary eifects of the cardiac nerves are similarly carried by or
through sympathetic plexuses.

Do the visceral sympathetic nerves have a similar central
origin ?

Yes, but they too are acted upon by the ganglia through which
the fibres pass, and in which new nerves arise from the nerve-cells.

What control has the sympathetic system over the secreting
glands ?
There has been demonstrated in some of the secreting glands —
and it is probably true for all — that functional stimuli, distinct
from the vaso-motor, come through the sympathetic nerves, and
that these fibres are closely associated with the vaso-motor fibres.
Thus, in the stomach the secretion of the gastric juice is only tem-
porarily suspended by the section of the vagi, and is resumed by
the action of the sympathetic, showing that the control is by the
sympathetic.

What is " arrest of action " ?

It is a temporary check upon the control of an organ by the
sympathetic system, which check comes through the cerebro-spinal
system. Such an action is frequent in the control of the glandular
organs, and usually is shown in the dilatation of the capillaries
through the arrest of the action of the vaso-motor nerves in response
to a sensory reflex. It is also seen in the sphincters, which keep
up a condition of tonic contraction to close the orifices of the body,
but relax in response to an impulse from the proper centre. The
sphincter ani in this way retains its hold upon the intestinal orifice
until the centre in the cord permits an arrest of action and relaxa-
tion of the muscle.

SPINAL CORD.
Describe, roughly, the spinal cord.

The spinal cord is that portion of the cerebro-spinal nervous sys-

SPINAL CORD.

105

tern contained within the spinal canal. It
connects with the brain through the medulla
oblongata, and terminates in a fine thread of
gray matter (the filum termiiiale) at about
the second lumbar vertebra. In form it is
irregularly cylindrical, and varies in the size
and shape of its cross-section at various lev-
els, as is shown in Fig. 27. It is incom-
pletely divided into symmetrical halves, and
its mid-line is indicated in front by a fissure
(anterior median fissure) which extends for
about one-third its antero-posterior diameter ;
behind by a deeper but narrower fissui'c (pos-
terior median fissure), which involves about
one-half of the same diameter. It is com-
posed of white and gray substance.

How are the white and gray matters ar-
ranged in the spinal cord?

The white substance is arranged externally
to the gray in each half of the cord, and is
so dispo.sed as to be conveniently divided for
purposes of description into three columns,
known respectively as the anterior, lateral,
and posterior columns of the cord. There is
also a thin band of white substance at the
base of the anterior median fissure (the white
commissure). The gray matter fills in the
central portion of the cord, and is variable in
its amount, the calibre of the cord at its en-
largements being increased by the increase
in the amount of gray matter at these points
(Fig. 27). The white substance will be no-
ticed to diminish quite regularly in the sec-
tions of the cord from above downward, as
seen in this .series. The gray substance is not
completely halved by the anterior and pos-
terior fissures of the cord, but is continuous
across the mid-line ; and in it at the centre
is a minute canal communicating with the
ventricles of the brain. The gray matter is
more abundant between the lateral and anterior and between the

Transverse Sect ions of the
.Si)inal (,"ord in .Man: I,
upi)pr cervical region ;

II, lower cervical region;

III, dorsal region; IV,
lumbar enlurgeuient ; V,
lower extremity.

106

NERVOUS SYSTEM.

Transverse Section of the Spinal Cord : n, h,
spinal nerves of right and left 'sides;
d, origin of anterior root; e, origin of pos-
terior root ; c, ganglion of posterior root.

lateral and posterior columns of the white substance, and the names
anterior and posterior horns (cornua) are given to these regions
respectively.

What are the nerve-roots of the cord ?

Issuing from the cord along its course are thirty-one pairs of
nerves. Each of these spinal nerves is made up of an anterior and

a posterior root (Fig. 28), of
Fig. 28. which the latter is the larger.

The anterior root arises between
the anterior and lateral white
columns, the posterior between
the posterior and lateral col-
umns. On each posterior nerve-
root is found a ganglion imme-
diately beyond its point of
emergence. The function of
this seems to be trophic.

What is the minute structure of the white substance ?

It is found to be made up of medullated nerve-fibres, which
collect to form the anterior and posterior nerve-roots, and commu-
nicate with other regions of the cord.

What is the minute structure of the gray matter ?

The gray matter contains multipolar cells of varying size and
shape, with axis-cylinders and " branching " processes lying in
the neuroglia (connective tissue). The multipolar cells are some
of them quite large. In the anterior horn of the gray substance
the axis-cylinder-processes of the nerve-cells connect directly with
fibres forming the anterior nerve-roots (Fig. 29) ; but in the poste-
rior cornu the communication is through the branching processes
joining the divided axis-cylinders of the posterior nerve-roots, form-
ing thus a minute plexus known as Gerlach's nerve-network.

Whence are the fibres derived which make up the nerve-roots ?

(a) Anterior nerve-roots are derived from (1) the anterior col-
umns of the cord, but some fibres come through the commissure
from (2) the opposite side, and some come from (3) the lateral
tract. Still other fibres arise from (4) the multipolar cells in the
anterior cornu of the gray matter. The fibres of the anterior
nerve-roots are efferent or motor fibres.

SPINA I, (T)Un.

107

(A) Posterior nerve-roots enter into the posterior horn of the
gray matter, and the fibres break up to form Gcrlach's network,
communicating with the large multipolar cells, but some fibres

Fig. 29.

Transverse Section of the Spinal Cord in Man (lumbar region).

cross through the gray commissure to the opposite side. The fibres
of the posterior roots arc aft'crent or sensory fibres.

If the anterior nerve-roots be cut, what is the result ?

The anterior nerve-roots are efferent or motor ; therefore their
divi.sion results in complete loss of motion in the parts supplied.
If the distal portion of the cut nerve-root be stimulated, muscular
action follows, while irritation of the proximal portion produces no
noticeable effect.

What follows division of the posterior roots ?

Loss of sensation without loss of motion. Stimulation of the
distal portion of the cut posterior root produces no result, either
in sensation or motion. Irritation of the proximal end will, how-
ever, cause very acute pain.

Is the course of the fibres through the spinal cord known ?
No, not fully. Certain fibres have been traced with fair accu-

108

NERVOUS SYSTEM.

racy through their length, notably fibres to the arm (direct pyra-
midal tract) in the anterior column, and to the leg (crossed pyra-
midal tract) in the lateral column.

Do all the fibres of the spinal nerves pass from the brain through
the spinal cord?

No. It has been calculated that only about one-half as many
fibres enter the spinal cord from the brain as leave it through the
nerves ; therefore it must follow that some fibres originate from the
cord. The increase in gray matter in the cervical and lumbar enlarge-
ments, where the fibres for the large plexuses of the nerves (brach-
ial and lumbar) are given ofi", confirms this view.

Where are the trophic centres for the anterior nerve-roots ?

The posterior nerve-roots, we have seen, seem to be dependent
upon the ganglia which are found upon them for trophic influence.
The anterior root in a similar way seems to depend upon a trophic
centre in the gray matter in the anterior horn.

What is degeneration of a nerve-fibre ?

Division of a nerve is followed by a degeneration or breaking
down of the axis-cylinders of its fibres within a day or two, the
loss of function being an earlier and immediate manifestation. This

Fig. 30.

Degeneration of Spinal Nerves and Nerve-roots after Section : A, section of nerve-trunk
beyond the ganglion; B, section of anterior root; C, section of posterior root; D,
excision of ganglion ; a, anterior root ; p, posterior root ; g, ganglion.

degeneration is centrifugal ; that is, does not proceed toward the
spine, but to the periphery. If the posterior root be cut, how-
ever, between its ganglion and its emergence from the cord, the
degeneration is toward the cord — i. e. centripetal — and the nerve

SPINAL CORD. 109

beyond the ganglion does not degenerate. The anterior root can-
not, however, be divided at any l><»iiit beyond its emergence without
centrifugal degeneration of the fibres (Fig. 30). The regeneration
takes place slowly if the continuity of the nerve is at once restored,
and may even follow after the nerve has degenerated for some months
and a complete loss of function has affected the part supplied by
it. The fact that the axis-cylinders are restored only in this way
is of interest, as showing the influence of the trophic centres on
the nerve-growth.

What are the functions of the spinal cord ?

(1) The conduction of impulses from the nerves to the brain
and from brain to nerves, and (2) the origination of action in
response to stimuli from the periphery — i. e. rcjicx action.

Explain the action of the cord as a conductor of nervous impulses.
Than by the spinal cord there is practically no other nervous
communication between the brain and the musciilo-cutaneous sys-
tem ; hence through it must come all the nerve-impulses which
pass to or from the brain. In other words, every sensory impulse
that is felt and every motion that is iriUcd. perception and volition
being attributes of the brain, must be conducted through the nerve-
fibres of the spinal cord to the brain, and vice versa. No better illus-
tration need be used than the abolition of both motor and sensory
function which follows a cerebral apoplexy : the nerve-centre being
destroyed, voluntary action and perception of sensation are lost,
and yet the reflex response is prompt, showing that the brain-
function is necessary in the chain of phenomena. Again, the
same paralysis follows the section of the cord, and we must
acknowledge their mutual dependence.

Does the gray substance act as conductor?

No, not when directly stimulated. The conducting fibres seem
to be in the white columns, and each portion contains fibres which
always conduct the same kind of impression.

What is the course of sensory impulses in the spinal cord ?

This is somewhat pniljloniatical, but certainly these impulses
enter the cord by the posterior nerve-roots. The fibres conducting
them break up to form Gerlachs network, and cross to the opposite
side of the cord through the gray commissure. It is probable that
after decussating the fibres communicate with multipolar cells, and

110 NERVOUS SYSTEM.

thus pass on as white fibres in the lateral columns. These fibres
enter the lateral columns (of the opposite side), and pass to the
medulla as a distinct tract — the antero-lateral ascending tract — at
the periphery of the lateral, extending into the anterior column.

What sensations are transmitted by this set of fibres ?

It is by this tract that sensations of pain and of temperature are
supposed to pass. There are also afi"erent fibres in the posterior
columns — the posterior median — by which the sensations of touch
and toeigJit (or muscular sensation) are believed to pass ; the latter,
however, does not decussate. To recapitulate : sensations of pain
and temperature are transmitted through the lateral columns, and
those of touch and weight in the posterior columns.

What is the path of the motor impulses ?

As has already been seen, these fibres are better demonstrated
than the sensory. Most of the motor fibres cross to the opposite
side in the medulla oblongata (decussation of the pyramids), and
the impulses pass down by the lateral columns in the crossed or
lateral pyramidal tract on the side opposite to that in which they
originate. There is also a set of motor fibres which do not cross,
but pass directly to the same side in the anterior columns, and
decussate in the anterior or white commissure near the point of
distribution. The destination of these fibres is varif\ble, for the
reason that the amount of decussation in the medulla is not con-
stant ; but, as a rule, the fibres in the direct tract go to the upper
portion of the body.

Do the motor tracts carry only the fiibres arising from the brain ?

No. The cells in the anterior cornu of the gray matter of the
cord originate many of the fibres which go to the nerves. This is
.demonstrated after division of the cord by stimulating these fibres :
a series of co-ordinated motions follows, and this stimulus may be
applied direct to the fibres or through the sensory nerves.

If one lateral half of the cord be cut through transversely, what
are the results?

1. Motor. — There will be paralysis of motion of one-half the body
below the section ; and the paralysis will be of the same side if the
section be below the decussation in the medulla ; if it be above, the
paralysis will cross to the opposite side.

2. Sensory. — Anaesthesia of the opposite side below the section,

SPINAL CORD. Ill

and the loss of sensibility will be complete. At the same time,
on the same sich: as the section the sensory function may be ex-
aiigorated, and there may be /ii/penxsfhtsiu to such a degree that
even a touch may cause exquisite pain.

What results follow electrical stimulation of the posterior columns
of the cord ?
If stimuli be applied to the posterior columns of the cord by
a galvanic current, signs of sensibility are shown in the reflex
actions ; but it is only near the nerve-roots that the sensibility
seems very marked. The intensity of the response increases with
the strength of the current.

What reaction follows a similar stimulation of the anterior col-
umns.
Motion in the parts below, and the motion is of a convulsive
character. No pain seems to accompany the convulsive contrac-
tions of the muscles.

What is the effect in the lateral columns?

The stimulation of the anterior portion results in motion, which
gradually decreases as one approaches the posterior nerve-roots,
and then merges into the signs of sensibility similar to those
excited by stimuli applied to the posterior columns.

What practical lesson does this impress?

That inflammatory changes in the meninges of the posterior
portion of the cord excite pain, while meningitis of the anterior
portion excites convuhsions.

What important function, besides conduction, does the spinal cord
perform ?
The origination of motion in response to stimuli, or rej^ex action.

What difficulties present themselves in the study of the reflex
function of the cord in mammals ?
The great shock which follows injury of the spinal cord in mam-
mals renders the study of its function difficult. It is sometimes
hours, or even days, before any experiments can be conducted after
the division of the cord in a warm-blooded animal, because of the
failure of the"reflexes to act; and when they do act the amount of
degeneration which has followed the operation is uncertain. Cold-
blooded animals (especially the fi'og) are used largely iu such

112 NERVOUS SYSTEM.

experiments for this reason, and it is probable that in them there
is a greater degree of this kind of response, though of the same
nature as in mammals.

How are the reflex actions of the cord classified?

Into cutaneous and muscular reflexes.

What are cutaneous reflexes?

Muscular actions which follow gentle stimuli applied to the skin.
The plantar reflex, or the motion 'of the toes and foot which occurs
on tickling the sole of the foot ; the cremaster reflex, or retraction
of the testicle by contraction of tne cremaster when the inner side
of the thigh is stimulated ; and the pupillary reflexes, contraction
of the pupil to the stimulus of light, — belong to this class of cuta-
neous reflexes.

What are muscular reflexes?

Muscular actions which follow a slight blow upon a muscle or
tendon when the muscle is in more or less tension. The patellar
reflex is a well-known example of this form of action : if the knee
be flexed to a right angle and the leg allowed to hang loosely, the
quadriceps femoris muscle is made moderately tense. A gentle
tap upon the tendon of the muscle below the patella will cause the
muscle to contract and the leg to be more or less extended. These
reflexes are sometimes called tendon reflexes.

What is inhibition of reflex action ?

The ability to control or modify reflex action by an efi"ort of the
will or by mental action which is not consciously voluntary. As
an example of this, if the palm of a sleeping child be touched by
the finger, the baby's hand will grasp the finger ; but if the child
is awake, no such reflex occurs, but is checked by mental action.
Again : one may avoid crying out when in pain by an effort of the
will, or may hold the feet still when the soles are tickled.

Are reflex actions frequent in the ordinary acts of life ?

They are. An ordinary act which has become habitual — for
example, walking — while at the first it is performed as a voluntary
muscular act, becomes reflex and is performed without conscious
control of the mind, and is more easily and more gracefully done
when no attempt is made to direct the actions of the muscles
involved.

TIIK MEDriJ.A OP.LONOATA. 113

Do the reflexes vary in strength with the strength of the
stimuli ?
A stroni!; stiimilus will excite a stronger reflex tluiii a mild one.
A i)iii-i)riik will cause the foot to react more violently than tickling
ihc soil'. In certain diseases and after certain pfiisons these actions
licconK! very much exaggerated: tetanus and strychnine-poisoning
])iit the corll in such a condition that a very slight skin-irritation
may throw the entire body into a violent convulsive condition.
Again, other diseases or drugs decrease the irritability of the cord.

What are special centres for reflex action ?

Certain actions are automatic — that is, may take phicc without
intervention of the will in response to special stimuli — and these
actions are dependent upon certain nerve-centres in the cord.
These centres have to do, noticeably, with sphincter action in the
pelvic region, and the centres themselves are located in the lumbar
region of the cord. To enumerate some of the automatic actions
of these centres is sufficient, as they are all dependent upon special
stimuli and special centres acting upon muscles peculiar to the
act. They are defecation, micturition, emission of semen, erection
of the penis, parturition. There are numerous other automatic
actions besides those of the pelvic sphincters, but the mode of
operation is well illustrated by these functions.

What other automatic action occurs in the spinal nerve-centres ?

Yaso-motor centres and sweat-control centres are in the cord,
and centres which control the nutrition of the muscles, as well as
keep them tense in readiness to contract effectively ; that is, main-
tain the tone of the muscles. The nutrition of the entire body is
dependent upon the maintenance of this automatic control of the
vaso-motor function, as is shown by the disorders of the skin and
of the bones and joints which follow spinal injury and disease.

What influence has the cord upon the functions controlled by the
sympathetic system?
Very great. The secretion of many of the body fluids and the
control of the organs is dependent for regulation upon the connec-
tion of the sympathetic nerves with the spinal cord.

THE MEDULLA OBLONGATA.

Describe, roughly, the medulla oblongata.

It is a column of white and gray nerve-substance, and is an en-
8— Phy.

114

NERVOUS SYSTEM.

larged portion of the spinal cord, connecting the brain with the
cord below. The white substance is composed of the medullary
fibres connecting brain and cord, and the gray matter is arranged
variously between the bands of white fibres. It has an anterior
and a posterior fissure, corresponding to those of the lower portion
of the cord, and the central canal of the cord here opens into the
fourth ventricle.

How do the columns of the cord arrange themselves in the
medulla ?

The medulla continues in a general way the arrangement of the
fibres in tracts of the cord below, but as the diameter is greater the
general shape is pyriform and the shape of the columns nearly pyra-
midal (Fig. 31). The anterior columns of the cord become the

Fig. 31.

Medulla Oblongata and Pons Varolii, anterior surface.

anterior pyramids of the medulla ; the posterior columns, the resti-
form bodies, and the lateral columns correspond to the lateral tract
of the medulla with the olivary bodies. The fibres, however, do
not follow this arrangement so closely, but the columns of thfe cord
distribute themselves variously in the medulla.

THE MEDULLA OBLONGATA.

115

How are the anterior pyramids made up?

TIk' anterior enluiiiiis of tlu' cord jscikI their fibres (the direct
pyramidal tract) up into the anterior pyramids, so that they are
continuous tracts. Other fibres from the lateral columns join the
fibres of the anterior pyramids, and here cross in bundles to the
opposite side. These fibres uiay be seen crossing the anterior
fissure between the pyramids by gently separating the auterior
])yramids. This is known as the decusuition of the pyrmnUIs. The
fibres which cross in this way belong in the cord to the portion of
the lateral column known as the crossed or lateral pyramidal tract.

How are the fibres of the anterior pyramids distributed to the
brain?
Most of the fibres pass on through the pons Varolii to be dis-
tributed in the cortex of the brain. Some of the fibres help to
make up the fiJht, and pass to the optic thalamus, while others
pass to the cerebellum. Fig. 32 shows these relations very sat-
isfactorily.

Fig. 32.

OPTIC .TnAUUtUl

CeRCBCU.UM,

Piagrani of the Course of the Fibres throiich the ^Fedulla to the Prain.

How does the lateral column of the cord communicate with the

brain through the medulla?

The lateral eoluniii of the cord is broken into three tracts in the

medulla: one, we have just seen, joins the anterior pyramid of the

opposite side by the decussation ; a second joins the restiform body

116 NERVOUS SYSTEM.

on its way to distribution in the cerebellum ; wliile the third set of
fibres goes to the fasciculus teres, and reaches the ganglia at the
base of the brain. (See Fig. 32.)

What is the mode of connection of the posterior column of the
cord?

Its fibres continue on as the posterior pyramid of the medulla
and restiform body. The former probably communicates with the
basal ganglia, though it has not been traced as far, and the latter
(restiform body) for the most part reaches the cerebellum.*

What are the olivary bodies?

Each is a mass of white nerve-substance containing a central
gray nucleus. There are communications between it and some of
the tracts from the cord, especially from those tracts of the ante-
rior and lateral columns which go to the ganglia at the base of the
brain.

How is the gray substance arranged in the medulla oblongata ?

As the fibres which form the crossed pyramidal tract pass from
the lateral tract to decussate into the anterior pyramid of the
opposite side, they push the anterior cornu of the gray matter
backward ; and this is still further accomplished by the olivary
body, until the gray matter is spread out upon the posterior sur-
face of the medulla at its upper part. Here the central canal of
the cord has widened out to form the fourth ventricle, and the
gray substance is aggregated to form the floor of the ventricle.
There are some other collections of gray matter — for example, in
the olivary bodies — but this is the principal accumulation.

What especial importance has this collection of gray substance in
the floor of the fourth ventricle ?

In this nucleus are the origins of some of the cranial nerves :
the spinal accessory, hypoglossal, pneumogastric, and glosso-pharyn-
geal nerves, and a root of the auditory of the facial, and of the
trigeminus nerves, arise in this important collection of gray matter.

* In speaking of these fibres it has been convenient to say that they
" pass " in certain directions or " are distributed " in some situation. It
must not be forgotten that they are afferent and efferent medullated nerve-
fibres, and that such terms must be considered as somewhat figurative. In
reality, it would not seem proper to speak of an efferent fibre as being " dis-
tributed " at its origin, but convenience and usage permit the use of these
and similar expressions.

THE MEDULLA OBLONGATA. 117

Of the sinaller t'ollection.s ui" gray substance, probably none has the
pot'uliar interest which the floor of the fourth ventricle possesses
for tliis reason.

What are the functions of the medulla oblongata ?

The luotlulhi has practically the same I'unctiuns as the cord,
conduction and reflexion ; but in both these qualities it excels the
cord, for in the conduction of impulses it has to transmit all that
pass between the brain and spinal system, and in the reflex actions
which it oriiiinates it is much more elaborate than the cord. The
automatic reflex actions of the medulla involve the rhythm of the
vital organs, respiration and heart-action.

How may the functions of the medulla be demonstrated in the
frog ?

If the spinal cord be removed up to the medulla, the respirations
continue, and in the same way they do not cease if the brain be
removed without disturbing this organ, or. if both cord and brain
be removed without disturbing the medulla, the movements of
breathing will continue. If the medulla is injured at the origin
of the pneumogastric nerve, however, the movements of respiration
cease and the animal dies. The same occurs when a similar injury
occurs in the higher animals and in man. Death occurs instanta-
neously in this way when the medulla is broken near the axis in
executions by hanging — " the neck is broken " — or an animal is
killed by " pithing " in laboratory experiments.

What are the special centres in the medulla ?

There are a considerable number of centres in the medulla
which control many important and complicated co-oi'dinatcd mus-
cular actions. These are centres of reflex action for the most part ;
that is, ai'e called upon to act in response to stimuli derived from
an aflTeront impulse or to a voluntary effort.

What is meant by automatism of the medulla?

The impulses wliicli are sent out to muscles without apparent afl^er-
ent stimuli, and without an eftort of the will, are called automatic.
Such rhythmic impulses as those which maintain the respiratory
function belong to this class. It is not to be doubted that such
actions are reflex and in response to stimuli. In the case of the
lungs, for example, the presence of deoxygcnated blood may serve
to excite an afferent impulse. Nevertheless, .some authors distin-

118 NERVOUS SYSTEM.

guish between automatism and reflex action. This automatic action
cannot be considered as at all the same as an action of the brain
proper, like volition, but rather as a high grade of reflex action.

What other functions are attributed to the medullary centres?

The control or inhibition of action through the nerves which are
distributed from this region and through the communications with
other centres in the cord. Further than this, there are supposed
to lie in the medulla centres which maintain the nutrition and tone
of the muscles. These are known as control and tonic centres.

Name some of the reflex functions depending upon the centres in
the medulla.

(1) The portion of digestion which is performed in the mouth is
dependent upon medullary reflexes — mastication, deglutition, and
the secretion of saliva, and, probably, of the pancreatic and other
digestive juices. In this connection the so-called vomiting centre
may be noted.

(2) The resph-atory_ functions are so-called automatic functions
of the medulla, and are capable of being sustained by the nerve-
force derived from the medulla alone. The centres for cotigliing
and sneezing are also here. The pneumogastrie and phrenic nerves
convey the afferent and eff"erent stimuli, though there may be
communications with other nerves whereby sensory stimuli are
applied.

(3) Regulation of the heart's action is found here, both inhihitory
and accelerator centres communicating through the vagus.

(4) Vaso-motor, — regulation of the unstriped muscular fibre
of the arteries is also accomplished by the medulla. A peculiar
vaso-motor disturbance is brought about by injur}'^ of one centre of
the medulla — namely, the interference with the glyeogen-function
of the liver and the appearance of sugar in the urine — the diabetic
centre.

(5) Various centres which have to do with the regulation of the
hody-temperature. The vaso-motor centres we have already men-
tioned. There are also found special sj^ea^centres ; and, further-
more, a control of the special sweat-centres found in the cord is
here maintained. Upon plausible theoretical grounds there is also
assumed to be a heat-inliihitory centre, by which the heat-produc-
tion is controlled without reference to vaso-motor conditions.

THE PONS VAROLII AND CRURA CEREBRI. 119

What other important functions are supposed to belong to the
gray matter of the medulla ?
The ()ri<z;iii of tlic roots of certain of the cranial nerves here lias
caused the special senses of he.nrlnij and of ((t^^tc, to be referred to this
region ; and the connection with the sympathetic system through the
cord has caused the centre for the dilatation of the j)^i}>il> to be located
in the medulla. Plionation is also dependejit upon the action of
nerves arising in this focus of gray matter, and no voluntary or
reflex sound can be produced by an animal in which the speech-
centre in the uiedulla is destroyed. The origin here of the hypo-
glossal and pneumogastric nerves, involving as they do the move-
ments of the tongue and glottis, controls both the acts of plionation
and articulation.

What is glosso-labio-laryngeal paralysis?

It is a progressive degeneration of the gray matter of the me-
dulla, and it shows itself first in a paralysis of the tongue, which
renders articulation of certain sounds indistinct : as the degenei'a-
tion progresses in the medulla the articulation becomes more and
more impossible and deglutition is affected. The disease continues
to aff'ect more and more of the functions dependent upon the me-
dulla, until death ensues as a result of involvement of the cardiac
and respiratory centres or of inability to take food. It is some-
times called bulbar paralysis.

With such varied and important powers, can the medulla be
classed as an organ of the mind ?

It cannot, for the reason that it has no voluntai'y control of any
of its poAvers. They are all reflex, or respond to volition originat-
ing elsewhere in the brain. Though the regulation of the action
of the heart and of the lungs is dependent upon the medulla, and
many other functions of absolute need nuiy be given to it, yet its
power is not of a character to permit it to be called an organ of
the mind.

THE PONS VAROLII AND CRURA CEREBRI.
What is the pons Varolii ?

It is a collection of nervous tissue lying innnediately above the
medulla. It consists of white fibres, with areas of gray matter
filling in the intervals between the fasciculi of white fibres. The
white fibres connect the brain with the medulla, and join the

120 NEEVOUS SYSTEM.

various parts of the brain one to another. What is the function
of the gray matter is little known, but it is directly continuous
with that of the medulla, and probably, like it, active as a centre
of nervous force. The median line of the pons is marked by the
decussation of many nerve-fibres, and it is probable that the fibres
of the facial nerve arising in the floor of the fourth ventricle decus-
sate here.

What peculiar paralyses are caused by lesions of the pons ?

The so-called crossed paralysis may follow lesions in the lower
portion of the pons ; that is, paralysis of sensation and motion,
more or less complete, of the opposite side of the body, with paraly-
sis of the facial muscles of the same side as the lesion.

Describe the crura cerebri.

The crura are formed largely of fibres passing from the medulla,
through the pons Varolii, to the hemispheres of the cerebrum. They
divide so as to form two sets of fibres : the more superficial (crusta)
are mostly motor or eiferent fibres which are continuous with the
pyramidal tracts in the cord ; while the deeper (tegmentum) layer
of fibres are afferent or sensory, and are derived largely from the
lateral and posterior tracts of the cord. Lying between these
bands of fibres is a mass of gray substance (locus niger) whose
function as a nerve-centre is not understood, though it has to do
with co-ordination of the muscles, and especially with regulation
of the muscles controlled by the motor oculi nerve.

What paralyses follow lesions in the crura cerebri?

Paralysis of the opposite side of the body, both of sensation and
motion, and of a degree of intensity depending upon the size of the
lesion, and, besides this, paralysis of the motor oculi nerve of the
same side as the lesion. There is a derangement of the ordination
of motions which follows lesions of this region beyond that which
belongs to the motor paralysis ; this is often shown in rotary move-
ments when the subject attempts to walk. It is inferred that there
are co-ordinating influences derived from the crura.

What is the function of the corpora quadrigemina ?

The corpora quadrigemina are the homologues of the optic lobes
in some of the lower animals, and may be regarded as important
centres for the visual and motor functions of the eyes. Not only
does blindness follow lesions of the corpora quadrigemina, but
there is often atrophy of them when the eyes are destroyed.

THE CEREBUUM. 121

Their action is crossed ; that is, lesions of tlic left side priiducc
right blindness. From these bodies also is derived the power of
co-ordination of the movements of the eyes and the control of the
the reflex of the pupil. These centres arc closely related, and
the disturbance of the one by a lesion in this part usually involves
the other.

THE CEREBRUM.
Describe briefly the cerebrum.

It is composed of two parts, or /leiiiisjilicrcti, connected by a com-
missure of white fibres, the corjms cal/osmn. The two hemispheres
are separated by a deep fissure extending fore and aft, and in the
interior of each is found a cavity known as the lateral ventricle.
The hemispheres are connected directly with the spinal system by
the crura cerebri and medulla, and with each other b}' the corpus
callosum. They are composed of white and gray nerve-substance,
and the latter is arranged largely at the periphery of the hemi-
spheres; the former being made up of communicating nerve-fibres
which connect the various portions of the hemispheres, and the
hemispheres with other parts of the cerehro-spinal system, thus
allowing a free control of the impulses arising from one cell or set
of cells by other cells in the gray matter.

How is the surface of the cerebrum marked ?

It is divided into regions bv' Jissiircs. -which separate one part
from another. These fissures are always present, and upon them
depends the determination of the division of the cerebrum into
lobes. The fissures which are of most use in locating the lobes of
cerebral matter are the fissure of Kolando, the fissure of Sylvius,
and the parieto-occipital fissure.

What are the convolutions of the cerebrum ?

The surface of the brain is further cut up by a number of other
clefts, known as sulci ; and these separate the surface into a num-
ber of distinct masses or convolutions. The depth of the sulci
and their number determine the quality of the brain in respect to
its degree of development ; thus, the convolutions in man are much
deeper and more numerous than in the lower animals. The sulci
are not invariable in position or number in different brains.

Into what regions is the cerebrum divided by the fissures ?

(1) Fro)itul L(j})e. — This lube is bounded by the fissure of Kolando,

122

NEEVOUS SYSTEM.

and contains several convolutions which include the forward por-
tion of the brain.

(2) The Parietal Lobe lies behind the fissure of Rolando, and
extends posteriorly to the occipito-parietal fissure. The convolu-
tions are well marked, and are separated by a well-marked sulcus

Fig. 33.

Plan of the Human Brain in Profile, showing its fissures and convolutions : S, fissure of
Sylvius ; S', anterior branch; S", posterior branch ; R, fissure of Rolando ; P, parieto-
occipital fissure.

(sometimes known as the parietal fissure), and the posterior branch
of the fissure of Sylvius is often enfolded by the inferior parietal
convolution. (In Fig. 33 this convolution is marked " Supramar-
ginal convolution.")

(3) The Temporo-sphenoidal Lobe is below the Sylvian fissure
and in front of the parieto-occipital. Its convolutions are well
marked.

(4) The Occipital Lobe is found at the posterior end of the cere-
bral hemisphere, and its convolutions are continuous with those of
the parietal and temporo-sphenoidal lobes, except within the longi-
tudinal fissure, where it is cut ofi' from them by the parieto-occipital
fissure.

THE CEREBRUM.

123

Hori/ontal Section of the IIeuiisi>lieres at the Level of the Cerebral Ganglia : 1, great
longitudinal fissure between frontal lobes; 2, great longitudinal fissure between
occipital lobes ; H, anterior part of curpus callosum ; 4, fissure of Sylvius ; fi, convolu-
tions of the insula; (!, caudate nucleus of corpus striatum; 7, lenticular nucleus of
corpus striatum; 8, optic thalamus; 9, internal capsule; 10, external capsule; 11,
claustrum.

(5) The Central Lohc. or hland of Rcil. is within the fissure of
Sylvius and covered by the convolutions of the frontal and parietal
lobes. (See 5 in Fig. 84.)

Besides these well-defined lobes, the portion of the cerebral sur-

124

NEEVOUS SYSTEM.

face which is within the longitu-
dinal fissure is marked by sulci
and conA'^olutions. The convolu-
tions of the frontal, parietal, and
occipital lobes are found here,
and the marginal (or calloso-
marginal) convolution, lying
above the corpus callosum, is
the principal landmark.

How is the gray matter of the
cerebrum arranged?

The increase in the area of
the surface of the hemispheres
by the infolding of the sulci
adds very greatly to the amount
of gray substance in the brain ;
for the entire surface is com-
posed of gi'ay substance, and this
follows the sulci and fissures
(Fig. 34) in all their folds, and
is not cut into by them. Be-
sides the gray matter in the con-
volutions there are certain other
gray masses in the substance of
the white matter : the optic
thalami, the corpora striata, and
the claustrum (Fig. 34) are the
chief of these gray masses.

What is the minute structure

of the gray matter of the

cortex ?

The gray matter of the cortex

is made up of ganglion-cells of

various shapes and sizes lying in

a loose connective-tissue stroma.

The connective tissue is more

abundant at the surface. The

cells are the source of numerous

nerve-fibres which pass out into

the white matter (Fig. 35). There

are counted five layers of these

Gray Matter of the Cerebral Cortex (Meynert). ganglionic tisSUes, and, while

THE CEREBRUM. , 125

these zones merge into one anotlier, tliey are tDlerably distiiiet. In
the niichlle (and widest) layer hirge niultijxdar cells are very nume-
rous, and the fibres may be seen to ])ass throiiiili the deej)er layers
in bundles into the white matter.

What chemical peculiarities does nervous tissue present?

It contains some peculiar bodies allied to the fats, but contain-
ing nitrogen : of these cerehrin and kcethin are the more prominent.
Aside from this, the constituents are proteid and fatty substances,
with salts, chiefly potassium and magnesium phosphates, and
water.

What is the weight of the adult brain ?

About 3 pounds. In size it exceeds the brains of all the lower
animals except the elephant and whale. Its weight is about one-
fortieth of the total body-weight, and this ratio is greater than in
the lower animals, with a few exceptions among the smaller birds
and monkeys. In women the weight is about one-tenth less than
in men.

Is the size of the brain a criterion of intellect ?

In some degree it is, but this is not absolute. The depth of the
sulci, and consequent size and complexity of the convolutions, are
a more efficient measui-e of the brain-power. In the largest of the
apes the brain of an adult animal is about the same in weight as
that of a human infant at birth. Idiots, as a rule, have brains
much smaller than the normal, and in them the convolutions are
apt to be ill-marked and uncomplicated, as is the case in the lower
animals.

What is known of the course of the fibres in the white substance
of the hemispheres ?

The course of these fibres may be classified in three groups :
1, commissural fibres; 2, fibres of association; and 3, medullary
fibres.

(1) The Commissural Fibres are those which connect one hemi-
sphere with the other, and it may be said that these fibres connect
each set of convolutions with the corresponding set of the opposite
side. The convolutions of the portion of the brain lying above the
fissure of Sylvius communicate by the corpus callosum, while those
at the base of the brain are joined by fibres passing through the
anterior commissure.

126 NERVOUS SYSTEM.

(2) Fibres of Association are those fibres which connect the
convolutions of one hemisphere. These fibres pass in bundles just
beneath the cortical gray matter of the convolutions, and it is
thought that most of the important convolutions of each hemi-
sphere intercommunicate in this way.

(3) The Medullary Fibres are those which connect the cerebrum
and medulla, and are regarded as indirect and direct, according as
they do or do not pass to the gray ganglia at the base of the brain.
In considering the course of the fibres from the medulla through
the crura cerebri it was noted that the motor and sensory fibres
were to some extent separated. The fibres pass from the crura to
the internal capsule, and here the course of the fibres is twofold :
the " direct fibres " pass to the cerebral convolutions through the
corona radiata, while the "indirect fibres" pass to the corpora
striata, and optic thalami, and communicate with ganglion-cells
there.

What is the function of the corpora striata and the optic thalami ?

These " basal ganglia," with the other collections of gray sub-
stance outside the convolutions, seem to have a controlling influ-
ence upon the spinal system. The crura throw their fibres largely
to these ganglia, the motor pyramidal tracts to the corpora striata,
and the sensory fibres from the lateral and posterior tracts to the
optic thalami. It is through these ganglia that all voluntary
impulses, except those by the direct medullary fibres, must pass.
These basal ganglia communicate through the corona radiata with
the convolutions of the cortex, and it is probable that we may
regard this part as acting as a middleman to elaborate and co-
ordinate the voluntary impulses of the cortex and to act in the
matters not requiring the intervention of the higher endowments
of the mind. This status of these ganglia is quite theoretical, but
the function may be considered as a sort having the properties of
both the automatism of the gray matter of the medulla and cord
and the voluntary function of convolutions. In this consideration,
however, we must not undervalue the communication with the
cortex which these basic ganglia possess.

Do lesions in these basic ganglia cause peripheral symptoms?

No. So far as has been observed, the corpora striata may be
involved by considerable lesions without causing persistent motor
or sensory disturbances, and the same may be said of the optic

THE CEREBRUM. 127

thalanii, but if the lesion eneroaclies upon the white matter of
the internal capsule or crura cerebri, the effect is to cause more
or less paralysis, depending upon the severity of the lesion and
its position.

What are the functions of the cerebrum ?

The motor and sensory functions which have been seen to belong
to other nuclei of gray matter are centred here, but infinitely
broadened, for the cells in the convolutions of the cerebrum can
originate the efferent and perceive the afferent nerve-impulses.
In fact, it is in this portion of the brain that the intelligence is
centred: it is the organ of the mind. Memory, reason, emotions,
and all the other attributes of the mind are dependent upon its
functional power.

What is the effect upon animals of the removal of the hemi-
spheres ?

In some of the lower animals the cerebrum may be entirely
removed without killing them. When this is done, for example,
in the case of a pigeon, the bird remains quiet in one position, and
is not disturbed by noises, or if thrown from its perch it flies and
alights in a nearly normal manner. If a foot be pinched, it with-
draws it and perhaps changes its position. The bird is capable
of reflex actions of various complicated kinds, but there is no
spontaneous exercise of volition : all its movements are excited
by the nerve-stimuli of the moment. There is no perception of
stimuli ; the intelligence is gone.

What is unilateral action of the brain ?

There are instances in which the injury or disease of one-half of
the brain has left the intellectual faculties not gravely impaired.
From a consideration of such cases it has been held that the action
of one of the hemispheres was sufficient for the purposes of the
mind. There is, however, an absolute dependence for motor and
sensory functions upon the integrity of both sides, for the one side
cannot act for the other in these functions. As a rule, it is safe
to assume that the two hemispheres act in unison.

Are the functions of the brain localized ?

While the brain is regarded as an nrgan of the mind, it is prob-
able that the various functions may be regarded as belonging to
definite portions of the convolutions which are appropriated for that

128 NERVOUS SYSTEM.

purpose. The functions of the convolutions have not been assigned,
except for a very small portion of the brain-surface and for some
of the simpler actions. For the most part, our knowledge of the
localization of brain-functions is confined to "motor areas," in which
it has been determined that stimulation of a certain group of cells
will cause a definite action. Besides this, certain other centres are
located, as of sight and speech.

How are the motor areas determined?

When the surface of the brain is exposed in animals or in man,
the stimulation of certain areas of the cortex by a mild electrical
current will give rise to motion in the peripheral muscles ; and it is
found that the stimulation of the same region in the same or other
animals will cause the same results. These centres of motor im-
pulses are situated almost entirely upon the convolutions about the
fissure of Rolando (Fig. 36).

What is known regarding the localization of sensory areas ?

This has not been, by any means, so definitely fixed as for motor
centres ; but the centres for sensation may be said to exist, and
probably in the convolutions of the posterior portion of the cere-
brum. The centre for vision in the convolutions about the poste-
rior branch of the fissure of Sylvius is generally accepted (14, 15,
in Fig. 36). The centre for hearing is tolerably defined in the
temporo-sphenoidal lobe along the posterior branch of this fissure
(16, Fig. 36). The speech-centre is also located with seeming ac-
curacy along the anterior branch of the fissure of Sylvius and in the
island of Reil. This centre seems to be much more developed upon
the left side of the brain. In Fig. 36 this centre may be indicated
roughly by reference to the tongue-centres (8 and 9).

Do the evidences of pathology agree with these experiments ?

Injuries and diseases involving the motor areas are followed by
paralysis so well defined that it is frequently possible to locate
the seat of the lesion from its result upon the inuscular system.
Tumors, abscesses, and depressed bone, for example, are capable
of accurate localization in this way. The more indefinite sen-
sory paralyses do not so accurately point out their origin. On
the whole, the evidence of pathology bears out in full the experi-
mental results. The crossed action of all the nervous structures
is especially to be noted. In the case of a right paralysis in

THE CEREBRUM.

129

which the speech is affected, as compared with a left heniiple<ria
and speech unaffected, this crossed action is impressed when we

Fio. 36.

Brain of Monkey, showing the position of the motor and sensory centres as ascertained
by Ferrier. The actions all occur on the side of the body opposite to the part of the
brain irritated : 1, the eyes open widely, the pupils dilate', and bead and eyes turn to-
ward opposite side ; 2, extension forward of the opposite arm and hand, as if to reach
something in front ; 3, movements of tail (and trunk) ; 4, retraction with adduction of
opposite arm ; 5, supination and Ilex ion of the forearm, by which the arm is raised to-
ward the mouth ; fi, action of zygonKities, by which the angle of mouth is retracted and
elevated; 7, elevation of alaof nose and upper lip; 8, opening of mouth with protnision
of tongue; 9, retraction of tongue; 10, retraction of opposite angle of mouth ; a,b,c,(l,
prehensile movements; 11, retraction and adduction of opposite arm ; 12, advance of
the opposite hind limb; 13, complex movements of thigh, leg, and foot; 14, 15, vision
(sensory) ; 16, hearing (sensory).

remember the localization of the centre for speech in the left
hemisphere near the motor area.

Mention some of the common terms used in defining paralysis.

Anaesthesia = loss of sensation.

Hemianaesthesia = loss of sensation in one lateral half of the
body.

Hemiplegia = loss of muscular power in one lateral half of the
body.

Paraplegia = symmetrical loss of muscular power in the lower
portion of the body and extremities.

9— Phy.

130 NERVOUS SYSTEM.

Aphasia = loss of power to talk — amnesic when words are for-
gotten ; ataxic when the power to articulate is lost, though the
words are known.

THE CEREBELLUM.
Describe the cerebellum.

It is a mass of nerve-substance situated posteriorly at the base
of the skull. It consists of a median lobe and two lateral hemi-
spheres, and is connected with the rest of the cerebro-spinal system
by numerous white fibres collected in bundles known as peduncles.
Of these, the larger peduncles pass to and largely make up the pons
Varolii (middle peduncles), thus connecting the lateral hemispheres
of the cerebellum. The superior peduncles (or processus e cerebello
ad testes) pass beneath the corpora quadrigemina, and the fibres pass
into the white matter of the cerebrum, decussating as they meet
beneath the corpora quadrigemina. The inferior peduncles pass to
the medulla, where they form the restiform bodies. Thus it is seen
that the entire cerebro-spinal system communicates very freely with
the cerebellum.

How is the gray matter of the cerebellum arranged ?

The arrangement in convolutions is not the same as in the cere-
brum, but there are numerous transverse sulci which divide and
subdivide, the gray matter being disposed about them in a thin
layer. This causes a section of the organ to have a peculiar tree-
like appearance, which originates the name, " arbor vitge," given to
the cortical matter of the cerebellum. Besides this, there is a cen-
tral collection of gray substance — the corpus dentatum.

What peculiarities does the gray matter of the cerebellar cor-
tex possess ?

Under the microscope it is found to consist of three layers (Fig. 37).
The outer is a layer of delicate connective tissue which supports
fine nerve-fibres and small spindle-shaped, branching nerve-cells.
The middle layer is characterized by irregularly disposed large gan-
glion-cells, and the branching processes from these ramify in the
superficial layer. These cells are known as Purkiuje's cells. The
inner layer is made up of a mass of small spheroidal cells, and
gradually merges into the white substance.

What is the function of the cerebellum ?

The cerebellum seems to exert no influence upon the sensory

TIIK CEREBELLUM.
Fio. 37.

131

Vertical Section tliidUirh the Cray Matter of the Iliiman CerebeHum (magnified about
llH) flinnietors : Klein and Nuble Smith): «, the external trray or cellular layer; b,
corpuscles of I'urkinje; '■, internal rust-colored jrranular layer; </, white substance.
Two branched capillaries are seen at the upper part passing into the gray matter
from the pia mater.

132 NERVOUS SYSTEM.

nerves, for sensibility is not aiFeeted by its injury or disease.
The motor system is, however, entirely disorganized by lesions
of the organ. Co-ordination of the voluntary muscles is accom-
plished by this portion of the brain, and it is originated in the gray
matter of the part. It has no effect upon the senses or upon the
intellect, so far as is known.

What is the effect of removing the cerebellum in animals ?

When small portions are removed the animals become feeble and
uncertain in their movements, but are able to move for ordinary
purposes. As the amount removed increases the want of co-ordi-
nation of the voluntary muscles increases. With the entire cere-
bellum gone the condition is absolute — animals cannot stand or
walk or bring any of the muscles into orderly action. If the ani-
mal is laid upon the back, it cannot recover itself, but struggles
vaguely in the attempt. The senses are apparently normal and the
will-power is present : if a blow is threatened, an attempt is made
to avoid it. When the lesion is confined to one hemisphere, the
lack of co-ordination is noticed in the opposite half of the body.
Under these circumstances the animals are apt to fall to the oppo-
site side and roll over and over rapidly. Such movements are
known as forced movements. This condition may persist for several
days. Pigeons from which the cerebellum is removed may live for
a considerable time, sometimes for several months, after the opera-
tion. In some cases there is a return of power to co-ordinate, after
partial removal, at the end of some days.

THE CRANIAL NERVES.
What are the cranial nerves?

They are a set of twelve pairs of nerves which arise from the
brain. They are varied in their functions, but all arise from gan-
glia of gray matter in the brain and medulla. The floor of the
fourth ventricle is particularly rich in nuclei in which these cranial
nerves originate.

How may the cranial nerves be classified ?

1. In the order of their emergence, by numbers: (I) Olfactory;
(II) Optic ; (III) Motor oculi ; (IV) Patheticus ; (V) Trigeminus ;
(VI) Abducens; (VII) Facial; (VIII) Auditory; (IX) Glosso-
pharyngeal ; (X) Pneumogastric ; (XI) Spinal accessory ; (XII)

THE CRANIAL NERVES. 133

Hypoglossal. -f^ In the relation of their functions they may be
arranged as nerves of special sense, nerves of common sensation,
motor nerves, and mixed nerves (t. e. both sensory and motor).

r (I) olfactory, (II) optic, (VIII) audi-
Nerves of special sense, < toryj-, and parts of (V) trigeminus

(^ and (IX) glusso-pharyngeal.
Nerves of common sen- ( The greater portion of the (V) trigem-
sation, | inus.

f (III) motor oculi, (lY) patheticus, (V)

■,r i lesser division of the trigeminus, (VI)

Motor nerves, < , ^ /^riT\.p ■ i i /vtt\ v,

' I abducens. (VH) lacial, and (XII) hy-

[ poglossal, (XI) spinal accessory (?).
Mixed nerves, \ ^^^> glosso-pharyngeal and (X) pneu-

' ( mogastric.

What is the distribution of the motor oculi or third nerve?

It arises from a nucleus of gray matter just in front of the me-
dulla, beneath the iter e tertio ad quartum ventriculum, passing
out through the crus cerebri, and emerging from the skull in the
orbit. It gives ofi" some fibres to the lenticular ganglion. It is
distributed to all the muscles of the eyeball, with the exception
of the superior oblique and the external rectus muscles. It also
supplies the levator palpebral superioris muscle, and by its con-
nection with the lenticular ganglion controls the ciliary and pupil-
lary muscles.

What is the function of the third nerve ?

It is a purely motor nerve. Its function is best described, per-
haps, by showing the paralyses which follow its division : by par-
alysis of the elevator of the upper lid we have jyfosis ; by the
paralysis of the muscles of the eyeball we have inability to move
the organ up or down or inward ; by the unopposed action of the
external rectus the eyeball becomes turned outward (external stra-
bismus) ; by the action upon the miiscle of the iris the pupil

* A convenient old medical-school mnemonic is useful in remembering the
names and order of these nerves — viz. On Old Moriah's Pointed Top A
French And German Picked Some Hops, tlie initial letter of each word giv-
ing the key. It is given witli an apology to many generations.

t Of the nerves of special sense, ( [) olfactory, ( II ) optic, and (VIII) audi-
tory will be explained later, and may be omitted from further consideration
for the present.

134 NERVOUS SYSTEM.

remains dilated and does not respond to light ; and by the paraly-
sis of the ciliary muscle the accommodation of the lens for near
vision is prevented. The control of the- pupil is not a voluntary
one ; but the effect of a strong voluntary effort, exerted through
the third nerve, shows itself in contraction of the pupil, as when
the eyeball is turned strongly inward and upward.

Describe and give the function of the patheticus or fourth cra-
nial nerve.

It arises close by the third nerve beneath the aqueduct of Syl-
vius, and emerges, after decussation, from the valve of Vieussens.
Thence, passing around the crus cerebri, it runs parallel with the mo-
tor oculi (third) nerve to the orbit, where it is supplied to the supe-
rior oblique muscle. Its paralysis prevents the muscle from main-
taining the horizontal plane of the eyeball. If this paralysis occurs,
there is double vision, and the image seen by the affected eye
appears oblique and inferior to the image of the other eye. This
may be corrected by inclining the head to "the opposite side. This
jierve is also known as the trochlearis or trochlear nerve.

What is the course and function of the sixth or abducens nerve ?

It arises from a nucleus of gray matter in the floor of the fourth
ventricle, and its nucleus is connected with those of the third, fourth,
and seventh nerves. It emerges without decussation at the poste-
rior border of the pons Varolii, and passes forward to the orbit
with the third and fourth nerves. In its course it has many com-
munications with the sympathetic nerves, but their significance is
unknown. It is supplied to the external rectus muscle of the eye,
and its stimulation causes external squint, and paralysis causes
internal.

What is the origin of the trigeminus or fifth nerve ?

This nerve resembles the spinal nerves in having a motor and a
sensory root, the latter possessing a ganglion (Gasserian). The
origin of the nerve seems to be in centimes, separate for motor and
sensory, in the floor of the fourth ventricle. There are fibres which
join the trunk of the nerve which are derived from the spinal cord
and from the cerebellum. It emerges from the pons Varolii as two
distinct nerve-roots. The larger of the two, the sensory, soon enters
the Grasserian ganglion, the motor root passing beneath without
communication. The nerve then breaks up into three branches :
of these the first and second are formed entirely from the sensory

THE CRANIAL NERVES.

135

root, ^vhilc the third carries all the iiuitor fibres, and with them some
of the sensory, so that the third branch of the nerve is partly sen-

FiG. 38.

Diagram of the Fifth Nerve and its Distribution ; 1, sensitive root ; 2, motor root; 3, Gas-
serian ganglion ; I, ophthalmic division ; 11, superior maxillary division ; III, infe-
rior maxillary division; 4, supraorbital nerve, distributed to the skin of the fore-
head, inner angle of the eye, and root of the nose; o, infraorbital nerve, to the skin
of the lower eyelid, side of the nose, and skin and mucous membrane of the upper
lip; 6, mental nerve, to the integument of the chin and edge of the lower jaw, and
skin and mucous membrane of the lower lip ; «, n, external terminations of the na^al
branch of the ophthalmic division, to the mucous membrane of the inner part of the
eye and the nasal passages, and to the base, tip, and wing of the nose; t, temporal
branch of the superior maxillary division, to the skin of the temjioral region ; m,
malar branch of the superior maxillary division, to the .skin of the cheek and neigh-
boring parts; h, buccal branch of the inferior maxillary division, passing along the
surface of the buccinator muscle, and distributed to the mucous membrane of the
cheek and to the mucous membrane and skin of the lips; I, lingual nerve, to the
mucous membrane of the anterior two-thirds of the tongue; a/, auriculo-temporal
branch of the inferior maxillary division, to the skin of the anterior part of the
external ear and adjacent temporal region ; x, x, x. muscular branches, to the tem-
poral, masseter, and internal ■■•ud external pterygoid muscles; y, muscular branch,
to the mylo-hyoid and anterior belly of the diagastric ; /, sensitive branch of com-
munication to the facial nerve.

sory and partly motor. There is a partial decussation of the fibres
in the medulla, but many pass direct to the same side.

What muscles are supplied by the motor root?

The 7nHKcIeF: of vidsticdtiou. The temporal, masseter, and both
pterygoid muscles, as well as the anterior belly of the digastric

136 NERVOUS SYSTEM.

muscle and the mylo-hyoid, receive their innervation from the motor
root of the fifth nerve. Besides this, the tensor palati and tensor
tympani muscles are supplied by this nerve through its communi-
cation with the otic ganglion of the sympathetic system. A branch
to the buccinator muscle is probably not motor, but sensory. Le-
sions of the nerves paralyze these muscles.

What is the distribution of the sensory root ?

The sensory fibres of the fifth nerve are distributed in all three
branches, and supply sensation to the skin of the face and anterior
portion of the head, emerging from the bony canals upon the face
at the supraorbital, infraorbital, and mental foramina ; it is also
supplied to the mucous membrane of the mouth and tongue (by
the lingual branch) and to the muscles of the part.

What results follow division of the sensory root of the fifth nerve ?
There is complete anaesthesia of the skin and mucous membranes
of the face.

What is the trophic influence of this nerve-root ?

It is of very great value. If it be divided, the complete anaes-
thesia of the conjunctiva, of the nostrils, and of the lips prevents
the reflex self-protection vrhich belongs to the parts, and they be-
come injured very easily. Aside from that, the direct influence
upon all the parts is great, so that vphen it is cut off there is a
rapid degeneration resulting, vphich is specially apparent in the
mucous membrane of the nose and in the cornea.

What influence has the sensory branch upon the special senses ?
(1) Its division causes total anaesthesia to the skin and mucous
membrane ; the loss of the sense of touch in the part is of great
importance, for the tongue and lips are used much for this.
(2) Upon the sense of sight it has a very controlling influence,
for, as we have seen, the trophic influence is essential to the
maintenance of the integrity of the eye. (3) Upon the sense of
smell. Here the influence is the same as with the eyes, trophic.
The smell is soon lost on account of degeneration of the mucous
membrane after division of the fifth nerve. (4) Taste, prob-
ably, is not a direct function of the nerve, but if the tactile sensi-
bility is gone and the trophic changes are begun, the sense of taste
soon disappears in the anterior portion of the tongue. (5) Upon
the hearing the effect is more gradual and less distinct. The seere-

TIIK CRANIAL NERVES.

137

tioiis of the cavity of the tyiiipanuin and of the external auditory
canal are of great importance in niaintaining normal conditions.
They arc under the trophic influence of the fifth nerve, both
throunh its auriculo-temporal branch and through its communica-
tion with the otic ganglion. The tensor tympani muscle is also
supplied by the motor root. Thus, the auditory apparatus is con-
siderably under the control of the nerve.

What painful afifections belong to this nerve?

Headaches of the scalp and deeper tissues, and more especially
the frontal sinuses, are common. Toothache and facial neuralgia

Fui. 39.

Diagram of the Facial Nerve and its Distrilnition : 1, Facial nerve at its entrance into the
internal auditory meatus ; 2, its exit at the stylo-niastoid foramen ; 3, 4, teni|i(iral and
posterior auricular brandies, distributed to the muscles of the external ear and to the
occipitalis; o, branches to tlie frontalis muscle; 0, branches to the stylo-hyoid and
digastric muscles; 7, branches to the upper part of the platysma myoides; .s, branch
of coninuinicatiou with the superficial cervical uerve of the cervical plexus.

are due to irritation or disease of parts of the nerves. Tic dou-
Ivurcux is a persistent neuralgia of some or all of the branches of
the nerve.

138 NEEVOUS SYSTEM.

What is the origin of the facial or seventh nerve ?

It arises in the floor of the fourth ventricle, and its fibres emerge
at the edge of the pons Varolii in company with the (eighth)
auditory nerve (sometimes known as the portio mollis ; the facial
being then called the portio dura of the seventh pair, when the
classification of the cranial nerves is made into nine pairs). It
passes into the internal auditory canal, and escapes from the
skull by way of the aqueduct of Fallopius and the stylo-mastoid
foramen.

How is the facial nerve distributed?

It is almost wholly a motor nerve, and is distributed to all of the
muscles of the face (Fig. 39) except those mentioned as controlled
by the motor branch of the trigeminus nerve. The muscles of the
eyelids and the muscles of the palate in part are innervated by it,
as well as the parotid and mhmaxillary glands^ through the chorda
tympani. In the neck it supplies the posterior belly of the digas-
tric and the platysma myoides muscles. It also sends branches to
the stapedius muscle of the internal ear and to all of the muscles
of the external ear. The branches passing to the salivary glands
are secretory in their function ; and this is the only exception to
the motor influence of the nerve.

What is the function of the facial nerve ?

It is the motor nerve which parallels in its distribution the
sensory root of the fifth ; it supplies the superficial muscles, as the
latter does the skin. It is the nerve of expression, by which the
features are made to reflect the emotions.

What is the effect of paralysis of this nerve ?

If the nerve be divided or diseased, the face of that side is
devoid of motion (Fig. 40), and becomes smooth and expression-
less, while the sound side is held in its customary pose. The
eyelids cannot close themselves, and the lips do not oppose properly,
on account of the defective action of the orbicular muscle. There
is difficulty in drinking and in articulation for the same reason.

State what influence is ascribed to the chorda tympani branch.

The chorda tympani is a small filament given off" from the facial
in the aqueduct of Fallopius, some of whose fibres are distributed to
the submaxillary gland. If this nerve be divided, the secretion of
saliva from the gland is greatly diminished, while stimulation of the

THE CRANIAI> NEKVKS.

139

norvo will excite a copious flow. This is an active secretion, ami is
nut a sinipli' filtration clue to vaso-uiotor chanfrcs. A similar influ-
ence is noted in the corresponding hall" of the tongue. There is a
similar distribution of tibres from the facial to the parotid gland

Fig. 40.

Facial Paralysis of the Right Side.

through the lesser petrosal nerve, but their action has not been so
thoroughly analyzed as in the case of the submaxillary and chorda
tynipani.

The chorda tympani has still further an effect upon the sense of
taste in the anterior portion of the tongue. If it be divided, the
taste is much blunted on the aff'ected ,side. It is not known if this
be due to the communication of the glosso-phai'vngeal or not, but
it seems probable that it cannot be ascribed to either the trifacial
or facial alone ; and it is considered to be a plausible explanation
tliat the chorda tympani does bear some fibres of the glosso-
pharyngeal.

140 NERVOUS SYSTEM.

Why is not the ocular paralysis of the seventh nerve as serious as
that of the fifth ?

The eyelids remain open in facial paralysis, and the conjunctiva
is subject to injury by drying. and by foreign bodies ; but the injury
is not so great as in paralysis of the fifth nerve, because the seventh
has no trophic influence.

What is the origin of the glosso-pharyngeal or ninth nerve ?

It arises in the medulla from centres near those for the vagus
and spinal accessory nerves. Its fibres pass through the substance
of the medulla and em^erge in company with those of the vagus and
spinal acessory to pass with them from the skull through the jug-
ular foramen. It gives off" a small branch which passes to the
tympanum and Eustachian tube (Jaeobson's nerve) while in the
jugular foramen, and presents a small ganglion, the petrosal ; and
it has communicating branches to the seventh and tenth nerves
and to the otic ganglion. It divides as it passes down, one branch
passing forward to the tongue, and one going to the pharynx
(whence its name).

How is the glosso-pharyngeal distributed ?

The portion which passes to the tongue is distributed to the pos-
terior portion of the organ, to the circumvallate papillae, and the
mucous membrane behind them, some fibres going to the lining of
the soft palate, pillars of the fauces, and tonsils. The other branch
is distributed to the mucous membrane of the pharynx, and by
direct branches and communications with other nerves to all the
muscles involved in swallowing.

What is the function of the glosso-pharyngeal nerve ?

(1) It is the nerve of taste; and (2) it is essentially a nerve of
deglutition.

Explain the action of the glosso-pharyngeal as a nerve of taste.

It is only in the latter part of the stay of food in the mouth that
it reaches the region supplied by this nerve. When the food is to
be swallowed, it is pressed by the base of the tongue against the
palate arch and pushed into the pharynx. It is then that the sense
of taste is exercised here. The reflex stimuli then excited start up
the motor chain which pushes the bolus on to the stomach. As
already said, there is considerable question as to whether the tri-
geminal or glosso-pharyngeal is really the conductor of this sense,
but it is quite likely that both are essential.

THE CRANIAL NERVES. 141

What is the function of the glosso-pharyngeal as a motor nerve ?

\\ lic'tlicr l)y reason of its coinuiiiiiifalioiis with otlier nerves or
not ill its distril)utioii, tlie nerve is a motor nerve as well as
sensory. Its distribution is to all the muscles of deglutition,
and stimulation causes contraction of the muscles, while division
paralyzes them. The very numerous connections of the nerve com-
plicate its anatomical origin very greatly, and interfere with a clear
comprehension of the unaided function of the nerve.

Where does the reflex for swallowing originate?

In the medulla oblongata, where the centre of origin of the nerve
is situated.

What is the origin of the pneumogastric or tenth nerve ?

It arises from the gray matter in tlie floor of the fourth ventri-
cle, its nucleus being very close to those of the glosso-pharyngeal,
spinal accessory, and hypoglossal. Its fibres pass through the sub-
stance of the medulla oblongata, and emerge from its lateral sur-
face with the roots of its associate nerves, the glosso-pharyngeal
and spinal accessory. It passes from the skull with them by the
jugular foramen. It has at this point a ganglionic enlargement.
From here it passes down the neck, and is distributed more diflFusely
than any other cranial nerve.

What synonyms has the tenth nerve?

Pneumogastric, from its distribution and function ; vagus or Par
Vagum, from its scattered distribution («<_(/««, Latin = wanderer).

What principal distributions has the pneumogastric?

It is supplied to the organs by which air and food enter the body,
and besides this has several important connections with the s^'mpa-
thetic system. (1) To the larynx it supplies sensation and motion
through the superior and inferior lari/iigeal branches. (2) In the
chest it forms the pidmonari/ plexuses, which innervate the bronchi
and lungs. (3) Branches to the cardiac plexus supply important
stimuli to the heart and great vessels. (4) There are branches to
the 2)har?/nffeal and asopluigeal plexuses which are both sensor)' and
motor, supplying both the mucous membrane and the muscular
structures of the parts. (5) Its terminal branches supply the sen-
sory and motor nerves to the stomach, the left nerve being dis-
tributed on its anterior wall, and the right posteriorly. (G) Branches

142 NERVOUS SYSTEM.

also pass to tlie liver and spleen and communicate with the solar
plexus.

Mention some of its communications with other nerves.

Soon after leaving its origin in the medulla the vagus enters into
so many communications with other nerves, both sensory and mo-
tor, that it is difficult to know the real fibres of the original root
and to determine what are original and what derived functions.
The sympathetic system sends fibres in all the branches of the
pneumogastric, and the pneumogastric sends branches to many of
the important sympathetic plexuses and ganglia ; the pharyngeal,
laryngeal, oesophageal, pulmonary, cardiac, and solar plexuses are
so made up by branches from both. The spinal accessory nerve is
an important contributor, in that it sends a large branch which is
incorporated in the vagus. There are also communications to the
glosso-phai'yngeal and hypoglossal nerves, and it also receives
motor fibres from the facial and upper two cervical nerves. The
original nerve is probably entirely sensory, and its motor function
is derived from these connections with motor nerves.

Where are the motor fibres from the spinal accessory nerve sup-
posed to be distributed?

Principally in the recurrent laryngeal nerve.

What is the function of the vagus in connection with respira-
tion ?

The nerve supplies, as has been said, the motor and sensory
functions of the larynx, and in this is of value to the respiratory
function both in the prevention of foreign substances entering the
rim a glottidis, and in the opening of that orifice for the entrance
of air. Besides this, it supplies sensory fibres to the pulmonary
plexus which transmit the reflex stimulus to the medulla, by which
the motor apparatus is excited to action.

What is its influence upon the voice?

The muscles of the larynx involved in the production of sound
are supplied by this nerve, and, as the approximation of the chor-
dae vocales is necessary for this, it follows that the voice is depend-
ent upon the fibres of the pneumogastric supplied by the inferior
or recurrent laryngeal nerve.

What effect upon respiration follows section of the vagi ?

The respiration is slowed immediately to about half its usual

THK CRANIAL NERVES. 143

rate, ami soon drops to five or six to tlu; niinuto, and oven slower.
Tlie respiration is easy — inspiration slow and full, ex])iration harsh
and sudden. Death follows this operation in a short time (one to
six days), and the animal during- the time is sluggish and appa-
rently suffers from slow earbonic-oxide nareosis. It is inferred
iVom this that the vagus is the nerve which carries to the auto-
matic centre the stimuli which arc needed to keep up the automat-
ism, and that the medulla is incapable of originating the motor
impulses unless controlled by afferent stimuli.

What is the function of the pneumogastric in deglutition ?

Deglutition both in the pharynx and oesophagus is under the influ-
ence of the vagus, which gives innervation directly to the thoracic
part of the latter and through the inferior laryngeal branch to the
cervical part. The sensory fibres act as conductors of the stimulus
Avhieli results in the reflex peristalsis by which the food is carried
on through the cesophagus. The sensory distribution to the larynx
must not be forgotten in this connection, for by it food is kept from
the respiratory organs. Section of the vagi causes paralysis of
swallowing, and food is apt. to pass the glottis on an attempt to
swallow, not even a cough being excited by such an accident. The
closure of the glottis in swallowing is caused by a reflex action
known as the " action of arrest," and is derived from the sensory
fibres of the vagus.

What is the physiological relation of this nerve to the stomach ?

Both sensory and motor. The stomach receives its warning of
the presence of food through the sensory fibres, and the muscular
fibres excite the organ to contract upon it and " churn " it about
during digestion. There is also a vaso-motor influence derived
from the vagus. When the nerve is cut but little food can reach
the stomach because of the paralysis of the oesophagus, and what
food does enter is digested very slowly, so that the function of the
pneumogastric may be considered essential to stomach digestion.
The connection with the solar plexus also involves the intestines in
the action of the vagus.

What important excito-motor reflexes depend upon the pneumo-
gastric for one or both stimuli?

Coughing and vomiting, as well as many other less essential
reflexes, such as sighing, hiccoughing, and the like.

144 NERVOUS SYSTEM.

What is the influence of the vagus upon the heart ?

There are numerous branches to the cardiac plexus from the
trunk of the vagus and from its inferior laryngeal branch. Stim-
ulation of the pneumogastric nerve diminishes the frequency, or,
if strong, entirely stops the heart in diastole. The nerve is there-
fore regarded as having an inhibitory action. This is an unusual
effect, for in other cases the stimulation of nerves going to muscles
causes contraction : the heart, however, becomes flaccid under the
influence of the stimulated vagus.

What is the origin of the spinal accessory or eleventh cranial
nerve ?

It is twofold. One root arises in the gray matter of the medulla
near the nucleus for the vagus, while the others arise from the
lateral tract of the cord as low as the fifth or sixth cervical vertebra,
and pass up between the anterior and posterior spinal nerve-roots to
join the medullary (or accessory) portion at its emergence from the
medulla. The united nerve passes out through the jugular foramen
with the glosso-pharyngeal and pneumogastric nerves.

How is the nerve distributed?

Soon after leaving the skull it again divides, the medullary root
joining the trunk of the pneumogastric, while the spinal root sup-
plies the sterno-mastoid and trapezius muscles.

What is the function of the spinal accessory nerve ?

The nerve is a motor to all intents, though it has some sensory
fibres, as is shown by the pain caused by pinching it.

(1) The anastomotic branch^ which joins the pneumogastric, is
apparently largely given off in the recurrent laryngeal nerve, but
its section does not produce the same effect upon the larynx as
section of the trunk of the vagus or of its inferior laryngeal
branch. There is paralysis of the voice, but not of the move-
ments of the glottis for respiration. There are probably some fibres
of this nerve also given off to the cardiac plexus.

(2) The muscular branch supplies the sterno-mastoid and trape-
zius muscles, but these muscles are also supplied by the cervical
spinal nerves, and their action is not paralyzed by the section of
this branch of the spinal accessory. It is found, however, that
the relation of these muscles to respiration is impaired by isolation
from this nerve ; that is, when the breath is held in any violent
exertion, as straining or pushing, or when a loud cry is uttered,

THE SENSES. 145

tlio sterno-niastoid aiul trapezius nmscles contract to fix the head
and hold the spine steady. This action seems to be prevented by
the section of this muscular branch of the spinal accessory.

What is the origin of the hypoglossal or twelfth cranial nerve ?

It arises in the gray matter at the inferior extremity of the
floor of the fourth ventricle, near the origin of the spinal accessory
and pneumogastric nerves. The fibres pass through the substance
of the medulla oblongata, skirting (and perhaps gaining fibres from)
the olivary body, and, emerging in a number of small bundles,
collect into a nerve-trunk which emerges from the skull by the
anterior condyloid foramen.

How is the hypoglossal nerve distributed?

It passes down the neck to about the level of the hyoid bone,
where it curves forward and into the tongue, giving off branches to
the muscles which move that organ.

What is the function of the hypoglossal nerve ?

It is a motor nerve, but possesses some sensory fibres derived
from the cervical spinal nerves and from the trigeminus, with
whose lingual branch it inosculates on the side of the tongue.
Filaments from it are distributed to all the muscles which move
the tongue, and to the depressors of the hyoid bone through its
descending branch.

What influence has this nerve upon digestion?

It is important in mastication, for its muscles move the food
about for the better action of the teeth. In animals, after division
drinking is impossible, because they are unable to lap up fluids, and
the food is swallowed with difficulty because it is not carried back
into the pharynx by the tongue after mastication.

What is its connection with speech?

Articulation of most sounds involves movements of the tongue.
Impaired articulation is an early symptom in bulbar or glosso-
labio-laryngeal paralysis.

THE SENSES.

What organs are necessary for sensation?

A peripheral organ for the reception of an impression, a nerve
for its conduction, and a centre in the brain for the perception.
10— Phy.

146 THE SENSES.

It is by means of impressions so received and conducted to it that
the mind is able to control the body and to take cognizance of the
external world.

Into what classes may the sensations be arranged ?

Common sensations and special sensations. These last are com-
monly called " the senses."

What is meant by the common sensations?

Such perceptions as cannot be distinctly located in any organ or
set of organs, such as fatigue, hunger, thirst, satiety. Besides this,
there are some sensations which involve certain organs which must
be classed under this head ; thus inclinations to cough or to sneeze
or to vomit are common sensations, and, similarly, to urinate or
defecate. Many of these sensations occupy a border-line between
common sensibility and the special sense of touch, such as itching
and tickling.

Is pain a common sensation?

It is, but is very closely allied to the sense of touch. The two
may be differentiated, however. If one touch a sharp instrument,
he may perceive its shape and condition, but if the pressure be
increased the ability to perceive its form is lost, and instead the
sensation of pain is established. The relation of the two is curi-
ously shown in partial anaesthesia by drugs, as when one takes
nitrous-oxide gas for the extraction of a tooth, and is able to feel
the operation and to know what has been done, without in the least
feeling pain.

What is the real seat of the senses ?

The brain or sensormm. The organ of the mind, which perceives
the thing which the organ of sense has taken an impression from,
is the fundamental structure in the necessary chain.

What is hallucination?

It is the perception of an object as a real presence without the
presence of the object to justify the perception ; that is, it is an
act of the brain which refers its action to an organ of the senses.
Thus, in delirium tremens a person may perceive many curious and
uncanny things, which his mind hears and sees and feels, but which
his senses could not take cognizance of, because they are only
" creatures of the mind."

TOUCH. 147

Do the nerves of special sense possess the property of common
sensibility ?

No. Till! six'cial nerves liave no other function than tlic special
one for wliich they arc set apart ; and when they are separated
from tlieir special organs for receiving impressions, they no hunger
respond to the customary stimuli.

What are the special senses?

Touch, taste, smell, hearing, and sight.

TOUCH.
What is the organ of touch ?

The skin and the mucous membranes adjoining it. The nails
and teeth too exercise a peculiar function in this regard, and the
hair in some regions — e. g. eyelashes. The sensations of touch are
communicated to the central nervous system through the agency
of the sensory nerves of the spinal and cranial systems.

What varieties of the sense of touch are found ?

(1) Tactile sensibility, or touch proper; (2) the sense of pressure
or weight ; (H) the sense of temperature. All of these, when car-
ried beyond moderate limits, are merged into the sensation of pain.

What factors determine the acuteness of touch ?

The (Jisfribiifioii of the eud-orgmis of the sensory nerves varies in
different parts of the body, and the more numerous the touch-cor-
puscles, the more acute the sensibility of the part. Again, the
thickness of the epidermis has marked influence in determining the
tactile ability, portions of the hands and feet, when callous, having
very blunted sensibility.

What qualities of bodies are determined by touch ?

Their hardness and elasticit}', the quality of tlie surface as to
smoothness, the size and form and the temperature and wet or dry
condition, are all easily determined by touch.

Why is the hand of especial value as an organ of touch ?

Jiocausc of the acuteness of its sensibility. Further than this,
it is so constructed as to be capable of forming impressions of
bodies by reason of its power to grasp them and to test them as
to weight.

148

THE SENSES.

How is the acuteness of touch measured ?

By means of a pair of compasses whose points are blunted. The
legs of the instrument are separated, and the distance, between
the points which can jvist be distinguished as two separate con-
tacts, measures the sensibility. From the accompanying table it
will be seen that the touch is most acute in the tip of the tongue
and in the fingers and tips, while in other portions the sense of
touch is so vague that two points of contact are not distinguished
until they are 21 in. apart. It is found that the points of the com-
passes must be more widely separated when the test is made in the
long axis of a limb than when across it. (The table is from Kirke's
Handhooh) :

Table of Variations in the Tactile Sensibility of Different Parts. —
(The measurement indicates the least distance at which the
two blunted points of a pair of compasses could be separately
distinguished. — E. H. Weber.)

Tip of tongue ^-^ inch.

Palmar surface of third phalanx of forefinger . . xV

Palmar surface of second phalanges of fingers . . \

Red surface of under lip \

Tip of the nose \

Middle of dorsum of tongue \

Palm of hand -f^

Centre of hard palate \

Dorsal surface of first phalanges of fingers .... -^^

Back of hand 1^

Dorsum of foot near toes \\

Gluteal region IJ

Sacral region 1\

Upper and lower parts of forearm 1^

Back of neck near occiput 2

Upper dorsal and mid-lumbar regions 2

Middle part of forearm 2\

Middle of thigh _ 2\

Mid-cervical region 2\

Mid-dorsal region 2|^

How is touch modified by education?

The sense of touch may be greatly educated and specialized.
This is seen in many of the arts where great dexterity obtains by
reason of an educated touch. The reading raised letters by the
blind is a familiar example of educated touch.

TOUCH. 149

What is pressure sensation?

Wlii-n weight is atkled to an ordinary touch, the sensation of the
pressure of the weight is felt, and by it one can judge with con-
siderable accuracy the amount of the pressui'e, and determine the
comparative pressure of two weights with approximate correct-
ness within limits of pressure. This is known as the sense of
pressure.

What is the muscular sense?

Ey taking a body in the hand and raising it we feel a sense of
resistance in the muscles, by whose intensity we can much more
accurately determine the weight. This is the muscular sense. It
is developed to an exceedingly fine degree in some occupations ;
for example, postal clerks detect overweight letters with wonderful
accuracy and quickness.

What is the origin of the muscular sense ?

It has been urged that the muscular sense is of central origin,
and depends upon the strength of the impetus which must be
sent to the muscles to cause them to do certain work. It may,
however, be due to a training of the sensibility of the muscle,
whereby the relative strength of a contraction is perceived as a
sensation.

What is temperature sense?

The surface of the body is very sensible of temperature changes ;
and that this is distinct from ordinary tactile sensation has been
inferred from the fact that when the ordinary touch is blunted the
temperature sense may remain unimpaired.

Are the sensations of temperature accurate from a thermometric
standpoint ?

No. They are relative ; that is, we infer from the temperiiture
of the skin or of our habitual surroundings the warmth or coldness
of the thing tested. It is related that Arctic explorers have found
the water feel warm when swimming in pools on icebergs, and a
drop of the mercury to 80° F. is said to feel cold in torrid climates.
A more simple illustration is that of immersing one hand in water
at 40° F. and the other in water at 120° F., and then both in water
at 80° F., when one hand will feel hot and the other cold, though
both are subjected to the same temperature. Again, during a chill
the temperature of the body is often very considerably elevated,
and yet the sensation is entirely of cold.

150 THE SENSES.

May the temperature sense be educated ?

Yes. For example, a skilled bath-attendant is able to determine
with an astonishing accuracy the temperature of water by immers-
ing his hand.

Does the delicacy of the temperature sense correspond with that
of touch proper ?

Yes, in the main, but there are some situations in which the
skin is very thin, and the temperature sense is relatively much
more delicate than the tactile.

TASTE.
What conditions are necessary for the sense of taste ?

Aside from the conditions which are always necessary for sense-
perception — viz. proper organs for receiving, communicating, and
perceiving the sensory impulse — there must be present a sapid sub-
stance which must be in solution. The solution in the case of dry
substances is effected by the saliva. It is also necessary that the
surface of the organs of taste shall be moist.

Where does the sense of taste arise ?

Chiefly from the tongue, though there is some power to taste
resident in the soft palate, fauces, tonsils, and pharynx. In the
tongue the taste is more acutely developed in the posterior portion,
though in most the tip and sides are sensitive to taste. The cen-
tral portion of the dorsum is not an actively sensitive taste-organ.
The under surface of the tongue is little if at all sensitive to taste.

What nervous supply conducts the taste-sense ?

Probably the glosso-pharyngeal. The lingual branch of the
fifth (or gustatory) is also a conductor of taste-impressions for
the front of the tongue.

Describe, roughly, the tongue.

The tongue is a flattened muscular organ covered by epithelium.
It is controlled by intrinsic and extrinsic muscles, which give it a
remarkable flexibility of movement ; the latter for its larger, and
the former for its more delicate, actions.

What kinds of papillae characterize the mucous membrane of the
tongue ?
There are three varieties found, which are known as filiform^
fungiform, and circumvallate papillae. These are set chiefly upon

TASTE.

151

the dorsum of the tongue, and over its whole surface are numer-
ous mucous follicles, whose secretions keep the tongue moist
(Fig. 41).

Fig. 41.

A/.

Upper Surface of the Tongue.

Describe the filiform papillae of the tongue.

The filiform papUhr. are set mostly upon the middle of the
dorsum, but are scattered over the entire surface, and are far more
numerous than any other kind. They are conical in shape, and
are covered with epithelium, which projects in a brush-like tuft
from the apex. Their function is mostly tactile, and in animals,
especially of the cat tribe, arc very prominent.

152 THE SENSES.

Describe the fungiform papillae.

They are chiefly distributed over the sides and tip of the organ,
and sparsely upon the dorsum. They are larger at the surface
than at the base, club-shaped, and are supplied with blood-vessels
and nerves. Their funx5tion is probably sensory.

Describe the circumvallate papillae.

They are somewhat similar in shape to the fungiform, but con-
siderably larger. They are situated at the posterior portion of the
dorsum in a V-shaped arrangement, and number only eight or ten.
In the circumvallate papillse are the taste-goblets, or gustatory buds,
which are the form of nerve-ending characterizing the parts where
this sense is developed.

What other functions are dependent upon the tongue besides
taste ?
The sense of touch is very highly developed here, and with it
the sense of temperature, pressure, pain, etc. : upon these touch
and muscular senses to a great extent depend the accuracy of the
tongue in many of its important uses — speech, mastication, deglu-
tition, sucking. The tactile sense is very important, too, in the
sense of taste, for with many substances the taste is largely due
to their mechanical condition : this is the case with mucilaginous,
oily, and chalky tastes.

What relation has the sense of smell to taste ?

It is important, for with many substances — particularly aromatic
substances — of food and drink the association of smell and taste is
very essential to a thorough appreciation of a flavor. Most cooked
foods lose their savor if the nose is obstructed ; thus with a " cold"
in the nose " everything tastes alike."

What kinds of flavors are appreciated by the tongue ?

The principal tastes are sweet, bitter, acid, alkaline, and saline.
Besides these, the general sensibility of the tongue detects pungent
or caustic and styptic tastes, as well as the oily and mucilaginous
tastes.

What degree of taste-sensibility has the tongue ?

It is quite acute. A solution of acid or bitter substances is tasted
when very dilute : strychnine is said to be tasted in a 1 : 600,000
solution ; sulphuric acid, 1 ; 1000.

SMELL. 1 53

Wliat is after-taste?

After an aromatic substance has been tasted there remains in the
mouth an impression of that flavor, and if such substances be taken
in rapid succession, the appreciation of their flavor is lost. This
impression, which is left by a strong flavorris called the after-taste,
and is utilized sometimes to cover the taste of a disagreeable medi-
cine, a strongly-flavored aromatic preceding it.

Wiat influence upon taste has the muscular action of the
tongue ?
Twofcild. It breaks the food up more thoroughly by its pressure
against the walls of the mouth, and so brings it into a better con-
dition to reach the nerve-endings ; and it carries the food about the
mouth, so that the taste-organs are able to reach it readily.

SMELL.
What are the conditions necessary to the sense of smell?

The special organs for this sense for the reception, conduction,
and perception of the stimulus, as in the case of any of the senses,
must be in their proper condition, and a stimulus (an odor; must
be present to excite them.

What are odors ?

They are caused either by minute particles of solid matter or by
gases which are in the atmosphere, and they must be capable of
sohition in the mucus of the Schneiderian membrane. The sub-
stance must pass in a current of air through the nostrils or it is not
perceived as an odor. This is accomplished by " sniffing " the air,
and thus creating an intermitting current which is tested by the
olfactory sense. In this way a trace of a gas or impalpable powder
may be detected which cannot be traced by chemical or other means.
If the substance be applied as a solution, it is not detected ; thus,
rose-water in a nasal douche is not noticed while the nostrils are
full of fluid, and yet as soon as the nostrils are free the odor
appears.

Where is the organ of the sense of smell ?

In tlie mucous membrane of the upper part of the nasal cavity.
The olfactorj- nerves are the functional nerves of the sense, and are
spread out in a fine network (Fig. 42) over the surface of the supe-
rior or turbinated bone and upper portion of the middle turbinated
bone, and on the upper third of the septum. The nerves end in

154

THE SENSES.
Fig. 42.

Distribution of Nerves in the Nasal Passages : 1, olfactory bulb, with its nerves ; 2, nasal
branch of the fifth pair ; 3, spheno-palatine ganglion.

special end-organs, known as olfactory cells, whicli lie under tlie
ciliated epithelium of the part.

Describe the origin of the olfactory nerves.

The nerves arise from a mass of gray matter lying beneath the
anterior lobe of the brain upon the cribriform plate of the ethmoid
bone. This is the olfactory bulb, and it is connected by the
olfactory tract with the cerebrum.

Is tactile sensibility a property of the olfactory nerve ?

No. The lining membrane of the nasal cavity is very sensitive
to irritation, but the nasal branch of the fifth nerve and branches
from the spheno-palatine ganglion furnish the ordinary and tactile
sense.

Do the perceptions by the olfactory and by the nerves of touch
resemble each other?

Often they do, and some stimuli aifect both nerves. The com-
mon sensibility is evoked by such substances as are irritating and
acrid : ammonia gas has no odor, but it stimulates the mucous mem-
brane by its irritating properties. The tactile or common sensibil-
ities remain when the olfactory are gone. The relation between

HEARING. 155

<lio two kinds of porcoption is lost to us, and we speak of the smell
of ammonia or of aleoliol when it is probably not an olfactory, but
a sensory, perception.

Is the sense of smell very acute ?

Vi's, but not so sharp in man as in many of the lower animals.
Tlu" distribution of the olfactory nerves is much wider in some of
the animals, and the cerebral development is correspondingly in-
creased. In man the range of susceptibility is, however, probably
greater. The variety of odors and the very minute quantity of
stimulant substance required to produce a sensation of smell are
quite wonderful. The most delicate analysis may fail to show
traces of the substances which can be appreciated by the sense of
smell.

Is the same odor agreeable to all men?

No. There are some odors pleasant to some which others find al-
most intolerable. Musk, for example, is a pleasant perfume to some,
while to others it is quite unendurable. In the same way, the
acuteness of this sense in some is more marked than in others, and
yet this may apply only to certain kinds of odors.

Is sneezing a reflex from the olfactory nerve?

Xo. It is excited through the fifth.

Are hallucinations of smell common ?

They often occur, and in cases of disease of the olfactory centres
there is often complaint of a constant bad smell. With normal
organs there may be a sensation of an odor which cannot be de-
tected by others present.

HEARINa.
How does the auditory or eighth cranial nerve originate?

The fibres arise from a nucleus of gray matter in the floor of the
fourth ventricle, and from this source pass out through the sub-
stance of the medulla in a number of small bundles which unite
with another root from the crrchdJinn to form a trunk. This passes
with the facial nerve into the internal auditory canal, and terminates
in special end-organs in the internal ear.

Describe, roughly, the auditory apparatus.

It consists of (1) the external ear; (2) the middle ear; and (3)
the internal ear.

156 THE SENSES.

What is the function of the external ear ?

It serves to receive tlie sound-waves and to indicate the direction
from which they come in animals who possess the power of moving
the organ. Through the external auditory canal the sound-waves
are conducted to the middle ear.

Describe the middle ear.

It is a cavity in the temporal bone which is shut off from the
external auditory canal by the tympanum. The Eustachian tube
connects this cavity with the pharynx. The lining of the middle
ear is ciliated epithelium, continued from the mucous membrane of
the pharynx through the Eustachian tube. There are two openings
of importance — the fenestra rotunda and the fenestra ovalis — in the
bony wall, but they are covered, the former by membrane, the latter
by the stapes. There is a chain of small bones (ossicles) which
connect the tympanum and the fenestra ovalis.

What is the tympanum?

It is a tough, tense, fibrous membrane set in the bony opening
of the external auditory canal. The degree of tension of the tym-
panum is regulated by the tensor tympani muscle.

Fig. 43.

Right Temporal Bone of the New-born Infant, seen from its inner side, showing the mem-
brana tympani and chain of bones in their natural position (Rudinger).

What is the function of the ossicles ?

They are three in number, and are so articulated as to commu-

HEARING.

157

nicate the vibration of the tvinpuiiuiii to the internal car (Fipj. 48).
The liaiulle of" the maUeus is attached to the tynipaiuuu, so that
this bone moves with each vi))ration. This motion is communi-
cated to the incus, whidi passes it on to the stapes. The stapes
I'nrms a sort of ])istoii in tlie foramen ovalis, and is therefore capa-
ble of transmitting to the fluid in the cavity of the labyrinth the
impulses which it receives.

Describe the arrangement of the internal ear.

The internal ear, or labyrinth, is situated in the dense petrous
portion of the temporal bone, and consists of three essential parts :
the vestibule (Fig. 44), and opening
from it the semicircular canals and the
cochlea. There is another opening,
the jequeductus vestibuli, whose use
is unknown, and still others for the en-
trance of the auditory nerve-filaments.
Within the bony structure is a mem-
brane of fibrous and epithelial tissue,
the membranous labyrinth, which fol-
lows the bony structure and contains
a colorless fluid, the endolymjjh, and a
fluid stirrounds this membranous laby-
rinth, the perilymph.

What is the fiinction of the semicir-
cular canals?
These canals are arched cylindrical
spaces in the solid bone which open at
each end of the arch in the vestibule.
They are three in number, and two
are nearly vertical and one is horizontal
in such a manner that the planes of the two vertical canals are at
right angles, one being fore and aft, and the other transverse (Fig.
44). Their use does not seem to be directly connected with the
auditory function of the part, but to be connected more with the
sense of equilibrium. The movement of the fltiids in the canals,
arranged in the directions of the three dimensions, may serve to
produce sensations which lead to the formation of accurate judg-
ment of changes in the position of the body.

What is the cochlea?

It is a part of the labyrinth which derives its name from its

External View of a fast of the Left
Labj-riuth (Heiile) : /, fenestra
cochleie, or round window ; a,
fenestra vestibuli, or oval win-
dow ; 6, ampulla of superior semi-
circular canal ; d, common shaft
of union of these two canals; e,
ampulla of the horizontal semi-
circular canal ; g, tractus spiralis
foraniinosus.

These canals are arranged

158

THE SENSES.

resemblance to a snail-shell. It is divided into two parts, by bony
and membranous structures, which run parallel from base to apex
of the spiral (Fig. 45). The upper passage opens into the vesti-

FiG. 45.

Bony Cochlea of the Human Ear, right side, opened from its anterior face (Cruveilhier).

bule, and is known as the scala vestibuli ; the lower, the scala
tympani, is shut oif by a membranous partition, which covers the
foramen rotundum. from the cavity of the tympanum. The scala
vestibuli is subdivided by a fibrous membrane (of Reissner) which
passes from the bony lamina spiralis to the wall of the scala ves-
tibuli, shutting off a triangular space (canalis cochlearis). The
floor of this space is the membranous partition (membrana basi-
laris) which separates the scala tympani from it, and upon this
membrane is the organ of Corti.

What is the function of the cochlea ?

It is to spread out, over as large a surface as may be, the mech-
anism for the reception of sounds by the organ of Corti, the end-
organ of the auditory nerve. It seems to be especially well adapted
for this purpose, because the solid spiral lamina connects it with the
bony framework of the skull, while it is contained in the mem-
branous labyrinth, whose fluid contents fit it for the response to
vibrations. It is further insulated by its suspension in the peri-
lymph. These peculiarities favor the conduction of semi-vibra-
tions through the bone, as well as of vibrations through the
mechanism of the middle ear.

HEARING. 159

Describe the organ of Corti.

l']i(iii (he hasihir iiu'iiiliraiic is arranged ;i S(!rlcs of rafter-like
bodies which roof in ;i small canal (Fig. 40) : upon this are spread

Fig. 46.

t

I'iagrainalic Sfi'tiou of the Org;in of Corti: 1, iiieiubrana basilaris ; 2, 3, internal aud
exlorual libres of the arch; 4, eiiitheliuiii cells uear its inner and outer borders;
5, Hair-cells lying in contact with the arch (magnified 500 diameters).

the functional nerve-endings of the auditory nerve. They are
large nucleated cells, the rods of Corti, having hair-like processes
which project into the canalis cochlearis or scala media. When
looked at from above the cells have an appearance similar to the
keyboard of a piano. Fibres of the auditory nerve spread to these
cells from the bony lamina spiralis.

What peculiarity of structure of the auditory nerve is noteworthy ?
Its hbres are non-medullated, and it contains numerous ganglion-
cells. In the cochlea there are many of these cells, and they form
plexuses of nerve-fibres to supply the hair-cells. The absence of
neurilemma in the auditory nerve gives it a soft feel which has
caused the name " portio mollis " to be given to it when it and the
facial are considered as a single nerve.

What is the physiological action of the organ of Corti ?

It is probable that each of the functitnial cells in the organ of
Corti responds to a particular shade of sound. How this occurs is
not understood, but the vibrations of the tympanum arc communi-
cated to the stapes by the other ossicles ; and these cells seem to be
able to respond each to a particular tone by its sensitiveness in
selecting its particular rate of vibration.

What is the musical range of human hearing ?

About seven octaves. There are about three thousand hair-cells
in the organ of Corti, and it will be easily seen that this would
allow an enormous capability to differentiate sounds and musical
tones.

160 THE SENSES.

What subjective sensations of hearing occur ?

They may be due to disturbances of the auditory apparatus or
to abnormal conditions of surrounding organs. Thus, buzzing or
ringing in the ears may result from the hypersemia of the parts
and exaggerated rush of blood, or from a defect in the circulating
apparatus (as by an aneurism), or from disease in the auditory
nerve or some other portion of the apparatus. Hallucinations of
hearing are very common among the insane.

How is the voice produced?

The vibration of the vocal cords is produced by the passage of
the air in expiration, never naturally in inspiration. The quality
of the voice as regards pitch depends upon the length of the vocal
cords, the crieo-thyroid muscles acting to increase the tension,
vrhile the thyro-arytenoid relax the cords and the crico-arytenoids
dilate and contract the rima glottidis. Falsetto and high-pitched
notes in a naturally low-pitched voice are due to vibration at the
edges of the cords. The hollow spaces about the oral and nasal
cavities are of use as resonators or sounding-boards.

What organs are used in the formation of articulate speech ?

The tongue and teeth in the formation of the Unguals and den-
tals, the nasal sounds by the cavity of the nose ; the other sounds
are formed largely by modifications in the shape of the mouth in
one or another part.

What range has the human voice in respect of pitch ?

From one to three octaves : in this cultivation and natural apti-
tude are factors which permit great variability. The total range
of the human voice from the highest soprano to the lowest bass is
about four octaves. Thus it will be seen that the range of sounds
which can be appreciated by the ear is far beyond the capacity of
the voice.

SIG-HT.

What is the function of the eye ?

The reception of stimuli of light, whereby we are able to per-
ceive the impressions of form, color, and conditions of our sur-
roundings in infinite variety. It is far the most complex in
structure of any of the organs of special sense, and the most rapid
and delicate in its actions.

SIGHT. 161

What is the origin of the optic or second cranial nerve ?

It arises l»y two roots — oiiu in the corpora (|uadrigeiiiiiia, and the
other in the optic thahimus — with many fibres derived from centres
of vision in the posterior portion of the cerebral lobes. These
fibres unite and form a nerve-trunk (the optic tract) which en-
circles the crus cerebri, meeting the tract of the opposide side just
in front of the pituitary body. Here there is a fusion of the two
optic tracts in a partial decussation, some fibres going to the eye
of the same side, and some decussating. The fibres then pass to
each eye as the optic nerve, which is distributed by special nerve-
endings in the retina.

Has the optic nerve any other physiological property than that of
conduction of special-sense impulses ?
No. Tt has no common sensibility. It is, however, the con-
ductor of afferent impulses for the iris reflex.

What is the effect of stimulation of the divided optic nerve ?

None, for the peripheral end ; for the central portion, a sensation
of light and contraction of the pupil.

What accessory apparatus is important to the protection of the
eye?
Eyelids and lachrymal gland.

Describe the eyelids.

Each eye has two lids, an upper and lower. Each consists of a
thin plate of elastic tissue with a covering of loose skin and a
smooth lining of mucous membrane — the conjunctiva — which is
reflected upon the eyeball. Along the edges of the lids are a
number of short curved hairs which screen the eye from foreign
bodies. The extreme sensitiveness of the conjunctiva helps in
this by giving immediate warning when any foreign substance
gets in the eye.

What is the lachrymal gland?

Tt is a small racemose gland lodged in the upper and outer part
of the orbit. It has several ducts, which lead to the surface of
the conjunctiva of the upper lid. The secretion of the gland is
usually just sufficient to keep the eye moist, but under the stimu-
lus of pain or intense emotion the secretion is increased, and ap-
pears in drops which flow from the eyes — tears. Under ordinary
circumstances a slight excess of this moisture is drained into the

11— Phy.

162

THE SENSES.

nasal cavity by the lachrymal duct. This secretion is slightly
alkaline, and contains about 1 per cent, of solids, chiefly sodium
chloride.

What are the Meibomian glands ?

They are a number of small racemose glands, lying beneath the
conjunctiva, which secrete an oily protective substance. The ducts
of these glands open along the edge of the lid.

Describe the eyeball.

It consists of a tough, opaque globe (Fig. 47), having a some-

FiG. 47.

Horizontal Section of the Eight Eyeball: 1, optic nerve; 2, sclerotic coat; 3, cornea;
4, canal of Schlemm ; .5, choroid coat; 6, ciliary muscle; 7, iris; 8, crystalline lens;
9, retina; 10, hyaloid membrane; 11, canal of Petit; 12, vitreous body.

what more sharply-curved translucent portion, the cornea, at the
front. It has in the anterior portion a lens^ and in front and
behind this are chambers which contain fluids : the one in front is

SIGHT.

163

[■

the anterior chnmher, and contains the aqueous fluid, while the
posterior is the vifreotts /iiniinr. These structures fill the eyeball
and give it a tense feel to the touch.

What are the coats of the eyeball ?

(1) Tlu! .«/iiii. or sc/<r"fic eodt, is external, and covers about
live-sixths of the globe. The cornea is continuous with it in front.
It is composed of tough white fibres arranged in interconinumi-
catiug layers. (2) The choroid coat is very vascular, being com-
posed of a mesh of capillaries. There
is outside of this a layer of connective Fig. 48.

tissue containing pigment-granules.
(3) The retina, which is the seat of
the end-organs of the optic nerve.

Describe the retina.

It consists of the nervous mechanism
of the eye lying in a loose connective
tissue, and beneath it n 2'>igment-Iayer.
Without entering into the details of
its numerous layers, we may say that
the fibres of the optic nerve spread
out, divested of neurilemma, in this
membrane, and communicate with
ganglion-cells, which are abundant.
The fibres pass inward and terminate
in the layer of rods and cones which
form the end-organs of the nerve.

Describe the rods and cones of the
retina.

They are closely packed at the sur-
face of the retina, the rods being the
more numeroiis in most situations.
The cones seem to be modifications ,. ^v^ -

of the rods, and their office is essen- SfCt^Jn'^^^f^^s^
tially similar. The rods (Fig. 48) are
straight cylindrical bodies of a trans-
parent substance, and are placed par-
allel to one another and perpendicular
to the surface of the eyeball. In length they are about five to seven
times the diameter of a red blood-corpuscle, and in diameter about

Diagrammatic Section from the pos-
terior Portion of the Human Ret-
ina: 1, layer of rods and cones;
2, layer of" nuclei (Schultze).

164 THE SENSES.

one-twentieth of their length. The cones are very similar, except
that their conical shape makes them appear to be of different cha-
racter. The cones do not always reach to the same level as the
rods. When viewed from the retinal surface, the ends of the rods
and cones give the appearance of a fine mosaic. These organs are
connected with the subjacent nervous tissue, but the mode of their
connection with the optic nerve is not fully understood.

Considered as an apparatus, how is the eye arranged?

It may be compared to the photographic camera. It contains vari-
ous media for the refraction of light, and a screen at the back for
receiving the image. The refracting media are the cornea, aqueous
humor, crystalline lens, and the vitreous humor : the screen is the
retina. The pigment of the retina and choroid makes the interior
dark, a necessary feature in such an apparatus. The mechanism of
the lens enables the eye to be focused for distance, while the iris
regulates the proper admission of light.

What is the structure of the cornea ?

It is continuous with the sclera in the front of the eye, and
occupies about one-sixth of the surface (3, Fig. 47). Its shape is
that of a small dome set upon the globe of the eye. It has in
front several layers of epithelial cells, and at the posterior surface
a thin epithelial lining (membrane of Descemet) ; but the main
body of the structure consists of interlacing connective-tissue fibres,
which have spaces in which are found branching cells peculiar
to the structure. The cornea is perfectly transparent : it has no
blood-vessels.

Describe the crystalline lens.

It is a double convex lens (8, Fig. 47) of high refractive power
which is suspended in the anterior portion of the eye immediately
behind the anterior chamber. Its function is to bring the rays of
light to a focus upon the retina. In structure the lens is com-
posed of concentric layers of long, slender fibres enclosed in a thin
capsule.

What are the aqueous and vitreous humors ?

(1) The aqueous humor is a watery fluid contained in the
anterior chamber. It acts with the cornea as a refracting medium
to concentrate rays of light upon the lens, to maintain the globular
form of the cornea, and to float the iris and allow it freedom of
motion.

SIGHT. 165

(2) The vitreous body (or humor) is a semifluid gelatinous
substance which fills the posterior chamber and constitutes about
four-fifths of the bulk of the eye. It is quite transparent, and
acts to maintain the tension of the eyeball, and as a refracting
medium through which the light reaches the retina.

What is the pupil?

The pupil is the aperture through which light enters the dark
chamber of the eye. It is a circular opening in the iris.

What is the iris?

It is a curtain of muscular tissue placed vertically in front of
the lens. The fibres of the muscular tissue are both circular and
radiating, so that they serve to decrease and increase the size of
the pupil as one or the other set of fibres acts. It has a pigment-
layer upon the inner surface, which is continued from the choroid,
and upon the amount of the coloring-matter depends the " color of
the eyes."

What nervous action controls the ciliary muscles?

Contraction or dilatation of the pupil is a reflex act, and the
afferent stimulus is carried through the optic nerve and the motor
through the third cranial nerve, acting from a centre just beneath the
aqueduct of Sylvius and the corpora quadrigemina. The increase
in the amount of light which reaches the retina causes a contrac-
tion of the pupil, and a decrease is followed by dilatation. Aside
from this, the needs of the eye regulate the amount of light ; thus,
for near work the pupil contracts, and dilates when the eye is
focused upon a distant object.

What other influences control the iris?

The pupil is controlled also through the sympathetic, and the
fifth nerve through the connection of the third and fifth nerves
with the ciliary ganglion of the sympathetic system. Drugs are
active also, both locally and internally, in controlling the action of
the iris without reference to the reflex fibres : atropine both locally
and internally dilates the pupil ; opium internally, and eserine locally
contract it.

What is accommodation in vision?

The eye is able to see objects close at hand and at a distance
with equal clearness, though perhaps not with equal regard for the

166 THE SENSES.

minuter details. This is known as tlie accommodation of the eye.
In optical instruments this j)rocess of accommodating the instru-
ment to the focal distance is called focusing. So is accommodation
an automatic focusing of the eye.

How is accommodation effected?

By the ciliary muscle. The crystalline lens is suspended in its
capsule by the suspensory ligament, and this is controlled by the
ciliary muscle. At rest the eye is focused for seeing at a distance,
and the lens is held somewhat flattened by the tension of the sus-
pensory ligament. When focusing upon a near object the ciliary
muscle contracts, and the lens is permitted to project more as the
tension of the ligament relaxes.

What is the near-point?

It is the nearest point to the eye at which vision is distinct, the
shortest focus of the crystalline lens. It is usually about 5 or 6
inches.

What is an emmetropic eye ?

It is the normal eye ; that is, an eye in which parallel rays or
rays from objects at a distance are focused upon the retina without
an effort at accommodation. Such a distance, for practical pur-
poses, is considered to be any point beyond 20 feet. Absolutely
emmetropic eyes are not common.

What is myopia ?

Near-sight. In this case the rays from a distance are focused in
front of the retina, and the image is blurred. Such an eye is per-
manently focused for near objects.

How is myopia produced?

In two ways, by the antero-posterior diameter of the eye being
too great, or by the convexity of the lens being exaggerated. In
either case the focus of the lens will fall in front of the retina.

How is myopia corrected?

By the use of a concave lens which diverges the rays, and in this
way prevents their coming to a focus too soon. Such glasses are
seldom needed except for distant vision.

What is hypermetropia ?

Far-sight. In this case the lens focuses behind the retina iia

SIGHT. 167

near vision, and the image is blurred as in myopia for distant
vision.

What are the causes of hypermetropia ?

Shortening of the antero-pusterior axis of the eye or abnormal
flattening of the lens, Avliich does not allow accommodation for near
vision.

How is hypermetropia corrected ?

By the use of convex lenses, which add to the refractive power
of the eye.

What is astigmatism?

A defect in the vision due to the irregularity in the globe of the
eye, whereby the diameter in one plane is greater than in another.
Thus, the retina may be an uneven surface, and the image focus
accurately in one part and falsely in another. In this condition
vertical and horizontal lines are not seen with equal distinctness.

How is astigmatism corrected?

By the use of cylindrical or prismatic glasses, which have to be
accurately adapted to the needs of each case. This error, if seri-
ous, is usually combined with other defects of vision, frequently
myopia.

What is presbyopia?

Defective vision due to the loss of power in advanced years. The
elasticity of the lens becomes less, and the convexity cannot be in-
creased for near vision. The ciliaiy muscle may also be weaker
and aid in the production of the error. A weak convex glass com-
monly corrects the lack of refraction-power.

Is the eye achromatic?

Yes. It may, however, be said that there may be a visible band
of color seen by some defective eyes where there is considerable
fault in the focus of the image on the retina.

What is the " blind spot " ?

The point of entrance of the optic nerve is not sensitive to light,
and at this point an image thrown upon the retina is not seen ;
therefore it is called the blind spot.

How is the blind spot demonstrated?

If the left eye is covered and the right directed steadily upon

168 THE SENSES.

the cross in Fig. 49, the circular spot will be visible at the same
time, though less distinctly. As the book is moved slowly back-
ward and forward, a point will be found at which the round spot

Fig. 49.

disappears, reappearing as the book is held nearer or farther or as
it is inclined in either direction and the image is carried away from
the blind spot.

What part of the retina possesses the most acute vision ?

The portion directly behind the lens, where the mi.cula lutea (yel-
low spot) with its central depression (fovea centralis) is situated.
Here are found none of the fibres of the optic nerve, but a great
increase in the number of the cones of the layer of rods and cones,
as well as an increase in their size. In looking at any object it is
upon this spot that its image is reflected by the media, and here
the power of the end-organs of the optic nerve is most highly
developed.

What conclusion is drawn from these facts ?

That the rods and cones (more especially the cones) are the
physiological agents for the reception of light stimuli : for upon the
blind spot is no layer of the rods and cones, while in the point of
sharpest sight the nerve-fibres are wanting, and these elements are
especially prominent.

What is the duration of visual sensations ?

The duration of a visual sensation is always greater than that
of the stimulus which has caused it. However brief the luminous
impression, the effect on the retina lasts about one-eighth of a sec-
ond. The spokes of a rapidly-revolving wheel for this reason do
not appear as spokes, but as a solid mass, each following one
another so rapidly that one impression cannot fade before another
has replaced it.

SIGHT. 169

What is the retinal red?

When tlio retina (»f a recently-killed animal is examined it is
colorless, but during life or if extracted without exposure to light,
it is of a purple-red hue, and the color is found in the rods of the
retina. It is derived iVom the pigment of the deeper part of the
retina. It is the "■ retinal red " or '• visual purple," as it is variously
named, which one sees in the reflex of the retina.

What effect has exposure to light upon the retinal red?

It destroys it, and for this reason it was long unknown. It dis-
appears after a brief exposure to sunlight, about half a minute.

How may the retinal red be seen?

By throwing a beam of light into the eye by a mirror, as by the
ophthalmoscope, a red glow is observed in the pupil. This is called
the retinal reflex.

What are optograms?

Pictures which appear upon the retina after exposure to light.
They are due to the fact that an exposure to light bleaches the
retinal red, leaving it dark in the shaded portions.

How are optograms obtained?

The eye is removed from an animal in a dark room and kept in
a covered box until exposed to a brightly illuminated skylight or
window for some minutes. The eye is then replaced in the dark
room and the retina examined. It will be found that the panes of
the window are shown in light color, while the sash is in dark out-
line. This soon fades on exposure to daylight, but if the retina is
dried in the dark the optogram is much more durable.

Is the pigment of the retina essential to vision ?

iNo, but it is of considerable use in rendering the eyeball a dark
box. which is of importance here as in all optical instruments.

How is the real image formed by a double convex lens?

It is an inverted imago at the point of focus of the lens if the
luminous object is placed at a distance (Fig. 50). Referring to
this figure, it will be seen that the rays originating at A will be
twice refracted, once by the lens and again in leaving it, so that all
rays from A reaching the lens are joined at a. The same is true for
B and h. Therefore a screen placed at the focus, F, will receive an
inverted image, a b, of the luminous object,^V B.

170

THE SENSES.
Fig. 50.

Formation of Image by Convex Lens.

Does the crystalline lens throw an inverted image upon the
retina ?
Yes. This may easily be demonstrated by looking at the image
from behind a fresh eye of an albino animal (white rabbit) or if
the sclera be thinned.

How is this inversion corrected?

The correction is made by the brain in its perception of the image.
It is an act of mental and not of physical origin. Thus, objects
which are projected upon the left of the retinal surface look to be,
as they are, on the right of the body ; and so with all the direc-
tions : the inversion of the retinal image is corrected by the mind.

What other visual perceptions are the result of mental processes ?

We are able to estimate by the aid of the brain the size, direc-
tion, distance, form, and speed of motion of a thing which we have
seen. All of these are judgments based largely upon previous
experience. All of these deductions are liable to error by reason
of faulty judgiuent or faulty vision, but this is the usual method
of forming such estimates.

How does the eye perceive colors ?

It is probable that particular rods and cones are capable of re-
sponding to rays of light of a certain wave-length, and to those rays
alone. It is well known that the rays of red light are of a certain
length of vibration. The same is true of yellow and of green rays.
We can conceive that each primary color has its own set of cones
and rods capable of responding to its stimulus, and that by combi-
nations of these stimuli the complementary colors and variations of
shade may be perceived by the resulting stimuli acting upon the
brain-centres. Such teaching is, of course, speculative, but this is
one theory which has acceptance.

SIGHT. 171

What is color-blindness?

All iiialiility tu perueivc some colors. The colors which are
usually mistaken are green and red. Frequently it is found that
a distinction cannot be made between these colors. This is some-
times known as Daltonism.

What is the cause of color-blindness ?

It is probably due to the absence of the rods and cones which
are capable of responding to the stimulus of rays of a certain wave-
length.

Is this an important defect?

Yes. In marine and land locomotion red and green signals are
used to indicate opposite conditions, and the failure to distinguish
them has freciuently been the cause of serious accidents.

How is color-blindness tested?

By laying a number of skeins of yarn of various colors in a
heap, and requiring the person to be tested to select all resembling
a certain skein from the hea}).

Do the eyes act both at once, or do we see with one at a time ?

AVe use both m ordinary vision at the same time.

What is diplopia?

It is the condition which results from a want of harmony in the
eyes, so that the image of each eye is perceived separately ; that
is, one sees double.

What are the common causes of diplopia ?

Paralysis or spasm in one of the lateral straight muscles, which
does not allow the eye to be turned in harmony with the other.
If the eyes are turned so that the axes of vision are separated, the
condition is known as external strabismus or squint ; if the axes
are crossed, it is called internal strabismus or cross-eye.

What benefits result from binocular vision?

'{'he ideas of form and distance are much more correctly judged
liy the perceptive fiiculties. This is due to the fact that the object
viewed is seen beyond its equator, so to speak, by each eye. and
the combined image is therefore less flat in appearance than in
monocular vision.

172 THE SENSES.

What instrument is devised to take advantage of this ?

The stereoscope. In this instrument two photographs are taken
hy cameras so placed as to represent the position of the eyes in
vision, and the two views of one object are then superimposed by
the use of prisms.

What determines the clearness of vision ?

The space between the cones in the point of clearest vision, the
macula lutea. It has been calculated that an object must sub-
tend an arc of at least 60 to 70 seconds in the field of vision to be
clearly seen. Such an object makes an image of about -12-5^^-0* of
an inch in the retina ; and this is about the distance between the
cones at the macula lutea. Similarly, two points to be clearly
distinguished must be separated sufficiently to allow this amount
of separation in the retinal image.

What are after-images?

It has already been noted that vision lasts longer than the
stimulus which excites it. Under some conditions it may last
a perceptibly long time : it is then known as an after-image.
If one looks at an intense light, the sun, the sense of light remains
for some time in the eye. Similarly, if one looks intently at a
white spot on a black background, and then turns to a white
surface, one has the image of a gray spot. The first of these
conditions cited is known as a positive after-image, and the latter
as a negative. In the first case the phenomenon results in a con-
tinuation of the same sensation, and in the latter a new perception
results.

What peculiarity do the after-images of colored objects present ?

They appear to have the complementary color of the original
object; thus, green excites a reddish after-image; orange, blue;
and so on.

How are after-images explained?

They may be explained as a result of exhaustion. The part of the
retina on which the image has fallen becomes tired, and when the
eye is turned upon a white ground, the white light coming to the
retina does not produce as much sensation in the tired portion.
The colored negative after-images may be similarly explained.

* Variously estimated at 12^ 00 to ^oVo of an inch.

EMBRYOLOGY. 173

EMBRYOLOGY.

REPRODUCTION.
What is a species?

It is a class of organized beings in which the individuals
composing it die ott", but which nevertheless repeats itself and
maintains its complement by the continued accession of similar
forms.

What is reproduction?

It is the process by which a species is perpetuated, notwith-
standing the limited existence of the individual members.

What law governs the reproduction of species ?

The young are of the same kind as their parents. By this law,
which is so commonly observed as to seem a truism, is maintained
the anatomical identity of individuals of a species, as well as the
physiological fact of an unbroken continuance of the species by
reproduction.

What is sexual generation?

It is reproduction of a species by a union of elements produced
separately by the female and the male. The female produces the
ovum, or egg, which is capable of being developed into a living
offspring only when it is fecundated or impregnated by the seminal
or spermatic element from the male.

What are the organs of generation of the female ?

They consist of two ovaries, in which the ova are formed, and
their oviducts or Fallopian tnhes, which carry the ova to the womb,
in which they may develop if fecundated by the male ; and the
vagina for the reception of the male organ in copulation and for
the subsequent discharge of the foetus (Fig. 51).

Describes the ovaries.

They are two organs lying one on each side of the uterus, in the
folds of the broad ligament. In size they are about l-l in. long, 1
in. wide, and •] in. in thickness. Besides lying between the layers
of the broad ligament, they are stayed in their position by an at-
tachment to the fundus of the uterus and to the fimbriated extrem-
ity of the Fallopian tube.

174

EMBRYOLOGY.

What is the minute structure of an ovary ?

It may be described as a ductless gland in which the component
elements are (1) a stroma of connective tissue and unstriped mus-

Generative Organs of the Human Female : «, a, ovaries ; 6, 6, Fallopian tubes ; c, body of
the uterus ; d, cervix ; e, vagina.

cle-cells, and with them a great number of peculiar spindle-shaped
branching cells ; and (2) the glandular portion, characterized by
the Graafian follicles.

What are the Graafian follicles?

They are best observed during the childbearing age. They lie
in the periphery, and present various appearances as they are more
or less matured. Some are large enough to be seen by the unaided
eye, while others are very minute. In the matured follicle the in-
terstitial tissue will be found to have collected in a wall, quite well
defined, which is lined by an epithelial layer ; and upon one side
this epithelium is heaped up into a mass, the germ-Mil (cumulus
proligerus), which contains the ovum. The remainder of the fol-
licle is filled with a colorless fluid.

How does the ovum leave the ovary ?

As the Graafian follicles mature, they approach, and often pro-

REPRODUCTION.

175

Fig. 52.

ject above, the surface of tlie ovary. The fluid contcnt.s of the
follit'Ie increases and the wall jjecoiues
thinner over it, until finally it bursts,
and the ovum with some of its sur-
rounding epithelium escapes.

What peculiarity of the ovary favors
the escape of the ovum?
Tlie ovary is covered with a thin
layer of epithelium (^tlie germinal epi-
fhcluini), and not by the serous mem-
brane which lines the abdominal sur-
f\ices of the rest of the viscera. This
is of great importance in the life of
the ovum, for it renders it possible for
it to enter the orifice of the Fallopian
tube without interfering with the peri-
toneum and without having to pass so
dense a structure. .

Fig. 53.

Human Ovum, rui)fured by
Pressure, showing tlie vitellus
partially expelled, the gernii-
native vesicle, with its germi-
uative spot, at a, and the
smooth fracture of the vitel-
line membrane.

Section of the Ovary (after Schron) : 1, outer covering; 1', attached border; 2, central
stroma; 3, peripheral stroma; 4, blood-vessels ; 5, Graafian follicles in their earliest
sta^e ; 6, 7, 8, more advanced follicles ; !), an almost mature follicle ; 9', follicle from
which the ovum has esciped ; 10, corpus luteum.

Whence is the ovum derived?

It is a very highly developed cell, wliich is derived from the
germinal epithelium covering the ovary. In the development of
the ovary this epithelium dips into the surface of the organ, and a

176

EMBRYOLOGY.

certain portion is finally walled off by growth of the surface cells.
Thus a ball of epithelial cells is introduced into the body of the
organ, and one cell develops the ovum, the rest going on to make
up the Graafian follicle and the trerm-hill. (See 5, 6, 7, 8, 9,
Fig. 53.)

Describe the ovum.

It is a minute globular cell containing a nucleus and nucleolus.
In diameter it is a little less than y^g in. (Fig. 54).

Fig. 54.

Semi-diagrammatic Representation of a Mammalian Ovum, highly magnified : sp, zona
pellucida; vi, vitellus ; gv, germinal vesiale; ffs, germinal spot.

What is the zona pellucida or vitelline membrane?

It is a thick hyaline membrane (cell-wall) which encloses the
cell.

What is the vitellus ?

It is a granular protoplasm which makes up the cell-body.

What is the germinal vesicle ?

It is the nucleus of the cell ; a somewhat large, transparent, and
well-defined body set somewhat eccentrically in the vitellus — the
yolk of the egg.

What is the germinative spot ?

The nucleolus of the cell. In addition to the nearly transparent

REPRODUCTION. 177

fluid which the nucleus contains, there is a small dark, almost
opaque spot, the germinal spot of the ovum.

Do all the Graafian follicles develop ova?

No. From puberty to the menopause the formation of new
Graafian follicles is continuous, and a very great number are pro-
duced, but many do not develop ova, and so waste away without
going through the changes described.

Describe the Fallopian tubes.

These tubes ai-e about 82 inches in length, and extend from the
fundus of the uterus laterally on each side. The calibre of the
tubes gradually narrows from without inward, until at the uterus
the opening is very minute. The external covering is peritoneum,
but the lining is of mucous membrane, having ciliated epithelium.
The outer end of the Fallopian tube is free and fringed — the fimbri-
ated extremity.

What is the function of the fimbriated end of the Fallopian
tube?

To grasp the ovary during sexual excitement and prevent the
escape of an ovum which may extrude — the " morsus diaboli."

What is the use of the ciliated epithelium ?

To carry the ovum to the uterus. This is also accomplished by
the action of the circular and longitudinal muscular fibres.

Describe the uterus.

It is a somewhat pear-shaped organ, and is about 3 in. in length,
its wider part being about 2 in. wide and the cervix 1 in. It is
described as consisting of a fundus, body, and cervix. The body
unites the fundus with the cervix, which extends into the vagina.

What structures compose the uterus?

It is covered over nearly all of its external surface by (1) peri-
toneum. Its bulk is made up of unstriped (2) muscle, which oc-
curs in longitudnal and circular bundles and layers. This muscu-
lar tissue increa.ses enormously during pregnancy, and by its
strength helps to extrude the foetus. Tlie lining is of (3) mucous
mcralirane, which is formed in its superficial layer of ciliated
columnar epithelium. In the mucous membrane of the cervix are
a number of follicles which secrete a viscid, tenacious mucus, by
which the os uteri is frequently found to be plugged.
12— Phy.

178 EMBRYOLOGY.

Describe the vagina.

It is a membranous canal about 5 in. long, extending from the
uterus to the external genitals. It is lined with mucous mem-
brane, which in the ordinary contracted state is thrown into folds,
its anterior and posterior walls being in contact. There is consider-
able erectile tissue in the mucous membrane. At the orifice of the
vagina externally is a sphincter which only partially contracts it,
and besides this there are longitudinal and transverse unstriped
muscle-fibres in the submucous tissue. The outlet of the vagina
is sometimes also partially closed in the virgin by the hymen, a
fold of mucous membrane.

What are the external organs of generation ?

The external organs of generation are not immediately connected
with the function of reproduction, and may be enumerated as the
labia majora and minora, clitoris, and the meatus urinarius.

What are the organs of generation in the male ?

The two testicles which produce the seminal fluid, and the vas
deferens; or duct leading from each to the seminal vesicles, where
the secretion is stored until it is discharged through the penis.

What is the structure of the testicles ?

Each testicle is made up of a dense connective-tissue framework
and a secreting portion. The connective-tissue stroma, tunica albu-
ginea, surrounds the outside of the organ, and sends incomplete
partitions into the central portion of the organ, dividing it into a
number of communicating cavities. In these cavities are winding
tubules which constitute the secreting portion of the organ. These
tubules inosculate in a sort of mesh (reti testis), and finally all
unite in the epididymis. The secreting tubules are called the
seminiferous tubules.

How do the seminiferous tubules secrete the spermatic fluid?

Each tubule has, in the active organ, a limiting membrane, upon
which are a number of layers of flattened cells. Internal to these
are seminal cells in two or more layers. The seminal cells contain
nuclei which are capable of division, so that each nucleus may de-
velop several new nuclei. The nuclei are the spermatoblasts, or cells
from which the spennatzoa originate. The cells before the division
of the nuclei resemble the oi'dinary cuboid epithelium, and it is in
the superficial layers (i. e. toward the lumen of the tubuli) that
this function of tlae cells takes place.

REPRODUCTIOlf.

179

Fig. 55.

How is the seminal fluid conveyed from the testis?

The .SL-miiiiitjruu.s tubules all cuiivergc toward the epididymis,
a tortuous tubule which is lined with mucous membrane, and lies
beside the testis in a long, convoluted mass which may be unrav-
elled, and is found to be about 20 feet long. This empties its con-
tents, or rather continues on, in the vas deferens, which conveys the
somen to the seminal vesicles. During this passage the mucous
membrane adds a viscid mucous secretion in which the spermato-
zoa are liberated and, so to speak, diluted.

What is the appearance of the spermatozoa ?

In the seminiferous tubules the developing spermatozoa may be
seen with the heads all united in the cells from which they arise,
the tails projecting brush-like into the cavity of the
tube. But they are soon separated. Tliey then con-
sist of a head and a tail (Fig. 55). In length they
are about ^^ to ^ij; of an inch. The head is some-
what elliptical and the tail gradually tapers. In other
animals than man the size and form vary from those
of man, though in a general way they conform.

What action of the spermatozoon permits it to enter
the uterus and Fallopian tube ?
There is a very active vibratory motion of the tail
of the spermatozoon, which allows it quite free motion
in a fluid medium. It is by this swimming motion, in
which it may be compared to a tadpole, that the semi-
nal cells are able to reach the ovum against the action
of the cilia in the uterus and Fallopian tube.

Is a single spermatozoon sufficient to fecundate an
ovnm?
It probablvis. There have been more than one seen
in an impregnated ovum, but it is probable that only
one enters into the formation of the male pronucleus,
the rest remainins inactive.

Human Sper-
niat ozoon :

1, in profile ;

2, viewed on
the flat: b,
head : c, mid-
dle-piece ; <l,
tail ; e, end-
piece of the
tail.

Where is the ovnm impregnated ?
In tile Fallopian tube.

What leads us to the conclusion that the egg is fecundated in
the Fallopian tube?
(1) The spermatozoa are found there. (2) Before the ovum

180 EMBRYOLOGY.

leaves the Fallopian tube it has gained an albuminous coat which
would probably be impervious to the spermatozoa. (3) The unim-
pregnated egg degenerates before it enters the uterus, and is then
probably incapable of impregnation.

What are the seminal vesicles ?

They are tubules which join the vasa deferentia, and lie upon
the base of the bladder, emptying into the urethra by the ejacu-
latory ducts through the prostate gland. In structure the vesiculae
seminales are convoluted. They are lined by a mucous membrane
which is convoluted and folded so as to give it a sacculated
appearance.

What is the prostate gland ?

. It is a gland lying at the base of the bladder and surrounding
the urethra at its beginning. It has the general structure of the
glandular organs, and in addition a considerable amount of muscu-
lar tissue. Its acini empty into ducts which empty in the urethra.
Its function is not exactly known.

Describe the penis.

It consists of three more or less cylindrical bodies of erectile
tissue enclosed in fibrous sheaths. The two corpora cavernosa lie
above, and receive between them, below, the corpus spongiosum, in
which the urethra is contained. The glans penis is continuous
with the corpus spongiosum. The covering of the penis is of
loose skin, but over the glans penis and lining the prepuce it
resembles mucous membrane. In this region there is an abundant
subcutaneous nerve-plexus, and the Pacinian bodies are quite
numerous, so that it is possessed of acute sensibility.

Describe the urethra.

It extends from the bladder through the corpus spongiosum to
the end of the penis. It is lined with mucous membrane, and is
furnished in its deeper layers with numerous muscular fibres.
There are a number of ducts of glands opening into it whose
function is not fully understood, though their secretion is sup-
posed to be added to that of the seminal vesicles to make up the
semen.

How is the erectile tissue of the penis arranged ?

The erectile tissue consists of a system of distensible veins lying
in the interstices of a fibrous connective tissue. The erector

REPRODUCTION. 181

penis muscle by its contraction compresses the veins of the organ,
and the veins become turgid with blood. The arteries enter the
structure of the erectile tissue along the pubic bone, and are not

pressed upon by the contraction of the muscle.

What is menstruation?

It is a periodical change which accompanies ovulation in women.

Is menstruation dependent upon the ripening and discharge of an
ovum?

No. The phenomena of menstruation may occur without the
rupture of a Graafian follicle, and, on the other hand, ovulation
may occur in amenorrhoeic women. As a rule, however, the two
processes are simultaneous, and the discharge of an ovum occurs
during the period.

What is the character of the menstrual discharge ?

It is a thin, bloody fluid of a dark color and having a peculiar
odor. It consists of blood, epithelium, and mucus from the uterus
and vagina, together with the decidua menstrualis. The blood
does not clot.

What is the decidua menstrualis?

It is a membrane developed by the uterine mucous membrane
for the purpose of furnishing a site for the implantation and growth
of an impregnated ovum. It occurs entirely within the body of
the organ, and does not extend into the cervix. If impregnation
does not occur, the decidua menstrualis breaks down and leaves its
vessels bleeding.

Why does not the menstrual blood clot?

Probably because of its mixture with the mucus of the uterus
and vagina.

What is the duration of menstrual life ?

ITsually in temperate climates from fourteen or fifteen to forty-five
or fifty years of age. The periods recur regularly at intervals of
about four weeks, but the occurrence of pregnancy causes a cessa-
tion which lasts through lactation, with occasional exceptions.

What is the corpus luteum?

After the escape of an ovum there is an effusion of blood into
the cavity of the Graafian follicle. The clot which follows is dis-
posed of by the same retrogressive processes which extravasated

182

EMBRYOLOGY.

blood may undergo in any part of the body. The serum is absorbed,
the cells disintegrate, and the coloring matter is in part taken up
by the tissues and in part crystallizes or takes up other constitu-
ents, and presents variations of coloring. Hand in hand with these
changes in the blood go important changes in the surrounding
tissues. The epithelial cells which are left behind proliferate and
form a soft yellowish, very vascular tissue, which presently under-
goes fatty degeneration. This yellow mass surrounding and en-
closing the remains of the extravasated blood constitutes the corpus
luteum, and as it disappears its place is occupied by a dense, firm
connective-tissue cicatrix, which may be pigmented.

How does the corpus luteum behave during pregnancy?

It then does not degenerate and disappear rapidly as after men-
struation, but continues fully as large for several months, and at
the end of pregnancy still remains as a clearly marked body. This
is shown in the following table from Dalton :

Corpus Luteum of Menstrua-
tion.

Gor-pus Luteum of Pregnancy
(Dalton).

At the end of

three weeks.

One month.

Two months.
Four months.

Six months.

Nine months.

f in. in diameter; central clot reddish; convoluted wall
pale.

Smaller ; convoluted wall
bright yellow ; clot still
reddish.

Reduced to the condition of
an insignificant cicatrix.

Absent or unnoticeable.

Absent.

Larger ; convoluted wall
bright yellow ; clot still
reddish.

I in. in diameter ; convo-
luted wall bright yellow ;
clot perfectly decolorized.

Size about as at two months ;
clot pale and fibrinous ;
convoluted wall dull yel-
low.

Still as large as at the end
of the second month. Clot
fibrinous. Convoluted wall
paler.

J in. in diameter ; central
clot converted into a radi-
ating cicatrix ; external
wall tolerably thick and
convoluted, but without
any bright yellow color.

At what time is the ovum liable to impregnation?

Probably most so immediately before the menstrual period, but

Absent.

DEVELOPMENT. 183

owing to the fact that both the female and male elements may
remain in the genital passages of the female for some days in a
healthy condition, it is difficult tu tix the time of actual impreg-
nation uf the ovum.

What facts lead to the supposition that impregnation takes place
most commonly before menstruation ?

(1) It is )iiol)able that in most instances the rupture of the
Graafian follicle occurs very early in the menstrual period. (2)
The uterus is in the most favorable condition to sustain the fecund
ovum at that time, because of the presence of the decidua men-
strualis. (3) Among the Jews, a remarkably prolific race, coitus
is prohibited by the religious law for a week after menstruation.

DEVELOPMENT.
What changes occur in the ovum before impregnation?

The ovum, after leaving the ovary and while still in the Fallo-
pian tube, undergoes certain changes. These changes are mostly
confined to the nucleus or germinal vesicle. The germinal spot or
nucleolus disappears, and the outline of the vesicle becomes indis-
tinct, elongated so that it has a spindle-shape. While in this con-
dition the spindle develops two or three vesicles, which collectively
form the female jjronucleus.

Wkat changes in the ovum follow impregnation?

The head of a spermatozoon penetrates the vitelline membrane
and enters the vitellus, where it remains surrounded by protoplasm.
This is the male pronucleus. The male and female pronuclei soon
join, and then follows a process of growth by the splitting up of
the nuclei to form new nucleated protoplasmic cells.

What is this splitting-up process called?

.Segmentation. The first cell which is formed by the union of
the male and female pronuclei is called the blastosphere or primi-
tive segmentation germ.

What other change then occurs ?

The ovum receives an addition of a layer of clear albuminous
material while still in the Fallopian tube, which adds considerably
to its bulk. This corresponds to the white of a hen's egg.

What is segmentation of the vitellus ?

The next change which occurs in the impregnated egg is the split-

184 EMBRYOLOGY.

ting up of the vitellus or yelk, first in halves, then in quarters, and
so on until the vitellus becomes a mass of minute granular-look-
ing nucleated cells (Fig. 56). The segmentation of the nucleus
continues with the corresponding change in the yelk.

Fig. 56.

Segmentation of the Vitellus in the Impregnated Egg of the Rabbit (Coste).

"Where does this change occur?

In the Fallopian tube. The human ovum probably remains in
the Fallopian tube for eight or ten days before reaching the uterus,
and while there does not materially alter its appearance. Barring
the fact that there is added to its circumference an albuminous
layer, it is unchanged in external looks.

What is the germinal membrane?

The outer layers of vitelline cells after segmentation are closely
packed and resemble polygonal epithelial cells, and in fact form a
sort of lining to the zona pellucida, holding the liquid of the vitel-
lus in a central cavity. This lining is the germinal membrane or
blastoderm.

Why does the segmentation of the vitellus take place ?

This is not known, nor is it understood how it occurs, but it fol-
lows the union of the male and female elements of generation only.

DEVELOPMENT.

185

How are changes in the developing ovum commonly studied?

la the devclupmont ol' the of;g of' the cuiniiioM I'uwl. I'his is
on account of the accuracy with whicli the time of development
may be watched, and the convenience to the observer of such sim-
ple growth by incubation compared with uterine growth. The pro-
cesses of development arc not materially different.

What changes occur in the blastoderm?

There appears at one point an opa<|uc streak (Fig. 57), which is

Fig. 57.

Diagram of the Area Germinativa, showing the primitive trace and area pellucida.

found to be due to the proliferation of the cells of the blastoderm.
This is ih.Q primitive trace, and it grows in length and breadth.

What changes occur in the arrangement of the cells of the blasto-
derm at this time?

They separate into three layers, the ejyihliut, virsohhtst, and hi/po-
hhisf (Fig. 58) ; and along the axis of the primitive trace a grot)ve
is formed which is destined to become the cerebro-spinal axis. This
is the primitive groove.

What changes occur in the zona pellucida at the entrance of the
ovum into the uterus?

The surface of the ovum becomes shaggy with tlie appearance of

186

EMBRYOLOGY.

numerous villi, whicli are probably derived from the epiblast. This
is known now as the chorion.

What changes occur in the uterus?

The decidua menstrualis has been mentioned as specially suitable
for the reception of the ovum. But if impregnation occur, it is
not called by this name, as menstruation does not occur. It is
then known as the decidua vera. It consists of a thick, succulent

Section of a Blastoderm at right angles to the long axis of the embryo, near its middle,
after eight hours' incubation (from Foster and Balfour) : A, epiblast formed of two
layers of cells ; B, mesoblast thickened below the primitive groove ; C, hypoblast,
formed of one layer of flattened cells; pr, primitive groove; mc, mesoblast cell;
bd, formative cells in the so-called segmentation or subgerminal cavity. (The line
of separation between the epiblast and mesoblast below the primitive groove is too
strongly marked in the figure.)

mucous membrane caused by the proliferation of the subepithelial
cells. Into this decidua the ovum falls, and its shaggy chorion
implants its villi in the crypts of the mucous membrane. The
decidua soon envelops it, and the portion which is reflected over
the ovum is known as the decidua reflexa.

What important changes now begin to occur in the blastoderm ?

The blastoderm, which is increasing in area from the rapid pro-
liferation of cells, folds at each end transversely and at the sides
longitudinally. These folds are of great importance, for it is in
this way that the contour of the body is outlined, and if it were
not for them the blastoderm would continue to develop as a flat
surface. The transverse folds are at each end, and are known as

DEVELOPMENT. 187

the heiid and tall folds. Tlie longitudinal folds define the outlines
of the body.

How does the medullary groove develop ?

The ridges in the epiblast on either side continue to thicken, and
finally coalesce at the back, leaving a lining of cells within a tube.
These cells develop the cerobro-spinal axis and follow the curves
of the blastoderm longitudinally. The head fold gradually becomes
constricted, and becomes the neck. Meanwhile the mesoblast has
developed a number of processes, which become a primitive spinal
column. It is to be noticed that the enclosure of the spinal canal
in this way is by a folding process, and all through the process of
development this peculiarity is very marked.

What is the mode of the formation of the pleuro-peritoneal cavity ?
The mesoblast divides near the median line, and one part of the
split mesoblast adheres to the epiblast, while the remainder joins
the hypoblast. The former is known as the somatopleure, and the
latter as the splanchnopleure. and the included space becomes the
pleuro-peritoneal cavity, which subsequently divides to form pleura,
pericardium, and peritoneum.

What structures are developed from the epiblast?

The epidermis and appendages of the skin, the great nervous
centres, the nerves, and the principal portions of organs of special
sense — eye, ear, nose.

What does the hypoblast develop?

The epithelial elements, including the glands and the mucous
membranes lining the alimentary and pulmonary tracts.

What does the mesoblast develop?

The bones, muscles, fascije, and connective tissues of the body.
It also develops the vascular system. It must be remembered that
very early in the embryonal life this tissue divides to join witli the
epiblast and hypoblast, and we can therefore understand how it
may develop the muscular structures of the intestinal canal.

What is the destiny of the splanchnopleure ?

The splanchnopleure (5', Fig. oit) folds in over the romainder of
the ovum, and .so walls off, so to speak, a portion of the vitellus which
communicates freely with the rest of the yelk-sac. Later on, after

188

EMBEYOLOGY.

the formation of the amnion, the yelk-sac forms a blind pouch which
is lined by hypoblast and has an external covering of mesoblast
(Fig. 59), as is shown at 6 in the accom-
FiG. 59. panying cut. The upper 6 is in the primi-

tive gut, which derives its epithelial ele-
ments from the hypoblast and its muscular
and serous coverings from the mesoblast.

What is the yelk-sac then called?

The umbilical vesicle.

What is the function of the umbilical
vesicle ?
From it the embryo derives its suste-
nance in the earlier stages. Early in the
development blood-vessels begin to form,
and they ramify over the surface of the
umbilical vesicle and help to absorb its
contents.

Transverse Sections through
the Embryo Chick, before
and some time after the
closure of the medullary
canal, to show the upward
and downward inflections
of the blastoderm (after Ee-
mak) on the third day in
the lumbar region: 1, uoto-
chord in its sheath ; 2, me-
dullary canal, now closed
in; 3, section of the medul-
lary substance of the spinal
cord; 4, corneous layer; 5,
somatopleure of the meso-
blast ; 5', splauchnopleure
(one figure is placed in the
pleuro-peritoneal cavity) ; 6,
layers of hypoblast in the
intestines, spreading also
over the yelk ; 4X5, part of
the fold of the amnion form-
ed by epiblast and somato-
pleure.

What is the amnion?

While the one portion of the split meso-
blast (splauchnopleure) unites with the
hypoblast to form the splanchnoblast and
alimentary organs, the outer layer (soma-
topleure) and epiblast are united to form
the skin and walls of the body as the soma-
toblast. The somatoblast now folds in
about the embryo. It must be remem-
bered, however, that the entire globe of
the ovum is lined with these cells, and
that in folding in this way the cells are in
a measure raised away from the wall of the ovum. The layers of
the somatoblast fold back until they meet and unite behind the
embryo, and in this way form a layer of membrane which lines
the ovum and another layer which encloses the embryo (Fig. 60).
This latter layer forms the amnion. (This is better understood
by reference to the cuts.)

What is the use of the amnion ?

It covers the embryo in the early stages very closely, but soon
becomes distended with a pale watery fluid, and serves to float

DEVELOPMENT.

189

the foetus and give it equal mechanical support on all sides. The
outer layer of the amnion becomes very thin and adheres to the
chorion.

Fig. 60. Fig. 61.

Fig. go. — Diagram of the Fecundated Egg, farther advanced : a, umbilical vesicle ; h, am-
niotic cavity ; c, allantoi.s.

Fig. 61.— Diagram of the Fecundated Egg, with allantois nearly complete: a, inner lam-
ina of amniotic fold; b, outer lamina of amniotic fold; c, point where the amniotic
folds come in contact. The allantois is seen penetrating between the inner and outer
lamina; of the amniotic tolds.

Fio. 62.

What is the composition of the amniotic fluid ?

It is water containing small quantities of albumin and urea.

What is the allantois?

During the development of the amnion from the somatoblast
a change has occurred in the splanchno-
blast. From the inferior extremity of
the included portion of the yelk-sac,
which is to become intestine, there has
budded a small mass which develops
rapidly, following the outline of the
amnion (see Figs. GO, Gl, G2), and grows
fast to its chorion layer. This structure,
the allantois, soon becomes very vascular
and carries its blood-vessels to the chorion.

What is the function of the allantois ?

It nourishes the growing embryo. The
chorion has already become tufted with
capillary loops, and has establi.shed a
connection with the decidua of maternal
growth. As the vessels of the allantois

Diagram of the Fecundated Egg,
with the allantois fully form-
ed : fl, umbilical vesicle ; b, am-
nion ; c, allantois.

communicate more and

more with the chorion, the embryo derives more of its sustenance

190 EMBRYOLOGY.

from the motlier, and the remains of the yelk-sac (umbilical ves-
icle) dwindle as the need is less and the substance is consumed.
(See Figs. 60, 61, and 62.)

What structures in the body are derived from the beginning
of the allantois ?
The urinary bladder and the urachus, an impervious cord extend-
ing from the bladder to the umbilicus.

How is the chorion made up ?

It consists of several layers which fuse into one vascular mem-
brane. The allantois, the outer layer of the amnion, and the vitel-
line membrane are united in the chorion. As the embryo develops
the vessels of the chorion become thinner on the side toward the
uterine cavity, and more distinct on the opposite side. This change
continiies as the embryo increases, until the placenta is formed by
the branching of the embryonic vessels and the increase of the
decidua at the corresponding point.

What changes occur in the uterus in developing the placenta ?

In the deeper part of the mucous membrane of the uterus at the
implantation of the chorion there are hollowed out spaces or si-
nuses in the tissues which communicate both with a maternal vein
and an artery ; that is, special arrangements are made for the rapid
circulation of a large amount of blood in the uterine mucous mem-
brane at the placental site. At the same time, the glandular struc-
tures of the uterine mucous membrane are increased, and the fol-
licles run deeply into the thick and succulent tissues.

How do the villi of the chorion become implanted in the uterine
wall ?

The villi dip down and develop new tufts of capillaries in the
deepened crypts of mucous membrane, so that the tufts of capil-
laries of the chorion may be said to resemble in a way a glove filled
with fcetal blood dipping into a vessel filled with maternal blood.

Does the blood of mother and foetus actually come in contact ?

No. There are four layers of cells between the maternal and
the foetal blood: 1, wall of chorion capillary; 2, cells of chorion ;
3, cells of uterine follicle ; and 4, wall of the uterine sinus.

Do the tissues of the placenta maintain an exchange of mate-
rial?
Yes. The mother's blood furnishes to the foetal blood food and

DEVELOPMENT.

191

oxygen, and in turn removes tlie earltonie acid and oxcromentitious
material wliieh the fetus must lose ; that is, the placental circula-
tion supplies the place taken in after-life by the alimentary and the
respiratory tracts.

Does the entire placenta leave the uterus immediately after the
birth of the chdld ?

No. The foetal part is almost all, excepting some of the capil-
lary tufts which are torn off, discharged in the after-birth ; but the
decidua is not entirely disposed of in this way, the portions remain-
ing being in part absorbed and in j)art found in the lochia which
occur i'or a few days after the birth.

What is the appearance of the placenta ?

It appears as a thick, cake-like disk of vascular tissue. Its ma-
ternal and foetal portions arc so intermingled that they cannot be
separated. In size it covers about one-third of the uterine wall.

At what period of gestation is the placenta formed ?

At about the third month of pregnancy. Before that time tlio
chorion is covered by the decidua reflexa and nourishes the embryo,
but as the placenta becomes more developed other parts of the
chorion atrophy.

From what tissues is the umbilical cord formed ?

From the vascular allantois, which
carries the arteries and vein. It has, Fig. 63.

however, an external coating of the
amnion and the shrivelled umbilical
vesicle and its duct (Fig. 63). How
this occurs will readily be seen by
reference to the accompanying cut.

Why do the maternal vessels not
bleed excessively after the pla-
centa is torn from its implan-
tation ?

There is, of course, a loss of the
blood contained in the uterine sin-
uses, but the general balance of the
circulation is not disturbed at child-
birth. The reason for this is the oblique entrance of the placental

Human Embryo anrt its Envelopes at
tlie I'-nd of the Tliinl Month, show-
ing the en hi rgeim-ut of the amnion.

192 EMBRYOLOGY.

vessels. They enter the sinuses at an angle, and are therefore
compressed by the muscular tissue of the uterus in its contracted
state.

How is the vertebral column developed?

Early in the development of an embryo there is formed beneath
the medullary groove in the mesoblast a thin thread of soft carti-
lage known as the chorda dorsalis, or notochord. This soon be-
comes included in a sort of fibrous sheath, and is the primary axis
from which the bodies of the vertebrae are developed. On either
side of the notochord are developed small centres which subse-
quently split. These are the protovertebrse. From these are de-
veloped the vertebrae and the heads of the ribs by the inner lat/er,
and by the outer (or posterior) lai/er the muscles and skin of the
back, the epidermis being derived from the epiblast.

How do the protovertebrse form the vertebrae?

It is not by direct ossification of the protovertebra3. but they
separate in such a way that adjacent protovertebrae each contribute
half to the vertebra formed. That is, two protovertebrae form parts
of two vertebrae, one above and the other below, and also form a
whole vertebra by their adjacent portions.

How is the cranium developed?

By the prolongation of the epiblast over the protovertebrae to the
cephalic end of the embyro. Here it develops three segments, cor-
responding to the three primary vesicles which are the forerunners
of the brain. These centres of ossification are at the base of the
skull, the bones of the vertex being developed from membranes.

How is the face formed in the embryo?

At the head fold of the embryo the mesoblast does not split into
two parts, as below, but folds in from the side, covered without and
within by the epiblast and hypoblast. These folds develop certain
clefts from which the face is derived, the mesoblast furnishing the
bone and muscle structures, and the epiblast the epidermis, while
the hypoblast gives the mucous membrane which lines its cavities.

Describe the cleft which develops the face.

Immediately below the anterior cranial vesicle there occurs on
either side a cleft in the lateral fold of the embryo extending to
the vesicle for the eye. In the space of this cleft there is devel-

DEVEI.OP^rENT.

193

Fi(i. <;4.

Developmeut during First Month.

Oped a sort of secondary cleavage of the parts, which by the rapid
growtli of the parts included between
the clefts resembles a budding (Fig.
64). It is by the growth of these
buds or processes that the outline of
the face is formed. From each side
sprouts the superior maxillary pro-
cess, and the processes unite in the me-
dian line, meeting the nasal or inter-
maxillary process from the upper bor-
der of the cleft. The portion below is
cut off by a branchial cleft, which, be-
coming the mandibular process, forms
the lower jaw.

What defects in the face are due to faulty development of these
processes ?

When the processes do not unite as they should, various defects
occur ; most common are those about the mouth, cleft palate and
hare-lip, by failure of the superior maxillary processes to unite or
by failure of the intermaxillary process to unite with the max-
illary.

Do the other branchial clefts persist in later life ?

No. They become closed as they accomplish their use in devel-
oping certain organs : as pathological factors, however, we are often
convinced of their non-union or of flaws in their development, cysts
and tumors of various kinds and certain fistula) being attributable
to this cause.

How are the extremities developed?

They develop as buds from the somatoblast early in foetal life,
and the formation of the joints and lesser details of structure are
gradually worked out. At about the third month the separation
of the fingers and division of the extremity into joints is about
completed. The arm develops somewhat in advance of the leg, and
grows rather more rapidly in the earlier period of intra-uterine life.

What two forms of circulation are found in the embryo ?

The earliest is the vitelline circulation, in which vessels from the
foetus pass over the yelk-sac and carry nutrition to the growing-
organism. There is formed a placental circulation, in which the
maternal blood furnishes the elements of food.
13— Phy.

194 EMBRYOLOGY.

What is the vascular area (area vasculosa) of the foetus 1

Among the earliest changes in the blastoderm, occurring in the
second week of impregnation, is the formation of blood-vessels
and blood-corpuscles. This occurs by the proliferation of certain
branched cells of the mesoblast, and these cells form a closed sys-
tem of branching capillaries, their nuclei acquiring a red color
and becoming the blood-corpuscles. This area is external to but
connected with the embryo.

How is the heart formed ?

At about this time certain cells of the visceral layer of the meso-
blast (splanchnopleure) develop a tube upon each side of the body,
and these two tubes soon coalesce to form a single tube (Fig. 65),
which receives two veins at its lower end and gives off two arteries
at its upper. This is the primitive heart, and pulsations begin in it

very feebly almost as soon as there is
Fig. 65. Fig. 66. a trace of the originating cells. This

2 ..2 structure soon develops a muscular tis-

I I -i -^^ X ^ ^^^' ^^'^ ^ circulating fluid which short-

ly presents the character of blood.

What is the next important change
in the form of the heart ?

'1^ I ' ' \>^_^ It bends itself so as to assume a U-

FiG. 65.— Earliest Form of the Foe- shape, which shortly is twisted in such
tai Heart: 1 venous extremity; manner that the arterial end of the

2, arterial extremity. • r. r> i

Fig. 66.— Foetal Heart bent upon heart crosses in front of the venous
Siki'4x?remity.'"'""^*'' '' (Fig- 66), and the loop suggests the

outline of the ventricles. The vitel-
line circulation in the human ovum is not very long-lived, for the
chorion is early formed and the stock of nutrient protoplasm in the
yelk-sac is very small.

What further modifications does the heart undergo ?

The septum between the ventricles grows, and separates the
heart into two divisions ; and at about the same time the auricles
are developed and the valves become well marked. These changes
occur in the fourth to the eighth week of embryonic life.

Describe the vitelline circulation.

The area vasculosa extends all about the blastoderm upon the

DEVELOPMENT.

195

Fi<;. G7

surface of the vitcUus. and as the folds of the embryo occur the

vessels are brought to enter the body

throuirh the space at which the vitel-

lus is shut in to form the primitive gut.

There are then two arteries and two veins,

which are known as the omphalo-mesen-

teric vessels. This form of circulation soon

gives way to the jilacental, and the vessels

passing to the umbilical vesicle waste,

those belonging to that portion of the

original vitelline cavity which forms the

intestine, becoming the mesenteric vessels.

What are the prominent features of the
placental circulation?

(1) In the arterial circulation some
conditions of the heart and great ves-
sels are necessary to modify the pulmo-
nary circulation before the air enters the
lungs at birth. (2) In the circulation of
the liver the veins present modifications to allow for the return
placental circulation.

Where do the arteries to the placenta arise?

They follow the allantois in its growth. Springing from the
internal iliac artery of each side, two arteries pass up the umbilical
cord and break into the branches in the placenta which terminate
in capillar}- tufts.

How does the blood return to the body from the placenta?

By the umbilical vein it is taken to the liver, where part of it cir-
culates through the liver-capillaries in the same manner as the blood
from the portal vein, the remainder passing through the ductus

Diagram of the F,ml)ryo and its
Vessels, showing the circula-
tion of the uniliilical vesicle,
and also that of the allantois,
beginning to be formed.

What is the ductus venosus?

It is a large vein which appears at the under surface of the
liver, and returns a large part of the blood from the umbilical
vein directly to the inferior vena cava, without circulation in the
capillaries of the organ.
How does the ductus venosus appear in adult life?

Soon after birth the umbilical vein and ductus venosus become
an impervious cord extending from the navel to the liver : the

1 96 EMBRYOLOGY.

former becomes the round ligament of the liver, while the ductus
venosus remains as a small fibrous cord.

What is the course of the foetal blood through the heart ?

It enters the right auricle, and is thence sent in part to the

right ventricle, and in part to the left auricle,

Fig. 68, through the foramen ovale, an opening left

in the development of the auricular septum.

The blood which enters the left ventricle

from the left auricle is forced out through

the aorta (Fig. 68). The right ventricle,

however, sends but a small part of its blood

to the lungs, but delivers it through the

ductus arteriosus to the aorta. The blood is

in this way sent into the systemic circulation,

Foetal Heart still farther a part going to the placenta through the inter-

pui.nonary arteTy fs, l\ "^^ ^^1^^, hypogastric, and umbilical arteries.

pulmonary branches ; 4, ttn. ^ re j. i 1.1 ■nj.-i.' 1

ductus arteriosus. What effect has the Eustachian valve upon

the blood-stream in the foetal heart ?

It throws the blood from the inferior vena cava through the
foramen ovale into the left auricle. In this way the stream of
blood coming from the superior vena cava crosses that from the
inferior cava on entering the heart, inasmuch as the blood from
the superior vena cava enters the right ventricle.

What effect does this division of the blood-stream have upon the
distribution of the blood in the foetus ?
The circulation of the blood is made more perfect, for the
branches of the aorta given off to the head and upper extremities
distribute blood from the inferior vena cava ; while the ductus
arteriosus, carrying the blood from the superior cava and right
ventricle, enters the aorta in such a way that most of its blood is
sent to the lower extremities and abdominal organs and umbilical
arteries. In this way the deoxidized blood is sent back to the
placenta for the renewal of its oxygen.

How does this result in the development of the lower extrem-
ities ?
They develop less rapidly than the upper. There are probably
two reasons for this: 1, the blood is less well aerated and less
nutritious ; 2, the internal iliac arteries, giving off the umbilical
arteries, probably divert a considerable portion of the blood-supply
of the external iliacs which go to the lower extremities.

DEVELOPMENT. 197

What changes occur in the circulation after the birth of the
foetus ?

The respiratory centre in the medulhi, whicli has been quiescent
because it lias been sufficiently well supplied with oxygen, is
awakened as soon as the connection with the uterine sinuses is
interrupted. As soon as the supply of oxygen sinks to a certain
point, an impulse of" inspiration is generated, and the infant breathes
and the lungs assume a condition of partial expansion. With the
diminished resistance in the expanded lungs the amount of blood
in the pulmonary circulation increases, and the amount passing
through the ductus arteriosus diminishes, and this is soon obliterated.
At the same time, the blood returning to the left auricle increases
in quantity, and the intra-auricular pressure is greater ; then, too,
the inferior vena cava sends less blood, for the ductus venosus no
longer carries the blood from the placental circulation, and there-
fore the foramen ovale is not used, and is soon closed by the
adhesion of its valve-like curtain. Thus we have the adult circu-
lation established in the place of the foetal in consequence of the
respiratory movements.

How is the spinal cord formed?

It will be remembered that the medullary canal encloses in its
cavity cells from the epiblast which line it. These cells by pro-
liferation and differentiation develop nerve-cells and nerve-fibres,
the latter at first not medullated. The cells also gradually close in
upon the medullary canal, and form a central canal lined with
epithelium, a layer of nerve-cells (gray matter), and a layer of
nerve-fibres (white matter).

How do we account for the obliquity of the spinal nerves and for
the Cauda equina?
When the spinal cord first appears it fills the entire spinal canal,
but at the time of birth the cord has apparently not grown so
rapidly as the vertebral column, for it then ends at the third
lumbar vertebra, and in the adult it ends at the first. Thus we
are able to explain the apparent origin of the spinal nerves above
their point of exit from the canal, and the increasing obliquity of
the nerves from above down, until finally, in the tuft of vertical
nerves below the extremity of the cord, we see the extreme degree
of this peculiarity.

How do the spinal nerves develop?

They are formed from cells arising from the epiblast lining the

198

EMBRYOLOGY.

medullary groove. Before the closure of this groove to form the
medullary canal an offshoot from the epiblast may be observed,
which is the source of the posterior nerve-roots ; and they become
attached to the cord as it develops. The anterior roots spring from
the cord after it has developed fibres. The two roots then join and
the nerve grows out into the mesoblast.

Are the cranial nerves similarly derived ?

In much the same way the cranial nerves arise primarily, except
the nerves of special sense. In function the motor nerves seem to
form a sort of anterior root for the sensory, so that they may be
arranged in pairs corresponding to the anterior and posterior roots
of the spinal nerves ; and it does not seem entirely fanciful to re-
gard their development as somewhat similar, thus :

Third, fourth, sixth, and seventh motor, fifth sensory. Twelfth
motor, ninth sensory. Eleventh motor, tenth sensory.

How does the earliest rudimentary brain appear?

The medullary canal is widened from the very beginning at its
anterior end, and very early develops three ves-
icles, which are shown diagrammatically in Fig.
69. These vesicles, with their lining of epiblast,
are the primitive brain.

How does the anterior cerebral vesicle become
changed ?

This vesicle is destined to become the third ven-
tricle of the brain, and from its anterior surface
are developed two protrusions which expand to
form the hemispheres of the brain ; thus, this ves-
icle is early divided into two parts, the fore-brain
or prosencephalon, and the inter-brain or thalam-
% encephalon.

I What is the middle primary vesicle called ?

I The mesencephalon. It corresponds to the

' aqueduct of Sylvius.

How is the posterior vesicle altered ?

This is destined to become the fourth ventricle,
and by a similar protrusion it develops a second

Fig. 69.

Formation of the Ce-
rebro-spiual Axis:
1, vesicle of the
hemisphere ; 2, ves-
icle of the tubercu

la quadrigeinina ; 3, portion, which becomes the cerebellum. These
duiia oblongata, divisions of the posterior cerebral vesicle are

DEVELOPMENT.

199

I. Anterior
primary
vesicle.

II. Middle
primary
vesicle.

III. Posterior
primary
vesicle.

known as the epencephalon, and the after-brain, or metenceph-
alon.

"What parts of the brain do these five vesicles respectively orig-
inate?

( Cerebral hemispheres, cor-
pora striata, corpus callo-
sum, fornix, lateral ven-
tricles, olfactory bulb.

f Thalami optici, third ven-

I tricle, optic nerve.

" Corpora quadrigemina,
crura cerebri, aqueduct
of Sylvius.
Cerebellum, pons Varolii,
anterior part of fourth
ventricle.
Medulla oblongata, fourth
ventricle, auditory nerve.

1. Prosencephalon.

j 2. Thalamencephalou.
[ 3. Mesencephalon.

4. Epencephalon.

5. Metencephalon.

What is the primary optic vesicle ?

About as soon as the cerebral vesicles are distinctly formed a
budding of two projections — one from either side of the anterior
vesicle — occurs. These are the primary optic vesicles. They are
formed before the vesicles which make the hemisphei'es (prosen-
cephalon). The projections approach the external epiblast, and at
that period consist of a finger-like process having a globular dilata-
tion at the end. This subsequently forms the optic nerve and the
retina.

How is the crystalline lens formed?

Opposite the optic vesicle the superficial epiblast is depressed
and forms a sort of pit. forcing the optic vesicle to fold in upon
itself. The follicle of epiblast is shut off at the surface, and a ball
of its substance left in the cup of the infolded optic vesicle. This
ball forms the rudimentary lens, and the anterior layer of the ves-
icle is the retina.

How are the other tissues of the eye evolved ?

The muscular and vascular structures, as well as the connective
tissue and humors, are derived from the mesoblast. which in part
enfolds the ocular vesicle and in part enters it between the lens

200i EMBRYOLOGY.

and the edge of the cup-like depression. The cornea is of later
formation, and is derived from the epiblast of the skin.

How is the auditory apparatus developed ?

Very early in the life of an embryo there is a depression on
either side of the head which passes through the same process as
that mentioned for the crystalline lens and for the germinal epi-
thelium in the formation of ova. The mass of epiblast thus sepa-
rated forms the epithelium of the labyrinth and vestibule, the
surrounding mesoblast furnishing the bony and muscular structures.
The auditory nerve is developed with other cranial nerves, and
grows in to its end-organs from its central origin.

How is the olfactory apparatus derived?

In a similar way to the internal ear and the lens. The nasal fossa
is primarily a depression in the superficial epiblast, which widens
and deepens and receives the nerve-filaments from the olfactory
lobe. This lobe is originally a bud from the prosencephalon. The
primary olfactory depression continues to widen until it opens into
the mouth, and is again shut off by the growth of the branchial
arch, which forms the superior maxilla. The nose is similarly
derived from the mesial and lateral nasal processes.

Describe the method of the development of the alimentary canal.

As has already been explained, the primitive alimentary canal is
formed from the involution of the splanchnopleure, and is really a
portion of the yelk-sac partially shut off from the rest. It is at
each end a blind pouch which follows the head and tail folds.
The portions have received the names fore-gut and hind-gut as they
occupy one or other of these folds.

How does the fore-gut become changed?

It joins with the mouth-cavity by the folding back of the epi-
blast in the formation of the branchial arches, and from it are
formed the pharynx, oesophagus, and stomach.

How does the hind-gut approach the surface ?

By a similar involution of the epiblast the anus and about half
of the rectum are formed, into which the hind-gut opens to
complete the alimentary tract.

What deformities in the new-born depend upon the defective
accomplishment of these changes ?
The oesophagus is sometimes impervious at birth, and the rectum

DEVELOPMENT. 201

or anus may also be imperforate. This is caused by the non-union
of the segments developed from the epiblast with those developed
from the hypoblast.

How are the glands of the alimentary tract developed ?

(1) The Hulivdry glaiuh are developed from the epiblast lining the
oral cavity. They appear primarily as a simple tube which devel-
ops branches, about which the alveoli are formed.

(2) The pancreas is similarly developed from the hypoblast of
the fore-gut.

(3) The liver is primarily a protrusion of the hypoblast of the
fore-gut, which appears as soon as the blood-vessels begin to show
themselves. The omphalo-mesenterie vein, from the umbilical
vesicle, breaks up into a capillary plexus, and the hepatic cells
develop about it.

How are the lungs derived?

They first appear as a bud at the junction of pharynx and
oesophagus which soon forms a separate tube (the trachea). The
cells from the hypoblast extend into the surrounding mesoblast,
and it is from this structure that all of the tissue of the lungs,
except its mucous membrane, are formed.

What is the Wolffian body?

It is a rounded body which is first seen as early as the third
week as an increase of the cells of the mesoblast, just inside of
its division into parietal and visceral layers, on each side of the
vertebral column. It is soon seen to consist of three parts, from
which are derived the genito-urinary organs. The largest of these
in early embryonic life retains the name Wolffian hodij, and is not
a permanent organ ; a second, lying just above, develops the internal
organs of generation ; while the third, lying behind the Wolfl&an
body, is the rudimentary kidney.

What is the function of the Wolffian body ?

The Wolffian body proper — that is, after its division into three
sections — is a temporary kidney. At first this is a large glandular
body, resembling the kidney in structure, which possesses a duct
leading to and opening into the hind-gut. At about the sixth
week of foetal life the kidney begins to grow and the temporary
organ to atrophy. As this occurs a duct for the kidney (the
ureter) is developed from the "Wolfliian duct. The use of the

202 EMBRYOLOGY.

organs seems to be that of temporary kidneys, but by the end of
the third month they have been replaced by the permanent organs,
and have almost entirely disappeared.

How do the testicle and ovary originate ?

The body (germinal epithelium) which appears on the inner side
of the Wolffian body is the nucleus of the future testicle or ovary,
while from the outer side there springs a duet (Mtiller's) which
passes down to the cloaca or lower end of the hind-gut. At first it
is impossible to determine the sex of the foetus.

How do the remaining genital organs of the female develop ?

The ducts of Mtiller join to form the uterus and vagina, while
the ununited portions remain as the Fallopian tubes. The AVolffian
ducts, which also spring from the Wolffian bodies, are rudimentary
in the female and appear as a part of the parovarium.

How do the remaining male organs of generation develop ?

The Wolffian ducts become convoluted tubules, and each is at-
tached to the testis as the epididymis. Mtiller's duct is rudimentary
in the male, and is only found as the sinus pocularis and the hy-
datids of Morgagni.

How are the external genitals formed ?

In both sexes in early foetal life the external genitals are alike,
consisting of a body resembling a penis with a fold of skin at
either side. In the female this body becomes proportionately
smaller, and appears as the clitoris, the two lateral masses becom-
ing the labia majora. In the male a groove on the under surface
unites at its borders to form the urethra, while the scrotum is formed
from the folds of skin at the side. This differentiated condition may
persist in adult life, and has been mistaken for hermaphroditism.

PARTURITION.

How is the foetus extruded from the uterus?

In part by the contraction of the uterine muscles, and in part by
the pressure exerted by the abdominal walls. The uterine contrac-
tions are the first to appear, and it is not until the foetus enters the
vagina that the abdominal muscles are brought into play.

What causes excite the uterine contractions?

As to this no satisfactory answer has been given. Why the

PARTURITION. 203

uterus should contain the o-rowing embryo for months, and then
be suddenly tlirown into action to expel it, cannot be explained.

What is the nature of the act of parturition ?

It is a reflex action (lepeiidiiii;- u])on a centre in the lumbar spi-
nal cord. Whence the stimuli are derived which excite the reflex
is unknown, but probably from the organ itself".

What is the character of the uterine contractions ?

They are rhythmical in character, and may be compared to the
contractions of the heart-muscle. P]acli " pain "' begins feebly, grad-
ually intensifies until it reaches a maximum, and then gradually
declines until it entirely dies away, to be succeded by another simi-
lar contraction and pause. This rhythmical action continues until
the utei'inc contents are expelled, and then the organ enters into a
condition of tonic contraction.

APPENDIX.

TABLE OF THE DEVELOPMENT OF AN EMBRYO.

(Modified from Gray's Anatomy.)

Isf WecJc. — Ovum in Fallopian tube. Segmentation of vitellus.

2d Week. — Ovum in uterine decidua. Chorion. Formation of blasto-
derm and division of mesoderm. Heart and medullary groove. Amnion
and umbilical vesicle formed. xVllantois.

3d Week. — Head and tail flexures. Closure of medullary canal, and
formation of primary cerebral vesicles and ocular and auditory vesicles.
Branchial ai'ches. Wolffian bodies. Limbs.

4th Week. — Limbs increased. Anal opening. Interventricular sep-
tum begins. Ant. spinal nerve-roots. Olfiictory fosste. Lungs. Plem-as.

5th Week. — Allantois vascular. Trace of feet and hands. Miiller's
duct and genital gland.

6th Week. — Umbilical vesicle disused. Branchial clefts close. Post-
spinal nerve-roots. Membranes of the nervous centres. Bladder. Kid-
neys. Tongue. Larynx.

7th Week. — Muscles perceptible. Many centres of ossification appear.

8th Week. — Joints appear in extremities; fingers and toes separate.
Crystalline lens. Salivary glands. Spleen. Interventricular septum
complete. Sympathetic nerves.

9th Week. — Distinction between ovary and testicle. Genital furrow.
Pericardium.

3d Month. — Formation of placenta. External genitals separate from
anus. E.yelids, hairs, and nails. Duct of Wolffian body joins testicle.

Jfth Month. — Middle-ear bones. Tympanum and labyrinth. Scrotum
and prepuce.

5th Month. — Germs of teeth. Hair- and sweat-glands. Brunner's
glands. Uterus and vagina distinctly separate.

6th Month. — Papillfe of skin. Sebaceous glands. Pej-er's patches.
Free border of nails.

7th Month. — Cerebral convolutions. Pupillary membrane disappears.

8th Month. — Descent of testis.

9th Month. — Opening of eyelids. Ossification of cochlea.

CHEMICAL TESTS USED COMMONLY IN PHYSIO-
LOGICAL ANALYSIS.
For Proteids :
Nitric Acid coagulates all except peptones.

P 206

206 APPENDIX.

Heat. — All are coagulated by boiling, except peptones.

Xanthoproteic Reaction. — A solution boiled with strong nitric acid
becomes yellow : the color is deepened by the addition of ammonia.

Biuret Reaction. — With a trace of copper sulphate and an excess of
potassium or sodium hydrate they give a purple reaction.

union s Reaction. — With a solution of metallic mercury in strong
nitric acid (Millon's reagent) they give a white or pinkish reaction, and
the color becomes more pink on boiling.

For Starch:

_ Iodine Reaction. — Add to a solution of starch a small quantity of
tincture of iodine, and a blue reaction results. The color disappears on
heating and returns on cooling.

_ Glycogen. — Same test gives reddish reaction, port-wine color, which
disappears on heating and returns on cooling.

For Sugar (Glucose) :

Moore's Test. — Boil solution of sugar with an excess of potassium
hydrate, brown color-reaction.

Trommer''s ^es^.— Add to solution a sufficient amount of potassium
hydrate to render it quite strongly alkaline. Then add a solution of
copper sulphate, drop by drop, until a distinct blue tinge is visible.
Heat, and the presence of sugar is shown by appearance of red, yellow,
or orange color-reaction.

Felilings Test Solution. — An alkaline copper solution by which a
quantitative test may be made. The solution is somewhat unstable, and
is for this reason to be tested by boiling before using. The strength of
the solution is such that 1 cubic cm. (15 minims) will be exactly decolor-
ized by 2^0 of a gramme (.075 grains) of glucose. This test is very
delicate, and is quite commonly used for urinary examinations to detect
glycosuria.

The Fermentation Test. — If a small quantity of yeast be added to a
sugar solution, the fungus of the yeast (saccharomyces) will cause the
sugar to be decomposed into carbonic acid and alcohol. If the process
be continued until the sugar is entirely broken up, the amount of car-
bonic acid evolved indicates the proportion of sugar present.

For Bile Salts :

Pettenlwfer s Test. — Upon the addition of sulphuric acid to a solution
of bile-salts in water thei'e is a precipitation of the salts, which are
redissolved by a further addition of the acid. If a drop of a solution
of cane-sugar be added, a deep cherry color is developed.

For Bile Pigments:

Gmelins Test. — Add a small quantity of nitroso- nitric acid to a solu-
tion of the bile-pigments, and a play of colors results, beginning with
green and changing to blue, violet, red, and yellow. This is seen best
on a white background ; therefore a plate is often used for this test.

MIIIIU

Millimetres.

APPENDIX.
METRIC SYSTEM.

I I I I I I I ' 1 Tncli

(uiiUmc'lros.

I 3

207

ID

The area of the figure within the heavy lines is
that of a square decimetre. A cube one of whose
sides is this area is a cubic decimetre or litre. A
litre of water at the temperature of 4° C. weighs a
kilogramme.

A litre is 1.76 p?««; a pint is 0.508 of a litre.

The smaller figures in dotted lines represent the
areas of a square centimetre and of a squre inch.

A cubic centimetre of water at 4° C. weighs a
gramme.

Square
Centi-
metre.

Metre = 39f inches.
Centimetre = f inch.
Millimetre = ^V inch.
Micromillimetre = 25000 inch.

Gramme = 15^ grains.
Centigramme = -^^ grain.
Milligramme = ^f^a grain.
Kilogramme = 2.2 pounds.

INDEX

A.

Absorption, 59-62
Accommodation, 16fj, 166
After-images, 172
Air: changes in the lungs, 40

composition, 39

course in lungs, 37

expired, 39
water, 39

introduction, 37

nitrogen, 40

reserve, 38

temperature, 39

tidal, 38
Allantois, 189, 190
Amnion, 1S3
Amylopsin, 54
Auinial heat, 62, 63
Appendix, 205

chemical tests (table), 205, 206

embryonal development (table), 205

metric system, 207
Area vasculosa, 194
Areas, motor, 128

sensory, 128
Arrest of action, 104
Arterial tension, 36 *
Arteries, 30
Astigmatism, 167
Atmosphere, composition, 39
Automatic action, 99, 113

B.

Bile, flow, 55

ingredients, 56

quantity, 56

uses, 58
Blastoderm, 184

changes. 185, 186
Blind spot, 167, 168

14

Blood, 22

arterial, 26

character, 22

chemical bases, 27

circulation, 27

clot, 22

coagulation, 23, 24

corpuscles, 24

gases, 27

lack of oxygen, 41

menses, 26

quantity, 22

uses, 26
Body expenditure, 90, 91

income, 90, 91
Branchial clefts, 193

c.

Capillaries, 30
Capillary force, 36
Cells, 17, 18
Cerebellum, anatomy, 130

function, 130

removal, 132
Cerebral vesicles, 198
Cerebrum, anatomy, 121-125

fibres, course of, 125, 126

functions, 127
localization, 127

unilateral action, 127

removal, 127
Chorion. 190

villi, 190
Chyle, 55

in the lacteals, 61

quantity, 62
Cliyme, 49
Circulation of the blood, 27

apparatus, 27

course, 28
Color-blindness, 171

209

210

INDEX.

Connective tissues, 19
Corium, 70
Corpora striata, 126

quadrigemiua, 120
Corpus luteum, 181, 182
Corpuscles, blood, 24

varieties, 24-26
Cranial uerves, auatomy, 13S-14o

functions, 133-145
Cream, 68
Crura cerebri, auatomy, 120

functions, 120

D.

Decidua menstrualis, 181

reflexa, 186

vera, 186
Defecation, 58

Degeneration of a nerve-fibre, 108
Deglutitiou, 44, 46
Development, 183-202

alimeutarv canal, 200

brain, 197, 199

cranial uerves, 197

cranium, 192

ear, 200

external genitals, 202
male, 202
female, 202

extremities, 193

eye, 199

face, 192

heart, 194

kidneys, 201

lungs," 201

olfactory apparatus, 200

ovary, 202

spinal cord, 197
nerves, 197

testicle, 202
Dialvsis, 59
Diastole, 33
Digestion, 42

gastric, 50
details of, 50

intestinal, 52

nervous mechanism, 51
Diplopia, 171
Ductus arteriosus, 196

venosus, 195

E.

Ear, anatomy, 155-159

Ear, divisions, 155-159

functions, 155-159
Embrvo, circulation, 193
Embryology, 173-203
Emmetropia, 1G6
Endothelium, 18
Energv, 91
Epibla-st, 185-187
Epidermis, 70
Epithelium, 18
Eustachian valve, 196
Exclusive diet, 92
Excretions, 64
Eye, anatomy, 162-165

function, 160
Eyelids, 161

P.

Fallopian tubes, 177

function, 177
Foetal circulation, 196

changes in, after birth, 197
Fore-gut; 200

G.

Grastric juice, 48
secretion, 49
function, 49
Germinal vesicle, 176
Germinative spot, 176
Glosso-labio-laryngeal paralysis, 119
Graafian follicles, 174

H.

Hearing, 155

subjective sensations, 160
Heart, 28

action, 32, 34

auricles, 32

cavities, 29

foetal circulation, 196

force, 34

nervous influences, 35

nourishment, 35

sounds, 34
cause, 34

valves, 29
function, 32, 33

ventricles, 32
action, 32

work, 34

INDEX.

211

Heat-centre, 64
Hiud-jrut, 200
Hypoblast, 1S5, 187

I.

Images, 169, 170
Inhibition, 99, 112
lusalivation, 43
Iris, 165
action, 165

Kidneys, anatomy, 73-75
function, 74

L.

Lachrymal gland, 161
Large intestine, 58
Liver. .55

functions, 57, 53
Lungs. 37
Lymph. 62

M.

Mammary glands. 67
Mastication. 42. 43

Medulla oblongata, anatomy, 113-116
automatism. 117
centres, 117. 113
functions, 117-119
Medullary groove. 1S7
Menstruation. ISl

character, ISl

duration, 181
Mesoblast, 1S5, 187
Metabolism, 63
Micturition, 77
Milk. OS. 69

sour. 6S
Milk-curdling ferments, 69
Muller's duct, 202
Muscle. 82

color, 84

composition, 85

contraction, etc., S6-SS

electrical condition, 85

fnnction, &5

varieties. 52, 83
Muscles, involuntary, 89

voluntary, 89

Myopia, 166
Myosin, 83

X.

Nerves, afferent. i>>

anatomy. 93, 94

classification, 95, 97

efferent, 96

function, 95

impulses, 97
Xitrogenous eqnilibriom, 91
Normal diet. 93
Nutrition, 89

o.

Olfactory nerves, 1-54
Optic nerve, 161
function, 161

thalami, 126
ftinction, 126

vesicle, 199
Optograms. 169
Ovaries, 173
Over-feeding, 92
Ovum, 176

changes after impregnation, 183-185

derivation, 175

escape, 175

impregnation, 179, 1^ 183

P.

Paralysis, varieties, 129
Pancreas, secretion. 53
Parturition, 202, 203
Penis. IH)
Pepsin. 49
Peptone, 49. 50
Personal error. 97

equation. 97
Perspiration, insensible, 70
Placenta. 19*3. 191
Placental circulation, 195
Pons Varolii, anatomy, 119

functions. 120
Primitive groove. 185
Presbyopia, 167
Prostate gland. 180
Protoplasm. 17
Protovertebne. 192
Proximatf principles, 19

classification, 20^ 21

212

INDEX.

Ptyalin, 43

starch, 44
sugar, 44
Pulse, 35

K.

Eefies action, 98, 99, 112, 113
Eeproduction, 173-183
Eespiration, 36

capacity, 38

carbouic acid, 39

eiFect on tlie blood, 40
on circulation, 42

force, 38

larynx, 39

mechanism, 37
nervous, 40

modifications, 40

nostrils, 39

oxygen, 39

rapidity, 38

rhythm, 39

vagus, 41
Eetinal, red, 169
Eeturn circulation, 36
Eigor mortis, 88, 89
Eumination, 51

S.

Saliva, 43

secretion, 44
Saponification, 54
Sebaceous glands, 72, 73
Secreting glands, 65

action, 66
Secretions, 64

correlation, 67
Segmentation, 183, 184
Sensation, common, 146

muscular, 149

pressure, 149

special, 146

temperature, 149
Seminal vesicles, 180
Sexual generation, 173
Sight, 160-172
Skin, 69, 73

Small intestine, anatomy, 52
Smell, 153-155
Species, 173

Spermatic fluid, 178, 179
conveyance, 179

Spermatic fluid, secretion, 178
Spermatozoa, 179

action, 179
Sphygmograph, 35
Spinal cord, anatomy, 104-106
automatic actions, 113
course of fibres, 107, 108

of impulses, 109, 110
division of lateral half, 110

of nerve-roots, 107, 108
function, 109
reflex actions, 112
stimulation. 111
Splanchuopleure, 187
Spleen, 82
Starvation, 92
Stereoscope, 172
Stomach, 46, 51

glands, 47
Strypsin, 54
Sweat, 71
amount, 72
glands, 70
ingredients, 72
nervous mechanism, 72
Sympathetic system, 99-104
Systole, 33

T.

Taste, 150

after, 153
Teeth, 42
Testicles, 178
Tetaaus, 88
Tongue, 150-153
Touch, 147

varieties, 147

acuteness, 148
Trypsin, 54

u.

Umbilical cord, 191

vesicle, 188
Urea, 80, 81
Urethra, 180
Urine, 77

abnormal matters, 81

acidity, 77

composition, 78

course, 77

how secreted, 76

quantity, 79

INDEX.

213

Urine, secretion, conditions iifVcctinfr,
7i)

specific gravity, 77
Uterine contractions, 203
Uterns, anatomy, 177

changes in pregnancy, 186, 190

V.

Vagina, anatomy, 178
Vascular glands, 81
Vaso-motor function, 103
Veins, 30

relative area, 31
Ventilation, 41, 42
Vesicular murmur, 38

Villi, r,n

VKelline circulation, 194

nienii)rane, 176
Vitellns, 176
Voice, 160
Vomiting, 51

W.

Wolffian body, 201
duct, 202

Z.

Zona pellucida, 176
cbanges, 185

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