DENTAL DEPARTMENT
Gift of
Major Nathan C. Pickles
HAND-BOOK
OF
PHYSIOLOGY
RLDDO-SPECTRA COMPARED WITH SPECTRUM DP ARGANQ- LAMP
1 Spectrum oF Ardand-lamp with FraunhoFers lines in position.
2 Spectrum aF Dxyhsmndlabin in diluted hlaad.
3 Spectrum oF Reduced nsmo^lobin.
4 Spectrum aF Carbonic oxide Hffimo^lobin.
5 Spectrum oF AcidHaEmatm in etherial solution.
6 Spectrum oF Alkaline Heamatin.
7 Spectrum aF CblnrnFarm extract of acidulated Dx-Bile.*
8 Spectrum oF MethaBmoglobin.
9 Spectrom oF HeamDchrornDgBn.
10 Spectrum aF Hsmatoporphyrin.
Most of the above Specfm have been drawn from observations byMTWLepraffc F.C.S.
KIRKES' HANDBOOK
OF
PHYSIOLOGY
Revised and Rewritten by
CHARLES WILSON GREENE, A.M., Ph.D
Professor of Physiology and Pharmacology
University of Missouri
Strtfo Bmerican tRevtston
WITH FIVE HUNDRED AND SEVEN ILLUSTRATIONS,
INCLUDING MANY IN COLORS
NEW YORK
WILLIAM WOOD AND COMPANY
MDCCCCVII
Copyright, 1907
By WILLIAM WOOD AND COMPANY
PREFATORY NOTE
THE general organization of the Handbook has been retained in
the present revision, but the anatomical discussions have been very
greatly reduced. The text has been largely rewritten throughout, and
many new illustrations of physiological experiments have been intro-
duced. An entirely new feature is the introduction, at the end of the
chapters, of directions for laboratory work. It is hoped that this will
greatly increase the utility of the book both to the teacher and to the
student. Acknowledgment is given my colleagues, Dr. C. M. Jack-
son for reading the manuscript on the Nervous System, and Miss
Caroline McGill for similar criticism of the chapter on the Elementary
Structure of the Tissues.
CHAS. W. GREENE.
COLUMBIA, MISSOURI, October 1, 1907.
CONTENTS
PAGE
CHAPTER I — THE PHENOMENA OF LIFE; Properties of Protoplasm, i
Structure of Protoplasm, .... . .
CHAPTER II — CELL DIFFERENTIATION AND THE STRUCTURE OF THE
ELEMENTARY TISSUES; The Structure of the Cell, The Structure of
the Elementary Tissues. I. The Epithelial Tissues. II. The Con-
nective Tissues. III. Muscular Tissue. IV. Nervous Tissue, . 17
CHAPTER III— THE CHEMICAL COMPOSITION OF THE BODY; The
Nitrogenous Bodies, Classes of Proteids, Oils and Fats, Carbohy-
drates, Inorganic Principles, Laboratory Experiments, . . .78
CHAPTER IV— THE BLOOD; Quantity of the Blood, Coagulation of the
Blood, Morphology of the Blood, Chemical Composition of the Blood,
Globulocidal and Other Properties of Serum, The Character and
Composition of Lymph, Laboratory Experiments, .... 101
CHAPTER V — THE CIRCULATION OF THE BLOOD; Anatomical Con-
siderations, The Action of the Heart, The Regulative Influence of the
Central Nervous System, The Circulation through the Blood- Ves-
sels, The Pulse, The Peripheral Regulation of the Flow of Blood,
Vaso-constrictor and Vaso-dilator Nerves for Individual Organs,
Laboratory Experiments, . .141
CHAPTER VI— RESPIRATION; The Respiratory Apparatus, The Move-
ments of the Respiratory Mechanism, Respiratory Changes in the Air
Breathed, The Respiratory Changes in the Blood, The Nervous
Regulation of the Respiratory Apparatus, The Effect of Respira-
tion on the Circulation, Laboratory Experiments in Respiration, . 243
CHAPTER VII— SECRETION IN GENERAL; Organs and Tissues of Secre-
tion, Secreting Glands, The Process of Secretion. Influence of the
Nervous System on Secretion, . . . . . . . . 291
v
vi CONTENTS
PAGE
CHAPTER VIII — Fooi> AND DIGESTION; Food and Food Principles,
The Process of Digestion, Digestion in the Mouth, Deglutition, Ner-
vous Mechanism of Deglutition, Digestion in the Stomach, Move-
ments of the Stomach, Digestion in the Intestines, Movements of
the Intestines, Laboratory Experiments in Digestion, Saliva and Sali-
vary Digestion, Gastric Juice and Gastric Digestion, Pancreatic Juice
and Pancreatic Digestion, . -297
CHAPTER IX — ABSORPTION; Absorption in the Stomach, Absorption in
the Intestines, Absorption from the Skin, the Lungs, etc., . . .361
CHAPTER X— EXCRETION; Structure and Function of the Kidneys,
General Structure, The Urine, The Method of Excretion of Urine,
The Discharge of the Urine, The Structure and Excretory Func-
tions of the Skin, Laboratory Experiments in Excretion, . . -371
CHAPTER XI — METABOLISM, NUTRITION, AND DIET; Metabolism of
Proteids, The Metabolism of Fats, The Metabolism of Carbohy-
drates, Requisites of a Normal Diet, The Influence of the Ductless
Glands on Metabolism, ......... 405
CHAPTER XII — ANIMAL HEAT; Heat-producing Organs, Variation in
the Loss of Heat, Variation in the Production of Heat, Influence of
the Nervous System on Heat Production, 433
CHAPTER XIII— MUSCLE-NERVE PHYSIOLOGY; Chemical Composi-
tion of Muscle, The Properties of Living Muscle, Single Muscle Con-
tractions, Conditions which Affect the Irritability of the Muscle and
the Character of the Contraction, Tetanic and Voluntary Muscular
Contractions, The Type of Contraction in Involuntary Muscle and in
Cilia, The Function of Nerve Fiber, Some Special Coordinated Motor
Activities, Locomotion, The Production of the Voice, Laboratory
Experiments on Muscle and Nerves, . . 440
CHAPTER XIV— THE NERVOUS SYSTEM; I. Function of the Nerve
Cell. II. The Structure and Function of the Spinal Cord, The Ar-
rangement of Nerve Cells in the Spinal Cord, Columns and Tracts in
the White Matter of the Spinal Cord, The Reflex Arc and Reflex
Action, Spinal Reflexes in Man and Mammals. III. The Brain
Stem, The Medulla Oblongata or Bulb, The Pons Varolii, The Mid-
brain, The Optic Thalami, The Cranial Nerves. IV. The Cere-
bellum. V. The Cerebrum, Structure of the Cerebral Cortex, Gen-
eral Functions of the Cerebrum, Localization of the Motor Function
of the Cerebral Cortex, Localization of Sensory Function in the Cere-
bral Cortex, Association Centers of the Cerebral Cortex, The Physiol-
ogy of Sleep. VI. The Sympathetic System, . .... 503
CONTENTS Vll
PAGE
CHAPTER XV— THE SENSES; I. The Senses of Touch, Pain, Tem-
perature, and the Muscle Sense. II. Taste and Smell, The Sense of
Taste, The Sense of Smell. III. Hearing and Equilibration, The
Anatomy of the Ear, The Physiology of Hearing, The Sense of Equi-
librium. IV. The Sense of Sight, The Eye, The Optical Apparatus,
Accommodation, Defects in the Optical Apparatus, Visual Sensa-
tions from Excitation of the Retina, Color Sensations, Binocular
Vision, Visual Judgments, Laboratory Directions for Experiments
on the Sense Organs, ......... 595
CHAPTER XVI— THE REPRODUCTIVE ORGANS; The Reproductive
Organs of the Male, The Reproductive Organs of the Female, Ovu-
lation and Menstruation, Menstrual Life, 679
CHAPTER XVII— DEVELOPMENT; Changes which Occur in the Ovum
Prior to Impregnation, Changes Following Impregnation, Circula-
tion of Blood in the Fetus, Parturition, Lactation, . , . .691
INDEX, 701
FAHRENHEIT
and
CENTIGRADE
SCALES.
MEASUR
FRENCH IN:
LENGTH.
1 metre 1
10 decimetres I = 39.37 English
100 centimetres f inches.
EMENTS.
CO ENGLISH.
A grain equals about 1.16 gram.,
a Troy oz. about 31 gram.,
a Ib. Avoirdupois about £$ Kilogrm.,
and 1 cwt. about 50 Kilogrms.
F.
500°
401
392
383
374
356
347
338
329
320
311
302 •
284
275
266
248
239
230
212
203
194
176
167
140
122
113
105
104
100
C.
260°
205
200
195
1,000 millimetres J (or 1 yd. and 3^ in.)
CAPACITY.
1,000 cubic decimetres ) = 1 cubic
1,000,000 cubic centimetres f metre.
190
180
175
170
1 decimetre )
10 centimetres V = 3.937 inches
100 millimetres ) (or nearly 4 inches.)
1 cubic decimetre j
365
160
155
150
140
185
130
120
115
110
100
95
90
80
75
60
50
45
40.54
40
37.8
1 centimetre ) = .3937 or about
10 millimetres j (nearly g inch.)
1 millimetre = nearly fa inch.
OR,
ONE METRE = 39.37079 inches.
(It is the ten-millionth part of a quarter
of the meridian of the earth.)
1 Decimetre = 4 in.
1 Centimetre = A in.
1 Millimetre = «ft in.
D6cametre = b2.80 feet.
Hectometre — 109.36 yds.
Kilometre = 0.62 miles.
One inch = 2.539 Centimetres.
One foot = 3.047 Decimetres.
or V = 1 litre.
1,000 cubic centimetres \
OR
ONE LITRE = 1 pt. 15 oz. 1 dr. 40.
(For simplicity, Litre is used to signify
1 cubic decimetre, a little less than 1
English quart.)
Decilitre (100 c.c.) = 3^ oz.
Centilitre (10 c.c.) = 2f dr.
Millilitre (1 c.c.) = 17 m.
Decalitre ' = 24 gal.
Hectolitre = 22 gals.
Kilolitre (cubic metre) = 27J^ bushels.
A cubic inch = 16.38 c.c. ; a cubic foot
= 28.315 cubic dec., and a gallon =
4.54 litres.
One mile = 1.60 Kilometre.
The cubic centimetre (15.432 grains— 1
gramme) is a standard at 4° C., the
grain at 16°. 66 C.
CONVERSION SCALE.
To convert GRAMMES to OUNCES avoir-
dupois, multiply by 20 and divide by 567.
To convert KILOGRAMMES to POUNDS,
multiply by 1,000 and divide by 454.
To convert LITRES to GALLONS, mul-
tiply by 22 and divide by 100.
To convert LITRES to PINTS, multiply
by 88 and divide by 50.
To convert MILLIMETRES to INCHES,
multiply by 10 and divide by 254.
To convert METRES to YARDS, multi-
ply by 70 and divide by 64.
98.5
95
86
77
68
50
41
32
23
14
+ 5
- 4
-13
-22
-40
-76
36.9
qe
30
25
20
10
5
0
- 5
-10
WEIGHT.
(One gramme is the weight of a cubic
centimetre of water at 4° C. at Paris).
1 gramme "j
10 decigrammes I = 15.432349 grs.
100 centigrammes j (or nearly 15^).
1,000 milligrammes j
SURFACE MEASURE.
1 square metre = about 1550 sq. inches.
Or 10.000 sq. centimetres, or 10.75 sq. ft.
1 sq. inch — about 6 4 sq. centimetres.
1 sq. foot - " 930 "
- 20
-25
-30
-40
-60
1 d6cigramme )
10 centigrammes V = rather more
100 milligrammes ) than 1J^ grain.
1 centigramme ) — rather more
1 deg F — 54°C
10 decigrammes f than 5% grain.
ENERGY MEASURE.
1 kilogrammetre=about7.24ft. pounds.
1 foot pound = " .1381 kgm.
1 foot ton = " 810 kgm.
1.8 " = 1°C.
3.6 " = 2°0.
4.5 " -.= 2.5°C.
5.4 " = 3°C.
1 milligramme = rather more
than 5&y grain.
OR
To convert de-
grees F. into de-
grees C., subtract
32, and multiply
byi-
1 Decigramme — 2 dr. 34 gr.
1 Hectogrm. = 3^ oz. (Avoir.)
1 Kilogrm. = 2 Ib. 3 oz. 2 dr. (Avoir.)
HEAT EQUIVALENT.
1 kilocalorie = 424 kilogrammetres.
ENGLISH :
Apothecaries Weight.
7000 grains = 1 Ib.
Or
437.5 grains = 1 oz.
MEASURES.
Avoirdupois Weight.
16 drams = 1 oz.
16 oz. = 1 Ib.
28 Ibs. =-• 1 quarter.
4 quarters = 1 cwt.
20 cwt. = 1 ton.
To convert de-
grees C. into de-
grees F., multiply
by f , and add 32°.
Measure of 1 decimetre, or 10 centimetres, or 100 millimetres.
1234 567
The micron (symbol, M.) is the unit of microscopic measurement
8 9 Ifl
mm. = nfov inch.
HANDBOOK OF PHYSIOLOGY
CHAPTER I
THE PHENOMENA OF LIFE
PHYSIOLOGY is the science which treats of the various processes or changes
which take place in the organs and tissues of the body during life. These
processes, however, must not be considered as by any means peculiar to the
human organism, since, putting aside the properties which serve to distinguish
man from other animals, the changes which go on in the tissues of man go on
in much the same way in the tissues of all other animals as long as they live.
Furthermore it is found that similar changes proceed in all living vegetable
tissues; they indeed constitute what are called vital phenomena, and are those
properties which mark out living from non-living material.
The lowest types of life, whether animal or vegetable, are found to consist
of minute masses of a jelly-like substance, which is generally known under the
name of protoplasm. Each such living mass is called a cell, so that these
minute elementary organisms are designated unicellular.
Not only is it true that the lowest types of life are made up of cells, but it
has also been shown that the tissues of which the most complex organisms are
composed consist of cells.
The phenomena of life are exhibited in cells, whether existing alone or de-
veloped into 'he organs and tissues of animals and plants. It must be at once
evident that a correct knowledge of the nature and activities of the cell forms
the very foundation of physiology; cells being, in fact, physiological no less
than morphological units.
The prime importance of the cell as an element of structure was first
established by the researches of the botanist Schleiden, and his conclusions,
drawn from the study of vegetable histology, were at once extended by Theo-
dor Schwann to the animal kingdom. The earlier observers defined a cell
as a more or less spherical body limited by a membrane, and containing a
smaller body termed a nucleus, which in its turn incloses one or more still
smaller bodies or nudeoli. Such a" definition applied admirably to most veg-
etable cells, but the more extended investigation of animal tissues soon showed
that in many cases no limiting membrane or cell-wall could be demonstrated.
The presence or absence of a cell-wall, therefore, was then regarded as
quite a secondary matter, while at the same time the cell-substance came
1 1
THE PHENOMENA OF LIFE
— ... Space contain-
ing liquid.
Protoplasm.
Nucleus.
Cell wall.
FIG. i.— Vegetable Cells.
gradually to be recognized as of primary importance. Many of the lower
forms of animal life, the Rhizopoda, were found to consist almost entirely
of matter very similar in appearance and chemical composition to the cell-
substance of higher forms; and this from its chemical resemblance to flesh was
termed Sarcode by Dujardin. When recognized in vegetable cells it was called
Protoplasm by Mulder, while Remak applied
the same name to the substance of animal cells.
As the presumed formative matter in animal
tissues it was termed Blastema, and in the be-
lief that, wherever found, it alone of all sub-
stances has to do with generation and nutrition,
Beale has named it Germinal matter or Bio-
plasm. Of these terms the one most in use at
the present day, as we have already said, is
protoplasm, and inasmuch as all life, both in
the animal and vegetable kingdoms, is associated
with protoplasm, we are justified in describing
it, with Huxley, as the "physical basis of life,"
or simply "living matter."
Properties of Protoplasm. Protoplasm
is a semi-fluid substance, which absorbs but
does not mix with water. It is transparent and generally colorless, with
refractive index higher than that of water but lower than that of oil. It is
neutral or weakly alkaline in reaction, but may under special circumstances
be acid, as, for example, after activity. It undergoes heat-coagulation at
a temperature of about 54.5° C. (130° F.), and hence no organism can live
when its own temperature is
raised above that point. It is
also coagulated and therefore
killed by alcohol, by solutions
of many of the metallic salts, by
strong acids and alkalies, and by
many other chemical substances.
Under the microscope it is
seen almost universally to be
granular, the granules consisting
of different mibstanre<; albii- FIG. 2. — Semidiagrammatic Representation of a Human
.CS, 1DU Ovum, showing the parts of an animal cell. (Cadia.)
minous, fatty, or carbohydrate
matter. The granules are not equally distributed throughout the whole
cell-mass, as they are sometimes absent from the outer part or layer,
and very numerous in the interior. In addition to granules, protoplasm
generally exhibits spaces or vacuoles, usually globular in shape, except-
ing during movement, when they may be irregular, and filled with a watery
ger-
minal vesicle.
L Nucleolus or ger-
minal spot.
Space left by re-
traction of yolk.
... Vitellus or yolk.
Vitelline mem-
brane.
CHARACTERISTICS OF PROTOPLASM 3
fluid. These vacuoles are more numerous and pronounced in vegetable than
in animal cells. Gas bubbles also sometimes exist in cells.
It is impossible to make any definite statement as to the exact chemical
composition of living protoplasm, since the methods of chemical analysis
necessarily imply the death of the cell; it is, however, stated that protoplasm
contains 75 to 85 per cent of water, and of the 15 to 25 per cent of solids the
most important part belongs to the class of substances called proteids or al-
bumins. Proteids contain the chemical elements carbon, hydrogen, nitrogen,
oxygen, sulphur, and phosphorus, the last two in very small quantities only.
A proteid-like substance, nuclein, found in the nuclei of cells, contains phos-
phorus in greater abundance. In the cell nucleus a compound of nuclein
with proteid, called nucleoproteid, forms the most abundant proteid sub-
stance. Other bodies are frequently found associated with the proteids, such
FIG. 3. — Phases of Ameboid Movement.
as glycogen, starch, cellulose, which contain the elements carbon, hydrogen, and
oxygen, the last two in the proportion to form water, and hence are termed
carbohydrates; fatty bodies, containing carbon, hydrogen, and oxygen, but not
in proportion to form water; lecithin, a complicated fatty body containing
phosphorus; cholesterin, a monatomic alcohol; chlorophyll, the coloring matter
of plants; inorganic salts, particularly the chlorides and phosphates of calcium,
sodium, and potassium; ferments, and other substances.
The Physiological Characteristics of Protoplasm. The properties
of protoplasm may be well studied in the microscopic animal called the
ameba, a unicellular organism found chiefly in fresh water. These properties
may be conveniently studied under the following heads: —
The Power of Spontaneous Movement. When an ameba is observed
with a high power of the microscope, it is found to consist of an irregular mass
of protoplasm containing one or more nuclei, the protoplasm itself being
more or less granular and vacuolated. If watched for a minute or two, an
irregular projection is seen to be gradually thrust out from the main body;
other masses are then protruded until gradually the whole protoplasmic sub-
stance is, as it were, drawn over to a new position, and when this is repeated
several times we have locomotion in a definite direction, together with a con-
tinual change of form. These movements, figure 3, when observed in other
cells, such as the colorless blood-corpuscles of higher animals, in the branched
corneal cells of the frog and elsewhere, are termed ameboid.
4 THE PHENOMENA OF LIFE
The remarkable movement of pigment granules observed in the branched
pigment cells of the frog's skin by Lister are also probably due to ameboid
movement. These granules are seen at one time distributed uniformly through
the body and branched processes of the cell, while at another time they collect
in the central mass leaving the branches quite colorless.
This movement within the pigment cells might also be considered an ex-
ample of the so-called streaming movement not infrequently seen in certain
of the protozoa, in which the mass of protoplasm extends long and fine pro-
cesses, themselves very little movable, but upon the surface of which freely
moving or streaming granules are seen. A gliding movement has also been
noticed in certain animal cells; the motile part of the cell being composed of
protoplasm bounding a central and more compact mass. By means of the
free movement of this layer, the cell may be observed to move along.
In vegetable cells the protoplasmic movement can be well seen in the hairs
of the stinging-nettle and Tradescantia and in the cells of Vallisneria and
Chara; it is marked by the movement of the granules nearly always embedded
in it. For example, if part of a hair of Tradescantia, figure 5, be viewed
under a high magnifying power, streams of protoplasm containing crowds of
FIG. 4. — Changes of Form of a White Corpuscle, Sketched at Brief Intervals,
show also the ingestion of two small granules. (Schafer.)
The figures
granules hurrying along, like the foot-passengers in a busy street, are seen flow-
ing steadily in definite directions, some coursing round the film which lines
the interior of the cell-wall, and others flowing toward or away from the irregu-
lar mass in the center of the cell-cavity. Many of these streams of protoplasm
run together into larger ones and are lost in the central mass, and thus ceaseless
variations of form are produced. The movement of the protoplasmic granule?
to or from the periphery is sometimes called vegetable circulation, whereas the
movement of the protoplasm round the interior of the cell is called rotation.
The first account of the movement of protoplasm was given by Rosel in
I755> as occurring in a small Proteus, probably a large fresh-water ameba.
His description was followed twenty years later by Corti's demonstration of
the rotation of the cell sap in characeae, and in the earlier part of the century
CHARACTERISTICS OF PROTOPLASM 5
by Meyer in Vallisneria, 1827; Robert Brown, 1831, in "Staminal Hairs of
Tradescantia." Then came Dujardin's description of the granular streaming
in the pseudopodia of Rhizopods and movements in other cells of animal
protoplasm (Planarian eggs, von Siebold, 1841; colorless blood-corpuscles,
Wharton Jones, 1846).
The Power of Response to Stimuli, or Irritability. Although the movements
of the ameba have been described above as spontaneous, yet they may be in-
creased under the action of external agencies which excite them and are there-
fore called stimuli, and if the movement has ceased for the time, as is the case if
the temperature is lowered beyond a certain point, movement may be set up by
raising the temperature. Contact with foreign bodies, gentle pressure, cer-
FIG. 5. — Cell of Tradescantia Drawn at Successive Intervals of two Minutes. — The cell- contents
consist of a central mass connected by many irregular processes to a peripheral film, the whole
forming a vacuolated mass of protoplasm, which is continually changing its shape. (Schofield.)
tain salts, and electricity produce or increase the movement in the ameba.
The protoplasm is, therefore, sensitive or irritable to stimuli, and shows its irri-
tability by movement or contraction of its mass.
The effects of some of these stimuli may be thus further detailed: —
a. Changes of Temperature. Moderate heat acts as a stimulant; the move-
ment stops below o° C. (32° F. ), and above 40° C. (104° F.); between these
two points the movements increase in activity; the optimum temperature is
about 37° to 38° C. Exposure to a temperature even below o° C. stops the
movement of protoplasm, but does not prevent its reappearance if the tem-
perature is raised; on the other hand, prolonged exposure to a temperature
of over 40° C. kills the protoplasm and causes it to enter into a condition of
coagulation or heat rigor.
b. Mechanical Stimuli. When gently squeezed between a cover and
object-glass under proper conditions, a colorless blood-corpuscle contracts
and ceases its ameboid movement.
c. Nerve Influence. By stimulation of the nerves of the frog's cornea,
contraction of certain of its branched cells has been produced.
d. Chemical Stimuli. Water generally stops ameboid movement, and by
imbibition causes great swelling and finally bursting of the cells. In some
cases, however (myxomycetes), protoplasm can be almost entirely dried up,
but remains capable of renewing its movements when again moistened.
THE PHENOMENA OF LIFE
Dilute salt-solution and many dilute acids and alkalies stimulate the move-
ments temporarily. Strong acids or alkalies permanently stop the movements;
ether, chloroform, veratrium, and quinine also stop it for a time.
Movement is suspended in an atmosphere of hydrogen or carbonic acid
and resumed on the admission of air or oxygen, but complete withdrawal of
oxygen will after a time kill the protoplasm.
e. Electrical. Weak currents stimulate movement, while strong currents
cause the cells to assume a spherical form and to become motionless.
The Power of Digestion, Respiration, and Nutrition. This consists in the
power which is possessed by the ameba and similar animal cells of taking in
food, modifying it, building up tissue by assimilating it, and rejecting what is
not assimilated. These various processes are effected in some one-celled ani-
mals by the protoplasm simply flowing around and enclosing within itself
minute organisms such as diatoms and the like. From these it extracts what
it requires, and then rejects or excretes the remainder, which has never formed
part of the body. This latter proceeding is done by the cell withdrawing
itself from the material to be excreted. The assimilation constantly taking
place in the body of the ameba is for the pur-
pose of replacing waste of its tissue consequent
upon manifestation of energy. The respiratory
process of absorbing oxygen goes on at the same
time.
The processes which take place in cells,
both animal and vegetable, are summed up
under the term metabolism (from peTafioty,
change). The changes which go on are of two
kinds, viz., assimilation, or building up, and
disassimilation, or breaking down ; they may
be also called, using the nomenclature of Gas-
kell, anabolism or constructive metabolism, and
catabolism or destructive metabolism. In the
direction of anabolism two processes occur,
viz., the building up of materials which it
takes in, and secondly, the building up of its
own substance by those or other materials.
As we shall see in a subsequent paragraph,
the process of anabolism differs to some ex-
tent in vegetable and animal cells. The catab-
olism of the cell consists in chemical changes which occur in the cell-
substance itself, or in substances in contact with it.
The destructive metabolism of a cell is increased by its activity, but goes
on also during quiescence. It is probably of the nature of oxidation, and re-
sults in the evolution of carbon dioxide and water on the one hand, and in the
FIG. 6. — Cells from the Staminal
Hairs of Tradescantia. A, Fresh
in water; B, the same cell after
slight electrical stimulation; a, b,
region stimulation; c, d, clumps
and knobs of contracted proto-
plasm. (KUhne.)
CHARACTERISTICS OF PROTOPLASM 7
formation of various more complex chemical substances on the other, some of
which may be stored up in the cell for future use, and are called secretions,
and others, like carbon dioxide, for example, and bodies containing nitrogen,
are eliminated as excretions.
The Power of Growth. In protoplasm it is seen that the two processes of
waste and repair go on side by side, and so long as they are equal the size
of the animal remains stationary. If, however, the building up exceed the
waste, then the animal grows; if the waste exceed the repair, the animal
FIG. 7. — Diagram of an Ovum (a) Undergoing Segmentation. In (6) it has divided into two.
in (c) into four; and in (d) the process has ended in the production of the so-called "mulberry mass."
(Frey.)
decays; and if decay go on beyond a certain point, life becomes impossible,
and the animal dies.
The power of increasing in size, although essential to our idea of life, is not,
it must be recollected, confined to living beings. A crystal of common salt,
for example, if placed under appropriate conditions for obtaining fresh mate-
rial, will increase in size in a fashion as definitely characteristic and as easily
to be foretold as that of a living creature; but the growth of a crystal takes
place merely by additions to its outside; the new matter is laid on particle by
particle, and layer by layer, and, when once laid on, it remains unchanged. In
a living structure, where growth occurs, it is by addition of new matter, not
to the surface only, but throughout every part of the mass, and this matter be-
comes an intimate part of the living substance.
The Power of Reproduction. The ameba, to return to our former illus-
tration, when the growth of its protoplasm has reached a certain point, mani-
fests the power of reproduction, by splitting up into (or in some other way pro-
ducing) two or more parts, each of which is capable of independent existence.
The new amebae manifest the same properties as the parent, perform the same
functions, grow and reproduce in their turn. This cycle of life is being con-
tinually passed through.
In more complicated structures than the ameba, the life of individual
protoplasmic cells is probably very short in comparison with that of the organ-
ism they compose ; and their constant decay and death necessitate constant re-
production. The mode in which this takes place has long been the subject of
controversy.
It is now very generally believed that every cell is descended from some
pre-existing mother cell. This derivation of cells from cells takes place by
gemmation, which essentially consists in the budding off and separation of
a portion of the parent cell; or by fission or division.
8
THE PHENOMENA OF LIFE
The exact manner of the division of cells is a matter of some difficulty, and
will not be described until the subject of the structure of protoplasmic cells has
been considered.
STRUCTURE OF PROTOPLASM.
Elemental Structure. Protoplasm was formerly thought to be
homogeneous. It is now generally found to consist of the elemental divisions
called cells. Each cell, from a morphological point of vi consists of dif-
ferentiated parts, the most constant of which are the cell nucleus and the cell
cytoplasm. The cytoplasm is differentiated further into two substances,
spongioplasm and hyaloplasm. The spongioplasm or reticulum forms a fine
network, increases in relative amount as the cell grows older, and has an
affinity for staining reagents. The hyaloplasm is less refractile, elastic, or
extensile, and has little or no affinity for stains; it predominates in young cells
Cell membrane —
Cell reticulum ....
Membrane of nucleus.
Achromatic substance of
nucleus.
Chromatic substance of
nucleus.
PlO. 8. — Cell with its Ketiailum Disposal K;u!i;illv; fn.ni Mir intrst.innl epithelium of n
worm. (Carnoy.)
is thought to be fluid, and fills the interspaces of the reticulum. The nodal
points of the reticulum, with the granular microsomes, found in the proto-
plasm, cause the granular appearance.
The arrangement of the reticulum varies considerably in different cells, and
even in different parts of the same cell. Sometimes, for example, figure 8,
the. meshwork has an elongated radial arrangement from the nucleus; at
others, the meshwork is more evenly disposed, as in figure 9. At the junctions
of the fibrils there are usually slight enlargements or nodes.
In some cells, particularly in plants, but also in some animal cells, there is
a tendency toward a formation of a firmer external envelope, constituting in
vegetable cells a membrane distinct from the more central and more fluid part
of the protoplasm. In such cases the reticulum at the periphery of the cell is
made up of very fine meshes. The membrane when formed is usually pierced
with pores by which fluid may pass in, or through which protrusion of the
protoplasmic filaments forming the cell's connection with other cells surround-
ing it may take place.
STRUCTURE OF PROTOPLASM 9
Tl is an exceedingly interesting question whether in cells the one part of the
protoplasm ran exist \vithout the other. Schafer summarizes the matter thus:
"There are cells, anil unirellular organisms both animal and vegetable, in
which no reticular structure can be made out, and these may be formed of
hyaloplasm alone. In that ease, this must be looked upon as the essential
part of protoplasm. So far as ameboid phenomena are concerned it is cer-
tainly so; but whether the chemical changes which occur in many cells are
effected by this or by spongioplasm is another matter."
The Cell Nucleus. All cells at some period of their existence pos-
sess nuclei. The origin of a nucleus in a cell is the first trace of the differentia-
tion of protoplasm. The existence of nuclei was first pointed out in the
l-'ii; o. — A: The IVI.M -U-ss \M,\\\ Corpuscle, Showing the Intracellular Network, and two
nuclei with intranuclear network. B; Colored blood-corpuscle of newt showing the intracellular
m-t \\ork ot fibrils. Also oval nucleus composed of limiting membrane and fine intranuclear net-
\\IM-W ot fibrils. X 800. (Klein and Noble Smith.)
Near iS^; by Robert Brown, who observed them in vegetable cells. They are
either small transparent vesicular bodies containing one or more smaller parti-
cles called nucleoli, always when in the resting condition bounded by a well-
defined envelope. In their relation to the life of the cell they are certainly
hardly second in importance to the cytoplasm itself, and thus Beale is fully
justified in comprising both under the term "germinal matter." They con-
trol the nutrition of the cell, and probably initiate the process of subdivision.
If a cell be mechanically divided, that portion not containing the nucleus dies.
Uistologists have long recognized certain important characters of nuclei.
One is their power of resisting the action of various acids and alkalies, particu-
larly acetic acid, by which theiroutlines are more clearly defined, and they are
rendered more easily visible. Another is their quality of staining in solu-
tions of carmine, hematoxylin, etc. This indicates some chemical difference
between the c\ toplasm of the cells and their nuclei, as the former is destroyed
by these reagents.
Nuclei are most commonly oval or round, and do not necessarily conform to
the diverse shapes of the cells; they are altogether less variable elements than
cells, even in regard to size, of which fact one may see a good example in the
uniformity of the nuclei in cells so multiform as those of epithelium. But
sometimes nuclei occupy almost the whole of the cell, as in the lymph corpuscles
10
THE PHENOMENA OF LIFE
of lymphatic glands, and in some small nerve cells. Their position in the cell
is very variable. -In many cells, especially where active growth is progressing,
two or more nuclei are present.
Cell Division and Growth. The division of a cell is preceded by
division of its nucleus, which may be either direct or indirect. Direct or simple
division, amitosis or akinesis, see figure 10, occurs without any change in the
arrangement of the intranuclear network. A constriction develops at the cen-
ter of the nucleus, possibly preceded by division of the nucleoli, and gradually
divides it into two equal daughter nuclei. A similar constriction of the pro-
toplasm of the cell occurs between the daughter nuclei and divides it into two
parts.
Indirect division, mitosis, or karyokinesis is the usual method, and consists
of a series of changes in the arrangement of the intranuclear network, resulting
a
FIG. 10. — Akinesis, Amitosis, or Direct Cell Division. A, Constriction of nucleus; B, division
of nucleus and constriction of cell body; C, daughter nuclei still connected by a thread, division
being delayed; D, division of cell body nearly complete. (After Arnold.)
in the exact division of the chromatic fibers into two parts, which form the
chromoplasm of the daughter nuclei. The changes follow a closely similar
course in both plant and animal cells.
Differences between Animals and Plants. Having considered at
some length the vital properties of protoplasm, as shown in cells of animal
as well as of vegetable organisms, we are now in a position to discuss the ques-
tion of the differences between plants and animals. It might at the outset
of our inquiry have seemed an unnecessary thing to recount the distinctions
which exist between an animal and a vegetable as they are in many cases so
obvious, but, however great the differences may be between the higher animals
and plants, in the lowest of them the distinctions are much less plain.
In the first place, it is important to lay stress upon the differences between
vegetable and animal cells, first as regards their structures and next as re-
gards their functions.
DIFFERENCES BETWEEN ANIMALS AND PLANTS
11
It has been already mentioned that in animal cells an envelope or cell-wall
is by no means always present. In adult vegetable cells, on the other hand,
a well-defined wall is highly characteristic; this is composed of cellulose,
is non- nitrogenous, and thus differs chemically as well as structurally from the
contained protoplasmic mass. Moreover, in vegetable cells, figure 12, B, the
FIG. ii. — Karyokinesis, Mitosis, or Indirect Cell Division (diagrammatic). A, Cell with rest-
ing nucleus; B, wreath, daughter centrosomes and early stage of achromatic spindle; C, chromo-
somes; D, monaster stage, achromatic spindle in long axis of nucleus, chromosomes dividing;
E, chromosomes moving toward centrosomes; F, diaster stage, chromosomes at poles of nucleus,
commencing constriction of cell body; G, daughter nuclei beginning return to resting state; H,
daughter nuclei showing monaster and wreath; 7, complete division of cell body into daughter
cells whose nuclei have returned to the resting state. (After Bohm and von Davidoff .)
protoplasmic contents of the cell fall into two subdivisions: i, a continuous
film which lines the interior of the cellulose wall; and, 2, a reticulate mass con-
taining the nucleus and occupying the cell-cavity. The interstices are filled
with fluid. In young vegetable cells such a distinction does not exist; a
FIG. 12.— A. Young Vegetable Cells.Showing Cell-Cavity Entirely Filled with Granular Pro-
toplasm Enclosing a Large Oval Nucleus, with one or more Nucleoli. B. Older cells from same
plant, showing distinct cellulose- wall and vacuolati.on o f protoplasm.
finely granular protoplasm occupies the whole cell-cavity, figure 12, A. As
regards the respective functions of animal and vegetable cells, one of the
most important differences consists in the power which vegetable cells possess
of being able to build up new complicated nitrogenous and non-nitrogenous
12 THE PHENOMENA OF LIFE
bodies out of very simple chemical substances obtained from the air and from
the soil. They obtain from the air oxygen, carbon dioxide, and water, as
well as traces of ammonia gas; and from the soil they obtain water, ammonium
salts, nitrates, sulphates, and phosphates in combination with such bases as
potassium, calcium, magnesium, sodium, iron, and others. The majority
of plants are able to work up these elementary compounds into other and more
complicated bodies. This they are able to do in consequence of their contain-
ing a certain coloring matter called chlorophyll, the presence of which is the
cause of the green hue of plants. In all plants which contain chlorophyll two
processes are constantly going on when they are exposed to light: one, which
is called true respiration and is a process common to animal and vegetable
cells alike, consists in the taking of the oxygen from the atmosphere and the
giving out of carbon dioxide; the other, which is peculiar apparently to bodies
containing chlorophyll, consists in the taking in of carbon dioxide and the
giving out of oxygen. It seems that the chlorophyll is capable of decomposing
the carbon dioxide gas and of fixing the carbon in the structures in the form of
new compounds, one of the most rapidly formed of which is starch.
Vegetable protoplasm by the aid of its chlorophyll is able to build up a large
number of bodies besides starch, the most interesting and important being
proteid or albumin. It appears to be a fact that the power which bodies pos-
sess of being able to synthesize is to a large extent dependent upon the chloro-
phyll they contain. Thus the power is present to a marked extent only in the
plants in which chlorophyll is found, and is absent in those which do not
possess it. It is probably present only in slight degree as one of the proper-
ties of animal protoplasm.
It must be recollected, however, that chlorophyll without the aid of the
light of the sun can do nothing in the way of building up substances, and a
plant containing chlorophyll when placed in the dark, while it continues to live,
and that is not as a rule long, acts as though it did not contain any of that sub-
stance. It is an interesting fact that certain of the bacteria have the chlorophyll
replaced by a similar pigment which is able to decompose carbon dioxide gas.
Animal cells do not possess the power of building up or synthesizing from
simple materials; their activity is chiefly exercised in the opposite direction,
viz., they have brought to them as food the complicated compounds produced
by the vegetable kingdom. With these foods they are able to perform their
complex functions, setting free energy in the direction of heat, motion, and
electricity, and at the same time eliminating such bodies as carbon dioxide and
water, and producing other bodies, many of which contain nitrogen, but are
derived from decomposition.
With reference to the substance chlorophyll it is necessary to say a few
words. It has been noted that the synthetical operations of vegetable cells are
peculiarly associated with the possession of chlorophyll and that these opera-
tions are dependent upon the light of the sun. It has been further shown that
DIFFERENCES BETWEEN ANIMALS AND PLANTS 13
a solution of chlorophyll has a definite absorption spectrum when examined
with the spectroscope, and that it is particularly those parts of the solar spec-
trum corresponding to these absorption bands which are chiefly active in the
decomposition of carbon dioxide. In the synthetical processes of the plant
then, by aid of its chlorophyll, the radiant energy of the sun's rays becomes
stored up or rendered potential in the chemical products formed. The poten-
tial energy is set free, or is again made kinetic, when these products simply by
combustion produce heat, or when they are taken into the animal organism
and used as food and to produce heat and motion.
The influence of light is not an absolute essential to animal life; indeed, it
is said not to increase the metabolism of animal tissue to any great extent,
and the animal cell does not receive its energy directly from the sun's light,
nor yet to any extent from the sun's heat, but from the potential energy of the
food stuffs. But it must be always kept in mind that anabolism is not peculiar
to vegetable, or katabolism to animal cells; both processes go on in each.
Some of the lowest forms of vegetable life, e.g., the bacteria, will live only in a
highly albuminous medium, and in fact seem to require for their growth
elements of food stuffs which are essential to animal life. In their metabolism,
too, they very closely approximate animal cells, not only requiring an atmos-
phere of oxygen, but giving out carbon dioxide freely, and secreting and excret-
ing many very complicated nitrogenous bodies, as well as forming proteid,
carbohydrates, and fat, requiring heat but not light for the due performance
of their functions. Certain bacteria grow only in the absence of oxygen.
There is, commonly, a difference in general chemical composition between
vegetables and animals, even in their lowest forms; for associated with the
protoplasm of the former is a considerable amount of cellulose, a substance
closely allied to starch and containing carbon, hydrogen, and oxygen only.
The presence of cellulose in animals is much rarer than in vegetables, but there
are many animals in which traces of it may be discovered, and some in which
it is found in considerable quantity. The presence of starch in vegetable cells
is very characteristic, though, as we have seen above, it is not distinctive, and
a substance, glycogen, similar in composition to starch, is very common in the
organs and tissues of animals.
Inherent power of movement is a quality which we so commonly consider
an essential indication of animal nature that it is difficult at first to conceive of
its existence in any other. The capability of simple motion is now known,
however, to exist in so many vegetable forms that it can no longer be held
as an essential distinction between them and animals, and ceases to be a mark
by which the one can be distinguished from the other. Thus the zoospores of
many of the Cryptogams exhibit ciliary or ameboid movements of a like
kind to those seen in amebae; and even among the higher orders of plants,
many, e.g., Dioncza muscipula ( Venus Js fly-trap), and Mimosa sensitive, (Sensi-
tive plant) exhibit such motion, either at regular times or on the applica-
14 THE PHENOMENA OF LIFE
tion of external irritation, as might lead one, were this fact taken by itself, to
regard them as sentient beings. Inherent power of movement, then, al-
though especially characteristic of animal nature, is, when taken by itself, no
proof of it.
Cell Differentiation and the Functions of Organized Cells. As we
proceed upward in the scale of life from the unicellular organisms, we find
another phenomenon exhibited in the life history of the higher forms, namely,
that of development. The one-celled ameba comes into being derived from
a previous ameba; it manifests the properties and performs the functions of
its life which have been already enumerated. In the higher organisms it is
different. Each, indeed, begins as a single cell, but the cells which result from
division and subdivision do not form so many independent organisms, but
adhere in one differentiated community which ultimately forms the complex
but co-ordinated whole, in man the human body.
Thus, from the ovum, or germ cell which forms the starting-point of ani-
mal life, in a comparatively short time there is formed a complete membrane
of cells, polyhedral in shape from mutual pressure, called the Blastoderm; and
FIG. 13. — Transverse Section through Embryo Chick (26 hours), a, Epiblast; b, mespblast;
c, hypoblast; d, central portion of mesoblast, which is here fused with epiblast; e, primitive
groove; /, dorsal ridge. (Klein.)
this speedily differentiates into two and then into three layers, chiefly from
the rapid proliferation of the cells of the first single layer. These layers,
figure 13, are called the Epiblast, the Mesoblast, and the Hypoblast. In the
further development of the animal it is found that from each of these layers is
produced a very definite part of the completed body. For example, from
the cells of the epiblast are derived, among other structures, the skin and the
central nervous system; from the mesoblast the muscles and connective
tissue of the body, and from the hypoblast the epithelium of the alimentary
canal, some of the chief glands, and so on.
It is obvious that the tissues and organs so derived will exhibit in a varying
degree the primary properties of protoplasm. The muscles, for example,
derived chiefly from certain cells of the mesoblast are particularly contractile
and respond to stimuli readily, while the cells of the liver, although possibly
contractile to a certain extent, have to do chiefly with the processes of nutrition.
SOURCES AND UTILIZATION OF PHYSIOLOGICAL MATERIAL 15
As the cells of the embryo increase in number in development there is a
corresponding differentiation of function among the groups of cells. The
various functions which the original cell may be supposed to discharge, and
the various properties it may be supposed to possess, become divided among
groups of cells in which the work of each group is specialized. As a result
of this division of labor the functions and properties are developed and made
more perfect, with a view to the more economic and effective accomplishment
of the activities of the body as a whole.
In studying the functions of the human body it is necessary first of all to
know of what it is composed, of what tissues and organs it is made up; this
can of course be ascertained only by the dissection of the dead body, and thus
it comes that Anatomy, the science which treats of the structure of organized
bodies, is closely associated with physiology, which treats of the function of
the same structures. So close, indeed, is the association that Histology,
which is especially concerned with the minute or microscopic structure of the
tissues and organs of the body, and which is strictly speaking a department
of anatomy, is often included in works on physiology. There is much to be
said in favor of such an arrangement, since it is impossible to consider the
changes which take place in any tissue during life, apart from the knowledge
of the structure of the tissues themselves. There is indeed an almost insep-
arable relation between the structure and the function of the differentiated
animal body in which the one is made the means to a knowledge of the other as
an end, and vice versa, according to the aims and purposes of the student.
An equally important essential to the right comprehension of the changes
which take place in the living organism is a knowledge of the chemical com-
position of the body. Here, however, we can deal directly only with the
composition of the dead body, and it is well at once to admit that there may
be many chemical differences between living and non-living tissues; but as it
is impossible to ascertain the exact chemical composition of the living tissues,
the next best thing which can be done is to find out as much as possible about
the composition of the same tissues after they are dead. This is the assistance
which the science of Chemistry can afford to the physiologist.
Having mastered the structure and composition of the body, we are brought
face to face with physiology proper, and have to investigate the vital changes
which go on in the tissues, the various actions taking place as long as the or-
ganism is at work. The subject includes not only the observation of the mani-
fest processes which are continually taking place in the healthy body, but
the conditions under which these are brought about, the laws which govern
them and their effects.
Sources and Utilization of Physiological Material. It may be well
to mention as a preliminary that the physiological information which we have
at our disposal has been derived from many sources, the chief of which are
as follows: From actual observation of the various phenomena occurring in
16 THE PHENOMENA OF LIFE
the human body from day to day, and from hour to hour, as, for example, the
estimation of the amount and composition of the ingesta and egesta, the res-
piration, the beat of the heart, and the like; from observations upon other
animals, the bodies of which we are taught by comparative anatomy approxi-
mate the human body in structure and may be supposed to be similar in function;
from observations of the changes produced by experiment upon the various
processes in such animals, or in the organs and tissues of animals; from ob-
servations of the changes in the working of the human body produced by dis-
eases; from observations upon the gradual changes which take place in the
functions of organs when watched in the embryo from their earliest beginnings
to their completed development.
The physiologist, in order to utilize the sources of material, must be familiar
with the gross structure of the animals or parts of animals which he proposes
to use in experimental procedure. So simple a matter as the determination of
arterial blood pressure involves familiarity with extensive anatomical structure.
Experimental procedure must also draw on the field of microscopic structure
or histology, and many of the most instructive bodies of physiological knowledge
have come directly from the utilization of the facts of comparative anatomy
and of biology. The problems in animal nutrition which are under such ex-
tensive investigation at the present time require for their solution not only
the use of the most complex methods of chemistry, both analytical and synthet-
ical, but also the principles and methods of physics. Indeed, since the work
of Helmholz, the interpretation of physiological phenomena by means of physi-
cal laws and methods has contributed more than any other means toward the
prominent scientific position of physiology at the present time. In a word,
physiology must utilize the facts of anatomy, histology, biology, physics, and
chemistry to interpret the phenomena of life.
CHAPTER II
CELL DIFFERENTIATION AND THE STRUCTURE OF THE
ELEMENTARY TISSUES
A CAREFUL examination of the human body shows that the functional unit
for the various and complicated life phenomena is the microscopical structure,
the cell. The cell, alone or in combination, is capable of all the activities
manifested by the living body. As a basis for brief review of the elementary
structures of the body we shall first discuss the structure and development of
the cell.
THE STRUCTURE OF THE CELL.
The typical tissue cell is a spherical or ovoid mass of protoplasm. Its
structure is quite complex, but the most general differentiation is into the cell
mass or cytoplasm, and its contained nucleus. The cytoplasm is sometimes
bounded by a definite cell membrane, but in differentiated animal tissues this
membrane is usually not present.
The Cell Body. The cell body or cytoplasm is a complex semi-
fluid mass, the detailed structure of which has presented problems of many
difficulties. It is usually described as having a framework of spongioplasm or
formed elements, and a homogeneous hyaloplasm. In some cells there are
formed materials resulting from the cellular activity called metaplasm, figure
14. These structural features are made more evident by their affinity for
certain staining reagents.
The spongioplasm or reticulum varies greatly in different types of cells,
and even in different parts of the same cell. It has considerable affinity for
stains which exhibit a fine network, the reticulum. It increases in amount
in older cells and also in constancy in the type of arrangement.
The hyaloplasm is more fluid, less refractile, and stains with great difficulty.
It fills the interspaces of the spongioplasm. In this material may be embedded
such substances as the metaplasts mentioned above.
Structure of the Nucleus. The nucleus when in a condition of rest
is bounded by a distinct membrane, the nuclear membrane, possibly derived
from the spongioplasm of the cell, which encloses the nuclear contents, nucleo-
plasm or karyoplasm. The membrane consists of an inner, or chromatic, and
of an outer, or achromatic layer , so called from their reaction to stains. The
nucleoplasm is made up of a reticular network, or chromoplasm, whose inter-
spaces are filled by the karyolymph, or nuclear matrix, a homogeneous sub-
2 17
18
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
stance which is rich in proteids, has but slight affinity for stains, and is supposed
to be fluid.
The network is composed of linin or achromatin, a transparent unstainable
framework; and of chromatin, which stains deeply. It is supported by the
linin, and occurs sometimes in the form of granules, but usually as irregular
anastomosing threads, both thicker primary fibers and thinner connecting
branches. The threads often form thickened nodes, karyosomes or false
nucleoli, at their points of intersection. It is now quite generally believed that
Cell membrane.
Metaplasm gran- <
ules.
Karyosome or net-
knob.
Hyaloplasm.
Spongioplasm.
Linin network.
Nucleoplasm.
Attraction sphere.
Centrosome.
, Plastids.
.-•"- Chromatin network
Nuclear membrane.
Nucleolus.
Vacuole.
FIG. 14. — Diagram of a Typical Cell. (Bailey.)
the chromatin occurs as short, rodlike, and highly refractive masses, which are
embedded in the linin in a regular series.
The nucleoli, or plasmosomes, are spherical bodies which stain deeply, and
may either lie free in the nuclear matrix or be attached to the threads of the net-
work.
The Centrosome and Attraction Sphere. In addition to the nucleus,
a minute spherical body called the centrosome is believed to be constantly
present in animal cells, though sometimes too small to be demonstrated.
The centrosome is smaller than the nucleus, close to which it lies, and exerts a
peculiar attraction for the protoplasmic filaments and granules in its vicinity,
so that it is surrounded by a zone of fine radiating fibrils, forming the attraction
sphere or archoplasm. Some authorities assert that the centrosome lies within
the nucleus in the resting state, and passes into the cell proper only in the earlier
stages of cell division. The attraction sphere is most distinctly seen in cells
about to divide. It plays an important role in nuclear division, but it is
doubted if it gives the initial impulse to the process.
Cell Multiplication. Cells increase in number by a process known
as cell division, of which the first act is nuclear division. In fact the nucleus is
the center of control of the cell-mass in the process of division. Cell multi-
CELL MULTIPLICATION
19
plication takes place by two recognized methods, direct (amitosis), in which
there is little disturbance of the nuclear network, and indirect (mitosis), in
which there is a complex series of nuclear network changes. These mitotic
changes result in the division of the chromatin fila-
ments into the two new parts which form the chromo-
plasm of the daughter nuclei.
The process may be divided into the following
stages:—
Prophase. The resting nucleus becomes somewhat
enlarged, and the centrosome (according to those who
regard it as lying normally within the nucleus) migrates
into the cell protoplasm. The centrosome then divides
into two daughter centrosomes which lie near the nucleus
but are separated by a considerable interval. Each is
surrounded by the radiating fibrils of the attraction
sphere, and some of these fibrils pass continuously from
one centrosome to the other, forming the achromatic
spindle. At the same time the intranuclear network be-
comes converted into a fine convoluted coil (spirem or
skein) which may be either continuous or else broken up into several threads.
The thread or threads then shorten and become thicker, while the convolutions,
which have become less numerous, arrange themselves in a series of con-
necting loops, forming the wreath. The nuclear membrane and the nucleolus
disappear, the latter passing at times into the cell protoplasm and disintegrat-
ing. The wreath then breaks up into V-shaped segments, the chromosomes,
of which each species of animal has a constant and characteristic number.
This varies in the different animals, but is sixteen in man.
The two centrosomes migrate to the poles of the nucleus, while the achro-
matic spindle which connects them occupies the long axis of the nucleus. The
FIG. 15 — Leucocyte
of Salamander Larva,
Showing Attraction
Sphere. (After Flem-
ming.)
FIG. 1 6. — Early Stages of Karyokinesis. A. The thicker primary fibers remain and the achro-
matic spindle appears. B. The thick fibers split into two and the achromatic spindle becomes
longitudinal. (Waldeyer.)
chromosomes, becoming much shorter and thicker, gather around the spindle
in its equatorial plane, with their angles directed toward the center, forming
the aster or monaster.
Metaphase. The actual division of the nucleus is begun at this time by the
splitting of each chromosome longitudinally into halves which lie at first close
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
together so that each seems doubled. Soon afterward the fibrils of the achro-
matic spindle begin to contract, and thus separate the halves of the chromosomes
in such a way that one-half of each is turned toward one pole, and the other
half toward the other. As this continues, the two groups, which are equal in
central _..
particle,
Polar r*u&*0en,
(Cyt«*t*r)
afav&tlon, sphere*
dear area
of nucleus-
cen&vtZ «•
jUxrUdo
FIG. 17. — Monaster Stage of Karyokinesis.
(Rabl.)
size, draw away from each other and from the equator, each group being
formed of daughter chromosomes.
Anaphase. The two groups (daughter chromosomes) now gradually ap-
proach their respective poles, or centrosomes, and the equator becomes free.
On reaching the pole, each group gathers in a form which is similar in arrange-
ment to the monaster and is known as the diaster. During this time the cell
body becomes slightly constricted by a circular groove at its equatorial plane.
Telophase. Soon afterward the fibrils of the chromatic spindle which
connect the two groups begin to grow dim and finally disappear. The daugh-
FIG. 18. — Stages of Karyokinesis. (Rabl.) A. Commencing separation of the split chromo-
somes. B. The separation further advanced. C. The separated chromosomes passing along
the fibers of the achromatic spindle.
ter chromosomes assume the form of threads twisted in a coil and develop
each a nuclear membrane and a nucleolus, forming a daughter nucleus. The
nuclei enlarge and the nuclear threads assume the appearance of the resting
state of the nucleus. Meanwhile, the constriction about the body of the cell
has become deeper and deeper until the protoplasm is divided into two equal
parts, or daughter cells, each with its daughter nucleus, and the process of
karyokinesis is completed.
MODES OF CELL CONNECTION 21
The Cell Types. All of the elementary tissues consist of cells and
of their altered equivalents. It will be as well therefore to indicate some of the
differences between the cells of the body. They are named in various ways,
according to their shape, origin, and junctions.
From their shape, cells are described as spherical or spheroidal, which is the
typical shape of the free cell; this may be altered to polyhedral when the pres-
sure on a mass of cells in all directions is nearly the same; of this the primitive
segmentation cells afford an example. The discoid form is seen in blood-
corpuscles, and the scale-like form in superficial epithelial cells. Some cells
have a jagged outline and are then called prickle cells. Cells of cylindrical,
conical, or prismatic form occur in various places in the body. Such cells may
taper at one or both ends into fine processes, in the former case being caudate,
in the latter fusiform. They may be greatly elongated so as to become fibers.
...-. Remains of spindle.
Line of division •-•-^^?T7>rr-'-"'r^^VA ""** Lighter substance
of cells. """ of nucleus-
Antipole of ^^^^^mWl ______ Cell protoplasm.
nucleus. MllllWwmJfcl^J/Jlllf
---- Hilus.
FIG. 19. — Final Stages of Karyokinesis. In the lower figure the changes are still more ad-
vanced than in the upper. (Waldeyer.)
Cells with hair-like processes, or cilia, projecting from their free surfaces, are
a special variety. The cilia vary greatly in size, and may even exceed in length
the cell itself. Finally, cells may be branched or stellate with long outstanding
processes.
From their function cells are called secreting, protective, sensitive, contractile,
and the like.
From their origin cells are called epiblastic and mesoblastic and hypoblastic
(ectodermic, mesodermic, and endodermic).
Modes of Cell Connection. Cells are connected together to form
tissues in various ways.
They are connected by means of a cementing intercellular substance. This
is probably always present as a transparent, colorless, viscid, albuminous
substance, even between the closely apposed cells of epithelium; while in
the case of cartilage it forms the main bulk of the tissue, and the cells only
appear as embedded in, not as cemented together by, the intercellular substance.
This intercellular substance may be either homogeneous or fibrillated. In
many cases, e.g., the cornea, it can be shown to contain a number of irregular
branched cavities, which communicate with each other, and in which branched
22 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
cells lie. Nutritive fluids can find their way through these branching spaces
into the very remotest parts of a non-vascular tissue. The basement mem-
brane (membrana propria) must be mentioned as a special variety of intercellu-
lar substance which is found at the base of the epithelial cells in most mucous
membranes, and especially as an investing tunic of gland follicles which deter-
mines their shape.
Cells are connected by anastomosis of their processes. This is the usual
way in which stellate cells, e.g., of the cornea, are united. The individuality
of each cell is thus to a great extent lost by its connection with its neighbors to
form a reticulum. As an example of a network so produced we may cite
the anastomosing cells of the reticular tissue of lymphatic glands.
Derived Elements. Besides the cell, which may be termed the
primary tissue element, there are materials which may be termed secondary
or derived elements or formed materials. Examples of this type of structure
are found in the matrix of cartilage, the fibers of connective tissue, bone, etc.
Decay and Death of Cells. There are two chief ways in which the
comparatively brief existence of cells is brought to an end, by mechanical abra-
sion and by chemical transformation.
The various epithelia furnish abundant examples of mechanical abrasion.
As it approaches the free surface, the cell becomes more and more flattened and
scaly in form and more horny in consistency, till at length it is simply rubbed
off as in the epidermis. Hence we find free epithelial cells in the mucus of
the mouth, intestine, and in the genito-urinary tract.
In the case of chemical transformation the cell-contents undergo a degener-
ation which, though it may sometimes be pathological, is very often a normal
process. Thus we have cells by fatty metamorphosis producing oil-globules
in the secretion of milk, fatty degeneration of the muscular fibers of the uterus
after the birth of the fetus. Calcareous degeneration is common in the cells of
many cartilages.
THE STRUCTURE OF THE ELEMENTARY TISSUES.
There are certain elementary structures formed in the process of differentia-
tion which alone or when combined in varying proportions form the whole
of the organs and tissues of the body. These elementary tissues are: The
Epithelial, The Connective, The Muscular, and The Nervous Tissues. To
these four some would add a fifth, looking upon the Blood and Lymph, con-
taining, as they do, formed elements in a fluid menstruum, as a distinct tissue.
I. THE EPITHELIAL TISSUES.
Epithelium is a tissue composed almost wholly of cells, with a very small
amount of intercellular substance which glues the cells together. In general
it includes all those cellular membranes which cover either an external or
CLASSIFICATION OF EPITHELIA 23
an internal free surface, together with the cellular portions of the glands which
are connected with, or developed from, these free surfaces.
Epithelium clothes (i) the whole exterior surface of the body, forming
the epidermis with its appendages ; becoming continuous at the chief orifices
of the body — nose, mouth, anus, and urethra — with (2) the epithelium which
lines the whole length of the respiratory, alimentary, and genito-urinary
tracts, together with the ducts and secretory cells of their various glands.
Epithelium also lines the cavities of (3) the brain and the central canal of the
spinal cord, (4) the serous and synovial membranes, and (5) the interior of
blood-vessels and lymphatics.
Epithelial cells vary in size and shape, pressure being the main factor in this
variation. The protoplasm may be granular, reticular, or fibrillar in appear-
ance. The nucleus is spherical or oval, usually there is only one, but
there may be two or more, present.
Epithelial tissues are non-vascular, that is to say, do not contain blood-
vessels, but in some varieties minute channels exist between the cells of certain
layers. Nerve fibers are supplied to the cells of many epithelia.
CLASSIFICATION OF EPITHELIA.
As to form and arrangement of cells.
I. Epithelia in the form of membranes (covering surfaces).
1. Simple epithelium. Cells only one layer in thickness.
(1) Squamous or pavement. Cells flattened.
(a) Non-ciliated. Alveoli of lungs, also includes endothelium,
lining the blood-vessels, and mesothelium, lining the large
serous spaces.
(b) Ciliated. The peritoneum of some forms at breeding season.
(2) Cubical epithelia. Cells with the three dimensions approxi-
mately equal, mainly glandular.
(a) Non-ciliated. The usual type. It is found lining both
ducts and secretory portions of most glands, the pigmented
layer of the retina, etc.
(b) Ciliated. Not common. Lining of some of the smaller
bronchial tubes.
(3) Columnar. Cells may be cylindrical, conical, or goblet shaped.
(a) Non-ciliated. Intestinal.
(b) Ciliated. Fallopian tube and uterus.
(c) Pseudo-stratified. Smaller bronchi, nasal duct, etc.
2. Stratified epithelia. Cells more than one layer in thickness,
(i) Squamous. Surface cells flattened.
(a) Non-ciliated. Skin, mouth, vagina, etc.
(b) Ciliated. Pharynx of embryo.
24 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
(2) Columnar. Surface cells columnar.
(a) Non-ciliated. Portions of male urethra.
(b) Ciliated. Trachea, bronchi, etc.
II. Epithelia not in the form of membranes, but in solid masses or cords,
usually glandular,
(i) Cells spheroidal, ova.
(.2) Cells polyhedral, liver, suprarenal, etc.
Epithelia, classified mainly as to function.
I. Protective. Skin, mouth, alimentary canal.
1. Cornified. Skin, nails, hair.
2. Cuticular border. Columnar cells of intestine.
II. Glandular.
1. Secretory. Cells of salivary glands, pancreas, etc.
2. Execretory. Cells of kidney.
3. Absorptive. Cells of alimentary canal.
III. Sensory Epithelium. Cells of olfactory membrane, organ of Corti,
taste buds, etc.
IV. Reproductive. Sex cells.
V. Pigmented. Pigmented layer of retina.
VI. Ciliated. Trachea, uterus, Fallopian tube, etc.
Only a few of the more important of the above-mentioned types of epithe-
lium will be described here.
Simple Epithelium. Simple Squamous. This form of epithelium
is found arranged in a single layer of flattened cells, for example, the lining of
the alveoli of the lungs and of the descending arm of Henle's loop of the kidney
tubule. Aside from endothelium as mesothelium it has very limited dis-
tribution in man. Endothelium and mesothelium are typical simple squamous
FIG. 20. — The Endothelium of a Small Blood-vessel. Silver-nitrate stain. X 35°.
epithelia. They consist of much flattened cells with clear or slightly granular
protoplasm and oval bulging nuclei, the edges of the cells are peculiarly wavy
or serrated.
The presence of endothelium in any locality may be demonstrated by stain-
ing with silver nitrate, which brings into view the intercellular cement sub-
SIMPLE EPITHELIUM 25
stance. When a small portion of a perfectly fresh serous membrane, for
example, figure 20, is immersed for a few minutes in a solution of silver
nitrate, and exposed to the action of light, the silver is precipitated in the in-
FIG. 21. — Abdominal Surface of Central Tendon of the Diaphragm of Rabbit, showing the
general polygonal shape of the endothelial cells; each cell is nucleated. (Klein.) X 300.
tercellular cement substance, and the endothelial cells are thus mapped out by
fine, dark, and generally sinuous lines of extreme delicacy.
Endothelial cells in certain situations may be ciliated, e.g., those of the
mesentery of the frog, especially during the breeding season.
On those portions of the peritoneum and other serous membranes in
which lymphatics abound, apertures, figure 22, are found surrounded by small,
more or less cubical, cells. These apertures are called stomata. They are
particularly well seen in the anterior wall of the great lymph sac of the frog,
FIG. 22.— Peritoneal Surface of a Portion ot the Septum of the great Lymph-Sac of Frog.
The stomata, some of which are open, some collapsed, are surrounded by endothelial cells. (Klein.)
Xi6o.
figure 22, and in the omentum of the rabbit. These are really the open mouths
of lymphatic vessels or spaces, and through them lymph-corpuscles and the
serous fluid from the serous cavity pass into the lymphatic system.
Simple N on-Ciliated Columnar Epithelium, figure 23, lines, a, the mucous
membrane of the stomach and intestines as a single layer, from the cardiac
26
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
orifice of the stomach to the anus, and 6, wholly or in part all the ducts of the
glands opening on its free surface, and c, many gland-ducts in other regions
of the body, e.g., mammary, salivary, etc. The intracellular and intranuclear
networks are well developed, and in some cases the spongioplasm is arranged
FIG. 23. — Simple Columnar Ephithelial Cells from the Human Intestinal Mucous Membrane.
a, Mucous (goblet) cell; b, basement membrane; c, cuticle; d, leucocyte nucleus; e, germinating
cell. (Bailey.)
in rods or longitudinal striae at one part of the cell, as in the cells of the ducts
of salivary glands. The protoplasm of columnar cells may be vacuolated
and may also contain fat or other substances seen in the form of granules.
Certain columnar cells transform a large part of their protoplasm into mucin,
goblet cells, figure 24, which is discharged by the open mouth of the goblet, leav-
FIG. 24.
FIG. 25.
FIG. 24. — Goblet Cells. (Klein.)
FIG. 25. — Cross- section of a Villus of the Intestine, e. Columnar epithelium with striated
border; g, goblet cell, with its mucus partly extruded; /, lymph-corpuscles between the epithelial
cells; b, basement membrane; c, sections of blood -capillaries; m, section of plain muscle fibers;
c.l, central lacteal. (Schafer.)
ing only a nucleus surrounded by the remains of the protoplasm in its narrow
stem. This transformation is a normal process which is continually going on
during life, the cells themselves being supposed to regenerate into their original
shape.
STRATIFIED EPITHELIUM 27
Stratified Epithelium. The term stratified epithelium is employed
to describe the type found in the skin or its derivatives in which the cells
forming the epithelium are arranged in a considerable number of superim-
posed layers. The shape and size of the cells of the different layers, as well
as the number of layers, vary in different situations. Thus the superficial cells
may be either squamous or columnar in shape and the deeper cells range
from polygonal to columnar in form.
Stratified Squamous. The intermediate cells are polygonal in shape and
approach more to the flat variety the nearer they are to the surface, and to the
FIG. 26. — Squamous Epithelium Scales from the Inside of the Mouth. X 260. (Henle.)
columnar as they approach the lowest layer. In many of the deeper layers
of epithelium in the mouth and skin, the outline of the cells is very irregular,
in consequence of processes passing from cell to cell across these intervals.
Such cells, figure 28, are termed " prickle " cells. These " prickles " are the in-
tercellular bridges which run across from cell to cell, the interstices being filled
by the transparent intercellular lymph. When this increases in quantity
FIG. 27.— Vertical Section of the Stratified Epithelium Covering the Front of the Cornea. Highly
magnified. (Schafer.) c, Lowermost columnar cells; p, polygonal cells above these; ft, flat-
tened cells near the surface. The intercellular channels, bridged by minute cell processes, are
well seen.
in inflammation the cells are pushed further apart, and the connecting fibrils
or " prickles" are elongated and more clearly visible.
The columnar cells of the deepest layer are distinctly nucleated; they
multiply rapidly by division; and as new cells are formed beneath, they press
the older cells forward, to be in turn pressed forward themselves toward the sur-
face, gradually altering in shape and chemical composition until they die and
are cast off from the surface.
28 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
Stratified squamous epithelium is found in the following situations: i.
Forming the epidermis, covering the whole of the external surface of the body;
2. Covering the mucous membrane of the nose, tongue, mouth, pharynx, and
esophagus; 3. As the con junctival epithelium, covering the cornea 54. Lining
the vagina and the vaginal part of the cervix uteri.
Stratified Columnar Epithelium. In this type of epithelium, the surface
cells alone are columnar, the deeper cells being irregular in shape From
FIG. 28. — Epithelial Cells from the Stratum Spinosum of the Human Epidermis, Showing
"Intercellular Bridges." X 700. (Szymonowicz.)
the surface cells long processes extend down among the underlying cells.
This type of epithelium is usually ciliated, as in the trachea, bronchi, etc.,
but may be non-ciliated, as in portions of the human male urethra.
Transitional Epithelium. This is a stratified epithelium consisting of only
three or four layers of cells. The superficial cells are large and flat, often
M
FIG. 29. — Stratified Columnar Ciliated Epithelium from the Human Trachea. A mucous
(goblet) cell also is present.
containing two nuclei. The under surfaces of these cells are hollowed out, and
into these depressions fit the large ends of the pyriform cells which form the
next layer. Beneath the layer of pyriform cells are from one to four layers
of polyhedral cells. This type of epithelium occurs in the bladder, ureter,
and pelvis of the kidney.
STRATIFIED EPITHELIUM
Specialized Epithelium. Glandular Epithelium forms the active secreting
agent in the glands; the cells are usually spheroidal, but may be polyhedral
from mutual pressure, or even columnar; their protoplasm is generally oc-
cupied by the materials which the gland secretes. Examples of glandular
FIG. 30. — Transitional Epithelium from the Human Bladder. (Bailey.)
epithelium are to be found in the liver, figure 31, in the secreting tubes of
the kidney, and in the salivary, figure 32, and gastric glands.
Ciliated epithelium consists of cells which are generally cylindrical in form,
figures 29, 30, but may be spheroidal or even squamous.
This form of epithelium lines: a. The mucous membrane of the respiratory
tract beginning just beyond the nasal aperture, and completely covers the nasal
passages, except the upper part to which the olfactory nerve is distributed,
FIG. 31
FIG. 32.
FIG. 3 1 .—A Small Piece of the Liver of the Horse. (Cadiat.)
FIG. 32. — Glandular Epithelium. Small lobule of a mucous gland of the tongue, showing
nucleated glandular cells. X 200. (V. D. Harris.)
and also the sinuses and ducts in connection with it and the lachrymal sac,
the upper surface of the soft palate and the naso-pharynx, the Eustachian tube
and tympanum, the larynx, except over the vocal cords, to the finest sub-
divisions of the bronchi. In part of this tract, however, the epithelium is in
several layers, of which only the most superficial is ciliated, so that it should
30
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
more accurately be termed transitional, page 28, or stratified, b. Some portions
of the generative apparatus in the male, viz., lining the "vasa efferentia" of
the testicle, and their prolongations as far as the lower end of the epididymis,
and much of the vas deferens; in the female, c, commencing about the middle
FIG. 33. — Specialized Pigmented Epithelial Cells of Retina.
of the neck of the uterus, and extending throughout the uterus and Fallopian
tubes to their fimbriated extremities, and even for a short distance on the per-
itoneal surface of the latter, d. The ventricles of the brain and the central
canal of the spinal cord are clothed with ciliated epithelium in the child, but
in the adult this epithelium is limited to the central canal of the cord.
FIG. 34-
FIG. 35.
FIG. 34. — Spheroidal Ciliated Cells from the Mouth of the Frog. X 300 diameters. (Sharpey.)
FIG. 35. — Ciliated Epithelium from the Human Trachea, a, Large, fully formed cell, b,
shorter cell; c, developing cells with more than one nucleus. (Cadiat.)
The cilia themselves are fine rounded or flattened homogeneous processes.
According to some observers these processes are connected with longitudinal
fibers which pass to the other end of the cell, but which are not connected writh
the nucleus.
CONNECTIVE TISSUES
31
Functions of Epithelium. According to function,
epithelial cells may be classified as: i, protective, e.g., in
the skin, mouth, blood-vessels, etc.; 2, protective and mo-
tive, ciliated epithelium; 3, secreting, glandular epithelium ;
4, germinal, as epithelium of testicle producing sperma-
tozoa; 5, absorbing and secreting, e.g., epithelium of intes-
tine; 6, sensory, e.g., olfactory cells, organ of Corti.
Epithelium forms a continuous smooth investment
over the whole body, being thickened into a hard, horny
tissue at the points most exposed to pressure, and develop-
ing various appendages, such as hairs and nails. Epi-
thelium lines also the sensorial surfaces cf the eye, ear,
nose, and mouth, and thus serves as the medium through
which all impressions from the external world — touch,
smell, taste, sight, hearing — reach the delicate nerve end-
ings, whence they are conveyed to the brain.
The ciliated epithelium which lines the air-passages
serves to promote currents of the air in the bronchial tubes
and to propel fluids and minute particles of solid matter out
of the body. In the case of the Fallopian tube, the cilia
assist the progress of the ovum toward the cavity of the
UterUS. FIG. 36. — Ciliated
Cell of the Intestine
The epithelium of the various glands, and of the of a Moiiusk. (En-
¥ gelmann.)
whole intestinal tract, has the power of secretion, i.e., of
producing certain materials by processes of metabolism in its protoplasm.
Epithelium is likewise concerned in the processes of transudation, diffusion,
and absorption.
II. THE CONNECTIVE TISSUES.
This group of tissues forms the skeleton with its various connections —
bones, cartilages, and ligaments — and also affords a supporting framework
and investment to the various organs composed of nervous, muscular, and glan-
dular tissue. Its chief function is the mechanical one of support, and for
this purpose it is so intimately interwoven with nearly all the textures of the
body that if all other tissues could be removed, an4 the connective tissues left,
we should have a wonderfully exact model of almost every organ and tissue in
the body.
General Structure of Connective Tissue. The connective tissue is
made up of two chief elements, namely, cells and intercellular or formed sub-
stance.
Cells. The cells are usually of an oval shape, often with branched
processes, which are united to form a network. They are most readily
32 CELL DIFFERENTIATION AND THE CONNECTIVE TISSUES
observed in the cornea, in which they are arranged, layer above layer, parallel
to the free surface. They lie in spaces in the intercellular or ground substance,
which form by anastomosis a system of branching canals freely communicating,
figure 37.
The flattened tendon corpuscles which are arranged in long lines or rows
parallel to the fibers belong to this class of cells, figure 39.
These branched cells often contain pigment granules, giving them a dark
appearance; they form one variety of pigment cell. Pigment cells of this
FIG. 37. — Horizontal Preparation of the Cornea of Frog, Stained in Gold Chloride; showing
the network of branched corneal corpuscles. The ground substance is completely colorless.
X 400. (Klein.)
kind are found in the outer layers of the choroid. In many of the lower ani-
mals, such as the frog, they are found widely distributed not only in the skin,
but also in internal parts, the mesentery, sheaths of blood-vessels, etc. Under
the action of light, electricity, and other stimuli, the pigment granules become
massed in the body of the cell, leaving the processes quite hyaline; if the
stimulus be removed, they will gradually be distributed again throughout the
processes. Thus the skin in the frog is sometimes uniformly dusky, and some-
times quite light-colored, with isolated dark spots.
Intercellular Substance. This is fibrillar, as in the fibrous tissues and in
certain varieties of cartilage; or homogeneous, as in typical mucoid tissue.
The fibers composing the former are of two kinds, white fibrous and yellow
elastic tissue.
The chief varieties of connective tissues may be thus classified:
White fibrous.
Elastic.'
Areolar.
Gelatinous.
THE WHITE FIBROUS TISSUE
Adenoid or retiform.
Adipose.
Neuroglia.
Cartilage.
1. Hyaline.
2. White fibrous.
3. Elastic.
Bone and dentine.
The White Fibrous Tissue. It is found typically in tendon; also
in ligaments, in the periosteum and perichondrium, the dura mater, the peri-
cardium, the sclerotic coat of the eye, the fibrous sheath of the testicle, in the
fasciae and aponeuroses of muscles, and in the sheaths of lymphatic glands.
Structure. To the naked eye, tendons and many of the fibrous membranes,
when in a fresh state, present an appearance as of watered silk. This is due
FIG. 38.
FIG. 38. — Mature White Fibrous Tissue of Tendon, Consisting Mainly of Fibers with a Few
Scattered Fusiform Cells. (Strieker.)
FIG. 39. — Caudal Tendon of Young Rat, Showing the Arrangement, Form, and Structure of the
Tendon Cells. X 300. (Klein.)
to the arrangement of the fibers in wavy parallel bundles. Under the micro-
scope the tissue appears to consist of long, often parallel, bundles of fibers of
different sizes. The cells in tendons, figure 39, are arranged in long chains in
the ground substance separating the bundles of fibers, and are more or less regu-
larly quadrilateral with large round nuclei containing nucleoli, generally
placed so as to be contiguous in two cells. Each of these cells consists of a
thick body from which processes pass in various directions into, and partially
fill up the spaces between, the bundles of fibers. The rows of cells are sep-
arated from one another by lines of cement-substance.
Yellow Elastic Tissue. Yellow elastic tissue is found chiefly in
the ligamentum nuchae of the ox, horse, and other animals; the ligamenta
subflava of man; the arteries, constituting the fenestrated coat of Henle;
3
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
the veins in the lungs and trachea; the stylo-hyoid, thyro-hyoid, and crico-
thyroid ligaments; in the true vocal cords; and in areolar tissue.
Structure. Elastic tissue occurs in various forms, from a structureless,
elastic membrane to a tissue whose chief constituents are bundles of fibers
crossing each other at different angles; when seen in bundles elastic fibers are
yellowish in color, but individual fibers are not
so distinctly colored. The varieties of the tissue
may be classified as follows:
a. Fine elastic fibrils, which branch and
anastomose to form a network. This variety
of elastic tissue occurs chiefly in the skin and
mucous membranes, in subcutaneous and sub-
mucous tissue, in the lungs and true vocal
cords.
b. Thick fibers, sometimes cylindrical, some-
times flattened, which branch, anastomose and
form a network: these are seen most typically in
the ligamenta subflava and also in the ligamen-
tum nuchae of such animals as the ox and horse,
in which that ligament is largely developed,
figure 40.
A certain number of connective-tissue cells
are found in the ground substance between the
elastic fibers which make up this variety of connective tissue, page 33.
Areolar Tissue. This variety of fibrous tissue has a very wide dis-
tribution and constitutes the subcutaneous, subserous, ' and submucous tis-
sue. It is found in the mucous membranes, in the true skin, and in the outer
sheaths of the blood-vessels. It forms sheaths for muscles, nerves, glands,
and the internal organs, and, penetrating into their interior, supports and con-
nects the finest parts.
Structure. To the naked eye it appears, when stretched out, as a fleecy,
white, and soft meshwork of fine fibrils, with here and there wider films joining
in it, the whole tissue being evidently elastic. The openness of the meshwork
varies with the locality from which the specimen is taken. Under the micro-
scope it is found to be made up of fine white fibers, which interlace in a most
irregular manner, together with a variable number of elastic fibers. On the
addition of acetic acid, the white fibers swell up, and become gelatinous in
appearance; but as the elastic fibers resist the action of the acid, they may still
be seen arranged in various directions, sometimes appearing to pass in a more
or less circular or spiral manner round a small gelatinous mass of changed
white fiber. The cells of areolar tissues are connective-tissue corpuscles.
Gelatinous Tissue. Gelatinous connective tissue forms the chief
part of the bodies of such marine animals as the jelly-fish. It is found in
FIG. 40. — Elastic Fibers from
the Ligamenta Subflava. X 200.
(Sharpey.)
ADENOID OR LYMPHOID TISSUE
35
many parts of the human embryo. It may be best seen in the " Whartonian
jelly" of the umbilical cord and in the enamel organs of developing teeth.
FIG. 41-
FIG. 42.
FIG. 41. — Mucous Connective Tissue from the Umbilical Cord, a, Cells; b, fibrils.
FIG. 42. — Part of a Section of a Lymphatic Gland, from which the Corpuscles have been for
the most part Removed, showing the Adenoid Reticulum. (Klein and Noble Smith.)
Structure. It consists of cells, which in the jelly of the enamel organ
are stellate, embedded in a soft jelly-like intercellular substance which forms
the bulk of the tissue.
Adenoid or Lymphoid Tissue. Distribution. This variety of tissue
makes up the stroma of the spleen and lymphatic glands, and is found also
FIG. 43. — Portion of Subtnucous Tissue of Gravid Uterus of Sow. a, Branched cells, more or
less spindle-shaped ; b, bundles of connective tissue. (Klein.)
in the thymus, in the tonsils, and in the follicular glands of the tongue; in
Peyer's patches, in the solitary glands of the intestines, and in the mucous
membranes generally.
Structure. Adenoid or retiform tissue consists of a verv delicate network of
36 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
minute fibrils, figure 46. The network of fibrils is concealed by being covered
with flattened connective-tissue corpuscles, which may be readily dissolved
in caustic potash, leaving the network bare. The network consists of white
fibers, the interstices of which are filled with lymph-corpuscles. The cement-
substance of adenoid tissue is very fluid.
Neuroglia. This form of connective tissue found in the nervous system
is described on page 77.
Development oj Fibrous Tissues. In the embryo the place of the fibrous
tissues is at first occupied by a mass of roundish cells, derived chiefly from
the mesoderm, but also from ectoderm and from entoderm. These develop
either into a network of branched cells or into groups of fusiform cells,
figure 43.
The cells are embedded in a semifluid albuminous substance derived
probably from the cells themselves. Later this formed material is converted
into fibrils under the influence of the cells. The process gives rise to fibers
arranged in the one case in interlacing networks, areolar tissue, in the other
FIG. 44. — Blood- Vessels of Adipose Tissue. A, Minute flattened fat-lobule, in which the vessels
only are represented, o, The terminal artery; v, the primitive vein; b, the fat-vesicles of one
border of the lobule separately represented. X 100. B, Plan of the arrangement of the capillaries.
c, on the exterior of the vesicles; more highly magnified. (Todd and Bowman.)
in parallel bundles, white fibrous tissue. In the mature forms of purely
fibrous tissue not only the remnants of the cell-substance, but even the nuclei,
may disappear. The embryonic tissue, from which elastic fibers are developed,
is composed of fusiform cells, and a structureless intercellular substance.
The fusiform cells dwindle in size and eventually disappear so completely
that in mature elastic tissue hardly a trace of them is to be found: mean-
while the elastic fibers steadily increase in size.
ADIPOSE TISSUE
37
Adipose Tissue. In almost all regions of the human body a larger
or smaller quantity of adipose or fatty tissue is present. Adipose tissue is
almost always found seated in areolar tissue, and forms in its meshes little
masses of unequal size and irregular shape, to which the term lobules is com-
monly applied.
Structure. Adipose tissue consists essentially of cells which present
dark, sharply denned edges when viewed with transmitted light; each
consisting of a structureless and colorless membrane or bag formed of the
remains of the original protoplasm of the cell, filled with fat. A nucleus
FIG. 45. — A Lobule of Developing
Adipose Tissue from an Eight- Months'
Fetus, a, Spherical or, from pressure,
polyhedral cells with large central
nucleus, surrounded by a finely retic-
ulated substance staining uniformly
with hematoxylin. b, Similar cells
with spaces from which the fat has
been removed by oil of cloves, c. Sim-
ilar cells showing how the nucleus
with enclosing protoplasm is being
pressed toward periphery, d. Nucleus
of endothelium of investing capilla-
ries. (McCarthy.) Drawn by Treves.
FIG. 46. — Branched Connective-
Tissue Corpuscles, Developing into
Fat-Cells. (Klein.)
is always present in some part or other of the cell protoplasm, but in the
ordinary condition of the loaded cell it is not easily or always visible. This
membrane and the nucleus can generally be brought into view by extracting
the fat with ether and by staining the tissue.
The ultimate cells are held together by capillary blood-vessels, figure 44;
while the little clusters thus formed are grouped into small masses, and
held so, in most cases, by areolar tissue. The oily matter contained in the
cells is composed chiefly of the compounds of fatty acids with glycerin, olein,
stearin, and palmitin.
Development of Adipose Tissue. Fat c'ells are developed from connective-
tissue corpuscles. In the infra-orbital connective tissue there are cells ex-
hibiting every intermediate gradation between an ordinary branched connec-
tive-tissue corpuscle and mature fat cells. Their developmental appearance
38 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
is as follows: a few small drops of oil make their appearance in the proto-
plasm, and by their confluence a larger drop is produced, figure 45. This
gradually increases in size at the expense of the original protoplasm of the
cell, which becomes correspondingly diminished in quantity till in the mature
cell it forms only a thin crescentic film with a nucleus closely pressed against
the cell-wall. Under certain circumstances this process may be reversed,
A large number of blood-vessels are developed in adipose tissue, which
subdivide until each lobule of fat contains a fine meshwork of capillaries
ensheathing each individual fat-globule, figure 44.
Adipose tissue serves as a storehouse of combustible matter which may
be reabsorbed into the blood when occasion requires, and, being used up
in the metabolism of the tissues, may help to preserve the heat of the body.
That part of the fat which is situated beneath the skin must, by its want of
conducting power, assist in preventing undue waste of the heat of the body
by escape from the surface.
CARTILAGE.
All kinds of cartilage are composed of cells embedded in a substance
called the matrix. The apparent differences of structure met with in the
various kinds of cartilage are more due to differences in the character of
the matrix than of the cells. With the exception of the articular variety,
FIG. 47. — Hyaline Articular Cartilage (Human). The cell bodies entirely fill the spaces in
the matrix. X 340 diams. (Schafer.)
cartilage is invested by a thin but tough firm fibrous membrane called the
perichondrium.
Cartilage exists in three different forms in the human body, viz., hyaline
cartilage, yellow elastic cartilage, and white fibro-cartilage.
Hyaline Cartilage. This variety of cartilage is met with largely in
HYALINE CARTILAGE
39
the human body where it invests the articular ends of bones, and forms the
costal cartilages, the nasal cartilages, and those of the larynx with the ex-
FIG. 48.— Fresh Cartilage from the Triton. (A. Rollett.)
ception of the epiglottis and cornicula laryngis, the cartilages of the trachea
and bronchi.
Structure. Like other cartilages it is composed of cells embedded in a
matrix. The cells are irregular in shape, generally grouped together in
patches, figure 47. The patches are of various shapes and sizes and placed
at unequal distances apart. They generally appear flattened near the free
FIG. 49. — Costal Cartilage from an Adult Dog, showing the Fat-Globules in the Cartilage Cells.
(Cadiat.)
surface of the mass of cartilage, and more or less perpendicular to the surface
in the more deeply seated portions.
The intercellular substance of hyaline cartilage, when viewed fresh or
after ordinary fixation, appears homogeneous. However, when subjected
to special methods, the seemingly homogeneous intercellular substance can
40
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
be shown to be made up of fibers, comparable with those found in white
fibrous tissue, embedded in the homogeneous matrix.
In the hyaline cartilage of the ribs the cells are mostly larger than in
the articular variety and there is a tendency to the development of fibers
FIG. 50.— Yellow Elastic Cartilage of the Ear. Highly magnified. (Hertwig.)
in the matrix, figure 49. The costal cartilages also frequently become calcified
in old age, as also do some of those of the larynx.
In the fetus cartilage is the material of which the bones are first con-
structed; the "model" of each bone being laid down, so to speak, in this
FIG. 51. — White Fibro- Cartilage. (Cadiat.)
substance. In such cases the cartilage is termed temporary. It closely
resembles the ordinary hyaline cartilage but the cells are more uniformly
distributed throughout the matrix.
BONE
41
Elastic and White Fibro-Cartilage. The first variety is found* in
the cartilage of the external ear; the latter in portions of the joints, the inter-
vertebral cartilages, etc.
Structure. Elastic and white fibro-cartilage are composed of cells and a
matrix; the latter being made up almost entirely of fibers closely resembling
those of fibrous connective tissue.
Development of Cartilage. Cartilage is developed out of mesoblast cells
with a very small quantity of intercellular substance. The cells multiply by
fission within the cell-capsules.
BONE.
The characteristic of bone is that the matrix is solidified by a deposit of
earthy salts, chiefly calcium phosphate, but some magnesium phosphate and
calcium carbonate.
To the naked eye there appear two plans of structure in different bones,
and in different parts of the same bone, namely, the dense or compact, and
the spongy or cancellous tissue. In a longitudinal section of a long bone,
as the humerus, the articular extremities are found capped on their surface
by a thin shell of compact bone, while their interior is made up of the spongy
or cancellous tissue. The shajt is formed almost entirely of a thick layer
of the compact bone which surrounds a central canal, the medullary cavity,
so called from its containing the medulla, or marrow. In the flat bones, the
parietal bone or the scapula, a layer of cancellous structure lies between
two layers of the compact tissue. In the short and irregular bones, as those
of the carpus and tarsus, the cancellous tissue alone fills the interior, while
a thin shell of compact bone forms the outside.
The Marrow. There are two distinct varieties of marrow — the
red and the yellow.
FIG. 52. — Cells of the Red Marrow of the Guinea- Pig. highly magnified, a, A large cell, the
nucleus of which appears to be partly divided into three by constrictions; b, a cell, the nucleus of
which shows an appearance of being constricted into a number of smaller nuclei; c, a so-called
giant cell, or myeloplaxe, with many nuclei; d, a smaller myeloplaxe. with three nuclei; e-i, proper
cells of the marrow. (Schafer.)
42 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
Red marrow is that variety which occupies the spaces in the cancellous
tissue; it is highly vascular, and thus maintains the nutrition of the spongy
bone, the interstices of which it fills. It contains a few fat cells and a large
number of marrow cells, many of which are undistinguishable from lymphoid
corpuscles, and has for a basis a small amount of fibrous tissue. Among
the cells are some nucleated cells containing hemoglobin like the blood-
corpuscles. There are also a few large cells with many nuclei, termed giant
cells or myeloplaxes, which are probably derived from the ordinary marrow
cells, figure 52.
Yellow marrow fills the medullary cavity of long bones, and consists
chiefly of fat cells with numerous blood-vessels. Many of its cells are in
every respect similar to lymphoid corpuscles.
From these marrow cells, especially those of the red marrow, the red
blood-corpuscles are derived.
The Periosteum and Nutrient Blood-Vessels. The surfaces of
bones, except the part covered with articular cartilage, are clothed by a
FIG. 53. — Transverse Section of Compact Bone (of humerus). Three of the Haver sum canals
are seen, with their concentric rings; also the lacuna, with the canaliculi extending from them across
the direction of the lamella. The Haversian apertures were filled with debris in grinding down
the section, and therefore appear black in the figure, which represents the object as viewed with
transmitted light. The Haversian systems are so closely packed in this section, that scarcely any
inteni'isal lamellae are visible. 'X 150. (Sharpey.)
tough, fibrous membrane, the periosteum, which is closely attached to the
surface of the bone. Blood-vessels are distributed in this membrane, and
minute branches from these periosteal vessels enter the Haversian canals
MICROSCOPIC STRUCTURE OF BONE
43
to supply blood to the solid part of the bone. The long bones are supplied
also by a proper nutrient artery which, entering at some part of the shaft
so as to reach the medullary canal, breaks up into branches for the supply
of the marrow, from which again small vessels are distributed to the interior
of the bone. Other small nutrient vessels pierce the articular extremities
for the supply of the cancellous tissue.
Microscopic Structure of Bone. Notwithstanding the differences
of arrangement just mentioned, the structure of all compact bone substance
is found under the microscope to be essentially the same.
Examined with a rather high power its substance is found to contain a
multitude of small irregular spaces, approximately fusiform in shape, called
lacuna, with very minute canals or canaliculi, as they are termed, leading
Fio. 54. — Longitudinal Section from the Human Ulna, Showing Haversian Canals, Lacunae, and
Canaliculi. (Rollett.)
from them, and anastomosing with similar prolongations from other lacunae,
figure 53. In very thin layers of bone, no other canals than these may be visi-
ble; but on making a transverse section of the compact tissue of a long bone,
as the humerus or ulna, the arrangement shown in figure 53 can be seen.
The bone seems mapped out into small circular districts, at or about the
center of each of which is a hole, around which are concentric layers, the
lamella, the lacuna and canaliculi following the same concentric distribution
around the center, with which indeed they communicate.
On making a longitudinal section, the central holes are shown to be
simply the cut extremities of small canals which run lengthwise through
the bone, anastomosing with each other by lateral branches, figure 54, and
44 CELL, DIFFERENTIATION AND THE ELEMENTARY TISSUES
are called Haversian Canals, after the name of the physician, Clopton
Havers, who first accurately described them.
The Haversian Canals. The average diameter of the Haversian canals
is 50 p.. They contain blood-vessels, and by means of them blood is con-
veyed to even the densest parts of the bone; the minute canaliculi and lacunae
absorbing nutrient matter from the Haversian blood-vessels and conveying
it still more intimately to the very substance of the bone which they traverse.
The blood-vessels enter the Haversian canals both from without from the
periosteum, and from within from the medullary cavity or from the can-
cellous tissue. The arteries and veins usually occupy separate canals.
The lacuna are occupied by branched cells, the bone-cells or bone-corpus-
cles, figure 55, which very closely resemble the ordinary branched connective-
tissue corpuscles. The processes of the bone-cells extend into the canaliculi.
Each cell controls the nutrition of the bone immediately surrounding it.
Each lacunar corpuscle communicates with the others in its surrounding
FIG. 55. — Bone-Corpuscles with their Processes as Seen in a thin Section of Human Bone.
(Rollett.)
district, and with the blood-vessels of the Haversian canals by means of the
ramifications just described.
It will be seen from the above description that bone bears a very close
structural resemblance to what may be termed typical connective tissue.
The bone corpuscles with their processes occupying the lacunae and canalic-
uli correspond exactly to the cornea-corpuscles lying in the branched spaces.
The Lamella of Compact Bone. In the shaft of a long bone three distinct
sets of lamellae can be clearly recognized: General or fundamental lamellae,
which are just beneath the periosteum and parallel with it, and around the
medullary cavity; Special or Haversian lamellae, which are concentrically
arranged around the Haversian canals to the number of six to eighteen around
each ; Interstitial lamellae, which connect the systems of Haversian lamellae,
DEVELOPMENT OF BONE
45
filling the spaces between them, and consequently attaining their greatest
development where the Haversian systems are few.
The ultimate structure of the lamellae appears to be fibrous. A thin
film peeled off the surface of a bone, from which the earthy matter has been
removed by acid, is composed of a finely reticular structure, formed apparently
of very slender fibers decussating obliquely, but coalescing at the points of
intersection, as if here the fibers were fused rather than woven together.
FIG. 56. — Lamellae Torn Off from a Decalcified Human Parietal Bone at some Depth from the
Surface, a, a, Lamellae, showing reticular fibers; b, b, darker part, where several lamellae are
superposed; c, perforating fibers. Apertures through which perforating fibers had passed, are
seen especially in the lower part, a, a, ot the figure. (Allen Thomson.)
The reticular lamellae are perforated by the perforating fibers of Sharpey,
which bolt the neighboring lamellae together, and may be drawn out when
the latter are torn asunder, figure 56. These perforating fibers originate from
ingrowing processes of the periosteum, and in the adult still retain their
connection with it.
Development of Bone. From the point of view of their develop-
ment, all bones may be subdivided into two classes:
Those which are ossified directly in membrane or fibrous tissue, e.g., the
bones forming the vault of the skull, parietal, frontal, and a certain portion
of the occipital bones;
Those whose form, previous to ossification, is laid in down hyaline carti-
lage, e.g., humerus, femur, etc.
The process of development, pure and simple, may be best studied in
bones which are not preceded by cartilage, i.e., membrane-formed. Without
a knowledge of ossification in membrane it is difficult to understand the much
more complex series of changes through which such a structure as the carti-
46 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
laginous femur of the fetus passes in its transformation into the bony femur
of the adult (ossification in cartilage).
Ossification in Membrane. The membrane, afterward forming the
periosteum, from which such a bone as the parietal is developed, consists
of two layers, an .external fibrous, and an internal cellular or osteogenetic.
The external layer consists of ordinary connective tissue, with branched
corpuscles here and there between the bundles of fibers. The internal layer
consists of a network of fine fibrils with nucleated cells and ground or cement
substance between the fibrous bundles. It is more richly supplied with
capillaries than the outer layer. The relatively large number of its cellular
elements, together with the abundance of blood-vessels, clearly mark it as
the portion of the periosteum which is immediately concerned in the for-
mation of bone.
In such a bone as the parietal there is first an increase in vascularity,
followed by the deposition of bony matter in radiating spicula, starting
from a center of ossification. These primary bony spicula are osteogenetic
fibers, composed of osteogen, in which calcareous granules are deposited.
Calcareous granules are deposited also in the interfibrillar matrix. By
the junction of the osteogenetic fibers and their resulting bony spicula a
meshwork of bone is formed. The osteoblasts, being in part retained within
the bone trabeculae thus produced, form bone-corpuscles. Lime salts are
deposited in the circumferential part of each osteoblast, and thus a ring
of osteoblasts gives rise to a ring of bone with the remaining uncalcified
portions of the osteoblasts embedded in it as bone-corpuscles. At the same
time the plate increases at the periphery by the extension of the bony spicula
and by deposits taking place from the osteogenetic layer of the periosteum.
The bulk of the primitive spongy bone is gradually converted into compact
bony tissue of the Haversian systems.
Ossification in Cartilage. Under this heading, taking the femur
as a typical example, we may consider the process by which the solid cartilag-
inous rod which represents the bone in the fetus is converted into the hollow
cylinder of compact bone with expanded ends formed of cancellous tissue
in the adult long bone.
The fetal cartilage is sheathed in a membrane termed the perichondrium,
which resembles the periosteum described above. Thus, the differences
between the fetal perichondrium and the periosteum of the adult are such
as usually exist between the embryonic and mature forms of connective tissue.
There are several steps in the transformation of the fetal cartilage to the
adult bone, due to the fact that there is first an impregnation of the cartilage
with lime salts, followed later by the resorption of this entire material with
formation of the embryonic spongy bone, which is later replaced by the per-
manent bone. The complicated phenomenon takes place in steps or stages as
follows:
OSSIFICATION IN CARTILAGE 4?
Stage of Proliferation and Calcification. The cartilage cells in and near
the center of ossification become enlarged, proliferate, and arrange them-
selves in rows in the long axis of the fetal cartilage, figure 57. Lime salts are
next deposited in fine granules in the hyaline matrix of the cartilage, and this
gradually becomes transformed into calcified trabeculae, figure 57. The en-
larging cartilage cells become more transparent, and finally disintegrate,
the spaces occupied by them forming the primordial marrow cavities. During
FIG. 57. — Developing Bone of Femur of the Rabbit. (Schafer, from Klein.) X 35°- a,
Cartilage cells; b, cartilage cells enlarged in the region of calcifying matrix; c, d, trabeculae of cal-
cifying cartilage covered- with e, osteoblasts; /, osteoclasts eroding the trabeculae; g, h, disappear-
ing cartilage cells. The osteoblasts are seen to be depositing layers of bony substance. Loops
of blood-vessels extend to the limit of the region in which the bone is forming.
this stage the perichondrium has become the periosteum, and is beginning
to deposit bone on the outside of the cartilage.
Stage of V ascularization of the Cartilage. Processes from the osteo-
genetic layer of the periosteum containing blood-vessels break through the
bone into the primordial marrow cavities and form the primary marrow,
48
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
beginning at the centers oj ossification, and spreading chiefly up and down
the shaft.
Stage of Substitution of Embryonic Spongy Bone for Calcified Cartilage.
The cells of the primary marrow arrange themselves as a continuous epi-
thelium-like layer on the calcified trabecula? and deposit a layer of bone,
\v.
FIG. 58. — Transverse Section through the Tibia of a Fetal Kitten, semidiagrammatic. X 60.
P, Periosteum. O, Osteogenetic layer of the periosteum, showing the osteoblasts arranged side by
side, represented as pear-shaped black dots on the surface of the newly formed bone. B, The peri-
osteal bone deposited in successive layers beneath the periosteum and ensheathing E, the spongy
endochondral bone; represented as more deeply shaded. Within the trabeculae of endochondral
spongy bone are seen the remains of the calcified cartilage trabeculae represented as dark wavy
lines. C, The medulla, with V, V, veins. In the lower half of the figure the endochondral spongy
bone has been completely absorbed. (Klein and Noble Smith.)
and ensheath them. The encased trabeculae are gradually absorbed by
the osteoclasts of Kolliker.
These stages are precisely similar to what goes on in the growing shaft
of a bone which is increasing in length by the advance of the process of ossifi-
cation into the intermediary cartilage between the diaphysis and epiphysis.
In this case the cartilage cells become flattened and, multiplying by division,
OSSIFICATION IN CARTILAGE
49
are grouped into regular columns at right angles to the plane of calcifi-
cation while the process of calcification extends into the hyaline matrix
between them.
The embryonic spongy bone, formed as above described, is simply a tem-
porary tissue occupying the place of the fetal rod of cartilage; the preceding
stages show the successive changes at the center of the shaft. Periosteal
bone is at the same time deposited in successive layers beneath the perios-
teum at the circumference of the shaft, exactly as described in the section
on ossification in membrane, and thus a casing of periosteal bone is formed
around the embryonic endochondral spongy bone. The embryonic spongy
FIG. 59. — Transverse Section of Femur of a Human Embryo about Eleven Weeks Old. a,
Rudimentary Haversian canal in cross- section; b, in longitudinal section; c, osteoblasts; d, newly
formed osseous substance of a lighter color; e, that of greater age; /, lacunae with their cells; g,
a cell still united to an osteoblast. (Frey.)
bone is absorbed, through the agency of the osteoclasts, until the trabeculae
are replaced by one great cavity, the medullary cavity of the shaft.
Stage of Formation of Compact Bone. The transformation of spongy
periosteal bone into compact bone is effected in a manner exactly similar
to that which has been described in connection with ossification in mem-
brane, page 46. The irregularities in the walls of the spongy periosteal
bone are absorbed by the osteoclasts, while the osteoblasts which line
them are developed in concentric layers, each layer in turn becoming ossified
till the comparatively large space in the center is reduced to a well-formed
Haversian canal, figure 59. When once formed, bony tissue grows to some
4
50
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
extent inter stitially, as is evidenced by the fact that the lacunae are rather
further apart in full-formed than in young bone.
It will be seen that the common terms ossification in cartilage and ossifi-
cation in membrane are apt to mislead, since they seem to imply two processes
radically distinct. The process of ossification, however, is in all cases one
and the same, all true bony tissue being formed from membrane, perichon-
drium or periosteum; but in the development of such a bone as the femur,
lime salts are first of all deposited in the cartilage; this calcined cartilage,
however, is gradually and entirely reabsorbed, replaced by bone formed
from the periosteum. Thus calcification of the cartilaginous matrix pre-
cedes the real formation of bone. We must, therefore, clearly distinguish
between calcification and ossification. The former is simply the infiltration
of an animal tissue with lime salts, while ossification is the formation of
true bone.
Growth of Bone. Bones increase in length by the advance of the
process of ossification into the cartilage intermediate between the diaphysis
and epiphysis. The increise in length indeed is due entirely to growth
at the two ends cf the shjjt. Increase in thickness in the shaft of a long
bone occurs by the deposition of successive layers beneath the periosteum.
If a thin metal plate be inserted beneath the "periosteum of a growing bone
it will soon be covered by osseous deposit, but if it be put between the fibrous
and osteogenetic layers it will never become enveloped in bone, for all the
bone is formed beneath the latter.
THE TEETH.
During the course of his life, man, in common with most other mammals,
is provided with two sets of teeth; the first set, called the temporary or milk-
teeth of infancy, are shed and replaced by the second or permanent set.
Temporary Teeth.
MIDDLE LINE OF JAW.
Molars.
2
Canine.
I
Incisors.
2
Incisors.
2
Canine.
I
Molars.
2 = IO
The figures indicate in months the age at which each tooth appears :
LOWER CENTRAL
INCISORS.
UPPER
INCISORS.
FIRST MOLAR AND
LOWER LATERAL
INCISORS.
CANINES.
SECOND
MOLARS.
6 to 9
8 to 12
12 tO 15
18 to 24
24 to 30
THE TEETH
51
Permanent Teeth.
MIDDLE LINE OF JAW.
Canine.
I
T -c.^ r1 „•„*» Bicuspids or True
Incisors. Canine. Molars.
The age at which each permanent tooth is cut is indicated in this table in years:
INCISORS.
BICUSPIDS OR PRE-
FIRST
MOLARS.
CANINES.
SECOND
MOLARS.
MOLARS OR
WISDOMS.
Centrals.
Laterals.
First.
Second.
6
7
8
9
10
12 tO 14
12 tO 15
17 to 25
Structure. A tooth is generally described as possessing a crown,
neck, and root or r00/s. The crown is the portion which projects beyond
the level of the gum. The neck is that constricted portion just below the crown
which is embraced by the free edges of the gum, and the root includes all
below this.
On making longitudinal and transverse sections through its center, figure
61, A, B, a tooth is found to be principally composed of a hard superficial
FIG. 60. — Normal Well-formed Jaws, from which the Alveolar Plate has been in great part
Removed, so as to expose the Developing Permanent Teeth in their Crypts in the Jaws. (Tomes.)
material, dentine or ivory, which is hollowed out into a central cavity which
resembles in general shape the outline of the tooth, and is called the pulp-
cavity.
The tooth pulp is composed of fibrous connective tissue, blood-vessels,
nerves, and large numbers of cells of varying shapes, and on the surface in
52 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
close connection with the dentine a specialized layer of cells called odonto-
blasts, which are elongated columnar cells with a large nucleus at the taper-
ing ends farthest from the dentine. The cells are all embedded in a mucoid
gelatinous matrix.
The blood-vessels and nerves enter the pulp through a small opening
at the apical extremity of each root.
A layer of very hard calcareous matter, the enamel, caps the dentine of
the crown; beneath the level of the gum is a layer of true bone, called the
cement or crusta petrosa. The enamel and cement are very thin at the neck
of the tooth where they come in contact, the cement overlapping the enamel.
The enamel becomes thicker toward the crown, and the cement toward
the lower end or apex of the root.
Dentine or Ivory. — Dentine closely resembles bone in chemical com-
position. It contains, however, rather less animal matter.
Structure. Dentine is finely channelled by a multitude of delicate tubes,
which by their inner ends communicate with the pulp-cavity, and by their
FIG. 61. — A. — A Longitudinal Section of a Human Molar Tooth, c, Cement; d, dentine; e,
enamel; v, pulp cavity (Owen). B. — Transverse section. The letters indicate the same as in A.
outer extremities come into contact with the under part of the enamel and
cement, and sometimes even penetrate them for a greater or less distance,
figures 63, 64. The matrix in which these tubes lie is composed of " a reti-
culum of fine fibers of connective tissue modified by calcification, and, where
that process is complete, entirely hidden by the densely deposited lime salts"
(Mummery).
The tubules of the dentine contain fine prolongations from the tooth-
pulp, which give the dentine a certain faint sensitiveness under ordinary
circumstances and, without doubt, have to do also with its nutrition. They
are probably processes of the dentine-cells or odontoblasts lining the pulp-
cavity. The relation of these processes to the tubules in which they lie is
ENAMEL,
53
precisely similar to that of the processes of the bone-corpuscles to the canalic-
uli of bone. The outer portion of the dentine, underlying the cement and
the enamel, figure 63, b, c, contains cells like bone-corpuscles.
Dentine —
Periosteum of
alveolus
Cemen
Enamel
Cement
, Lower jaw bone
PIG. 62. — Premolar Tooth and Surrounding Bone of Cat.
Enamel. The enamel, which is by far the hardest portion of a
tooth, is composed chemically of the same elements that enter into the
composition of dentine and bone, but the animal matter amounts only to
a
FIG. 63. — Section of a Portion of the Dentine and Cement from the Middle of the Root of an
Incisor Tooth, a, Dental tubuli ramifying and terminating, some of them in the interglobular
spaces b and c, which somewhat resemble bone lacunae; d, inner layer of the cement with numerous
closely set canaliculi; e, outer layer of cement; /, lacunae; g, canaliculi. X 350. (Kolliker.)
about 2 or 3 per cent. It contains a larger proportion of inorganic matter
and is harder than any other tissue in the body.
54
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
Structure. Enamel is composed of fine hexagonal fibers, figures 64, 65.
These are set on end vertical to the surface of the dentine, and fit into cor-
responding depressions in the same.
Like the dentine tubules, they are disposed in wavy and parallel curves.
The fibers are thus marked by transverse lines. They are mostly solid,
but some of them may contain a very minute canal.
FIG. 64.
FIG. 64. — Thin Section of the Enamel and a Part of the Dentine, a, Cuticular pellicle of the
enamel (Nasmyth's membrane); b, enamel fibers, or columns with fissures between them and cross
striae; c, larger cavities in the enamel, communicating with the extremities of some of the dentinal
tubuli (d). X 350. (Kolliker.)
FIG. 65. — Section of the Upper Jaw of a Fetal Sheep. A. — i, Common enamel germ dipping
down into the mucous membrane; 2, palatine process of jaw; 3, rete Malpighi. (Waldeyer.) B. —
Section similar to A, but passing through one of the special enamel germs here becoming flask-
shaped; c, c', epithelium of mouth; /, neck; /', body of special enamel germ. (Rose.) C. — A later
stage; c, outline of epithelium of gum; /, neck of enamel germ; /', enamel organ; p, papilla; 5,
dental sac forming; fp, the enamel germ of permanent tooth; m, bone of jaw; v, vessels cut. across.
(Kolliker.) Copied from Quain's "Anatomy."
The enamel prisms are connected together by a trace of hyaline cement-
substance.
Development. The first step in the development of the teeth consists
in a downward growth, figure 65, A, i, from the deeper layer of stratified
ENAMEL 55
epithelium of the mouth, which first becomes thickened in the neighborhood
of the maxillae or jaws, now also in the course of formation. This epidermal
papilla grows downward into a recess of the imperfectly developed tissue of the
embryonic jaw. It forms the primary enamel organ or enamel germ, and
its position is indicated by a slight groove in the mucous membrane of the
jaw. The next step consists in the elongation and the inclination outward
of the deeper part, figure 65, B, /', of the enamel germ, followed by an
increased development at certain points corresponding to the situations of
the future milk-teeth. The enamel germ becomes divided at its deeper
portion, or extended by further growth, into a number of special enamel
germs corresponding to each of the milk-teeth, and connected to the com-
mon germ by a narrow neck. Each tooth is thus placed in its own special
recess in the embryonic jaw, figure 65, c, f '.
As these changes proceed, there grows up from the underlying tissue
into each enamel germ, figure 65, c, p, a distinct vascular papilla, dental
FIG. 66.— Part of Section of Developing Tooth of a Young Rat, showing the Mode of Deposi-
tion of the Dentine. Highly magnified, a, Outer layer of fully formed dentine; b, uncalcified
matrix with one or two nodules of calcareous matter near the calcified parts; c, odontoblasts send-
ing processes into the dentine; d, pulp; e, fusiform or wedge- shape cells found between odonto-
blasts; /, stellate cells of pulp in fibrous connective tissue. The section is stained in carmine, which
colors the uncalcified matrix but not the calcified part. (E. A. Schafer.)
papilla, and upon it the enamel germ becomes molded, and presents the
appearance of a cap of two layers of epithelium separated by an interval,
figure 65, c, I'. While part of the sub-epithelial tissue is elevated to form
the dental papillae, the part which bounds the embryonic teeth forms the
dental sacs, figure 65, C, s; and the rudiment of the jaw sends up processes
forming partitions between the teeth. The papilla, which is really part
of the dental sac, is composed of nucleated cells arranged in a meshwork,
in the outer layer of which are the columnar cells called odontoblasts. The
odontoblasts form the dentine, while the remainder of the papilla forms the
pulp. The method of the formation of the dentine from the odontoblasts
is said to be as follows: The cells form elongated orocesses at their outer
surfaces which are directly converted into the tubules of dentine, figure 66, c,
and into the contained fibrils.
66 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
Each papilla early takes the shape of the crown of the tooth to which
it corresponds, but as the dentine increases in thickness the papilla diminishes
until when the tooth is cut only a small amount remains as the pulp. It is
supplied by vessels and nerves which enter at the end of the root. The roots
are not completely formed at the time of the eruption of the teeth.
FIG. 67. — Vertical Transverse Section of the Dental Sac, Pulp, etc., of a Kitten, a, Dental
papilla or pulp; b, the cap of dentine formed upon the summit; c, its covering of enamel; d, inner
layer of epithelium of the enamel organ; e, gelatinous tissue; /, outer epithelial layer of the enamel
organ; g, inner layer, and h, outer layer of dental sac. X 14- (Thiersch.)
The enamel cap is formed by the enamel cells, by the deposit of a keratin-
like substance, which subsequently undergoes calcification. Other layers
are formed in the same manner meanwhile.
The temporary or milk-teeth are speedily replaced by the growth of the
permanent teeth.
The development of the temporary teeth commences about the sixth
week of intra-uterine life, after the laying down of the bony structure of
the jaws. Their permanent successors begin to form about the sixteenth
week of intra-uterine life.
III. MUSCULAR TISSUE.
There are two chief kinds of muscular tissue, differing both in minute
structure as well as in mode of action, viz., (i) the smooth or non-striated, and
(2) the striated.
SMOOTH OR NON-STRIATED MUSCLE
SMOOTH OR NON-STRIATED MUSCLE.
57
Non-striated muscle forms the proper muscular coats of the digestive
canal from the middle of the esophagus to the internal sphincter ani; of
the ureters and urinary bladder; of the trachea and bronchi; of the ducts
of glands; of the gall-bladder; of the vesiculae seminales; of the uterus and
Fallopian tubes; of the blood-vessels and lymphatics; and of the iris and
some other parts of the eye. This form of tissue also enters largely into the
FIG. 68. — Isolated Smooth Muscle Cells from Human Small Intestine. X 400. Rod-shaped
nucleus surrounded by area of finely granular protoplasm; longitudinal striations of cytoplasm.
composition of the tunica dartos of the scrotum. Unstriped muscular tissue
occurs largely also in the true skin generally, being especially abundant in the
interspaces between the bases of the papillae, and, when it contracts, the
papillae are made unusually prominent, giving rise to the peculiar roughness
of the skin termed cutis anserina, or goose flesh. It also occurs in all parts
FIG. 69. — Smooth Muscle from Intestine of Pig, Showing Syncytial Structure. a, Pro-
toplasmic process connecting two muscle fibers; b, end-to-end union of two muscle fibers, showing
the continuity of protoplasm and myofibrils; c, nucleus of muscle fiber; d, granular protoplasm at
the end of muscle nucleus; e, coarse myofibril; f, Fine myofibril; g, connective-tissue cell with
connective-tissue fibrils surrounding it; h, elastic fiber. (New figure by Caroline McGill.)
where hairs occur, in the form of flattened roundish bundles which lie
alongside the hair-follicles and sebaceous glands.
Structure. Unstriated muscle fibers are elongated, spindle-shaped,
mononucleated cells, 7 to 8 p, in diameter by 40 to 200 //, in length, figures
68 and 69. The protoplasm of each cell, the contractile substance, is
marked by longitudinal striations representing fibrils which have been
described as contractile. The nucleus is an oblong mass placed near the
58
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
center of the cell. It is covered by a nuclear membrane which encloses a
network of anastomosing fibrils.
Development. In the pig the smooth muscle of the alimentary
canal originates in the syncytium of the mesodermal cells which surround
the entoderm. The cells soon begin to grow into the adult spindle-shape
form and the fibrils make their appearance. Even in the adult muscle the
syncytial connections are retained according to Miss McGill.
Striated Muscle.
Striated or striped muscle constitutes the whole of the muscular apparatus
of the skeleton, of the walls of the abdomen, the limbs, etc.— the whole
FIG. 70.— Transverse Section through Muscular Fibers of Human Tongue. The deeply stained
nuclei are situated at the inside of the sarcolemma. Each muscle fiber shows Cohnheim s fields,
that is, the sarcous elements in transverse section separated by clear (apparently linear) interstitial
substance. X 450. (Klein and Noble Smith.)
FIG. 71.
FIG. 72.
FIG. 71. — Muscle Fiber Torn Across; the sarcolemma still connects the two parts of the fiber.
(Todd and Bowman.)
FIG. 72. — Part of a Striped Muscle Fiber of a Water Beetle prepared with Absolute Alcohol.
A, Sarcolemma; B, Krause's membrane. The sarcolemma shows regular bulgings. Above and
below Krause's membrane are seen the transparent " lateral discs." The chief massof a muscular
compartment is occupied by the contractile disc composed of sarcous elements. The substance ot
the individual sarcous elements has collected more at the extremity than in the center; hence this
latter is more transparent. The optical effect is that the contractile disc appears to possess a
"median disc" (Disc of Hensen). Several nuclei, C and D, are shown, and in them a minute net-
work. X 300. (Klein and Noble Smith.)
of those muscles which are under the control of the will and hence termed
voluntary; also the muscle of the heart.
SKELETAL MUSCLE 59
For the sake of description, striated muscular tissue may be divided
into two classes, (a) skeletal, which comprises the whole of the striated mus-
cles of the body except (b) the heart.
Skeletal Muscle. The muscle fibers of the skeletal muscles are
usually grouped in small parallel bundles, fasciculi. The fasciculi extend
through the muscle, converging to their tendinous insertions. Connective-
tissue sheaths, endomysium, surround the fasciculi and support the blood-
vessels, while a stronger sheath, the perimysium, encases the entire muscle.
FIG. 73. — A, Portion of a Medium-sized Human Muscle Fiber. B, Separated bundles of fibril
equally magnified; a, a, larger, and b, b, smaller collections; c, still smaller; d, d, the smallest which
could be detached, possibly representing a single series of sarcous element. X 800. (Sharpey.)
The unit of muscular structure is the fiber. Each muscle fiber is a long
cylinder with fusiform ends. The fibers vary in diameter from 10 to 100 JJL,
while the length may reach as much as 40 mm. Each fiber is enclosed in
a distinct sheath, the sarcolemma. The sarcolemma is a transparent structure-
less sheath of great resistance which surrounds each fiber, figure 71.
The substance of the fiber enclosed by the sarcolemma, the contractile
substance, contains a number of oval nuclei distributed along the length of
the fiber and lying just under or through the sarcolemma. Each nucleus is
accompanied by a small mass of granular protoplasm at its poles. The main
mass of the fiber is characterized by transverse light and dark bands, figure
73, from which the name striated muscle arises.
Longitudinal striation is also apparent under certain modes of treat-
ment, figure 81. The muscle fibers can be split longitudinally into fibrils,
called sarcostyles, figures 73 and 74, each of which exhibits the characteristic
60
CELL, DIFFERENTIATION AND THE ELEMENTARY TISSUES
striation of the whole fiber. Under certain treatment the sarcostyles break
transversely into smaller discs by cleavage at the line of Krause's membrane.
The sarcostyle is, therefore, composed of a number of smaller elements
joined end to end. These are the sarcous elements of Bowman. The sar-
FIG. 74. — Diagram of Segment of Muscle Fiber, showing Sarcostyle A, Sarcous element B.
Krause's line C, Hensen's line D.
cous element has a highly refractive denser middle piece surrounded by a
less refractive more fluid material. The polarizing microscope reveals the
fact that the middle piece which corresponds in position to the dark trans-
FIG. 75.
FIG. 76.
S'.Ei
S.E..
FIG. 75. — Sarcostyles from the Wing-Muscles of a Wasp. A, A', Sarcostyles showing degrees
of retraction; B, a sarcostyle extended with the sarcous elements separated into two parts, C,
sarcostyles moderately extended (semidiagrammatic). (E. A. Schafer.)
FIG. 76. — Diagram of a Sarcomere in a Moderately Extended Condition, B. K, K, Krause's
membranes; H, plane of Henson; 5, E, poriferous sarcous element. (E. A. Schafer.)
verse band is doubly refractive, isotropic, while the surrounding material,
the light band, is singly refractive, anisotropic.
HEART MUSCLE
(51
In transverse section, figure 70, the area of the muscle substance is mapped
out into small polygonal areas by a network of clear lines called Cohnheim's
areas. The lines represent the substance between the sarcostyles. This
substance probably represents the less differentiated contractile substance,
called sarco plasm. In figure 81 the interfibrillar sarcoplasm is indicated
by the longitudinal and transverse lines.
Heart Muscle. The muscle substance of the heart is composed
of mononucleated masses of protoplasm, cardiac muscle cells, in which the
substance of the cell presents the transversely striated appearance char-
acteristic of the voluntary muscle just
described. But the heart muscle is phys-
iologically much more like an involuntary
muscle. The cells are rather small, two
i .jfc.. .11
to four times as long as thick, and the nu-
A y | cleus is usually situated near the middle of
FIG. 77.
FIG. 78.
FIG. 77-— A Section of Cardiac Muscle, Diagrammatic. (From E. A. Schafer, after Heiden-
hain.)
FIG. 78.— Intercellular Continuity of Muscle Fibrils in Cardiac Muscle. (From E. A. Schafer
after Przewosky.)
the cell, figure 79. There is no sarcolemma; on the other hand, the cells
present branched and irregular outlines, but adjacent cells interlock in
close-fitting contact.
Certain observers have described fibrils as extending across the so-called
cell boundary and noted that not all such boundaries enclose nuclei. These
observations suggest that cardiac muscle belongs to the group of tissues
possessing a syncytium. However, the section of cardiac tissue may very
possibly cut many cells without enclosing a nucleus. The continuity of
62 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
fibrils is an important observation from the physiological point of view; see
Circulation Chapter.
In certain parts of the heart, the cardiac tissue is not completely differ-
entiated and retains in the adult somewhat embryonic characters; for ex-
FIG. 79-
FIG. 80.
FIG. 79. — Muscular Fiber Cells from the Heart. (E. A. Schafer.)
FIG. 80. — From a Preparation of the Nerve Termination in the Muscular Fibers of a Snake.
a, End plate seea o.ily broad-surfaced: b, end plate seen as narrow surface. (Lingard and Klein.)
ample, the bundle of His running in the septum from the auricles to the
ventricles and the cells containing Purkinje's fibers lying immediately under
the endocardium.
Blood and Nerve Supply. The muscles are freely supplied with
blood-vessels; the capillaries form a network with oblong meshes around
the fibers. Nerves also are supplied freely to muscles; the striated voluntary
muscles receiving them from the cerebro-spinal nerves, and the cardiac
muscle from both the cerebro-spinal and the sympathetic nerves.
In striped muscle the nerves end in motor end-plates. The nerve fibers
are medullated; and when a branch passes to a muscle fiber, its primi-
tive sheath becomes continuous with the sarcolemma, and the axis-cylinder
forms a network of its fibrils on the surface of the muscle fiber. This net-
work lies embedded in a flattened granular mass containing nuclei of several
kinds; this is the motor end-plate, figures 80 and 81. There is considerable
variation in the exact form of the nerve end-plate in the muscle. In
batrachia the nerve fiber ends in a brush of branching nerve fibrils which
are accompanied here and there by attached oval nuclei.
Development. The striated muscle of the voluntary variety is
usually developed from the mesoderm. The embryonic cells increase enor-
mously in size, the nuclei multiply by fission and distribute themselves be-
neath the sarcolemma. There is a differentiation of the cell protoplasm
DEVELOPMENT 63
which takes place by the formation of sarcostyles. This begins nearest the
surface of the cells and proceeds toward the center of the mass.
The sarcolemma is apparently produced from embryonic connective
tissue.
The cardiac muscle cells are at first spindle-shaped embryonic cells
which elongate more and more. In further differentiation their protoplasm
FIG. 8 1.
FIG. 82.
FIG. 81. — Two Striped Muscle Fibers of the Hyoglossus of Frog, a, Nerve end- plate; b, nerve
fibers leaving the end-plate; c, nerve-fibers terminating after dividing into branches; d, a nucleus in
which two nerve-fibers anastomose. X 600. (Arndt.)
FIG. 82. — Developing Striated Muscular Fibers, Showing Different Stages of Development and
Different Positions of the Unstriated Protoplasm. A. — Elongated cell with two nuclei; the longi-
tudinal striation is beginning to show on the right side. From a fetal sheep. (Wilson Fox.) B. —
Developing muscular fiber, showing both longitudinal and transverse striations at the periphery,
and a central unstriated cylinder of protoplasm containing several nuclei. From a human fetus
near the third month. (Ranvier.) n. Nucleus (there is usually a mass of glycogen near each
nucleus); p, central unstriated protoplas-n; s, peripheral striated substance. C. — Developing mus-
cular fiber, showing a lateral position of the unstriated protoplasm. From a three-months' human
fetus. (Ranvier.) n, Nucleus; p, unstriated protoplasm at one side of the fiber; s, striated
sarcous substance with longitudinal and transverse striations.
exhibits faint striations which pervade the cell as it grows in the great increase
in size. The rhythmic contractions begin long before the striations appear.
64
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
IV. NERVOUS TISSUE.
Nervous tissue has usually been described as being composed of two
distinct substances, nerve-fibers and nerve-cells. The modern view of the
nature of nerve tissue is, however, that the nerve-cell and the nerve fibers
are to be considered together as one unit, called the neurone. The neurone
is embedded in and supported by a substance called neuroglia. This neurone
consists of a cell body, a number of branching processes termed dendrites,
and a long process running out from it, the neuraxone, or axone, which be-
comes eventually a nerve fiber. The nerve-cell and the nerve fiber are parts
of the same anatomical unit, and the nervous centers are made up of those
units, arranged in different ways throughout the nervous system, figure 81, A
NERVE FIBERS.
While the nerve fiber is really to be considered as a process of the nerve-
cell, it is convenient to describe it separately. Nerve fibers are of two kinds,
medullated or white fibers, and non-medullated or gray fibers.
Medullated Fibers. Each medullated nerve fiber is made up of
the following parts: An external sheath, called the primitive sheath, neuri-
S.N.
FIG. 83. — Diagram Showing the Arrangement of the Neurons or Nerve Units in the Architecture
of the Nervous System. (Raymon y Cajkl.) A, Pyramidal neurone of cerebral cortex; B, anterior-
horn motor cell of spinal cord ; D, collateral branches of A ; E, medullary neurone with ascending
axone: F, spinal-ganglion neurones; G, sensory axones of F\ I, collaterals of F in the cord.
MEDULLATED NERVE FIBRES
65
C--
lemma, or nucleated sheath of Schwann; an inter-
mediate, known as the medullary or myelin sheath,
or white substance of Schwann; and a central thread,
the axis-cylinder, or axial fiber.
The Primitive Sheath. This is a pellucid mem-
brane forming the outer investment of the nerve
fiber. The sheath is constricted at intervals of a
millimeter or less, the nodes of Ranvier. Each in-
ternodal segment bears a single nucleus surrounded
by a variable amount of protoplasm. This mem-
brane is described as having its origin in the meso-
blastic cells, and the nuclei are the indications of the
cellular nature of each nodal segment.
The Medullary or Myelin Sheath. This is the
part to which the peculiar opaque white aspect of
medullated nerves is due. The thickness of this
layer of a nerve fiber varies considerably. It is a semifluid, fatty substance
of high refractive power. It possesses a fine reticulum (Stilling, Klein), in
FIG. 84. — Two Nerve
Fibers of the Sciatic Nerve.
A, Node of Ranvier, B.
axis-cylinder; C, sheath
of Schwann, with nuclei.
X 300. (Klein and Noble
Smith.)
FIG. 85. — A Node of Ranvier in a Medullated Nerve Fiber, viewed from above. The medul-
lary sheath is interrupted, and the primitive sheath thickened. Copied from Axel Key and Retzius.
X 750. (Klein and Noble Smith.)
FIG. 86. — Gray, Pale, or Gelatinous Nerve Fibers. A, From a branch of the olfactory nerve
of the sheep; two dark-bordered or white fibers from the fifth pair are associated with the pale
olfactory fibers , B, from the sympathetic nerve. X 450. (Max Schultze.)
the meshes of which is embedded the fatty material. It stains well with
osmic acid.
The Axis-Cylinder. The central thread of a medullated nerve fiber is
the axis-cylinder. It is the prolongation of a nerve-cell and extends un-
5
66
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
interrupted for the full length of the fiber. It consists of a large number of
primitive fibrillce, as shown in the cornea, where the axis-cylinders of nerves
break up into minute fibrils which form terminal networks. From various
considerations, such as its invariable presence and unbroken continuity in
all nerves, there can be little doubt that the axis-cylinder is the essential con-
FIG. 87. — Transverse Section of a Portion of the Sciatic Nerve of the Rabbit, Hardened in
Chromic Acid and Stained with Picro- carmine, to show medullated fibers in end view. X 275. a,
Perifascicular connective tissue; b, lamellar sheath; e, axis-cylinder.
ducting part of the fiber, the other parts having the subsidiary function of
support and possibly of insulation.
The size of the nerve fibers varies, figure 87. The largest fibers are
found within the trunks and branches of the spinal nerves, in which the
majority measure from 14 y. to 19 //. in diameter. In the so-called visceral
or autonomic nerves of the brain and spinal cord medullated nerves are found,
the diameter of which varies from 1.8 [j. to 3.6 /*. In the hypoglossal nerve
they are intermediate in size, and generally measure 7.2 fj. to 10.8 //.
Non-medullated Fibers. The fibers of the second kind, figure
86, which are also called fibers of Remak, constitute the principal part of
the trunk and branches of the sympathetic nerves, the whole of the olfactory
nerve, and are mingled in various proportions in the cerebro-spinal nerves.
They differ from the preceding chiefly in not possessing the outer layer of
medullary substance; their contents being composed exclusively of the axis-
cylinder.
The non-medullated nerves are only about one-third to one-half as large
as the medullated nerves, they do not exhibit the double contour, and they
NERVE TRUNKS
67
are grayer than the medullated nerves. The non-medullated fibers fre-
quently branch.
It is worthy of note that in the fetus, at an early period of development,
all nerve fibers are non-medullated.
"S-
Ar.
FIG. 88. — Transverse Section of the Sciatic Nerve of a Cat, about X 100. It consists of bundles
(Funiculi) of nerve fibers ensheathed in a fibrous supporting capsule, epineurium, A; each bundle
has a special sheath (not sufficiently marked out from the epneurium in the figure) or perineurium,
B, the nerve fibers, N, f; L, lymph spaces; A r, artery; V, vein; F, fat. Somewhat diagrammatic.
(V. D. Harris.)
Nerve Trunks. Each nerve trunk is composed of a variable num-
ber of different-sized bundles, juniculi, of nerve fibers which have a special
FIG. 89.— Small Branch of a Motor Nerve of the Frog, near its Termination, Showing Divis-
ions of the Fibers; a, into two; b, into three. X 350. (Kolliker.)
68
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
sheath, perineurium. The funiculi are enclosed in a firm fibrous sheath,
epineurium; this sheath also sends in processes of connective tissue which
connect the bundles together. In the funiculi between the fibers is a delicate
supporting tissue, the endoneurium. There are numerous lymph-spaces
both beneath the connective tissue investing individual nerve fibers and
also beneath that which surrounds the funiculi.
Bundles of fibers run together in the nerve trunk, but they merely lie
in approximation to each other, they do not unite. Even when nerves anas-
tomose, there is no union of fibers, but only an interchange of fibers between
the anastomosing bundles. Although each nerve fiber is thus single through
most of its course, yet, as it approaches the region in which it terminates, it
may break up into several subdivisions before its final ending.
Nerve Collaterals. It has been discovered through the researches
of Golgi, and confirmed by the further studies of Cajal and other anatomists,
that each individual nerve fiber in the central nervous system gives off in its
FIG. 90. — Terminal Ramifications of a Collateral Branch Belonging to a Fiber of the Posterior
Column in the Lumbar Cord of an Embryo Calf.
course branches which pass out from it at right angles for a short distance,
and then may run in various directions. These branches are called collaterals.
They end in fine, brush-like terminations known as end-brushes, or in little
bulbous swellings which come in close contact with some nerve cell, figure 90.
In the nerve-centers, that is, in the brain and spinal cord, the different
NERVE COLLATERALS
69
nerve fibers end just as the collaterals do, by splitting up into fine branches
which form the end-brushes. Collaterals of the nerve fibers and end-brushes
are chiefly found in the nervous centers. The nerve fibers of the peripheral
nerves end in the muscles, glands, or special sensory organs, such as the
eye and ear, each by its own special type of ending. Here, however, some
analogy to the end-brush can also be discovered. As the peripheral nerve
fibers approach their terminations, they lose their medullary sheath, and
consist then merely of an axis-cylinder and primitive sheath. They may
even lose the latter, and only the axis-cylinder be left. Finally, the axis-
cylinder breaks up into its elementary fibriHae, to end in various ways to
be described later.
FIG. 91.
FIG. 92.
FIG. 91. — Nerve Cell with Short Axis-Cylinder from the Posterior Horn of the Lumbar Cord of
an Embryo Calf, measuring 0.55 cm. (After Van Gehuchten.)
FIG. 92. — Scheme of Lower Motor Neurone. The cell body, protoplasmic processes, axone,
collaterals, and terminal arborizations in muscle are all seen to be parts of a single cell and together
constitute the neurone. (Barker.) c, Cytoplasm of cell body containing chromophilic bodies, neuro-
fibrils, and perinbrillar substance; n, nucleus; n', nucleolus; d, dendrites; ah, axone hill free from
chromophilic bodies; ax, axone; sf, side fibril (collateral); m, medullary sheath; nR, node of
Ranvier where side branch is given off; si, neurilemma and incisures of Schmidt; m, striated mus-
cle fiber; tel, motor end plate.
70
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
THE NERVE CELL BODY.
The nerve-cell body is the nodal and important part of the neurone, and
from it are given off the dendrites and axis-cylinder process or axone. It
consists of a mass of protoplasm, of varying shape and size, containing within
\\
FIG. 93 . — Large Nerve Cells with Processes, from the Ventral Cornua of the Cord of Man. X 3 50 .
On the cell at the right two short processes of the cell body are present, one or the other of which
may have been an axis-cylinder process (Deiters). A similar process appears also on the cell at
the left.
FIG. 94. — Multipolar Nerve Cell of the Cord of an Embryo Calf.
it a nucleus and nucleolus. All nerve cells give off one or more processes
which branch out in various directions, dividing and subdividing like the
THE NERVE CELL BODY
71
branches of a tree, but never anastomosing with each other or with other cells.
These branches are what have already been referred to as the dendrites of
'
FIG. 05— Ganglion Cells, Showing Neurofibrils. A, Anterior-horn cells of human; B, cell
from tnT facial nucleus of rabbit; C, dendrite of anterior-horn cell of human. (Bethe.)
FIG. 96.-Cell of the Anerior Horn of the Human Spinal Cord, Stained by Nissl's Method,
showing ckromophiles. (After Edmger.)
the cell. They were formerly called the protoplasmic processes, figures 91,
93 It is thus seen that the neurone or nerve unit consists of a number of
subdivisions, namely, the cell body, with its nucleus and nucleolus, the
72 CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
dendrites or protoplasmic processes, and the axone or axis-cylinder process,
which forms what is known as a nerve fiber.
The protoplasm of the cells is shown by various dyes to consist of neuro-
fibrils, perifibrillar substance, and in most cells chromophilic bodies. Apathy
and others have demonstrated that a network of interlacing and anasto-
mosing fibrils traverses both the cell body and its branches, figure 95.
FIG. 97. — An Isolated Sympathetic Ganglion Cell of Man, Showing Sheath with Nucleated Cell
Lining, B. A, Ganglion cell, with nucleus and nucleolus; C, branched process or dendrite, D,
unbranched process or axone. (Key and Retzius.) X 75°-
The perifibrillar substance is a fluid or semifluid substance in which the
fibrils are embedded. By treating nerve-cells with special stains granular
bodies of varying size are found embedded in the cytoplasm. These bodies
are the chromophilic bodies, figure 96.
Ganglion cells are generally enclosed in a transparent membranous
capsule similar in appearance to the external nucleated sheath of nerve -
fibers; within this capsule is a layer of small flattened cells.
Nerve Terminations.
Nerve fibers terminate peripherally in four different ways; i, by the ter-
minal subdivisions which pass in between epithelial cells, and are known
as inter-epithelial arborizations; 2, by motor-plates which lie in the muscles;
3, by special end-organs, connected with the senses of sight, hearing, smell,
and taste; and, 4, by various forms of tactile corpuscles.
The Inter-epithelial Arborizations. This forms a most common
mode of termination of the sensory nerves of the body. The nerve fibers
THE INTER-EPITHELIAL ARBORIZATIONS
73
to the surface of the skin or mucous membrane lose their neurilemma and
myelin sheath, the bare axis-cylinder divides and subdivides into minute
ramifications among the epithelial cells of the skin and mucous membrane.
In the various glands of the body this form of termination also prevails.
FIG. 98. — Sensory-Nerve Terminations in Stratified Pavement Epithelium. Golgi's rapid
method. (After G. Retzius.)
The hair-bulbs, the teeth, and the tendons of the body are supplied by this
same process of terminal arborization, figures 98, 99.
The motor nerves to the muscles end in what are known as muscle-plates,
the details of whose structure have been already described.
The special sensory end-organs will be described later in the chapter
on the Special Senses.
A fourth form of termination consists of corpuscles that are more or less
encapsulated, and these are known as the corpuscles of Pacini, the tactile
FIG. 99. — Sensory-Nerve Termination in the Epithelium of the Mucosa of the Inferior Vocal
Cord and in the Ciliated Epithelium of the Subglottic Region of the Larynx of a Cat Four Weeks Old.
(After G. Retzius.) Golgi's rapid method, n, Nerve-fibers rising from the connective-tissue layer
into the epithelial layer, where they terminate in ramified and free arborizations.
corpuscles oj Meissner, the tactile corpuscles of Krause, the tactile menisques,
and the corpuscles of Golgi.
The Pacinian Corpuscles. These nerve endings, named after
their discoverer Pacini, are elongated oval bodies situated on some of the
cerebro-spinal and sympathetic nerves. They occur on the cutaneous
nerves of the hands and feet, the branches of the large sympathetic plexus
about the abdominal aorta, the nerves of the mesentery, and have been
observed also in the pancreas, lymphatic glands, and thyroid glands, figure 100.
Each corpuscle is attached by a narrow pedicle to the nerve on which it is
situated, and is formed of several concentric layers of fine membrane, each.
74
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
layer being lined by endothelium, figure 100. A single nerve fiber passes
through its pedicle, traverses the several concentric layers, enters a central
cavity, and terminates in a knob-like enlargement or in a bifurcation.
The physiological import of these bodies is still obscure.
FIG. 100.
FIG. ioi.
FIG. ioo. — Pacinian Corpuscle of the Cat's Mesentery. The stalk consists of a nerve fiber, n,
with its thick outer sheath. The peripheral capsules of the Pacinian corpuscle are continuous
with the outer sheath of the stalk. The intermediary part becomes much narrower near the en-
trance of the axis-cylinder into the clear central mass. A hook-shaped termination with the end-
bulb, a, is seen in the upper part. (Ranvier.)
FIG. ioi. — Summit of a Pacinian Corpuscle of the Human Finger, showing the Endothelial
Membranes Lining the Capsules. X 220. (Klein and Noble Smith.)
The Tactile Corpuscles of Meissner. They are found in the papillae
of the skin of the fingers and toes, or among its epithelium. When simple
they are small, slightly flattened transparent bodies composed of nucleated
cells enclosed in a capsule. When compound, the capsule contains several
small cells. The nerve fiber penetrates the corpuscles, loses its myelin
sheath, and divides and subdivides to form a series of arborizations. The
terminal arborizations occupy the central part of the corpuscle, and are
surrounded by a great number of marginal cells. The touch or tactile
corpuscles of Meissner have been regarded at one time as epithelial, at
another time as nervous, but they are to-day proved to be mesodermic cells,
and differentiated for the special purpose of the sense of touch (Dejerine).
The Corpuscles of Krause or End-Bulbs. These exist in great
numbers in the conjunctiva, the glans penis, clitoris, lips, skin, and in tendon
of man. They resemble the corpuscles of Pacini, but have much fewer
concentric layers to the corpuscle, and contain a relatively voluminous central
TACTILE MENISQUES
75
mass composed of polyhedral cells. In man these corpuscles are spherical
in shape, and receive many nerve fibers which wind through the corpuscles
and end in the free extremities, figure 103.
FIG. 102. — Tactile Corpuscle of Meissner, Tactile Cell and Free Nerve Ending. (Merkel-
Henle.) a, Corpuscle proper, outside of which is seen the connective-tissue capsule; b, fiber end-
ing on tactile cell; c, fiber ending freely among the epithelial cells.
Tactile Menisques. In different regions of the skin of man, one
meets, in the superficial layers and in the Malpighian layers, nerves
which, after having lost their myelin sheath, divide and subdivide to form
FIG. 103.
FIG. 104.
FIG. 103. — End-,Bulb ot Krause. a, Medullated nerve fiber; b, capsule of corpuscle.
FIG. 104.— A Termination of a Medullated Nerve Fiber in Tendon, lower half with Convoluted
Medullated Nerve Fiber. (Golgi.)
extremely beautiful arborizations. The branches of these arborizations
are the tactile menisques. These menisques, which simulate the form of a
leaf, represent a mode of terminal nervous arborization (Ranvier).
76
CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES
The Corpuscles of Golgi. These are small terminal plaques placed
at the union of tendons and muscles, but belonging more properly to the
FIG. 105.— Neuroglia Cells in the Cord of an Adult Frog. (After Cl. Sala.) A, Ependyma
cells with their peripheral extremities atrophied and ramified; B, C, D, neuroglia cells in different
degrees of emigration and separation from the ependymal canal; their central extremity is atro-
phied and much contracted; their peripheral extremity, on the other hand, is greatly extended;
the ramifications of the latter, terminating in conical buttons, /, end under the pia mater.
FIG. 106. — Different Types of Neuroglia Cells. (After Van Gehuchten.) b, Neuroglia cells of
the white substance, and c, of the gray substance of the cord of an embryo calf.
THE NEUROGLIA 77
tendon. They are fusiform in shape and are flattened upon the surface of
the tendon close to its insertion into the muscular fibers. They are composed
of a granular substance, enveloped in several concentric hyaline membranes
which contain some nuclei. The nerve fiber passes into this little corpuscle,
splitting itself up into fine terminals. The corpuscles of Golgi are believed
to be related to the muscular sense, figure 104.
THE NEUROGLIA.
The neuroglia, while not a nervous tissue, is closely mingled with it and
forms an important constituent of the nervous system. It consists of cells
giving off a fine network of richly branching fibers. Neuroglia is a form
of connective tissue, and it is in its functions strictly comparable to the con-
nective tissue which supports the special structures of other organs, like the
lungs and kidneys, figure 106. In the adult animal the neuroglia-tissue is
composed of cells from which are given off immense numbers of fine processes.
These extend out in every direction, and intertwine among the nerve-fibers
and nerve-cells, figure 105. The neuroglia cell differs in size and shape
very much in different parts of the nervous system in accordance with the
arrangement of the nervous structures about it. The cell is composed of
granular protoplasm, and lying in it is a large nucleus, within which is a
nucleolus. The body of the cell is small in proportion to the nucleus.
CHAPTER III
THE CHEMICAL COMPOSITION OF THE BODY
OF the eighty chemical elements which have been isolated, no less than
seventeen combine in varying quantities to form the chemical basis of the
animal body. The substances which contribute the largest share are the
non-metallic elements, Oxygen, Carbon, Hydrogen, and Nitrogen — oxygen
and carbon making up altogether about 85 per cent of the whole. The most
abundant of the metallic elements are Calcium, Sodium, and Potassium*
These elements do not exist in the animal body in the free state, but are
combined into complex chemical compounds. Of course we cannot analyze
the living protoplasm and isolate its compounds.
The first step in the act of separating the composition products of proto-
plasm produces changes which destroy the chemical and physical relations
of these products which maintain the state of life. Dead protoplasm, how-
ever, yields a number of substances which must be very directly derived
from the living protoplasm. On the other hand, certain products can be
isolated from the animal body which are evidently not a part of the proto-
plasm itself, but products of protoplasmic activity. Some of these, like fat,
glycogen, etc., are constructive products, others are disintegration products
of protoplasmic activity.
A large number of the animal compounds, particularly those of the nitrog-
enous group, are characterized by their complexity. Many elements enter
into their composition, and many atoms of the same element occur in each
molecule. This latter fact no doubt explains the reason of their instability.
Of the numerous compounds that have been isolated from the animal
body, only a very few of the most important will be discussed in this chapter.
* The following table represents the relative proportion of the various elements in
the body. (Marshall.)
Oxygen 72.0
Carbon 13.5
Hydrogen 9.1
Nitrogen 2.5
Calcium i .3
Phosphorus 1.15
Sulphur 0.1476
Sodium o.i
Chlorine 0.085
78
Fluorine 0.08
Potassium 0.026
Iron o.oi
Magnesium 0.0012
Silicon 0.0002
(Traces of copper, lead, and alu-
minum)
THE NITROGENOUS BODIES 79
THE NITROGENOUS BODIES.
Nitrogenous bodies take the chief part in forming the solid tissues of the
body, and are found also to a considerable extent in the circulating fluids
(blood, lymph, chyle), the secretions and excretions. They often contain,
in addition to carbon, hydrogen, nitrogen, and oxygen, the elements sulphur
and phosphorus; but although the composition of most of them is approxi-
mately known, no general rational formula can at present be given for the
proteids.
Proteids. The nitrogenous substances constitute the most im-
portant and complex compounds of the body. According to their chemi-
cal composition and reactions they are divided into three main classes, viz.,
i, simple proteids; 2, compound proteids; and 3, albuminoids.
The proteids are the chief of the nitrogenous organic compounds and
exist in both plants and animals, one or more of them entering as an essential
part into the formation of all living tissue. They exist abundantly in the
lymph, chyle, and blood. Very little is known with any certainty about
their exact chemical composition. Their formulae are unknown, the chem-
ists who have attempted to construct the structural formulae differing very
greatly among themselves. In fact the very term proteid is an extremely
arbitrary one. It simply means a body which, according to Hoppe-Seylerr
contains in its molecule the elements carbon, hydrogen, nitrogen, oxygen,
and sulphur, in certain arbitrary but varying amounts, thus — Carbon, from
51.5 to 54.5; Hydrogen, from 6.9 to 7.3; Nitrogen, from 15.2 to 17; Oxy-
gen, from 20.9 to 23.5; Sulphur, from 0.3 to 2. Some proteids contain from
0.8 to 4.5 per cent of phosphorus; a small amount of iron is usually associ-
ated with proteids, but it is not certain whether or not it is an integral part
of the molecule. Chittenden defines a proteid as a substance which con-
tains carbon, hydrogen, oxygen, nitrogen, and sulphur, the nitrogen being
in a form which serves the physiological needs of the body; and yields, on
decomposition, a row of crystalline amido-acids and crystalline nitrogenous
bases; nearly all contain 52 per cent of carbon and 16 per cent of nitrogen.
Properties of Proteids. Proteids are for the most part amorph-
ous and non-crystallizable. Certain of the vegetable proteids have been
crystallized, and according to Hofmeister, egg albumin is also capable of
crystallization. They possess as a rule no power (or scarcely any) of passing
through animal membranes. They are soluble, but undergo alteration in
composition in strong acids and alkalies; some are soluble in water, others
in neutral saline solutions, some in dilute acids and alkalies, none in alcohol
or ether. Their solutions exercise a left-handed rotation on polarized light.
The hope that it may be possible in the immediate future to synthesize
proteids is not very great, because of the extraordinary variety of compounds
obtained by the decomposition of proteids by various chemical methods,
80 THE CHEMICAL COMPOSITION OF THE BODY
the compounds differing according to the method employed. In the body
it seems clear that living proteid is built up by the food supplied to it, which
necessarily contains proteid derived from either a vegetable or an animal
source; how this process takes place we are yet unable to say. Recently
Taylor has been able to synthesize proteid, protamin, by the reversible
action of trypsin on the amido-acids which were previously obtained by the
digestion of protamin. The reaction is indicated by the equation:
Protein -[- Water +± Amido-acids.
Robertson has demonstrated a similar reversible reaction of pepsin on para-
nuclein derived from the digestion of casein. These experiments lend a new
stimulus to the efforts to build up proteids in the chemical laboratory along
the lines of catalytic action of enzymes.
In the course of later chapters in this book we shall endeavor to trace
the steps of the breaking up of proteid in the body, but we may anticipate
by mentioning that it is now generally believed that the chief ultimate prod-
ucts of this decomposition are urea, a body the formula of which is
CO (NHa)a> carbon dioxide and water, while the intermediate substances or
by-products are chiefly ammonia compounds. When proteid material is
decomposed by putrefaction, by the action of chemical reagents, acids, alka-
lies, or by heat, various bodies are produced, of which amido-acids (acids
in which one or more of the hydrogen atoms of the radical of the acid are
replaced by amidogen, NH2) and bodies belonging to the aromatic or benzene
series predominate. Hence it comes that various theories of the way in
which proteids are built up have arisen. The one which has appeared to
have received the greatest support is that of Latham. This observer has
suggested that proteid may be considered as made up of a series of cyan-
alcohols (bodies obtained by the union of any aldehyde with hydrocyanic
acid) with a benzene nucleus. Taking ordinary ethyl alcohol, CH3CH2OH,
as the type, the aldehyde of which is CH3CHO, the corresponding cyan-
alcohol would be CHsCHCNOH.
CLASSES OF PROTEIDS.
Simple Proteids.
Native Albumins.
Albumins; serum albumins, egg albumins, lactalbumin.
Globulins; serum globulin, myosinogen, cytoglobulin, etc.
Derived Albumins.
Albuminates; acid and alkali albumins.
Coagulated proteids ; heat coagulated and enzyme coagulated proteid.
Proteose, Peptones, Polypeptids; all derived as cleavage-products
of enzyme action on other proteids.
PROTEIDS 81
Histons ; contain 35 to 42 per cent of their nitrogen as basi * nitrogen.
Protamins; contain 63 to 88 per cent of their nitrogen as basic nitro-
gen.
Compound Proteids.
Hemoglobin; decomposes into a proteid and a chromogen.
Nucleoproteid; decomposes into a proteid and nucleic acid.
Glycoproteid ; decomposes into a proteid and a reducing substance,
mucin.
Albuminoid substances; mucin, keratin, albumoid, collagen, elastin,
etc.
The Albumins. Of native albumins there are several varieties:
egg albumin; serum albumin; lact albumin, etc.
When in solution in water it is a transparent, frothy, yellowish fluid,
neutral or slightly alkaline in reaction. It gives all of the general proteid
reactions. On digestion it yields 8 per cent of argenin, 22.6 per cent of
leucin, and 2 per cent of tyrosin.
At a temperature not exceeding 40° C. it is dried up into a yellowish,
transparent, glassy mass, soluble in water. At a temperature of 70° C. it is
coagulated into a new substance, coagulated proteid, which is quite insoluble
in water. It is coagulated also by the prolonged action of alcohol; by strong
mineral acids, especially by nitric acid; also by tannic acid, or carbolic acid;
and by ethers. The coagulum is soluble in caustic soda.
With strong nitric acid the albumin is precipitated at the point of contact
with the acid in the form of a fine white or yellow ring.
Serum Albumin is contained in blood serum, lymph, serous and synovial
fluids, and in the tissues generally; it may be prepared from serum after
removal of paraglobulin, by a saturation with sodium sulphate. It appears
in the urine in the pathological condition known as albuminuria.
It gives similar reactions to egg albumin, but differs from it in not being
coagulated by ether. It also differs from egg albumin in not being easily
precipitated by hydrochloric acid, and in the precipitate being easily soluble
in excess of that acid. Serum albumin, either in the coagulated or precipi-
tated form, is more soluble in excess of strong acid than egg albumin.
Globulins. Globulins are found in egg; in blood, lymph, and
other body fluids; and in most protoplasm.
The globulins give the general proteid tests; are insoluble in water; are
soluble in dilute saline solutions; are soluble in acids and alkalies forming
the corresponding derived albumin.
Most of them are precipitated from their solutions by saturation with
solid sodium chloride, magnesium sulphate, or other neutral salt. They
are coagulated, but at different temperatures, on heating.
A globulin is obtained from the crystalline lens by rubbing it up with
6
82 THE CHEMICAL COMPOSITION OF THE BODY
powdered glass, extracting with dilute saline solution, and by passing through
the extract a stream of carbon dioxide. It differs from other globulins in
not being precipitated by saturation with sodium chloride.
The globulin, myosin, may be prepared from muscle by removing all
fat, tendon, etc., and washing repeatedly in water until the washing con-
tains no trace of proteids, mincing it, and then treating with 10 per cent solu-
tion of sodium chloride, or similar solution of ammonium chloride or magne-
sium sulphate. The salt solution will dissolve a large portion into a viscid
fluid, which filters with difficulty. If the viscid filtrate be dropped little by
little into a large quantity of distilled water, a white flocculent precipitate
of myosin will occur.
Myosin is soluble in 10 per cent saline solution; it is coagulated at 60° C.
into coagulated prcteid; it is soluble without change in very dilute acids;
it is precipitated by picric acid, the precipitate being redissolved on boiling;
it may give a blue color with ozonic ether and tincture of guaiacum.
Serum globulin is contained in plasma and in serum, in serous and syno-
vial fluids, and may be precipitated by saturating plasma after removal of
fibrinogen, or by saturating serum with solid sodium chloride or magne-
sium sulphate. Globulin separates as a bulky flocculent substance which
can be removed by filtration. It may also be prepared by diluting blood-
serum with ten volumes of water, and passing carbonic-acid gas rapidly
through it. The fine precipitate may be collected on a filter, and washed
with water containing carbonic-acid gas. It is very soluble in dilute saline
solutions, 5 to 8 per cent, from which it is precipitated by carbonic-acid gas
or by dilute acids. Its solution is coagulated at 72° C. Dilute acids and
alkalies convert it into acid or alkali albumin.
Fibrinogen is contained in blood plasma, from which it may be prepared
by the addition of sodium chloride to the extent of 13 per cent. It may
also be prepared from hydrocele fluid or from other serous transudation by
a similar method. Its general reactions are similar to those of paraglobulin.
But its solution is coagulated at 55°-56° C. Its characteristic property
consists in the facility with which it forms the insoluble proteid fibrin.
Edestin is a globulin which is found in many edible vegetables, grain,
etc. A solution may be prepared by adding hempseed to a 10 per cent
solution of sodium chloride and heating to 50° C.
Albuminates. There are two principal substances belonging to
this class: a, acid albumin; b, alkali albumin.
Acid Albumin. Acid albumin is made by adding small quantities of
dilute acid (of which the best is hydrochloric, 0.4 to i per cent) to either
egg or serum albumin diluted with five to ten times its bulk of water, and
keeping the solution at a temperature not higher than 50° C. for not less than
half an hour. It may also be made by dissolving coagulated native albumin
in strong acid, or by dissolving any of the globulins in acids. Solid acid
COAGULATED PROTEIDS 83
albuminate may be formed by adding strong acid drop by drop to a strong
solution of proteid matter (e.g., undiluted egg albumin) until solidifica-
tion occurs.
It is not coagulated on heating, but on exactly neutralizing the solution
a flocculent precipitate is produced; if it is then heated to 70° C. it will co-
agulate and cannot then be distinguished from any other form of coagu-
lated proteids. This may be shown by adding to the acid albumin solution
a little aqueous solution of litmus and then adding, drop by drop, a weak
solution of caustic potash from a buret until the red color disappears. The
precipitate is the derived albumin. It is soluble in dilute acid, dilute alka-
lies, and dilute solutions of alkaline carbonates. The solution of acid
albumin gives the proteid tests. The substance itself is coagulated by strong
acids, e.g., nitric acid, and by strong alcohol; it is insoluble in distilled water,
and in neutral saline solutions; it is precipitated from its solutions by satura-
tion with sodium chloride. On boiling in lime-water it is partially coagu-
lated, and a further precipitation takes place on addition to the boiled solu-
tion of calcium chloride, magnesium sulphate, or sodium chloride.
Alkali Albumin. If solutions of native albumin, or coagulated albu-
min, or other proteid be treated with dilute or strong fixed alkali, alkali
albumin is produced. Solid alkali albumin (Lieberkiihn's jelly) may also
be prepared by adding caustic soda or potash, drop by drop, to undiluted
egg albumin, until the whole forms a jelly. This jelly is soluble in an excess
of the alkali or in dilute alkalies on boiling. A solution of alkali albumin
gives the tests corresponding to those of acid albumin. It is not coagulated
on heating except after neutralization, as in the case of acid albumin. It
is thrown down on neutralizing its solution, except in the presence of alkaline
phosphates, in which case the solution must be distinctly acid before a pre-
cipitate falls.
To differentiate between acid and alkali albumin, the following method
may be adopted: Alkali albumin is not precipitated on exact neutralization
if sodium phosphate has been previously added. Acid albumin is precipi-
tated on exact neutralization, whether or not sodium phosphate has been
previously added.
Coagulated Proteids. These are formed by the action of heat
or of ferments upon other proteids; the temperature necessary to produce
coagulation varying in the manner previously indicated. They may also
be produced by the prolonged action of alcohol upon proteids; the process
is one of dehydration. They are soluble in strong acids or alkalies; slightly
so in dilute; are soluble in digestive fluids (gastric and pancreatic), and are
insoluble in water or saline solutions (except fibrin).
Fibrin is formed by the action of fibrin ferment on fibrinogen and can be
obtained as a soft, white, fibrous, and very elastic substance by whipping
blood with a bundle of twigs and washing the adhering mass in a stream of
84 THE CHEMICAL COMPOSITION OF THE BODY
water unto all the blood-coloring matter is removed. It is soluble to a cer-
tain extent in strong sodium-chloride solutions.
Proteoses. These are intermediate substances of the digestion
of other proteids, the ultimate product of which is peptone or lower cleavage
products. They are produced by the action of the gastric and pancreatic
juices and also, slowly, by boiling with dilute acids. The term is a general
one, the proteose of albumin being albumose, that of globulin being globu-
lose, etc. They are divided into primary and secondary groups representing
the stages of progression from proteids to peptones, so that there may be a
primary and a secondary albumose, etc. As digestion is a process of hydra-
tion with cleavage, the successive stages present progressively simpler sub-
stances. Each group reacts to fewer reagents than the preceding one; e.g.,
none of the proteoses can be coagulated by boiling. Nitric acid will precipi-
tate the primary proteoses but not the secondary ones.
Peptones. Peptone is formed by the action of the digestive fer-
ments, pepsin or trypsin, on other proteids, and on gelatin. It is a still
simpler form of substance than the proteoses and reacts to still fewer reagents.
Peptones will be considered in connection with the physiology of digestion,
as will also be the intermediate compounds.
Histons. Histons are decomposition products but present well-
defined proteid reactions. They are strongly basic and have a large con-
tent of hexon bases. Histons are soluble in water; are precipitated by weak
ammonia; are soluble in acids; do not coagulate by heat in water solutions
unless salts are present. They are not changed by and may be recovered
from the salt heat coagulation. They do not contain phosphorus. They
give the biuret reaction, but do not give Millon's reaction.
Protamin. This substance is of special interest in that it is the
simplest of the proteids. It is a cleavage product which exists in nature in
fish sperm as a nucleic acid compound. It gives the biuret but not Millon's
reaction, is not coagulated by heat. It yields amido-acids as cleavage-prod-
ucts. These cleavage-products have been recently resynthesized by Taylor
by the action of trypsin.
Compound Proteids. The compound proteids are compounds
of a simple proteid with some other molecule. According to their chemical
composition and characteristics they are divided into several classes, viz.:
Chromo proteids. This is a combination of a proteid substance with some
form of pigment. For example, hemoglobin is a combination of a globulin
with hematin, an iron-containing radicle. Hemoglobin is described more
fully in the chapter on the Blood. Nucleo proteids. Nucleoproteids are a
combination of a proteid substance with a nucleic acid; they are divided
into two groups according to the character of the acid. The true nucleo-
proteids contain true nucleic acid; the para-nucleoproteids or pseudo-nucleo-
proteids contain para-nucleic acid. Both acids, and therefore both groups,
MUCIN 85
contain phosphorus; but the true nucleoproteids yield nuclein (xanthin)
bases while the para-nucleoproteids do not. The nucleoproteids are found
in the nucleus and protoplasm of every cell. The para-nucleoproteids are
found in milk, as caseinogen, and in the yolk of egg, as vitellin. Glyco-
proieids. Glycoproteid is a combination of a proteid substance with a carbo-
hydrate radicle. Examples are mucin, which is found in mucous secre-
tions; and mucoids, which are found in certain tissues, cartilages, etc.
Mucin. Mucin is a compound of a globulin with a carbohydrate
radicle, and is the characteristic component of mucus; it is contained also
in fetal connective tissue, in tendons, and in salivary glands. It can be obtained
from mucus by diluting with water, filtering, treating the insoluble portion
with weak caustic alkali, and reprecipitating with acetic acid. The mucins
derived from different sources probably have different compositions.
Mucin has a ropy consistency. It can be coagulated; is insoluble in
water, salt-solution, and very dilute muriatic acid; is soluble in alkalies and
concentrated sulphuric acid. It gives the proteid reaction with Millon's
reagent and with nitric acid. Neither mercuric chloride nor tannic acid
gives a precipitate. It does not dialyze. When treated with sulphuric acid
and then neutralized with solid potassium hydrate, it will give both the biuret
test, denoting the presence of proteid matter, and also Fehling's test, show-
ing the presence of a sugar.
Nucleins. The substance known as nuclein and found in all cells
is really a compound proteid and consists of a series of bodies made up of pro-
teid and nucleic.acid in varying proportions; there is almost no limit to the
possible variations. At one end of the series is nucleic acid (C30H52N9P3O17,
according to Kossel), a body containing the maximum (9 to n per cent)
of phosphorus but without any proteid, and found as such only in sper-
matozoa; in the middle are the nucleins proper; and at the other end
are the nucleoproteids, containing the minimum of phosphorus. As phos-
phorus is the characteristic component of nucleic acid, its amount will meas-
ure the amount of the acid present in any molecule.
The chemical differences in the action of cytoplasm and karyoplasm
toward solvents are due also to the proportion of nucleic acid and proteid
which they contain. These differences are qualitative and not quantitative.
All of the nucleoproteids in the cell body are true ones in that they yield
nuclein bases.
Caseinogen. Caseinogen, the chief proteid of milk, yields para-
nuclein on digestion. It bears the same relation to casein that fibrinogen
does to fibrin. When acted on by rennin it splits into two parts of which
one, the smaller, is peptone-like in character. The other, and larger part,
is known as soluble casein and does not solidify in the absence of calcium
salts. As calcium is always present in milk, it there unites with it and forms
insoluble calcium casein; strictly speaking, therefore, the curd of milk is
86 THE CHEMICAL COMPOSITION OF THE BODY
the calcium compound of soluble casein. Caseinogen may be prepared
by adding dilute hydrochloric acid to milk until the mixture is distinctly
acid, when a flocculent precipitate of caseinogen will be thrown down and
may be separated by nitration. The fat which is carried down with this
precipitate may be removed by washing with alcohol and then with ether.
Caseinogen may also be prepared by adding to milk an excess of crys-
tallized magnesium sulphate or sodium chloride, either of which salts causes
it to separate out. Caseinogen gives the biuret ' and Millon's reactions.
It is soluble in distilled water, dilute or strong alkalies, and sulphuric acid,
but insoluble in sodium chloride and 0.2 per cent of hydrochloric acid.
Vitellin. Vitellin is prepared from yolk of egg by washing with
ether until all the yellow matter has been removed. The residue is then
dissolved in 10 per cent saline solution, filtered, and poured into a large
quantity of distilled water. The precipitate which falls is impure vitellin.
It gives the same tests as myosin, but is not precipitated on saturation with
sodium chloride; it coagulates at about 75° C.
Albuminoids. The albuminoids belong to the simple tissues of
the body which are derived from the epiblast and are characterized by a
lack of any degree of activity, either physiological or chemical. They are
nitrogenous bodies derived from proteid matter in the cells, and give crys-
talline amido-acids and nitrogenous bases on decomposition, but differ from
true proteids in not having their nitrogen in a form fit for the physiological
needs of the body. In other words, they are not true nitrogen-supplying
foods, though gelatin has a certain indirect value as it protects the body
proteids from work in many ways. The albuminoids are soluble in dilute
acids or alkalies; they may be distinguished from albumin or globulin by
being insoluble in water or salt solution respectively. Typical albuminoids
are gelatin, elastin, chondrin, keratin, etc.
Gelatin. Gelatin is contained in the form of collagen, its anhy-
dride, in bone, ossein, teeth, fibrous connective tissues, tendons, ligaments,
etc. It may be obtained by prolonged action of boiling water or of dilute
acetic acid.
The percentage composition is O 25.24 per cent, H 6.56 per cent, N
17.81 per cent, C 50 per cent, SO 25 per cent. It contains more nitrogen
and less carbon and sulphur than proteids. It is amorphous, and trans-
parent when dried. It does not dialyze; it is insoluble in cold water, but
swells up to about six times its volume; it dissolves readily on the addition
of very dilute acids or alkalies. It is soluble in hot water, and forms a jelly
on cooling, even when only i per cent of gelatin is present. It is also soluble
in hot salt solution. Prolonged boiling in dilute acids or in water destroys
the power of forming a jelly on cooling. On decomposition it gives 2 per
cent of leucin and 2.6 per cent of argenin, but no tyrosin, and a large amount
of glycocoll (amido-acetic acid or glycin), a crystalline substance.
ELASTIN 87
A fairly strong solution of gelatin, 2 per cent to 4 per cent, gives the
xanthoproteic test, but with no previous precipitate by nitric acid; the biuret
test, the Millon's test, but with no precipitate. It is precipitated with tannic
acid, with alcohol and picric acid. It is not precipitated with acetic acid,
hydrochloric acid, mercuric chloride, nor with potassium ferrocyanide,
and acetic acid.
Elastin is found in elastic connective tissue, in the ligamenta
subflava, ligamentum nuchae, etc. It is insoluble in all ordinary reagents,
but swells up both in cold and hot water. It is slowly soluble in strong
caustic soda, when heated. It is precipitated by tannic acid and does not
gelatinize. It gives the proteid reactions with strong nitric acid and am-
monia, and imperfectly with Millon's reagent. On decomposition it gives
4.5 per cent of leucin, a small amount of argenin, and a mere trace of tyrosin.
It is prepared by boiling with water, then treating with artificial gastric and
pancreatic juices, then boiling again in water, and then extracting with
acids, alcohol, and ethers; the remainder is elastin.
Chondrin is found in the condition of chondrigen in cartilage.
It is obtained from chondrigen by boiling. It is soluble in hot water, and
in solutions of neutral salts, e.g., sulphate of sodium, in dilute mineral acids,
caustic potash, and soda. It is insoluble in cold water, alcohol, and ether.
It is precipitated from its solutions by dilute mineral acids (excess redis-
solves it), by alum, by lead acetate, by silver nitrate, and by chlorine water.
On boiling with strong hydrochloric acid, it yields grape-sugar and certain
nitrogenous substances. Prolonged boiling in dilute acids, or in water,
destroys its power of forming a jelly on cooling.
Keratin is obtained from hair, horns, finger-nails, etc. Its com-
position is very similar to that of ordinary albumin and is approximately
€49.5, H 6.5, N 16.8, S 4, O 23.2; the keratins obtained from the various
substances are distinct and differ slightly though closely related. Sulphur
is the characteristic body found in keratin and occurs as a sulphur-contain-
ing radicle. A large amount of mercaptan sulphur can usually be obtained.
On decomposition, keratin yields argenin 2.26 per cent, leucin 10 per cent,
and tyrosin 4 per cent.
Keratin is insoluble in water, salt, sodium carbonate, and dilute hydro-
chloric acid. It is slowly soluble when warmed in caustic potash or sul-
phuric acid. It gives Millon's and the xanthoproteic reactions.
Neurokeratin is a form of keratin which is found in the white substance
of Schwann around the axis-cylinders of nerves. It yields argenin 5 per
cent, leucin 10 per cent, and tyrosin 3.5 per cent.
Products of Proteid Decomposition. The products of proteid de-
composition under the influence of oxidizing and hydrolyzing agents are
of the greatest significance in indicating the character and composition of
the proteid molecule. Cleavage-products of widely varying degrees of com-
88 THE CHEMICAL COMPOSITION OF THE BODY
plexity are obtained. But, running through the cleavage compounds are
certain nuclei or constitution complexes, which in all probability are found
in the proteid itself, in fact form the basic structure of the molecule. The
following account is taken from the excellent discussion by Witthaus (" The
Medical Student's Manual of Chemistry"):
"Active oxidizing agents attack the proteid molecule profoundly, yield-
ing products which are for the most part far removed from the original sub-
stance, and which are themselves products of decomposition of the 'atomic
complexes' above referred to; acids and aldehydes of the fatty, oxalic, and
benzoic series and their nitrils, including hydrocyanic acid, ketones, amido-
acids, carbon dioxid, and ammonia. With HNO3 various nitro derivatives
are obtained, and with Cl, Br, and I halid derivatives. By oxidation with
K2Mn2O8 an acid, oxyprotosulfonic, containing the sulfonic group, is
formed, and by continued oxidation peroxyprotonic acid. In oxidation with
BaMn2O8 guanidin is one of the products.
" Fusion with caustic alk'alies also causes deep decomposition, the prod-
ucts being ammonia, mercaptan, fatty acids, amido fatty acids, tyrosin,
indol, and skatol.
" By boiling with dilute mineral acids, or with HC1 -j- SnQ2, the pro-
teids are hydrolyzed with formation of hydrogen sulfid, ethyl sulfid and
ammonia as simple products, and amido-acids, hexon bases, pyrrolidin and
oxypyrrolidin carboxylic acids, and melanoidins, the last-named being also
products of decomposition of the melanins, substances to which the hair
and other dark portions of the body owe their color. The amido-acids,
including serin, tyrosin, and cystin, produced in this and other hydrolytic
decompositions probably exist in the proteids as polypeptids, formed by
the union of several amido-acid complexes.
" Considering the nitrogen which is split off, in more or less complex
combination, on hydrolysis of proteids by boiling with dilute acids, it appears
to have existed in the parent proteid in five forms of combination, corre-
sponding to five classes of decomposition products: i, Easily separable,
so-called amino-nitrogen, given off as NH3; 2, Urea-forming nitrogen, in the
guanidin remainder of argenin; 3, Basic nitrogen, or diamido-nitrogen,
contained in basic nitrogen compounds, precipitable by phosphotungstic
acid; 4, Monamido-nitrogen, in monamido-acids; 5, Humus nitrogen, in
humus-like melanoidins, dark-colored, amorphous, nitrogenous remainders.
" The quantitative distribution of nitrogen in these five groups differs in
different proteids : i. Is entirely absent in protamins; i to 2 per cent in gela-
tin; 5 to 10 per cent in other animal proteids; 13 to 20 per cent in vegetable
proteids. 2, In protamins 22 to 44 per cent; in histons 12 to 13 per cent;
in gelatin 8 per cent; in other proteids 2 to 5 per cent. 3, In protamins
63 to 88 per cent; in histons 35 to 42 per cent; in other animal proteids
15 to 25 per cent; in vegetable proteids 5 to 37 per cent. 4, The greater
PRODUCTS OF PROTEID DECOMPOSITION 89
part of the nitrogen, 55 to 76 per cent, in proteids other than protamins is
in this form. 5, Varies within wide limits.
"The sulfur, the amount of which varies greatly in different proteids,
is given off on hydrolysis as cystin, cystein, a-thiolactic acid, mercaptans,
and ethyl sulfid.
"The nitrogen-containing products of hydrolysis of proteids may be
thus classified:
I. Aliphatic. A. Containing no sulfur:
1, Guanidin remainder. H2N.C : NHj (-f-ornithin=argenin);
2, Monobasic monamido acids: glycocoll, alanin, amido-valerianic
acid, leucin, serin;
3, Dibasic monamido-acids: aspartic and glutamic;
4, Monobasic diamido-acids: ornithin, lysin;
B. Containing nitrogen and sulfur: Cystin, cystein;
II. Carbocyclic: phenylamidopropionic acid, tyrosin;
III. Heterocyclic : A. Pyrrol derivatives: pyrrolidin and oxypyrrolidin
carboxylic acids;
B. Glyoxalin derivatives (?): histidin;
C. Indole derivatives: indol, skatol, tryptophane."
The amido-acids, although belonging to the different seriesf are, accord-
ing to Fischer's views, supposed to be combined into more and more com-
plex groupings. In the simplest combinations two or more molecules of
the same or of different amido-acids combine with the elimination of water.
This is the reverse of the hydrolytic process and results in Fischer's peptids.
Protamin, the simplest of the proteids, yields a relatively simple series of
amido-acids and according to Taylor's work, already referred to, is evidently
a polypeptid of comparatively complex structure.
"All proteids except the protamins and some of the peptones contain
sulfur. One fraction of this, referred to as 'loosely combined' sulfur, is
given off as hydrogen sulfid by boiling with alkaline solutions. It is this
fraction which causes the formation of a brown or black color, or even a
black precipitate, .when a proteid is heated with a solution of caustic alkali
in the presence of lead acetate, in the 'sulfur test' for the proteids. The
second fraction is not separable in this manner, but only, as a sulfate, by
fusion with saltpeter and sodium carbonate, or, as a sulfid, by fusion with
caustic potash. The ratio of loosely combined sulfur to total sulfur varies
notably in different proteids, from § in serum to f in hemoglobin. It would
appear from this constant difference in separability of different portions of
sulfur from proteids that the molecules of these substances must contain at
least two atoms of sulfur in different forms of combination. This conclu-
sion, is, however, invalidated by the fact that both cystin and cystein only
give off one-half of their sulfur, and that very slowly, by boiling with alka*
90 THE CHEMICAL COMPOSITION OF THE BODY
line solutions, yet the two atoms of sulfur in cystin are symmetrically com-
bined, and the molecule of cystein contains but one sulfur atom.
"Many proteids, not only the glycoproteids, but also true albumins, as
egg albumin, serum albumin, serum globulin, the nucleoproteids, etc., re-
act with Molisch's reagent, and, on hydrolysis, split off a carbohydrate
group, which is an amido-sugar, usually glucosamin, CHO.CHNH2 (CHOH)3-
CH2OH, probably existing in the proteid as a polysaccharid complex. Some
of the nucleoproteids yield a pentose group, others laevulinic acid. Other
proteids, as casein, myosin, and fibrinogen, yield no carbohydrate.
"The decomposition of proteids by the proteolytic enzymes, pepsin,
trypsin, and papain, consists of a series of hydrolyses, and results first in
the formation of albumoses and peptones, and later by trypsin, particularly
of polypeptids, amido acids, hexon bases, tryptophane, amins, diamins, and
ammonia. These changes occur in the processes of digestion."
The Pigments, etc. A number of pigments make their appear-
ance in the body; for example, bilirubin, C16H18N2O3, is the common bile
pigment. Its crystals are bluish-red in color and are probably derived from
hematin of the blood. Biliverdin, C16H18N2O4, is an oxidation product
of bilirubin.
Urochrome and Urobilin occur in bile and in urine; the latter is prob-
ably identical with stercobilin, which is found in the feces. Uroerythrin is
one of the coloring matters of the urine. It is orange red and contains iron.
Melanin is a dark brown or black pigment which occurs especially in
epidermal tissues, where it is associated with keratin. It is found in the
lungs, bronchial glands, hair, choroid, skin, etc.; also in the urine and in
melanotic diseases, e.g., sarcoma. It is a transformation product of pro-
teids, from which it can be derived by boiling proteid with sulphuric acid.
Lipochromes are pigments, usually yellow or yellowish-red, which are
associated with fat, being almost always present in adipose tissue. Little is
known about them, but they are thought to consist only of C, H, and O.
OILS AND FATS.
The animal oils and fats are for the most part mixtures of tri-palmitin,
C3H5(O.C16H310)3, tri-stearin, C3H5(O.C18H35O)3, zndtri-olein, C3H5(O.C18-
NsaO);,, in different proportions. They are formed by the union of three
molecules of fatty acid with one molecule of the triatomic alcohol, glycerin,
C3H5(OH)3, and are ethereal salts or esters of that alcohol. Palmitic acid
is C15H31COOH, stearic acid is C^H^COOR; oleic acid is Cl7HnCOOH.
Human fat consists of a mixture of tri-palmitin, tri-stearin, and tri-olein,
of which the two former contribute three-quarters of the whole. Olein is
the only liquid constituent. The fat of milk (and butter) is tributyrin;
butyric acid is C4H8O2.
CARBOHYDRATES 91
Fats are insoluble in water and in cold alcohol; soluble in hot alcohol,
ether, and chloroform. Colorless and tasteless ; easily decomposed cr saponi-
fied by alkalies or superheated steam into glycerin and the fatty acids.
Certain of the monatomic Fatty Acids are found in the body,
viz., Formic CH2O2, acetic C2H4O2, and propionic C3H3O3, present in sweat,
but normally in no other human secretion. They have been found else-
where in diseased conditions. Butyric acid, C4H8O2, is found in milk and
in sweat. Various others of these acids have been obtained from blood,
muscular juice, feces, and urine.
Of the diatomic fatty acids, one acid, Lactic acid, C3H6O3, exists in a
free state in muscle-plasma, and is increased in quantity by muscular con-
traction, but is never contained in healthy blood.
Soaps. The fatty acids in combination with soda or potash,
or similar bases, form soaps which are soluble in water, while the fats are
not soluble.
CARBOHYDRATES.
The carbohydrates are bodies composed of C, H, and O, as aldehydes
and ketols. They are classified as monosaccharides, dextrose, galactose,
etc. These are the simplest molecules of the hexoses. They are sweet,
odorless, soluble in water, and oxidize readily, hence their reducing power.
They form crystalline osazones. They rotate polarized light. Their for-
mula is C6H12O6. Disaccharides, maltose, saccharose, lactose, etc. They
are formed by the union of two simpler molecules and the elimination of a
molecule of water. They have the formula C12H.22On. And poly saccharifies,
glycogen, starch, dextrin, gum, etc. They are much less soluble, can be
hydrolyzed into the simpler forms, and have the formula (C6H10O5)n.
Monosaccharides are especially soluble and polysaccharides are espe-
cially insoluble; monosaccharides and disaccharides do not give colored
solutions with iodine, while polysaccharides do; monosaccharides and (ex-
cept saccharose) disaccharides reduce Fehling's solution, while polysaccha-
rides do not.
Of these the most important are:
Starch. It is contained in nearly all plants, and in many seeds,
roots, stems, and some fruits. It is a soft white powder composed of granules
having an organized structure, consisting of granulose .(soluble in water)
contained in a coat of cellulose (insoluble in water); the shape and size
of the granules vary according to the source whence the starch has been
obtained. It is not crystalline and will not dialyze. It is insoluble in cold
water, in alcohol, and in ether; it is soluble after boiling for some time, and
may be filtered, in consequence of the swelling up of the granulose, which
bursts the cellulose coat, and, becoming free, is entirely dissolved in water.
This solution is a solution of soluble starch or amydin. It gives a blue color-
92 THE CHEMICAL COMPOSITION OF THE BODY
ation with iodine, which disappears on heating and returns on cooling. It
is converted into maltose by diastase, and by boiling with dilute acids into
dextrose.
Glycogen. Glycogen is a polysaccharide contained in the liver,
and also present in all muscles, but especially in those of very young animals,
in the placenta, in colorless corpuscles, and in embryonic tissues. It is
sometimes called animal starch and gives many reactions proper to starch
itself. It is freely soluble in water, and its solution looks opalescent; it
gives a port-wine coloration with iodine, which disappears on heating and
returns on cooling. It is precipitated by basic lead acetate and is insoluble
in absolute alcohol and in ether. It exists in the liver during life, but very
soon after death is changed into sugar. It may be prepared by grinding
muscle with sand till a pasty mass is formed, boiling the mass in water for
twenty minutes, filtering, and then precipitating the glycogen from the
filtrate by adding a little more than an equal quantity of 95 per cent alcohol.
It is converted into sugar by diastase ferments, or into dextrose by boiling
with dilute acids.
Dextrin. This substance is made in commerce by heating dry
potato-starch to a temperature of 400°. It is also produced in the .process
of the conversion of starch into sugar by diastase, and by the salivary and
pancreatic ferments. A yellowish amorphous powder, soluble in water,
but insoluble in absolute alcohol and in ether. It corresponds almost ex-
actly in tests with glycogen; but one variety (achroo-dextrin) does not give
the port-wine coloration with iodine.
Cane-Sugar, or Saccharose. It is contained in the juices of many
plants and fruits, and is extracted from the sugar-cane, from beet-root, or
from the maple. It is crystalline and is precipitated from concentrated
solutions by absolute alcohol. It has no power of reducing copper salts
on boiling. It is dextro-rotatory. It is not subject to alcoholic fermenta-
tion, until by inversion it is converted into glucose, it chars on addition of
sulphuric acid, and on heating with potassium or sodium hydrate.
Lactose. Lactose is the chief carbohydrate of milk. It is less
soluble in water than glucose; it is not sweet, and is gritty to the taste; but
it is insoluble in absolute alcohol. In digestion it yields a molecule of dex-
trose and a molecule of galactose. It undergoes alcoholic fermentation
with extreme difficulty; gives the tests similar to glucose, but less readily.
It is dextro-rotatory + 59°.
Maltose. This sugar is produced by the action of the saliva and
pancreatic juice on starch. It is also formed by the action of malt upon
starch by the action of the ferment diastase. It is converted into dextrose
by dilute sulphuric acid. It is dextro-rotatory; ferments with yeast; reduces
copper salts; and crystallizes in fine needles.
Dextrose, or Glucose. Dextrose pccurs widely diffused in the
INORGANIC PRINCIPLES 93
vegetable kingdom, in diabetic urine, in the blood, etc. It is usually ob-
tained from grape-juice, honey, beet-root, or carrots. As prepared, it really
is a mixture of two isomeric bodies, Dextrose or grape-sugar, which turns
a ray of polarized light to the right (-f- 56°), and L&vulose or fruit-sugar,
which turns the ray to the left.
It is easily soluble in water and in alcohol; not so sweet as cane-sugar;
the relation of its sweetness to that of cane-sugar is as 3 to 5. It is not so
easily charred by strong sulphuric acid as cane-sugar. It is not entirely
soluble in alcohol. It undergoes alcoholic fermentation with yeast.
Dextrose is the characteristic carbohydrate of the blood. It has the
power of reducing the salts of silver, bismuth, mercury, and copper, either
to the form of the metal in the first three cases, or to the form of the sub-
oxide in the case with cuprous salts. Upon this property the chief tests for
the sugar, e.g., Trommer's and Bottcher's, depend. It undergoes alcoholic
fermentation with yeast, and lactic-acid fermentation with bacteria lactis.
It forms caramel when strongly heated, and is also charred with strong acids.
Levulose is one of the products of the decomposition of cane-sugar by
means of dilute mineral acids, or by means of the ferment invertin in the
alimentary canal. It reacts to the same test as glucose, but is non-crystal-
lizable, and is laevo-rotatory. It is soluble in water and in alcohol. Its com-
pound with lime is solid, whereas that with dextrose is not.
Galactose. This monosaccharid is formed from lactose by the
action of dilute mineral acids, or inverting ferments; it may also be ob-
tained from cerebrin. It undergoes alcoholic fermentation, and reduces
copper salts to the suboxide.
Inosite. Inosite occurs in the heart and voluntary muscles, as
well as in beans and other plants. It crystallizes in the form of large color-
less monoclinic tables, which are soluble in water, but insoluble in alcohol
or ether. It has the formula of glucose, but is not a sugar. Inosite may
be detected by evaporating the solution containing it nearly to dryness, and
by then adding a small drop of solution of mercuric nitrate, and afterward
evaporating carefully to dryness, a yellowish-white residue is obtained;
on further cautiously heating, the yellow changes to a deep rose-color, which
disappears on cooling, but reappears on heating. If the inosite be almost
pure, its solution may be evaporated nearly to dryness. After, the addition
of nitric acid, the residue mixed with a little ammonia and calcium chloride,
and again evaporated, yields a rose-red coloration.
INORGANIC PRINCIPLES.
Salts. The inorganic principles of the human body are numerous.
They are derived, for the most part, directly from food and drink, and pass
through the system unaltered. But some salts are decomposed on their
94 THE CHEMICAL COMPOSITION OF THE BODY
way, as chloride of sodium, of which only four-fifths of the quantity ingested
are excreted in the same form. Some are newly formed within the body-
as, for example, a part of the sulphates and carbonates.
Much of the inorganic saline matter found in the body is a necessary
constituent of its structure, as necessary in its way as albumin or any other
organic principle. Another part is important in regulating or modifying
various physical processes, as absorption, solution, and the like. A part
must be reckoned only as matter which is, so to speak, accidentally present,
whether derived from the food or the tissues, and which will, at the first
opportunity, be excreted from the body. The principal salts present in
the body are:
Sodium and Potassium Chlorides. These salts are present in nearly
all parts of the body. The former seems to be especially necessary, judging
from the instinctive craving for it on the part of animals in whose food it is
deficient, and from the diseased condition which is consequent on its with-
drawal. The quantity of sodium chloride in the blood is greater than that
of all its other saline ingredients taken together, but it is present chiefly in
the fluids of the body. In the tissues, the muscles for example, the quantity
of sodium chloride is less than that of the chloride of potassium, which
forms a constant ingredient of protoplasm.
Calcium Fluoride. It is present in minute amount in the bones and
teeth, and traces have been found in the blood and some other fluids.
Calcium, Potassium, Sodium, and Magnesium Phosphates. These phos-
phates are found in nearly every tissue and fluid. In- some tissues — the bones
and teeth — the phosphate of calcium exists in very large amount. The phos-
phate of calcium is intimately incorporated with the organic basis or matrix,
but it can be removed by acids without destroying the general shape of the
bone. After the removal of its inorganic salts, a bone is left soft, tough,
and flexible.
Potassium and sodium phosphates, with the carbonates, maintain the
alkalinity of the blood.
Calcium Carbonate. It occurs in bones and teeth, but in much smaller
quantity than the phosphate. It is found also in some other parts. The
small concretions of the internal ear (otoliths) are composed of crystalline
calcium carbonate, and form the only example of inorganic crystalline matter
existing as such in the body.
Potassium and Sodium Carbonates and Sulphates. These are found in
the blood and most of the secretions and tissues.
Silicon. A very minute quantity of silica exists in the urine and in the
blood. Traces of it have been found also in bones, hair, and some other parts.
Iron. The especial place of iron is in hemoglobin, the coloring-matter
of the blood, of which a full account will be given with the chemistry of the
blood. Iron is found, in very small quantities, in the ashes of bones, mus-
LABORATORY EXPERIMENTS 95
cles, and many tissues, and in lymph and chyle, albumin of serum, fibrin,
bile, milk, and other fluids. A salt of iron, probably a phosphate, exists in
the hair, black pigment, and other deeply colored epithelial or horny substances.
Water. Water forms a large proportion, more than two-thirds,
of the weight of the whole body. Its relative amount in some of the principal
solids and fluids of the body is shown in the following table (from Robin
and Verdeil):
Quantity of Water in Per Cent.
Teeth 10.0 Bile 88.0
Bones 13.0 Milk 88.7
Cartilage 55 -° Pancreatic juice 9°-°
Muscles 75-° Urine 93-6
Ligament 76.8 Lymph 96.0
Brain 7&-9 Gastric juice 97-5
Blood 79 . 5 Perspiration 98 . 6
Synovia 80.5 Saliva 99-5
In all the fluids and tissues of the body — blood, lymph, muscle, gland,
etc. — water acts the part of a general solvent, and by its means alone circula-
tion of nutrient matter is possible. It is the medium also in which all fluid
and solid aliments are dissolved before absorption, as well as the means by
which all, except gaseous, excretory products are removed. All the various
processes of secretion, transudation, and nutrition depend of necessity on
its presence for their performance.
The greater part, by far, of the water present in the body is taken into
it as such from without, in the food and drink. A small amount, however,
is the result of the chemical union of hydrogen with oxygen in the oxida-
tions of the body.
The loss of water from the body is intimately connected with excretion
from the lungs, skin, and kidneys, and, to a less extent, from the alimentary
canal. The loss from these various organs may be thus apportioned (quoted
by Dalton from various observers):
From the Alimentary canal (feces) 4 per cent
" Lungs 20 "
" Skin (perspiration) 30 "
" Kidneys (urine) 46 "
LABORATORY EXPERIMENTS ON THE CHEMISTRY OF THE
BODY.
Proteid General Reactions. Certain tests depending on the pres-
ence of one or more of the constituent groups in the proteid molecule,
while not conclusive each in itself, when taken together serve for proteid
96 THE CHEMICAL COMPOSITION OF THE BODY
identification. Dilute some white of egg with ten volumes of water, filter
off the precipitated globulin, and use the egg albumin in the following tests:
1. Color Reactions of Proteids. a. Xanthoproteic. Add concentrated
nitric acid to 2 c.c. of the egg albumin in a test tube, a lemon-yellow color
appears on gently heating. Add excess of ammonia, the color deepens to
orange, or with potassium hydrate to reddish brown. Egg albumin is also
precipitated by the acid, but peptone gives only the color change. This re-
action depends upon the presence of the tyrosin nucleus, or that of indol,
in the proteid molecule.
b. Milton's reaction. Millon's reagent (mercuric and mercurous nitrate
in weak nitric-acid solution) added to albumin solution gives a white co-
agulum in the cold which turns purple-red on heating to 70° C. or more.
The reaction is due to the tyrosin grouping.
c. The biuret reaction. Excess of sodium or potassium hydrate with a few
drops of 2 per cent copper sulphate in albumin solution when heated gives a
violet color. Albumoses give a pinkish violet, and peptones a pink color in
this reaction, but care must be taken not to use an excess of copper sulphate.
The reaction seems to depend on the presence of the polypeptid groups.
d. Adamkiewicz reaction. If dilute glyoxylic acid be added to proteid
solution, and concentrated sulphuric acid run under the mixture, a ring of
colors is produced at the junction of the layers when gentle heat is applied;
red at the bottom, then green and violet. When shaken the whole becomes
violet. The reaction depends upon the tryptophane group.
2. Precipitations, a. Acid precipitation. Proteids form insoluble salts
with tannic acid, phospho-tungstic acid, hydroferrocyanic acid, picric acid,
etc. The proteid is changed in the reaction and cannot be recovered by
breaking up the salt. Strong mineral acids, hydrochloric acid, nitric acid,
etc., precipitate proteids, but the peptones are soluble in excess.
b. Heavy metal precipitation. Proteids form insoluble compounds with
mercuric chloride, lead acetate, copper sulphate, silver nitrate, etc.
c. Alcohol. Proteids are precipitated and coagulated by an excess of
alcohol. Peptone alone is recoverable from alcoholic precipitation.
d. Heat coagulations. Make the egg-albumin very faintly acid with
2 per cent acetic and heat to boiling, a white cloudy coagulum appears.
Albumoses and peptones are not heat-coagulated.
e. Precipitation by neutral salts. Add crystals of ammonium sulphate
to egg albumin solution to saturation, a white flocculent precipitate forms.
The precipitate can be recovered as unchanged albumin by removing the
excess of salt by dialysis.
Reactions Characteristic of Individual Proteids. The proteid
groups most often met by the student are the albumins, globulins, albumi-
nates, albumoses, peptones, enzyme-coagulated proteid, and heat-coagulated
proteid. Each has certain characteristics.
REACTIONS CHARACTERISTIC OF INDIVIDUAL PROTEIDS 97
3. Albumins, a. Solubility in water and in neutral salts. Test
each statement. Albumin is soluble in distilled water, dialyze out the traces
of salts. It is soluble in saturated sodium chloride and saturated magnesium
sulphate. It is insoluble in saturated ammonium sulphate.
b. Heat coagulation. Mount a test tube containing 5 c.c. faintly acid
egg-albumin in a 500 c.c. beaker of water which is supported by a gauze and
ring stand. Suspend a thermometer bulb in the middle of the albumin
solution. Gradually heat the beaker of water, stirring constantly, thus uni-
formly heating the albumin. Coagulation takes place at from 73° to 75° C.,
but turbidity a little earlier.
4. Globulins, a. Solubility in water and in neutral salts. Test
the following statements, using serum globulin. Globulin is insoluble in
distilled water. It is soluble in dilute neutral salt solutions — sodium chlo-
ride, magnesium sulphate, ammonium sulphate. Globulin is precipitated
by adding sodium chloride or magnesium sulphate to complete saturation.
Fibrinogen is precipitated by half -saturated magnesium sulphate. Globulins
are precipitated by adding to their solution an equal volume of saturated
ammonium sulphate, i.e., by half -saturated solution.
b. Heat coagulation. Test the temperature at which globulins are heat
coagulated by the method described above, on a sample of salted plasma
for nbrinogen which coagulates at 56° C., and on serum globulin which
coagulates at 73° C.
5. Albuminates. Digest egg albumin in 0.2 per cent hydrochloric
acid for an hour and test:
a. Solubility. It is insoluble in neutral solutions and in saturated neu-
tral salts, but soluble in dilute acids and alkalies.
b. Heat coagulation. It is not coagulated by heat.
6. Albumoses and Peptones. These proteids are formed in
the alimentary canal in the process of digestion under the influence of the
enzymes, pepsin and trypsin. Make a 5 per cent solution of Armour's pep-
tone (which contains chiefly albumoses) and test:
a. Heat coagulation. These proteids are not coagulated.
b. Alcohol. When added to excess, a precipitate occurs, but when
collected on a filter the precipitate may be redissolved in water.
c. General proteid reactions. These proteids fail to give many of the
precipitations, but give the color changes. The biuret test yields a rose
pink color.
d. Neutral salts. Albumoses are insoluble in saturated ammonium
sulphate. Filter and test the filtrate for proteid. It gives the biuret test.
This is due to peptones which are soluble in all salt solutions.
7. Ferment and Heat-Coagulated Proteids. Boiled egg white
should be used for the example of the former, and fibrin for the latter. Test
for the color reactions, experiment i, which they both give. These pro-
7
98 THE CHEMICAL COMPOSITION OF THE BODY
teids are insoluble in the usual solvents, though fibrin is slightly soluble in
10 per cent sodium chloride.
Carbohydrate Reactions. The carbohydrate representatives that
should be examined are:
8. Starch. Make a solution of starch by boiling i gram of
starch in 100 c.c. of distilled water and test.
a. Iodine test. Shake up three or four drops of dilute iodine solution
with 2 c.c. starch. A deep blue color appears. The color is discharged in
dilute alkali and reappears on acidifying again. Heat also discharges the color.
b. Fehling's test. Commercial starch often contains reducing sugar.
Boil 2 c.c. of starch solution with i c.c. of fresh Fehling. If a reddish-yellow
precipitate settles on standing, the starch contains reducing sugar as an
impurity. Starch does not reduce copper in the presence of an alkali.
c. Hydrolysis of starch. Boil starch solution with 5 per cent sulphuric
acid for fifteen minutes. Test with Fehling's solution, first neutralizing the
excess of acid. A copious precipitate of cuprous oxide shows that the starch
has been converted to reducing sugar.
9. Dextrin. Make a 5 per cent solution of dextrin in distilled
water and test:
a. Iodine. This gives a rich reddish-brown color which is characteristic.
b. Fehling. Not reduced by dextrin.
10. Dextrose. Test a 5 per cent solution of dextrose:
a. Iodine test. No reaction.
b. Trommer's test. Add caustic soda in excess and a few drops of 2 per
cent copper sulphate and boil, or use Fehling's solution. A reduction of the
copper takes place. Barfoid's solution also is reduced by dextrose, but not
by maltose.
11. Glycogen. Make up 10 c.c. of a i per cent solution of gly-
cogen and repeat the tests:
a. Iodine. This gives a wine-red color very much like that given by
dextrin. The color is discharged by heating, but reappears on cooling.
b. Lead acetate. It gives a precipitate, but one must guard against
the presence of proteid as an impurity.
c. Trommer's test. Glycogen does not reduce copper.
The Fats. The common fats are the oleins, palmitins, and
stearins. These are glycerin salts of the fatty acids. The animal fats are
mixtures of these fats in different proportions.
12. Neutral Fat. a. Melting-point. Compare neutral olive oil,
some fresh rendered lard, and some tallow. The former is fluid at ordinary
room temperature. Determine the melting-points of the lard and of the
tallow by the method of Wiley. Fill a test tube, one-half full of water and
add a two-inch top layer of alcohol. Prepare a thin flake of fat and suspend
it in the test tube at the dividing line of the water and alcohol. Insert the
FAT ACIDS 99
bulb of a thermometer at the same level. Mount the test tube with the
thermometer in a beaker on a ring stand, fill the beaker with water above the
level of the content of the test tube, and gradually heat with stirring of the
water in the beaker. At the melting temperature the flake of fat will run
into a round drop.
b. Solubility. Fat is insoluble in water, but soluble in ether, chloro-
form, benzol, and in alcohol.
c. Saponification. Heat some fat in an evaporating-dish, add sodium
hydrate, and boil. Saponification takes place. The soap is soluble in water.
Add 25 per cent sulphuric acid to some of the soap, the fatty acid is liber-
ated and collects on the surface of the solution.
13. Fat Acids. Collect some of the fatty acids, wash to remove
excess of alkali, and dissolve in ether.
a. Acid reaction. Add ether solution of the fatty acid to neutral litmus,
or to faintly alkaline phenolphthalein. The former turns red, and the red of
the latter is discharged, the acid reaction.
b. Acrolein test. Evaporate the ether from 2 c.c. of the solution, add
potassium bisulphate crystals to the acid in a test tube, and raise to a high
heat over a bunsen. No acrolein is given off. Repeat on neutral fat and
on glycerin. Both liberate the irritating fumes of acrolein.
14. Emulsification. a. Shake up neutral olive oil and water, no
emulsion is formed and the oil quickly separates.
b. Add a couple of drops of fatty acid, a very good but temporary emul-
sion is now formed.
c. Use rancid fat, a temporary emulsion is formed.
d. Add a little soap to either of the above, i.e., c. A good permanent
emulsion is now formed.
15. The Salts. A goodly series of salts is present in the body,
the most important elements of which are sodium, potassium, calcium, mag-
nesium, and iron, as chlorides, sulphates, and phosphates. Burn 50 c.c. of
blood at a dull red heat, take up in water and test:
a. Chlorides. Add i per cent nitrate of silver, a white precipitate, in-
soluble in nitric acid, soluble in ammonia, and reprecipitated by nitric acid.
b. Sulphates. Add barium chloride, a white precipitate, which quickly
settles and is insoluble in nitric acid.
c. Phosphates. Add nitric acid and a few drops of i per cent ammonium
molybdate, a yellow granular precipitate of phosphorus. It is soluble in
ammonia, reprecipitated in nitric acid.
d. Calcium. Make a hydrochloric acid extract of the ash of blood
above, add ammonia to excess, then a solution of ammonium oxalate, a deli-
cate white precipitate where traces are present.
e. Iron. Add hydrochloric acid and a few drops of ferrocyanide of po-
tassium. A blue color indicates the presence of iron.
PLATE II
VARIETIES OF LEUCOCYTES
a. Polymorphonuclear Neutrophiles. Note the varieties in size and shape of gran-
ules, the regular staining of the nuclei, the light space around them, their relatively central
position in the cell.
b. Myelocytes. Note the identity of granules with those just described; the even, pale
stain of nuclei, their position near the surface (edge) of the cell. The two cells figured
indicate the usual variations in size of the whole cell.
c. Small Lymphocytes. In the cell at the left note the transparent protoplasm; in the
cell next to it note the very pale pink of protoplasm around the nucleus which is deeply
stained, especially at the periphery. The next cell has an indented nucleus; its protoplasm
relatively distinct. The cell on the extreme right shows no protoplasm and is probably
necrotic. In all note absence of granules with this stain. With basic stains a blue net-
work appears in the protoplasm.
d. Large Lymphocytes. Note the pale stain of nuclei and protoplasm, regularity of
outline; indented nucleus in one. Every intermediate stage between these and the
"small " lymphocytes occurs, and the distinction between them is arbitrary.
e. Eosinophile. Note regular shape, loose connection of granules, their copper color,
their uniform and relatively large size, and spherical shape.
/. Eosinophilic Myelocyte. Note similarity to the ordinary myelocytes 6, except as
regards granules. Color of granules may be, as in e, ordinary eosinophile.
All the above were stained with the Ehrlich triacid stain, and drawn with camera
lucida. Oil immersion objective ^ and ocular No. iii. of Leitz. ^ Cabot.)
CHAPTER IV
THE BLOOD
THE blood is the fluid medium of which all the tissues of the body are
nourished. By means of the blood materials absorbed from the alimentary
canal as well as oxygen taken from the air in the lungs are carried to the tissues,
while substances which result from the metabolism of the tissues are carried
to the excretory organs to be removed from the body. The blood also acts
as a medium of exchange for products of glandular activity between the various
tissues themselves, internal secretions, and it is a factor in the regulation
of body temperature. The blood is a somewhat viscid fluid, and in man
and in all other vertebrate animals, with the exception of two of the lowest,
is red in color. The exact color of the blood is variable; that taken from
the systemic arteries, from the left side of the heart and from the pulmonary
veins is of a bright scarlet hue; that obtained from the systemic veins, from
the right side of the heart, and from the pulmonary artery is of a much
darker color, which varies from bluish-red to reddish-black. At first
sight the red color appears to belong to the whole mass of blood, but on
further examination this is found not to be the case. In reality blood con-
sists of an almost colorless fluid, called plasma or liquor sanguinis, in which
are suspended numerous minute masses of protoplasm, called blood-corpus-
cles. The corpuscles are of the two varieties, the white ameboid corpuscles,
or leucocytes, and the red corpuscles, erythrocytes. The latter compose
by far the larger mass of blood-cells and contain the red pigment, hemoglobin,
to which the color of the blood is due.
The plasma or fluid part of the blood is a remarkably complex chemical
mixture. It is kept in constant rapid circulation through the blood-vessels
of the body and is, therefore, thoroughly mixed and homogeneous in character.
Quantity of the Blood. The quantity of blood in any animal
under normal conditions bears a fairly constant relation to the body weight.
The amount of blood in man averages -£•$ to YJ of the body weight. In
other mammals the proportion of blood is also fairly constant, varying from
^ to -^g- of the body weight. In many of the lower vertebrates the relative
quantity of blood is very much less.
An estimate of the quantity in man which corresponded very nearly
with this proportion has been more than once made by methods illustrated
by the following data: A criminal was weighed before and after decapita-
101
THE BLOOD
tion; the difference in the weight representing the quantity of blood which
escaped. The blood-vessels of the head and trunk were then washed out
by the injection of water until the fluid which escaped had only a pale red
or straw color. This fluid was then also weighed, and the amount of blood
which it represented calculated by comparing the proportion of solid matter
contained in it with that of the first blood which escaped on decapitation.
Two experiments of this kind gave precisely similar results (Weber and
Lehmann).
This quantity of blood is distributed in the different parts of the body,
chiefly in the muscles, the liver, the heart, and larger blood-vessels, as shown
by the following figures determined on the rabbit by Ranke (from Vierordt) :
Per cent.
Spleen 0.23
Brain and cord i . 24
Kidney i . 63
Skin 2.10
Abdominal viscera 6. 30
Cartilage 8 . 24
Heart, lungs, and large blood-vessels 22.76
Resting muscle 29 . 20
Liver 29.30
It should be remembered, in connection with these estimations, that
the quantity of the blood must vary very considerably, even in the same
animal, with the amount of both the ingesta and egesta of the period im-
mediately preceding the experiment. It has been found, for example, that
the quantity of blood obtainable from the body of a fasting animal rarely
exceeds a half of that which is present soon after a full meal.
COAGULATION OF THE BLOOD.
The most characteristic property which the blood possesses is that of
clotting or coagulating. This phenomenon may be observed under the
most favorable conditions in blood which has been drawn into an open vessel.
In about two or three minutes, at the ordinary temperature of the air, the
surface of the fluid is seen to become semi -solid or jelly-like, and this change
takes place, in a minute or two afterward, at the sides of the vessel in which
it is contained and then quickly extends throughout the entire mass. The
time which is occupied in these changes is about eight or nine minutes. The
solid mass is of exactly the same volume as the previously liquid blood, and
adheres so closely to the sides of the containing vessel that if the latter be
inverted none of its contents escape. The solid mass is the crassamentum
or dot. If the clot be watched for a few minutes, drops of a light, straw-
colored fluid, the serum, may be seen to make its appearance on the surface,
and, as it becomes greater and greater in amount, to form a complete super-
COAGULATION OF THE BLOOD 103
ficial stratum above the solid clot. At the same time the fluid begins to
transude at the sides and at the under surface of the clot, which in the course
of an hour or two floats in the liquid. The appearance of the serum is due
to the fact that the clot contracts, thus squeezing the fluid out of its mass.
The first drops of serum appear on the surface about eleven or twelve minutes
after the blood has been drawn; and the fluid continues to transude for from
thirty-six to forty-eight hours.
The clotting of blood is due to the development in the plasma of an in-
soluble substance called -fibrin. This fibrin forms threads or strands through
the mass in every direction. The strands adhere to each other wherever
they come in contact, thus forming a very dense tangle and meshwork which
incloses within itself the blood-corpuscles. The clot when first formed,
therefore, includes the whole of the blood in an apparently solid mass, but
soon the fibrinous meshwork begins to contract and the serum is squeezed
out. When a large part of the serum has been squeezed out the clot is found
to be smaller, but firmer and harder, as it is now made up largely of fibrin
and blood-corpuscles. Thus in coagulation there is a rearrangement of the
constituents of the blood; liquid blood being made up of plasma and blood-
corpuscles, and clotted blood of serum and clot.
Liquid Blood.
Plasma. Corpuscles.
Serum. Fibrin.
I
Clot.
Clotted Blood.
The rapidity with which coagulation takes place varies greatly in different
animals and at different times in the same animal. Where coagulation is
very slow the red corpuscles, which are somewhat heavier than plasma,
often have time to settle considerably before the fibrin is formed. If the
blood is rapidly cooled to something approaching o° C. then the clot is very
greatly delayed. Horse's blood is particularly favorable for demonstrating
this point. In it clotting occurs so slowly that very often the red corpuscles
will completely settle out, and when the blood is again warmed and the clotting
takes place there is a superficial stratum differing in appearance from the
rest of the clot, and is of a grayish-yellow color. This is known as the buffy
coat or crusla phlogistica. The buffy coat, produced in the manner just
described, commonly contracts more than the rest of the clot, on account of
the absence of colored corpuscles from its meshes. When the clot is allowed
to stand the white corpuscles migrate to the surface by ameboid movement,
104
THE BLOOD
often in such numbers that they form a distinct superficial layer, grayish-
white in appearance.
That the clotting of blood is due to the gradual appearance in it of fibrin
may be easily demonstrated. For example, if recently drawn blood be
whipped with a bundle of twigs or wires, the fibrin may be withdrawn from
the blood before it can entangle the blood-corpuscles within its meshes, as
it adheres to the twigs in stringy threads relatively free from corpuscles.
The blood from which the fibrin has been withdrawn no longer exhibits the
power of spontaneous coagulability and it is now called defibrinated blood.
Although these facts have long been known, the closely associated problem
as to the exact manner in which fibrin is formed is by no means so simple.
Fibrin is derived from the plasma. Pure plasma may be procured by
delaying coagulation in blood by keeping it at a temperature slightly above
-4V
FIG. 107. — Reticulum of Fibrin, from a Drop of Human Blood, after Treatment with Rosanilin.
(Ranvier.)
freezing point, until the colored corpuscles have subsided to the bottom of
the containing vessel. The blood of the horse is specially suited for the pur-
poses of this experiment. A portion of the colorless supernatant plasma,
if decanted into another vessel and exposed to the ordinary temperature of
the air, will coagulate, producing a clot similar in all respects to blood clot,
except that it is colorless from the absence of red corpuscles. If some of
the plasma be diluted with twice or three times its bulk of normal saline
solution (0.9 per cent), coagulation is delayed, and the stages of the gradual
formation of fibrin in it may be conveniently watched. The viscidity which
precedes the complete coagulation may be actually seen to be due to the
formation of fibrils of fibrin — first of all at the edge of the fluid-containing
vessel, and then gradually extending throughout the mass. If a portion of
plasma, diluted or not, be whipped with a bundle of twigs the fibrin may
be obtained as a solid, stringy mass, just in the same way as from the ei .ire
THEORIES OF COAGULATION
105
blood, and the resulting fluid no longer retains its power of spontaneous
coagulability.
Theories of Coagulation. It is evident that the blood plasma
contains some substance or substances which take part in the formation of
fibrin. By numerous investigations it has been found that the direct ante-
cedent of the fibrin is the proteid substance, fibrinogen. This fibrinogen
exists in the blood plasma at all times, but is somewhat increased under
certain conditions. The fibrinogen is reacted on by another substance
known as thrombin, or by the historical term fibrin ferment. We shall not
present the numerous theories which have been held concerning blood coagu-
lation, many of which have been more or less disproven, but shall try to present
Blood
Tissue Cells
Plasma
Blood Plates Corpuscles
Neutral Salts Fibrinogen Calcium Salts
(for dissolving
fibrinoRen)
Fibrin-globulin
Prothrombin
Thrombokinase
Thrombin
Fibrin
FIG. 108. — Schema of Coagulation.
the condensed statement of the present explanations of this intricate phenom-
enon. One may start from the statement that the fibrinogen of the plasma
when acted upon by the thrombin, also of the plasma, produces an insoluble
substance, fibrin. The chief interest centers around the origin and char-
acter of the fibrinogen, the origin and nature of the thrombin, and the condi-
tions which influence its activity.
The fibrinogen is present in blood plasma of the circulating blood of the
body at all times. It can be separated from plasma by various chemical
means, and when purified can be made to form fibrin under proper conditions.
All observers are agreed that this proteid is the immediate precursor of the
insoluble fibrin. Its origin in the blood has been traced with some degree
of certainty to the disintegration of the white blood-corpuscles.
The thrombin is the substance which reacts on the fibrinogen in the proc-
esses of fibrin formation. It does not exist in the living blood-vessels, or at
THE BLOOD
least is present only in minute traces, but makes its appearance immediately
the blood is drawn. Its origin is therefore of peculiar interest.
It has been claimed by some, notably Peckelharing, that thrombin is a
calcium compound. At any rate, it is definitely proven that calcium is a
necessary element in the formation of the clot.
The substance thrombin, fibrin ferment, quickly appears in consider-
able quantity when blood is drawn under ordinary conditions. Its appearance
is due to at least three antecedent substances, prothrombin (thrombogen),
calcium, and thrombokinase. The sources of these substances and the
part taken by each in the process of coagulation are as follows: If blood
be drawn, centrifugalized, and the blood plates separated, freed from plasma,
and suspended in water, their solution will cause the formation of fibrin
from fibrinogen in the presence of calcium and thrombokinase. The blood
platelets are, therefore, the source of the thrombogen. The thrombokinase
can be traced to its origin in the tissue cells and the formed elements of the
blood, especially the leucocytes. If blood is drawn from the vessels with
due precautions not to allow it to come in contact with the cut vessel, or other
tissue, clotting is very much delayed. The plasma if separated by the cen-
trifuge will remain unclotted for a long time as shown by Howell for the
terrapin's plasma. This plasma will quickly clot at any time if a few drops
of tissue extract in salt solution be added. A solution of extract of washed
white corpuscles acts to increase the rapidity of coagulation. If precautions
are taken to draw the blood in such a manner as to remove the calcium from
the plasma, no clot is formed.
The calcium which exists in solution in the plasma to the extent of 0.026
per cent can be removed by precipitation with oxalate solution, or by fluorides.
Oxalate plasma contains both prothrombin and thrombokinase, and when-
ever calcium chloride is added to slight excess coagulation takes place. In
fluoride plasma one must add both calcium and thrombokinase as that sub-
stance seems to prevent the setting free of thrombokinase from the corpuscles.
The prothrombin is not interfered with by fluoride.
In a word, one may say that the coagulation of the blood takes place
because of the formation of fibrin from fibrinogen by the action of thrombin.
The fibrinogen is constantly present in the plasma. The thrombin is formed
by the interaction of three substances, prothrombin, thrombokinase, and cal-
cium. The prothrombin arises chiefly from the disintegration of the blood
platelets when the blood leaves the blood-vessels. The thrombokinase
originates in tissue cells of the blood and of the organs of the body in general.
The calcium is present in the blood plasma at all times.
Conditions Affecting Coagulation. From the preceding discussion
it is evident that the rapidity of the coagulation of the blood will be influenced
by anything that will influence the formation of the fibrin factors or their
interaction. The most important influences are the following:—
MORPHOLOGY OF THE BLOOD 107
Temperature. Cold retards coagulation. Gentle warmth, 40° C., hastens
but a temperature above 56° C. destroys clotting, since that temperature heat-
coagulates the fibrinogen.
Contact with Foreign Bodies. Such contact hastens clotting. This is
due to the influence of such bodies on the formation of fibrin factors, es-
pecially the substances that arise from the disintegration of the leucocytes.
Condition of the Blood-Vessel Walls. Intra vascular clotting often takes
place upon injury of the endothelial lining of the blood-vessel, probably
from the liberation of thrombokinase in quantity too great for elimination
by the healthy portion of the wall. The healthy endothelium no doubt is
an important factor in eliminating the small amounts of the fibrin factors
that must be constantly forming. The open wounds and lacerations of
tissue that accompany the loss of blood by accident are the very conditions
most favorable to clotting, since large amounts of tissue extract, thrombo-
kinase, are formed under these conditions.
Neutral Salts. The addition of neutral salts in the proportion of 2 or 3
per cent and upward. When added in large proportions, most of these
saline substances prevent coagulation altogether. Coagulation, however,
ensues on dilution with water. The time during which salted blood can be
thus preserved in a liquid state, and coagulated by the addition of water,
is quite indefinite.
Oxalates and Fluorides. These and other precipitants of calcium pre-
vent clotting by removing this substance.
Peptone. The injection of commercial peptone in the blood-vessels of
an animal to the extent of 0.5 gram of peptone per kilo weight of the body
of the animal will deprive the blood of the power of coagulation. If a smaller
quantity be injected the coagulation of the blood will be delayed. If peptone
blood is drawn and centrifuged, the plasma obtained, which is called peptone
plasma, can be made to coagulate by diluting sufficiently with water and
letting it stand a long time. Peptone plasma in the blood-vessels of the ani-
mal gradually regains the power to coagulate.
MORPHOLOGY OF THE BLOOD.
The corpuscles floating in the fluid plasma of the blood, when separated
by a centrifugal machine are found to make up 45 to 50 per cent of the total
mass of the blood. These corpuscles, or formed elements, are of three
varieties, the red corpuscles or erythrocytes, the wrhite corpuscles leucocytes,
and the blood platelets which have been called thrombocytes .
Red Corpuscles or Erythrocytes. Human red blood-corpuscles
are circular, biconcave discs with rounded edges, from 7 /j. to 8 p. in diameter,
and about 2 p. in thickness. When viewed singly they appear of a pale
yellowish tinge; the deep red color which they give to the blood being ob-
108 THE BLOOD
servable in them only when they are seen en masse. They are composed
of a colorless, structureless, and transparent filmy framework or stroma,
infiltrated in all parts by the red coloring matter, the hemoglobin. The
stroma is tough and elastic, so that as the corpuscles circulate they admit
of elongation and other changes of form in adaptation to the vessels, yet
recover their natural shape as soon as they escape from compression.
Number and Character of the Red Corpuscles. The normal number of red
blood-cells in a cubic millimeter of human blood was estimated by Welcker,
in 1854, to be 5,000,000 in men and 4,500,000 in women. Numerous recent
observations, however, have shown that these estimates are a little low,
especially in men, and the average number has been placed by different
authorities at various points between 5,000,000 and 5,500,000. Still the
original numbers as given by Welcker are accepted at the present day as being
sufficiently accurate for ordinary purposes. It has been also shown that
there are many distinct physiological variations in the number, depending
FIG. 109. FIG. no.
FIG. 109. — Red Corpuscles in Rouleaux. The rounded corpuscles are white or uncolored.
FIG. no. — Corpuscles of the Frog. The central mass consists of nucleated colored corpuscles.
The other corpuscles are two varieties of the colorless form.
on the time of day, digestion, sex, etc. The number of red cells usually
diminishes in the course of each day, while the leucocytes increase in number.
It has been suggested that this is due to the influence of digestion and exercise.
It has generally been found that within half an hour or an hour after a
full meal the number of red cells begins to diminish, and that this keeps up
for from two to four hours, when it is followed by a gradual rise to the normal.
The usual fall is 250,000 to 750,000 per cubic millimeter. These results
are most marked after a largely fluid meal, and are probably due to dilution
of the blood as a result of the absorption of fluids. In animals the number
of red cells is increased by fasting, but in man the results are variable, some
authorities claiming an increase and others a decrease. In childhood there
RED CORPUSCLES OR ERYTHROCYTES
109
is no difference between the sexes in the number of red cells per cubic milli-
meter, but after menstruation is established a relative anemia develops in
women. Welcker's original estimate placed the difference at 500,000 per
cubic millimeter, and these figures have been generally accepted, though
Leichtenstein asserts that the difference is 1,000,000.
Menstruation in healthy subjects has practically no effect, as not more
than ico-200 cubic centimeters of blood are lost normally in the course of
FIG. in. — The Illustration is Somewhat Altered from a Drawing by Gulliver, in the
Proceed. Zool. Society, and exhibits the typical characters of the red blood-cells in the main
Divisions of the Vertebrata. The fractions are those of an inch, and represent the average diameter.
In the case of the oval cells, only the long diameter is here given. It is remarkable, that although
the size of the red blood-cells varies so much in the different classes of the vertebrate kingdom,
that of the white corpuscles remains comparatively uniform, and thus they are, in some animals,
much greater, in others much less, than the red corpuscle existing side by side with them.
several days. Under such circumstances the normal diminution of red cells
per cubic millimeter is probably less than 150,000, though Sfameni has placed
the loss at about 225,000. In fact an increase has been claimed. The
leucocytes are slightly increased during menstruation. It is now the general
opinion that pregnancy has little or no effect on the number of red cells, and
110 THE BLOOD
that any anemia must be due to abnormal conditions. Post-partum anemia
should not last longer than two weeks.
The red corpuscles are not all alike. In almost every specimen of blood
a certain number of corpuscles smaller than the rest may be observed. They
are termed microcytes, or hematoblasts, and are probably immature corpuscles.
A peculiar property of the red corpuscles, which is exaggerated in in-
flammatory blood, may be here again noticed, i.e., their great tendency to
adhere together in rolls or columns (rouleaux), like piles of coins. These
rolls quickly fasten together by their ends, and cluster; so that, when the
blood is spread out thinly on a glass, they form a kind of irregular network,
with crowds of corpuscles at the several points corresponding with the knots
of the net, figure 109. Hence the clot formed in such a thin layer of blood
looks mottled with blotches of pink upon a white ground.
The red corpuscles are constantly undergoing disintegration in different
parts of the circulatory system, particularly in the spleen. The liberated
hemoglobin contributes to the formation of the bile pigments in the liver.
Development of the Red Blood-Corpuscles. — The first formed
blood-corpuscles of the human embryo differ much in their general characters
FIG. 112. — Part of the Network of Developing Blood- Vessels in the Vascular Area of aGuinea-
Pig. bl, Blood-corpuscles becoming free in an enlarged and hollowed-out part of the network; a,
process of protoplasm. (E. A. Schafer.)
from those which belong to the later periods of intra-uterine, and to all periods
of extra-uterine life. Their manner of origin is at first very simple.
Surrounding the early embryo is a circular area, called the vascular area,
in which the first rudiments of the blood-vessels and blood-corpuscles are
developed. Here the nucleated embryonal cells of the mesoblast, from
which the blood-vessels and corpuscles are to be formed, send out processes
in various directions, and these, joining together, form an irregular mesh-
work. The nuclei increase in number, and collect chiefly in the larger masses
of protoplasm, but partly also in the processes. It appears that hemo-
DEVELOPMENT OF THE RED BLOOD-CORPUSCLES
111
globin then makes its appearance in certain of these nucleated embryonal
cells, which thus become the earliest red blood-corpuscles. The proto-
plasm of the cells and their branched network in which these corpuscles
lie then become hollowed out into a system of canals enclosing fluid, in which
the red nucleated corpuscles float. The corpuscles at first are from about
10 /A to 16 p, in diameter, mostly spherical, and with granular contents, and
a well-marked nucleus. Their nuclei, which are about 5 p in diameter,
FIG. i
PIG. 114.
FIG. 113.— Multiplication of the Nucleated Red Corpuscles. Marrow of young kitten after
bleeding, showing above karyo kinetic division of erythroblast, and below the formation of mature
from immature erythrocytes. (Howell.)
FIG. 114. — Shows the Way in which the Nucleus Escapes from the Nucleated Red Corpuscles.
1,2,3, 4, represent different stages of the extrusion noticed upon the living corpuscles, a, Specimen
from the circulating blood of an adult cat, bled four times; b, specimen from the circulating blood
of a kitten forty days old, bled twice; c, specimens from the blood of a fetal cat, 9 cm. long. Others
from the marrow of an adult cat, two of the figures showing the granules present in the corpuscles,
which have been interpreted erroneously as a sign of the disintegration of the nucleus. (Howell.)
are central, circular, very little prominent on the surfaces of the corpuscles,
and apparently slightly granular.
The corpuscles then strongly resemble the colorless corpuscles of the
fully developed blood but for their color. They are capable of ameboid
movement and multiply by division.
When, in the progress of embryonic development, the liver is formed,
the multiplication of blood-cells in the whole mass of blood ceases, and new
blood-cells are produced by this organ, and also by the spleen. These are
at first colorless and nucleated, but afterward acquire the ordinary blood tinge,
and resemble very much those of the first set. They also multiply by division.
The bone marrow also begins to form red corpuscles, though at first in small
amounts only. This function develops rapidly, however, so that at birth
the marrow represents the chief seat of production of the red cells. Never-
theless, nucleated red cells are usually found at birth, sometimes in con-
siderable quantities in the liver and in the spleen. Non-nucleated red cells
begin to appear soon after the first month of fetal life, and gradually increase
so that at the fourth month they form one-fourth of the whole amount of
112 THE BLOOD
colored corpuscles. At the end of fetal life they almost completely replace
the nucleated cells. In late fetal life the red cells are formed in almost the
same way as in extra-uterine life.
Various theories have prevailed as to the mode of origin of the non-nu-
cleated colored corpuscles. For a time it was thought that they were of
endoglobular origin, and merely fragments of some original cell, being pro-
duced by subdivision of the cell body itself. This theory easily accounted
for the absence of the nuclei, but it has not been supported by recent investi-
gations. At present it is the general belief that the non-nucleated cells, or
erythrocytes, are derived from nucleated cells by a process of mitotic division,
and further that their nuclei gradually shrink or fade and are then extruded.
FIG. itc — Colored Nucleated Corpuscles, from the Red Marrow of the Guinea-Pig. (E. A.
Schafer.)
The use of some of the more recent stains seems to prove that there are traces
of nuclear material in the non-nucleated corpuscles.
After infancy and early childhood the origin of erythrocytes is practically
limited to the red marrow of the bones. The mother cells, or erythroblasts,
are constantly forming and setting free erythrocytes, the rate varying greatly
at different periods.
The Colorless Corpuscles or Leucocytes. In human blood the
white corpuscles, leucocytes, are nearly spherical masses of granular proto-
plasm without cell wall. In all cases one or more nuclei exist in each cor-
puscle. The corpuscles vary considerably in size but average 10 p, in diameter.
The number of leucocytes in a cubic millimeter of blood is estimated
at 7,500 to 8,000. The proportion of white corpuscles to red, therefore, is
about one of the former to 700 of the latter. This proportion is not very
constant in health and great variations cccur under the influence of disease,
especially in certain infectious diseases in which the number of wrhite corpus-
cles is markedly increased.
After a full meal the white cells in a healthy adult are increased in number
about one-third, the increase beginning within an hour, attaining a maxi-
mum in three or four hours, and then gradually falling to normal. This
process is frequently modified by the character of the food, the greatest
increase occurring with an exclusively meat diet, while a purely vegetarian
diet has usually no effect. The increase is also more marked in children,
and especially in infants. The essential factor is probably the absorption
of albuminous matter in considerable quantities. This causes proliferation
of leucocytes in the adenoid tissue of the gastro-intestinal tract.
In pregnancy there is often a moderate increase in the number of white
THE COLORLESS CORPUSCLES OR LEUCOCYTES 113
cells during the later months. This does not begin until after the third
month, and is most marked and constant in primiparse. After parturition
the leucocytes gradually diminish under normal conditions, and usually
reach the normal within a fortnight. The essential factor is probably the
general stimulation in the maternal organism. It is well established that the
white cells are very numerous in the new-born, though different observers
have made very conflicting estimates. Still all agree that there is a very
rapid decrease in their numbers during the first few days, and that this is
followed by a less marked increase, which continues for many months.
According to Rieder, who is perhaps the most reliable, there are at birth
from 14,200 to 27,400 per cubic millimeter, and after the fourth day from
12,400 to 14,800.
Varieties of Leucocytes, The colorless corpuscles present greater diversi-
ties of form than the red ones, plate II. They are usually classified according
to their reaction to staining agents, or to the presence or absence of granules
in their cytoplasm. Kanthack and Hardy offer the following classification,
based upon both phenomena:
Leucocytes.
A. Oxyphile (staining with acid dyes). . . J1' Finel>r granular.
| 2. Coarsely granular eosmopmle.
B. Basophile (staining with basic dyes) . . i. Finely granular.
C. Hyaline .. . . J T' Sma11 lymphocyte.
( 2. Large myelocyte.
The finely granular oxyphile constitutes 75 per cent of all leucocytes.
It has an average diameter of 10 ^it, and possesses phagocytic action to a
marked degree — that is, it possesses the power of ingesting foreign particles.
Its nucleus consists of several lobes united by threads of chromatin. This
cell was formerly known under the term neutrophile, because of its supposed
reaction to neutral dyes.
The coarsely granular form of eosinophile constitutes only 2 per cent of
the leucocytes. It has a diameter of 12 p, and a reniform nucleus.
The basophile cell is rarely found in normal blood. It may occur occa-
sionally during periods of digestion. It is a small, spherical cell, with an
irregular nucleus and a diameter of 7 p,.
The small hyaline leucocyte is also called a lymphocyte, because of the
large numbers found in adenoid tissue, and is supposed to be an immature
form. The nucleus is proportionally large, and is surrounded by but little
protoplasm in which no granules can be detected. The cell is about the
size of a red blood-cell, and constitutes from 10 to 20 per cent of all leucocytes.
The large hyaline or myelocyte varies in diameter from 8.5 to 10 p,. Its
nucleus is spherical or reniform, and is surrounded by more protoplasm than
in the case of the lymphocyte. It forms about 10 per cent of the leucocytes.
Ameboid Movement of Leucocytes. The remarkable property of the color-
8
114 THE BLOOD
less corpuscles of spontaneously changing their shape was first demonstrated
by Wharton Jones in the blood of the skate. If a drop of blood be examined
with a high power of the microscope, under conditions by which loss of mois-
ture is prevented, and at the same time the temperature is maintained at
about that of the body, 37° C., the colorless corpuscles will be observed
slowly to alter their shapes, and to send out processes at various parts of their
\
C
FIG. 116. — (a) Red blood- corpuscle for comparison; (b) small hyaline cell or lymphocyte;
(c) large hyaline cell or myelocyte; (d) fine granular oxyphile; (e) coarse granular oxyphile or eosino-
phile; (;) basophile. (F. C. Busch.)
circumference. The ameboid movement which can be demonstrated in
human colorless blood-corpuscles, can be most conveniently studied in the
newt's blood. Processes are sent out from the corpuscle. These may be
withdrawn, but more often the protoplasm of the whole corpuscle flows
gradually forward to the position occupied by the process, thus the corpuscle
changes its position. The change of position of the corpuscle can also take
place by a flowing movement of the whole mass, and in this case the loco-
FIG. 117. — Human Colorless Blood-Corpuscle, Showing its Successive Changes of Outline Within
Ten Minutes when kept Moist on a Warm Stage. (Schofield.)
motion is comparatively rapid. The activity both in the processes of change
of shape and also of change in position is much more marked in some cor-
puscles than in others. Klein states that in the newt's blood the changes
are especially noticeable in a variety of the colorless corpuscle, which consists
of a mass of finely granular protoplasm with jagged outline and contains
CHEMICAL COMPOSITION OF THE BLOOD 115
three or four nuclei, or in large irregular masses of protoplasm containing
from five to twenty nuclei,
The property which the colorless corpuscles possess of passing through
the walls of the blood-vessels will be described later on.
The Blood Plates or Thrombocytes. A third variety of corpuscle
found in the blood is known as the blood plate. They are circular or elliptical
in shape, of nearly homogeneous structure, and vary in size from 0.5 to 5^,.
FIG. 118. — Blood Plates, Showing Chromatic Centers Regarded by some as Nuclei, and Ex-
hibiting Ameboid Movement. (Schafer, from Kopsch.)
Hence they are smaller than the red corpuscles. They vary in number from
5,000 to 45,000 per cubic millimeter and are preserved by drawing fresh
blood directly into Hayem's or other preserving fluid. Chemically they
contain a nucleo-proteid, *and it is supposed that they take part in the phe-
nomenon of coagulation. According to Deetjen and others, ameboid move-
ment has been demonstrated in these bodies.
CHEMICAL COMPOSITION OF THE BLOOD.
In considering the chemical composition of the blood, it will be convenient
to take in order the composition of the various chief factors into which the
blood may be separated, viz., The Plasma ; The Serum ; The White Cor-
puscles ; The Red Corpuscles.
The Composition of the Plasma. The plasma is the liquid part
of the blood in which the corpuscles float.
It contains the fibrin factors, inasmuch as when drawn from the blood-
vessels it undergoes coagulation and splits up into fibrin and serum. It
differs from the serum in containing fibrinogen, but in appearance and in
reaction it closely resembles that fluid. Its alkalinity, however, is greater
than that of the serum obtained from it. It may be freed from corpuscles
by the centrifugal machine, or by the other means enumerated below.
116 THE BLOOD
The chief methods of obtaining plasma free from corpuscles are: i. By cold. The
temperature should be about o° C. and may be two or three degrees higher, but not
lower. 2. The addition of neutral salts, in certain proportion, either as solids or in
solution, e.g., of sodium sulphate, if solid i part to 12 parts of blood; if a saturated solu-
tion i part to 6 parts of blood. Or magnesium sulphate, saturated solution i part to
4 of blood. 3. By mixing frog's blood with an equal part of a 5 per cent solution of
cane sugar, and getting rid of the corpuscles by nitration. 4. By the injection of com-
mercial peptone into the veins of certain mammals previous to bleeding them to death,
allowing the corpuscles to subside or by subjecting the blood to the action of a centrif-
ugal machine by the rapid rotation of which the whole of the solids are driven to the
outer end of the tubes in which the blood is placed.
PERCENTAGE COMPOSITION OF PLASMA.
Water 90.29
Solids—
1. Proteids —
Fibrinogen }
Paraglobulin I 8.289
Serum albumin )
2. Extractives 566
3. Inorganic salts 8 ;o
9.71
Water. The water of the plasma varies in amount according to the
amount of food, drink, and exercise, or other circumstances. It amounts
to about 90 per cent.
Proteids. Fibrinogen is the substance in plasma which is converted into
fibrin on coagulation. It belongs to the class of proteids called globulins.
It is precipitated from plasma with serum globulin by saturation with MgSO4
and NaCl. It is soluble in dilute salt solutions but is not soluble in water.
It can be distinguished from serum globulin by a number of special reactions;
i. Its coagulation temperature is lower, 55° to 56° C. 2. It is completely
precipitated by saturation with NaCl as well as with MgSO4. 3. It gives
rise to an insoluble proteid, fibrin. It may be, however, that fibrinogen is
not a simple proteid, but a mixture or loose chemical combination of two
or more proteids. Fibrinogen is present in plasma to the extent of 0.2 to
0.5 per cent.
Serum globulin or paraglobulin is similar to fibrinogen in its reactions.
It is completely precipitated by MgSO4; incompletely by NaCl, and co-
agulates at a temperature of 75° C. It is likewise soluble in dilute salt solu-
tions but insoluble in water. It is present in plasma in from 3.5 to 4 per cent.
Serum albumin is the proteid which predominates in human plasma.
It is readily obtained in crystalline form; is soluble in MgSO4 and NaCl
solutions, but insoluble in saturated ammonium sulphate solutions; and
coagulates in neutral or acid solutions at from 73° to 75° C.
Extractives. The extractives are the nitrogen-containing substances
such as urea, uric acid, creatin, creaiinin, etc.; glycogen, dextrose, choles-
THE COMPOSITION OF THE WHITE CORPUSCLES 117
terin, etc., a total of 0.5 to 0.6 per cent. The dextrose content amounts
to from o.i to 0.15 per cent.
Ferments are also found in blood; first, a diastatic ferment converting
amyloids into sugars; second, a glycolytic ferment causing a disappearance
of sugar; third, a fat-splitting ferment, lipase; and fourth, fibrin ferment
(thrombin), or its 'precursor, prothrombin.
Inorganic Substances. The blood plasma contains about 0.8 per cent
of inorganic salts distributed as follows, the sodium chloride predominating:
Parts in 1,000 of plasma.
Chlorine 3-536
Sulphuric acid 1 29
Phosphoric acid 145
Potassium 314
Sodium 3-410
Phosphate of lime 298
Phosphate of magnesia 218
Oxygen 455
The Serum. The serum is the liquid part of the blood or of the
plasma which remains after the fibrin has been formed and removed. It is
a transparent, yellowish, faintly alkaline fluid, with a specific gravity of
from 1025 to 1032. Serum may be obtained from blood-corpuscles by allow-
ing blood to clot in large test tubes, or by subjecting test tubes of whipped
blood to the action of a centrifugal machine for some time. Serum is chemi-
cally very much the same as plasma except that it has lost the fibrinogen in
the process of clotting and has gained the by-products of that process — throm-
bin, thrombokinase, and fibrin-globulin. The salts of serum are practically
those of plasma.
The Composition of the White Corpuscles. The white corpuscles
are comparatively undifferentiated cellular elements, hence possess the chemi-
cal composition of protoplasm. Lillienfeld has made an analysis of the
leucocytes of thymus gland from the calf, which contain 11.49 Per cent of
solids, as follows:
In 100 Parts of Dry Substance of Corpuscles of Calf.
Per cent.
Proteid i . 76
Leuconuclein 68. 78
Histon 8.76
Lecithin 7.51
Fat 4-02
Cholesterin 4.40
Glycogen 0.80
96.03
118 THE BLOOD
The most noteworthy substance in this table is the nucleohiston content,
first isolated by Kossel and Lillienfeld. Beside the substances in the above
table, the white corpuscles contain salts of potassium, sodium, calcium, and
magnesium. The potassium phosphate is present in greatest amount.
The Composition of the Red Corpuscles. Analysis of a thousand
parts of moist blood-corpuscles shows the following result:
Water 688
Solids-
Organic 303.88 )
Mineral 8.12 f 3» = i,ooo
Of the solids the most important is Hemoglobin, the substance to which
the blood owes its color. It constitutes, as will be seen from the appended
table, more than 90 per cent of the organic matter of the corpuscles. Be-
sides hemoglobin the corpuscles contain proteid and fatty matters, the former
chiefly consisting of globulins, and the latter of cholesterin and lecithin.
In 1,000 parts of organic matter are found:
Hemoglobin 905 .4
Proteids 86. 7
Fats 7.9 = 1,000
Of the inorganic salts of the corpuscles, the iron omitted, there are present,
in 1,000 parts of corpuscles (Schmidt):
Potassium chloride 3 . 679
Potassium phosphate 2 . 343
Potassium sulphate 132
Sodium phosphate 633
Calcium phosphate 094
Magnesium phosphate 060
Soda 341 — 7 . 282
Hemoglobin. Of the substances in the erythrocytes, by far the
most important from every point of view is the pigment, hemoglobin. It
composes about 90 per cent of the total solids of the corpuscles; there-
fore, between 14 and 15 per cent of the blood itself. Hemoglobin is the most
complex compound in the body, having a molecule of the enormous molec-
ular weight of 16,669. Hemoglobin is intimately distributed throughout
the stromaof the corpuscle, and when dissolved out it undergoes crystallization.
Its percentage composition is C 53.85; H 7.32; N 16.17; O 21.84;
S 0.63; Fe 0.42. Jacquet gives the empirical formula for the hemoglobin
of the dog, C758H1203N195S3FeO218. The most interesting of the properties
of hemoglobin are its powers of crystallizing and its attraction for oxygen
and other gases.
Hemoglobin Crystals. The hemoglobin (oxyhemoglobin) of the blood of
various animals possesses the power of crystallizing to very different ex-
HEMOGLOBIN
119
tents. In some the formation of crystals is almost spontaneous, whereas
in others it takes place either with great difficulty or not at all. Among
the animals whose blood coloring-matter crystallizes most readily are the
guinea-pig, rat, squirrel, and dog; and in these cases to obtain crystals it
is generally sufficient to dilute a drop of recently drawn blood with water
FIG. 119. — Crystals of Oxyhemoglobin — Prismatic, from Human Blood.
and to expose it for a few minutes to the air. In many instances other means
must be adopted, e.g., the addition of alcohol, ether, or chloroform, rapid
freezing, and then thawing, the application of an electric current, a tempera-
FIG. 120. — Oxyhemoglobin Crystals — Tetrahedral, from Blood of the Guinea-pig.
ture of 60° C., the addition of sodium sulphate, or the addition of decom-
posing serum of another animal.
.The hemoglobin of human blood crystallizes with difficulty, as does also
that of the ox, the pig, the sheep, and the rabbit.
120
THE BLOOD
The forms of hemoglobin crystals, as will be seen from figures 119 and
120, differ greatly. Hemoglobin crystals are soluble in water. Both the
crystals themselves and also their solutions have the characteristic color of
arterial blood.
A dilute solution of oxyhemoglobin gives a characteristic appearance
with the spectroscope. Two absorption bands are seen between the solar
lines D, which is the sodium band in the yellow, and E, see the frontispiece,
one in the yellow, with its middle line some little way to the right of D. This
band is very intense, but narrower than the other, which lies in the green
near to the left of E. Each band is darkest in the middle and fades away
at the sides. As the strength of the solution increases, the bands become
broader and deeper. Both the red and the blue ends of the spectrum be-
come encroached upon until the bands coalesce to form one very broad band
when only a slight amount of the green and part of the red remain unab-
FIG. 121. — Hexagonal Oxyhemoglobin Crystals, from Blood of Squirrel. On these hex-
agonal plates prismatic crystals, grouped in a stellate manner, not unfrequently occur (after Funke) .
sorbed. Any further increase of strength leads to complete absorption of
the spectrum.
If crystals of hemoglobin are exposed to an atmosphere of oxygen they
take up oxygen and form oxyhemoglobin, each gram of the pigment fixing
a definite amount of oxygen, see chapter on Respiration. When subjected
to a mercurial air pump the oxygen is given off, and the crystals become
of a purple color. A solution of the oxyhemoglobin in the blood-corpuscles
may be made to give up oxygen, and to change color in a similar manner.
One gram of oxyhemoglobin liberates 1.59 c.c. oxygen, or according to Hiif-
ner's later determinations, 1.34 c.c.
This change may be also effected by passing through the solution of
blood or of oxyhemoglobin, hydrogen or nitrogen gas, or by the action of
ACTION OF GASES ON HEMOGLOBIN 121
reducing agents, of which Stokes's fluid* or ammonium sulphide are the
most convenient.
With the spectroscope, a solution of deoxidized or reduced hemoglobin
is found to give an entirely different appearance from that of oxidized hemo-
globin. Instead of the two bands at D and E we find a single broader but
fainter band occupying a position midway between the two, and at the same
time less of the blue end of the spectrum is absorbed. Even in strong solu-
tions this latter appearance is found, thereby differing from the strong solu-
tion of oxidized hemoglobin which lets through only the red and orange
rays; accordingly, to the naked eye the one (reduced-hemoglobin solution)
appears purple, the other (oxy hemoglobin solution) red. The deoxidized
crystals or their solutions quickly absorb oxygen on exposure to the air,
becoming scarlet. If solutions of blood be taken instead of solutions of
hemoglobin, results similar to the whole of the foregoing can be obtained.
Venous blood never, except in the last stages of asphyxia, fails to show
the oxyhemoglobin bands, inasmuch as the greater part of the hemoglobin
even in venous blood exists in the more highly oxidized condition.
Action of Gases on Hemoglobin. Carbonic oxide gas passed
through a solution of hemoglobin causes it to assume a cherry-red color and
to present a slightly altered spectrum; two bands are still visible but are
slightly nearer the blue end than those of oxyhemoglobin, see plate I. The
amount of carbonic oxide taken up is equal to the amount of the oxygen
displaced. Although the carbonic-oxide gas readily displaces oxygen, the
reverse is not the case, and upon this property depends the dangerous effect
of coal-gas poisoning. Coal-gas contains much carbonic oxide, and, when
breathed, the gas combines with the hemoglobin of the blood and produces
a compound which cannot easily be reduced. This compound (carboxyhemo-
globin) is not an oxygen-carrier, and death may result from suffocation due
to the want of oxygen, notwithstanding the free entry of pure air into the
lungs. Crystals of carbonic-oxide hemoglobin closely resemble in form those
of oxyhemoglobin.
Nitric oxide produces a similar compound to the carbonic-oxide hemo-
globin, which is even less easily reduced.
Nitrous oxide reduces oxyhemoglobin, and therefore leaves the reduced
hemoglobin in a condition actively to take up oxygen.
Sulphuretted hydrogen, if passed through a solution of oxyhemoglobin,
reduces it and an additional band appears in the red. If the solution be
then shaken with air, the two bands of oxyhemoglobin replace that of re-
duced hemoglobin, but the band in the red persists.
* Stokes's Fluid consists of a solution of ferrous sulphate, to which ammonia has been
added and sufficient tartaric acid to prevent precipitation. Another reducing agent is a
solution of stannous chloride, treated in a way similar to the ferrous sulphate, and a third
reagent of like nature is an aqueous solution of yellow ammonium sulphide, NH4HS.
THE BLOOD
Methemoglobin. If an aqueous solution of oxyhemogJobin is ex-
posed to the air for some time, its spectrum undergoes a change; the two
d and e bands become faint, and a new line in the red at c is developed. The
solution, too, becomes brown and acid in reaction, and is precipitable by basic
lead acetate. This change is due to the decomposition of oxyhemoglobin,
and to the production of methemoglobin. On adding ammonium sulphide,
reduced hemoglobin is produced, and on shaking this up with air, oxyhemo-
globin is again produced. Methemoglobin is probably a stage in the deoxida-
tion of oxyhemoglobin. It appears to contain less oxygen than oxyhemo-
tio. 122. — rleischl's Hemoglobinometer.
globin, but more than reduced hemoglobin. Its oxygen is in more stable
combination, however, than is the case with the former compound.
Estimation of Hemoglobin. The most exact method is by the esti-
mation of the amount of iron (dry hemoglobin containing 0.42 per cent
of iron) in a given specimen of blood, but as this is a somewhat complicated
process, various methods have been proposed which, though not so exact,
have the advantage of simplicity. Of the several varieties of hemoglobinom-
eter, one of the best adapted to its purpose is that invented by Professor
Fleischl, of Vienna. In this instrument the amount of hemoglobin in a
solution of blood is estimated by comparing a stratum of diluted blood with
a standard solid substance of uniform tint similar spectroscopically to diluted
blood. The Fleischl instrument has been recently modified and made more
accurate by Miescher. The Fleischl-Miescher apparatus consists of a
stand with a metal plate having a circular opening and a plaster mirror below,
S, figure 122, which casts light through the opening. Beneath the plate is a
metal framework containing a colored glass wedge, and along the side of
ESTIMATION OF HEMOGLOBIN 123
the same is a scale graduated so as to indicate the percentage of hemoglobin
corresponding to the shades of the different parts of the wedge. This frame-
work can be moved by the wheel T which fits into a rack on its lower surface.
The scale can be read through a small opening M in the plate. Into the
large circular opening of the plate fits a cylindrical metal cell G with a glass
bottom and divided by a metal partition into two equal parts. One of these
halves lies over the wedge and is filled with distilled water. The other con-
tains the solution of blood in which the hemoglobin is to be estimated. The
apparatus is usually supplied with three cells. Of these, the first two are
used in estimating the hemoglobin according to Miescher's modification
of FleischPs original method. This is the method now generally used.
These cells are furnished with a glass cover having a groove which fits
upon the partition of the cell. Over this cover is placed a diaphragm
with a longitudinal slit, which only permits of the central part of each
side of the cell being seen. The third cell is for use when the original
Fleischl method is employed.
The patient's ear or finger is pricked, and the blood from the wound
sucked up into the graduated pipet until it reaches the mark £, §, or |, a
one per cent solution of sodium carbonate is then sucked in until the upper
mark is reached. The pipet is then well shaken in order to mix the blood
thoroughly. One-half of each of the two cells, which are respectively 12
and 15 millimeters high, are then filled with the mixture, the other half
being filled with water. An important point is that the liquids should com-
pletely fill the cells. The cover-glasses and diaphragms are then applied
and the cells are ready for examination. This must be done by artificial
light. Moreover, in order to have accurate results, light of the same inten-
sity should be always used. One of the cells is placed on the plate and the
wheel T turned until the colors of the two halves exactly correspond. When
this point is reached, the result is read off on the scale through the opening M.
This should be repeated several times with each of the cells, and the average
of the readings taken. The result obtained with the 12-millimeter cell
should be multiplied by J to bring it up to that of the larger. For example,
suppose the result of several readings to be:
With the large cell (15 mm.) 54-°°
With the small cell (12 mm.) 42.00
If the readings obtained with the large cell are exactly correct, then the read-
ings with the smaller one should be 43.2, since 54 X £=43.2. Or, if the
readings with the smaller cells are exact, the readings with the larger should
be 52.5, since 42X1=52.5. Hence the mean of 54 and 52.5, namely 53.25,
should be taken as the correct figure. On looking at the corrected table of
hemoglobin values supplied with each instrument, we would find that this
number on the scale corresponds to a solution containing 400 milligrams
124 THE BLOOD
of hemoglobin per 1,000 cubic centimeters of solution. But our original
dilution was either i : 200, i : 300, or i : 400, according as our pipet had been
filled with blood up to the mark ^, §, or ^; so that in order to obtain the actual
percentage of hemoglobin in the blood under examination we should be
obliged to multiply our result by 200, 300, or 400. In the example we have
taken, the amount of hemoglobin would be, if our dilution was i : 200, 400 X
200=80,000 milligrams = 80 grams in 1,000 cubic centi meters — 8 grams
in 100 cubic centimeters, or 8 per cent.
Another very simple method of approximately determining the hemo-
globin percentage is the hemoglobin scale devised by T. W. Talquist. This
consists of a series of shades of color corresponding to undiluted blood of
various hemoglobin values, ranging from ten to one hundred per cent of an
arbitrary scale. This scale is included in a book, the remaining pages of
which consist of filter paper, which is used for absorbing the specimen of
blood whose hemoglobin percentage is to be estimated. The blood-stained
filter paper is compared with the hemoglobin scale by direct daylight until
a shade is found with which it corresponds. For approximate results this
method has proved very satisfactory.
Derivatives of Hemoglobin. Hematin. By the action of heat cr
of acids or alkalies in the presence of oxygen, hemoglobin can be split up
into a substance called Hemaiin, which contains all the iron of the hemo-
globin from which it was derived, and a proteid residue. Of the latter it is
impossible to say more than that it probably consists of one or more bodies
of the globulin class. If there be no oxygen present, instead of hematin a
body called hemochr onto gen is produced, which, however, will speedily under-
go oxidation into hematin.
Hematin is a dark brownish or black non-crystallizable substance of
metallic luster. Its percentage composition is C, 64.30; H, 5.50; N, 9.06;
Fe, 8.82; O, 12.32; which gives the formula C^HyoNgFeaO^ (Hoppe-
Seyler). It is insoluble in water, alcohol, and ether; soluble in the caustic
alkalies; soluble with difficulty in hot alcohol to which is added sulphuric
acid. The iron may be removed from hematin by heating it with fuming
hydrochloric acid to 160° C., and a new body, hematoporphyrin, the so-called
iron-free hematin, is produced. Hematoporphyrin (C^^NgO^, Hoppe-
Seyler) may also be obtained by adding blood to strong sulphuric acid, and
if necessary filtering the fluid through asbestos. It forms a fine crimson
solution, which has a distinct spectrum, viz., a dark band just beyond D,
and a second all but midway between D and E. It may be precipitated from
its acid solution by adding water or by neutralization, and when redissolved
in alkalies presents four bands, a pale band between C and D, a second
between D and E, nearer D, another nearer E, and a fourth occupying the
chief part of the space between b and F.
Hematin in Acid Solution. If an excess of acetic acid is added to
DERIVATIVES OF HEMOGLOBIN 125
blood, and the solution boiled, the color alters to brown from decomposition
of hemoglobin and the setting free of hematin; by shaking this solution
with ether, a solution of hematin in acid solution is obtained. The spectrum
•of the ethereal solution shows no less than four absorption bands, viz., one
in the red between C and D, one faint and narrow close to D, and then two
broader bands, one between D and E, and another nearly midway between
b and F. The first band is by far the most distinct, and the acid aqueous
solution of hematin shows it plainly.
Hematin in Alkaline Solution. If a caustic alkali is added to blood and
the solution is boiled, alkaline hematin is produced, and the solution becomes
clive green in cclor. The absorption band of the new compound is in the
red, near to D, and the blue end of the spectrum is absorbed to a considerable
extent. If a reducing agent be added, two bands resembling those of oxy-
FIG. 123. — Hematoidin Crystals. (Frey.) FIG. 1233.. — Hemin Crystals. (Frey.)
hemoglobin, but nearer to the blue, appear; this is the spectrum of reduced
hematin, or hemochromogen. On violently shaking the reduced hematin
with air or oxygen the two bands are replaced by the single band of alkaline
hematin.
Hematoidin. This substance is found in the form of yellowish crystals,
figure 123, in old blood extravasations and is derived from the hemoglobin.
Their crystalline form and the reaction they give with fuming nitric acid
seem to show them to be closely allied to Bilirubin, the chief coloring matter
of the bile, and in composition they are probably either identical or isomeric
with it.
Hemin. One of the most important derivatives of hematin is hemin.
It is usually called Hydrochloride of Hematin, but its exact chemical com-
position is uncertain. Its formula is said to be C32H30N4FeO3HCl, and it
contains 5.18 per cent of chlorine, but by some it is looked upon as simply
crystallized hematin. Although difficult to obtain in bulk, a specimen may
be easily made for the microscope in the following way: — A small drop of
dried blood is finely powdered with a few crystals of common salt on a glass
slide and spread out; a cover-glass is then placed upon it, and glacial acetic
acid added by means of a capillary pipet. The blood at once turns a brownish
color. The slide is then heated, and the acid mixture evaporated to dryness
126 THE BLOOD
at a high temperature. The excess of salt is washed away with water from
the dried residue, and the specimen may then be dried and mounted. A
large number of small, dark, reddish black crystals of a rhombic shape,
sometimes arranged in bundles, will be seen if the slide be subjected to micro-
scopic examination, figure 1233,.
The formation of these hemin crystals is of great interest and importance
from a medico-legal point cf view, as it constitutes the most certain and
delicate test we have for the presence of blood (not of necessity the blood
of man) in a stain on clothes, etc. It exceeds in delicacy even the spectro-
scopic test. Compounds similar in composition to hemin, but containing
hydrobromic or hydriodic acid, instead of hydrochloric, may be also readily
obtained.
Variations in the Composition of Healthy Blood. The conditions
which appear most to influence the composition of the blood in health are
these : Diet, Exercise, Sex, Pregnancy, and Age.
Sex. The blood of men differs from that cf women, chiefly in being of
somewhat higher specific gravity, from its containing a relatively larger
quantity of red corpuscles.
Pregnancy. The blood cf pregnant women has rather lower than the
average specific gravity. The quantity of the colorless corpuscles is increased
in the later months, especially in primiparae; it is also claimed that the
fibrin is increased in amount.
Age. The blood of the fetus is very rich in solid matter, and especially
in colored corpuscles; and this condition, gradually diminishing, continues
for some weeks after birth. The quantity of solid matter then falls during
childhood below the average, rises during adult life, and in old age falls again.
Diet. Such differences in the composition of the blood as are due to the
temporary presence of various matters absorbed with the food and drink,
as well as the more lasting changes which must result from generous or poor
diet respectively, need be here only referred to.
Effects oj Bleeding. The result of bleeding is to diminish the specific
gravity of the blood, and so quickly that in a single venesection the portion
of blood last drawn has often a less specific gravity than that of the blood that
flowed first. This is, of course, due to absorption of fluid from the tissues
of the body. The physiological import of this fact, namely, the instant
absorption of liquid from the tissues, is the same as that of the intense thirst
which is so common after either loss of blood, or the abstraction from it of
watery fluid, as in cholera, diabetes, and the like.
For some little time after bleeding, the want of colored corpuscles is well
marked, but with this exception: no considerable alteration seems to be
produced in the composition of the blood for more than a very short time;
the loss of the other constituents, including the colorless corpuscles, being
very quickly repaired.
VARIATIONS IN THE COMPOSITION OF HEALTHY BLOOD 127
Variations in Different Parts of the Body. The composition of the blood,
as might be expected, is found to vary in different parts of the body. Thus
arterial blood differs from venous; and although its composition and general
characters are uniform throughout the whole course of the systemic arteries,
they are not so throughout the venous system, the blood contained in some
veins differing markedly from that in others.
Differences between Arterial and Venous Blood. The differences between
arterial and venous blood are these:
Arterial blood is bright red, from the fact that almost all its hemoglobin
is combined with oxygen, oxyhemoglobin, while the purple tint of venous
blood is due to the deoxidation of a certain quantity of its oxyhemoglobin,
and its consequent reduction to the purple variety (deoxidized, or purple
hemoglobin).
Arterial blood coagulates somewhat more quickly.
Arterial blood contains more oxygen than venous, and less carbonic
acid.
Some of the veins contain blood which differs from the ordinary standard
considerably. These are the Portal, the Hepatic, and the Splenic veins.
Portal Blood. The blood which the portal vein conveys to the liver is
supplied from two chief sources; namely, from the gastric and mesenteric
veins, which contain the soluble elements of food absorbed from the stomach
and intestines during digestion, and from the splenic vein. It must, there-
fore, combine the qualities of the blood from each of these sources.
The blood in the gastric and mesenteric veins will vary much according
to the stage of digestion and the nature of the food taken, and can therefore
be seldom exactly the same. Speaking generally, and without considering
the sugar and other soluble matters which may have been absorbed from
the alimentary canal, this blood appears to be deficient in solid matters,
especially in colored corpuscles, owing to dilution by the quantity of water
absorbed, to contain an excess of proteid matter, and to yield a less tenacious
kind of fibrin than that of blood generally.
The blood of the portal vein, combining the peculiarities of its two factors,
the splenic and mesenteric venous blood, is usually of lower specific gravity
than blood generally, is more watery, contains fewer colored corpuscles,
more proteids, and yields a less firm clot than that yielded by other blood,
owing to the deficient tenacity of its fibrin.
Guarding (by ligature of the portal vein) against the possibility of an
error in the analysis from regurgitation of hepatic blood into the portal vein,
recent observers have determined that hepatic venous blood contains less
water, proteids, and salts than the blood of the portal veins ; but that it yields
a much larger amount of extractive matter, in which is one constant element,
namely, grape-sugar, which is found, whether saccharine or farinaceous
matter has been present in the food or not.
128 THE BLOOD
GLOBULOCIDAL AND OTHER PROPERTIES OF SERUM.
Cytolysis. It has been known for some time that the sera of certain
animals when injected into the circulation of animals of another species will
cause destructive changes in the blood-corpuscles, accompanied by symptoms
of poisoning, which may even end fatally. These results served to bring into
disrepute the use of foreign blood in transfusion, which has consequently
been practically abandoned. This discharge of the hemoglobin of the red
blood-corpuscles and solution in the plasma (laking) is now included in the
general term Cytolysis, and more specifically known as Hemolysis. Agents
which produce such an effect are known as hemolytic or hemotoxic agents.
Sera of one species are not hemolytic for blood of all other species, but the
serum of one animal may be made to acquire such properties for the blood
of another.
This adaptation is brought about in the following way: For instance,
the blood of the guinea-pig, which is not normally lytic for the red cells of the
rabbit, may be adapted to the latter by previously, at several successive
intervals (three to seven days) injecting into the abdominal cavity or sub-
cutaneous tissues of the guinea-pig small quantities of rabbit's blood. If
now a small quantity of serum be obtained from the guinea-pig by the usual
methods and mixed in a test tube with some of the rabbit's blood diluted
with physiological salt solution, hemolysis occurs. That is, the coloring
matter of the rabbit's red blood-cells goes into solution and the cells appear
under the microscope as shadow corpuscles or ghosts, devoid of hemoglobin.
Such an artificially produced hemolytic serum is only lytic for the blood of
the animal species for which it has been adapted. It is true that it may also
show slightly lytic properties for closely allied species. It has therefore been
suggested as a possible valuable aid in determining relationships of various
animal species.
Concerning the nature of the lytic substance, it has been found that it
probably consists of two bodies acting conjointly, for if the serum be heated
to 56° C. for a short time, its lytic powers are lost, but may be restored by
adding a little serum of another animal of the same species which has not
been adapted, and whose serum is consequently not in itself lytic. Of these
two bodies, therefore, one is stable and is formed only in the adapted serum,
while the other is more unstable or labile (destroyed at 56° C.) and exists
normally iri the blood plasma. The former is known as the immune body
and the latter as alexin. Lysis occurs only when both are present at the same
time, and not through the agency of one or the other singly.
This cytolytic adaptation has been extended to include other cells besides
the red blood-corpuscles. Thus in a similar manner leucolytic, hepatolytic,
nephrolytic, and a number of other lytic sera have been developed.
It is further possible, under certain circumstances, that substances may
AGGLUTINATIVE SUBSTANCES
120
be developed in the tissues which are lytic for other .tissue cells of the same
animal, autolytic substances. This may be an important physiological process
in the elimination of worn-out tissue cells, cellular elements in injury, in-
flammation, etc.
Agglutinative Substances. A further property of adapted sera is
that of agglutination. The adaptation is secured in the same way as in
the production of cytolysins. In fact, both cytolysis and agglutination may
occur at the same time. The normal blood serum of some animals may
be agglutinative for the blood-cells of some other species. In normal serum,
agglutinative and cytolytic properties may be present together or one only
may be normally present.
The activity of agglutinative substances is not destroyed at a tempera-
ture of 56° C. They do become inert, however, at 70° C., and, furthermore,
they cannot be restored by adding normal serum, as is the case with cytolysins.
Precipitins. Other forms of adaptive substances which may be
found in animal serum are these which, when mixed with the substances
by means of which adaptation has been secured, form a precipitate. By
this means blood of different species cf animals may be detected even when
in a dried state. It has been suggested as a possible valuable aid in medico-
legal cases, since human blood in a dilution of i to 50,000 has been recognized
by this means.
Physical Factors. Diffusion, Osmosis, Dialysis. The term diffusionhzs long been
applied to the regular mixing cf the molecules of two gases when brought into contact
in a confined space, this interpenetration being due to the to-and-fro movements of their
molecules. More recently it has been applied to the mixing of the molecules of two
solutions when brought into contact, as it has been found that
they act in the same way and obey the same laws as gases. If,
however, the two solutions are separated by a membrane, perme-
able to the solutions, diffusion will still occur. To this form of
diffusion the term Osmosis has been applied in the case of water,
and Dialysis in the case of diffusible substances. All bodies can
be divided into two groups, crystalloids and colloids. To the for-
mer group belong bodies having a crystalline form, which readily
go into solution in water. All such bodies are diffusible (dialyz-
-T
FIG. 124.
FIG. 125.
130 THE BLOOD
able), their power of dialysis, however, varying considerably. To the second group belong
such bodies as have no crystalline form (amorphous). These are generally bodies with a
large molecule, which form colloidal suspensions in water, and are only slightly or not at all
diffusible. An exception to this second group is hemoglobin, which has a very large mole-
cule but is crystalline and is diffusible. The following may serve as simple illustrations:
Take a jar and divide it in two equal parts by an animal membrane, M, figure 143,
and place an equal amount of distilled water in the two sides, A and B. Now, since
the molecules of water act like those of a gas, and are continually moving to and fro,
bombarding all the surfaces of their retainer, the molecules of water in A and B will be
continually striking all the surfaces of A and B ; but since the membrane is permeable
to the water molecules, there will be a continual interchange of molecules between A and
B. If now, in one side A we place a solution of sodium chloride, still keeping water
in B, the membrane being permeable to the sodium chloride, the first thing we should
notice would be an increase in the amount of water in A . Formerly it would have been
said that " the salt had attracted the water." Now we should say that the salt had a cer-
tain osmotic pressure. The salt, however, being able to pass (dialyze) through the mem-
brane, will do so, and this will continue until the strength of the two salt solutions, and
therefore the osmotic pressure on both sides, is equal.
Osmotic Pressure. If now in A we place a solution of some soluble colloidal sub-
stance to which the membrane is impermeable, or else replace the membrane, M, we
used in our former experiment by one which is not permeable to the sodium chloride, and
arrange our jar as in figure 1 25, so as to be able to read off any increase of water which may
pass into .4, we will notice that the amount of liquid in A will continue to increase up to a
certain point. Once that point is reached, there will be no further change, since the sub-
stance in solution, in A , cannot pass through the membrane as in the previous example.
This pressure can be measured and expressed in millimeters of mercury. It is constant for
all solutions of this substance that are of the same concentration when measured under like
conditions of temperature and pressure, and is called the Osmotic pressure of this solution.
Of the numerous explanations regarding the nature of osmotic pressure which have
been more or less satisfactory, a simple one, and one that can be easily understood, is as
follows: In figure 125 one surface of the membrane is being bombarded by the molecules
of a non-diffusible substance mixed with those of a diffusible one (water) ; while the other
surface is being bombarded entirely by water molecules. The former condition per-
mits less water to diffuse out, since fewer molecules get to the surface of the membrane;
while the latter permits all of the molecules which reach it to pass through.
Osmotic pressure can be estimated in several different ways in addition to the above,
viz., the determination of the freezing point of the solution, determination of the boiling
point, determination of the electrical conductivity. The results obtained with the various
methods agree very closely. The following solutions have the same osmotic pressure:
Sodium chloride, 0.64 per cent; potassium nitrate, 1.09 per cent; sugar 5.5 per cent.
Isotonic Solutions. Solutions that have the same osmotic pressure are called iso-
tonic. The term isotonic is a relative one, implying a comparison with some other solu-
tion taken as a standard. In physiology it has been customary to take blood-plasma
as a standard. A solution of 0.64 per cent sodium chloride is isotonic for the blood -plasma
of the frog, and a 0.9 per cent solution for that of man. Further, any solution which is
of a lower osmotic pressure than the standard solution is said to be hypoisotonic (hypotonic)
in relation to that solution. A solution of a higher osmotic pressure is said to be hyper-
isotomc (hypertonic).
Water passes in the Direction of the Arrows.
Hypertonic saline solution (2 per cent)
I
Blood -plasma
ft
Isotonic saline solution (0.64 per cent)
I
Hypotonic saline solution (0.3 per cent)
THE CHARACTER AND COMPOSITION OF LYMPH 131
If a hypotonic solution be mixed with blood, water from the hypotonic solution passes
through the cell membrane of the red corpuscles into the stroma, and causes it to swell.
The hemoglobin at the same time passes out and goes into solution in the diluted plasma.
On the other hand, the addition of a hypertonic solution to the plasma causes the red cor-
puscles to lose their water and become crenated. The principles of osmosis have been
derived from the action of substances separated by dead animal or plant membranes. It
must be, however, remembered that in the application of these principles to processes
occurring in the living organism, the cells, forming the various membranes, are an im-
portant modifying factor. It is probable that physico-chemical processes, occurring in
the protoplasm the cell, may change its permeability to the same substance at different
THE CHARACTER AND COMPOSITION OF LYMPH.
The lymph is the fluid which immediately surrounds the tissue cells of
the living body. It fills up the spaces between the cells themselves and
between the cells and the blood-vessels which ramify among the cell-masses.
The lymph, therefore, is an intermediate fluid between blood-plasma on the
one hand, and the tissue cells on the other, receiving its ingredients by the
passage of fluid from the plasma through the walls of the finer blood-vessels
in the one direction, and by the discharge of the substances from the cells
themselves in the other.
The Chemical Composition of the Lymph. Since the chief source
of the lymph is the blood-plasma, one would naturally expect that its chemical
composition would be very similar to that of plasma, which is in fact the case.
The variations that are noted in lymph taken from definite sources no doubt
have their origin in the fact that the lymph passes through these organs slowly,
and that ingredients peculiar to the necessities of the function and growth
of the differentiated tissue of the organ are taken from the lymph in special
organs. Lymph obtained from a human lymphatic fistula has been analyzed;
the figures from Hammarsten are as follows, though considerable variations
appear in the analyses from other authorities:
ANALYSIS OF LYMPH.
Per cent
Water .• 94.5 to 96.5
Solids 3.7 to 5.5
Albumins 3.4 to 4.1
Ethereal extract 0.06 to 0.13
Sugar o.i
Salts 0.8 to 0.9
Sodium chloride '. 0.55 to 0.58
Sodium carbonate 0.24
Disodic phosphate 0.028
The most notable fact to be derived from this composition table is the
low percentage of proteids present in the lymph.
The Formation of Lymph. The manner in which the substances
in the lymph pass through the walls of the capillaries from the plasma is a
132 THE BLOOD
question which has been surrounded with considerable difficulty. It is
thought by Ludwig and many of his followers that the process involved
is merely one of nitration. Certainly the blood pressure in the capillaries
is in the main greater than that of the pressure of the lymph in the surround-
ing tissues, and this positive pressure will contribute so much to the direct
ingredients of the blood-plasma through the capillary walls. It is true, as a
matter of experiment, that anything which contributes to an increase in the
capillary pressure is very apt to produce an edema of the corresponding
tissues. Since the colloidal materials represented by the proteid are non-
diffusible, one would by this theory expect to find a diminished percentage
in the lymph, which is true, though not to the extent which the theory demands.
Heidenhain was the first to question the adequacy of the blood
pressure and filtration hypothesis. He showed that many of the conditions
under which lymph formation takes place are not sufficient to produce filtra-
tions of the material found. He advanced the hypothesis that the living
endothelial lining of the blood-vessels exerted a secretory activity in lymph
production. He discovered that various substances known as lymphagogues
when introduced into the circulatory system produce a remarkable increase
in the flow of lymph from the thoracic duct. Further, he noticed that the
concentration of the lymph was changed, i.e., increased. It has been sug-
gested that these substances act to change the normal resistance of the endo-
thelial cells, and this has been offered as a criticism. Nevertheless many
drugs act to increase the flow of lymph in a way which cannot be presumed
to be other than normal, i.e., they stimulate the physiological processes going
on in the endothelial cells. Such observations contribute strongly to the
view advanced by Heidenhain. Many investigations have been brought to
the support of the hypothesis that lymph formation is largely a process of
secretion, yet it seems at the present time that we cannot wholly deny that
filtration and osmosis play a part in the processes. Certainly the permea-
bility or activity of the endothelial lining of the blood-vessels varies greatly
at different times in the life of an individual, and this variation in function is
associated with the marked change in the character and quantity of lymph
produced.
The second factor in lymph formation, the activity of the tissue in taking
up or discharging materials into the lymph-mass, must not be ignored alto-
gether.
LABORATORY EXPERIMENTS FOR THE EXAMINATION OF
THE BLOOD.
i. Microscopical Examination of the Blood. Mount a drop of frog's
blood in 0.7 per cent sodium chloride and examine with the low power of a
compound microscope. The red corpuscles will appear as oval nucleated
iCTION OF FLUIDS ON THE BED CORPUSCLES 133
discs with a faint yellowish color, figure no. Here and there white granular
cells of irregular outline will be noted, the white corpuscles. Examine the
drop of blood with a high magnifying power and sketch the outline of the
blood cells. Select the white corpuscle which is most irregular in outline
and make a series of outline drawings once every minute to show its ame-
boid movements, figure 117.
Draw a drop of your own blood by puncturing the tip of the finger, under
sterile conditions, and mount in a drop of 0.9 per cent physiological saline.
Examine with a high power, note the small biconcave red corpuscles which
appear faintly yellow in color and even adhere in rouleaux, figure 109. The
white corpuscles will appear as somewhat larger granular discs differing in
form and size. By mounting a drop of blood on a warm stage the ameboid
movements of the white corpuscles can be observed with comparative ease.
2. Action of Fluids on the Red Corpuscles. Water. When water is
added gradually to frog's blood, the oval disc-shaped corpuscles become
spherical and gradually discharge their hemoglobin, a pale, transparent
stroma being left behind. Human red blood cells change from a discoidal
o
FIG. 126. FIG. 127. FIG. 128. FIG. 129.
FIG. 126. — Effect of Hypertonic Salt-Solution on the Red Blood-Corpuscles of Man.
FIG. 127. — Effect of Acetic Acid. FIG. 128. — Effect of Tannin. FIG. 129. — Effect of Boric Acid.
to a spheroidal form and discharge their cell-contents, becoming quite trans-
parent and all but invisible (ghost corpuscles).
Hypertonic Salt-Solutions. Mount a drop of human blood in 2 per cent
sodium-chloride solution. The red blood cells lose their disc shape and be-
come sp*herical with spinous projections or crenations, figure 126.
The original form of the red blood cells can be restored by transferring
them to isotonic salt-solution.
Dilute Acetic Acid. This reagent causes the nucleus of the red blood
cells in the frog to become more clearly defined; if the action is prolonged,
the nucleus becomes strongly granulated, and all the coloring matter seems
to be concentrated in it, the surrounding cell-substance and outline of the
cell becoming almost invisible; after a time the cells lose their color altogether.
The cells in figure 127 represent the successive stages of the change. A
similar loss of color occurs in the red cells of human blood, which, from the
absence of nuclei, seem to disappear entirely.
Alkalies. Alkalies cause the red blood-corpuscles to absorb water and
finally to disintegrate,
134 THE BLOOD
Chloroform and Ether. These reagents when added to the red blood
cells of the frog cause them to part with their hemoglobin; the stroma of the
cells becomes gradually broken up. A similar effect is produced on the human
red blood cell.
Tannin and Boric Acid. When a 2 per cent fresh solution of tannic acid
is applied to frog's blood it causes the appearance of a sharply denned little
knob, projecting from the free surface (Roberts' macula). The coloring
matter becomes at the same time concentrated in the nucleus, which grows
more distinct, figure 128. A somewhat similar effect is produced on the
human red blood-corpuscle.
A 2 per cent solution of boric acid applied to nucleated red blood cells
of the frog will cause the concentration of all the coloring matter in the nucleus;
the colored body thus formed gradually quits its central position, and comes
to be partly, sometimes entirely, protruded from the surface of the now
colorless cell, figure 129. The result of this experiment led Briicke to dis-
tinguish the colored contents of the cell (zooid) from its colorless stroma
(ecoid). When applied to the non-nucleated mammalian corpuscle its effect
merely resembles that of other dilute acids.
3. Phagocytosis in White Corpuscles. Mix some very fine pigment
granules, powdered vermilion, or charcoal with a few drops of frog's blood,
let stand for 10 or 20 minutes, then mount a drop on the glass slide and ex-
amine under a high-magnifying microscope. In a favorable field here and
there will be found some white corpuscles which have taken up the pigment.
Colored corpuscles have been observed with fragments of pigment embedded
in their substance. White corpuscles have also been seen in diseased states
of the body to contain micro-organisms, for example, bacilli, and are said to have
the power of destroying these organisms, which gives them the name phagocytes.
4. Enumeration of the Blood-Corpuscles. Several methods are
employed for counting the blood-corpuscles, most of them depending upon
FIG. 130. — Thoma-Zeiss Hemacytometer, glass slide.
the same principle, i.e., the dilution of a minute volume of blood with a
given volume of a colorless solution similar in specific gravity to blood-plasma,
so that the size and shape of the corpuscles are altered as little as possible.
A minute quantity of the well-mixed solution is then taken, examined under
the microscope, either in a flattened capillary tube (Malassez) or in a cell
(Hayem and Nachet, Gowers) of known capacity, and the number of corpus-
cles in a measured length of the tube, or in a given area of the cell, is counted.
The length of the tube and the area of the cell are ascertained by means of
a micrometer scale in the microscope ocular; or in the case of Gowers' modi-
THE PERCENTAGE OF CORPUSCLES AND PLASMA
135
fication, by the division of the cell area into squares of known size. Having
ascertained the number of corpuscles in the diluted blood, it is easy to find
out the number in a given volume of normal blood.
The hemacytometer, which is most used at the present time, is known as
the Thoma-Zeiss hemacytometer. It consists of a carefully graduated
pipet, in which the dilution of the blood is done; this
is so formed that the capillary stem has a capacity
equalling one-hundredth of the bulb above it. If the
blood is drawn up in the capillary tube to the line marked
i, figure 131, the saline solution may afterward be
drawn up the stem to the line 101; in this way we have
101 parts of which the blood forms i. As the content
of the stem can be displaced unmixed we shall have in
the mixture the proper dilution. The blood and the
saline solution are well mixed by shaking the pipet, in
the bulb of which is contained a small glass bead for
the purpose of aiding the mixing. The other part of
the instrument consists of a glass slide, figure 130, upon
which is mounted a covered disc, m, accurately ruled
so as to present one square millimeter divided into 400
squares of one-twentieth of a millimeter each. The
micrometer thus made is surrounded by another annu-
lar cell, c, which has such a height as to make the cell
project exactly one-tenth millimeter beyond m. If a
drop of the diluted blood be placed upon w, and c be
covered with a perfectly flat cover-glass, the volume of
the diluted blood above each of the squares of the mi-
crometer, i.e., above each 4^-0", will be 4-0 ~o of a cubic
millimeter. An average of ten or more squares is then taken, and this num-
ber multiplied by 4000 X 100 gives the number of corpuscles in a cubic
millimeter of undiluted blood. A separate pipet is used for making dilu-
tions for counts of leucocytes. In this, the dilution is made of one part of
blood and ten parts of diluting fluid. Acetic acid, 0.2 of one per cent, is
usually employed for this purpose.
5. The Percentage of Corpuscles and Plasma in Human Blood.
Fill the two graduated capillary tubes of a hematocrite with blood drawn
from the tip of your own finger, insert into the instrument, and centrifuge as
rapidly as possible. The experiment must be performed within the time
limit of clotting in order to be successful. The corpuscles will be thrown
down and the percentage of plasma and corpuscles can be read off directly.
Should one fail to fill the tube exactly full, then the percentage of plasma and
corpuscles can be calculated from the proportion which each bears to the
quantity in the tube,
FIG. 131. — Thoma-
Zeiss Hemacytometer,
pipet.
136 THE BLOOD
6. Estimation of the Percentage of Hemoglobin. The per cent of
hemoglobin in a sample of blood can be obtained by the instrument known
as Fleischl's hemometer, see figure 122. The principle of this instrument
rests on a comparison of the color of the sample of dilute blood with a stand-
ard glass wedge of uniform tint similar to that of blood. Fill one of the
chambers in the cells of the instrument half full with a 2 per cent solution of
sodium carbonate. Now draw a drop of blood from the tip of a finger.
Touch the drop with the end of the standardized capillary tube, using care
to fill it accurately. Quickly wash this sample of blood out in the carbonate
solution in the cell and finish filling the cell. Put distilled water in the other
half of the cell, mount in the instrument, and examine in a dark room, using
candle-light. The glass wedge is graduated in percentage which can be
read off directly. This instrument is usually provided with several cells, in
which case as many samples may be taken and the average of the readings
used to determine the percentage.
Perhaps a more convenient and certainly a quicker method for deter-
mining the percentage of hemoglobin is Talquist's hemoglobinometer. By
this method a drop of blood is drawn directly on to absorbent paper furnished
with the instrument, and the resulting stain is compared directly with a paper
color scale which is graduated in percentage. In this method the comparison
is made in ordinary daylight, and because of its rapidity it is very convenient
for clinical examinations.
7. Reaction of Blood-Plasma. Wet a piece of neutral litmus
paper (some prefer glazed paper), then touch one end of the strip with a
drop of blood drawn from your finger under sterile conditions. After a few
moments wash off the excess of corpuscles in neutral distilled water. The
deeper blue at the point of contact with the blood indicates alkalinity.
8. The Specific Gravity of Blood. From standard mixtures of
chloroform and benzol with specific gravity of 1.050, 1.060, and 1.070 make
up a set of specific-gravity solutions of 1.050, 1.052, 1.054, etc., to 1.070.
These standards may be kept in stoppered 4-dram vials, or in test tubes.
The specific gravity of blood is determined by inserting with a pipet
a drop of freshly drawn blood into the middle of one of the solutions, say
1.056. Since the blood does not mix with the chloroform and benzol the
drop will rise or sink according to its relative specific gravity. By a few
trials one may quickly find a specific gravity in which the drop of blood
floats without rising or sinking. This represents the specific gravity of the
drop of blood.
This method permits rapid clinical application and has proven of con-
siderable interest in the hands of clinists.
9. The Isotonicity of Blood. The absorption or loss of water
by the corpuscles of blood in solutions of other concentrations than that of
blood-plasma can be used as a means of determining the isotonicity of blood.
COAGULATION OF BLOOD
137
Make up a series of solutions of sodium chloride, varying by tenths, from
0.5 to 1.2 per cent. Prepare a series of slides with vaseline rings and mount
drops of human blood in drops of saline of 0.6, 0.7, 0.8, 0.9, i, and i.i per
cent, examine every ten minutes under a high-power microscope. The
corpuscles of some of the slides will swell up and may disintegrate, others
will show crenation as in figure 126. In the isotonic solutions the corpus-
cles will appear of their normal size and condition.
10. Coagulation of Blood, a. Normal Clot. Anesthetize a dog,
insert a cannula into the carotid or femoral artery, and draw samples of
blood into two or three clean, dry test tubes. Draw one sample into a test
cube that has had its sides oiled. Note the exact time at which the blood
was drawn into the test tubes and set the test tubes in a test-tube rack. Ex-
amine at intervals of 30 seconds by gently inclining the test tubes. Presently
FlG. 132. — Miscroscopic View of Clot Showing Fibrin Network.
it will be noted that the blood becomes more viscous and does not flow freely
up the sides of the test tubes. Later the whole mass will become jelly-like
and will retain the form of the test tube. Note the time of the first slight
change, and also when the clot becomes more perfect. The sample in the
oiled test tube will be found to clot more slowly.
If the test tubes of clotted blood are left standing for a day, the coagulum
will become similar in size and a transparent yellowish blood will make its
appearance on the surface or between the sides of the clot and the test-tube
wall. This fluid is the serum and it is squeezed out by the shrinking of the
fibrin which holds the corpuscles in its meshes.
b. Microscopic Examination of the Process oj Clotting. Take a drop of
138 THE BLOOD
fresh blood from the tip of your finger under sterile conditions and mount
on a microscopic slide in a few drops of salt-solution, and examine immediately
under the high power. Small threads of fibrin will presently be seen to
form across the field, usually being most clearly obvious where fragments
of white corpuscles are noted, see figures 107 and 132. The threads of
fibrin become more apparent when stained with rosanilin.
c. Whipped Blood. Draw a sample of blood into a glass tumbler,
enough to fill it one-half or two-thirds full. Immediately begin vigorously
stirring the blood with a bunch of stiff wires or a pencil, and keep it up until
the time of clotting has passed, 5 or 10 minutes. In this instance the wires
will break up and collect the fibrin as fast as it forms, and no firm mass will
be produced. The remaining fluid is called whipped blood. The fibrin can
be removed from the wires and washed in tap water until all the adherent
red corpuscles are removed. This mass of fibrin is white, elastic, and com-
posed of a network of thread-like fibers. It is these fibers extending through
and through the mass of blood which makes it retain the form of the vessel
when undisturbed clotting occurs.
d. The Influence of Salt-Solution on Blood-Clotting. Add 20 c.c. of satu-
rated magnesium sulphate, i per cent sodium oxalate, and 2.5 per cent of
sodium chloride in each of 3 beakers. Draw into each beaker 50 to 60 c.c. of
blood and immediately mix thoroughly and let stand. The magnesium and
oxalate beakers will not coagulate even though they stand for days, but the
sodium-chloride blood will clot in a few minutes.
The magnesium-sulphate blood will coagulate if diluted with a sufficient
amount of distilled water or physiological saline solution. Make a series
of dilutions and note when coagulation takes place. The sodium-oxalate
blood will coagulate when a sufficient excess (i per cent) of calcium chloride
is added to neutralize the excess of sodium oxalate. Demonstrate this on
a series of samples.
If a liter or so of magnesium or oxalate blood is secured and separated
by a centrifuge, or by leaving stand for a sufficient time, a sample of salted
plasma will be obtained. This sample will coagulate when it is treated as
just described for salted blood, showing that the antecedents of fibrin are
found in the plasma.
e. Action of Tissue Extracts on Coagulation. Wash out the blood of
a small animal by circulating 0.9 per cent saline through the arteries until
the outflowing fluid from the veins is clear. Take an organ, the liver for
example, grind it up in a sausage mill by running it through the mill two
or three times, then extract with 0.9 per cent physiological saline. The
macerating mass should be shaken up at intervals, and may be kept from
spoiling by adding an excess of chloroform or by keeping on ice. A few
cubic centimeters of this fluid extract added to a sample of freshly drawn
blood will very greatly hasten the rapidity of coagulation. This tissue ex-
THE CHEMISTRY OF BLOOD-PLASMA 139
tract is called thrombokinase, as it is an activator which hastens the formation
of thrombin from thrombogen.
11. The Chemistry of Blood-Plasma (or Serum). The blood-
plasma contains all the chemical substances which are utilized by the
tissues in their nutrition or which are thrown off by the tissues as a re-
sult of their activity. It is therefore a very complex mixture. The serum
contains the same substances in the same proportion, with the exception of
the antecedents of fibrin. It may, therefore, be used as a substitute for
plasma in most cases.
a. Proteids oj Plasma. There are three principal proteids in blood-
plasma: serum-albumin, serum-globulin, and fibrinogen. These may be
isolated as follows: To a sample of blood-plasma add an equal quantity of
sodium-chloride solution that has been saturated at 40° C. A white floccu-
lent precipitate of fibrinogen comes down. Filter off, and add to the nitrate
an equal volume of saturated ammonium sulphate. A second heavier pre-
cipitate of serum-globulin separates out. When this is separated, and crys-
tals of ammonium sulphate are added to the nitrate to complete saturation
at 40° C., a third precipitate of serum-albumin separates.
Each of these precipitates may be redissolved and purified by reprecipi-
tation and can be tested by the characteristic proteid reactions, see page 96,
which they all give.
b. Sugars of Blood-Plasma or Serum. If a quantity of blood-serum is
diluted with about 5 to 10 times its' volume of water, and the proteids are
removed by slight acidulation with acetic acid and boiling and filtering, the
filtrate will contain reducing sugar and the various solids of blood-plasma.
To a concentrated sample of the filtrate add Fehling's solution and boil.
A reddish precipitate indicates the presence of reducing sugar. If this ex-
periment is done quantitatively, about from o.i to 0.2 per cent of sugar will
be found.
c. The Salts oj Blood-Plasma. The salts of blood-plasma are tested
best by evaporating some of the blood serum to dryness, and burning the
residue to oxidize the organic matter and dissolving the ash in water. Test
as follows: To a sample add i per cent of silver nitrate; a white precipitate
soluble in an excess of ammonia, but not soluble in nitric acid, indicates
chlorides.
To a second sample add i per cent barium chloride. If sulphates are
present there will be a white precipitate which settles out quickly.
Acidify a third sample with nitric acid and add ammonium molybdate
and heat. A yellow precipitate indicates the presence of phosphates.
To the fourth sample add an excess of strong ammonia and i per cent
ammonium oxalate, heat. A white precipitate indicates the presence of
calcium.
12. Blood-Corpuscles. The characteristic substance in the composi-
140 THE BLOOD
tion of the corpuscles is the pigment known as hemoglobin, and this is the
only chemical factor that will be considered in these experiments.
a. Hemoglobin Crystals. Take a sample of dog's blood, or if a centri-
fuge is available separate and wash the sample of blood-corpuscles, and
mix with about three volumes of saturated ether water, or if blood is used dilute
with two or three volumes of water and add about 10 per cent of pure ether
and shake thoroughly. Crystals of oxyhemoglobin will be formed, and this
can be mounted and examined with a microscope.
b. Spectrum of Hemoglobin and its Compounds.
1. Oxyhemoglobin. Dilute a sample of defibrinated blood with about
ten volumes of distilled water. From this stock solution make five solutions
all differing by 33^ per cent. Examine these with a direct-vision spectroscope.
Make a drawing showing the absorption spectrum of each sample as com-
pared with the solar spectrum. Compare with the spectrum shown in the
frontispiece.
2. Hemoglobin. The oxygen can be driven out from the hemoglobin
by adding to the above samples a few drops of ammonium sulphide and
gently warming. Re-examine with the direct-vision spectroscope and map
as before.
3. Carbon-Monoxide Hemoglobin. Pass a stream of ordinary illumi-
nating gas through the dilutions of hemoglobin. The carbon monoxide
of the gas will form a compound with the hemoglobin, which now turns a
bright scarlet color. When examined with the spectroscope, the absorp-
tion bands are found to be very similar to those of oxyhemoglobin. How-
ever, map the spectrum to the scale as usual. Add the reducing agent,
warm, and shake vigorously and re-examine. It is very difficult to break up
the combination of hemoglobin with carbon monoxide, hence the poisonous
action of this gas.
CHAPTER V
THE CIRCULATION OF THE BLOOD
THE blood is contained in a system of closed vessels through which it is
kept in circulation during the life of an individual. The energy to keep up
this motion is supplied by the heart, which is a large muscular organ con-
sisting of four great divisions, the right and left auricles and right and left
ventricles. The right ventricle discharges its blood into the pulmonary artery,
FIG. 133.— Diagram of the Circulation in an Animal with a Completely Separated Right
and Left Ventricle and a Double Circulation. (After Huxley.) Ad, Right auncle receiving the
superior and inferior venae cavae, Vcs and Vci; Dth, thoracic duct, the main trunk of the lymphatic
system; Ad, right auricle; Vd, right ventricle; Ap, pulmonary artery; P, lung; Vp, pulmonary
vein; As, left auricle; Vs, left ventricle; A o, aorta; D, intestine; L, liver; Vp, portal vein; Lv,
hepatic vein.
through which it passes to the lungs, returning through the pulmonary veins to
the left auricle, and into the ventricle. From the left ventricle the blood fc
pumped into the great aorta, and through its branches distributed to the entire
body. The terminal arteries are continuous with the general capillaries of the
141
142 THE CIRCULATION OF THE BLOOD
body, and these in turn with the veins, which conduct the blood back to the
right side of the heart again. It will be seen, therefore, that the circulatory
apparatus consists of two great divisions, the pulmonary and the systemic cir-
culation. This arrangement is illustrated by the accompanying figure.
A study of this figure will show that in certain regions of the systematic circu-
lation there are two capillary beds between the main arteries and the main
veins. This subordinate stream through the liver is called the portal cir-
culation, and the similar arrangement existing in the kidney is called the
renal circulation. This, in general, is the outline of the course of the blood
in its circulation.
To make a study of the various phenomena manifested in the physiology
of the circulatory apparatus, it is obvious that we have to do with certain
fundamental activities; first, the physiology of the pumping organ, the heart;
second, the behavior of the blood in the arteries, capillaries, and veins; third,
the coordination of these various divisions of the apparatus through the
nervous system. To understand this it will be necessary to have in mind in
detail the anatomical structure of the apparatus itself.
ANATOMICAL CONSIDERATIONS.
The Heart. The heart is contained in the chest or thorax, and
lies between the right and left lungs, figure 134, enclosed in a membranous
sac, the pericardium. The pericardium is made up of two distinct parts,
an external fibrous membrane, and an internal serous layer, which not only
lines the fibrous sac, but als6 is reflected on to the heart, which it completely
invests. These form a closed sac, the cavity of which contains just enough
fluid to lubricate the two surfaces, and thus to enable them to glide smoothly
over each other during the movements of the heart. The vessels passing in
and out of the heart receive investments from this sac to a greater or less degree.
The heart is situated in the chest behind the sternum and costal carti-
lages, being placed obliquely from right to left. It is of pyramidal shape,
with the apex pointing downward, outward, and toward the left, and the
base backward, inward, and toward the right. The heart is suspended in
the chest by the large vessels which proceed from its base, but, excepting
at the base, the organ itself hangs free within the sac of the pericardium.
The part which rests upon the diaphragm is flattened, and is known as the
posterior surface, while the free upper part is called the anterior surface.
On examination of the external surface, the division of the heart into
parts which correspond to the chambers inside of it may be traced, for a
deep transverse groove, called the auriculo-ventricular groove, divides the
auricles from the ventricles; and the interventricular groove runs between
the ventricles, both in front and in the back, separating the one from the
other. The anterior groove is nearer the left margin, and the posterior nearer
THE HEART 143
the right, as the front surface of the heart is made up chiefly of the right
ventricle and the posterior surface of the left ventricle. The coronary ves-
sels which supply the tissue of the heart with blood run in the furrows or
grooves; also the nerves and lymphatics, which are embedded in more or
less fatty material, are found in this groove.
The Chambers oj the Heart. The interior of the heart is divided by a
longitudinal partition in such a manner as to form two chief chambers or
cavities, the right and the left. Each of these chambers is again subdivided
transversely into an upper and a lower portion, called respectively the auricle
FIG. 134. — Outline of Heart, Lungs, and Liver to Show their Relations to each other and to
the Chest Wall. (Heusman and Fisher's "Anatomical Outlines.")
and the ventricle, which freely communicate. The aperture of communica-
tion, however, is guarded by valves so disposed as to allow blood to pass
freely from the auricle into the ventricle, but not in the opposite direction.
There are thus four cavities ;*i the heart, the auricle and ventricle of one
side being quite separate from those on the other, figure 135.
The right auricle, the right part of the base of the heart as viewed from
the front, is a thin-walled cavity of more or less quadrilateral shape, prolonged
at one corner into a tongue-shaped portion, the right auricular appendix,
which slightly overlaps the exit of the aorta from the left ventricle.
The interior of the auricle is smooth, being lined with the general lining
membrane of the heart, the endocardium. The superior and inferior venae
cavse open into the auricle. The opening of the inferior cava is protected
and partly covered by a membrane called the Eustachian valve. In the
posterior wall of the auricle is a slight depression called the fossa ovalis,
144
THE CIRCULATION OF THE BLOOD
which corresponds to an opening between the right and left auricles, exist-
ing in fetal life. In the appendix are closely set elevations of the muscular
tissue, covered with endocardium, and on the anterior wall of the auricle are
similar elevations arranged parallel to one another, called musculi pectinati.
FIG. 135. — The Right Auricle and Ventricle Opened and a Part of their Right and Anterior Walls
Removed so as to Show their Interior, i, Superior vena cava; 2, inferior vena cava; 2', hepatic
veins cut short; 3, right auricle; 3', placed in the fossa ovalis, below which is the Eustachian valve;
3", is placed close to the aperture of the coronary vein; t, t, placed in the auriculo- ventricular
groove, where a narrow portion of the adjacent walls of the auricle and ventricle has been pre-
served; 4, 4, cavity of the right ventricle, the upper figure is immediately below the semilunar
valves; 4', large columna carnea or musculus papillaris; 5, 5', 5", tricuspid valve; 6, placed in the
interior of the pulmonary artery, a part of the anterior wall of that vessel having been removed
and a narrow portion of it preserved at its commencement where the semilunar valves are attached ;
7, concavity of the aortic arch close to the cord of the ductus arteriosus; 8, ascending part or sinus
of the arch covered at its commencement by the auricular appendix and pulmonary artery; 9,
placed between the innominate and left carotid arteries; 10, appendix of the left auricle; n, n,
outside of the left ventricle the lower figure near the apex. (Allen Thomson.)
The right ventricle forms the right margin of the heart. It takes no
part in the formation of the apex. On section its cavity is semilunar or
crescentic, figure 137. Into it are two openings, the auriculo-ventricular
orifice at the base, and the opening of the pulmonary artery, also at the base
but more to the left. The part of the ventricle leading to the pulmonary
artery is called the conus arteriosus or infundibulum; both orifices are guarded
by valves, the former called the tricuspid and the latter the semilunar.
THE HEART
145
In this ventricle are also the projections of the muscular tissue called the
columncE carnecB.
The left auricle is situated at the left and posterior part of the base of
the heart. The left auricle is only slightly thicker than the right and its
FIG. 136.— The Left Auricle and Ventricle Opened and a Part of Their Anterior and Left Walls
Removed. Magnified £. The pulmonary artery has been divided at its commencement; the
opening into the left ventricle is carried a short distance into the aorta between two of the segments
of the semilunar valves; and the left part 9f the auricle with its appendix has been removed. The
right auricle is out of view, i, The two right pulmonary veins cut short; their openings are seen
within the auricle; i', placed within the cavity of the auricle on the left side of the septum and on
the part which forms the remains of the valve of the foramen ovale, of which the crescentic fold is
seen toward the left hand of i'; 2, a narrow portion of the wall of the auricle and ventricle preserved
round the auriculo- ventricular orifice; 3, 3', the cut surface of the walls of the ventricle, seen to
become very much thinner toward 3", at the apex; 4, a small part of the anterior wall of the left
ventricle which has been preserved with the principal anterior columna carnea or musculus papil-
laris attached to it; 5, 5, musculi papillares; 5', the left side of the septum, between the two ven-
tricles, within the cavity of the left ventricle; 6, 6', the mitral valve; 7, placed in the interior of the
aorta near its commencement and above the three segments of its semilunar valve which are hang-
ing loosely together; 7', the exterior of the great aortic sinus; 8, the root of the pulmonary artery
and its semilunar valves; 8', the separated portion of the pulmonary artery remaining attached to
the aorta by 9, the cord of the ductus arteriosus; 10, the arteries rising from the summit of the aor-
tic arch. (Allen Thomson.)
form and structure" are the same as in the right. The left auricula-ventricu-
lar orifice is oval and a little smaller than that on the right side of the heart.
There is a slight vestige on the septum of the foramen between the auricles.
10
146 THE CIRCULATION OF THE BLOOD
The left ventricle occupies the posterior and apical portion of the heart,
and is connected directly with the great aorta. It is separated from the
auricle by the bicuspid or mitral valves, and the opening into the great aorta
is guarded by the semilunar valves. The walls of the left ventricle are two
or three times as heavy as those of the right, and may be as much as half an
inch in total thickness.
The left ventricle is capable of containing 90 to 120 c. c. of blood. The
capacity of the auricles is considerably less after death owing to their con-
tracted condition. The whole heart is about 12 cm. long by 8 cm. at its
greatest width, and 6 cm. in thickness. The average weight in the adult is
about 300 grams.
The walls of the heart are constructed almost entirely of layers of muscu-
lar fibers; but a ring of connective tissue, to which some of the muscular
fibers are attached, is inserted between each auricle and ventricle and forms
FIG. 137. — Cross-section of a Completely Contracted Human Heart, at the Level of the Lower
and Middle Thirds. (According to Krehl.)
the boundary of the auricula-ventricular opening. Fibrous tissue also exists
at the origins of the pulmonary artery and aorta. The muscular fibers of
each auricle are in part continuous with those of the other, and in part separate;
and the same holds true for the ventricles. The fibers of the auricles are,
however, quite separate from those of the ventricles, the bond of connection
between them being the fibrous and the embryonic muscular tissue of the
auriculo-ventricular rings and the bundle of His in the septum.
The development of the heart shows that it is derived from an embryonic
tube, which in its growth becomes twisted upon itself and divided into the
THE HEART
147
two main divisions that we know in the adult. Anatomical dissections have
shown that the muscles of the ventricles form spiral sheaths extending from
FIG. 138.
FIG. 138. — Cardiac Muscle Cells, Showing their Form, Branches, Nuclei, and Striae. From
the heart of a young rabbit. Magnified 425 diameters. (Schafer.) a, Line of junction between
the cells (intercellular cement) ; b, c, branches of the cells.
FIG. 139.— Cardiac Muscle Cells of the Left Ventricle of a Child at Birth (full term), to show
the form of the cells, their structural details, their relations to one another, and their general agree-
ment with those of cold-blooded vertebrates. A, Large cell with two nuclei; this cell has nearly
the proportions of those of the adult; B, group of cells in their natural relatipn. At the right of
the middle cell are two spaces or fissures, n. Nucleus. The transverse striations cross the nuclei
in all the cells, and each nucleus possesses several nucleoli. (Gage.)
FIG. 140.
FIG. 141.
FIG. 140. — Diagram of the Course 9f the Superficial Muscle Layers Originating in the Right
and Left Auriculo- ventricular Rings and in the Posterior Half of the Tendon of the Conus. (After
MacCallum.) C, Anterior papillary muscle.
FIG. 141. — Diagram of the Course of the Superficial Muscle Layers Originating in the Anterior
Half of the Tendon of the Conus. (After MacCallum. ) A , Posterior papillary muscle; B, papillary
muscle of the septum.
148
THE CIRCULATION OF THE BLOOD
the base of the two ventricles in spiral bands toward the apex. These bands
of muscle are wound about the surface of the ventricles in the right-to-left
direction. At the apex they extend up into the deeper tissue. If the super-
ficial muscles are dissected off, there is left a great central core of muscle,
FIG. 142.
FIG. 143-
FIG. 142. — Diagram of the Course of the Layer Superficial to the Deepest Layer of the Muscle
of the Left Ventricle, which is shown in outline. The deepest layer is also shown. (After Mac-
Callum.) A, Posterior papillary muscle; B, papillary muscle of the septum.
FIG. 143. — Diagram of a Layer still more Superficial to that Shown in Fig. 142, and Ending
in the Anterior Papillary Muscle. The deeper layers are represented in dotted lines. (After
MacCallum.) A, Posterior papillary muscle; B, papillary muscle of septum; C, anterior papillary
muscle.
which is described by MacCallum as running more transversely around the
wall of one ventricle, then through the septum and around the other in a
reverse scroll, figure 142.
The Valves of the Heart. The valves of the heart are arranged
so that the blood can pass only in one direction. These are the tricuspid
valve, between the right auricle and right ventricle, figure 135, and the semi-
lunar valves of the pulmonary artery, the mitral valve between the left auricle
and ventricle, and semilunar valves of the aorta. The bases of the tricuspid,
figure 152, and mitral valves are attached to the walls of the auriculo-ven-
tricular rings, respectively. Their ventricular surfaces and borders are
fastened by slender tendinous fibers, the chorda tendinece, to the internal
surface of the walls of the ventricles at points which project into the ventricu-
lar cavity in the form of bundles or columns, the columns carnece.
The semilunar valves guard the orifices of the pulmonary artery and of
the aorta. They are nearly alike on both sides of the heart, but the aortic
valves are altogether thicker. Each valve consists of three parts which are
of semilunar shape, the convex margin of each being attached to a fibrous
ring at the place of junction of the artery to the ventricle, and the concave
or nearly straight border being free, so as to form a little pouch like a pocket,
7, figure 136. In the center of each free edge of the valves which contains
a fine cord of fibrous tissue, is a small fibrous nodule, the corpus Arantii.
THE ARTERIES
149
The Arteries. The arterial system begins at the left ventricle in
a single large trunk, the aorta, which, almost immediately after its origin,
gives off in the thorax three large branches for the supply of the head, neck,
and upper extremities; it then traverses the thorax and abdomen, giving
off branches, some large and some small, for the supply of the various organs
and tissues it passes on its way. In the abdomen it divides into two chief
branches. The arterial branches, wherever given off, divide and subdivide
until the caliber of each subdivision becomes very minute. These smallest
arteries are called arterioles. These arterioles are continuous with the capil-
laries. Arteries frequently communicate or anastomose with other arteries.
The arterial branches are usually given off at an acute angle, and the areas
of the branches of an artery generally exceed that of the parent trunk, and,
, , m
FIG. 144.
FIG. 145.
FIG. 146.
FIG. 144. — Minute Artery Viewed in Longitudinal Section, e, Nucleated endothelial mem-
brane, with faint nuclei in lumen, looked at from above; *', thin elastic tunica intima; ra, muscular
coat or tunica media; a, tunica adventitia. (Klein and Noble Smith.)
FIG. 145. — Transverse Section through a Large Branch of the Inferior Mesenteric Artery of a
Pig. e, End9thelial membrane; *", tunica elastica interna, no subendothelial layer is seen; m,
muscular tunica media, containing only a few wavy elastic fibers; e, c, tunica elastica externa, di-
viding the media from the connective-tissue adventitia, a. (Klein and Noble Smith.) Magnifica-
tion 350 diameters.
FIG. 146. — Muscular Fiber Cells from Human Arteries. Magnified 350 diameters. (Kolliker.)
a, Nucleus; B, a fiber cell treated with acetic acid.
as the distance from the origin is increased, the area of the combined branches
is increased also. As regards the arterial system of the lungs, the pulmonary
artery and its subdivisions, they are distributed in much the same manner
as the arteries belonging to the general systemic circulation.
The walls of the arteries are composed of three principal coats, the ex-
ternal or tunica adventitia, the middle or tunica media, and the internal or
tunica intima. The external coat, figures 144 and 145, a, the strongest and
toughest part of the wall of the artery, is formed of areolar tissue, with which
is mingled throughout a network of elastic fibers. The middle coat, figure
150
THE CIRCULATION OF THE BLOOD
145, m, is composed of both muscular and elastic fibers with a certain pro-
portion of areolar tissue. In the larger arteries, figure 145, its thickness is
comparatively as well as absolutely much greater than in the small arteries,
constituting, as it does, the greater part of the arterial wall. The muscular
fibers are unstriped, figure 146, and are arranged, for the most part, trans-
versely to the long axis of the artery, figure 144, m, while the elastic element,
taking also a transverse direction, is disposed in the form of closely inter-
woven and branching fibers intersecting in all parts the layers of muscular
fiber. In arteries of various size there is a difference in the proportion of
FIG. 147. — Vein and Capillaries. Silver-nitrate and hematoxylin stain, to show outlines
of endothelial cells and their nuclei. (Bailey.)
the muscular and elastic element, elastic tissue preponderating in the largest
arteries and unstriped muscle in those of medium and small size. The
arteries are quite elastic in both large and small vessels. The internal coat
is formed by a layer of elastic tissue, called the jenestrated membrane of Henle.
It is peculiar in its tendency to curl up when peeled off from the artery, and
FIG. 148.— Network of Capillary Vessels of the Air Cells of the Horse's Lung Magnified, a, a,
Capillaries proceeding from b, b, terminal branches of the pulmonary artery. (Frey.)
in the perforated and streaked appearance which it presents under the micro-
scope. The inner surface of the artery is lined with a delicate layer of elon-
gated endothelial cells, figure 145, e, which make it smooth and polished and
furnish a nearly impermeable surface along which the blood may flow with
the smallest possible amount of resistance from friction.
THE CAPILLARIES
151
Nerves. Most of the arteries are surrounded by a plexus of nerves or
nerve fibers, which twine around the vessel. The smaller arteries also have
a delicate network of similar nerve fibers many of which appear to end near
the nuclei of the transverse muscular fibers.
The Capillaries. In all vascular textures, except some parts of
the corpora cavernosa of the penis, of the uterine placenta, and of the spleen,
FIG. 149. — Capillaries of Striated Muscular Tissue. From a cat. Magnified 300 diameters.
(Heitzmann.) A, Artery; V, vein.
the transmission of the blood from the minute branches of the arteries to the
minute veins is effected through a network of capillaries. They may be
seen in all minutely injected preparations.
The point at which the arteries terminate and the capillaries commence
cannot be exactly defined, for the transition is gradual. The capillaries
maintain essentially the same diameter throughout. The meshes of the
network that they compose are more uniform in shape and size than those
formed by the anastomoses of the minute arteries and veins.
152 THE CIRCULATION OF THE BLOOD
The walls of the capillaries are composed of a single layer of elongated
or radiate, flattened and nucleated endothelial cells, so joined and dove-
tailed together as to form a continuous transparent membrane, figure 147.
Outside these cells in the larger capillaries there is a structureless supporting
membrane on the inner surface of which they form a lining.
The diameter of the capillary vessels varies somewhat in the different
textures of the body, the most common size being about 12 micromillimeters,
-joinr °f an mcn- Among the smallest may be mentioned those of the
brain and of the follicles of the mucous membrane of the intestines; among
the largest, those of the skin, and especially those of the medulla of the bones.
The form of the capillary network differs in the different organs of the
body, but is usually adjusted to the structural arrangement of the cells of
any given organ.
The capillary network is closest in the lungs and in the choroid coat of
the eye. In the human liver the interspaces are of the same size, or even
smaller than the capillary vessels themselves. In the human lung the spaces
are smaller than the vessels; in the human kidney, and in the kidney of the
dog, the diameter of the injected capillaries, compared with that of the inter-
spaces, is in the proportion of one to four, or of one to three. The brain
receives a very large quantity of blood; but its capillaries are very minute
and are less numerous than in some other parts. In the mucous mem-
branes, for example in the conjunctiva and in the cutis vera, the capillary
vessels are much larger than in the brain and the interspaces narrower,
namely, not more than three or four times wider than the vessels. In the
periosteum and in the external coat of arteries the meshes are much larger,
their width being about ten times that of the vessels. It may be held as a
general rule that the more active the functions of an organ are, the more
vascular it is.
The Veins. The venous system begins in small vessels which are
slightly larger than the capillaries from which they spring. These vessels
are gathered up into larger and larger trunks until they terminate in the two
venae cavse and the coronary vein which enter the right auricle, and in' four
pulmonary veins which enter the left auricle. The total capacity of the
veins diminishes as they approach the heart; but their capacity exceeds by
two or three times that of their corresponding arteries. The pulmonary
veins, however, are an exception to this rule. The veins are found after
death more or less collapsed, and often contain blood. They are usually
distributed in a superficial and a deep set which communicate frequently
in their course.
The coats of veins bear a general resemblance to those of arteries, figure
150. Thus, they possess outer, middle, and inner coats. The outer coat is
constructed of areolar tissue like that of the arteries, but is thicker. In some
veins it contains muscular cells arranged longitudinally. The middle coat
THE VEINS
153
is considerably thinner than that of the arteries; it contains circular un-
striped muscular fibers mingled with a large proportion of yellow elastic and
white fibrous connective tissue. In the large veins near the heart the middle
FIG. 150. — Transverse Section through a Small Artery and Vein of the Mucous Membrane
of a Child's Epiglottis; the artery is thick- walled and the vein thin- walled. A, Artery; the letter
is placed in the lumen of the vessel, e, Endothelial cells with nuclei clearly visible; these cells
appear very thick from the contracted state of the vessel. Outside it a double wavy line marks
the elastic tunica intima. m. Tunica media consisting of unstriped muscular fibers circularly ar-
ranged; their nuclei are well seen, a, Part of the tunica adventitia, showing bundlespf connective-
than that of the artery. X 350. (Klein and Noble Smith.)
FIG. 151. — A, Vein with valves open. B, vein with valves closed; stream of blood passing
off by lateral channel. (Dal ton. )
154 THE CIRCULATION OF THE BLOOD
coat is replaced for some distance from the heart by circularly arranged
striped muscular fibers continuous with those of the auricles. The internal
coat of veins consists of a fenestrated membrane lined by endothelium. The
fenestrated membrane may be absent in the smaller veins. The veins are
supplied with valves in certain regions of the body, especially in the veins of
the arms and legs. The general construction of these valves is similar to
that of the semilunar valves of the aorta and pulmonary artery already
described. Their free margins are turned in the direction toward the heart,
so as to prevent any movement of blood backward. They are commonly
placed in pairs, at various distances in different veins. In the smaller veins
single valves are often met with, and three or four are sometimes placed
together or near one another in the larger veins such as in the subclavians
at their junction with the jugular veins. During the period of their in-
action, when the venous blood is flowing in its proper direction, they lie by
the sides of the walls of the veins; but when in action, they come together
like valves of the arteries, figure 151. Their situation in the superficial
veins of the forearm is readily discovered by pressing along its surface, in a
direction opposite to the venous current, i.e., from the elbow toward the wrist,
when little swellings, figure 151, B, will appear in the position of each pair
of valves.
Lymphatic spaces are present in the coats of both arteries and veins;
but in the tunica adventitia or external coat of the large vessels they form
a distinct plexus of more or less tubular vessels. In smaller vessels they
appear as sinus spaces lined by endothelium. Sometimes, as in the arteries
of the omentum, mesentery, and membranes of the brain, the pulmonary,
hepatic, and splenic arteries, the spaces are continuous with vessels which
distinctly ensheath them, perivascular lymphatic sheaths. Lymph channels
are said to be present also in the tunica media.
THE ACTION OF THE HEART.
The heart's action in propelling the blood consists in the successive alter-
nate contraction, systole, and relaxation, diastole, of the muscular walls of
the auricles and the ventricles. This activity furnishes the power which
keeps the blood moving through the arteries, capillaries, and veins. The
heart in its activity is like a great force pump in that it injects a certain quan-
tity of blood at each contraction into the great arteries. Owing to the inter-
action between this heart-beat and the peripheral resistance to the flow of
blood, together with the elasticity of the vessels themselves, a high pressure
in the arteries is maintained all the time. The heart's contractions then,
pumping against this high arterial tension, are sufficient to maintain a constant
flow of blood through the capillaries, and, therefore, through the active tissues.
The heart beats at an average rate of about 72 times per minute during
ACTION OF THE HEART 155
life. Each successive contraction really begins in the great veins, which
are muscular, and extends over the auricles and ventricles in regular sequence.
The contraction of each successive part is called its systole and the relaxation
its diastole. The diastole covers the period of active relaxation of the muscle
and the pause before beginning its next contraction. Each muscular cham-
ber of the heart may, therefore, be said to have its systole and diastole. The
whole series of events from the beginning of one contraction until the cor-
responding event in the next contraction is described as the cardiac cycle.
Action of the Auricles. The description of the action of the heart
may be commenced at that period in each cycle in which the whole heart is
at rest. The heart is then in a passive state. The auricles are gradually
filling with the blood flowing into them from the veins, and a portion of this
blood is passing at once through the auricles into the ventricles, the opening
between the cavity of each auricle and that of its corresponding ventricle
being free during the entire pause. The auricles, however, receiving more
blood than at once passes through them to the ventricles, become, near the
end of the pause, passively distended. At this moment a contraction wave
begins on the bases of the venae cavae and, running down from the walls of
the veins, passes to the muscular walls of the auricle. The contraction of the
auricles, the right and left contracting at the same time, forces the blood
into the ventricles.
The contraction of the muscular walls of the great veins maintains a
condition of constriction of these veins during the time of the auricular con-
traction. This hinders the reflux of blood from the auricles into the veins
during the auricular systole. Any slight regurgitation from the right auricle
is limited by the valves at the junction of the subclavian and internal jugular
veins beyond which the blood cannot move backward, and by the coronary
vein which is supplied with a valve at its mouth. The force of the blood
propelled into the ventricle at each auricular systole is transmitted in all
directions, but, being insufficient to open the semilunar valves, it is expended
in distending the walls of the ventricle.
Action of the Ventricles. The dilatation of the ventricles which
occurs during the latter part of the diastole of the auricles, is completed by
the forcible injection of the contents of the latter. The ventricles, now dis-
tended with blood, immediately begin to contract. The tricuspid valves
are closed by the initial reflux of blood, or possibly by the currents of blood
formed by the sudden injection of the ventricles by the auricular contraction.
The ventricular systole follows the auricular systole so closely that it seems
continuous with it. As a result of the ventricular systole sufficient pressure
is produced on its contents to overcome the pressure against the semilunar
valves of the aorta, and the pulmonary artery and the ventricles are thus
emptied completely. After the whole of the blood has be",n expelled from
the ventricles, the walls remain contracted for a brief period.
156 THE CIRCULATION OF THE BLOOD
The form and position of the fleshy columns on the internal walls of the
ventricles no doubt help to produce the obliteration of the ventricular cavity
during contraction. The completeness of the closure may often be observed
on making a transverse section of a heart shortly after death in any case in
which rigor mortis is very marked, figure 137. In such a case only a central
fissure may be discernible to the eye in the place of the cavity of each ventricle.
The arrangement of the muscles of the heart, as described on page 148, is
such as to expend the whole force of the contraction in diminishing the cavity
of the ventricle, or, in other words, in expelling its contents.
On the conclusion of the systole the ventricular diastole begins. The
muscular walls relax and, by virtue of their elasticity, a slight negative press-
ure is set up. This negative or suctional pressure on the left side of the
heart is of importance in helping the pulmonary circulation. It is some-
what inconstant in appearance, but has been found to be equal to as much as 20
mm. of mercury, and is said to be quite independent of the aspiratory power
of the thorax itself, which will be described in a later chapter. The ventricles
now remain in a state of relaxation or rest until the next systole begins.
The duration of the ventricular systole and diastole has been variously
estimated. A computation of the time of these two phases, for man, in
figure 153, reproduced from Hurthle, gives for the systole 0.38 of a second,
and for the diastole 0.4 of a second, with a total of 0.78 of a second. This
is equivalent to a rate of 77 per minute. Variations in the time of the systole
and the diastole of the ventricle falls chiefly on the pause of the diastole.
The ventricles undergo little or no change of shape in the unopened chest.
At the moment in the systole when the ventricles begin to discharge their
contents into the aorta and pulmonary arteries, respectively, there is a sharp
decrease in size of the ventricles. This decrease takes place in all dimensions.
Action of the Valves. The Auriculo-ventricular Valves. Dur-
ing the diastole of both auricles and ventricles blood flows directly through
the auricles into the ventricles, the auricles during this period acting as
continuations of the large veins which empty into them. At the end of
the period the ventricle on each side has already been filled and distended
by the pressure of blood from the veins. The systole of the auricle com-
pletes this filling and slightly overdistends the ventricle. When the force
of the auricular contraction is spent, the ventricular walls rebound slightly
toward their former position and in so doing exert some pressure upon the
ventricular side of the auriculo-ventricular valves which floats them upward
toward the auricle. In this connection another force comes into play, viz.,
vortex or back currents resulting from the flow of blood into the ventricle
under the pressure of the auricular systole. These currents aid in floating
the valve leaflets into apposition. Thus, the auriculo-ventricular openings
are closed at the end of the auricular systole, i.e., the end of the ventricular
diastole. The ventricular systole which follows simply serves to place the
ACTION OF THE VALVES
157
valves under greater tension, thus closing them still more firmly. It should
be recollected that the diminution in the breadth of the base of the heart in
its transverse diameters during the ventricular systole is especially marked
in the neighborhood of the auriculo-ventricular rings, and this aids in render-
ing the auriculo-ventricular valves competent to close the openings by greatly
diminishing the diameter. The cusps of the auriculo-ventricular valves
meet not by their edges only, but by the opposed surfaces of their thin outer
borders. The margins of the valves are still more secured in apposition
with one another by the simultaneous contraction of the muscular papillae,
FIG. 152. — The Tricuspid Valves of the Ox, Closed. Vertical section. (Krehl.)
whose chordae tendineae have a special mode of attachment for this very
object. They compensate for the shortening of the ventricular walls and
thus prevent the valves from being everted into the auricle, an event that
does occur in certain valvular lesions.
The actions of the tricuspid and mitral valves on the right and left
sides of the heart are essentially the same.
The Semilunar Valves. The commencement of the ventricular systole
precedes the opening of the semilunar valves by a fraction of a second. The
intraventricular pressure increases with the progress of the systole until
there is a distinct increase over the arterial pressure, then the opening of the
valves takes place at once. They remain open as long as this difference
continues. When the diastole of the ventricle begins and the arterial blood
pressure exceeds the intraventricular pressure, there is an initial reflux of
blood toward the heart which closes the semilunar valves.
158 THE CIRCULATION OF THE BLOOD
The dilatation of the arteries is peculiarly adapted to bring -this about.
The lower borders of the semilunar valves are attached to the inner surface
of the tendinous ring which bounds the orifice of the artery. The tissue of
this ring is tough and inelastic and the valves are equally inextensible, being
formed mainly of tough fibrous tissue with strong interwoven cords. The
effect, therefore, of each propulsion of blood from the ventricle is to dilate
the wall of the first portion of the artery in the three pouches behind the
valves, while the free margins of the valves are drawn inward toward its center.
This position of the valves and arterial walls is maintained while the ventricle
continues in contraction; but as soon as it relaxes, and the dilated arterial
walls can recoil by their elasticity, the blood is forced backward toward the
ventricles and onward in the course of the circulation. Part of the blood
thus forced back lies in the pouches (sinuses of Valsalva) between the valves
and the arterial walls; and the valves are pressed together till their thin
lunated margins meet in three lines radiating from the center to the circum-
ference of the artery, 7 and 8, figure 136. The corpora Arantii at the middle
of the free margins insure a more effective closure.
The Sounds of the Heart. When the ear is placed over the region
of the heart, two sounds may be heard at every beat. They follow in quick
succession, and are succeeded by a pause or period of silence. The first
sound is dull and prolonged; its commencement coincides with the impulse
of the heart against the chest wall, and just precedes the pulse at the wrist.
FIG. 153. — Simultaneous Tracings of the Cardiac Impact, or Cardiogram (lower), and the
Heart Tones (upper), of Man. The cross strokes at the beginning of the cardiac sound tracing
and on the cardiogram mark the synchronous events. (Hurt hie.)
The second is shorter and sharper, with a somewhat flapping character.
The periods of time occupied respectively by the two sounds taken together
and by the pause between the second and the first are unequal. According
to Foster, the interval of time between the beginning of the first sound and
the second sound is 0.3 of a second, while between the second and the suc-
ceeding first it is nearly 0.5 of a second, see figures 153, 154, and 158. The
relative length of time occupied by each sound, as compared with the other,
may be best appreciated by considering the different forces concerned in
the production of the two sounds. In one case there is a strong, compara-
tively slow contraction of a large mass of muscular fibers, urging forward
THE SOUNDS OF THE HEART
159
a certain quantity of fluid against considerable resistance; while in the other
it is a strong but shorter and sharper recoil of the elastic coat of the large
arteries — shorter because there is no resistance to the flapping back of the
semilunar valves as there was to their opening. The sounds may be ex-
pressed by the words lubb — dUp. The beginning of the -first sound cor-
responds in time with the beginning of the contraction of the ventricles, the
closure of the auriculo-ventricular valves, and the first part of the dilatation
of the auricles. The sound continues through a somewhat longer interval
than the second sound. .The second sound, in point of time, immediately
FIG. 154. — Simultaneous Tracings of the Heart Tone and Pulse of the Carotid in the Dog.
A i and Az, First and second sounds; P, pulse; S, time in tenths and fiftieths of a second. (Ein-
thoven and Geluk.)
follows the cessation of the ventricular contraction, and corresponds with
the commencing dilatation of the ventricles and the opening of the auriculo-
ventricular valves, figure 154.
The exact cause of the first sound of the heart is not known. Two factors
probably enter into it. First, the vibration of the auriculo-ventricular valves
and of the chordse tendineae. Second, the vibration of the muscular mass
of the ventricles themselves. The same mechanical conditions produce
equal tension on the ventricular muscle itself and, according to the second
view, this is sufficient to account for the first sound. Looking upon the
contraction of the heart as a simple contraction and not as a series of con-
tractions, or tetanus, it is at first sight difficult to see why there should be
any muscular sound when the heart contracts.
The cause of the second sound is more simple and definite than that of
the first. It is entirely due to the vibration consequent on the sudden closure
of the semilunar valves when they are pressed down across the orifices of
the aorta and pulmonary artery. The influence of these valves in producing
the sound was first demonstrated by Hope who experimented with the hearts
of calves. In these experiments two delicate curved needles were inserted,
one into the aorta, and another into the pulmonary artery below the line of
160
THE CIRCULATION OF THE BLOOD
attachment of the semilunar valves. After being carried upward about
half an inch the needles were brought out again through the coats of the
respective vessels, so that in each vessel one valve was held back against
the arterial walls. Upon applying the stethoscope to the vessels it was found
that after such an operation the second sound had ceased to be audible.
Tube to communicate
with the tambour
\
Ivory Tape to attach
knob instrument to the chest
Tympanum
FIG. iS5- — Cardiograph. (Sanderson's.)
Disease of these valves, when sufficient to interfere with their efficient action,
also demonstrates the same fact by modifying the second sound or destroying
its distinctness.
The Cardiac Impulse. The heart may be felt to beat with a slight
shock or impulse against the walls of tlie chest at the level of the fifth inter-
Screw to adjust the lever
i
Writing lever
Tambour
Tube to the cardiograph
FIG. 156. — Marey's Tambour, to which the Movement of the Column of Air in the Cardiograph
is Conducted by a Tube, and from which it is Communicated by the Lever to a Revolving Cylinder
so that the tracing of the movement of the cardiac impulse is obtained.
costal space on the left side. Its extent and character vary in different
individuals, a factor of considerable clinical significance, and therefore es-
pecially discussed in works on clinical diagnosis. The cause of the cardiac
impulse has been variously described. It will be remembered that during
THE CARDIAC IMPULSE 161
the period which precedes the ventricular systole the quiet heart rests with its
apex against the wall of the chest. When the ventricles contract, their walls
suddenly become firm and tense. Being firmly attached at the base the effect
of the movement is to press the hardened ventricle against the chest wall.
The discharge of the contents of the ventricle into the curved aorta intensi-
fies this pressure by its mechanical effect in tending to straighten the curve
of that vessel and thus holds the ventricle in firm contact with the chest.
It is this sudden pressure of the contracting heart against the chest wall that
is felt on the outside. The impact or shock is possibly more distinct because
of the partial rotation of the whole heart toward the right and front along
its long axis. The movement of the chest wall produced by the ventricular
contraction against it may be registered by means of an instrument called
the cardiograph; and the record or tracing, called a cardiogram, corresponds
FIG. 157. — Tvpical Cardiogram (upper trace) from the Dog. Taken simultaneously with the
aortic pressure (middle) and intra ventricular pressure (lower) tracings. Time in o.oi of a second.
(HUrthle.)
almost exactly with a tracing obtained by an instrument applied over the
contracting ventricle itself.
The cardiograph, figure 156, consists of a cup-shaped metal box over
the open front of which is stretched an elastic India-rubber membrane upon
which is fixed a small knob of hard wood or ivory. This knob, however,
may be attached, as in the figure, to the side of the box by means of a spring,
and may be made to act upon a metal disc attached to the elastic membrane.
The knob is for application to the chest wall over the place of the greatest
impulse of the heart. The box or tambour communicates by means of an
air-tight tube with the interior of a second or recording tambour supplied
with a long and light writing lever. The shock of the heart's impulse being
communicated to the ivory knob, and through it to the first tambour, the
effect is, of course, at once transmitted by the column of air in the elastic
11
162
THE CIRCULATION OF THE BLOOD
tube to the interior of the second recording tambour, also closed, and through
the elastic and movable disc of the latter to the writing lever which is ad-
justed to a registering apparatus. This latter generally consists of a cylinder
or drum covered with smoked paper and revolving by clock-work with a
definite velocity. The point of the lever writing upon the paper produces
a tracing of the heart's impulse or cardiogram.
Endocardiac Pressure. The effect of the muscular contractions
and relaxations of the walls of the heart during its systole and diastole is to
FIG. 158. — Double Cardiac Sound for Simultaneous Registration of the Blood Pressure in the
Right Auricle and Ventricle, or in the Aorta and Left Ventricle. (Hiirthle.)
produce varying changes of pressure on its content of blood. When this
pressure is measured by the proper instrument it is found that the pressure
in the left ventricle varies between wide ranges. With the beginning of
the muscular contraction, the pressure rises till it slightly exceeds that of
the pressure of the aorta, remains high for a brief interval of time, then slowly
and quietly decreases to less than that of atmospheric pressure and remains
low until the beginning of the next systole. For the right ventricle the events
and variations are relatively the same.
ENDOCARDIAC PRESSURE
163
In order to determine the endocardiac pressure communication must
be established with the cavities of the heart. This is accomplished by a
tube known as a sound, which is introduced into the left ventricle by passing
FIG. 159. — Simultaneous Registration of Curves of the Left Intraventricular Pressure (lower),
the Aortic Pressure (middle), and the Cardiac Impact (upper). Time o.oi of a second. (Hiirthle.)
Systole
Diastole/.
FIG. 160. — Schematic Cardiogram I, and Intraventricular Pressure Curves from the Dog.
(Hiirthle.) The ventricular pressure curve of the descending type is represented by the dotted line.
Pressure in millimeters of mercury, time in tenths of a second.
it down the common carotid artery, or into the right auricle and ventricle
through the jugular vein. When such tubes are introduced and connected
with some form of pressure-recording apparatus, accurate tracings of the
variations in pressure during the heart-beat are obtained.
164 THE CIRCULATION OF THE BLOOD
Chauveau and Marey have been able to record and measure with much
accuracy the variations of the endocardiac pressure and the comparative
duration of the contractions of the auricles and ventricles. They placed
three small India-rubber air-bags or sounds in the interior, respectively, of
the right auricle, the right ventricle, and in an intercostal space in front of
FIG. 161. — Apparatus of MM. Chauveau and Marey for Estimating the Variations of Endo-
cardiac Pressure, and Production of the Impulse of the Heart.
the heart of living animals — the horse. These bags were connected by
means of long narrow tubes with three levers arranged one over the other
in connection with a registering apparatus, figure 161. The synchronism
of the impulse with the contraction of the ventricles is also well shown by
FIG. 162. — Tracings of i, Intra-auricular; 2, Intraventricular Pressures; and 3, of the Cardiac
Impulse of the Heart. To be read from left to right. Obtained by Chauveau and Marey.
means of the same apparatus, and the causes of the several vibrations of
which it is really composed have been demonstrated.
In the tracing, figure 162, the intervals between the vertical lines rep-
resent periods of a tenth of a second. The parts on which any given vertical
line falls represent simultaneous event?. It v/iU be seen that tt.° Contraction
ENDOCARDIAC PRESSURE
165
of the auricle, indicated by the marked curve at A in the first tracing, causes
a slight increase of pressure in the ventricle which is shown at Ar in the second
tracing, and produces also a slight impulse, which is indicated by A" in the
third tracing. The closure of the semilunar valves causes a momentarily
increased pressure in the ventricle at D', affects the pressure in the auricle D,
and is also shown in the tracing of the cardiac impulse D".
The large curve of the ventricular and the impulse tracings, between
A' and Z>', and A" and D", are caused by the ventricular contraction, while
the smaller undulations, between B and C, Bf and C', B" and C", are caused
FIG. 163. — '•Apparatus for Recording the Endocardiac Pressure. (Rolleston.)
by the vibrations consequent on the tightening and closure of the auriculo-
ventricular valves.
It seems by no means certain that Marey's curves properly represent
the variations in intraventricular pressure. Objection has been taken to
his method of investigation: First, because his tambour arrangement does
not admit of both positive and negative pressure being simultaneously re-
corded; second, because the method is applicable only to large animals,
such as the horse; third, because the intraventricular changes of pressure
are communicated to the recording tambour by a long elastic column of air;
and fourth, because the tambour arrangement has a tendency to record
inertia vibrations. H. D. Rolleston, who has pointed out the above im-
perfections of Marey's method, has reinvestigated the subject with a more
suitable apparatus.
166 THE CIRCULATION OF THE BLOOD
The method adopted by Rolleston is as follows:
A window is made in the chest of an anesthetized and curarized animal, and an appro-
priately curved glass cannula introduced through an opening in the auricular appendix.
The cannula is then passed through the auriculo-ventricular orifice without causing any
appreciable regurgitation, into the auricle, or it may be introduced into the cavity of the
right or left ventricle by an opening made in the apex of the heart. In some experiments
the trocar is pushed through the chest wall into the ventricular cavity. His apparatus
FIG. 164. — Endocardiac Pressure Curve from the Left Ventricle of the Dog. The thorax was
opened and a cannula introduced through the apex of the ventricle; the abscissa is the line of at-
mospheric pressure. G to D represents the ventricular contraction; from D to the next rise at G
represents the ventricular diastole. The notch, at the top of which is F, is a post- ventricular rise
in pressure from below that of the atmosphere, and not a presystolic or auricular rise in pressure.
is filled with a solution of leech extract in 0.75 per cent saline solution, or with a solution
of sodium bicarbonate of specific gravity 1083.
The animals employed were chiefly dogs. The movement of the column of blood is
communicated to the writing lever by means of a vulcanite piston which moves with little
friction in a brass tube connected with a glass cannula by means of a short connecting
tube.
When the lower part of the tube, A , is placed in communication with one of the cavities
of the heart, the movements of the piston are recorded by means of the lever, C. Attached
to the lever is a section of a pulley, H, the axis of which coincides with that of the steel rib-
FlG. 165. — Curve with a Dicrotic Summit from the Left Ventricle; the Abscissa Shows the At-
mospheric Pressure.
bon, E ; while, firmly fixed to the piston, is the curved steel piston rod, /, from the top of
which a strong silk thread, /, passes downward into the groove on the pulley.
This thread, /, after being twisted several times round a small pin at the side of the lever,
enters the groove in the pulley from above downward, and then passes to be fixed to the
lower part of the curve on the piston rod as shown in the smaller figure.
The movement of the lever, C, is controlled by the resistance to torsion of the steel
ribbon, E, to the middle of which one end of the lever is securely fixed by a light screw
clamp, F. At some distance from this clamp, the distance varying with the degree of re-
ENDOCARDIAC PRESSURE
167
sistancc which it is desired to give to the movements of the lever, are two holders, G, G',
which securely clamp the steel ribbon.
As the torsion of a steel wire or strip follows Hooke's law, the torsion being proportional
to the twisting force, the movements of the lever point are proportional to the force em-
ployed to twist the steel strip of ribbon — in other words to the pressures which act on the
piston, B. To make it possible to record satisfactorily the very varying ventricular and
auricular pressures, the resistance to torsion of a steel ribbon adapts itself very conven-
iently.
This resistance can be varied in two ways, ist, by using one or more pieces of steel
ribbon or by using strips of different thicknesses; or, 2d, by varying the distance between
the holders, G, G', and the central part of the steel ribbon to which the lever is attached.
Rolleston's conclusions are: That there is no distinct and separate
auricular contraction marked in the pressure curves obtained from the right
or the left ventricle, the auricular and ventricular rises of pressure being
merged into one continuous rise. He concludes that the auriculo-ventricular
FIG. 166. — Hiirthle's Spring Manometer. A, Viewed from the side; B, viewed from the top.
valves are closed before any great rise of pressure within the ventricle above
that which results from the auricular systole, a, figure 165. The closure of
the valve "occurs probably in the lower third of the rise AB, figure 165, and
does not produce any notch or wave. It is shown that the semilunar valves
open at the point in the ventricular systole, situated at C, about or a little
above the junction of the middle and upper thirds of the ascending line AB,
and the closure about or a little before the shoulder, D. The figures show,
finally, that the minimum pressure in the ventricle may fall below that of the
atmosphere, but that the amount varies considerably.
On the whole, the most satisfactory recording instrument for the measure-
ment of endocardiac pressures is the membrane manometer devised by
Hiirthle. This instrument avoids mechanical errors in a most satisfactory
manner. By simultaneous tracings of the pressure in the ventricle and in
the aorta by Hurthle's differential manometer, the exact moment of the
168
THE CIRCULATION OF THE BLOOD
opening and closing of the semilunar valves has been determined. By
similar methods we have been able to fix synchronism between other events
occurring during the beat. These we will summarize in the following section.
Cardiac Cycle. The entire series of occurrences in a single heart-
beat is called the Cardiac Cycle. If the condition of the heart is considered
at that moment when its muscular walls are at rest it will be found that the
auriculo-ventricular valves are open, that the blood is flowing from the great
PAUSE
DIASTOLE
AURICLE
VENTRICLE
IMPULSE
FIG. 167. — Diagrammatic Representation of the Events of the Cardiac Cycle. For events
which occur in sequence, read in the direction of the curved arrow; for synchronous events, read
from the center to the periphery in any direction. (Coleman.)
veins into the auricle and ventricle, which form a continuous cavity, and
that the pressure is about that of the atmosphere, but slowly rising. Now a
wave of contraction begins on the great veins and extends toward the auri-
cles, which immediately contract and discharge their blood into the ventri-
cles, somewhat distending their walls. At this moment the ventricular
systole begins, the tricuspid (and mitral) valves are closed, the flow of blood
into the ventricles is checked, and the first heart sound is heard. The con-
traction of the ventricles produces a rapidly rising pressure on the enclosed
CARDIAC CYCLE 169
contents until the pressure exceeds that in the pulmonary artery (and aorta),
the semilunar valves open, and the blood is discharged into the arteries.
The ventricles ordinarily remain contracted for a brief moment after their
contents are emptied.
The ventricular diastole begins next and with the initial relaxation, and
the first slight fall of the intraventricular pressure below that of the aorta,
the semilunar valves close and the second sound is heard. The relaxation
rapidly proceeds and the intraventricular pressure drops to below atmos-
pheric pressure, the auriculo-ventricular valves fall open, the blood that has
been accumulating in the auricles flows into the ventricles, and the whole
heart is in the state of pause described as the point of beginning.
The duration of the cardiac cycle varies with the heart rate. With a
rate of 75 per minute, the cardiac cycle will take 0.8 of a second. In round
numbers the systole of the auricle takes o.i of a second with a diastole of
0.7 of a second, 0.6 of which is in the pause or rest period. The ventricle
requires about 0.3 of a second for the systole, 0.5 of a second for the dias-
tole, with 0.2 to 0.3 of this for the pause. It is evident that the whole heart
is at rest at the same instant for from o.i to 0.2 of a second.
The relations of the cardiac sounds to the systole and the diastole have
been graphically recorded by Hiirthle, figure 153, page 158, and by Einthoven
and Geluk, figure 154, page 159. The former found that in a heart-beat last-
ing 0.76 of a second the interval of time between the beginning of the first
and second sounds was 0.25 of a second, and that the sounds occur just at the
beginning of the ventricular systole and diastole respectively.
During the cardiac cycle the ventricles are completely closed from the
moment of the beginning of the ventricular systole until the pressure amounts
to a little greater than the pressure in the corresponding arteries, which
takes about 0.2 of a second. From the opening of the semilunar valves
until the closure of those valves, about 0.15 of a second, the ventricular cavity
is in open communication with the arteries. There is, during the diastole,
a second moment of complete closure of the ventricles, from the time of the
closing of the semilunar valves until the ventricular pressure falls below the
auricular pressure which permits the auriculo-ventricular valves to open.
The Force of the Cardiac Action. In estimating the amount of
work done by a machine it is usual to express it in terms of work units. A
convenient work unit for this purpose is the amount of energy required to
lift a unit of weight, i.e., i gram or i kilogram, through a unit of height, i.e.,
i centimeter or i meter, the work required being i gramcentimeter for small
units, and i kilogrammeter for large units, respectively. The average work
done by the heart at each contraction can be readily computed by multi-
plying the weight of blood expelled by the ventricle by the height through
which it would have to be lifted to overcome the resistance to its discharge
from the cavities into the arteries.
170 THE CIRCULATION OF THE BLOOD
The quantity of blood expelled and the pressure of the arteries can only
be estimated for man. But the computations from indirect observations
on other mammals indicate that the quantity of blood discharged from each
ventricle at a single contraction is from 80 to 100 c.c. The pressure of the
aorta, see page 192, is an average of say 150 mm. of mercury, or 200 cm. of
blood. The pressure in the pulmonary artery is much less, say 30 mm. (20
to 40), of mercury or 40 cm. of blood. Collecting these facts we have the
following computation:
The left ventricle
The right ventricle
Blood
Discharged.
90 C.C.
go c.C.
Against
Pressure
Column of
Blood.
200 cm.
40 cm.
Work in
Gramcenti-
meters.
18,000
•? 600
Total 90 c.c. 240 cm. 21,600
This computation shows that each heart- beat expends 21,600 gramcenti-
meters (21.6 grammeters) of work. The amount of energy developed in the
contractions of the auricles may be ignored in this calculation, which is at
best only of relative value. Calculations based on the determinations of
Vierordt, also other earlier determinations, give much higher figures than
are presented here.
The Properties of the Heart Muscle. It is evident that if we are
to arrive at any adequate explanation of the action of the heart, one of the
first questions that must be considered is, what are the fundamental properties
of heart muscle, as such?
It has already been shown, page 61, that the muscular fibers of the
heart differ in structure from skeletal muscle fibers on the one hand, and
from unstriped muscle on the other, occupying an intermediate position
between the two varieties. The heart muscle, however, possesses a property
which is not possessed by skeletal muscle, or by unstriped muscle to such a
degree, namely, the property of contracting rhythmically.
Rhythmicity. The property of rhythmic contraction is shown by the
action of the heart within the body; its systole is followed by its diastole in
regular sequence throughout the life of the individual. The force and fre-
quency of the systole may vary from time to time as occasion requires, but
there is no interruption to the action of the normal heart or any interference
with its rhythmical contractions. Further, in an animal rapidly bled to
death, the heart continues to beat for a time, varying in duration with the
kind of animal experimentally dealt with and depending on whether or not
there is entire absence of blood within the heart chambers. Furthermore,
if the heart of an animal be removed from the body, it still continues, for a
varying time, its alternate systolic and diastolic movements. Thus we see
that the power of rhythmic contraction depends neither upon connection
with the central nervous system nor yet upon the stimulation produced by
THE PROPERTIES OF THR HEART MUSCLE
171
the presence of blood within its chambers. Whether or not rhythmicity is
a property of heart muscle, as such, was conclusively settled by Gaskell and
by numerous later investigators by a very simple process. Gaskell cut thin
FIG. 168.
FIG. 169.
FIG. 168. — The Heart of a Frog (Rana esculentd), from the Front. V, Ventricle; Ad, right
auricle; As. left auricle; B, bulbus arteriosus, dividing into right and left aortae. (Ecker.)
FIG. 169. — The Heart of a Frog (Rana esculentd), from the Back. s. v., Sinus venosus opened;
c. s. s., left vena cava superior; c. s. d., right vena cava superior; c. i., vena cava inferior; v. p.,
vena pulmonales; A. d., right auricle; A. s. left auricle; A. p., opening of communication between
the right auricle and the sinus venosus. X 2^-3. (Ecker.)
strips of the apex of the ventricle of the terrapin, which is free from the nerve
cells, at least nerve ganglia, and found that they contracted rhythmically
for hours. This experiment has become a classic one for the study of the car-
FIG. 170. — Automatic Contractions of Sinus Muscle from the Terrapin's Heart in 0.7 per cent
Sodium Chloride. Time in minutes. (New figure by L. Frazier.)
diac muscular tissue. Strips of cardiac muscle cut from the auricle and
from the contractile walls of the venae cavse, or sinus venosus, of the terra-
pin also contract rhythmically. If the strips of muscle are kept moist with the
same blood or serum, then the rhythm of the sinus is greater than that of the
172
THE CIRCULATION OF THE BLOOD
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Ja
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s«>
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auricle, and that of the auricle greater than that of the ventricle, a difference
that is based on a physiological differentiation of the tissue. The sinus
muscle is also more delicately responsive to stim-
uli than is the ventricular muscle, i.e., it is more
irritable.
Porter has performed the more difficult ex-
periment of isolating a small disc of muscle from
the ventricle of the dog, leaving only the delicate
nutrient artery through which the muscle was
fed with defibrinated blood. This isolated small
piece of ventricle contracted vigorously for many
minutes. We may conclude, then, that the
mammalian heart muscle is also automatically
rhythmic.
Tonicity. Cardiac muscle is characterized by
its maintaining a constant degree of partial con-
traction described as muscle tone, or tonicity.
This property is possessed by all parts of the
heart. In the auricle, however, and especially in
the muscular walls of the sinus and veins, there is
considerable variation in tonicity. Botazzi showed
that in the auricle of the toad the variations of
tone were wave-like and periodic, even though the
auricle were contracting with its ordinary funda-
mental rhythm. Howell has published numerous
experiments showing tone waves in auricular and
sinus muscle of the terrapin, in which muscle there
may or may not be occurring at the same time
the ordinary fundamental rhythmic contractions,
figure 170.
Irritability of Heart Muscle. Mention was
made above of the difference in irritability of heart
muscle chosen from different parts of the heart.
The irritability of the muscle of each part also
varies during the different stages of the contrac-
tion. When a contraction occurs, experiment
shows that the muscle is not irritable to a special
stimulus applied at any time from the beginning
of the contraction until the summit of the con-
traction is reached. This is called the refractory
period. From the summit, through the relaxation
and succeeding pause, the irritability rapidly in-
creases until the beginning of the next contraction.
J8S
*> o
•
3 >»
&$~
•*-, * <0
a|§
Us
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ill
THE PROPERTIES OF THE HEART MUSCLE
173
Considering the automatically contracting muscle, the point in which the
automatic contraction is released, i.e., begins, is the point of maximal irri-
tability. It is the moment when the irritability is so great that the muscular
equilibrium is no longer stable, and the physiological contraction results.
FiG.^72. — Automatic C9ntractions of a Strip of Ventricular Muscle from the Apex of the
Terrapin's Heart contracting in 0.7 percent Sodium Chloride; from -j- to + 0.03 per cent Potassium
Chloride is added to the Sodium Chloride. The rhythm is recovered very slowly when the muscle
isreturnedto o.y-per-cent sodium chloride. Time in minutes (upper) and seconds (lower stroke).
(New figure by Watkins and Elliott.)
The irritability of heart muscle is very sharply influenced by its condition
of nutrition, especially by the inorganic salts present in the blood and lymph,
see page 1 78. The salt content of the blood comprises about 0.7 per cent sodium
FIG. 173. — Automatic Contractions of a Strip of Ventricular Muscle from the Apex of the
Terrapin's Heart, a. Contracting in 0.7 per cent sodium chloride; b, when 0.03 per.cent calcium-
chloride solution is added. Time in minutes. (New figure by L. Frazier.)
chloride, 0.03 per cent potassium chloride, and 0.025 to 0.03 per cent cal-
cium (phosphate probably), as well as traces of other metal bases. The
heart muscle has been shown by numerous investigators to be delicately
174 THE CIRCULATION OF THE BLQOD
responsive to the proportions of these salts in the blood, or in any artificial
solution which may be substituted for blood. If the rhythm is to be taken
as an index of the irritability, then an increase of sodium and calcium salts
increases the irritability (rhythm), while the influence of an increase in potas-
sium is to depress the irritability (rhythm).
Cardiac Contractions Always Maximal. The heart muscle exhibits
another property which distinguishes it from ordinary skeletal muscle, viz., the
way in which it reacts to stimuli. The latter, Chapter XIII, reacts slightly
to a stimulus little above the minimal, and with an increase of the strength
of the stimulus will give contractions of increasing amplitude until the maxi-
mum contraction is reached. In the case of the heart-beats this is not so,
FIG. 174. — Refractory Period in the Ventricular Strip of the Terrapin.
since the minimal stimulus which has any effect is followed by the maximum
contraction; in other words, the weakest effectual stimulus brings out as
great a contraction as the strongest. If a contraction is induced earlier than
it would automatically occur, then the succeeding pause is longer, i.e., there
is a compensatory pause. Also the contraction induced is smaller and the
one following the compensatory pause is proportionately larger. This ob-
servation can easily be demonstrated on the heart strip, see figure 174, or on
the whole ventricle of the frog, which was originally used by Bowditch.
Nerve influence, nutrition, temperature, etc., will of course affect
the extent of the contractions, but under a given set of conditions it is held
that the contractions which occur are maximal for the particular state. This
is more readily understood when taken in connection with the fact that when
a contraction originates in a cardiac cell it is conducted throughout the ex-
tent of all the cells of the muscular mass.
Theories of the Heart-Beat. The cause of the rhythmic power
of the heart as a whole has been the subject of much discussion and experi-
mental observation. Two leading hypotheses have given inspiration to
THEORIES OF THE HEART-BEAT
175
investigators, and now one, now the other theory has attracted followers
as new facts have been discovered. The hypotheses that have been ad-
vanced to explain the heart-beat are known as the neurogenic theory and the
myogenic theory, respectively.
The heart has long been known to have the power of rhythmic contrac-
tions after removal from the body and after all connection with the central
nervous system has been destroyed. The isolated heart, even of man, will
contract with good rhythm when kept at the proper temperature and given
the proper nutritive fluid.
The Neurogenic Theory, The neurogenic theory attributes the remark-
able power of the heart to continue its contractions after removal from the
body, and presumably while in the body, to the presence of the local collec-
tions of nerve cells. The local nervous mechanism in the frog consists of
FIG. 175. — Course of the Nerves in the Auricular Partition, Heart of a Frog, d, Wall of the
dorsal branch; v, ventral branch. (Ecker.)
three chief groups of cells or ganglia. The first group is situated in the
wall of the sinus venosus at the junction of the sinus with the right auricle,
Remak's ganglia; the second group is placed near the junction between
the auricles and ventricles, Bidder's ganglia; and the third in the septum
between the auricles, von Bezold's ganglia. Small ganglia have been de-
scribed for the base of the ventricle, but no ganglia are present in the apical
part of the ventricles, though isolated cells have been found. The nerve-
cells of which these ganglia are composed are generally unipolar, seldom
bipolar. Sometimes two cells are said to exist in the same envelope, con-
stituting the twin cells of Dogiel. The cells are large, and have very large
round nuclei and nucleoli, figure 176. As regards the automatic move-
ments of the heart when removed from the body, our knowledge has been
derived from the study of the hearts of the frog, tortoise, dog, cat, and rabbit.
176
THE CIRCULATION OF THE BL(X)J)
If removed from the body entire, the frog's or terrapin's heart will con-
tinue to contract for many hours and even days, and the contraction has no
apparent difference from the contraction of the heart before removal; it
will take place, as we have mentioned, without the presence of blood or
other fluid within its chambers. Not only is this the case, but the auricles
and ventricle may be cut of! from the sinus, and both parts continue to pul-
sate; and, further, the auricles may be divided from the ventricle, with the
same result. If the heart be divided lengthwise, its parts will continue to
pulsate rhythmically. The ventricle remains comparatively quiet, contrac-
tions occurring at longer intervals, if at all. However, the ventricle remains
irritable so long as bathed in blood, and will contract upon receiving a slight
stimulus; in fact a single stimulus will often call forth a series of contractions
of the ventricle. The frog's ventricle, when its muscular and nervous con-
FIG. 176. — Isolated Nerve Cells from the Frog's Heart. /, Usual form; II, twin cell; C,
capsule; N, nucleus; P, process. (From Ecker.)
nections with the auricle are physiologically severed, as by crushing, will
remain quiet when fed by its own blood, but contracts rhythmically when
fed with physiological salt-solution.
It will be thus seen that the rhythmical movements appear to be more
marked in the parts supplied by the ganglia, that ventricular pieces con-
tract when still connected with the auricles, and that rhythmic contractions
of the ventricles do not readily occur in the ordinary condition when irri-
gated with blood. These are regarded as facts peculiarly in favor of the
neurogenic theory.
The Myogenic Theory. In the myogenic theory the heart's rhythmical
contractions are explained as due to the inherent property of the cardiac
muscle itself. Most convincing facts in support of this theory have been
arrived at by a study of cardiac muscle, as such, and by studies on the
whole heart, particularly by Gaskell's method of blocking. The term
blocking is explained as follows: It will be remembered that under normal
conditions the wave of the contractions in the heart starts at the sinus and
travels down over the auricles to the ventricles, the irritability of the muscle
THEORIES OF THE HEART-BEAT 177
and its power of rhythmic contractions being greatest in the sinus, less in
the auricles, and least in the ventricles. By an arrangement of ligatures
or by a system of clamps, one part of the heart may be more or less isolated
from any other portion. With such a clamp the contraction waves can be
more or less completely interrupted in their passage from the sinus end of
the heart past the clamp toward the ventricular end. If the clamp is com-
plete, so as to interrupt the physiological continuity between the parts, then
any contractions in the apical portion will be entirely independent of those
in the sino-auricular portion. If the blocking is partial only, then the ventric-
ular end of the heart always contracts in unison with the sino-auricular,
although its rate may be as i to i, i to 2, i to 3, etc. In other words, only
every second or every third sino-auricular contraction will be able to pass
the block.
The effects of blocking are due to the interruption of muscle continuity
rather than nerve continuity. This is beautifully demonstrated by an experi-
ment of zigzag cutting of the ventricle in the terrapin, since it cannot be
supposed that any nerves would pass through the ventricular mass by such
a zigzag course. In this experiment the contraction wave passes down
over the muscle and around the end of the cuts until it reaches the apex,
and the apex contracts in sequence with the auricle and base of the ventricle.
If the zigzag cuts are made almost complete so as to reduce to a minimum
the muscular tissue which bridges from one cut to the next, then it happens
that occasional contractions will be unable to pass and the apex contracts
in the ratio of i to 2, or i to 3, etc., as described above. Thus, division of
the muscle has the same effect as partial clamping in the same position.
It was thought for a long time that in the mammal there is no mus-
cular continuity between the auricles and ventricles to conduct the contrac-
tion wave, but a well-marked muscular bridge, the bundle of His, has been
shown to pass between these two parts. This fact has proven to be of strongest
support to the myogenic theory. Erlanger has recently shown, by an in-
genious device for partially clamping this muscular band, that even the
mammalian ventricle exhibits the phenomenon of heart block. In his experi-
ments the ventricle contracts in unison with every auricular contraction, or
only every second or every third, according to the degree of blocking.
It was shown long ago that the isolated apex of the ventricle of the frog
remains quiet when filled with blood, but readily gives good rhythmic con-
tractions in physiological saline and other artificial solutions. The inac-
tivity in blood is not necessarily, therefore, due to nervous isolation from
the ganglionated parts of the heart. Contractions occur in the small bits
of ventricular muscle as isolated by Gaskell, and these may continue for
hours. It is well known also that the embryonic heart contracts rhythmically
before nerve cells have reached the organ.
The phenomena of heart block, the contractions of the ventricular apex
12
178 THE CIRCULATION OF THE BLOOD
when physiologically isolated from the parts of the heart which contain the
ganglia, the behavior of isolated strips of the heart, especially of the ventricle,
and the rhythm of the embryonic heart are all held to be in favor of the myo-
genic theory.
Automaticity of the Heart. Whether one adopts the neurogenic
or myogenic theory of the heart's beat, he has still to explain the origin of
the heart's rhythm. In the former case one must look to the nervous
apparatus for the origin of the rhythm; in the latter case, the muscular ap-
paratus, a fact to which Brown-Sequard long ago called attention. In the
former view the problem is to explain not only the periodic origin of the
nerve discharges from local cardiac ganglia, but also to explain the orderly
discharge of nerve impulses which maintains the proper sequence between
sinus, auricle, and ventricle.
To perhaps the majority of physiologists the facts are best explained
by the myogenic theory. The origin of the rhythm is here supposed to be
due to the automatic property of the muscle itself. The sequence is ex-
plained on the observed facts, first, that muscular contraction in cardiac
muscle is conducted throughout the continuity of the mass, and second,
the most highly rhythmic part of the muscular tissue of the heart, the sinus,
sets the rhythm for the entire heart.
The function of the nervous system, by this view, is not to originate the
rhythm, but to regulate it, the detail of which will be discussed below.
Relation of Rhythm to Nutrition. The whole heart, like the
muscular parts of which it is composed, responds delicately to its condition
of nutrition. In the frog's and turtle's hearts the muscular fibers are brought
in intimate contact with the blood contained within its cavities. In the
mammalian heart, on the other hand, a distinct system of vessels, the coronary
vessels and the vessels of Thebesius, supply blood to the organ. If the heart
is supplied with nutrient fluid similar to its normal blood, and with proper
aeration to insure plenty of oxygen, it contracts with a strong rhythm for
many hours. This rhythm, however, responds quickly to changes in the
composition of the nutrient fluid. An abundant supply of oxygen is absolutely
necessary to the maintenance of rhythm in the mammalian heart, though the
heart, especially a cold-blooded heart, will contract for a time in an atmos-
phere of hydrogen. No doubt the organic constituents of blood are very
essential to the prolonged maintenance of rhythm in the heart, but the heart
is not dependent on these ingredients for its immediate reactions. The in-
organic salts seem to be peculiarly closely related to the development and
character of the cardiac rhythm, figures 172 and 173. Both the cold-
blooded heart and the mammalian heart respond very quickly to the influ-
ence of these salts. The details of this influence have been discussed on
page 173. It is somewhat surprising, however, that the highly organized
mammalian heart will contract rhythmically for hours on purely inorganic
INFLUENCE OF THE CENTRAL NERVOUS SYSTEM 179
nutrient fluid, provided only that the oxygen be supplied in sufficient
quantity and under high enough tension.
THE REGULATIVE INFLUENCE OF THE CENTRAL NERVOUS
SYSTEM ON THE HEART.
The heart is capable of automatic rhythmic movement, yet while in the
body its beats are under the constant control of the central nervous system.
The influence which is exerted by the central nervous system is of two kinds:
first, in the direction of slowing or inhibiting the beats, and, second, in the
direction of accelerating or augmenting the beats. The influence of the
first kind is brought to bear upon the heart through the fibers of the pneumo-
gastric or vagus nerves, and that of the second kind through the sympathetic
nerves.
The Inhibitory Nerves. It has long been known, indeed ever
since the experiments of the Weber brothers in 1845, tnat stimulation of one
or both vagi produces slowing of the rhythm of the heart. It has since been
FIG. 177. — Effect on the Heart Rate and on the Arterial Blood Pressure of Stimulating the
Right Vagus of the Dog. Stimulus applied at the mark " on " and removed at " off." Pressure in
millimeters of mercury shown by the scale to the left. Time in seconds. (New figure by Hill and
Chilton.)
shown, in all of the higher vertebrate animals experimented with, that this
is the normal reaction to vagus stimulation. Moreover, . a section of one
vagus, or at any rate of both vagi, produces acceleration of the pulse; and
stimulation of the distal or peripheral end of the divided nerve normally
produces slowing or stopping of the heart's beats.
180 THE CIRCULATION OF THE BLOOD
It appears that any kind of stimulus, either chemical, mechanical, elec-
trical, or thermal, produces the same effect, but that of these the most potent
is a rapidly interrupted induction current. A certain amount of confusion
has arisen as to the effects of vagus stimulation in consequence of the fact
that fibers of the sympathetic nerve run within the trunk of the vagus nerves
of some animals.
The result of stimulation also depends, to some extent, upon the exact
position of the application, of the stimulus. Speaking generally, however,
FIG. 178. — Tracing Showing Actions of the Vagus on the Heart of the Frog. Aur, Auricular;
vent, ventricular tracing. The part between perpendicular lines indicates a period of vagus stimu-
lation. C. 8 indicates that the secondary coil was 8 cm. from the primary. The part of tracing
to the left shows the regular contractions of moderate height before stimulation. During stimu-
lation, and for some time after, the beats of auricle and ventricle are arrested. After they com-
mence again they are single at first, but soon acquire a much greater amplitude than before the
application of the stimulus. (After Gaskell.)
excitation of any part of the trunk of the vagus produces inhibition, the
stimulus being particularly potent if applied to the points where the nerves
enter the substance of the heart at the situation of the sinus ganglia. The
stimulus may be applied to either vagus with like effect.
The effect of the stimulus of the vagus is twofold — to slow the rate, or
even to bring the heart to a complete standstill, and to produce a decrease
FIG. 179. — Tracing Showing Diminished Amplitude and Slowing of the Pulsations of the Auricle
and Ventricle without Complete Stoppage during Stimulation of the Vagus. (After Gaskell.)
in the amplitude. The slowing does not take place until after the lapse of
a short latent period during which one or more contractions may occur.
The stoppage may be due either to prolongation of the diastole or to diminu-
tion of the systole. Vagus stimulation inhibits the spontaneous beats of
the heart only, it does not entirely suppress the irritability of the heart-muscle,
THE INHIBITORY NERVES
181
since mechanical stimulation may bring out a beat during the pause caused
by vagus stimulation. The inhibition of the beats varies in duration accord-
ing to the strength of the stimulus and the animal stimulated. The heart
of the terrapin can be completely inhibited for hours with a strong stimulus.
The heart of a dog escapes from inhibition in a few seconds. When the
beats reappear, the first few are usually feeble, and may be auricular only;
after a time the contractions become more and more strong, and very soon
exceed both in amplitude and frequency those which occurred before the
application of the stimulus. This phenomenon is shown in figure 178,
which illustrates the action of the vagus on the frog's heart.
The inhibitory fibers have their origin in nerve cells in the motor nucleus
of the vagus and of the glosso-pharyngeal located in the floor of the fourth
ventricle. These cells have not been exactly identified, but the center is
FIG. 1 80. — Arterial Blood Pressure of the Dog, Showing the Effect on the Heart Rate of Cutting
both Vagus Nerves as marked. The scale to the left shows the pressure in millimeters of mercury.
Time in seconds. The momentary inhibition just before the nerves were cut is probably due to
mechanical stimulation of the nerves. (New figure by Hill and Chilton.)
called the cardio-inhibitory center. The center is a bilateral one and the
fibers from it pass into the great vagus trunk to be distributed to the heart
through superior and inferior cardiac branches which help to form the cardiac
plexus. Within the heart the inhibitory fibers form synapses with cells whose
axones reach the cardiac muscle cells. The cardiac-inhibitory center is in
constant tonic activity, and the tonic influence is eliminated when both nerves
are cut, figure 180.
The center is also influenced by afferent impulses which may reach it
from the heart itself, by the depressor nerve, or from other parts of the body.
These reflex stimulations of the heart through the vagus center are constantly
occurring during our daily life and are the most potent factor in the coordi-
nations going on between the heart and the rest of the body.
Rhythmical alterations of the heart rate occur in association with the
effects of the mechanical variations of pressure of the thorax on the heart
and blood-vessels. Apparently the cardio-inhibitory center is stimulated
182
THE CIRCULATION OF THE BLOOD
during the fall of blood pressure. The activity of the center produces a
slower rate of the heart during expiration, shown in figure 241. This vari-
ation in heart rate disappears when the vagi are cut off from the center.
FIG. 181. — Diagrammatic Representation of the Origin and Course of the Cardiac Nerves in
the Dog. Vag. Syn, Vago-sympathetic nerve; D1, D6, first to fifth dorsal spinal nerves. In-
hibitory fibers in red, accelerators in black. (Modified from Moret.)
The Accelerator Nerves. The influence of the accelerator nerves
reaching the heart through the sympathetic is the reverse of that of the vagus.
Stimulation of the sympathetic, even of one side, produces acceleration of
the rate of the heart-beats, and, according to certain observers, section of the
nerve produces slowing. The acceleration produced by stimulation of the
sympathetic fibers is accompanied by increased force, and so the action of
the nerve is more properly termed augmentor. The sympathetic differs
from the vagus in several particulars other than the augmentation which it
produces; first, the stimulus required to produce any effect must be more
THE ACCELERATOR NERVES 183
powerful than is the case with the vagus stimulation; second, a longer time
elapses before the effect is manifest; and third, the augmentation is followed
by exhaustion, the beats being after a time feeble and less frequent. The
stimulation of the vago-sympathetic in the frog, which usually produces
inhibition, will occasionally produce acceleration, especially if the heart is
beating feebly at the time of the stimulation.
The fibers of the sympathetic system, which influence the heart-beat in
the frog, leave the spinal cord by the anterior root of the third spinal nerve.
They pass by the ramus communicans to the third sympathetic ganglion,
thence to the second ganglion, the annulus of Vieussens (around the
subclavian artery), through the first ganglion, and along the main trunk
of the sympathetic to near the exit of the vagus from the cranium. There
the two nerves join and run down to the heart within a common sheath,
forming the vago-sympathetic trunk.
In the dog the augmentor fibers leave the cord by the anterior roots of
the second and third dorsal nerves, and possibly also by the first, fourth,
and fifth dorsal nerves. They pass by the rami communicantes to the gan-
glion stellatum, or first thoracic ganglion, around the annulus of Vieussens
to the inferior cervical ganglion of the sympathetic. Fibers from the annulus
or from the inferior cervical ganglion proceed to the heart, figure 181. The
course of the augmentor fibers in the spinal cord is not so well known except
that they originate in an augmentor center in the medulla. The circulation
of venous blood appears to stimulate the augmentor center, and of highly
oxygenated blood the inhibitory center.
The accelerator center, like the inhibitory, is in constant tonic activity;
and the cardiac acceleration on cutting the vagi, shown in figure 180, is in
part to be ascribed to this tone. When both nerves are stimulated together,
the resulting rate is the algebraic sum of the opposed influences, according
to Hunt. The accelerator center is influenced by afferent impulses arising
throughout the body, and these reflexes contribute to the general coordina-
tion of the chest with the activities of the body.
In addition to direct and reflex stimulation, impulses passing down from
the cerebrum may have a similar effect.
Other Influences Which Affect the Heart. A great variety of spe-
cial conditions influence the heart's action in the normal body, conditions
that are not discussed directly under any of the categories treated above.
Of these may be mentioned the coronary circulation, temperature, mechanical
tension, age, sex, etc.
The Coronary Circulation. The contractions of the heart cannot long
be maintained without a due supply of blood or other nutrient fluid. The
nutrient fluid for the heart of man and the mammals is supplied from the
coronary arteries and the vessels of Thebesius. The coronary arteries arise
from the base of the aorta, where they receive the benefit of the highest arterial
184 THE CIRCULATION OF THE BLOOD
pressure. The coronary arteries are terminal arteries; that is, they do not
permit the establishment of a collateral circulation when one of their branches
is blocked. If the block be complete, that portion of the heart wall supplied
by the branch dies. The immediate effect of the closure of a large coronary
branch, in the dog, may be occasional and transient irregularity, or arrest
of the ventricular contractions preceded by irregularities in the force of the
contractions and a diminution in the amount of work performed. The
force, rather than the rate, of the ventricular contractions is closely dependent
upon the blood supply to the coronary arteries. Porter and others have
shown that the pressure in the coronary vessels follows closely the pressure
in the aorta and that there is not, as formerly claimed, a closure of these
vessels by the pressure of the systole of the ventricle.
The vessels of Thebesius, which have been demonstrated to open both
into the auricular and ventricular cavities, must now be looked upon, ac-
cording to the investigations of Pratt, as an important source of cardiac
nutrition. Blood may pass through them by way of connecting branches
to the coronary arteries and veins. Pratt succeeded in maintaining cardiac
contractions for several hours when the only source of nutrition was from
these vessels. This source of nutrition may account for the survival of
hearts for years where pronounced arterio-sclerosis of the coronary arteries
exists.
Alteration of Temperature. The effect of cold is to slow the rate of the
heart-beat, and if the heart of a frog be cooled down to o° C. it will stop beat-
ing. It is said that the frog's heart may be frozen, and when thawed will
renew its spontaneous beats. The effect of heat is to quicken and shorten
the heart-beats, but at a moderate temperature, 20° C., the contractions are
increased in force.
The isolated mammalian heart is influenced by temperature variations
in much the same way as that of the frog. It will contract slowly in a low
temperature and rapidly in a temperature higher than that normal to the
body. The very rapid heart in some high fevers is in part due to the in-
crease in temperatures which affects the heart directly.
Mechanical Tension. The mechanical factors produced by the heart
beat are so prominent that it would be surprising indeed if there were no
reaction of these mechanical conditions on the heart itself. The isolated
cardiac muscle responds very quickly to variations in tension. Beginning
with a low tension the activity of heart muscle is increased up to a certain
optimum tension, after which further increase is unfavorable to the develop-
ment of automatic rhythm. A quite strong stretching will paralyze the muscle.
Tension on the whole heart influences its activity, not only through the
effects on the muscle, but indirectly through the nervous mechanism. High
tension, such as contracting against a high aortic pressure, stimulates sensory
nerves of the heart which, acting through the depressor nerve on the inhibitory
OTHER INFLUENCES WHICH AFFECT THE HEART 185
center, produce reflex slowing of the heart, as well as reflex vaso-dilatation,
both of which relieve the high tension. This nerve reaction takes place with
a tension which still mechanically stimulates the cardiac-muscle substance,
and the inhibitory effects must therefore first overcome the direct stimulating
effect of the tension on the muscle fibers.
Age, Sex, etc. The average heart rate for the normal adult man is 72
times a minute, but this rate will vary much in different individuals accord-
ing to the age, sex, size, and personal equation. The frequency of the heart's
action gradually diminishes from the commencement to near the end of life,
but is said to increase again somewhat in extreme old age, thus:
Before birth the average number of pulsations per minute is 150
Just after birth 130 to 140
During the first year 115 to 130
During the second year 100 to 1 15
During the third year 90 to 100
About the seventh year 85 to 90
About the fourteenth year 80 to 85
In adult age 70 to 80
In old age 60 to 70
In decrepitude 65 to 75
The heart rate is greater in woman than in man. It is also greater in
small than in large individuals. The rate varies from the type in certain
individuals where no cause can be assigned other than personal equation.
Poisons and Other Chemical Substances. A large number of chemical
substances have a distinct effect upon the cardiac contractions. Of these
the most important are atropine, muscarine, digitalis, barium, etc.
FIG. 182. — The Effect of an Intravenous Injection of Atropine on the Dog's Heart Rate Meas-
ured by Means of a Blood-Pressure Curve. (New figure by Doolev.)
Atropine produces considerable augmentation of the heart-rate, and
when acting upon the heart prevents inhibition by vagus stimulation. Its
effects are produced by poisoning the nerve endings of the vagus within
186 THE CIRCULATION OF THE BLOOD
the heart. With these endings poisoned, stimuli arising in the inhibitory
center of the medulla (tonic activity), or artifically applied to the vagus,
cannot reach the heart muscle, and inhibition is impossible.
Muscarine, which is obtained from various species of poisonous fungi,
produces marked slowing of the heart-beats, and, in larger doses, stoppage
of the heart. It produces an effect similar to that of prolonged vagus stimu-
lation. The effect can be removed by the action of atropine, hence is
supposed to stimulate the nerve endings of the vagus.
Digitalis slows the heart by stimulating the vagi at their origin in the
inhibitory center in the medulla. The heart muscle itself is also rendered
more excitable.
Veratrine and aconitine have a somewhat similar effect.
THE CIRCULATION THROUGH THE BLOOD-VESSELS.
Blood Pressure. The subject of blood pressure has been already
incidentally mentioned more than once in the preceding pages ; the time has
now arrived for it to receive more detailed consideration.
That the blood exercises pressure upon the walls of the vessels containing
it is due to the following facts:
The heart at each contraction forcibly injects a considerable amount of
blood, 80 to 100 c.c., suddenly and quickly into the arteries.
The arteries are highly distensible and stretch to accommodate the extra
amount of blood forced into them. The arteries are already full of blood
at the commencement of the ventricular systole, since there is not sufficient
time between the heart-beats for the blood to pass into the veins.
There is a distinct resistance interposed to the passage of the blood from
the arteries into the veins by the enormous number of minute vessels, small
arteries (arterioles) and capillaries, into which the main artery has been
ultimately broken up. The sectional area of the capillaries is several hundred
times that of the aorta, and the friction generated by the passage of the blood
through these minute channels opposes a considerable hindrance or resistance
in its course. The resistance thus set up is called peripheral resistance.
The friction is greater in the arterioles, where the current is comparatively
rapid, than in the capillaries, where it is slow.
The interaction of these factors — heart-beat, elastic vessels, and periph-
eral resistance — is sufficient to maintain a continuous flow of blood through
the entire circulatory system. It is the interrelation of these factors which
maintains an even and steady flow through the capillaries and past the tissues,
where it is desirable that the conditions of blood flow should be most con-
stant. In fact, we shall find that it is through the interaction of this same
group of factors, together with the possibility of variations through the regu-
lation of their nerve-motor mechanisms, that we have the great variations
ARTERIAL BLOOD PRESSURE 187
and adjustments of blood pressure, speed of flow, volume of flow, and the
regulation of volume in particular parts of the body.
Arterial Blood Pressure. That the blood exerts considerable pres-
sure upon the arterial walls in keeping them in a stretched or distended
condition may be readily shown by puncturing any artery; the blood is
instantly projected with great force through the opening, and the jet rises to
a considerable height, the exact level of which varies with the size of the artery
experimented upon. If a large artery be punctured the blood may be pro-
jected upward for several feet, whereas if it is a small artery the jet does not
rise so high. Another characteristic of the jet of blood from a cut artery,
particularly well marked if the vessel be a large one and near the heart, is the
intermittent character of the outflow. If the artery be cut across, the jet
issues with force, chiefly from the central end. If there is considerable
anastomosis of vessels in the neighborhood the jet from the peripheral end
may be as forcible and as intermittent as that from the central end. The
intermittent flow in the arteries which is due to the action of the heart, and
which represents the systolic and diastolic alterations of blood pressure,
may be felt if the finger be placed upon a sufficiently superficial artery. The
finger is apparently raised and lowered by the intermittent distention of the
vessel occurring at each heart-beat. This intermittent distention of the
artery is what is known as the Pulse, to the further consideration of which
we shall presently return, but we may say here that in the normal condition
the pulse is a characteristic of the arterial, and is absent from the venous, flow.
At the same time it must be recollected that in the veins also the blood
exercises a pressure on its containing vessel which is small when compared
with the arterial pressure. As might be expected, therefore, the blood is
not expelled with so much force if a vein be punctured or cut. The flow
from the cut vein is continuous and not intermittent, and the greater amount
of blood comes from the peripheral and not from the central end, as is the
case when an artery is severed.
Methods of Measuring Arterial Blood Pressure. The pressure in
an artery may be measured by cutting the vessel and introducing into it a
glass tube which has a tall vertical limb. A column of blood will rise in the
tube at once to the height that can be supported by the pressure in that par-
ticular vessel. If the vessel be an artery, the blood will rise several feet,
according to the distance of the vessel from the heart, and when it has reached
its highest point it will be seen to oscillate with the heart-beats. This ex-
periment shows that the pressure which the blood exerts upon the walls of
the contained artery equals the pressure of a column of blood of a certain
height. In the case of the rabbit's carotid it is equal to 90 to 120 cm. of blood,
or rather more than the same height of water. In the case of the vein, if a
similar experiment be performed, blood will rise in the tube only for 8 or
10 cm. or less.
188 THE CIRCULATION OF THE BLOOD
The usual method of estimating the amount of blood pressure differs
somewhat from the foregoing simple experiment. Instead of a simple straight
tube of glass inserted into the vessel, a U-shaped tube containing mercury,
the mercurial manometer, is employed. The artery is connected with the
manometer by means of a small cannula which is inserted into the vessel,
an arrangement being made whereby the cannula, tubes, etc., are filled with
a saturated saline solution to prevent the clotting of blood when it is allowed
FIG. 183. — Diagram of Ludwig's Kymograph and Mercurial Manometer. A, Revolving cylin-
der, worked by a clock-work arrangement contained in the box (B), the speed being regwlated by a
fan above the box; cylinder supported by an upright (b), and capable of being raised or lowered
by a screw (a), by a handle attached to it; D, C, E, represent a mercurial manometer, a somewhat
different form of which is shown in the next figure.
to pass from the artery into the apparatus. The loss of blood is prevented
during the preparation of the details of the experiment by a clamp or bull-
dog forceps. The free end of the U-tube of mercury contains a very fine
glass or metal rod with a bulb which floats upon the surface of the mercury
and oscillates with the oscillations of the mercury. As soon as there is free
communication between the artery and the tube of mercury, the blood rushes
out and pushes before it the column of mercury. The mercury will there-
fore rise in the free limb of the tube, and will continue to do so until a point
is reached which corresponds to the mean pressure of the blood-vessel used.
The blood pressure is thus communicated to one limb of the mercurial column;
METHODS OF MEASURING ARTERIAL BLOOD PRESSURE 189
and the depth to which the latter sinks, added to the height to which it rises
in the other limb, the weight of the saline solution being substracted, will
give the height of the mercurial column which the blood pressure balances.
For the estimation of the amount of blood pressure at any given moment,
no further apparatus than this is necessary; but for accurately noting the
variations of pressure in the arterial system, as well as its absolute amount,
the instrument is usually combined with a recording apparatus, called a
kymograph, figure 183, and permanent records are made of the observations.
The recording apparatus consists of a revolving cylinder, figure 183, A,
which is moved by clock-work, and the speed of which is capable of regula-
tion. The cylinder is covered with glazed paper, blackened in the flame
of a lamp, and the mercurial manometer is so fixed, figure 183, D, that its
FIG. 184. — Ludwig's Mercury Manometer. The manometer is shown in figure 183, D, C, E.
The mercury which partially fills the tube supports a float in the form of a piston, nearly filling the
tube; a wire is fixed to the float, and the writing style or pen is guided by passing through the brass
cap of the manometer tube; the pressure is communicated to the mercury by means of a flexible
metal tube filled with fluid.
float, provided with a style, writes on the cylinder as it revolves. There are
many ways in which the mercurial manometer may be varied; in figure 184
is seen a form which is known as Ludwig's. In order to obviate the necessity
of a large quantity of blood entering the tube of the apparatus, it is usual to
have some arrangement by means of which the mercury may be made to
rise in the tube of the manometer to the level corresponding to approxi-
mately the mean pressure of the artery experimented with, so that the writing
style simply records the variations of the blood pressure above and below
the mean pressure. This is done by causing the saline solution, generally
a saturated solution of sodium carbonate or a 10 per cent magnesium sul-
190
THE CIRCULATION OF THE BLOOD
phate, to fill the apparatus from a bottle suspended at a height about that
of the pressure to be measured, and capable of being raised or lowered as
required for the purpose. The cannula inserted and tied into the artery
may be of several different kinds. A glass T-tube with the end drawn out
FIG. 185. — Arterial Cannula. T-form for convenience in washing out clots.
and cut so that it is oblique, and provided with a slightly constricted neck
to prevent its coming out of the artery easily, is a very convenient form,
figure 185. Of the two free ends of the T-cannula one is connected with the
manometer, the other with the pressure bottle. The peripheral end of the
to
*-*-*
FIG. 186. — Tracing of Normal Arterial Pressure in the Dog, Obtained with the Mercurial Man-
ometer. The smaller undulations correspond with the heart-beats; the larger curves with the re-
spiratory movements. Pressure is in millimeters of mercury as shown by the scale to the left.
Time in seconds. (New figure by March and Nugent.)
cut artery is tied to obviate the escape of blood. By this means, the pressure
communicated to the column of mercury is the forward, and not the lateral,
pressure of blood, but there is very little difference.
As soon as the experiment is begun, the writing float is seen to oscillate
METHODS OF MEASURING ARTERIAL BLOOD PRESSURE 191
in a regular manner, and a curve of blood pressure is traced upon the smoked
paper by the style (or, if a continuous roll of unsmoked paper be used, the
trace is made by an inked pen) when a figure similar to figure 186 will be
obtained. This indicates two main variations of the blood pressure. The
smaller excursions of the lever correspond with the systole and diastole of the
heart, and the larger curves correspond with the respirations, being called
the respiratory undulations of blood pressure, to which attention will be directed
in the next chapter. Of course, the undulations spoken of are seen only in
records of arterial blood pressure. They are more clearly marked in the ar-
teries nearer the heart than in those more remote. The amount of the
pressure in the smaller arteries as well as the indication of the systolic rise
of pressure is, comparatively speaking, small.
In order to record the details of the undulations of arterial pressure, it is
better for some purposes to use the Hiirthle membrane manometer than the
mercurial manometer. Two views of this instrument are shown in figure 166.
FIG. 187.— Tracing of Normal Arterial Pressure Taken from the Rabbit with a Hiirthle Manom-
eter. The horizontal lines show zero pressure. Time in seconds. (Dreyer.)
The instrument consists of a hollow tube and cup covered with rubber sheet
against which a disc supported by a metal spring is adjusted. The apparatus
is filled with fluid, the interior of which is connected with the artery by means
of a metal tube and cannula. The pressure transmitted to the apparatus
tends to stretch the rubber and bend the spring, and the movement thus
produced is communicated by means of a lever to a writing style and so to
a recording apparatus. This instrument obviates the errors which might
be caused by the inertia of the mercury in the mercurial manometer; it also
shows in more detail the variations of the blood pressure in the vessel during
and after each individual beat of the heart.
As regards the actual amount of blood pressure, from observations which
have been made by means of the mercurial manometer, it has been found
192
THE CIRCULATION OF THE BLOOD
that the pressure of blood in the carotid of a rabbit is capable of supporting
a column of 90 to 120 mm. of mercury; in the dog 100 to 175 mm.; in the
horse 152 to 200 mm.; and in man the pressure is estimated to be about the
same as in the horse. To measure the absolute amount of this pressure
in any artery multiply the area of its transverse section by the height
of the column of mercury which is already known to be* supported
by the blood pressure in any part of the arterial system. The weight of a
column of mercury thus found will represent the absolute pressure of the
blood. Calculated in this way, the blood pressure in the human aorta is
equal to 1.93 kilogrammeters; that in the aorta of the horse being 5.2 kilo-
grammeters; and that in the radial artery at the human wrist only 0.08
kilogrammeter. Supposing the muscular power of the right ventricle to be
only one-fourth that of the left, the blood pressure in the pulmonary artery
will be only 0.5 kilogrammeter. The amounts above stated represent the
arterial tension at the time of the ventricular contraction.
The arterial pressure is greatest at the beginning of the aorta, and de-
creases toward the capillaries. It is greatest in the arteries at the period of
the ventricular systole, and least during the diastole. The blood pressure
gradually lessens as we proceed from the arteries near the heart to those more
remote, and again from these to the capillaries, as it does, also, from the
capillaries along the veins to the right auricle.
Arterial Blood Pressure Measurements in Man. A number of
instruments have been devised for estimating blood pressure in man for
FIG. 1 88.— Riva-Rocci Apparatus (schematic) for Determining Blood Pressure in Man.
PRESSURE MEASUREMENTS IN MAN
193
clinical purposes. Some of these, though excellent in principle, are too com-
plicated for general use. The first simple and approximately accurate form
of apparatus was that devised by Riva-Rocci in 1896. This has been modi-
FIG. 189. — Erlanger's Sphygmomanometer, Shown with the Rubber Bag Attached to the Arm.
The picture is taken at the end of an experiment after the pressure in the instrument is run up again
to above the systolic pressure. The upper part of the cylinder shows a sphygmogram taken with
the instrument. (Experiment and photo by Hill and Watkins.)
fied and improved in minor points since, but the principles of the original
instrument remain practically the same.
In brief, the apparatus, figure 188, consists of an elastic tube ending in
a rubber bag which can be adjusted about the arm or forearm, and a mercury
manometer connected with this tube and also with some form of air pump
used for inflating the tube about the arm and thus exerting pressure upon
its blood-vessels. The elastic tube is covered by some inelastic tissue, usually
a leather cuff, in order that the inflation of the bag may cause the full increase
of pressure to be exerted upon the encased arm. By inflating the bag until
the pulse at the wrist just disappears, and reading the height of the column
of mercury in the manometer, the maximum or systolic pressure is obtained
13
194 THE CIRCULATION OF THE BLOOD
in millimeters of mercury. If now the pressure on the arm is reduced until
the widest oscillations of the mercury column are obtained, the lowest position
of the mercury meniscus represents the diastolic pressure.
The apparatus depends on the principle that an external pressure just
equal to the maximal pressure within an artery will hold the vessel in the
collapsed condition, a fact that has been proven for vessels that are exposed.
An external pressure that will just equal the minimal or diastolic pressure
will cause a complete collapse of a vessel during diastole and will allow a
complete expansion of an artery to ib maximal limits during the systolic
period of pressure. In other words, the mercury of the manometer will
oscillate to its maximal. If the pressure is reduced to a still lower point, it
will not be sufficient to compress the artery completely, and the mercury
oscillations will again become smaller. In applying the instrument to the
FIG. 190. — Tracing taken with Erlanger's Sphygmomanometer. The figures indicate pres-
sure in millimeters of mercury. Systolic pressure, 160; diastolic pressure, 120. (New figure by Hill.)
brachial artery, one must, of course, deal with a vessel deeply buried in mus-
cular and other tissues. These latter tissues probably consume a certain
small percentage of the pressure, an error which may be ignored for all com-
parative purposes.
Erlanger has perfected a form of sphygmomanometer which contains a
very ingenious and compactly arranged recording device, figure 189. This
instrument has a mercury manometer from which the pressures are read off
directly. On a side limb of the manometer there is a rubber bag enclosed
in a glass bell. The cavity of the bell outside of the rubber bag is connected
with a recording tambour, the entire apparatus being fully supplied with
the necessary valves and adjusting devices which make it mechanically very
perfect. The instrument is mounted on a stand with a small clock and
recording cylinder adapting it to convenient clinical use.
The brachial arterial pressure of man when taken by this form of appara-
tus has been found to vary greatly, but Erlanger gives no mm. of mercury
as the average of observations on young adults in the determination of the
VENOUS BLOOD PRESSURE AND CAPILLARY PRESSURE 195
systolic pressure, i.e., the maximal arterial pressure. He gives for the dias-
tolic pressure 40 to 45 mm. of mercury below the systolic pressure. Other
observers using the same method find a somewhat higher average pressure,
see figure 190, which represents a fair type of observation.
The Venous Blood Pressure and Capillary Pressure. The blood
pressure in the veins is nowhere very great, but is greatest in the small veins,
while in the large veins near the heart the pressure may become negative, or,
in other words, when a vein is put in connection with a mercurial manom-
eter the mercury may fall in the arm farthest away from the vein and will
rise in the arm nearest the vein, the action being that of suction rather than
pressure. In the large veins of the neck the tendency to suck in air is es-
pecially marked, and is the cause of death in some accidents or operations in
that region. The amount of pressure in the brachial vein is said to support
9 mm. of mercury, whereas the pressure in the veins of the neck may fall to
a negative pressure of from — 3 to — 8 mm.
The variations of venous pressure during systole and diastole of the
heart are very slight, and a distinct pulse is never seen in veins except under
extraordinary circumstances. In certain forms of cardiac valvular insuffi-
ciency there may be considerable regurgitation of the blood with a strong
venous pulse.
Careful observations upon the web of the frog's foot, the tongue and mesen-
tery of the frog, the tails of newts and small fishes, and upon the skin of the
finger behind the nail (von Kries) ; as well as estimations of the amount of
pressure required to empty the vessels of blood under various conditions,
all indicate that the capillary blood pressure is subject to very great varia-
tions. Apparently the variations follow the variations of pressure in the
arteries, though the measurements of the capillary pressure of the skin
in man indicate that it is occasionally markedly influenced by the venous
pressure variations.
The pulse in the arterioles, capillaries, and venules becomes more and
more evident as the extravascular pressure is increased. The pressure in
the web of the frog's foot has been found to be equal to about 14 to 20 mm. of
mercury; in other capillary regions the pressure is found to be equal to from
one-fifth to one -half of the ordinary arterial pressure.
General Variations in Blood Pressure. The arterial blood pressure
may be made to vary by alterations in either of the chief factors upon which
the pressure in the vessels depends, but primarily by the cardiac contrac-
tions and the peripheral resistance. Thus, increase of blood pressure may
be brought about by either, i, a more frequent or more forcible action of
the heart, or, 2, by an increase of the peripheral resistance. On the other
hand, diminution of the blood pressure may be produced, either by 0, a
diminished force or frequency of the contractions of the heart, or by b, a
diminished peripheral resistance. These different factors, however, although
196
THE CIRCULATION OF THE BLOOD
varying constantly, are so combined that the general arterial pressure re-
mains fairly constant. For example, the heart may, by increased force or
frequency of its contractions, distinctly increase the blood pressure, but this
increased action is almost certainly followed by diminished peripheral re-
sistance, and thus the two altered conditions may balance, with the result
of bringing back the blood pressure to what it was before the heart began
to beat more rapidly or more forcibly.
It will be clearly seen that the circulation of the blood within the blood
vessels must depend upon the diminution of the pressure from the heart
to the capillaries, and from the capillaries to the veins, the blood flowing in
FIG. 191. — Schema Showing the Relation between Blood Pressure, Velocity of Flow, and
Vascular Area, in the Arteries, Capillaries, and Veins. Ordinates represent height of pressure and
speed of flow. The abscissa, b-c, represents zero pressure and speed. Space between lines a-b and
d-e represents arterial system ; between d-e and f-g, capillary system, and between f-g and /»-*', the
venous system. Line A-B equals pressure; line C-D, speed of flow; and line E-F, vascular area.
(Modified from Gad.)
the direction of least resistance. We shall presently see further that the
local flow also depends upon the relations between the heart's action and
the peripheral resistance both general and local.
The Arterial Flow. The character of the flow of blood through
the arterial system depends to a very considerable extent upon the structure
of the arterial walls, and particularly upon the elastic tissue which is so highly
developed in them.
The elastic tissue of the arteries, first of all, guards them from the sud-
denly exerted pressure to which they are subjected at each contraction of the
ventricles. In every such contraction, as is above seen, the contents of the
ventricles are forced into the arteries more quickly than they are discharged
through the capillaries. The blood, therefore, being for an instant resisted
in its onward course, a part of the force with which it is impelled is directed
against the sides of the arteries; under this force their elastic walls dilate,
THE ARTERIAL FLOW
197
stretching enough to receive the blood, and becoming more tense and more
resisting as they stretch. Thus by yielding they break the shock of the
force impelling the blood. On the subsidence of the pressure, should the
ventricles cease contracting, the arteries are able by the same elasticity to
resume their former caliber.
The elastic tissue in the same way equalizes the current of blood by main-
taining pressure on it in the arteries during the period at which the ventri-
FIG. 192. — Cross Section of the Aorta to Show Elastic Tissue; e, elastic elements. (Bailey.)
cles are at rest or are dilating. If the arteries were rigid tubes, the blood,
instead of flowing as it does in a constant stream, would be propelled through
the arterial system in a series of spurts corresponding in time to the ventric-
ular contractions and with intervals of almost complete rest during the in-
action of the ventricles. But in the actual condition of the vessels, the force
of the successive contractions of the ventricles is expended partly in the
direct propulsion of the blood, and partly in the dilatation of the elastic ar-
teries; and in the intervals between the contractions of the ventricles, the
force of the recoil is employed in continuing the flow onward. Of course
the pressure exercised is equally diffused in every direction, and the blood
198 THE CIRCULATION OF THE BLOOD
tends to move backward as well as onward. All movement backward,
however, is prevented by the closure of the semilunar valves, which takes
place at the very commencement of the recoil of the arterial walls.
The Arterial Flow is Rhythmic. By the exercise of the elasticity
of the arteries, all the force of the ventricles is expended upon the circulation.
That part of the force which is used up or rendered potential in dilating the
arteries is restored or made active or kinetic when they recoil. There is no
loss of force, neither is there any gain; for the elastic walls of the artery
cannot originate any force for the propulsion of the blood; they only restore
that which they receive from the ventricles.
Since the ventricular discharge is intermittent, there will be intermittent
accessions of pressure, and therefore the flow of blood in the arteries will
be periodically accelerated. The volume of blood discharged from a cut
artery increases and decreases with the systole and diastole of the ventricles,
or with the systolic and diastolic pressures of the arteries themselves, see
page 187.
This equalizing influence of the resistance of the successive arterial
branches reacts so that at length the intermittent accelerations produced
in the arterial flow by the discharge of the heart cease to be observable, and
the jetting stream is converted into the continuous and even movement of
the blood which we see in the capillaries and veins. In the production of a
continuous stream of blood in the smaller arteries and capillaries, the resist-
ance which is offered to the blood stream in these vessels is a necessary agent.
Were there no greater obstacle to the escape of blood from the larger arteries
than exists to its entrance into them from the heart, the stream would be
intermittent, notwithstanding the elasticity of the walls of the arteries.
The muscular element of the middle coat cooperates with the elastic in
adapting the caliber of the vessels to the quantity of blood which they contain ;
for the amount of fluid in the blood-vessels varies quite considerably even
from hour to hour, and can never be quite constant; and were the elastic
tissue only present, the pressure exercised by the walls of the containing
vessels on the contained blood would be sometimes very small, and some-
times inordinately great. The presence of a muscular element, however,
provides for a certain uniformity in the amount of pressure exercised; and
it is by this adaptive, uniform, gentle muscular contraction that the normal
tone of the blood-vessels is maintained. Deficiency of this tone is the cause
of the soft and yielding arterial pulse, and the sluggish blood flow through
the arterioles.
Incidentally it may be mentioned that the elastic and muscular contrac-
tion of an artery may also be regarded as fulfilling a natural purpose when,
the artery being cut, the sudden contraction at first limits, and then, in con-
junction with the coagulated fibrin, completely arrests, the flow of blood.
It is only in consequence of such contraction and coagulation that we are
THE VELOCITY OF THE ARTERIAL BLOOD FLOW 199
free from danger through even very slight wounds; for it is only when the
artery is closed that the processes for the more permanent and secure pre-
vention of bleeding are established.
The Velocity of the Arterial Blood Flow. The velocity of the
blood current at any given point in the various divisions of the circulatory
system is inversely proportional to their united sectional area at that point.
If the united sectional area of all the branches of a vessel were always the same
as that of the vessel from which they arise, and if the aggregate sectional
area of the capillary vessels were equal to that of the aorta, the mean rapidity
of the blood's motion in the small arteries and in the capillaries would be the
same as in the aorta. If a similar correspondence of capacity existed in the
veins there would be an equal correspondence in the rapidity of the circula-
tion in them. But the arterial and venous systems may be represented by
two truncated cones with their apices directed toward the heart ; the area of
their united bases, the sectional area of the capillaries, being four hundred
to eight hundred times as great as that of the truncated apex representing
the aorta. Thus the velocity of blood in the smallest arterioles and the
capillaries is not more than one-four-hundredth of that in the aorta.
The velocity of the stream of blood is greatest in the neighborhood of
the heart. The rate of movement is greatest during the ventricular systole
and diminishes during the diastole. The rate of flow also decreases along
the arterial system, becoming least in the parts of the system most distant
from the heart. Chauveau has estimated the rapidity of the blood stream
in the carotid of the horse at over 20 inches per second during the heart's
systole, and nearly 6 inches during the diastole (520-150 mm.), see figure 191.
The Capillary Flow. It is in the capillaries that the chief resistance
is offered to the progress of the blood; for in them the friction of the blood
is greatly increased by the enormous multiplication of the surface with which
it is brought in contact.
When the capillary circulation is examined in any transparent part of a
full-grown living animal by means of the microscope, figures 193, 194, the
blood is seen to flow with a constant equable motion; the red blood-corpus-
cles moving along, mostly in single file, and bending in various ways to ac-
commodate themselves to the tortuous course of the capillary, but instantly
recovering their normal outline on reaching a wider vessel,
At the circumference of the stream and adhering to the walls of the larger
capillaries, but especially well marked in the small arteries and veins, there
is a layer of plasma which appears to be motionless. The existence of this
still layer, as it is termed, is inferred both from the general fact that such a
one exists in all fine tubes traversed by fluid, and from what can be seen in
watching the movements of the blood-corpuscles. The red corpuscles occupy
the middle of the stream and move with comparative rapidity; the color-
less corpuscles run much more slowly by the walls of the vessels; while next
200
THE CIRCULATION OF THE BLOOD
to the wall there is a transparent space in which the fluid appears to be at
rest; for if any of the corpuscles happen to be forced within it, they move
more slowly than before, rolling lazily along the side of the vessel, and often
adhering to its wall, figure 194. Part of this slow movement of the colorless
corpuscles and their occasional stoppage may be due to their having a tend-
ency to adhere to the walls of the vessels. Sometimes, indeed, when the
motion of the blood is not strong, many of the white corpuscles collect
in a capillary vessel, and for a time entirely prevent the passage of the red
corpuscles.
When the peripheral resistance is greatly diminished by the dilatation of
the small arteries and capillaries, so much blood passes on from the arteries
into the capillaries at each stroke of the heart that there is not sufficient
remaining in the arteries to distend them. Thus, the intermittent current
of the ventricular systole is not always converted into a continuous stream
by the elasticity of the arteries before the capillaries are reached; and so
intermittency of the flow occurs both in capillaries and veins and a venous
pulse is produced. The same 'phenomenon may occur when the arteries
FIG. 193. — Capillary Network from Human Pia Mater, Showing also an Arteriole in " Optical
Section "; and a Small Vein. X 35°. A, Vein; B, arteriole; C, large capillary; D, small capillaries.
(Bailey.)
become rigid from disease, and when the beat of the heart is so slow or so
feeble that the blood at each cardiac systole has time to pass on to the capil-
laries before the next stroke occurs; the amount of blood sent at each stroke
being insufficient properly to distend the elastic arteries.
It was formerly supposed that the occurrence of any transudation from
the interior of the capillaries into the midst of the surrounding tissues was
confined, in the absence of injury, strictly to the fluid part of the blood; in
THE CAPILLARY FLOW
201
other words, that the corpuscles could not escape from the circulating stream,
unless the wall of the containing blood-vessel was ruptured. It is true that
the English physiologist Augustus Waller affirmed in 1846 that he had seen
blood-corpuscles, both red and white, pass bodily
through the wall of the capillary vessel in which
they were contained (thus confirming what had
been stated a short time previously by Addison),
and that as no opening could be seen before their
escape, so none could be observed afterward, so
rapidly was the part healed. But these observations
did not attract much notice until the phenomenon
of escape of the blood-corpuscles from the capil-
laries and minute veins, apart from mechanical injury,
was rediscovered by Cohnheim in 1867.
Cohnheim's experiment demonstrating the. pas-
sage of the corpuscles through the wall of the blood-
vessel is performed in the following manner: A frog
is curarized, that is to say paralysis is produced by
injecting under the skin a minute quantity of the
poison called curari. The abdomen is then opened,
a portion of the small intestine is drawn out, and its
transparent mesentery spread out under a microscope.
After a variable time, occupied by dilatation following
contraction of the minute vessels and the accom-
panying quickening of the blood stream, there ensues a retardation of the
current and the red and white blood-corpuscles begin to make their way
through the capillaries and small veins.
The white corpuscles pass through the capillary wall chiefly by the ame-
boid movement with which they are endowed. This migration occurs to a
limited extent in health, but in inflammatory conditions is much increased.
The process of diapedesis of the red corpuscles, which occurs under cir-
cumstances of impeded venous circulation, and consequently increased
blood pressure, resembles closely the migration of the leucocytes, with the
exception that they are squeezed through the wall of the vessel, and do not,
like the leucocytes, work their way through by ameboid movement.
Various explanations of these remarkable phenomena have been sug-
gested. Some believe that pseudo-stomata between contiguous endothelial
cells provide the means of escape for the blood-corpuscles. But the chief
share in the process is probably due to mobility and contraction of the parts
concerned, both of the corpuscles and of the capillary wall itself.
The Speed of the Blood in the Capillaries. The velocity of the
blood through the capillaries must, of necessity, be largely influenced by
that which occurs in the vessels on both sides of them, in the arteries and
FIG. 194. — A Large Cap-
illary from the Frog's
Mesentery Eight Hours
after Irritation had been
set up, Showing Emigra-
tion of Leucocytes. a,
Cells in the act of travers-
ing the capillary wall; b,
some already escaped.
(Frey.)
202 THE CIRCULATION OF THE BLOOD
the veins, their intermediate position causing them to respond at once to any
alteration in the size or rate of the arterial or venous blood stream. Thus, the
apparent contraction of the capillaries, on the application of certain irritating
substances or during certain mental states, and their dilatation in blushing
may be referred primarily to the corresponding action of the small arteries.
The Measurement of Velocity in the Capillaries. The observation of
Hales, E. H. Weber, and Valentin agree very closely as to the rate of the
blood current in the capillaries of the frog; and the mean of their estimates
gives the velocity of the systemic capillary circulation at about 0.5 mm. per
second. The velocity in the capillaries of warm-blooded animals is greater,
in the dog 0.5 to 0.75 mm. per second. This may seem inconsistent with the
facts, which show that the whole circulation is accomplished in about half
a minute. But the whole length of capillary vessels, through which any
given portion of blood has to pass, probably does not exceed 0.5 mm. There-
fore the time required for each quantity of blood to traverse its own appointed
portion of the general capillary system will scarcely amount to more than a
second. This comparatively slow velocity is evidently favorable to the
nutritive interchanges that go on through these thin-walled vessels between
the blood within the capillaries and the outside active tissues.
The Venous Flow. The blood current in the veins is maintained,
a, primarily by the contractions of the left ventricle ; but very effectual assist-
ance to the flow is afforded, b, by the action of the muscles capable of pressing
on the veins with valves, and c, by the aspiration of the thorax and possibly,
d, by the aspiration of the heart itself.
The effect of muscular pressure upon the circulation may be thus ex-
plained: When pressure is applied to any part of a vein, and the current of
blood in it is obstructed, the portion behind the seat of pressure becomes
swollen and distended as far back as the next pair of valves, which are in
consequence closed. Thus, whatever force is exercised by the external
pressure of the muscles on the veins, is distributed partly in pressing the blood
onward in the proper course of the circulation, and partly in pressing it
backward and closing the valves behind.
The circulation might lose as much as it gains by such an action, if it
were not for the numerous communications, or venous anastomoses; for owing
to these anastomoses the closing up of the venous channel by the backward
pressure is prevented from being any serious hindrance to the circulation,
since the blood which is arrested in its onward course by the closed valves
can at once pass through some anastomosing channel, and proceed on its
way by another vein. Thus the effect of muscular pressure upon veins
which have valves is turned almost entirely to the advantage of the circula-
tion; the pressure of the blood onward is all advantageous, and the pressure
of the blood backward is prevented from being a hindrance by the closure
of the valves and of the anastomoses of the veins.
THE VELOCITY IN THE VEINS 203
The venous flow is also assisted by the aspiration of the thorax and to
some extent by that of the heart, since at some time during every cardiac
cycle the intraauricular and intraventricular pressure falls below that of
the atmosphere. This activity will be considered more fully in the chapter
on Respiration. In this connection it may be said, however, that the pressure
in the great veins falls during inspiration and rises during expiration.
The Velocity in the Veins. The velocity of the blood is greater
in the veins than in the capillaries, but less than in the arteries; this fact
depending upon the relative capacities of the arterial and venous systems.
If an accurate estimate of the proportionate areas of arteries and the veins
corresponding to them could be made, we might, from the velocity of the
arterial current, calculate that of the venous. The usual estimate is that
the capacity of the veins is about two or three times as great as that of the
arteries, and that the velocity of the blood's motion is, therefore, about one-half
or one-third as great in the veins as in the arteries, i.e., 200 mm. a second.
The rate at which the blood moves in the smallest venules is only slightly
greater than that in the capillaries, but the speed of flow gradually increases
the nearer the vessel approaches to the heart, for the sectional area of the
venous trunks, compared with that of the branches opening into them, be-
comes gradually smaller as the trunks advance toward the heart, figure 191.
The Velocity of the Circulation as a Whole. It would appear
that a portion of blood can traverse the entire course of the circulation, in
the horse, in half a minute. Of course it would require longer to traverse
the vessels of the most distant part of the extremities than to go through
those of the neck, but taking an average length of the vessels to be traversed
it may be concluded that half a minute represents the average rate. Stewart
estimated that the circulation time in man is probably not less than twelve
nor more than fifteen seconds.
Satisfactory data for these estimates are afforded by the results of experi-
ments to ascertain the rapidity with which chemicals introduced into the blood
are transmitted from one part of the vascular system to another. The time
required for the passage of solutions of potassium ferrocyanide, mixed with
the blood, from one jugular vein, through the right side of the heart, the
pulmonary vessels, the left cavities of the heart, and the general circulation,
to the jugular vein of the opposite side, varies from twenty to thirty seconds
in the dog. The same substance is transmitted from the jugular vein to the
great saphenous vein in twenty seconds; from the jugular vein to the mes-
enteric artery in between fifteen and thirty seconds; to the facial artery,
in one experiment, in between ten and fifteen seconds; in another experi-
ment, in between twenty and twenty-five seconds; in its transit from the
jugular vein to the metatarsal artery, it occupies between twenty and thirty
seconds. The result is said to be nearly the same whatever the rate of the
heart's action. In more recent methods some innocuous dye like methylene
204 THE CIRCULATION OF THE BLOOD
blue is used, since it permits the determination without the loss of blood,
the change in color being visible through the walls of the blood-vessels.
Stewart has made most accurate measurements of the circulation time
by the electrical-resistance method. Strong salt solutions injected into the
jugular vein on one side when they reach the other jugular (or any other
vessel) are instantly detected by a decrease in the electrical resistance through
the vessel when it is laid between the poles of the proper conductivity
apparatus.
In all these experiments it is assumed that the substance injected moves
with the blood and at the same rate, and does not move from one part of
the organs of circulation to another by diffusing itself through the blood or
tissues more quickly than the blood moves. The assumption may be ac-
cepted that the times above mentioned as occupied in the passage of the in-
jected substances are the times in which the portion of blood itself is carried
from one part to another of the vascular system.
Another mode of estimating the general velocity of the circulating blood
is by calculating it from the quantity of blood supposed to be contained in
the body, and from the quantity which can pass through the heart in each
of its contractions. But the conclusions arrived at by this method are less
satisfactory. For the total quantity of blood, and the capacity of the cavities
of the heart, have as yet been only approximately ascertained. Still the most
careful of the estimates thus made accord very nearly with those already
mentioned; and it may be assumed that the blood may all pass through
the heart in about twenty-five seconds.
THE PULSE.
The most characteristic feature of the arterial pressure and blood flow
is its intermittency, and this intermittent flow is seen or felt as waves of change
in diameter of the arteries, known as the Pulse.
The pulse is generally described as a wave-like expansion of the artery
produced by the injection of blood at each ventricular systole into the already
full aorta. The force of the left ventricle is expended in pressing the blood
forward and in dilating the aorta. With the injection of each new quantity
of blood into the aorta there is a wave of dilatation which passes on, expanding
the arteries as it goes, running as it were over the more slowly traveling blood
contained in them, and producing the pulse as it proceeds. -A sharp dis-
tinction must be made between the passage of the pulse wave along an artery
and the rate of flow of the blood in the vessel. The pulse produced by any
given beat of the heart is not felt at the same moment in all parts of the body.
Thus, it can be felt in the carotid a short time before it is perceptible in the
radial artery, and in this vessel before it occurs in the dorsal artery of the
foot. Careful measurements of the intervals between the time of the pulse
THE SPHYGMOGRAPH
205
at the carotid and at the wrist shows that the delay in the beat is in proportion
to the distance of the artery from the heart. The difference in time between
the pulse of any two arteries probably never exceeds one-sixth to one-eighth
of a second. The rate at which the pulse travels in the arteries is from five to
ten meters per second.
The distention of each artery increases both its length and its diameter.
In their elongation the arteries change their form, the straight ones becoming
slightly curved, and those already curved becoming more so; but they re-
cover their previous form as well as their diameter when the ventricular
contraction ceases, and their elastic walls recoil. The increase of their
curves which accompanies the distention of arteries, and the succeeding
recoil, may be well seen in the prominent temporal artery of an old person.
In feeling the pulse, the finger cannot distinguish the sensation produced
by the dilatation from that produced by the elongation and curving. That
which it perceives most plainly, however, is the dilatation and return more
or less to the cylindrical form of the artery, which has been partially flattened
by the finger.
The Sphygmograph. Much light has been thrown on what may
be called the form of the pulse wave by an instrument called the sphygmo-
FIG. 195. — Diagram of the Lever of the Sphygmograph.
graph, figures 195 and 196. The principle on which it acts will be seen
on reference to the figures.
A small button replaces the finger in the act of taking the pulse. This
button is made to rest lightly on the artery the pulsations of which it is de-
sired to investigate. The up-and-down movement of the button is com-
municated to the lever, to the hinder end of which is attached a light spring.
The spring is adjusted to the proper tension to follow the movements of the
artery wall during the pulse wave. The Sphygmograph is bound on the
wrist while taking a record.
It is evident that the beating of the pulse will cause an up-and-down
movement of the lever, the pen of which will write the effect on a smoked
card moved by the clock-work of the instrument.
206 THE CIRCULATION OF THE BLOOD
Thus a tracing of the pulse is obtained, and in this way much more deli-
cate changes can be seen than can be felt by the mere application of the finger.
The principle of the sphygmometer of Roy and Adami is shown in the diagram, figure
197.
The apparatus consists of a box, a, which is moulded to fit over the end of the radius
so as to oriage over the radial artery. Within this is a flexible bag, b, filled with water,
and connected by a T-tube with a rubber bag, h, and mercurial manometer. The fluid
in the box may be raised to any desired pressure, and may then be shut off by tap, c. At
the upper part of the box is a circular opening, and resting upon b is a flat button, d,
which by means of a short light rod, e, communicates the movement of b to the lever, /.
At the axis of rotation of this lever is a spiral watch-spring, g, which can be tightened at
will, so that the lever can be made to take a vertical position at any desired hydrostatic
FIG. 196. — Dudgeon's Sphygmograph.
pressure within the box. The movements of the lever are recorded upon a piece of black-
ened glazed paper made to move in a vertical direction past it. When in use, the box
is fixed upon the wrist by an appropriate holder, and the pressure is raised to any desired
height to which the lever is adapted by tightening or slackening the spring; the tap, c, is
then closed. The pressure within the box acts in all directions, and is correctly indicated
by the manometer.
Sphygmogram. The tracing of the pulse obtained by the use of
the sphygmograph, called a sphygmogram, differs somewhat according to
the artery from which it is taken, but its general characters are much the
same in all cases. It consists of a sudden upstroke, or anacrotic limb, figure
198,^4, which is somewhat higher and more abrupt in the pulse of the carotid
and of other arteries near the heart than in the radial and other arteries
more remote; and a gradual decline or catacrotic limb, B, less abrupt, and
taking a longer time than A. It is seldom, however, that the decline is an
uninterrupted fall; it is usually marked about half-way by a distinct notch,
SPHYGMOGRAM
207
C, called the dicrotic notch, followed immediately by a second more or less
marked ascent of the lever called the dicrotic wave, D. Not infrequently
there is also at the beginning of the descent a slight wave previous to the
dicrotic notch; this is called the pre-dicrotic wave, and in addition there
may be one or more slight waves after the dicrotic, called post-dicrotic, E.
The interruptions in the downstroke are called the catacrotic waves to dis-
tinguish them from an interruption in the upstroke, called the anacrotic
wave, which is sometimes met with.
The explanation of these tracings presents some difficulties, not, how-
ever, as regards the two primary factors, viz., the upstroke and downstroke,
To manometer.
FIG. 197. — Diagrammatic Sectionr.l Representation of the Sphygmometer. a, Box by which
the portion of the artery is covered; b, thin- walled india-rubber bag filled with water, and com-
municating through tap, c, with the manometer and thick- walled rubber bag, h ; d, piston con-
nected by rod, e, with recording lever, /; g, spiral spring, attached to axis of lever, and by which
the pressure in b, against the piston, d, is counterbalanced; k, skin and subcutaneous tissue; m,
end of radius seen in section; n, radial artery seen in section. (Roy and Adami.)
because they are universally taken to mean the sudden injection of blood
into the already distended arteries, and the gradual recovery of the arteries
by their recoil. These points may be demonstrated on a system of elastic
tubes, with a pump to inject water at regular intervals, just as well as on the
radial artery, or on the arterial schema, a more complicated system of tubes
in which the heart, the arteries, the capillaries and veins are represented.
If we place two or more sphygmographs upon such a system of tubes at in-
creasing distances from the pump, we may demonstrate, first, that the rise
of the lever commences earliest in that nearest the pump, and, second, that
it is higher and more sudden. So in the arteries of the body the wave gradu-
ally gets less and less as we approach the periphery of the arterial system,
and is lost in the capillaries.
208 THE CIRCULATION OF THE BLOOD
The origin of the secondary waves is to some extent a matter of uncer-
tainty. The anacrotic wave occurs when the peripheral resistance is high;
that is, when, for some time during the systole, the flow from the aorta toward
the periphery is slower than the flow from the ventricle into the aorta. Thus
it is seen in some cases of nephritis where the arteries ase rigid and the periph-
eral resistance is high.
The dicrotic wave is the most important of the secondary waves, and
has been the subject of much discussion. It is constantly present in pulse-
FIG. 198. — Diagram of Pulse Tracing. A , upstroke or anacrotic limb; B, downstroke or kat-
acrotic limb; C, pre-dicrotic wave; D, dicrotic; E, post-dicrotic wave.
tracings, but varies in height. In point of time the dicrotic wave occurs
immediately after the closure of the aortic semilunar valves. In certain
conditions, generally of disease, it becomes so marked as to be quite plain
to the unaided finger. Such a pulse is called dicrotic. The generally ac-
cepted view of the cause of the dicrotic wave is that it represents a rebound
from the closed aortic valves. During systole, as the blood is forcibly in-
jected into the aorta, there is an overdistention of the artery. The systole
suddenly ends, the aorta by reason of its elasticity tends to recover itself,
FIG. 199. — Sphygmogram from the Radial Artery Taken with Marey's Sphygmograph.
(Langendorff.)
the blood is driven back against the semilunar valves, closing them and at
the same time giving rise to a wave, the dicrotic wave, which begins at the
heart and travels onward toward the periphery like the primary wave. Ac-
cording to Foster, the conditions favoring the development of dicrotism are:
i, a highly extensible and elastic arterial wall; 2, a comparatively low mean
blood pressure, leaving the extensible reaction free scope to act; 3, a vigorous
and rapid stroke of the ventricle discharging into the aorta a considerable
PERIPHERAL REGULATION OF THE FLOW OF BLOOD
209
quantity of blood. The other secondary waves are probably due to the os-
cillations in the elastic recoil of the arteries, though some of them at least
may be due to the inertia of the instruments used.
In the use of the sphygmograph care must be taken in the regulation of
the pressure of the spring. If the pressure be too great, the characters of
23456 7
B
FIG. 200. — A, Normal Pulse- Tracing from Radial of Healthy Adult Obtained by the Sphyg-
mometer; B, from same artery, with the same extra-arterial pressure, taken during acute nasal
catarrh.
the pulse may be almost entirely obscured, or the artery may be completely
obstructed and no tracing is obtained. On the other hand, if the pressure is
too slight, a very small part of the characters may be represented on the tracing.
THE PERIPHERAL REGULATION OF THE FLOW OF BLOOD.
The flow of blood through the circulatory system depends on the inter-
action of several factors which have already been mentioned in another con-
nection: The rate and volume of the heart-beat, the elasticity of the blood-
vessels, the resistance of the microscopic peripheral vessels, and the volume
of blood in the body. We have already learned, page 179, that both the
rate and the volume of the contractions of the heart are under very minute
and intimate regulation and control through the cardiac nervous mechanism.
Also we have found that there is intimate coordination between the activity
of the circulatory and the activity of all other parts of the body, a coordina-
tion accomplished through the, nervous system. All regulation which affects
14
210 THE CIRCULATION OF THE BLOOD
the heart must of necessity affect the general blood pressure and, therefore,
not directly any particular part.
The general elasticity of the blood-vessels, and of the arteries in par-
ticular, which makes the general arterial pressure possible, is dependent
primarily on the presence of a large amount of elastic connective tissue in
the walls of the vessels. The elasticity of this tissue is a purely passive
property which can be utilized only by some positive source of energy, in
this instance the heart.
The Variations in Peripheral Resistance. Certain arteries and
veins, especially the smallest ones, the arterioles, are supplied with muscular
tissue in their walls. The activity of these muscles in the vascular com-
plex makes the peripheral regulation of the flow of blood possible. They
supply a tissue which not only exhibits a passive elasticity comparable to that
of the yellow elastic connective tissue, but upon the proper stimulation they
actively contract or relax, thus securing to the peripheral resistance an active
adjustment to the ever- varying dynamic conditions of the vascular apparatus.
The muscular tissue in the walls of the vessels increases relatively in
amount as the arteries become smaller, so that in the arterioles it is developed
out of all proportion to the other elements. In fact, in passing from the
arterioles to the capillary vessels, made up as we have seen of endothelial
cells with a supporting ground substance only, the last change on the side
of the arteries, which occurs as the vessels become smaller, is the disappear-
ance of muscular fibers.
The office of the muscular coat is to adjust the size of the arterioles and,
therefore, the flow of the blood, to regulate the quantity of blood to be received
by each part or organ, and to adjust the quantity to the requirements of each,
according to various circumstances, but chiefly according to the degree of
activity which each organ at different times exhibits. The amount of work
done by each organ of the body constantly varies, and the variations often
quickly succeed each other, so that, as in the muscles for example, within
the same hour a part may be now very active and now quite inactive. In
all its active exercise of function, such an organ requires a larger supply of
blood than is sufficient for it during the times when it is comparatively
inactive.
It is evident that the heart cannot regulate the blood supply to each part
of the body at different periods independently of the other parts. Neither
could this be regulated by any general and uniform contraction of the arteries.
But it may be regulated by the power which the arteries of each part have,
through their muscular tissue, of contracting or relaxing so as to diminish
or increase the supply of blood, according to the requirements of the par-
ticular part of the body to which the vessels are distributed. Thus, while
the ventricles of the heart determine the total quantity of blood to be sent
onward at each contraction, and the force of its propulsion, and while the
DISCOVERY OF THE VASO-MOTOR NERVES 211
large and merely elastic arteries distribute the blood and equalize its stream,
the smaller arteries by means of their muscular tissue regulate and deter-
mine the proportion of the whole quantity of blood which shall be distributed
to each particular organ.
The variation of the size of arterioles and, therefore, of the resistance
to the flow of the blood in them is secured by the muscular tissue, but the
muscles are regulated in their contraction by the nervous system. The
muscular tissue in the blood-vessels of the different organs of the body is also
coordinated by the same regulative and controlling influence of the nervous
system.
The Discovery of the Vaso-motor Nerves. More than half a
century ago it was shown by Claude Bernard that if the cervical sympathetic
nerve is divided, the blood-vessels of the corresponding side of the head and
FIG. 201. — Small Artery and Vein of the Frog's Web. A, Under normal conditions; B, upon
stimulation of the sciatic nerve; A -, artery; V, vein. In this experiment the vein also showed
well-marked vaso- constriction. (New figure by Greene.)
neck become dilated. This effect is best seen in the ear, which if held up to
the light is seen to beceme redder, and the arteries to become larger. The
whole ear is distinctly warmer than the opposite one. This effect is pro-
duced by removing the arteries from the influence of the central nervous sys-
tem, which influence normally passes along the course of the divided nerve.
If the peripheral end of the divided nerve be stimulated in its course
toward the organ, i.e., that farthest from the brain, the arteries which were
before dilated return to their natural size, and the parts regain their former
condition. And, besides, if the stimulus is very strong or very long continued,
THE CIRCULATION OF THE BLOOD
the amount of normal constriction is passed and the vessels become much
more contracted than before. The natural condition, which is midway
between extreme contraction and extreme dilatation, is called the natural
tone of an artery. If this is not maintained, the vessel is said to have lost
FIG. 202. — Arm Plethysmograph. Apparatus for measuring the change in volume in the
arm due to variation in the blood supply. The arm is enclosed in a glass cylinder which is com-
pletely filled with fluid, the opening through which the arm is inserted being closed by a rubber
sleeve, A . The cavity of the glass cylinder communicates through the tube, F, G, with the test tube
M, which is supported in the jar, P. Any variation in volume in the arm will cause water to flow
out or into the test tube, M, which is lowered as the tube fills, and raised as it empties. The rise
and fall of the test tube, M, is communicated over the pulley, L, to the writing-pen, N, which re-
cords the movements on the smoked cylinder. Kymograph not shown. (Mosso.)
tone, or, if it is exaggerated, the tone is said to be too great. The effects
described as having been produced by section of the cervical sympathetic
and by subsequent stimulation are not peculiar to that nerve and the vessels
to which it is distributed.
It has been found that for every part of the body, except the brain, there
exists a nerve the division of which produces the same effects, viz., dilatation
of the vessels. Such may be cited as the case with the sciatic, the splanch-
nic nerves, and the nerves of the brachial plexus; when these are divided,
dilatation of the blood-vessels in the parts supplied by them takes place.
It appears, therefore, that nerves exist which have a distinct control over the
vascular supply of every part of the body. These are called vaso-motor or
vaso-constrictor nerves. But the arterioles are also under the influence of
VASO-CONSTRICTOR NERVES 213
a second set of nerves, also discovered by Claude Bernard, which produce
exactly the opposite influence, i.e., dilatation. These nerves are called vaso-
dilator nerves.
Mall has also shown that veins, at least the portal vein, possess a vaso-
motor nerve supply as well as arteries.
Vaso- constrictor Nerves. The presence of vaso-constrictor nerves
can be shown in several different ways, of which the most convincing is that
of direct inspection. If a vascular membrane, like the web of the frog's
foot or the bat's wing, be adjusted on the stage of a microscope for direct
inspection, and the smaller arterioles are under observation, then upon the
stimulation of the general nerve supplying the part these arterioles will sharply
decrease in size. In fact the vaso-constriction is often so great as com-
FIG. 203.— Plethysmogram of the Hind Limb of a Cat, showing Vaso-constriction upon Stimu-
lating the Sciatic 64 times per second. To be read from right to left. (Bowditch and Warren.)
pletely to occlude the vessel. Very soon after the stimulation the vessel
again dilates to its normal size.
The presence and course of the vaso-constrictor nerve supply to the
organs of the body have been demonstrated not by direct inspection, but
by the use of various forms of the plethysmograph. A plethysmograph is an
instrument designed to measure the variations in the volume of an organ.
If the finger, the whole hand, the spleen, or the kidney be placed in such an
instrument and the proper steps be taken to record the volume changes, it
will be found that the volume of the enclosed organ is constantly changing
with every variation of the blood pressure. If the nerves to the organ are
stimulated by the usual rapidly interrupted induction current, for example,
the splanchnics to the kidney, then there is a decrease in the volume of the
organ. This decrease takes place even when there is a simultaneous in-
crease of the arterial blood pressure, a result that can be explained only on
the assumption of vascular decrease in the organ. The decrease in the flow
of blood to the specific organ can be induced only by a great decrease in the
size of the arterioles produced by contractions of the circular muscles of
their walls.
214
THE CIRCULATION OF THE BLOOD
Vaso-motor Tone. Vaso-constrictor changes are constantly occur-
ring in the blood-vessels of the organs of the body, a fact that has been
abundantly demonstrated by the plethysmographic experiments just men-
tioned. Direct inspection of the ear of an albino rabbit will show that the
arteries, and veins as well, are now full and large and red, and the interspaces
filled with blood, and now pale and constricted, and the interspaces apparent-
ly bloodless. If the cervical sympathetic is cut as in Bernard's experiment,
then the ear vessels remain dilated, that is, they lose their tone, showing
that the condition is dependent primarily on the constant discharges cf nerve
impulses from the nervous system. It is said that
the vessels regain their tone after a time when the
nerves are cut. The regained power may be ascribed
to the muscle fibers themselves.
Vaso-constrictor Center. When the tonic in-
fluence exerted by the nerve-fibers on the arterioles
is traced back into the central nervous system, it is
found to be associated with the activity of certain
groups of nerve-cells, or centers, which are called
the vasp-constrictor centers. This determination is
made in part by the method of sectioning. A lesion
of the cerebro-spinal axis below the corpora quad-
rigemina is followed by partial or complete general
dilatation of the blood-vessels and great fall of blood
pressure. This is due to the isolation of the vaso-
constrictor center, which lies in the floor of the fourth
ventricle, a millimeter or two caudal to the corpora
quadrigemina, and extends longitudinally over an area
of about three millimeters. Owsjannikow has shown
that the center is composed of two halves, each half
lying in the lateral column to the side of the median
line. This center is in constant action during life,
and its discharges are responsible for the vascular
tone described in the previous paragraph. The
vaso-constrictor center varies in its activity, sometimes
producing wave-like contractions with relaxations of
the arterial walls, producing variations in the blood
pressure known as Traube-Hering waves. They are
more often observed in mammalian blood-pressure
experiments after prolonged operations, when the center may be supposed
to be itself in a weakened condition.
Secondary vaso-motor centers are present in the spinal cord as proven
by Goltz. Under normal conditions they do not act independently of the
medullary center; but when the function of the latter has been interrupted
FIG. 204. — Diagram
Showing the Paths of the
Vaso- constrictor Fibers
along the Cervical Sympa-
thetic and the Abdominal
Splanchnic. Aur, Artery
of ear; G.Cs, superior
cervical ganglion; An. V,
annulus of Vieussens; G.St.
stellate ganglion; D.I,
D.I I, D.V, thoracic spinal
nerves; Abd. Spl, abdomi-
nal splanchnic. The arrows
indicate the direction of
vaso-constrictor impulse.
VASO-CONSTRICTOR REFLEXES 215
by section of the cord, then after a few days the spinal cells below the section
take on central functions and bring about a re-establishment of the lost
vascular tone. If these centers be destroyed by the destruction of the cord,
then the tone of the vessels immediately disappears but is regained after the
lapse of a much longer time. This can be ascribed to the presence of possi-
ble sympathetic constrictor centers or more probably to a fundamental prop-
erty of the muscles themselves. This experiment was carried out by Goltz
and Oswald, who found that after destruction of the lower part of the spinal
cord, the tone of the vessels of the hind limbs, lost as a result of the opera-
tion, was later re-established.
Vaso- constrictor Reflexes. Under normal conditions the medul-
lary center responds to afferent stimuli by vaso-motor reflexes. The second-
ary vaso-motor centers in the spinal cord, when removed from the influence
of the bulbar center, can and do respond to afferent impulses by similar
vaso-motor action.
The afferent impulses which excite reflex vaso-motor action may proceed
from the terminations of sensory nerves in general, or possibly from the
blood-vessels themselves, and the constriction which follows generally occurs
in the area whence the impulses arise. Yet the reflex may appear elsewhere.
Impulses proceeding to the vaso-motor center from the cerebrum may cause
vaso-dilatation, as in blushing, or vaso-constriction, as in the pallor of fear
or of anger.
Afferent influence upon the vaso-motor centers is well shown by the action
of the depressor nerve, the existence of which was demonstrated by Cyon
and Ludwig. The depressor is a small afferent nerve which passes up to
the medulla from the heart, in which it takes its origin. It runs upward in
the sheath of the vagus or in the superior laryngeal branch of the vagus or
as an independent branch, as in the rabbit, communicating by filaments
with the inferior cervical ganglion as it proceeds from the heart. If, in a
rabbit, this nerve be divided and the central end stimulated during a blood-
pressure observation, a remarkable fall of blood pressure takes place, figure 205.
The cause of the fall of blood pressure is found to proceed primarily
from the dilatation of the vascular district within the abdomen supplied by
the splanchnic nerves, in consequence of which the vessels hold a much
larger quantity of blood than usual. The engorgement of the splanchnic
area very greatly diminishes the amount of blood in the vessels elsewhere,
and so materially diminishes the blood pressure. The function of the de-
pressor nerve is that of conveying to the vaso-motor center afferent nerve
impulses from the heart, which produces an inhibition of the tonic activity
of the vaso-motor center and, therefore, a diminution of the tension in the
blood-vessels, thus relieving the heart from the overstrain of propelling blood
into the already too full or too tense arteries. It has been shown by Porter
and Beyer that the fall in blood pressure, following stimulation of the depres-
216
THE CIRCULATION OF THE BLOOD
sor nerve, will still occur, even when the abdominal vaso-constriction
is kept constant by a simultaneous stimulation of the splanchnics. It is
therefore evident that the inhibitory effect of depressor-nerve stimulation is
a general one and not confined to the splanchnic area alone.
The action of the depressor nerve in causing an inhibition of the vaso-
motor center illustrates the more unusual effect of afferent impulses, that is,
inhibition of the vaso-constrictor tone. As a rule, the stimulation of the
central end of an afferent nerve, such as the sciatic or the internal saphenous,
produces the reverse, i.e., a pressor effect, and increases the tonic influence
FIG. 205. — Blo9<i- Pressure Record (lower) and Respiratory Record (upper) Obtained from a
Dog upon Stimulating the Central End of the Divided Vagus, Both Vagi being Cut. The marked
fall in blood pressure is due to the effect of stimulating the depressor fibers contained in the vagus
trunk of the dog. (New figure by Dooley and Dandy.)
of the center which by causing constriction of the arterioles raises the blood
pressure. Thus the effect of stimulating an afferent nerve may be either
to constrict or to dilate the arteries. These reflexes may be general enough
to influence the general blood pressure, but the local effects are the all-im-
portant ones, since by these the local regulation of the blood flow is accom-
plished.
Traube-Hering Curves. The vaso-motor center sends out rhythmi-
cal impulses by which andulations of blood pressure of a large and sweeping
character are produced, quite independent of the so-called respiratory un-
dulations. The action of this center in producing such undulations is de-
monstrated in the following observations. In an animal under the influence
of curari and with both vagi cut, and a record of whose blood pressure is being
taken, if artificial respiration be stopped, the blood pressure rises sharply
at first. After a time the rhythmical undulations shown in figure 206
occur. These variations are called Traube's or Traube-Hering curves.
There mav be upward of ten of the respiratory undulations in one Traube-
VASODILATOR NERVES 217
Hering curve. They continue until the vaso-motor center is asphyxiated
and the heart exhausted, when the pressure falls. The undulations cannot
depend upon anything but the vaso-motor center, as the mechanical effects
of respiration have been eliminated by the curari and by the cessation of
artificial respiration, and the effect of the cardio-inhibitory center has been
removed by the division of the vagi. The rhythmic rise of blood pressure
is most likely due to a rhythmic constriction of the arterioles followed by a
FIG. 206. — Traube- Bering's Curves. (To be read from left to right.) The curves i, 2, 3, 4.
and 5 are portions selected from one continuous tracing forming the record of a prolonged observa-
tion, so that the several curves represent successive stages of the same experiment. Each curve
is placed in its proper position relative to the base line, which is omitted; the blood pressure rises
in stages from i to 2, 3, and 4, but falls again in stage 5. Curve i is taken from a period when arti-
ficial respiration was being kept up, but, the vagi having been divided, the pulsations on the ascent
and descent of the undulations do not differ; when artificial respiration ceased, these undulations
for a while disappeared, and the blood pressure rose steadily while the heart-beats became slower.
Soon, as at 2, new undulations appeared; a little later, the blood pressure was still rising, the heart-
beats still slower, but the undulations still more obvious (3); still later (4), the pressure was still
higher, but the heart-beats were quicker, and the undulations flatter; the pressure then began to fall
rapidly (5), and continued to fall until some time after artificial respiration was resumed. (M.
Foster.)
rhythmic fall of pressure and relaxation, both being due to the action of the
vaso-motor center. The vaso-motor center, therefore, is capable of pro-
ducing rhythmical undulations of blood pressure.
Vaso-dilator Nerves. Claude Bernard discovered that the blood
flow was increased through the salivary glands by stimulation of the nerves
(the chorda tympani for the submaxillary, and the tympanic branch of the
glossopharyngeal for the parotid), thus proving that the arteries have not
218 THE CIRCULATION OF THE BLOOD
only vaso-constrictors, but also vaso-dilator nerves. Vaso-dilator nerves
have been described for most parts of the body. In general they are dis-
tributed in the same nerve trunks which bear the vaso-constrictors.
It is not supposed that the vaso-dilators produce widening of the arterioles
by stimulation to active muscular contraction; in fact the circular arrange-
ment of the muscle fibers would seem to exclude such a deduction. It is
probable that there is local inhibition of the tonic contraction of the muscles,
thus allowing the mechanical factor of the general blood pressure to dilate
FIG. 207. — Plethysmogram of the Hind Limb of a Cat, Showing Vaso-dilatation upon Stimulating
the Sciatic Once per Second. To be read from right to left. (Bowditch and Warren.)
the vessels. The vaso-dilator nerves are characterized by their response
to slowly developed stimuli, shown by Bowditch and Warren, and by the
retention of irritability after degeneration of the constrictors has taken place,
see figure 207.
Vaso-dilator Centers. No distinct medullary center has yet been
shown to regulate the vaso-dilator nerve activity. Such centers, if they
exist, should be influenced by isolating them from their efferent paths, on
the one hand, or by stimulation by afferent channels, on the other. The
former method of study has revealed nothing that can be compared to the
tonic activity of the constrictor center. Efferent dilator-nerve impulses can
be reflexly produced by sensory stimulation. The isolated lumbar cord of
a dog is capable of reflex vaso-dilator activity, since stimulation of the skin
of the penis leads to reflex vaso-dilatation, indicating the presence of local
vaso-dilator centers in this portion of the spinal cord.
Vaso-dilator Reflexes. Perhaps the only unquestioned case of
reflex vaso-dilatation is that of the lumbar cord just mentioned. It is true
that many apparent reflexes can be noted, for example the increased flow
of blood in the salivary glands under gustatory reflexes, the blushing of the
skin on exposure to sudden warmth, or even the blushing of emotional origin,
which on first thought might be regarded as vaso-dilator reflexes. But each
of these instances can be just as readily explained as inhibitions of the vaso-
constrictor tonic activity. This double explanation can, as a matter of fact,
VASOCONSTRICTOR AND VASO-DILATOR ACTIVITY 219
be applied to the action of the depressor nerve described above, page 217.
On the whole, however, while we cannot directly and unquestionably prove
the fact, yet it is probable that each of the above examples may be accepted
as examples of reflex vaso-dilatation by direct action on a vaso-dilator center
or centers in the cord.
The Relation of Vaso- constrictor and Vaso-dilator Activity. The
distribution of two sets of regulative fibers for the muscular walls of the
blood-vessels, when considered in connection with the other factors of the
vascular apparatus, gives a wonderfully complete mechanism for the coordi-
nation of the vascular supply with the activity of the different organs. General
and broadly distributed activity of the constrictors produces increase of general
blood pressure, of the dilators decrease of pressure, but local activity of either
set will produce a great reduction or increase of blood in the local organ
with little or no effect on the general pressure. When a vaso-dilatation is
produced locally in one organ and there is an accompanying vaso-constric-
tion in other regions, as usually happens, it is evident that the result may be
a flooding of the local region. This is exactly the thing that is accomplished
in the muscles in violent exercise, in the glands during secretion, in the
stomach during digestion. It is this mechanism that is utilized to throw a
large volume of blood to the skin when the temperature of the body is above
the average, or to blanch the skin when the temperature is low.
Normally, certain regions of the body are associated in that when vaso-
dilatation occurs in one region, vaso-constriction occurs in the other. This is
particularly true with the skin or surface of the body and the viscera or deeper
organs. The same relation is said to exist between some of the visceral
organs.
General Course of the Vaso- constrictor and Vaso-dilator Nerves.
The cell bodies forming the medullary vaso-motor center give off axones,
axis-cylinder processes, some of which go to the nuclei of origin of certain
cranial nerves, while others pass down the cord to end at different levels
in contact with certain cells, probably small cells in the anterior horn and
lateral part of the gray matter. These cells constitute the spinal centers.
The neuraxones of the spinal cells leave the cord in certain spinal nerves in
the anterior roots, pass by the white rami to the sympathetic ganglion chain,
where they end in physiological connection with the ganglionic cells. Axones
from these latter cells pass by an uninterrupted course to their terminations
on the blood-vessel walls. The vaso-constrictor fibers leave the central
nervous axis by the ventral roots of all the dorsal nerves and the first two
lumbar roots, a comparatively restricted region. The vaso-dilators have
the same origin with two exceptions, viz., the vaso-dilators of the salivary
glands found in the seventh and ninth cranial nerves, and the nervi erigentes,
which arise in the roots of the second and third sacrals. The nerves to the
viscera pass direct to their blood-vessels, but the vascular nerves for the skin,
220 THE CIRCULATION OF THE BLOOD
muscles, limbs, etc., rejoin the main divisions of the spinal nerves through
the gray rami, see figures 417 and 418, and pass to the blood-vessels along
with the general nerves of the organ or organs.
VASO-CONSTRICTOR AND VASO-DILATOR NERVES FOR IN-
DIVIDUAL ORGANS.
The particular paths for the vaso-motor nerves has been pretty definitely
established by numerous researches, especially by those of Langley and
his students.
The course of the vaso-constrictor and the vaso-dilator nerve fibers has
been followed satisfactorily in many of the important parts of the body,
though the supply for some regions is yet obscure. This is particularly
true for the brain, where such supply is apparently absent. The two groups
of fibers run the same course, except in the cephalic and sacral regions already
mentioned. They may, therefore, be described together.
The Vascular Nerve Supply for the Head. The vascular nerves
for the head, face, and mouth have their origin in the cord from the first to
the fifth dorsal spinal nerves. They pass through the white rami to sym-
pathetic ganglia, through the stellate ganglion and up the cervical sympa-
thetic nerve to the superior cervical ganglion. From this ganglion they run
to their distribution, either along with the arteries, as with the salivary sup-
ply, or with the sensory nerves, as in the nerves to the mucous membrane
of the mouth, etc. The vascular nerves supplied to the base of the ear follow
the above course, but the nerves for the tip leave the stellate ganglion in the
ramus vertebralis, run to the third cervical nerve, and pass with its auricular
branch to the ear, a circuitous route determined by Fletcher.
The great exception to the above origin is with the vaso-dilator group.
Dilator fibers leave the base of the brain in the direct path of the seventh
cranial nerve to supply the submaxillary and sublingual glands, in the ninth
cranial nerve to the parotid gland, and in both these to the tongue.
The Vascular Regulation in the Brain. The brain requires a large
and uniform supply of blood for the due performance of its functions. This
object is effected through the number and size of its arteries; the two internal
carotids, and the two vertebrals. It is also desirable that the force with
which this blood is sent to the brain should be subject to less variation from
external circumstances than it is in other parts, an effect that is accomplished
by the free anastomoses of the large arteries in the circle of Willis. This
arrangement insures that the supply of blood will be uniform even though
it may be limited through operation or accident to one or more of the four
principal arteries. Uniformity of supply is further insured by the arrange-
ment of the vessels in the pia mater. Previous to their distribution to the
substance of the brain the large arteries break up and divide into innumer-
VASCULAR REGULATION IN THE BRAIN
able minute branches. These capillaries after frequent communication with
one another enter the brain in a very uniform and equable distribution.
The arrangement of the veins within the cranium is also peculiar. The large
venous trunks or sinuses are formed so as to be scarcely capable of change
of size; and composed, as they are, of the tough tissue of the dura mater,
and in some instances bounded by the bony cranium, they are not com-
pressible by any force which the fulness of the arteries might exercise through
FIG. 208. — Showing the Origin and Course of the Vascular Nerves for the Head. (Modified
from Moret.)
the substance of the brain. Nor do they admit of distention when the flow
of venous blood from the brain is obstructed.
The mechanical conditions in the brain and skull formerly appeared
enough to justify the opinion that the quantity of blood in the brain must
be at all times the same. But it was found that in animals bled to death
without any aperture being made in the cranium, the brain became pale and
anemic like other parts. And in death from strangling or drowning, there
was congestion of the cerebral vessels; while in death by prussic acid, the
quantity of blood in the cavity of the cranium was determined by the position
in which the animal was placed after death, the cerebral vessels being con-
gested when the animal was suspended with its head downward, and com-
THE CIRCULATION OF THE BLOOD
paratively empty when the animal was kept suspended by the ears. Thus
although the total volume of the contents of the cranium is probably nearly
always the same, yet the quantity of blood in it is liable to variation, its in-
crease or diminution being accompanied by a simultaneous diminution or
increase in the quantity of the cerebro-spinal fluid. The cerebro-spinal
fluid being readily removed from one part of the brain and spinal cord to
another, and capable of being rapidly absorbed and as readily effused, would
serve as a kind of supplemental fluid to the other contents of the cranium
to keep it uniformly filled. Although the arrangement of the blood-vessels
insures to the brain an amount of blood which is tolerably uniform, yet with
every beat of the heart, and every act of respiration, and under many other
circumstances, the quantity of blood in the cavity of the cranium is con-
stantly varying.
The brain, however, is entirely dependent upon the general blood pres-
sure for variations in the quantity of blood which it receives. During a
high blood pressure the amount of blood that flows in a given unit of time is
greater and during low blood pressure less. Howell has shown that in the
decapitated dog's brain the flow of blood is directly proportional to the differ-
ence in pressure. Numerous attempts have been made to show vaso-motor
mechanisms for the cerebral arteries, but without success. Huber has shown
nerve endings in such arteries by histological methods. Bayless, Hill, and
Gulland make the statement that " no evidence has been found of the exist-
ence of cerebral vaso-motor nerves, either by means of stimulation of the
vaso-motor center or central end of the spinal cord, after division of the cord
in the upper dorsal region, or by stimulation of the stellate ganglion, and
that is to say the whole sympathetic supply to the carotid and vertebral
arteries." Vaso-motor regulation of the flow of blood through the brain
can be accomplished only by the indirect mechanism of regulation of general
blood pressure through variations in the heart's activity, or through the
effects of vaso-constrictions or dilatations in large areas other than the brain.
The Vascular Nerves for the Thoracic Viscera. Numerous efforts
have been made to determine the vaso-motor nerve supply for the thoracic
organs, the heart and lungs. In the heart the observation is rendered com-
plex by the fact of the rhythmic contractions which produce mechanical
pressure on the coronary arteries. Martin, by direct observation through a
lens, and Porter, by measuring the outflow of the coronaries upon vagus
stimulation, came to exactly opposite views; the former that the vagus con-
tained vaso-dilators, the latter that it contained vaso-constrictors. Still
other experiments have been made to prove either constrictor or dilator
nerves for the coronary arteries.
The lesser circulation through the lungs has also proven a difficult situa-
tion to interpret as regards any nervous regulation of the pulmonary arterioles.
The evidence, while not conclusive, is that the vaso-constrictor supply to the
VASCULAR NERVES FOR THE ABDOMINAL VISCERA
223
lungs is from the third to the fifth thoracic nerves, but that the vaso-constric-
tion produced is slight in comparison with regions of the systemic circulation.
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The Vascular Nerves for the Abdominal Viscera. The vaso-con-
strictors and the vaso-dilators for the organs of the abdominal cavity have
a broad origin in the cord; from the first dorsal to the fourth lumbar in
the dog and cat. The nerves pass to the organs by the splanchnic nerves,
THE CIRCULATION OF THE BLOOD
and by the solar, celiac, and mesenteric ganglia. The vascular nerves for
the different organs may be given in tabulated form:
Vascular Nerves for the Abdominal Viscera.
Organ. Spinal Origin of the Vascular Nerves. Course to the Organ.
Stomach and in- i T_n yT (Splanchnic nerves and
testine. [ 5' ' 7' ' 9' IO' ' ' 3 ' '( solar and celiac ganglia.
( Splanchnic nerves and
Spleen 3, 4, 5, 6, 7, 8, 9, 10, n, 12, 13 D, i L j golar and celiac ganglia.
j Splanchnic nerves and
Liver 3> 4, 5, 6, 7, 8, 9, i°> " D \ solar and celiac ganglia.
; 4, 5, 6, 7, 8, 9, 10, n, 12, 130, i, 2, 3, { Splanchnic and celiac
Kidnev \ 4 L \ ganglia.
< Inferior splanchnic and in-
Pelvic viscera. . . . i, 2, 3, 4~L -j ferfor mesenteric ganglia.
The Vascular Nerves for the External Genital Organs. The vaso-
dilators for these organs arise from the second and third sacral nerves and
pass to the organs by the nervi erigentes and the pelvic plexus. They form
the second great exception to the region of general outflow of vascular nerves.
The constrictors, on the other hand, arise in the spinal nerves from the last
dorsal and first four lumbar. They run the same course as given in the table
for the pelvic viscera.
The greatest variations in the quantity of blood contained at different
times in the external genital organs are found in certain structures which
contain what is known as erectile tissue. These organs, under ordinary cir-
cumstances, are soft and flaccid, but at certain times they receive an un-
usually large quantity of blood, become distended and swollen by it, and
pass into the state termed erection. Such structures are the corpora cavernosa
and corpus spongiosum of the penis of the male, and the clitoris in the female.
The nipple of the mammary gland in both sexes, and, according to some
authors, certain nasal membranes contain erectile tissue.
The corpus cavernosum of the penis, which is the best example of an
erectile structure, has an external fibrous membrane or sheath. From the
inner surface of the sheath numerous fine lamellae project into the cavity,
dividing it into small compartments, like cells when they are inflated. Within
these cells there is a plexus of veins upon which the erectile property of the
organ mainly depends. The plexus consists of short veins with very close
interfacings and anastomoses with very elastic walls admitting of great varia-
tions in size. They collapse in the passive state of the organ, but are capable
of an amount of dilatation which exceeds beyond comparison that of the arteries
and veins which convey the blood to and from them. The strong fibrous
tissue lying in the intervals of the venous plexuses, and the external fibrous
membrane or sheath with which it is connected, limit the distention of the
vessels and give to the organ its condition of tension and firmness. The
same general condition of vessels exists*in the corpus spongiosum urethrae,
VASCULAR NERVES FOR THE TRUNK AND LIMBS
225
but the fibrous tissue around the urethra is much weaker than around the
body of the penis, while around the glans there is none. The venous blood
is returned from the plexuses by comparatively small veins; all of which
are liable to the pressure of muscles when they leave the penis. The mus-
cles chiefly concerned in this action are the erector penis and accelerator
urinae. Erection results from the distention of the venous plexuses by a
sudden influx of blood resulting from the action of the nervous vascular re-
flexes. It is facilitated by the special muscular mechanism which prevents
the outflow of blood.
The Vascular Nerves for the Trunk and Limbs. The skin and
muscles of the trunk receive their cutaneous and motor nerves by a seg-
mental arrangement in which the innervation is by bands corresponding
FIG. 210. — Plan of Distribution of Vaso-constrictor Nerves for the Fore Limbs. An. vi,
Annulus of Vieussens. (Modified from Moret.)
with the segments of the cord and the spinal nerves. It is much the same
with the vascular nerves; they are distributed to the skin and walls of the
trunk in the same segment in which they arise. Langley says that the suc-
cessive bands overlap somewhat.
In the fore legs or arms the vascular nerves arise from the first to the
fifth dorsal spinal nerves, run to the stellate ganglia, then by the gray rami
15
226 THE CIRCULATION OF THE BLOOD
back through the ramus vertebralis to join those cervical nerves that enter
into the brachial plexus, figure 210.
The nerves for the blood-vessels of the lower limbs arise from the tenth
dorsal to the second lumbar nerves. These pass to the ganglionic chain,
and gray rami are given off which join the lumbar plexus and run with the
divisions of that nerve complex to their distribution in the skin and muscles.
Vaso-constrictors and vaso-dilators have a common course to the lower limbs.
The Vaso- constrictor Nerves for the Veins. Mall has proven
that vaso-constrictors are present for the portal vein. These fibers are
present in the splanchnic nerves. Other evidences have been observed
which render the view probable that vaso-motors for the veins in general
exist. Hough, for example, in an extended study of the capillary pressure
found many variations which were readily explained only on the assump-
tion of veno-motor activity, see figure 201.
LABORATORY EXPERIMENTS ON THE CIRCULATION.
1. The Rate of the Human Heart-beat. Determine the rate of
the heart-beat per minute by counting the radial pulse, using a watch for
the time. Make the determination after sitting quietly in a chair for five
minutes. Take the average of at least ten determinations for your own case.
Determine the heart-rate under the same conditions for as many different
persons as you can. Tabulate these determinations in a table which shows
age, sex, weight, and height of the different individuals, and compute a
general average for your entire set.
Note the effect on the averages obtained above after the person lies down
for five minutes, after standing quietly for the same time, and after five minutes'
brisk walk. Tabulate as directed.
Count the heart-rate immediately after two minutes' fast running, allow-
ing the person immediately to sit in a chair. Count the rate by two minutes
until there is a complete return to the normal, as determined above. Tabu-
late these results and compare the figures obtained from several different
individuals.
Count your own heart-rate at intervals during one entire day, giving
special attention to the rate just before and just after meals, but in every
case make the count after sitting quietly for five minutes. A marked diurnal
variation will usually appear. Determine these rates on several individuals,
and tabulate as before.
2. Human Cardiogram. Apply a Burdon-Sanderson cardiograph
to the thorax over the point between the fifth and sixth ribs of the left
side, at which point the cardiac impulse is felt most distinctly. Connect
the cardiograph with a recording tambour, Marey's form, adjust the tension
of the cardiograph and the pressure of the air within the system, and take a
THE FROG S HEART
227
tracing of the movements of the lever of the recording tambour on the smoked
paper of the kymograph. The kymograph cylinder should travel at the rate
of about two to three centimeters per second. Take the time of the move-
ments of the kymograph by means of an electric magnet connected with an
electric clock beating seconds. After the record is secured the proper de-
scription should be written with a pencil on the smoked paper, and the paper
removed from the kymograph carefully and the whole record fixed in shellac.
When the record is dry, count the rate of the heart-beat from the record
and measure the time of the cardiac systole and diastole, and the time of
pause at the end of the diastole. If these facts are taken from records secured
under different conditions of exercise, etc., as outlined in the preceding ex-
periment, then they may be brought together in a table for convenience of
inspection. A comparison of such results will usually show that with the
higher heart-rates the decrease of the time of the cardiac cycle is at the ex-
pense of the time of the diastole; in other words, the time of the systole re-
mains fairly constant while the time of the diastole increases or decreases
with the rate, a fact to which Hiirthle has drawn attention, figure 157.
3. The Rate and Sequence of the Contractions of the Frog's
Heart. Destroy the brain of the frog and open the thorax, but do
not destroy the pericardium. Count the rate of the heart per minute, then
FIG. 2ii.— Heart Lever for Frog or Turtle Hearts.
remove the pericardium and make a second determination after the heart is
exposed to the air. The different parts of the heart when exposed are easily
identified and the contractions which take place in definite sequence can be
determined without difficulty. Make this determination for the ventricle,
auricle, and sinus venosus by direct observation.
228
THE CIRCULATION OF THE BLOOD
Prepare a cardiac lever as shown in figure 211, taking special care to ar-
range the foot so that it will not bind on the lever when in motion. Adjust
the foot of the lever on the exposed ventricle and bring its point to write on
the smoked paper of a recording cylinder. This cylinder should travel at
the rate of about i cm. per second and its speed be determined by the writing
point of an electric magnet which is connected with the electric-clock circuit
marking seconds. Take care to adjust the time magnet in a vertical line
with the writing point of the heart lever, placing the heart lever about i cm.
above the magnet lever. The tracing of the ventricle's movement, or cardio-
gram, will show alternate contraction, relaxation, and pause of the ventricle.
It will also enable one to measure the exact proportion of the total time of the
FIG. 212. — Cardiogram Showing Contractions of the Auricle, a, and Ventricle, v, of a Frog. Time in
seconds. The record shows the sequence of the auricle and ventricle. (New figure by Dooley.)
cardiac cycle consumed by the systole and diastole, and also that portion of
the diastole in which the ventricle is wholly at rest.
After one has obtained the ventricular tracings and has learned the diffi-
culties of adjusting the apparatus, a second heart lever should be adjusted
so that its foot rests upon the auricle, and the auricular movements may
therefore be traced on the smoked paper of the recording cylinder at the same
time as those of the ventricle. If some care is taken to adjust these two
writing points in a vertical line a splendid tracing showing synchronism
between auricle and ventricle is obtained. Measure the rate and the time
of the different phases of the contraction of the auricle and ventricle and
tabulate them in the following form, always expressing fractions in the
decimal system:
Rate per
Minute.
Time of Systole
in Seconds.
Time of Diastole
in Seconds.
Time of Pause ,
in Seconds.
Auricle
Ventricle
4. The Contractions of the Excised Heart of the Frog. Pith a
frog and expose the heart, as described in the preceding experiment. Re-
INFLUENCE OF DIFFERENT NUTRIENT1 FLUIDS 229
move it completely from the body by first cutting the arteries at their branch-
ing in front of the bulbus arteriosus, then carefully lifting up the parts of
the heart and cutting away the great veins where they enter the sinus. This
will remove the entire heart, including all its contractile parts. The frog's
heart when thus removed and still wet with its own blood will continue con-
tracting rhythmically and in its natural sequence for some hours. Place
such an isolated heart in a watch-glass and take a record of its contractions,
by the apparatus described in the preceding experiment.
Set this watch-glass on the metal warming-box supplied, and arrange
for the circulation of water of different temperatures through the box. Vary
the temperature of the box, and therefore of the heart placed upon it, by
allowing water of o° C., 10° C., 20° C., 30° C., 40° C. to flow through it.
Record the contractions of the heart at each of these temperatures on the
recording drum as described in experiment 3 above. The heart being ex-
posed will not take the same absolute temperature as the box, but the relative
temperature will be decreased or increased. Tabulate the rates at these
different temperatures by the plan previously described.
5. The Influence of Different Nutrient Fluids on the Excised
Heart. Expose a frog's heart, as previously described, and insert a can-
nula into the ascending vena cava just where it enters the sinus. Ligate
the descending vena cava, introduce a cannula into one of the branches of
the aorta, and carefully separate the heart from the body without injuring its
cavities within the points of ligature. Or the ligatures may be laid and the
cannulae inserted without separating the heart from the body. Connect
the venous cannula with a Mariotte's bottle filled with physiological saline,
0.7 per cent sodium chloride. Adjust the constant level tube for a pressure
of 6 cm. of fluid and allow the saline to flow through the heart. The arterial
cannula should be connected with a short rubber tube the mouth of which
allows the fluid to flow into a beaker or glass tumbler. The outlet of the
arterial tube should be about 2 cm. above the level of the heart so that the heart
must work against a slight pressure. The heart will continue its contractions
in good sequence and with a fairly rapid rate. Record the contractions on
the smoked paper of the recording drum, together with a time tracing in
seconds, the drum traveling at the rate of about 2 to 5 mm. per second.
Use the tracing obtained under the influence of physiological saline solution
as a normal and compare with it the rate and amplitude of the contractions
when the heart is perfused with Ringer's solution; with Locke's solution; with
saline and potassium in the proportion found in Ringer's solution; with
saline and calcium in the proportion found in Ringer's solution; with milk
diluted 6 vols. with saline; with normal serum or blood; with blood or serum
diluted four times with saline. Tabulate the rates and amplitude of the
heart under these different influences by the method previously followed.
6. The Heart Volume. Isolate a frog's heart by the method de-
230
THE CIRCULATION OF THE BLOOD
scribed for irrigating it with fluid in the preceding experiment. Connect
it up in a Roy's tonometer, see figure 213, adjust the lever of the tonometer
for a tracing on the smoked paper of the recording cylinder. Use a time-
marker. This instrument records the change in volume with each heart
FIG. 213. — Roy's Tonometer.
contraction. The influence of pressure, varied between 2 and 10 cm., and of
nutrient fluids on the heart volume may be determined.
7. The Isolated Heart of the Terrapin. The heart of the terrapin,
being somewhat larger and somewhat more responsive than the heart of the
frog, may be substituted in the two immediately preceding experiments.
The facts obtained from it will be essentially the same as those obtained
from the frog's heart.
8. The Isolated Mammalian Heart. The mammalian heart
may be isolated from the body and kept alive and contracting for many
hours, as has been demonstrated by numerous recent observations. It is
only necessary to keep the temperature approximately that of the normal
body and to irrigate the hear: through the coronary circulation with blood,
or diluted blood, containing sufficient hemoglobin to supply the heart with
the requisite amount of oxygen. Or, the heart may be kept alive on the inorganic
salt solutions, provided these are supplied with oxygen under considerable
tension (Porter, Howell). Even the human heart has been isolated and
kept contracting for seme hours in the above manner (Kuliabko). The
method used is to insert a supply cannula into the aorta and irrigate the heart
through the coronary circulation, as described by Langendorff. Many in-
teresting experiments and demonstrations can be made on the mammalian
AUTOMATIC CONTRACTIONS OF THE CARDIAC MUSCLE 231
heart, but, as this experiment is usually a demonstration experiment, the detail
of procedure is left to be supplied by the demonstrator.
9. Automatic Contractions of the Cardiac Muscle. Isolated por-
tions of the dog's ventricle have been kept in rhythmic contraction by
Porter, but the best laboratory material is supplied by the heart of the terra-
pin. Cut a strip from the ventricle of the terrapin extending around its
curved apex, as shown by the dotted line in the accompanying figure, 214.
Split this strip longitudinally into two parts, each of which will then be about
3 to 5 mm. in diameter. Use care to cut smooth, straight strips. Tie a silk
thread around the extreme tips of each end of the strip, tying a loop of about
i cm. long at one end, and about locm. long at the other. Suspend the strip
over a glass hook, figure 215, by the short loop, and connect it with a heart
lever by the long loop, as shown in the same figure. Use a tension of one
gram. Contractions of this strip as arranged will be recorded with a mag-
nification of about five and with the upstroke of the lever, which is convenient
FIG. 214. — Heart of the Terrapin to Show the Method of Cutting the Apex Strip. V, Ventricle;
Au, auricles; Vc, venae cavae; Ao, aorta.
for reading and interpretation. The strip may be kept moist with physio-
logical saline in a specimen tube of about i by 3 inches in size, and the
arrangement of apparatus figured makes it possible easily and quickly to
change this solution for any other that may be desirable.
Contractions of the ventricular strip in saline usually begin in from 10 to
40 minutes after the preparation is made and go through a regular sequence of
slight increase in rate and amplitude for from 10 to 20 minutes, followed by
a very constant rate, but gradually decreasing amplitude for a period of from
2 to 3 hours, figure 171.
This preparation makes possible many instructive experiments tending
to show fundamental properties of cardiac muscle. The preparation con-
232
THE CIRCULATION OF THE BLOOD
tains no nervous mechanism and its behavior may be safely attributed to
the muscle substance itself.
Try the following experiments: Submit the strip to saline solutions of
different temperatures, varying through steps of 5 degrees from o° C. to
40° C. Try the effect of the different ingredients in Ringer's solution; com-
bine potassium with saline, figure 172; calcium with saline, figure 173; and
potassium, calcium, and saline. Also try Locke's solution; solution of blood
diluted with saline; solution of milk with saline in the proportion of one
part milk to four of saline.
Cut and mount strips from the auricle and from the sinus, letting
the latter extend out on to the vena cava. In these last preparations
care must be taken to balance the lever, as a slight overtension paralyzes
the muscle. Immerse these strips in pure serum, compare their behavior
FIG. 215. — Arrangement of Apparatus for Studying the Contractions of the Strip of the Apex
of the Ventricle.
with that of the ventricle in pure serum. The sinus and usually the auricle
will be found rhythmic in serum, while the ventricle, if it contracts at all,
will contract with a very slow rhythm. Often there is a distinct progressive
decrease in the rhythm, the sinus having the same rhythm as the whole heart,
the auricle a considerably slower rhythm, and the ventricle with a very slow
rhythm or even quiet. The sinus preparation will show beside the funda-
mental rhythm a characteristic slow contraction and relaxation, which has
been described as tone, figure 170.
10. Influence of the Cardiac Nerves on the Frog's Heart. Care-
fully pith a frog so as not to break the blood-vessels at the base of the brain,
and thus permit the loss of the blood of the animal. Expose the heart as
previously described, make a cut through the manubrium, continue it througn
INFLUENCE OF THE CARDIAC NERVES ON THE FROG'S HEART 233
the skin and muscles, at the angle of the jaw, thus exposing the vagus nerve.
The vagus runs diagonally downward and backward along the edge of the
delicate muscle toward the heart. The glossopharyngeal is just in front
of the vagus and the hypoglossal just behind it. The latter runs parallel
with the vagus near its origin, but lower down turns across the vagus and runs
to its distribution in the tongue muscles. These two nerves serve to aicl the
student in the identification of the vagus, see figure 216. It is usually better
to cut the hypoglossal away, and also to cut the brachial and the laryngeal
nerves.
Prepare an induction coil, see Laboratory experiments on muscle. Use
platinum electrodes of the Harvard pattern, set the coil for a mild stimulus when
tested by the lips or the tongue, lift up the vagus gently and lay it on the platinum
tips of the electrodes, taking care that the electrodes do not come in contact
FIG. 216. — Diagram Showing the Relations of the Vago-sympathetic Nerve to the Heart, in the
Frog. Hy, Hypoglossal; Gl, glosso-pharyngeal; Lar, laryngeal; V, vago- sympathetic; H, heart;
L, lung.
with the adjacent tissue. Arrange a signal magnet as shown in the diagram,
so that the signal magnet and the stimulating key of the induction coil may
be closed and opened at the same instant. When all is ready stimulate the
vagus for five to ten seconds, recording the time with the signal magnet and
allowing the record to continue until the heart has returned to its normal
rate and amplitude. Most students fail in this experiment by not allowing
sufficient time in the record for a normal before stimulation, and by not
allowing sufficient time after stimulation for a return to the normal. It will
be better to take one good tracing, showing the facts of the experiment, than
several partial tracings, none of which are complete. With these sugges-
THE CIRCULATION OF THE BLOOD
tions in mind, repeat the above experiment, using stimulating currents of
increasing intensity until complete cardiac inhibition is produced. Perform
experiments showing the influence of the time of the stimulus on the inhibi-
tion, i.e., stimuli of i second, 2 seconds, 10 seconds, and 30 seconds.
In the frog the vagus or inhibitory, and sympathetic or accelerator fibers,
are found in one trunk, the vago-sympathetic, but the stimuli will usually
produce inhibitions and not acceleration. Occasionally with very weak
preparations direct acceleration may be produced. To get the pure inhibi-
tory or pure accelerator effects one must dissect back to the origin of the vagus
before it is joined by the sympathetic fibers; or to the sympathetic trunk
between the third spinal nerve and the point where it joins the vagus trunk.
In the study of the conditions in the above experiments one should note
the rate per minute and the amplitude in the normal, the period just before
stimulation, the rate and amplitude during the period of stimulation, and the
same at different times after the stimulation until constant results are ob-
tained. A tabulation of these results will usually enable one to judge the
influence of each of the various factors recommended in the experiment.
11. Influence of the Cardiac Nerves on the Terrapin's Heart.
Instead of the frog one may use the terrapin in the above experiment.
In this animal the sympathetic can very readily be isolated, and accelerator
fibers have been described for it. In the experience of the laboratory of
the author no experiments have yet demonstrated unquestionable cases of
cardiac acceleration. The vagus produces inhibitions which differ from
the effects in the frog in that complete inhibitions of the ventricle are followed
by contractions that are apparently at once maximal. In the frog the con-
tractions when they reappear are at first slight, but gradually increase in
amplitude until they have their former value.
12. The Arterial Blood Pressure in a Mammal. The arterial
blood pressure may be measured on the anesthetized cat, dog, or rabbit.
Simple blood pressure was originally measured by Bale's method of connect-
ing the artery with a vertical tube and allowing the blood to flow freely into
the tube until a column was raised to the height which balanced the pressure
in the vessel. This simple method is decidedly the best for the beginner,
since it does not necessitate the use of very complicated apparatus. At the
same time it gives practice in anesthesia and in operations of vivisection,
and therefore serves as a good preparation for the more complicated ex-
periments which follow.
The necessary apparatus should be prepared first, as follows: A vertical
tube supported on a stand with a scale graduated in the metric system, as-
sorted cannulae of approximately the size of the carotid artery of the animal
to be operated on, linen thread ligatures, dissecting set in good condition,
an animal-holder with strings or straps firmly to fasten the anesthetized
animal, a chloroform -ef>er mixture for dogs (or other anesthesia according
ARTERIAL BLOOD PRESSURE IN A MAMMAL 235
to the animal to be used). Four men should be assigned to perform this
experiment. While two are anesthetizing and preparing the animal, two
should arrange the apparatus as nearly ready for connecting with the artery
as possible. When all the apparatus is arranged and the animal anesthetized,
it should be tied firmly to the animal-holder. Let one experimenter attend
strictly and at all times to anesthetizing the animal; recovery jrom the
anesthesia must not occur. Let the operator quickly expose about 3 cm. of
the carotid artery by making an incision through the skin of the neck 5 cm.
long, and dissecting down between the muscles. Separate the carotid from
the adherent vagus nerve by tearing the connective tissue with the scalpel
handle, freeing the vessel from about 2 to 3 cm. cf its length. Lay two loose
ligatures of linen thread around the vessel, place a small bulldog forceps
on the exposed artery nearest the heart, and ligate the end nearest the head
with one of the ligatures. Take up the intervening artery with strong forceps
and make a V-shaped cut near the ligature, pointing the cut toward the heart,
and letting it extend about half way across the artery. Introduce a cannula
through the opening toward the heart, and tie it firmly with the second liga-
ture. Connect the cannula with the rubber tubing to the vertical glass tube.
When all is ready remove the bulldog forceps on the artery, following
which the blood will flow freely from the artery into the tube until the pressure
from the column of liquid is just equal to that inside the artery itself. If an
anti-coagulating fluid, 10 per cent magnesium sulphate, is first introduced
into the vertical tube of fortunate height little blood will be lost and probably
clotting at the cannula will be delayed for some minutes. The mounting t
of the blood into the empty tube makes indeed a more striking demonstration,
but it has the disadvantage of quickly forming a clot which stops the experi-
ment itself.
An accurate measure of the height of the top of the column above the
level of the cannula at the artery represents the arterial blood pressure in
terms of blood, or of 10 per cent magnesium sulphate. The specific gravity
of magnesium sulphate is 1.030; of blood 1.056; of mercury 13.6. Record
the pressure you obtain in terms of blood and of mercury. Note also the
variations in pressure and account for the rhythm of each. There will be
a general variation of pressure, depending upon the degree of anesthesia.
If anesthesia is light and muscular movements happen, there will be an in-
crease in the blood pressure. If the anesthesia is heavy, then the blood pres-
sure falls. These points of variation should be marked, or recorded at once in
note-books. Make full notes of all accessory facts which would aid you to
explain the variation in blood pressure, such as size of the animal, rate of res-
piration, rate of heartbeat, the variations in anesthesia, the presence of the
reflexes, etc., etc.
Chloroform the animal to kill it, and note the change in blood pressure
during the process
236 THE CIRCULATION OF THE BLOOD
13. The Circulation Time. The circulation time is most satis-
factorily determined in the laboratory by introducing a saline solution of
methylene blue into the jugular vein on one side. Note directly the time
with a stop-watch until the color appears in the jugular artery and the jugular
vein of the opposite side.
Anesthetize a cat or dog with a chloroform-ether mixture, tie it on the
animal-holder and, when the eye reflexes are lost, expose the jugular vein on
the right side, the carotid artery and the jugular vein on the left. Fill a
2-cm. hypodermic syringe with i per cent methylene blue in physiological
saline, insert the needle into the right jugular vein, pointing it toward the heart.
Lift the left carotid artery and place under it a strip of moist white paper
2 cm. wide; prepare the left jugular vein in the same way. Place the animal
so that these vessels are lighted to the best advantage. At a given moment
inject the contents of the hypodermic syringe, noting the time with a stop-
watch. Observe the color of the left carotid and the left jugular, respec-
tively, very carefully, and take the time when the first appearance of the
methylene blue is noted. The color will appear first in the artery, second
in the vein. The difference in time between the moment of injection and
the moment of color in the artery represents, with a slight correction, the
circulation time of the pulmonary or lesser circulation. The time from the
injection until the color in the jugular vein represents the total time of circu-
lation.
Stewart has made these determinations even more correctly by the elec-
trical-resistance method. He injected 10 per cent salt solution and deter-
mined the variation in resistance by a galvanometer. If the galvanometer
is available, then check the above determinations by the electrical method,
arranging the apparatus under the direction of an instructor.
14. The Blood -Pressure Model. An artificial model of the cir-
culatory apparatus, which illustrates all mechanical parts involved, has
been arranged by Porter, figure 217. Other forms, which show these as well,
are usually available or can be easily constructed. The model should have
the following possibilities: A pump, which permits of rhythmic action at a
varying rate and varying force; a resistance to the outflow liquid, which can
be increased or decreased; and an elastic set of vessels into which the pump
discharges.
If Porter's schema is used, determine the following points: The pressure
in terms of mercury in the arterial and venous limbs of the apparatus when the
pump makes a rate of 72 per minute; the influence on these two pressures
when the rate is increased, when it is decreased ; the effect on these pres-
sures when the peripheral resistance is great, when it is low. If a sphygmo-
graph is available, take a tracing of the pulse in the elastic tube representing
the arterial side of the schema.
If an ordinary bulb syringe and simple apparatus is used, then deter-
THE ARTERIAL PULSE 237
mine the following: The character and rate of the outflow when water is
pumped into the rigid glass tube with no resistance to the outflow; when a
glass tube of smaller caliber is connected with the end of the larger glass
tube so as to produce, high resistance to the outflow. Pump the water into
a rubber tube of smalle^ ^ize and compare with the proceeding in which
there is no resistance to the outflow ; also when a glass tube of small caliber
is introduced into the end in order to produce high resistance to the outflow.
Determine the amount of resistance necessary to produce a constant out-
flow when the pump has a rate of 72 beats per minute. In this experiment
what effect is produced on the outflow if you vary the rate of the pump ? if
you vary the force of the stroke? if you vary the elasticity of the rubber
tube representing the artery? if you vary the resistance represented by the
size of the glass tube at the outflow ?
15. The Arterial Pulse. The form of the arterial pulse may be
taken by one of the various sphygmographs applied to the radial
artery at the wrist or the common carotid in the neck. If the tambour
method is used, apply a sphygmograph tambour on the wrist with the central
pressure over the radial artery. Fasten it in place by the proper bands,
adjusting the tension by flexing the wrist. Connect the receiving tambour
with a delicately balanced, small-sized recording tambour, which should
write its movements on a cylinder revolving at the rate of i to 2 cm.
per second.
A more convenient clinical instrument is the Dudgeon or the Jacquet
sphygmograph. These are to be applied at the wrist and give tracings
showing delicate variations in the form of the pulse wave with great magnifi-
cation and a considerable degree of accuracy. Make a comparison of the
form of the pulse wave from tracings taken from at least six different
individuals.
The sphygmogram from the carotid artery may best be taken by apply-
ing a tambour sphygmograph to the neck over the carotid and fastening it
in position, usually by a spring.
16. The Rate of Propagation of the Pulse Wave. Apply tambour
sphygmographs to the carotid in the neck and to the radial at the wrist, and
make simultaneous record on a recording drum, adjusting the writing levers
of the two recording tambours in an exact "vertical line. Let the recording
drum travel at the speed of 2 cm. or more per second, and record the speed
by a 50 double-vibration tuning-fork. The carotid pulse will be found to
precede the radial pulse by the fraction of a second. This short interval,
which can be determined in hundredths of a second by comparison with the
time tracing below, represents the time required for the pulse wave to travel
the distance from the carotid to the radial. Measure the distance on the
individual used in the experiment and calculate the rate of propagation of
the pulse wave in centimeters per second.
238 THE CIRCULATION OF THE BLOOD
If the writing points of the recording levers in this experiment are made
of very delicate strips of note paper, so as to offer little resistance to the sur-
face of the drum, the detail of the pulse wave at the two points will be
accurately transcribed and may be compared.
17. The Capillary Circulation. The capillary circulation is best
demonstrated in the laboratory by direct observation on the web of the frog's
foot by the use of the compound microscope. Give a 40-gram frog a hypo-
dermic injection of 0.3 c.c. of ether under the skin of the back. Wet a piece
of cheese cloth the size of a handkerchief with tap water and wrap the etherized
frog so as to cover the entire body with the exception of the foot. When the
anesthesia has progressed so as to destroy voluntary movements, bind the
foot on an ordinary frog board and spread the web over the window in the
board. Choose an area of the skin which shows small arteries, capillaries,
and veins, and in which the blood is flowing freely and rapidly. Examine
with a low-power compound microscope. In a favorable field small arteries,
capillaries, and veins with blood flowing rapidly through them will be easily
found. Choose one such field, cover with, a piece of thin cover glass, moisten-
ing with a drop of water if necessary, and examine with a high powrer. Note
in the small artery the pulsating current; the border of clear fluid along the
side of the main stream of blood; the slight pulsations; and the white cor-
puscles that will be found flowing along the borders of the current. In the
small veins there are usually no pulsations and the speed of the current is
somewhat less. In the capillaries a careful examination will reveal a deli-
cate wall, the individual corpuscles, and the fact that the red .corpuscles are
actually larger than the diameter of the capillary at some points and must
be bent to pass through. Note that the capillaries form an intricate and
anastomosing network; ttiat the current may occasionally reverse itself in
some of the anastomoses.
The anesthetizing effect of the dose of ether recommended will usually con-
tinue about 15 to 20 minutes. If the observation is more prolonged a second
dose of ether should be given. The capillaries in the tails of small fish are
of ten very readily observed and these may be substituted for the frog's web.
18. Capillary Blood Pressure. Measure the capillary blood pres-
sure in your own finger by von Krie's method. This apparatus consists
of a small piece of glass an inch square, or less, which is placed across the
knuckle of the finger just back of the nail. A small weight pan is suspended
by a loop of thread over this glass plate so that weights put in the pan will
bring varying pressure on the plate above. Add weights to the pan until
an area of the skin, about 5 mm. in diameter, is blanched by the pressure.
Mark the outline of this bloodless area on the glass, take off the apparatus
and measure the exact area of glass so marked, weigh the entire apparatus
and compute the pressure per square centimeter for the area. This pres-
sure in terms of mercury represents the capillary blood pressure in the vessels
BLOOD PRESSURE IN A MAMMAL AND ITS REGULATION 239
of the skin of the finger at that level. Vary the experiment by measuring
the pressure with the finger held at the level of the top of the head; with the
finger held as low as possible; held at the level of the heart. Tabulate the
measurements. The capillary blood pressure at the level of the heart is
usually from 40 to 50 mm. of mercury.
19. The Arterial Blood Pressure in a Mammal and Its Nervous
Regulation. After the student has measured the arterial blood pres-
sure by Hale's method, described above, he is in a position to study the
variations and coordinations in the blood circulatory apparatus. The re-
cording apparatus consists of writing pens, seconds time marker, signal marker,
blood-pressure manometer preferably Ludwig's mercury manometer, and
a continuous paper kymograph preferably Ludwig's weight-driven form
for a continuous record of the arterial blood pressure. Connect the cannula
with the mercury manometer which is provided with a pressure bottle.
Use a cannula of the form shown in figure 185, connecting the side limb of
the cannula with the mercury manometer, and the end limb with the pressure
bottle. When the apparatus is ready anesthetize a mammal (dog, cat, or
rabbit), and bind it down to the animal-holder. Let one operator attend
strictly and at all times to the anesthetic, for the animal must not under any
condition recover consciousness during the experiment.
Expose the carotid artery in the neck, as described in experiment 12 above,
arrange it with ligatures for inserting the cannula, expose the vagus nerve
with the same care, and throw ligatures around it for convenience in lifting
it out of its bed. Make in the carotid a V-shaped cut directed toward the
heart, insert and ligate the cannula as previously described. Before begin-
ning the experiment one should see that all the tubes are filled with the anti-
coagulating liquid and that the manometer is under pressure from 100 to
150 mm. mercury. When all is ready start the kymograph, ink the recording
pens, see that they are recording properly and that the adjustments are se-
cured, remove the bulldog forceps from the artery, and the pressure record
begins.
1. Take a tracing of the normal arterial pressure and heart rhythm with
the recording paper moving at the rate of 0.5 cm. per second.
2. Stimulate the vagus nerve with a mild-strength induction current.
If this stimulus is strong enough to produce change in blood pressure or in-
hibitions of the heart rate, then allow sufficient time following the stimulus
for the blood pressure to return to the previous normal. Observing these
rules, vary the intensity of the stimulus from that which produces no ap-
parent effect to that which produces complete inhibition of the heart. Vary
the time of the stimulus from i to 10 seconds, using different strengths.
3. Allow the vagus to fall back in its warm bed and stimulate the skin
of the animal at some sensory surface, say the lips, the ear, or the foot. By
varying the intensity of the stimulus, a strength will be found which will
240 THE CIRCULATION OF THE BLOOD
produce no reflexes of the voluntary muscles, but which will produce marked
effects on the heart rate and on the blood pressure. Expose the sciatic nerve,
or any other general nerve trunk, cut it, and stimulate the central end for 5
seconds. With a proper strength of stimulus a greater effect is produced on
the heart and on the blood pressure than by stimulating a small spot of skin.
4. Cut the right vagus nerve and mark the exact time on the tracing by
the signal marker. After 10 to 15 seconds cut the left vagus, marking the
time of cutting with the same care on the tracing. As soon as the nerves are
cut, the heart-rate will be observed to increase sharply and the blood pressure
to rise. The respirations also change in rate and depth, a fact which can
be noted on the blood-pressure tracing. Do not disturb the animal or record
until stable equilibrium is again reached.
5. Now lift up the distal end of the divided vagus, and stimu-
late it with an electric current of the strength which previously just
produced inhibition. Repeat the experiment on the proximal end of the
divided vagus. The stimulation of the proximal end of the vagus produces
no direct effect on the heart rate when both vagi are cut, but does produce
profound changes on the blood pressure owing to vaso-motor effects.
6. If the rabbit is used, stimulate the depressor nerve, which produces
marked fall in blood pressure from reflex effects.
7. Repeat the stimulation of the central end of the sciatic as described
in 3, now that the vagus nerves are cut. The stimulation of this nerve no
longer produces changes in the heart-rate, but the blood pressure is influenced
as before, showing that the vaso-motor centers are reflexly stimulated.
8. When you have finished the outline of experiments, give an excess of
the anesthetic to kill the animal and continue the record until the animal is
dead. The blood pressure will fall rapidly, the heart-rate will become slower
but does not cease for a long time.
Should a clot form in the cannula, put a bulldog forceps on the artery,
disconnect the manometer tube, and wash the clot out by a stream of liquid
from the pressure bottle. Use care not to allow this fluid to enter the ex-
posed wound.
Represent the results of each individual experiment in the above series
in tabulated form which shall show i, the blood pressure and heart rate
just before each experiment; 2, during the experiment; and 3, at different
times after the experiment until the normal is reached. After the facts are
taken from the tracings and arranged in tabular form, make a study of these
facts and draw all the conclusions you can concerning the nervous regula-
tions of the heart and of the blood pressure.
20. Arterial Blood Pressure in Man. The arterial blood pressure
in man can be measured only indirectly by measuring the pressure which it
takes around the arm completely to close the artery. Some form of the
Riva-Rocci apparatus, preferably Erlanger's sphygmomanometer, should
VASO-MOTOR CHANGES IN THE FINGER 241
be used. Adjust the rubber bag and leather sleeve of the Erlanger appara-
tus, figure 189, to an arm, and connect it to the sphygmomanometer, set the
valve and quickly pump the pressure up to a point which occludes the pulse.
Adjust the writing point of the recording tambour to the smoked paper on
the cylinder, then lower the pressure by lo-mm. steps until the first pulse
appears. Now proceed with care, changing the pressure by 5-mm. steps
until a record has been obtained which passes the maximal amplitude. Now
release the pressure from the arm. The first point in the decreasing pressure
at which the pulse tracing begins to increase is known as the systolic pres-
sure; the point in the pressure which records the highest point in the ampli-
tude of the pulse wave is known as the diastolic pressure. The systolic
pressure will vary from 120 to 150 mm. of mercury; the diastolic from 90 to
120 in different individuals of the average physiology class.
21. The Vaso-motor Changes in the Finger, the Plethysmogram.
Insert the finger in the Porter finger plethysmograph, fill the tube with
water, and connect it with a small-sized air tambour. The variations in
volume of the finger are slight, so that one must use a rather long, delicately
balanced recording lever. Take a tracing on a recording cylinder moving
at a slow speed, i mm. per second. The finger and its plethysmograph
should be supported by a swinging support so that no mechanical move-
ments will destroy the accuracy of the record. Observations through several
minutes will usually show variations in volume of the finger, which will be
recorded by the tambour. Cold air in the face or cold water on the hand
will usually be marked by a decrease in volume indicating vaso-constriction.
Application of heat to other fingers of the same hand will lead to in-
crease m volume.
22. The Vaso-motors of the Frog's Web. Prepare a frog for ob-
servation of the circulation of the web under the microscope, as described
above; but give it just enough i per cent curari to destroy voluntary move-
ments. Quickly dissect the sciatic nerve in the thigh, using extreme care
not to interfere with the circulation. Mount the preparation, pick out an
active field of capillaries, small arteries, and veins with the low power of the
microscope, then adjust the high power to a field which shows one or more
small arteries. Make a drawing of a diameter of these arteries, using pig-
ment cells for land-marks. Now quickly stimulate the exposed sciatic nerve
while keeping the selected artery under constant observation. After a short
stimulation the diameter of the vessels will be seen to decrease considerably,
sometimes to the point of complete occlusion. When the stimulation ceases,
the vessel will remain contracted for a few seconds, then will slowly regain
its usual caliber, figure 201 . This is an exceptionally good method for direct
observation of the vaso-motor changes in the smaller vessels.
23. The Plethysmogram of the Kidney. Anesthetize a dog or cat,
see experiments 12 and 19 above, and take blood-pressure tracings on the con-
16
THE ciftcyLATioN OF THE BLOOD
tinuous-paper kymograph. Now open the abdominal wall by an incision
along the median line, expose the left kidney and carefully dissect off its cap-
sule, taking care not to injure its artery and vein. Enclose the kidney in
the renal onkometer, fill the onkometer with oil, and connect it with a record-
ing apparatus. Brodie's bellows recorder is probably the best recording
apparatus for this purpose. Adjust the recording apparatus in the vertical
line with the manometer and signal pens.
Stimulation of the nerves which affect the general blood pressure through
the medium of the heart will be found to produce changes in the volume of
the kidney in the same direction as the blood-pressure change. On the
other hand, stimuli which give variations of the blood pressure without
direct change in the heart itself affect the volume of the kidney independent
of the blood pressure:
1. Dissect out and stimulate the splanchnic nerves just where they pass
through the pillars of the diaphragm. Stimulation of these nerves will
cause vaso-constriction in the kidney, which takes place without sharply
affecting the blood pressure.
2. Stimulate the depressor nerve or the central end of the divided vagus.
In this case the volume of the kidney will increase though the general blood
pressure decreases, showing that the fall of blood pressure is due to periph-
eral vascular dilatation.
3. Stimulate the peripheral end of the divided vagus so as to slow or
even completely stop the heart. 'The sharp fall in blood pressure is
now accompanied by decrease in the volume of the kidney, showing that the
kidney change is merely passively following that of the blood pressure.
CHAPTER VI
RESPIRATION
THE maintenance of animal life necessitates the continual absorption of
oxygen and the excretion of carbon dioxide by the living tissues. The blood
is the medium, in all animals which possess a well-developed blood-vascular
system, by which these gases are carried. Oxygen is absorbed by the blood
from without and conveyed to all parts of the organism; and carbon dioxide
which comes from the cells within is carried by the blood to the surfaces,
from which it may escape from the body. The two processes — absorption
of oxygen and excretion of carbon dioxide — are complementary, and their
sum is termed the process of Respiration.
In all Vertebrata, and in a large number of Invertebrata, certain parts,
either lungs or gills, are specially constructed for bringing the blood into
proximity with the aerating medium (atmospheric air, or water containing
air in solution). In some of the lower Vertebrata (frogs and other naked
Amphibia) the skin is important as a respiratory organ, and is capable of
supplementing to some extent the functions of the proper breathing ap-
paratus.
A lung or a gill is constructed essentially of a fine transparent membrane,
one surface of which is exposed to the air or water, as the case may be, while
on the other surface is a network of blood-vessels. The only separation be-
tween the blood and aerating medium is the thin wall of the blood-vessels
and the fine membrane on which the vessels are distributed. The difference
between the simplest and the most complicated respiratory membrane is
one of degree only.
In the mammals and the higher vertebrates the respiratory membrane
is included within a respiratory cavity, the chest or thorax, which carries on
regular movements, the respiratory movements, to bring changes of air into
close contact with the respiratory surface.
The complexity of the respiratory membrane, the kind of aerating medium,
and the respiratory movements are not, however, the only conditions which
cause a difference in the respiratory capacity of different animals. The
quantity and composition of the blood, especially as regards the number
and size of the red corpuscles, and the vigor and efficiency of the circulatory
apparatus in driving the blood to and fro between the lungs and the active
tissues, these are conditions of equal, if not greater, importance.
It may be as well to state here that the lungs are only the medium for the
243
244
RESPIRATION
exchange, on the part of the blood, of carbon dioxide for oxygen. The
living tissues are the seat of those combustion processes which consume
oxygen and produce carbon dioxide. These processes occur in all parts of
the body in the substance of the living active tissues, and are the true respira-
tory processes, sometimes called internal or tissue respiration.
THE RESPIRATORY APPARATUS.
The object of the respiratory movements being the interchange of gases
in the lungs, it is necessary that the atmospheric air shall pass into them
and that the changed air shall be expelled from them. The lungs are con-
tained in the chest or thorax, which is a closed cavity having no communica-
FIG. 218. — Outline Showing the General Form of the Larynx, Trachea, and Bronchi, as seen
from Before, h, The great cornu of the hyoid bone; e, epiglottis; t, superior, and *', inferior cornu
of the thyroid cartilage; c, middle of the cricoid cartilage; tr, the trachea, showing sixteen cartilag-
inous rings; b, the right, and b', the left bronchus. X £. (Allen Thomson.)
THE LARYNX 245
tion with the outside except by means of the respiratory passages. The air
enters these passages through the nostrils or through the mouth, thence it
passes through the larynx into the trachea or windpipe, which about the
middle of the chest divides into two tubes, the bronchi, one to each lung.
The Larynx. The upper part of the passage which leads exclu-
sively to the lung is formed by the thyroid, cricoid, and arytenoid carti-
lages, figure 218, and contains the vocal cords, by the vibration of which the
voice is chiefly produced. These vocal cords are ligamentous bands covered
with mucous membrane and attached to certain cartilages which are capable
of movement by muscles. By their approximation the cords can entirely
close the entrance into the larynx; but under ordinary conditions the entrance
of the larynx is formed by a more or less triangular opening between them,
called the rima glottidis. Projecting at an acute angle between the base of
the tongue and the larynx, to which it is attached, is a leaf-shaped cartilage
with its larger extremity free. This is called the epiglottis. The whole of
the larynx is lined by mucous membrane, which, however, is extremely thin
over the vocal cords. At its lower extremity the larynx joins the trachea.
Taste buds have been found in the epithelium of the posterior surface of
the epiglottis, and in several other situations in the laryngeal mucous mem-
brane.
The Trachea and Bronchi. The trachea extends from the cricoid
cartilage, which is on a level with the fifth cervical vertebra, to a point oppo-
site the third dorsal vertebra, where it divides into the two bronchi, one for
each lung, figure 218. The trachea measures, on an average, four or four
and a half inches, 12 to 14 cm., in length, and from three-quarters of an inch
to an inch, 2 to 2.5 cm., in diameter, and is essentially a tube of fibro-elastic
membrane within the layers of which are enclosed a series of cartilaginous
rings, from sixteen to twenty in number. These rings extend only around
the front and sides of the trachea, about two-thirds of its circumference, and
are deficient behind; the interval between their posterior extremities being
bridged over by a continuation of the fibrous membrane in which they are
enclosed, figure 219, h.
Immediately within this tube and at the back is a layer of unstriped
muscular fibers. This muscular layer extends transversely between the
ends of the cartilaginous rings to which it is attached, and also opposite the
intervals between them; its evident function being to diminish the caliber
of the trachea by approximating the ends of the cartilages. Outside there
are a few longitudinal bundles of muscular tissue, which, like the preceding,
are attached both to the fibrous and to the cartilaginous framework.
The mucous membrane, figures 219 and 220, consists largely of adenoid
tissue, separated from the stratified columnar epithelium, which lines it, by a
homogeneous basement membrane. This is penetrated here and there by
channels which connect the adenoid tissue of the mucosa with the inter-
246
RESPIRATION
cellular substance of the epithelium. The stratified columnar epithelium
is formed of several layers, of which the most superficial layer is ciliated and
the cells often branched downward. Many of the superficial cells are of the
goblet variety. In the deeper part of the mucosa are many elastic fibers
between which lie connective-tissue corpuscles and capillary blood-vessels.
Numerous mucous glands are situated on the exterior and in the substance
of the fibrous framework of the trachea; their ducts perforating the various
FIG. 219. — Section of the Trachea, a, Columnar ciliated epithelium; bandc, proper structure
of the mucous membrane, containing elastic fibers cut across transversely; d, submucous tissue
containing mucous glands, e, separated from the hyaline cartilage, g, by a fine fibrous tissue, /,
h, external investment of fine fibrous tissue. (S. K. Alcock.)
structures which form the wall of the trachea, and opening through the
mucous membrane into the cavity of the trachea.
The two bronchi into which the trachea divides resemble the trachea
in structure, with the difference that in them there is a distinct layer of un-
striped muscle arranged circularly beneath the mucous membrane, forming
the, muscularis mucosa. On entering the substance of the lungs the carti-
laginous rings, although they still form only larger or smaller segments of
THE TRACHEA AND BRCNCHI
£47
a circle, are no longer confined to the front and sides of the tubes, but are
distributed impartially to all parts of their circumference.
The bronchi divide and subdivide in the substance of the lungs into
smaller and smaller branches, which penetrate into every part of the organ
FIG. 220. — Ciliary Epithelium of the Human Trachea, a. Layer of longitudinally arranged
elastic fibers; b, basement membrane; c, deepest cells, circular in form; d, intermediate elongated
cells; e, outermost layer of cells fully developed and bearing cilia. X 350. (Kolliker.)
until at length they end in the smaller subdivisions of the lungs called
lobules.
All the larger branches have walls formed of tough membrane, contain-
ing portions of cartilaginous rings, by which they are held open, and un-
striped muscular fibers, as well as longitudinal bundles of elastic tissue.
FIG. 22i. — Transverse Section of a Bronchus, about $ inch in Diameter, e, Epithelium
(ciliated); immediately beneath it is the mucous membrane or internal fibrous layer, of varying
thickness; m, muscular layer; 5. m, submucous tissue; /, fibrous tissue ; c, cartilage enclosed within
the layers of fibrous tissue; g, mucous gland. (F. E. Schulze.)
They are lined by mucous membrane, the surface of which, like that of the
larynx and trachea, is covered with ciliated epithelium; but the several
layers become less and less distinct until the lining consists of a single layer
of more or less cubical cells covered with cilia, figure 221. The mucous
membrane is abundantly provided with mucous glands.
£48 RESPIRATION
As the bronchi become smaller and smaller and their walls thinner, the
cartilaginous rings become fewer and more irregular, until in the smaller
bronchial tubes they are represented only by minute and scattered cartilag-
inous flakes. And when the bronchi by successive branches are reduced
to about ^Q- of an inch, c.6 mm., in diameter, they lose their cartilaginous ele-
ment altogether and their walls are formed only of a tough, fibrous, elastic
membrane with circular muscular fibers. They are still lined, however,
by a thin mucous membrane with ciliated epithelium, the length of the cells
bearing the cilia having become so far diminished that the cells are almost
cubical. In the smaller bronchi the circular muscular fibers are relatively
more abundant than in the larger bronchi and form a distinct circular coat.
The Lungs and Plurae. The lungs occupy the greater portion
of the thorax. They are of a spongy elastic texture, and on section appear
to the naked eye as if they were in great part solid organs, except where
branches of the open bronchi or air-tubes may have been cut across and show
on the surface of the section. In fact, however, the lungs are hollow organs
FIG. 222. — Transverse Section of the Chest.
composed of a mass of air cavities all of which communicate finally with
the common air-tube, the trachea.
Each lung is enveloped by a serous membrane, the pleura, which ad-
heres closely to its surface and provides it with its smooth and slippery
covering. This same membrane lines the inner surface of the chest wall.
The continuity of this membrane, which forms a closed sac as in the case
of other serous membranes, will be best understood by reference to figure 222.
The appearance of a space, however, between the pleura which covers the
lung, visceral layer, and that which lines the inner surface of the chest, parietal
layer, is inserted in the drawing only for the sake of distinctness. These
layers are, in health, everywhere in contact, one with the other; and between
them is only just as much fluid as will insure frictionless movement in their
expansion and contraction.
THE FINER STRUCTURE OF THE LUNG
249
When considering the subject of normal respiration, one may discard
altogether the notion of the existence of any space or cavity between the
lungs and the wall of the chest. If, however, an opening be made so as to
permit air or fluid to enter the pleural sac, the lung in virtue of its elasticity
recoils, and a considerable space is left between it and the chest wall. In
other words, the natural elasticity of the lungs would cause them at all times
to contract away from the ribs were it not that the contraction is resisted by
atmospheric pressure which bears only on the inner surface of the air-tubes
and air-cells.
The pulmonary pleura consists of an outer or denser layer and an inner
looser tissue in which there is a lymph-canalicular system. Numerous lym-
phatics are to be met with, which form a dense plexus of vessels, many
of which contain valves. They are simple endothelial tubes, and take origin
in the lymph-canalicular system of the pleura proper. Scattered bundles
of unstriped muscular fiber occur in the pulmonary pleura. They are es-
pecially strongly developed on the anterior and internal surfaces of the lungs,
the parts which move most freely in respiration. Their function is doubt-
less to aid in expiration.
The Finer Structure of the Lung. Each lung is partially subdi-
vided into separate portions called lobes; the right lung into three lobes,
FIG. 223.
FIG. 224.
FIG. 223. — Terminal Branch of a Bronchial Tube, with its Infundibula and Air-cells, from the
Margin of the Lung Injected with Quicksilver; Monkey, a, Terminal bronchial twig; b, b, in-
fundibula and air-cells. X 10. (F. E. Schulze.)
FIG. 224. — Two Small Infundibula, a, a, with air-cells, b, b, and the ultimate bronchial tubes,
c, c, with which the air-cells communicate. From a new-born child. - (Kolliker.)
and the left into two. Each of these lobes, again, is composed of a large num-
ber of minute parts, called lobules. Each pulmonary lobule may be considered
to be a lung in miniature, consisting, as it does, of a branch of the bronchial
tube, of air-cells, blood-vessels, nerves, and lymphatics, with a small amount
of areolar tissue-
250
RESPIRATION
On entering a lobule, the small bronchial tube, the structure of which
has just been described, #, figure 210, divides and subdivides; its walls at
the same time becoming thinner and thinner, until at length they are formed
only of a thin membrane of areolar and elastic tissue, lined by a layer of
squamous epithelium, no longer provided with cilia. At the same time they
are altered in shape; each of the minute terminal branches widening out
funnel-wise, and its walls being pouched out irregularly into small saccular
dilatations, called air-cells, figure 223, b. Such a funnel-shaped terminal
branch of the bronchial tube, with its group of pouches or air-cells, has been
Called an infundibulum, figures 223 and 224, and the irregular oblong space
in its center, with which the air-cells communicate, an intercellular passage.
FIG. 225.— From a Section of the Lung of a Cat, Stained with Silver Nitrate. A. D, Alveolar
duct or intercellular passage; S, alveolar septa, N, alveoli or 'air-cells, lined with large flat,
nuleated cells, with some smaller polyhedral nucleated cells; M, unstriped muscular fibers Cir-
cular muscular fibers are seen surrounding the interior of the alveolar duct, and at one part is seen
a group of small polyhedral cells continued from the bronchus. (Klein and Noble Smith.)
An inflated and dried turtle's lung is the homologue of a lobule. Such a
preparation can be cut across to illustrate the intercellular passage, the in-
fundibulum, and the air-cells.
The air-cells, or air-vessels, are sometimes placed singly, like recesses
from the intercellular passage, but more often they are arranged in groups
or even rows, like minute sacculated tubes, so that a short series of vesicles
all communicating with one another open by a common orifice into the tube.
The vesicles are of various forms according to the mutual pressure to which
THE FINER STRUCTURE OF THE LUNG 251
they are subject. Their walls are nearly in contact, and they vary from 0.5
to 0.3 mm. in diameter. Their walls are formed of fine membrane similar
to that of the intercellular passages and continuous with it. The membrane
is folded on itself so as to form a sharp-edged border at each circular orifice
of communication between contiguous air-vesicles, or between the vesicles
and the bronchial passages. Numerous fibers of elastic tissue are spread
out in the walls between contiguous air-cells, and many of these are attached
to the outer surface of the wall of which each cell is composed, imparting to
it additional strength and the power of recoil after distention.
The air-cells are lined by a layer of epithelium, figure 225, the cells of
which are very thin and plate-like. The thin epithelial membrane is free on
one side, where it comes in contact with the air of the lungs, but on the other
FIG. 226. — Section of Injected Lung, Including Several Contiguous Alveoli. (F. E. Schulze.)
Highly magnified, a, a, Free edges of alveoli; c, c, partitions between neighboring alveoli, seen in
section; b, small arterial branch giving off capillaries to the alveoli. The looping of the vessels to
either side of the partitions is well exhibited. Between the capillaries is seen the homogeneous
alveolar wall with nuclei of connective-tissue corpuscles and elastic fibers.
side a network of pulmonary capillaries is spread out so densely, figure 226,
that the interspaces or meshes are even narrower than the vessels. These
are on an average -g-oVo of an inch, or 8 micromillimeters, in diameter. Be-
tween the atmospheric air-cells and the blood in these vessels, nothing in-
tervenes but the thin walls of the cells and capillaries. The exposure of the
blood to the air is the more complete because the wall between contiguous
air-cells, and often the spaces between the walls of the same, contain only
a single layer of capillaries both sides of which are at once exposed to the air,
252 RESPIRATION
The air-vesicles situated nearest to the center of the lung are smaller
and their networks of capillaries are closer than those nearer to the circum-
ference. The vesicles of adjacent lobules dp not communicate. Those of
the same lobule or proceeding from the same intercellular passage com-
municate as a general rule only near angles of bifurcation, so that when any
bronchial tube is closed or obstructed the supply of air is lost for all the blood-
vessels of that lobule and its branches.
Blood-supply. The lungs receive blood from two sources: a, the
pulmonary artery; b, the bronchial arteries. The former conveys venous
blood to the lungs for its oxidation, and this Wood takes no share in the
nutrition of the deeper pulmonary tissues through which it passes. The
branches of the bronchial arteries are nutrient arteries which ramify in the
FIG. 227. — Capillary Network of the Pulmonary Blood-vessels in the Human Lung. X 60.
(Kolliker.)
walls of the bronchi, in the walls of the larger pulmonary vessels, and in the
interlobular connective tissue, etc. The blood of the bronchial vessels is re-
turned chiefly through the bronchial, but partly through the pulmonary, veins.
Lymphatics. The lymphatics are arranged in three sets: i. Ir-
regular lacunae in the walls of the alveoli or air-cells. The lymphatic
vessels which lead from these accompany the pulmonary vessels toward
the root of the lung. 2, Irregular anastomosing spaces in the walls of the
bronchi. 3, Lymph-spaces in the pulmonary pleura. The lymphatic vessels
from all these irregular sinuses pass in toward the root of the lung to reach
the bronchial glands.
Nerves. The nerves of the lung are to be traced from the anterior
and posterior pulmonary plexuses, which are formed by branches of the
vagus and sympathetic. The nerves follow the course of the blood-vessels
and bronchi, and many small ganglia are situated in the walls of the latter.
INSPIRATION 253
THE MOVEMENTS OF THE RESPIRATORY MECHANISM.
Respiratory movement consists of the alternate expansion and contrac-
tion of the thorax, by means of which air is drawn into or expelled from
the lungs.
A movement of the side walls or floor of the chest to increase its diameter
or length will enlarge the capacity of the interior. By such an increase of
capacity there will be of course a diminution of the pressure of the air in the
lungs, and a fresh quantity of air will enter through the larynx and trachea
to equalize the pressure on the inside and outside of the chest. This move-
ment is called inspiration.
The movement which diminishes the capacity of the chest and increases
the pressure in the interior expels air until the pressure within and that without
the chest are again equal. This movement is called expiration. In both
cases the air passes through the trachea and larynx, whether in entering or
FIG. 228. — Schematic Representation of Diaphragm. In expiration (7), quiet inspiration (//),
and deep inspiration (///). (After Schaffer.)
leaving the lungs, there being no other communication with the exterior of
the body. And the lung, for the same reason, remains closely in contact
with the walls and floor of the chest under all the circumstances described.
To speak of expansion of the chest is to speak also of expansion of the lung,
and vice versa.
Inspiration. The enlargement of the chest during inspiration is
due to muscular action, which brings about an increase in the size of the
chest cavity through the contraction of the inspiratory muscles, the role
played by the lungs being a passive one. The chest cavity is increased in*
its three axes, the vertical, lateral, and antero-posterior diameters. The
muscles engaged in ordinary inspiration are: the diaphragm, the external inter-
costals, and the scaleni and levatores costarum. During forced inspiration
254
RESPIRATION
every muscle is brought into play which by its contraction tends to elevate
the ribs and sternum or which will fix points against which these muscles
can act. This includes almost every muscle of the trunk and neck.
Changes in the vertical diameter are due, first, to the contraction of the
diaphragm. This muscle has the shape of a flattened dome, its highest
Esophagus
Left subclavian artery
Left common carotid artery
Left superior intercostal vein
Left innominate vein
Parietal pleura
(cut edge)
Pericardium
Parietal pleura
(cut edge)
Aortic arch
Pulmonary artery
Bronchus
Pulmonary veins
Esophagus
Diaphragm
FIG. 229. — Thorax from the Left, Showing Left Pleural Sac, and the Diaphragm. The lung is
removed.
point being the central tendon. While passive, its lower portions are in
apposition with the chest walls, figure 228, 7. On contraction, the dome is
pulled downward and the lower portion is pulled away from the chest walls,
the downward displacement varying from 6 to 12 mm. in normal respira-
tion, and in forced respiration may amount to as much as 45 mm. The
tendency of the diaphragm to pull the lower ribs and lower part of the sternum
INSPIRATION 255
'nward is counteracted by the outward pressure of the' abdominal viscera,
and by the action of the quadrati himborum, which by their attachment to
the last ribs fix these and, in case of deep inspiration, may even pull them
downward. The serrati postici inferiores also aid, being attached to the
four lower ribs.
Changes in the lateral and antero-posterior diameters are effected by the
raising of the ribs, which are attached very obliquely to the spine and sternum.
The elevation of the ribs takes place both in front and at the sides — the
hinder ends being prevented from performing any upward movement by
their pivot attachment to the spine. The movement of the front extremities
of the ribs is of necessity limited by an upward and forward movement of the
PIG. 230. — Diagram of Axes of Movement of Ribs.
sternum to which they are attached, the movement being greater at the lower
end than at the upper end of the sternum.
The axes of rotation in these movements are two: one corresponding
with a line drawn through the two articulations which the rib forms with
the spine, a, b, figure 230, and the other with a line drawn from one of these
(head of rib) to the sternum, A B, figure 230; the motion of the rib around
the latter axis being somewhat after the fashion of raising the handle of a
bucket. The elevation of the ribs is accompanied by a slight opening out of
the angle which the bony part forms with its cartilage, and thus an additional
means is provided for increasing the antero-posterior diameter of the chest.
The movements of all the ribs except the twelfth consist of a rotation up-
ward, forward, and outward. The twelfth presents only rotation down-
ward and backward.
256 RESPIRATION
The muscles involved in these movements of the ribs are the external
intercostals and the part of the internal intercostals situated between the
costal cartilages. Their action is to widen the intercostal spaces. The
scaleni fix the first and second ribs, thereby making a fixed point of action
for the other muscles involved. The serrati postici superiores assist the above
and also raise the third, fourth, and fifth ribs. The levatores costarum longi
and brevi elevate and evert all the ribs from the first to the tenth.
In extraordinary or forced inspiration, which may be due either to violent
exercise or to interference with the due entrance of air into the lungs, all the
above muscles act more strongly. The diaphragm descends lower, the scaleni
raise the first and second ribs instead of merely fixing them, as in ordinary
respiration, as do also the sterno-cleido-mastoids. These, together with the
erector spina, which straighten the spine, increase the vertical diameter.
The trapezii and the rhomboidii assist in increasing the antero-posterior and
lateral diameters by fixing the shoulders and thus giving a fixed point for the
action of the pectorals and latissimi dorsi.
The enlargement of the chest during inspiration presents peculiarities
in different persons. In children of both sexes the principal muscle in-
volved seems to be the diaphragm, and this type of breathing is known as
abdominal breathing. In men, the chest and sternum, together with the
front wall of the abdomen, are subject to a wide movement; this type of
breathing is called the inferior costal. In women, the movement appears
less extensive in the lower and more extensive in the upper part of the chest,
which is called the superior costal type. This has been shown to be due
rather to mode of dress than to a real difference in the sexes (Mosher).
Expiration. Quiet expiration is a passive act due to the return
of the thorax and its contained lungs to their normal position when the mus-
cles involved in inspiration relax. This elastic recoil is sufficient in ordinary
quiet breathing to expel air from the lungs. In forced expiration, however,
which may occur to a slight degree in speaking, singing, etc., as well as in
the case of many involuntary and reflex acts, such as coughing, sneezing,
etc., other muscles are involved. Of these the principal are the abdominal
muscles, obliquus externus and internus, rectus abdominis, transfer salis ab-
dominis and pyramidalis. These act, first, by pressing the abdominal
viscera against the diaphragm and thereby forcing it up, their descent into
the pelvic cavity being prevented; second, by their attachments to the lower
ribs and cartilages, they draw these downward and inward, thereby lessening
the size of the thoracic cavity; lastly, by their contraction, they form a fixed
point for the action of that part of the internal intercostals, not involved in
inspiration, to approximate the ribs.
When by the efforts of the expiratory muscles the chest has been squeezed
to less than its average diameters, it again, on relaxation of the muscles,
returns to the normal dimensions by virtue of its elasticity. The construe-
RECORDING RESPIRATORY MOVEMENTS 257
tion of the chest walls, therefore, admirably adapts them for recoiling against
and resisting as well undue contraction as undue dilatation.
Respiratory Movements of the Nostrils and of the Glottis. During
the action of the inspiratory muscles which directly draw air into the chest,
those which guard the opening through which the air enters are also active.
In hurried breathing the dilatation of the nostrils is well seen, although
under ordinary conditions it may not be noticeable. The opening at the
upper part of the larynx, however, the rima glottidis, is dilated at each in-
spiration for the more ready passage of air, and becomes smaller at each
expiration; its condition, therefore, corresponds during respiration with
that of the walls of the chest. There is a further likeness between the two
acts in that, under ordinary circumstances, the dilatation of the rima glot-
tidis is a muscular act and its contraction chiefly an elastic recoil; although,
under various special conditions to be hereafter mentioned, there may be
considerable muscular contraction exercised.
Methods of Recording Respiratory Movements. The movements of respiration
may be recorded graphically in several ways. The ordinary method is to introduce a
tube into the trachea of an animal, and to connect this tube by some gutta-percha tubing
with a T-piece, the side branch of which is connected with a Marey's tambour, which may
be made to write on a recording surface, figure 173. If the tube attached to the free limb
of the T-piece be partially closed with a screw compress, the movements of inspiration
FIG. 23 1 . — Stethogr-vph or P -eumograph. h. Tambour fixed at right angles to plate of steel, f ;
c and d, arms by which i strument is attached to chest by belt, e. When the chest expands, the
arms are pulled asunder, which bends the steel plate, and the tambour is affected by the pressure of
6, which is attached to it on the one hand, and to the upright in connection with horizontal screw, g.
(Modified from Marey's instrument.)
and expiration are larger than if it were open. The alteration of the pressure within the
lungs on inspiration and expiration is shown by the movement of the column of air in the
trachea and in its extension to the T-piece. By these means a record of the respiratory
movements may be obtained.
Various instruments have been devised for recording the movements of the chest
by application of apparatus to the exterior. Such is the stethometer of Burdon-Sanderson,
figure 233. This consists of a frame formed of two parallel steel bars joined by a third
17
258
RESPIRATION
at one end. At the free end of the bars is attached a leather strap, by means of which
the apparatus may be suspended from the neck. Attached to the inner end of one bar is
a tambour and ivory button, to the end of the other an ivory button. The apparatus is
suspended with the transverse bar posteriorly, the button of the tambour is placed on the
part of the chest the movement of which it is desired to record, and the other button is
made to press upon the corresponding side of the chest, so that the chest is held as between
a pair of calipers. The receiving tambour is connected through a T-piece with a recording
tambour of Marey's, and with a bulb by means of which air can be squeezed into the
cavity of the tympanum. When adjusted, the tube connected with the air ball is shut off
by means of a screw clamp. The movement of the chest is thus communicated to the
recording tambour.
A simpler form of this apparatus, called a pneumograph or stethograph, consists of a
thick India-rubber bag of elliptical shape about three inches long, to one end of which a
rigid gutta-percha tube is attached. This bag may be fixed at any required place on the
chest by means of a strap and buckle. By means of the gutta-percha tube the variations
of the pressure of air in the bag, produced by the movements of the chest, are communicated
FIG. 232. — Tracing of Thoracic Respiratory Movements obtained by means of Marey's Pneu-
mograph. (Foster.) A whole respiratory phase is comprised between a and a; inspiration during
which the lever descends, extending from a to b, and expiration from b to a. The undulations at
c are caused by the heart's beat.
to a recording tambour. This principle is applied in a modified form in Marey's pneumo-
graph, figure 231.
The variations of intrapleural pressure may be recorded by introducing a cannula into
the pleural or pericardial cavity. The cannula should be previously connected with a
mercury or other form of manometer by tubing filled with physiological saline.
Finally, it has been found possible in various ways to record the diaphragmatic move-
ments. This can be done by inserting a receiving tambour into the abdomen below the
diaphragm, by the insertion of needles into different parts of the diaphragm and recording
the movement of the free ends of needles about the fulcrum formed where the chest wall
is pierced, or by recording the contraction of isolated strips of the diaphragm directly.
These records all give an accurate picture of the movements of the diaphragm.
The Relative Time of Inspiration and Expiration and the Respira-
tory Movement. The acts of inspiration and expiration take up, un-
der ordinary circumstances, a nearly equal time. The time of inspiration,
however, especially in women and children, is a little shorter than that of
expiration, and there is commonly a very slight pause between the end of
expiration and the beginning of the next inspiration, see figure 232. The
ratio of the respiratory rhythm may be thus expressed:
Inspiration 6
Expiration 7 to 8
Pause Very slight
QUANTITY OF AIR BREATHED
259
If the ear be placed in contact with the wall of the chest, or be separated
from it only by a good conductor of sound or a stethoscope, a faint respiratory
murmur is heard during inspiration. This sound varies somewhat in different
parts, being loudest or coarsest in the neighborhood of the trachea and large
bronchi (tracheal and bronchial breathing), and fading off into a faint sighing
as the ear is placed at a distance from these (vesicular breathing). It is
heard best in children. In them a faint murmur is heard in expiration also.
The cause of the vesicular murmur has received various explanations. Most
Tambour.
Ivory button.
Tube to commu-
nicate with re-
cording tam-
bour,
Ball to fill appa-
ratus-With air.
FIG. 233. — Stethometer. (Burdon- Sanderson.)
observers hold that the sound is produced in the glottis and larger bronchial
tubes, but that it is modified in its passage to the pulmonary alveoli. In
disease of the lungs the vesicular murmur undergoes various modifica-
tions, for a description of which one must consult text-books on physical
diagnosis.
The Quantity of Air Breathed. Tidal air is the quantity of air
which is habitually and almost uniformly changed in each act of breathing.
In a healthy adult man it is about 30 cubic inches, or about 500 c.c. or half
a liter. In college students the tidal air is somewhat less, varying from 300
to 400 c.c.
The Complemental Air is the quantity of air which can be drawrn into the
lungs by the deepest inspiration over and above that which is in the lungs
260
RESPIRATION
at the end of an ordinary inspiration. Its amount varies, but may be reck-
oned as 100 cubic inches, or about 1,600 c.c.
The Reserve Air is that which may be expelled by a forcible and deeper
expiration, after an ordinary expiration, such as that which expels the tidal
air. The reserve air amounts to from 1,200 to 1,500 c.c. This is also termed
the supplemental air.
The Residual Air is the quantity which still remains in the lungs after
the most violent expiratory effort. Its amount depends in great measure
FIG. 234. — Tracing of the Normal Diaphragm Respirations of the Rabbit, a, With quick
movement of drum; b, with slow movement; /, inpiration; E, expiration. To be read from left
to right. (Marckwald.)
on the absolute size of the chest, but may be estimated at about 1,000 c.c.
to 1,200 c.c.
The total quantity of air which passes into and out of the lungs of an
adult, at rest, in 24 hours, is about 686,000 cubic inches. This quantity,
however, is largely increased by exertion; the average amount for a hard-
working laborer in the same time being 1,568,390 cubic inches.
The Respiratory Capacity. The greatest respiratory capacity or vital
capacity of the chest is indicated by the quantity of air which a person can
expel from his lungs by a forcible expiration after the deepest possible in-
spiration. The vital capacity is the sum of the reserve, tidal, and comple-
mental airs. It expresses the power which a person has of breathing in the
emergencies of active exercise, violence, and disease. The average capacity
of an adult, at 15.4° C. (60° F.), is about 225 to 250 cubic inches, or 3,500
to 4,000 c.c.
THE RESPIRATORY CAPACITY
261
The respiratory capacity, or as John Hutchinson called it, vital capacity, is usually
measured by a modified gasometer or spirometer, into which the experimenter breathes,
making the most prolonged expiration possible after the deepest possible inspiration.
The quantity of air which is thus expelled from the lungs is indicated by the height to
which the air chamber of the spirometer rises; and by means of a scale placed in con-
nection with this, the number of cubic inches or centimeters is read off.
In healthy men, the respiratory capacity varies chiefly with the stature,
weight, and age.
Circumstances Affecting the Amount of Respiratory Capacity. For every inch of
height above the standard the respiratory capacity is increased, on an average, by eight
inches; and for every inch below, it is diminished by the same amount.
The influence of weight on the capacity of respiration is less manifest, and consider-
ably less than that of height. It is difficult to arrive at any definite conclusions on this
FIG. 235. — Diagram of Hutchinson's Spirometer. (Landois.) A , Graduated cylinder serving
as a receiver for the breath; it is supplied with a stopcock at the top for the ready expulsion of air,
and is balanced by weights passing over pulleys. B, Mouthpiece with tube reaching nearly to the
top of the graduated receiver (A) when the latter is sunk in the reservoir ready for an experiment;
there is a stopcock in this tube near the first angle, to prevent regurgitation of air. C, Reservoir
for the graduated receiver. In using the spirometer the reservoir and graduated receiver are filled
with water, or, to prevent the absorption of carbon dioxide, with a saturated aqueous solution of
common salt (NaCl). When ready for an experiment, the stopcock at the top of the receiver
is closed and that in the tube of the mouthpiece opened, and the breath forced into the receiver.
The receiver rises as fast as the breath displaces the water. After the breath is forced into the re-
ceiver the stopcock in the tube of the mouthpiece is closed, and the water outside and inside the
receiver brought to the same level, so that the air within the receiver shall be at the atmospheric
pressure. The amount of breath within the receiver is then read directly from the scale attached
to the receiver. For accurate measurement the breath should stand a few minutes to acquire the
temperature of the liquid over which it is collected ; then the various corrections for aqueous vapor
tension, and the variations from the standard temperature and pressure, should be made.
point, because the natural average weight of a healthy man in relation to stature has not
yet been determined.
By age, the capacity appears to be increased from about the fifteenth to the thirty-
fifth year, at the rate of five cubic inches per year; from thirty-five to sixty-five it di-
minishes at the rate of about one and a half cubic inches per year; so that the capacity of
respiration of a man sixty years old would be about thirty cubic inches less than that
of a man forty years old, of the same height and weight. (John Hutchinson.)
RESPIRATION
The number of respirations in a healthy adult person usually ranges
from 14 to 1 8 per minute. It is greater in infancy and childhood. It varies
also much according to different circumstances, such as exercise or rest,
health or disease, etc. Variations in the number of respirations correspond
ordinarily with similar variations in the pulsations of the heart. In health
the proportion is about i to 4, or i to 5 ; and when the rapidity of the heart's
action is increased, that of the chest movement is commonly increased also,
but not in every case in equal proportion. It happens occasionally in disease,
especially of the lungs or air-passages, that the number of respiratory acts
increases in quicker proportion than the beats of the pulse; and, in other
affections, much more commonly, that the number of the pulses is greater
in proportion than that of the respirations.
The Force of Inspiratory and Expiratory Muscles. The force
which the inspiratory muscles are capable of exerting on the chest is greatest
in individuals of the height of from five feet seven inches to five feet eight
inches, and is equal to a column of three inches of mercury. Above this
height the force decreases as the stature increases; so that the average
power of men of six feet is measured by about two and a half inches of mer-
cury. The force manifested in the strongest expiratory acts is, on the
average, one-third greater than that exercised in inspiration. But this
difference is in a great measure due to the power exerted by the elastic
reaction of the walls of the chest; and it is also much influenced by the
disproportionate strength which the expiratory muscles attain from their
being called into use for other purposes than that of simple expiration.
The force of the inspiratory act is, therefore, better adapted than that of
the expiratory for testing the muscular strength of the body (John
Hutchinson).
It has been shown that within the limits of ordinary tranquil respiration
the elastic resilience of the walls of the chest favors inspiration; and that it
is only in deep inspiration that the ribs and rib-cartilages offer an opposing
force to their dilatation. In other words, the elastic resilience of the lungs,
at the end of an act of ordinary exhalation has drawn the chest walls within
the limits of their normal degree of expansion. Under all circumstances, of
course, the elastic tissue of the lungs opposes inspiration and favors expiration.
It is possible that the contractile power which the bronchial tubes and
air-vesicles possess, by means of their muscular fibers may assist in expiration.
But it is more likely that its chief purpose is to regulate and adapt, in some
measure, the quantity of air admitted to the lungs, and to each part of them,
according to the supply of blood. The muscular tissue contracts upon and
gradually expels collections of mucus, which may have accumulated within
the tubes, and which cannot be ejected by forced expiratory efforts, owing
to collapse or other morbid conditions of the portion of lung connected with
the obstructed tubes (Gairdner). Apart from any of the before-mentioned
COMPOSITION OF THE ATMOSPHERE 263
functions, the presence of muscular fiber in the walls of a hollow viscus, such
as a lung, is only what might be expected from analogy with other organs.
Subject as the lungs are to such great variation in size, it might be antici-
pated that the elastic tissue, which enters so largely into their composition,
would be supplemented by the presence of much muscular fiber.
RESPIRATORY CHANGES IN THE AIR BREATHED.
Composition of the Atmosphere. The atmosphere we breathe has,
in every situation in which it has been examined in its natural state, a
nearly uniform composition. It is a mixture of oxygen, nitrogen, carbon
dioxide, and watery vapor, with, commonly, traces of other gases, as argon,
ammonia, sulphureted hydrogen, etc. Of every 100 volumes of pure at-
mospheric air, 79 volumes, on an average, consist of nitrogen and argon,
the remaining 21 of oxygen. The proportion of carbon dioxide is extremely
small; 10,000 volumes of atmospheric air contain only about 3 of that gas.
The quantity of watery vapor varies greatly according to the tem-
perature and other circumstances, but the atmosphere is never without
some. In this country the average quantity of watery vapor in the atmos-
phere varies greatly according to the region. In some of our Western arid
plains in the dry season the air is almost free of moisture.
Composition of Air which Has Been Breathed. The changes
effected by respiration in the atmospheric air are: i, an increase of tem-
perature; 2, an increase in the quantity of carbon dioxide; 3, a diminution
in the quantity of oxygen; 4, a diminution of volume; 5, an increase in the
amount of watery vapor; 6, the addition of a minute amount of organic
matter and of free ammonia.
Temperature of the Expired Air. Expired air, after its contact with the
interior of the lungs, is hotter (at least in most climates) than the inspired air.
Its temperature varies between 36° and 37.5° C. (97° and 99.5° F.), the lower
temperature being observed when the air has remained but a short time in
the lungs. Whatever may be the temperature of the air when inhaled, it
acquires nearly that of the blood before it is expelled from the chest.
The Carbon Dioxide of Expired Air. The percentage of carbon dioxide
is increased, but the quantity exhaled in a given time is subject to change
from various circumstances. From every volume of air inspired 4 to 5 per
cent of oxygen is abstracted; while a rather smaller quantity, 4.38 per cent,
of carbon dioxide is added in its place; the expired air will contain, there-
fore, 438 volumes of carbon dioxide in 10,000. The total quantity of carbon
dioxide exhaled into the air breathed by a healthy adult, calculating that
15.4 c.c.of the 35oc.c.of the average air breathed out at each expiration con-
sists of carbon dioxide, and that the rate of respiration is on an average 16,
would be about 400 liters in the twenty-four hours. From actual experiment this
264
RESPIRATION
amount seems to be a trifle too great, since from the average of many inves-
tigations the total amount of carbon dioxide excreted per day by the entire
body has been found to be about 400 liters, weighing 800 grams, and con-
sisting of 218 grams of carbon, and 582 grams of oxygen. From the 218
grams of carbon must be deducted about 10 grams excreted in other ways
FIG. 236.— Apparatus for Estimating Oa and CO2 in Expired Air. (Waller.)
than by the lungs, which leaves about 215 grams as the amount of carbon ex-
creted by the average healthy man by respiration each day and night. These
quantities must be considered approximate only, inasmuch as various cir-
cumstances, even in health, influence the amount of carbon dioxide excreted,
and, correlatively, the amount of oxygen absorbed.
Circumstances Influencing the Amount of Carbon Dioxide Excreted. Age and Sex.
The quantity of carbon dioxide exhaled into the air breathed by males, regularly in-
creases from 8 to 30 years of age; from 30 to 50 the quantity, after remaining stationary for
a while, gradually diminishes, and from 50 to extreme age it goes on diminishing, till it
scarcely exceeds the quantity exhaled at 10 years old. In females (in whom the quantity
exhaled is always less than in males of the same age) the same regular increase in quantity
goes on from the 8th year to the age of puberty, when the quantity abruptly ceases to in-
crease, and remains stationary so long as they continue to menstruate. When menstrua-
tion has ceased, the carbon dioxide output soon decreases at the same rate as it does in
old men.
AMOUNT OF CAKbONT DIOXIDE LXCU171KD 265
Respiratory Movements. The quicker the respirations, the smaller is the percentage
of carbon dioxide contained in each volume of the expired air. Although the propor-
tionate quantity of carbon dioxide is thus diminished, tne absolute amount exhaled
within a given time is increased thereby, owing to the larger quantity of air which is
breathed in the time. The last half of a volume of expired air contains more carbonic
acid than the half first expired; a circumstance which is explained by the later portion
of air coming from the remote part of the lungs, where it has been in more immediate
and prolonged contact with the blood than the first portion exhaled has, which comes
chiefly from the larger bronchial tubes.
External Temperature. The observation made by Vierordt at various temperatures
between ^.4°-2^.8° C. (38° F. and 75° F.) show, for warm-blooded animals, that within
this range every rise equal to 5.5° C. (10° F.) causes a diminution of about 33 c.c. (2
cubic inches) in the quantity of carbon dioxide exhaled per minute.
Season of the Year. The season of the year, independently of temperature, materi-
ally influences the respiratory phenomena since it influences the metabolism of the body;
spring being the season of the greatest, and autumn of the least, activity of the respira-
tory and metabolic functions.
Purity of the Respired A ir. The average quantity of carbon dioxide given out by the
lungs constitutes about 4.38 per cent of the expired air; but if the air which is breathed
be previously impregnated with carbon dioxide (as is the case when the same air is fre-
quently respired), then the quantity of carbon dioxide exhaled becomes relatively much
greater.
Hygrometric State oj the Atmosphere. The amount of carbon dioxide exhaled is con-
siderably influenced ty the degree of moisture of the atmosphere, much more being given
off when the air is moist than when it is dry.
Period of the Day. The respiratory quotient, i.e., the ratio between carbon dioxide
eliminated and oxygen absorbed, is greater during the day than during the night. In
the day, therefore, the COa exhaled in relation to the O2 absorbed is increased, and it
is diminished during the night. This is probably due to the increased production of
COa as a result of increased tissue activity during the day, and, consequently, the
breaking down or catabolism of more substances.
Food and Drink. By the use of food the quantity of CO2 is increased, while by fast
ing it is diminished; it is greater when animals are fed on farinaceous food than wheif
fed on meat. The effects produced by spirituous drinks depend much on the kind ot
drink taken. Pure alcohol in very small amounts tends rather to increase than to lessen
respiratory changes, and the amount, therefore, of carbon dioxide expired. Rum, ale, and
porter, also sherry, have very similar effects. On the other hand, brandy, whisky, and
gin in greater amounts almost always lessen the respiratory changes, and, consequently,
the amount of the gas exhaled. This is primarily due to their influence on the rate of
metabolism in each instance.
Exercise. Bodily exercise, in moderation, increases the quantity of CO 2 expired by at
least one-third more than it is during rest. For about an hour after exercise the volume
of the air expired in the minute is increased nearly 2,000 c.c., or 118 cubic inches; and the
quantity of carbon dioxide about 125 c.c., or 7.8 cubic inches per minute. Violent exercise,
such as full labor or athletic competition, still further increases the amount of the carbonic
acid exhaled.
The Oxygen is Diminished. Pettenkofer and Voit have found that the
mean consumption of oxygen during 24 hours, by a man weighing 70 kilos,
is about 700 grams or 490 liters. The quantity of oxygen absorbed increases
with muscular exercise, and falls during rest. In general terms the quantity
absorbed varies with the activity of the metabolic processes, following very
closely the variation of carbon dioxide under the conditions outlined above.
The Volume of the Respired Air is Diminished. When allowance has
been made for the expansion in heating, the volume of expired air is decreased.
266 RESPIRATION
the loss being due to the fact that a portion of the oxygen absorbed is not
returned in the form of carbon dioxide. Since the oxygen of a given volume
of carbon dioxide would have the same volume as the carbon dioxide
itself at a given temperature and pressure, a portion of the oxygen absorbed
must be used for other purposes than the formation of carbon dioxide.
In fact, some of it is used in the formation of urea, some in the formation
of water, etc. The oxygen in the carbon dioxide exhaled, divided by the
oxygen absorbed, gives what is known as the respiratory quotient ; thus
CO3 exhaled
Oa absorbed
Normally in man on a mixed diet the respiratory quotient is
4.0 to 4.5
— = 0.8 to 9.9.
But it is subject to variation through several causes. For example, through
variation in diet. On a pure carbohydrate diet the respiratory quotient
will rise above 0.9, i.e., to i.o, since carbohydrates contain enough oxygen
to oxidize the hydrogen in their molecule. On a diet containing much fat
it is lowest, since relatively more oxygen is needed completely to oxidize fat.
The theoretical respiratory quotient for fats is 0.7. The same is true, but to
a less degree, in the case of proteids which also require much oxygen for their
complete oxidation. Muscular exertion raises the respiratory quotient, because
in its performance carbohydrates are used up in relatively greater quantity.
The Watery Vapor in Respired Air is Increased. The quantity emitted
is, as a general rule, sufficient to saturate the expired air, or very nearly so.
Its absolute amount is, therefore, influenced by the following circumstances:
i, By the quantity of air respired; for the greater this is, the greater also
will be the quantity of moisture exhaled; 2, By the quantity of watery
vapor contained in the air previous to its being inspired; because the greater
this is, the less will be the amount to complete the saturation of the air; 3,
By the temperature of the expired air; for the higher this is, the greater will
be the quantity of watery vapor required to saturate the air; 4, By the length
of time which each volume of inspired air is allowed to remain in the lungs;
for although, during ordinary respiration, the expired air is always saturated
with watery vapor, yet, when respiration is performed very rapidly, the air
has scarcely time to be raised to the highest temperature or be fully charged
with moisture ere it is expelled.
The quantity of water exhaled from the lungs in 24 hours ranges (accord-
ing to the various modifying circumstances already mentioned) from about
200 to 800 c.c., the ordinary quantity being about 400 to 500 c.c. Some of
this is probably formed by the chemical combination of oxygen with hydro-
gen in the system; but the far larger proportion of it is water which has been
PRESSURE AND DIFFUSION OF THE AIR 267
absorbed, as such, into the blood from the alimentary canal, and which is
exhafed from the surface of the air-passages and cells, as it is from the free
surfaces of all moist animal membranes, particularly at the high tempera-
ture of warm-blooded animals.
A Small Quantity of Ammonia is added to the ordinary constituents of
expired air. It seems probable, however, both from the fact that this sub-
stance cannot be always detected and from its minute amount when present,
that the whole of it may be derived from decomposing particles of food left
in the mouth, or the teeth, and that it is, therefore, only an accidental con-
stituent of expired air.
The Quantity of Organic Matter in Expired Air is Increased. It was
formerly supposed that this organic matter was injurious and gave rise to
the unpleasant symptoms which are experienced in badly ventilated rooms.
But this has been strongly questioned so that the matter cannot be considered
settled at the present time.
THE RESPIRATORY CHANGES IN THE BLOOD.
Pressure and Diffusion of the Air. It must be remembered that
the tidal air in the lungs amounts only to from 300 to 500 c.c. at each in-
spiration. This amount at once mixes with the reserve and the residual
air already in the lungs. The mixture is facilitated by the air currents set
up in the deeper parts of the lungs by the sudden entrance of the tidal air;
but, after all is considered, it will be found that diffusion is the greatest factor
in producing a uniform mixture of the gases in the alveoli and in the air-cells
of the lungs. Just as a fresh supply of oxygen introduced within the door
of a closed room will quickly diffuse throughout the space of the entire room
so will the fresh tidal air diffuse into the space of the lungs. When the
tidal air is expired its average composition has been changed so it has only
about 1 6 per cent of oxygen instead of the usual 20.96 per cent of oxygen in
air. The oxygen content of the air still left in the lungs is probably some-
what less than the percentage in this expired air for the reason that the air
of the respiratory tree, the trachea, bronchi, and bronchioles, is never fully
mixed with the alveolar air.
The partial pressure of the oxygen of the air measured under standard
conditions is 159 mm. of mercury, that is, 20.96 per cent of 760 mm. of mer-
cury, the standard pressure of one atmosphere. The partial oxygen pressure
in expired air with 16 per cent of oxygen is only 122 mm. of mercury. These
figures show a diffusion pressure of at least 37 mm. of mercury to carry
oxygen into the deeper recesses of the lungs. The constant loss of oxygen
to the blood probably keeps the mean difference greater.
The Gases of the Blood. Turning now to the consideration of
the gases of the blood in the lungs, a somewhat different picture presents
RESPIRATION
itself. The blood is a mass of corpuscles floating in the fluid plasma. An
analysis of the blood shows that it contains oxygen, carbon dioxide, and
nitrogen, the gases of the air. The usual method is completely to extract
the blood gases by an air-pump, figure 237, and determine the quantities in
cubic centimeters per 100 c.c. of blood.
The Extraction of the Gases from the Blood. As the ordinary air-pumps are not suf-
ficiently powerful for the purpose, the extraction of the gases from the blood is accomplished
by means of a mercurial air-pump, of which there are many varieties, those of Ludwig,
Alvergnidt, Geissler, and Sprengel being the chief. The principle of action in all is much
the same. Ludwig's pump, which may be taken as a type, is represented in figure 237.
It consists of two fixed glass globes, C and F, the up-
per one communicating by means of the stopcock, D,
and a stout India-rubber tube with another glass globe,
L, which can be raised or lowered by means of a pul-
ley; it also communicates by means of a stopcock, B,
and a bent glass tube, A , with a gas receiver (not repre-
sented in the figure), A dipping into a bowl of mercury,
so that the gas may be received over mercury. The
lower globe, F, communicates with C by means of the
stopcock, E, with / in which the blood is contained by
the stopcock, G, and with a movable glass globe, My
similar to L, by means of the stopcock, H, and the
stout India-rubber tube, K.
In order to work the pump, L and M are filled
with mercury, the blood from which the gases ire to
be extracted is placed in the bulb 7, the stopcocks H,
E, D, and B being open, and G closed. M is raised
by means of the pulley until F is full of mercury, and
the air is driven out. E is then closed, and L is raised
so that C becomes full of mercury, and the air driven
off. B is then closed. On lowering L the mercury
runs into it from C, and a vacuum is established in C.
On opening E and lowering M, a vacuum is similarly
established in F ; if G be now opened, the blood in 7 will
enter ebullition, and the gases will pass off into F and C,
and on raising M and then L, the stopcock B being
opened, the gas is driven through A, and is received
into the receiver over mercury. By repeating the ex-
periment several times the whole of the gases of the
specimen of blood is obtained, and may be estimated.
FIG. 237. — Ludwig's Gas -pump.
Pfluger's analysis of the arterial blood of
the dog gave the following volumes per cent:
oxygen 22.6, carbon dioxide 34.3, and nitrogen
1.8. The analysis for the venous blood gives
a very much lower oxygen and a higher carbon dioxide per cent. The
average oxygen content of venous blood is 10 to 12 per cent and the carbon
dioxide 45 per cent. The blood in different veins of the body varies within
wide limits as regards its gas content.
Oxygen.
100 c.c. Arterial blood 22.6 c.c.
100 c.c. Venous blood 12. c.c.
Carbon
Dioxide.
34 C.C.
45 c-c-
Nitrogen.
1.7 c.c.
1.7 c.c.
COMBINING POWER OF HEMOGLOBIN WITH OXYGEN
The large quantity of oxygen found in arterial and in venous blood is the
more striking when the facts of absorption of gases by liquids are reviewed.
A liquid such as water will, when exposed to a gas, take up the gas by absorp-
tion according to definite physical laws. Under constant temperature the
amount of gas absorbed, oxygen for example, varies directly as the pressure
of the gas, or partial pressure if ,the gas is a mixture. The oxygen absorbed
by water from pure air as compared with expired air is in direct proportion
to the partial pressure of oxygen in the two airs, which is as 159 to 122.
The amount of gas absorbed for a unit of fluid under standard tempera-
ture and pressure (one atmosphere at o° C.), called its absorption coefficient,
is about the same for blood-plasma as for water. Before one can determine
the actual amount of oxygen in the plasma, the tension or absorption pressure
must be determined.
The tension of the oxygen in arterial blood is found by an instrument
which enables one to measure the pressure at which oxygen is neither ab-
sorbed nor given off. The instrument commonly used is called an aerotonom-
eter. The principle of the instrument depends upon the fact that blood
exposed to mixtures of the gases in air tends to give up or absorb gases from
the air until complete equilibrium is established.
By this means observers have measured the tensions of the blood gases.
The results have not been very constant, but the oxygen tension has been
found to be from 4 (Strassburg) to 10 (Herter) per cent of an atmosphere.
Many determinations have been given of both lower and higher percentages,
but, accepting the above limits for a working average, the oxygen tension
in arterial blood would be from 30.4 to 76 mm. of mercury.
Blood-plasma exposed to an air with a partial pressure of 30.4 to 76 mm.
of mercury would absorb only from o.i to 0.3 (0.26 c.c. Pfliiger) of a cubic
centimeter of oxygen for 100 c.c. of blood. As a matter of fact, 100 c.c. of whole
blood contains from 20 to 22 c.c. of oxygen. It is evident that blood cannot
hold the oxygen in simple solution, but must retain it in chemical combina-
tion. The red blood-corpuscles have been shown to carry the excess of
oxygen by virtue of the special respiratory pigment, hemoglobin.
Combining Power of Hemoglobin with Oxygen. One hundred
cubic centimeters of blood contain about 14 grams of hemoglobin, page 120.
Each gram of hemoglobin, when fully saturated with oxygen, according to
Hufner's earlier determination, combines with 1.56 c.c. of oxygen. By later
more careful work he gets the determination of 1.34 c.c. for hemoglobin of
ox blood. This last figure indicates that the combining power of the hemo-
globin is dependent upon the iron in the molecule, in which one atom of iron
combines with one atom of oxygen. The later investigation of the conditions
under which hemoglobin combines with oxygen are by Hiifner, on the one
hand, and Loewy, on the other. The former worked with purified solutions
of hemoglobin, the latter with blood. The average results of the investigations
270 RESPIRATION
of these two observers show that when the oxygen tension in the air, which is in
contact with the blood, is lowered below a certain point, the amount of oxygen
which will be liberated from combination with hemoglobin will be very great,
whereas a lowering of the tension of oxygen by an equal amount where the
pressures are relatively high leads to practically no liberation of hemoglobin,
and the converse is equally true. The critical oxygen pressure in so far as
its combination with hemoglobin is concerned varies according to observers.
With Loewy the critical dissociation pressure is at or below 76 mm. of mer-
cury, 10 per cent of an atmosphere. Strassburg gives the oxygen tension of
arterial blood as 29.64 mm. of mercury, and for venous blood 22.04 mm. of
mercury. That is to say, during the brief interval in which the blood is
in the pulmonary capillaries the oxygen tension has increased by 7.6 mm.
of mercury, an increase of tension which would produce very little increase
in simple absorption of oxygen. Yet is it sufficient to cause fixation of
from four to five volumes per cent of oxygen by the hemoglobin.
Oxygen Pressure in the Atmosphere 159 mm. of mercury
" " " Alveolar air 122 mm. of mercury
i
" " " Venous blood 22.04 mm. of mercury
It is evident that there will be diffusion of oxygen from the high tension
toward the lower and in the direction indicated by the arrows in the table
above. As fast as the oxygen diffuses into the venous blood, thus tending to
raise the pressure of the gas in solution, it is taken up and fixed by the hemo-
globin. This process proceeds during the interval the blood is fh the pul-
monary capillaries far enough to raise the oxygen tension from 22.04 mm.
of mercury to 29.64 mm. of mercury, and far enough to permit of the fixation
of from four to five volumes per cent of oxygen.
Liberation of Oxygen in the Tissue Capillaries. When the arterial
blood reaches the capillaries of the tissues, then the situation which we have
just found holding good in the lungs is reversed. As rapidly as the oxygen
reaches the living protoplasm of the tissues it enters into fixed combination,
thus rendering it inert. The oxygen tension in the tissue cells will, there-
fore, be zero. Under these conditions the difference in pressure level be-
tween the oxygen tension in the blood and that in the tissues is sufficient to
cause a rapid diffusion of oxygen through the capillary walls with correspond-
ing liberation of the oxygen from the hemoglobin according to the laws of
combination given in the table above. The total effect of this process is to
maintain a relatively high diffusion pressure of the oxygen in the blood.
During the time the blood remains in the capillaries the total oxygen tension
will have been lowered from 29.64 to 22.04 mm- of mercury, yet this slight
lowering of tension is sufficient to liberate from four to five volumes per cent of
oxygen. This figure, of course, is comparative. In many of the very active
ELIMINATION OF CARBON DIOXIDE 271
tissues, such as in muscle, a much larger per cent of oxygen will have been
disassociated and the oxygen tension correspondingly lowered so that the
venous blood returning through such an active organ may not have more
than half the average amount of oxygen found in venous blood.
Considering the pressure relations of oxygen from the time of its intro-
duction into the body with the fresh air to its fixation in the tissues we have
the following schema:
Oxygen Pressure in the Atmosphere 159 mm.
I
Alveolar Air 122 mm.
i
Venous Blood 22 .04 mm.
Tension of Oxygen in the Arterial Blood 29 .64 mm.
i
" " " Tissues o.oo mm.
Elimination of Carbon Dioxide by the Blood and the Respiratory
Apparatus. The principles of absorption of gas by liquids discussed
in the preceding pages apply equally well for carbon dioxide with the exception
that carbon dioxide is about three times as soluble in blood as is oxygen.
The carbon dioxide results from the oxidative processes going on in the tis-
sues, and this gas is present in large quantities in the tissues and their im-
mediately surrounding lymph. An analysis of the carbon-dioxide content
of venous blood reveals the presence of about 45 c.c. of the gas in 100 c.c. of
blood. This gas, like oxygen, is held in such large quantity by virtue of the
fact that it forms loose chemical combinations in the blood. Of the total
quantity not more than 5 per cent is held in simple solution. From 10 to
15 per cent of the total volume is found in firm combination in such forms
as carbonates, bicarbonates, etc. The remaining 80 and more volumes
per cent is held in loose chemical combination, a combination which is broken
up under the same conditions of variation in carbon-dioxide tension as were
found to exist for oxygen in combination with hemoglobin. In the case of
carbon dioxide an analysis of plasma reveals the fact that the gas is in com-
bination with some compound of the plasma, probably a proteid. In fact,
there is some evidence to show that carbon dioxide combines with the globulin
group. Carbon dioxide also forms loose chemical compounds with the con-
stituents of the red corpuscles, probably with the proteid portion of the hemo-
globin molecule. The pressure relations of this gas as regards its diffusion
in the process of elimination are shown in the following table:
Carbon -dioxide Tension in the Tissues 58 mm. of mercury
i
" " " " Venous Blood 41 " "
I
" « " " Alveolar Air ,23 to 38mm. of "
i
« « " " Expired Air 5.8 mm. " "
272 RESPIRATION
Theories of Interchange of Gases in the Lungs and in the Tissues.
The above discussion is on the basis of the mechanical interpretation of the
transfer of gases in the lungs and in the tissues. By this theory it is assumed
that the oxygen passes from the air in the lungs through the moist pulmonary
membrane of the alveoli to the capillary walls into the blood-plasma, obeying
the physical laws of gas diffusion. Likewise in the tissues this theory pre-
supposes the difference in the mechanical tension in the capillary blood-
plasma, the lymph, and the living tissue will lead to diffusion of the oxygen
in the direction of lowest pressure.
Some facts have indicated that we cannot account for the transference
of oxygen by the purely mechanical theory. The idea has been advanced
that the living epithelial wall of the lung, as well as that of the capillary, exerts
a distinct influence on the passage of oxygen of such nature as might be re-
garded as a secretion of this gas. This theory finds some additional support
in the fact that in the air bladders of certain fishes a distinct secretion of oxygen
has been proven.
THE NERVOUS REGULATION OF THE RESPIRATORY
APPARATUS.
Like all other functions of the body the discharge of which is necessary
to life, the respiratory movement is essentially an involuntary act. Unless
this were the case, life would be in constant danger, and would cease on the
loss of consciousness for a few moments, as in sleep. It is, however, of ad-
vantage to the body that respiration should be to some extent under the
control of the will. For, were it not so, it would be impossible to perform
those respiratory acts such as speaking, singing, and the like.
The Respiratory Nerve Center. It has been known for centuries
that there exists a region of the central nervous system on the destruction of
which both respiration and life cease. Flourens, 1842, after many series
of experiments as to the exact position of what he called the "knot of life"
(nceud vital], placed it in the fourth ventricle, at the point of the V in the
gray matter at the lower end of the calamus scriptorius; a district of consider-
able size, 5 mm., on both sides of the middle line. Observers subsequent to
Flourens have attempted to show that the chief respiratory center, on the
one hand, is situated higher up in the nervous system, in the floor of the third
ventricle (Christiani), or in the corpora quadrigemina (Martin and Booker,
Christiani, and Stanier), or lower down in the spinal cord. The balance
of experimental evidence, however, is to prove that the sole centers for respira-
tion are in a limited district in the medulla oblongata in close connection with
the vagus nucleus on each side, with which they are probably identical.
The destruction of this region stops respiration. If the center be left in
connection with the muscles of respiration by their nerves, although the
THE RESPIRATORY NERVE CENTER 273
remainder of the central nervous system be separated from it, respiration
continues. It may be considered almost certain that the medullary center
is the only true respiratory center. Langendorff states that in newly born
animals in which the medulla has been immediately cut across at a level a
few millimeters below the point of the calamus scriptorius, respiration con-
tinues for some time, but this is questionable. Normal respiration does
not occur after separation of the bulb from the cord, and the so-called
respiratory movements noticed by Langendorff are merely tetanic contrac-
tions of the respiratory muscles in which often enough other muscles take
part.
The action of the medullary center is to send out impulses during in-
spiration, which cause contractions of the inspiratory muscles — a, of the
nostrils and jaws, through the facial and inferior division of the fifth nerves;
b, of the glottis, chiefly through the inferior laryngeal branches of the vagi;
c, of the intercostal and other muscles which produce raising of the ribs,
chiefly through the intercostal nerves, and d, of the diaphragm, through the
phrenic nerves. If any one of these sets of nerves be divided, respiratory
movements of the corresponding muscles cease. Similarly it may be supposed
that the center sends out impulses during expiration to certain other muscles.
It has been suggested, however, that the center is double, that it is made up
of inspiratory cells which are constantly in action, and of an expiratory group
of cells which act less generally, inasmuch as ordinary tranquil expiration
is seldom more than an elastic recoil, and not a muscular act to any marked
degree.
The respiratory center is also bilateral, as has been proven by the method
of antero-posterior section of the medulla. The tracts from each half of the
center are separate and distinct. If the cervical cord be split into a right
and left half, and one side sectioned at the level of the second cervical verte-
bra, then the respiratory movements of that side of the diaphragm cease
while on the opposite side they continue their rhythm.
Assuming this view of the quadruple nature of the respiratory centers
to be correct, there is some difference of opinion of the exact mode of action;
it is thought that the center may act automatically, but normally is influenced
by afferent impulses from the periphery, as well as by impulses passing down
from the cerebrum. The center is, in other words, both automatic and
reflex. It will be simplest to discuss its reflex function first.
Action of Afferent Stimuli on the Respiratory Rhythm. Action
of the vagi. If both vagi be divided in the neck, the respirations become
much slower and deeper. This may be the case, but to a less marked degree,
if one of the nerves is divided instead of both. If the central end of the
divided nerve be stimulated with a weak but properly adjusted strength of
interrupted current, the effect is that the respirations are quickened, and if
the stimuli are properly regulated the normal rhythm of respiration may
18
274 RESPIRATION
be resumed. If the stimuli be repeated with stronger currents, the breathing
is brought to a standstill, sometimes at the height of inspiration, by tetanus
of the diaphragm. Usually, however, stimulation of the central end of the
divided vagus produces still greater slowing than that which follows the division
so that the respirations cease with the diaphragm in a condition of complete
relaxation.
The action of the vagus may be to call forth either inspiration or expira-
tion— the impulses passing up the vagi being necessary to the production
of the normal respiratory rhythm. The fibers of the vagus are used under
the following circumstances: those fibers which tend to inhibit expiration
and to stimulate inspiration are stimulated at their origin in the lung when the
on- off
FIG. 239. — The Effect of Stimulating the Vagus Nerve on Respiratory Rate. The stimulus
was applied between the points " on " and " off." The inhibition lasts some seconds after the stim-
ulus is removed. Time in seconds. The intratracheal pressure is recorded.
lung is empty and in a condition of expiration, and the fibers which tend
to inhibit inspiration and to promote expiration are stimulated when the
lung is fully expanded. The afferent impulses by this view are the results
of mechanical stimulation, and do not depend altogether upon the chemical
nature of the gases within the pulmonary alveoli.
Action of the Superior Laryngeal Nerves. If the superior laryngeal
branch of the vagus be divided, which usually produces no apparent effect,
and the central end be stimulated, the effect is very constant, — respirations
are slowed, but there is a tendency toward expiration, as is shown by the
contraction of the abdominal muscles. Thus, the vagus contains fibers
which stimulate inspiration and inhibit expiration, as well as other fibers
which have the reverse effect ; while the superior laryngeal fibers inhibit in-
spiration and stimulate expiration.
The superior laryngeal nerves are true expiratory nerves, and are nor-
mally set in action when the mucous membrane of the larynx is irritated.
They are not in constant action like the vagi.
Action of the Glosso-pharyngeal Nerves. It has been ascertained,
by the researches of Marckwald, that while division of the glosso-^)haryngeal
nerves produces no effect upon respiration, stimulation of them causes in-
hibition of inspiration for a short period. This action accounts for the very
necessary cessation of breathing during swallowing. The effect of the stimu-
lation is only temporary, and is followed by normal breathing movements.
Action of Other Sensory Nerves. The respiratory center is in-
AUTOMATIC ACTION OF THE RESPIRATORY CENTERS 275
fluenced strongly by afferent nerve impulses having their origin in general
sensory nerves, particularly the nerves of the skin. Cold water suddenly
applied to the surface of the skin is almost invariably followed by a deep
inspiration. Stimulation of the splanchnics and of the abdominal branches
of the vagi produces expiration. Stimulation of the isolated sciatic nerve of
the dog or the rabbit causes a marked acceleration both of the rate and
the amplitude of the respiratory movements, see figure 246. This accelera-
tion is due to afferent impulses which reach the respiratory center in the me-
dulla over sensory paths, paths which are not necessarily special respiratory
afferent paths, but rather are general afferent paths which affect the respira-
tory center through their numerous collaterals in the brain stem.
It must be remembered that, although on stimulation many sensory nerves
may be made to produce an effect upon the respiratory centers, there is no
evidence to show that any one of them, except the vagi, is constantly in action.
The vagi indeed are, as far as we know, the normal regulators of respiratory
movements, yet one must remember that it is possible reflexly to influence
the respiration rate and depth through reflexes that may have their sensory
origin in any part of the body.
The respiratory center is also influenced by nerve activity of the cerebral
cortex, psychic activity. This is illustrated by the limited voluntary control
of the respiration movements.
Automatic Action of the Respiratory Centers. Although it has
been very definitely proved that the respiratory centers may be affected by
afferent stimuli, and particularly by those reaching them through the vagi,
there is reason for believing that the center is capable of sending out efferent
impulses to the respiratory muscles without the action of any afferent stimuli.
Thus, if the brain be removed above the bulb, respiration continues. If the
spinal cord be divided immediately below the bulb, the facial and laryngeal
respiratory movements continue, although no afferent impulses can reach
the center except through the cranial sensory nerves, and these indeed may
be divided without producing any effect, when the bulb and cord are intact.
As has been shown, too, respiration continues when the vagi are divided.
Isolation of the respiratory center from its sensory relations does not destroy
respiratory movements so long as the motor paths through the phrenic nerve
are intact. All of these experiments render it highly probable that afferent
impulses are not required in order that the respiratory centers should send
out efferent impulses to the respiratory muscles. The center, then, is auto-
matic.
Method of Automatic Stimulation of the Respiratory Center. The
respiratory center is capable of working automatically apart from afferent
impulses, and this fact has been explained by the supposition that it is stimu-
lated to action by the condition of the blood circulating through it. When
the blood becomes more and more venous the action of the center becomes
276 RESPIRATION
more and more energetic, and if the air is prevented from entering the chest,
the respiration in a short time becomes very labored. If the aeration of the
blood is much interfered with, not only are the ordinary respiratory muscles
employed, but also those muscles of extraordinary inspiration and expira-
tion which have been previously enumerated. Thus, as the blood becomes
more and more venous, and by venous we mean that the blood contains a
relatively large amount of carbon dioxide and a diminished amount of oxygen,
the action of the medullary center becomes more and more profound. The
question has been much debated as to what quality of the venous blood it is
which causes this increased activity; whether it is its deficiency of oxygen
or its excess of carbon dioxide. It has been answered to some extent by ex-
periments which offer no obstruction to the exit of carbon dioxide, as when
an animal is placed in an atmosphere of nitrogen. Under these conditions
dyspnea occurs, showing that blood which contains a diminished amount
of oxygen stimulates the cells of the respiratory center. On the other hand,
if the normal amount of oxygen is supplied while the carbon dioxide of the
blood is prevented from escaping and thus allowed to accumulate in the
blood, there is also a great increase in the respiratory activity of the center;
an excess of carbon dioxide in the blood, flowing through the respiratory
center, stimulates the cells to greater activity. It is highly probable, there-
fore, that the respiratory centers may be stimulated to action both by the
absence of sufficient oxygen in the blood circulating in it, and by the presence
of an excess of carbon dioxide.
These facts are particularly well supported by the experiments of Zuntz
who varied the oxygen and the carbon-dioxide content of the air breathed,
and measured the volume breathed per minute. When the oxygen of the
air breathed was reduced by 10 to 50 per cent, the air breathed was increased
only slightly, 5 to 10 per cent. When the oxygen of the air was reduced
by 60 per cent, the volume of air breathed was increased 30 to 40 per cent,
and even more. Other observations show us that the oxygen in the blood
in these experiments will fall in much less per cent than the reduction in
the oxygen of the air would lead us to suspect.
When Zuntz kept the oxygen content of the air about constant, but in-
creased the carbon-dioxide content, then the amount of air breathed was
greatly increased. Air containing 18.4 per cent of oxygen and 11.5 per cent
of carbon dioxide increased the amount breathed per minute from 7.5 liters
to 32.5 liters. These experiments indicate that within the limits of the
normal variations in blood the carbon dioxide has a much greater influ-
ence than oxygen on the irritability of the cells of the respiratory center.
But this is not all, since it has been observed by Marckwald that the
medullary center is capable of acting for some time in the absence of any
circulation, and after excessive bleeding. The view taken by this author
with regard to the action of the center is as follows: The respiratory center
RESPIRATORY MOVEMENTS AT BIRTH 277
is set to act by the condition of its metabolism, much in the same way as
the heart is set to beat rhythmically. When anabolism is completed, catab-
olism or discharge occurs, and this alternate but crude and spasmodic
action will occur without a definite blood supply so long as the centers are
properly nourished and stimulated by their own intercellular fluid. It is
unreasonable to think, however, that the respiratory center is independent
of the character of the blood supply, either as regards quantity or quality
of the blood. It has also been shown that the presence of the products of
great muscular metabolism in the blood will greatly increase the irritability
of the respiratory center, even if the blood itself be not particularly venous
in character.
The Establishment of Respiratory Movements at Birth. From
the preceding paragraph it appears that the regulation of the respiratory
movements is normally due to the automaticity of the respiratory center as
influenced, first, by the blood flowing through it and, second, by the afferent
nerve impulses which reach the center. The fetus in the womb is supplied
by arterial blood from the blood-vessels of the mother. The fetus does not
ordinarily give respiratory movements before birth, but it may be made to
do so by experimental procedure. At birth the placental circulation is sud-
denly interrupted, and the blood rapidly increases in venosity until the skin,
lips, and mucous membranes are very cyanotic in appearance. It is at this
time that the respiratory center begins its rhythmic discharges, being aroused
by the direct stimulating effects of the strongly venous blood. It is more
than possible that the irritability of the center is also increased by the stimu-
lation of the skin by the air, the contact with clothing, and the hands of the
nurse. We have already seen that cutaneous stimulation leads to increase
in both respiratory rate and amplitude even in the adult. The primary
stimulus for the establishment of the respiratory rhythm at birth, then, is
the venosity of the blood, but this cause is supported by the general reflexes
which reach the respiratory center.
Certain Special Types of Respiration. Whatever the exact quality
of the venous blood which excites the respiratory center to produce normal
respirations, there can be no doubt that, as the blood becomes more and more
venous from obstruction to the entrance of air into the lung, or from the
blood not taking up from the air its usual supply of oxygen, the respiratory
center becomes either less or more active and excitable. Conditions ensue
which have received the names Apnea (diminished breathing), Hyper pnea
(excessive breathing), Dyspnea (difficult breathing), and Asphyxia (suffoca-
tion).
Apnea. This is a condition of diminished respiratory movement. When
we take several deep inspirations in rapid succession by voluntary effort,
we find that we can do without breathing for a much longer time than usual;
in other words, several rapid respirations seem to inhibit for a time normal
278 RESPIRATION
respiratory movements. The reason for this partial cessation of respira-
tion, or apnea, is not that we overcharge our blood with oxygen, as was once
thought, for Hering has shown that animals in a condition of apnea may
have less oxygen in their blood than in a normal state, although the carbon
dioxide is less. It is probable that the cause of apnea is that by rapid in-
flations of the lungs impulses pass up by the vagi, by means of which in-
spiration is after a while inhibited; or that by the repeated stimulation of
the center by vagus impulses which result in rapid respiratory movements,
anabolism is at last arrested. Apnea is with difficulty produced, if at all,
when the vagi are divided.
Asphyxia. The condition of stress in the respiratory apparatus brought
about by insufficient respiratory activity leads to a condition of asphyxia.
Progressive asphyxiation may be brought on by anything which interferes
with the normal interchange of the respiratory gases of the blood.
Asphyxia may be produced by the prevention of the due entry of oxygen
into the blood, either by direct obstruction of the trachea or other part of the
respiratory passages, or by introducing instead of ordinary air a gas devoid
of oxygen, or, by interference with the due interchange of gases between
the air and the blood.
The symptoms of asphyxia may be divided into three groups, which
correspond with the stages of the condition which are usually recognized;
these are: i, the stage of exaggerated breathing, hyperpnea; 2,. the stage of
convulsions, dyspnea; 3, the stage of exhaustion, asphyxiation.
In the first stage the breathing becomes more rapid and at the same time
deeper than usual, the inspirations at first being especially exaggerated and
prolonged. This is soon followed by a similar increase in the expiratory
efforts being aided by the muscles of extraordinary expiration. This stage is
usually called hyperpnea. Hyperpnea soon passes into a condition of labored
breathing in which there is marked increase of the force of the expiratory
as well as the inspiratory act, a condition described as dyspnea. All the
muscles capable of aiding either directly or indirectly in respiration are ulti-
mately brought into action. These respiratory convulsions are followed by
rather sudden onset of paralysis of the respiratory center and death.
The conditions of the vascular system in asphyxia are: i, more or less
interference with the passage of the blood through the systemic and the pul-
monary blood-vessels; 2, accumulation of blood in the right side of the heart
and in the systemic veins; 3, circulation of impure (non-aerated) blood in
all parts of the body, especially through the respiratory center.
Cheyne-Stokes' breathing is a rhythmical irregularity in respirations which
has been observed in various diseases. Respirations occur in groups; at the
beginning of each group the inspirations are very shallow, but each succes-
sive breath is deeper than the preceding, until a climax is reached, after which
the inspirations become less and less deep, until they cease altogether for
EFFECTS OF VITIATED AIR 279
a time, after which the cycle is repeated. This phenomenon appears to be
due to the want of action of some of the usual cerebral influences which pass
to and regulate the discharges of the respiratory center.
Effects of Vitiated Air. Ventilation. As the air expired from
the lungs contains a large proportion of carbon dioxide and a minute amount
of organic matter, it is obvious that if the same air be breathed again and
again, the proportion of carbon dioxide and organic matter in it will con-
stantly increase till it becomes unfit to breathe; long before this point is
reached, however, uneasy sensations occur, such as headache, languor, and
a sense of oppression. It is a remarkable fact, however, that the organism
after a time adapts itself to a very vitiated atmosphere, and that a person
soon comes to breathe, without sensible inconvenience, an atmosphere which,
when he first enters it, feels intolerable. Such an adaptation, however, can
take place only at the expense of a depression of all the vital functions, which
must be injurious if long continued or often repeated. This power of adapta-
tion is well illustrated by an experiment of Claude Bernard. If a sparrow
is placed under a bell-glass of such size that it will live for three hours, be taken
out at the end of the second hour (when it could have survived another hour),
and a fresh healthy sparrow introduced, the latter will die at once.
It must be evident that provision for a constant and plentiful supply of
fresh air, and the removal of that which is vitiated, are of greater importance
than the actual cubic space per person of occupants. Not less than 2,000 cubic
feet per individual should be allowed in sleeping apartments (barracks, hos-
pitals, etc.), and with this allowance the air can be maintained at the proper
standard of purity only by such a system of ventilation as provides for the
supply of 1,500 to 2,000 cubic feet of fresh air per person per hour.
Effects of Breathing Gases Other than the Atmosphere. Asphyxiation is
produced by the direct poisonous action of such gases as carbon monoxide,
which is contained to a considerable amount in common coal gas. The
fatal effects often produced by this gas (as accidents from burning charcoal
stoves in small, close rooms) are due to its entering into combinations with
the hemoglobin of the blood-corpuscles and thus preventing the formation
of oxyhemoglobin because of the more stable carbon-monoxide hemoglobin.
The partial pressure of oxygen in the atmosphere may be considerably in-
creased without much effect in displacing the carbon monoxide, hence this
is rapidly fatal when breathed. Hydrogen may take the place of nitrogen
with no marked ill effect, if the oxygen is in the usual proportions. Sul-
phureted hydrogen destroys the hemoglobin of blood and thus produces oxygen
starvation. Nitrous oxide acts directly on the nervous system as a narcotic,
and may also form a compound with hemoglobin. Certain gases, such as
carbon dioxide in more than a certain proportion, sulphurous acid gases, am-
monia, and chlorine, produce spasmodic closure of the glottis and prevent
respiration.
280 KESPIRATION
Alteration in the Atmospheric Pressure. The normal condition of breath-
ing is that the oxygen of the air breathed should be at the pressure of 20.96
per cent of the atmosphere, that per cent of 760 mm. of mercury, or 159 mm.
But it is found that life may be carried on by gradual diminution of the oxygen
pressure to considerably less than one-half of this, to a partial pressure of
76 mm. of oxygen, i.e., the oxygen of one-half an atmosphere. This
pressure is reached at an altitude above 15,000 feet.* Any pressure
less than this may begin to produce alterations in the relations of
the gases in the blood, and if an animal is subjected suddenly to a
marked decrease of barometric pressure, and so of oxygen pressure
(below 7 per cent of oxygen), it is thrown into convulsions. It is found that
the gases are set free in the blood-vessels, no doubt carbon dioxide and oxygen
as well as nitrogen, although the latter is the only one of the three gases the
presence of which has been proven in the vessels in death from this condition
of affairs. The other gases are said to be reabsorbed. Other derangements
may precede this, bleeding from the nose, dyspnea, and vascular incoordina-
tion, etc. On the other hand, the oxygen may be gradually increased to a con-
siderable extent without marked effect, even to the extent of 8 or 10 atmos-
pheres, but when the oxygen pressure is increased up to 20 atmospheres the
animals experimented upon by Paul Bert died with severe tetanic convulsions.
THE EFFECT OF RESPIRATION ON THE CIRCULATION.
As the heart, the aorta, and pulmonary vessels are situated in the air-
tight thorax, they are exposed to a certain alteration of pressure when the
capacity of the latter is varied in respiration. The disturbance of pressure
which occurs during inspiration causes, first, a decrease in the intrathoracic
cavity, a decrease in pressure which affects all the organs of the thorax — the
lungs, the great blood-vessels, the heart. The expansion of the elastic lungs
counterbalances this change in pressure in part, but it never does so entirely,
since part of the pressure within the lungs is expended in overcoming their
elasticity. The amount thus used up increases as the lungs become more and
more stretched, so that the intrathoracic pressure during inspiration, as far
as the heart and great vessels are concerned, never quite equals the intra-
pulmonary pressure, and at the conclusion of inspiration is considerably
less than the atmospheric pressure. It has been ascertained that the amount
of the pressure used up in the way above described varies from 5 to 7 mm. of
mercury in ordinary inspiration, to 30 mm. of mercury at the end of a deep
inspiration. So it will be understood that the pressure to which the heart
and great vessels are subjected diminishes as inspiration progresses, and at
* For an interesting account of the symptoms produced by diminished atmospheric
pressure by very high altitudes, consult Whymper's "Travels amongst the Andes of the
Equator."
EFFECT OF RESPIRATION ON THE CIRCULATION
281
its minimum is less by from 7 to 30 mm. than the normal atmospheric pres-
sure, 760 mm. of mercury. It will be understood from the accompanying
diagram how an increase in the volume of the thorax will have the effect of
pumping blood into the heart from the veins. During inspiration the pressure
outside the heart and great vessels is diminished, and they, by virtue of their
elasticity, have therefore a tendency to expand and to diminish the intra-
vascular pressure. The diminution of pressure within the veins passing
to the right auricle and within the right auricle itself, will draw the blood
into the thorax, and so assist the circulation. This suction action of the thorax
is the cause of the slight negative pressure of the ventricle previously de-
scribed. The effect of more blood in the right auricle will, cczteris paribus,
increase the amount passing through the right ventricle, and through
the lungs into the left auricle and ventricle, and thus into the aorta.
This all tends to increase the blood pressure. The effect of the
FIG. 240. — Diagram of an Apparatus Illustrating the Effect of Inspiration upon the M >art and
Great Vessels within the Thorax. I, The thorax at rest; II, during inspiration; D represents the
diaphragm when relaxed; D', when contracted (it must be remembered that this position is a mere
diagram), i.e., when the capacity of the thorax is enlarged; H, the heart; V, the veins entering
it, and A, the aorta; Rl, LI, the right and left lung; T, the trachea; M, mercurial manometer in
connection with pleura. The increase in the capacity 9f the box representing the thorax is seen to
dilate the heart as well as the lungs, and so to pump in blood through V, whereas the valve pre-
vents reflux through A . The position of the mercury in M shows also the suction which is taking
place. (Landois.)
diminished pressure upon the pulmonary vessels will also help toward the
same end, an increased flow through the lungs, so that, as far as the mechani-
cal effects on the heart and its veins are concerned, inspiration increases
the blood pressure in the arteries. The effect of inspiration upon the aorta
and its branches within the thorax would be, however, contrary; for as the
external pressure is diminished, the vessels would tend to expand, and thus
to diminish the tension of the blood within them, but, inasmuch as the rela-
tive variation in pressure on the large arteries is slight, the diminution of
arterial tension caused bv this means will be insufficient to counteract the
282 RESPIRATION
increase of blood pressure produced by the effect of inspiration upon the
volume of discharge of the veins of the chest, and the balance of the whole
action would be in favor of an increase of blood pressure during the inspira-
tory period. When a blood-pressure tracing is taken at the same time that
the respiratory movements are being recorded, it will be found that, although,
speaking generally, the arterial tension is increased during inspiration, the
maximum of arterial tension does not correspond with the acme of inspira-
tion, figure 241. In fact, at the beginning of inspiration the pressure con-
tinues to fall for a brief moment, then gradually rises until the end of
inspiration, and continues to do so for a moment after expiration has com-
menced. For explanation of the influence of heart rate- in this variation of
blood pressure, associated with the respiratory movement, see page 181.
In ordinary expiration all this would be reversed, but if the abdominal
muscles are violently contracted, as in extraordinary expiration, the same
FIG 241. — Comparison of Blood -Pressure Curve with Curve of Intrathoracic Pressure (To
be read from left to right.) a is the curve of blood pressure with its respiratory undulations, the
slower beats on the descent being very marked; b is the curve of intrathoracic pressure obtained
by connecting one limb of a manometer with the pleura! cavity. Inspiration begins at * and expira-
tion at e. ihe intrathoracic pressure rises very rapidly after the cessation of the inspiratory
ettort, and then slowly falls as the air issues from the chest; at the beginning of the inspiratory
effort the fall becomes more rapid. (M. Foster.)
relative effect would be produced as by inspiration. The immediate effect
during inspiration of the diminished intrathoracic pressure upon the pul-
monary vessels is to produce an initial dilatation of both artery and veins,
and this delays for a moment the passage of blood toward the left side of the
heart, resulting in an initial fall in the arterial pressure, but the fall of blood
pressure is immediately followed by a steady rise, since the flow is increased
by the initial dilatation of the vessels. The converse is the case with ex-
piration. As, however, the pulmonary veins are more easily dilatable than
the pulmonary artery, their greater distensibility increases the flow of blood
as inspiration proceeds, while during expiration, except at its beginning,
this property of theirs acts in the opposite direction, and diminishes the flow.
Thus, at the beginning of inspiration the diminution of blood pressure, which
LABORATORY EXPERIMENTS 283
commenced during expiration, is continued, but after a time the diminution
is succeeded by a steady rise. The reverse is the case with expiration — at
first a rise and then a fall.
As regards the effect of expiration, the capacity of the chest is diminished
and the intrathoracic pressure returns to the normal, which is still slightly
below the atmospheric pressure. The effect of this on the veins is to in-
crease their extravascular and so their intravascular pressure, and to di-
minish the flow of blood into the left side of the heart, and with it the general
blood pressure. Ordinary expiration does not produce a distinct obstruction
to the circulation, as even when the expiration is at an end the intrathoracic
pressure is less than the extrathoracic. The effect of violent expiratory
efforts, however, does have a distinct action in obstructing the current of
blood through the lungs, as seen in the congestion in the exaggerated con-
dition of straining, this condition being produced by pressure on the entire
group of pulmonary vessels.
There are other mechanical factors, such, for example, as the effect of
the abdominal movements, both in inspiration and in expiration, upon the
arteries and veins within the abdomen and of the lower extremities, and
the influence of the varying intrathoracic pressure upon the pulmonary
vessels, both of which ought to be taken into consideration. As regards
the first of these, the effect during inspiration — as the cavity of the abdomen
is diminished by the descent of the diaphragm — should be twofold: on
the one hand, blood would be sent upward into the chest by compression
of the vena cava. inferior; on the other hand, the passage of bbod down-
ward from the chest in the abdominal aorta, and upward in the veins of the
lower extremity, would be to a certain extent obstructed.
LABORATORY EXPERIMENTS IN RESPIRATION.
1. Respiratory Rate in Man. Count your respirations for from
2 to 4 minutes while sitting quietly, and determine the average number per
minute. Repeat the counting after standing for 5 minutes, and after brisk
exercise. These determinations involve the element of consciousness, under
which condition it is difficult for a person to breathe with his normal rate
and depth.
Make a series of determinations of respiratory rates of persons who are
sitting quietly but unconscious of your determinations. Count the rates
in a number of persons of different ages; where possible, take into considera-
tion height, weight, etc. Tabulate the results for a comparison and for
future reference.
2. The Character of Respiratory Movements in Man. A number
of instruments have been devised for measuring human respiratory move-
ment, many of which measure the change in diameter of the chest in respira-
284
RESPIRATION
tory movemen- Adjust one of these, for example Burdon-Sanderson's
stethograph, to the thorax, and record the movement of the receiving tam-
bour on a smoked-paper kymograph which travels at the rate of i cm. per
second. This record, called a stethogram, will exhibit the respiratory rate,
the relative time of the inspiratory and expiratory phases, and the character
of each.
3. The Actual Change of Diameter in the Chest in Respiration.
Use a caliper provided for the purpose and measure the dorso-ventral diam-
eter of the chest at a series of points along the sternum, taking the reading
FIG. 242. — Change in Diameter of the Body in Respiration, Costal Type, a, Outline of the
body in forced expiration. In the heavy continuous line, b, the outer margin indicates the contour of
the body in ordinary inspiration and the inner margin that of ordinary expiration, c, Contour
of forced inspiration. (After Hutchinson.)
at the height of the inspiratory phase and of the expiratory phase in ordi-
nary respiration. Repeat the measurement in forced respiration. Map
the results on millimeter paper, as indicated in figure 242.
Repeat these measurements in the transverse diameter at the first, fifth,
and tenth ribs.
Using the chest pantograph, figure 243, record the outline of the chest
at the level of the middle of the sternum during expiration and at the end
of inspiration.
4. The Volume of Air Breathed by Man. Determine the average
volume of air breathed per respiration, using Hutchinson 's spirometer, figure
235, set the instrument at the zero point, exhale into the instrument through
the tube, using all possible care to breathe with your normal rate and depth.
Better results will be obtained by taking the average from sets of ten consecu-
tive inspirations into the instrument. From the average of the volume per
VITAL CAPACITIES
285
respiration, and the average number of respirations per minute, determined
in experiment i, calculate the amount of air breathed per hour and per day.
5. Vital Capacities. Using the spirometer as in the preceding
experiment, set the instrument at zero and exhale into it: a, Begin with the
fullest possible inspiration and exhale the greatest possible amount of air
from the lungs. This is known as the vital capacity.
b, Beginning at the end of an ordinary expiration exhale into the instru-
ment the greatest possible amount. This is called the reserve air.
c, Following ordinary inspiration exhale into the instrument until you
reach the ordinary state of expiration. This involves the conscious fixing
of two points in the respiratory act, namely, the summit of inspiration and
expiration, which are ordinarily automatically adjusted by the body. The
error of the determination is therefore great. It is better to make this measure-
ment in sets of ten, as in the preceding experiment, and take the average.
FIG. 243. — The Chest Pantograph for Recording the Outlines of the Chest. The fixed point
in the instrument is /; the points a, b, x, y, are movable joints; when point t is made to trace
the outline of the chest, point r will give a corresponding movement and can be made to trace this
movement on recording paper. (Hall.)
This reduces the error. This quantity of air is known as the tidal air. One
can measure the tidal air and the reserve air together, check them against
the sum of the twro, as in a and b separately.
The sum of the tidal and reserve air taken from the vital air will leave
the amount which one may inspire over and above that in the chest at the end
of ordinary inspiration. This is called complemental. The complemental
can be measured by inspiring the air from the spirometer, but this is not
good hygiene where large numbers are using the same instrument, unless
the instrument be thoroughly cleaned before the inspiration is taken.
6. The Respiratory Pressure in Man. Measure the respiratory
pressure, the pressure of the air in the air- passages, by means of the mercury
manometer, or by a graduated Marey's tambour. Connect the piece of
280
RESPIRATION
gas tubing with the proximal limb of the mercury manometer and provide
it with a glass mouthpiece. Insert this mouthpiece well back into the
cavity of the mouth, closing the lips firmly about it, leaving the pharyngeal
muscles relaxed. Note the variations in pressure at the height of ordinary
inspiration and expiration, with the nasal passages open. Repeat with
forced inspiration and expiration, close the nasal passages, and make the
maximal expiratory and inspiratory effort. The manometer may be ad-
justed to write on the smoked paper, or one may read the variations directly
from the manometer schedule, in which case it facilitates the reading if one
clamps the rubber tube at the moment the reading is desired.
7. Demonstration of Carbon Dioxide in Expired Air. Arrange
two flasks, as in figure 244, filling each one-third full of baryta water, or
FIG. 244. — Apparatus for Demonstrating Excess of CO2 in Expired Air. Flasks filled with
lime-water.
lime-water. Close the lips around the mouthpiece of the apparatus and
inhale and exhale the air through it; close the nostrils if necessary. The
inspired air will come through a, the expired air out through b. The baryta
water in b will quietly become clouded with a white precipitate, while that
in a will remain clear or only very slightly clouded, showing the excess of
carbon dioxide in expired air.
8. Quantitative Determination of Carbon Dioxide and Oxygen in
Inspired Air and in Expired Air, by HempePs Method. Inspired
Air. Fill a gas buret, see figure 236, with water and close the pinch-
cock. Fill it with air taken outside the laboratory. Measure the vol-
ume of gas contained at the ordinary temperature and barometric pressure
of the laboratory. Connect with a potash pipet, drive the air over into the
bulb of the pipet, shake it up until all the carbon dioxide is absorbed. Draw
the air back into the buret and measure. The amount of carbon dioxide
in the external air is usually so small that it is difficult to measure by this
method. Now connect the buret with a pipet containing pyrogallic acid,
run the air over into the pyrogallic-acid bulb and shake up thoroughly until
no further excess is absorbed, then remeasure the excess in the buret. The
loss in volume is due to the absorption of oxygen; the air remaining in the
RESPIRATORY MOVEMENTS IN THE MAMMAL
287
huret is nitrogen. Compute the amount of carbon dioxide, oxygen, and
nitrogen from the results of your test.
Expired Air. Take a large sample of expired air by breathing through
a large tube into a gallon aspirator bottle. This is large enough to hold
six or eight expirations. Now fill the gas buret with a sample of this expired
air and analyze as before, first for carbon dioxide, then for oxygen; com-
pute the percentage of each gas, including nitrogen. The expired air will
usually be found to have lost from 4 to 5 per cent of oxygen and have gained
a little more than that quantity of carbon dioxide.
From the percentages obtained in these experiments, and the volume
of air breathed per unit of time, computed in experiment 4 above, determine
the amount of carbon dioxide exhaled per hour per kilogram of weight for
your own body. Compute also the amount of oxygen consumed.
9. The Rate and Character of ttie Respiratory Movements in the
Mammal, a, The rate of respiration can be best determined by
direct count per minute, an effort being made to keep the animal under as
FIG. 245. — Arrangement of Tracheal Cannula and Marey's Tambour for Recording the Changes
in Intratracheal Pressure during Respiration. (Langendorff.)
nearly normal conditions as possible; make the same determinations on a
cat, a dog, and guinea-pig, b, The character of the respiratory movements
can be recorded by one of the various forms of stethograph adapted to the
size of the animal, or by the arrangement shown in figure 245. It is usually
better to make the determination with the animal under the influence of an
anesthetic.
10. The Determination of Carbon Dioxide Given Off in the Mam-
mal. This determination can be made only by placing the animal
in a respiratory calorimeter, and making the following measurements:
a. The amount of air which passes through the animal chamber, the
calorimeter.
b. The percentage of carbon dioxide in the air which is in the chamber.
288 RESPIRATION
c. The percentage of carbon dioxide in the air which leaves the chamber.
If the animal is small enough, for example, the guinea-pig or a mouse,
the absorption tubes may be constructed of proper size to absorb all the
carbon dioxide passing through the chamber, and the total quantity of any
unit of time determined directly in grams. If now the animal is weighed
at the moment it is introduced into the cage, then the amount of carbon
dioxide per kilo weight can be quickly computed.
Calorimeters for larger animals require a larger volume of ventilation,
and the usual procedure is to measure the percentage in a sample as directed
above.
ii. The Nervous Mechanism of Respiratory Movement.
a. The Effect oj Stimulating Cutaneous Nerves. Use a small dog or a
cat for this experiment; anesthetize and introduce a tracheal tube with a
side branch adapted for measuring the variations of pressure during respira-
tion. Connect the free limb of the tracheal tube with an ether apparatus
and adjust to secure constant anesthesia. Connect the side branch of the
on
FIG. 246.— ^Change in Respiration on Stimulating the Central End of the Sciatic Nerve. The
rate is sharply increased and the amplitude more than doubled. The stimulation is between the
points marked on and off, time in seconds. The inspiratory movement following the stimulation
was greater than the limit of the recording tambour.
tracheal tube with a Marey's recording tambour of medium size and supply
with a comparatively delicate membrane. The amplitude of the move-
ments of the tambour may be regulated by a screw compress on a connecting
tube. Arrange an induction coil with platinum electrodes in the usual
manner, figure 318, for stimulating, by means of the interrupted current.
Record the results of the experiment along with the variations of blood pres-
sure on a continuous-paper kymograph; the instrument should be supplied
with a time signal, a stimulating signal, etc.
DEMONSTRATION OF APNEA, DYSPNEA, AND ASPHYXIA 289
Now stimulate the skin of the abdominal region, the groin, with a com-
paratively strong induction current, figure 246. Dissect out the sciatic
nerve, cut it, stimulate the central end with a mild to medium strength of
current. The stimulus should be graduated carefully, for there is often such
a great increase in respiratory rate and volume that the animal may become
overanesthetized.
b. The Effect oj Stimulating the Vagus Nerve. Isolate and stimulate
the vagus nerve with a medium strength of stimulus. The effect is usually
complete inhibition of respiratory movements. By means of graduated
stimuli one may demonstrate the accelerator effects from the stimulation
of the vagus. Stimulate also the superior laryngeal, and compare with the
effects of stimulating the whole vagus.
c. The Effect oj Cutting the Vagus Nerves. Isolate both vagus nerves
and section them as nearly at the same moment as possible. Be sure to
mark on the tracing the exact moment at which the nerves are cut. This
experiment should be performed with every accessory condition as constant
as possible, and the animal should not be disturbed for one or two minutes
so that the effects of the section will be recorded uncomplicated. The re-
sult is always a marked deepening and slowing of the respiratory movements.
d. The Effect oj Stimulating the Central End oj the Vagus. Upon stimu-
lating the central end of the vagus after section, the respiration rate will be
inhibited as in b, showing that the vagus nerves carry afferent respiratory
fibers, figure 239.
e. The Effect oj Stimulation oj the Phrenic Nerves. Isolate the right
phrenic nerve at its origin from the brachial plexus and stimulate it with a
medium strength of stimulus. Upon stimulating a nerve the diaphragm
will remain in contraction and the record will show that the thorax is in the
inspiratory phase.
Section this nerve and note the change in the character of respiratory
movements; make direct observations on the diaphragm, examining from
the abdominal side.
12. Demonstration of Apnea, Dyspnea, and Asphyxia. Produce
deep anesthesia, then disconnect the ether bottle and connect the tracheal
tube with a hand bellows. Produce deep and forced artificial respiration for
twenty to thirty seconds. Stop the artificial respiration ; the animal will re-
main quiet without any effort at breathing. This is the condition of apnea.
Allow the animal to recover its normal respiration rate and again produce
deep anesthesia. Now clamp off the tracheal tube so that the animal can no
longer receive air and leave it so until death. As the blood becomes more
and more venous there will first be a marked increase in the respiration rate
and depth. This is known as hyperpnea. This stage is followed by one
of increasing respiratory amplitude in which the accessory respiratory mus-
cles not previously active are brought into forcible contractions, both inspira-
19
290 RESPIRATION
tory and expiratory phases are now forced, dyspnea. The movements con-
tinue to increase, and the muscles of the neck, larynx, mouth, and nostrils
now take part. There is rather a sudden decrease in the respiratory move-
ments, an extension of the limbs, and gasping movements of the mouth, after
which the animal remains quiet, death being produced by asphyxia.
13. Respiratory Interchange, Calorimetry. The experiments are
conducted in such a manner that comparative analyses may be made between
the air inspired and that expired. Generally an animal is placed in a cham-
ber, called the respiratory chamber, which is then closed except for two
openings, one for the entrance of the inspired air, the other for the escape
of expired air. Some form of pump is used for renewing the air in the
chamber. . Both the inspired and expired air is made to pass through agents
which will absorb the contained carbon dioxide, such as baryta water or soda
lime, and in turn through agents which will absorb the watery vapor. When
the experiment is completed the differences between the two are determined.
The difference in oxygen has to be calculated, and is open to error.
The famous respiratory chamber of Pettenkofer is large enough to per-
form such experiments on man, and is of very elaborate construction.
But the most perfect apparatus assembled for this purpose is the respira-
tion calorimeter of Atwater constructed for man, and the respiration ap-
paratus of Armsby for cattle.
CHAPTER VII
SECRETION IN GENERAL
ALL tissues of the body produce certain chemical changes as a result of
their protoplasmic activity. But in certain cells chemical elaborations have
come to be the chief function, the cells have been differentiated in that direc-
tion, and the name secreting tissue or gland tissue is applied. The end result
of metabolism in gland tissue is the extrusion on the free borders of the cells
of the products of their metabolism. The products are known as secretions
and the process itself is the act of secretion. Certain secretions which are
in the nature of waste products to the body as a whole, such as urine in the
kidney, are often called excretions, but the use of the term should not be allowed
to confuse the general similarity of this to other secretions as regards the
physiological changes involved in its production.
Most secretions accomplish some definite office in the economy of the
body. Those that are discharged on some free mucous surface, as the saliva,
gastric juice, tears, etc., are called external, or true secretions, or merely secre-
tions. Substances that are discharged back into the blood stream later to
influence the metabolism of tissues other than the ones which produced them,
are called internal secretions.
Gland cells, like other tissues, draw their nourishment from the blood
and lymph. The product or secretion of gland cells may, in fact usually
does, contain some of the substances found in the blood, but there are also
present new materials elaborated by the cells, and even where the same sub-
stance exists both in the secretion and in the blood and lymph it can make
its appearance in the secretion only, under the control of the protoplasm of
the gland cells. The saliva secreted by the salivary cells, for example, con-
sists of about 98 to 99 per cent water containing in solution small quantities
of certain salts, also found in the lymph, and a small percentage of the en-
zyme, ptyalin. This enzyme is peculiar to the salivary secretion and is manu-
factured by the salivary-cell protoplasm. As is well known, it acts vigorously
in extreme dilution, hence the high per cent of water in the secretion. The
passage of water from a solution as concentrated as blood plasma to a solu-
tion as dilute as saliva requires a high amount of osmotic energy, an amount
that can be supplied only from the chemical energy liberated by the cell in
its protoplasmic activity. After the removal of the special organ by which
each secretion is manufactured, the secretion is no longer formed. Cases
291
SECRETION IN GENERAL
sometimes occur in which the secretion continues to be formed by the natural
organ, but, not being able to escape toward the exterior, on account of some
obstruction, is reabsorbed and accumulates in the blood. It may be dis-
charged from the body in other ways; but these are not instances of true
vicarious secretions, and must not be so regarded.
Organs and Tissues of Secretion. The principal secreting organs
are the following: i, The serous and synovia! membranes; 2, The mucous mem-
branes with their special glands, e.g., the buccal, gastric, and intestinal glands;
3, The salivary glands and pancreas; 4, The liver; 5, The mammary glands;
6, The lachrymal glands; 7, The kidney and skin; and 8, the testes and
ovaries.
The special structure and functions of the secreting organs will be given
in greater detail in the chapters which immediately follow. The general
types of structure and general conditions that influence the functions are
introduced at this point.
Structural Types of Secreting Organs. Serous and Synomal Type.
The serous membranes form closed sacs lining visceral cavities like the
abdominal, pericardial, or pleural cavities. The organs are, as it were, pushed
into this s:ic and carry before them an investment of membrane. The serous
membranes consist of a single layer of flattened polygonal cells resting on a
supporting membrane of connective tissue, supporting a ramification of blood-
vessels, lymphatics, and nerves.
In some instances, i.e., synovial membranes, the secreting layer is in-
creased by finger-like elevations. This type of secreting organ producer
ordinarily only enough secretion to keep the surface moist.
The Mucous Type. The mucous tracts, and different portions of e::ch
of them, present certain structural peculiarities, adapted to the functions
which each part has to discharge; yet in some essential characters the mucous
membrane is the same, from whatever part it is obtained. In all the princi-
pal and larger parts of the several tracts it presents an external layer of epithe-
lium, situated upon a basement membrane, and beneath this a stratum of
vascular tissue of variable thickness, containing lymphatic vessels and nerves.
The vascular stratum, together with the basement membrane and epithelium,
in certain cases is elevated into minute papillae and villi, in others depressed
into involutions in the form of glands. But in the invaginations of the secreting
membrane of gland cells, the supporting basement membrane and the network of
capillaries are still reta ined in their relative position. With increasing complexity
of involution the simple mucous membrane becomes packed away in an ap-
parently solid mass. The equivalent of a large amount of secreting surface
is thus condensed into a small space. In the process of invagination some
differentiation occurs in that certain of the gland tubes become conducting
and have their secretory activity somewhat reduced. But there is no distinc-
tion that can be drawn between simple mucous membranes and gland cells.
SECRETING GLANDS
293
Secreting Glands. The secreting glands present, amid manifold
diversities of form and composition, a general plan of structure; but all are
constructed with particular regard to the arrangement of the cells which has
just been described.
Secreting glands are classified according to certain structural types, as:
i. The simple tubular gland, A, figure 247, examples of which are furnished
by the follicles of Lieberkiihn, and the tubular peptic glands of the stomach.
FIG. 247. — -Plans of Extension of Secreting Membrane by Inversion or Recession in the Forms of
Cavities. A, Simple glands, viz., g, straight tube; h, sac; i, coiled tube. B, Multilocular crypts:
k, of tubular form; /, saccular. C, Racemose or saccular compound gland : m, entire gland, show-
ing branched duct and lobular structure; n, a lobule, detached with o, branch of duct proceeding
from it. D, Compound tubular gland. (Sharpey.)
They are simple tubes of mucous membrane, the walls of which are lined with
secreting cells arranged as an epithelium. To the same class may be referred
the elongated and tortuous sudoriferous glands.
2. The compound tubular glands, D, figure 247, form another division.
These consist of main gland tubes, which divide and subdivide. Each gland
may be made up of the subdivisions of one or more main tubes. The ulti-
294 SECRETION IN GENERAL
mate subdivisions of the tubes are sometimes highly convoluted. They are
formed of epithelium of various forms, supported by a basement membrane.
The larger tubes may have an outside coating of fibrous areolar or muscular
tissue. The salivary glands, pancreas. Brunner's glands, kidney, testes, with
the lachrymal and mammary glands, are examples of this type, but presf nt
more or less marked variations among themselves.
3. The racemose glands, in which a number of vesicles or acini are arranged
in groups of lobules, C, figure 247. The Meibomian follicles are examples
of this kind of gland. There seem to be glands of mixed character, com-
bining some of the characters of the tubular with others of the racemose ty pe ;
these are called tubulo-racemose or tubulo-acinous glands. The acini are
formed by a kind of fusion of the walls of several vesicles, which thus combine
to form one large cavity with recesses lined or filled with secreting cells. The
smallest branches of the gland-ducts sometimes open into the centers of these
cavities; sometimes the acini are clustered round the extremities, or by the sides
of the ducts; but, whatever secondary arrangement there may be, all have the
same essential character of rounded groups of vesicles containing gland-cells,
and opening by a common central cavity into minute ducts, which in the
large glands converge and unite to form larger and larger branches, and at
length one common trunk which opens on a free surface.
The Process of Secretion. The process of secretion is dependent
upon the activity of the secreting cells. In the case of the water and salts the
physical processes of filtration and diffusion may play a part.
The chemical processes constitute the process of secretion properly so called,
as distinguished from mere transudation spoken of above. In the process of
secretion, various materials which do not exist as such in the blood are manu-
factured by the agency of the gland-cells, using as a nutrient fluid the blood,
or, to speak more accurately, the lymph which fills the interstices of the gland
textures.
Evidences in favor of this view are: i. That gland cells are constituents
of ah1 glands, however diverse their outer forms and other characters, and
they are placed in all glands on the surfaces or in the cavity whence the secre-
tion is poured. 2. That certain materials of secretions are visible with the
microscope in the gland cells before they are discharged. Thus, granules
probably representing the precursors of the ferments of the pancreas may
be discerned in the cells of that gland. Granules of uric acid are found in
the cells of the kidneys of birds and fish, and fatty particles, like those of milk,
in the cells of the mammary gland.
Certain secreting cells, like the cells of the sebaceous glands, appear to
develop, grow, and attain their individual perfection by appropriating nutri-
ment from the fluid exuded by adjacent blood-vessels and building it up so
that it shall form part of their own substance. In this perfected state the cells
subsist for some brief time and then appear to dissolve, wholly or in part, and
CIRCUMSTANCES INFLUENCING SECRETION 295
yield their contents to the peculiar material of the secretion. The changes
which have been noticed from actual experiment in the cells of the salivary
glands, pancreas, and peptic glands will be described more fully in the chapter
on Digestion.
Discharge of secretions from the glands may either take place as soon as
formed, or the secretion may be long retained within the gland or its ducts.
The former is the case with the sweat glands. But the secretions of those
glands whose activity of function is periodical are usually retained in the cells
in an undeveloped form during the period of the gland's inaction.
When discharged into the ducts, the further course of secretions is affected:
(1) partly by the pressure from behind; the fresh quantities of secretion pro-
pelling those that were formed before. In the larger ducts, its propulsion is
(2) assisted by the contraction of their walls. All the larger ducts, such as
the ureter and common bile-duct, possess in their coats plain muscular fibers;
they contract when irritated, and sometimes manifest peristaltic movements.
Rhythmic contractions in the pancreatic and bile ducts have been observed,
and also in the ureters and vasa deferentia. It is probable that the contractile
power extends along the ducts to a considerable distance within the substance
of the glands whose secretions can be rapidly expelled. Saliva and milk, for
instance, are sometimes ejected with much force.
Circumstances Influencing Secretion. The principal conditions
which influence secretion are variations in the quantity of blood, and varia-
tions in nerve impulses passing to the gland cells over secretory nerve fibers.
An increase in the quantity of blood traversing a gland, as in nearly all
the instances before quoted, coincides generally with an augmentation of its
secretion. Thus the mucous membrane of the stomach becomes florid when,
on the introduction of food, its glands begin to secrete. The mammary gland
becomes much more vascular during lactation. All circumstances which give
rise to an increase in the quantity of material secreted by an organ produce,
coincidently, an increased supply of blood. But we shall see that a discharge
of saliva may occur under extraordinary circumstances without increase of
blood-supply, and so it may be inferred that this condition of increased blood-
supply is not absolutely essential to the immediate formation of secretion,
but that it favors the prolonged activity of glands.
Influence of the Nervous System on Secretion. The process of
secretion is largely regulated through the nervous system. The exact mode
in which the influence is exhibited must still be regarded as somewhat obscure.
In part, it exerts its influence by increasing or diminishing the quantity of
blood supplied to the secreting gland, in virtue of the power which it exercises
over the contractility of the smaller blood-vessels. It also has a more direct
influence, as is described at length in the case of the ^ubmaxillary gland, upon
the secreting cells themselves. This may be called trophic influence. Its
influence over secretion, as \veil as over other functions of the body, may be
296 SECRETION IN GENERAL
excited by causes acting directly upon the nervous centers, upon the nerves
going to the secreting organ, or upon the nerves of other parts. In the latter
case a reflex action is produced: thus the impression produced upon the sen-
sory nerves by the contact of food in the mouth leads to afferent nerve impulses
to the secretory center in the central nervous system which is reflected by the
nerves supplying the salivary glands, and produces, through these, a more
abundant secretion of the saliva.
Through the nerves, various conditions of the brain also influence the
secretions. Thus, the thought of food may be sufficient to excite an abundant
flow of saliva. And, probably, it is the mental state which excites the abun-
dant secretion of urine in hysterical paroxysms, as well as the perspirations,
and occasionally diarrhea, which ensue under the influence of terror, and the
tears excited by sorrow or excess of joy. The quality of a secretion may also
be affected by mental conditions, as in the cases in which, through grief or
passion, the secretion of milk is altered, and is sometimes so changed as to
produce irritation in the alimentary canal of the child.
CHAPTER VIII
FOOD AND DIGESTION
THE term digestion includes those changes taking place in the body which
bring the materials of the food into such condition that they may be taken up
by the blood and lymphatic vessels and thus rendered available for the metab-
olism of the tissues. In the process the foods are rendered more soluble
and more diffusible. Certain bodies which are already soluble and diffusible
are converted into forms which are more available for the tissues; as an ex-
ample cane-sugar, although both soluble and diffusible, cannot be readily
used by the body until it is converted from a disaccharide to a monosaccharide.
In fact few of the food materials are fit for immediate use when taken into
the body and are therefore practically useless until digested.
FOOD AND FOOD PRINCIPLES.
We have been accustomed to classify foods into certain main groups, chiefly
according to their chemical character, as follows :
Proteids. Such as albumin, myosin, gluten, casein, etc.; gluco-
proteid, nucleoproteid, etc.; gelatin, elastin, etc. These furnish nitrogen in
available form.
Carbohydrates. Such as starch, dextrose, cane-sugar, etc.
Fats. Such as olein.
Minerals. The various salines found in animal and vegetable food.
Water.
The classes of foods just enumerated usually exist in mixtures rather than
in simple forms, as, for example, a beef roast contains a representative of each
of the five classes enumerated, though it is composed chiefly of proteids and
fats. The human body is capable of using materials of a great variety of
forms, but most of these have the foods mixed in such a way as to give repre-
sentatives of each of the classes above in certain general proportions.
Nitrogenous Foods. The Flesh of Animals, e.g., beef, veal, mutton,
pork, bacon, ham, chicken, eggs, milk, etc., are typical nitrogenous foods.
Of these, beef and eggs are richest in nitrogenous matters, containing about
20 per cent. Mutton contains about i8 per cent, veal 16.5, and pork 10.
Beef is firmer, more satisfying, and is supposed to be more strengthening than
297
298
FOOD AND DIGESTION
mutton, whereas the latter is more digestible. The flesh of young animals, such
as lamb and veal, is less digestible and less nutritious. Pork contains a large
amount of fat and is, therefore, comparatively indigestible.
PERCENTAGE COMPOSITION AND FUEL VALUE PER POUND OF SOME COMMON FOOD STUFFS.
(AT WATER AND BRYANT.)
Water.
Per Cent.
Proteid.
Per Cent.
J
*£
si
&*
&&
Ash.
Per Cent.
Fuel
Value.
Per Cent.
Meat (Beef round)
73.6
22.6
2.8
I ?
CAO
52.0
16.6
30.1
I .O
I, ego
Fish (King salmon) .......
63.6
17.8
17.8
I i
i 080
73-7
J3-4
10.5
I.O
720
Milk (Cow's)
87.0
3-3
4.0
s.o
0.7
^2S
Milk (Human) ....
89.7
2 .O
7.1
6.0
O 2
Cheese (American)
31.6
28.8
7C.Q
o. 3
3-4
2 O^ ?
Butter
II. O
I.O
85.0
3-O
3,6o5
Bread (White)
33-2
IO.Q
I . -?
« 6
I O
I 2<C^
Bread (Corn)
38.Q
7.0
4-7
46. 3
2.2
I 2O?
Rice
12. 3
8.0
O.T.
70 -O
0.4
1,6^0
Oatmeal
7 3
16.1
7 -2
67 <
I 0
I 860
Beans (Dry) . . . ..........
12.6
22. ?
1.8
^0-6
3- ^
i,6o<
Potatoes (White)
78 3
2 2
O I
18 4.
I O
38^
Potatoes (Sweet)
60 o
I 8
0.7
27 4
I 2
^7o
Fruit (Strawberries)
QO.4
I -O
0.6
7-4
0.6
180
Watermelon (Edible portion)
O2.4
O-4
O.2
6.7
o. 3
140
Meat contains: (i) Nitrogenous bodies; chiefly myosin, and one or more
globulins, serum albumin, gelatin (from the interstitial fibrous connective
tissue), elastin (from the elastic tissue), as well as hemoglobin. (2) Fats,
including lecithin and cholesterin. (3) Extractives, some of which are agreeable
to the palate, and others weakly stimulating. Besides, there are sarcolactic
and inositic acids, taurin, xanthin, and others. (4) Salts, chiefly of potassium,
calcium, and magnesium. (5) Water, the amount of which varies from 15
per cent in dried bacon to 39 in pork, 51 to 53 in fat beef and mutton, and 72
per cent in lean beef and mutton. (6) A certain amount of carbohydrate
material is found in the meat of some animals, in the form of inosite, dextrin,
grape sugar, and glycogen.
TABLE OF PERCENTAGE COMPOSITION OF BEEF, MUTTON, PORK, AND VEAL. (LETHEBY.)
Water.
Bee] — Lean 72
" Fat 51
Mutton — Lean 72
Fat 53
Veal 63
Pork — Fat 39
Proteid. Fats. Salts.
14.8
18.3
12.4
16-5
9.8
3-6
29.8
4-9
3i-i
iS-8
48.9
5-1
4-4
4-8
3-5
4-7
2-3
NITROGENOUS FOOD 299
TABLE OF PERCENTAGE COMPOSITION or POULTRY AND FISH. (LETHEBY.)
Water. Proteid. Fats. Salts.
Poultry 74 21. 3.8 1.2
White Fish 78 18.1 2.9 i.
Salmon 77 16.1 5.5 1.4
Eels (very rich in fat) 75 9.9 13.8 1.3
Oysters 75.74 11.72 2.42 2.73
The flesh of nearly all animals has been occasionally eaten, and we may
presume that except for difference of flavor, etc., the average composition
is nearly the same in every case.
Milk. Milk is the entire food of young animals, and contains all the
elements of a typical diet. Albuminous substances are represented in the
form of caseinogen, and serum or lad albumin; fats in the cream; carbo-
hydrates in the form of lactose or milk-sugar; salts, chiefly as calcium phos-
phate; and water. From milk we obtain a number of food preparations such
as cheese rich in proteid and fat, butter and cream, buttermilk rich in proteids
and peculiarly well adapted for invalid diet, and whey which contains aH
the sugar salts- and the albumin.
TABLE OF COMPOSITION or MILK, BUTTERMILK, CREAM, AND CHEESE. (LETHEBY
AND PAYEN.)
Nitrogenous
Matters. Fats. Lactose. Salts. Water.
Milk(Cow) 4.1 3.9 5.2 86
Buttermilk 4.1 .7 6.4 .8 88
Cream 4.1 26.7 2.8 1.8 66
Cheese — Skim 44-8 6.3 4.9 44
Cheese — Cheddar 28.4 31-1 4-5 36
Eggs. The yolk and albumin of eggs of oviparous animals bear the
same relation as food for the embryos that milk bears to the young of mam-
malia, and afford another example of the natural admixture of the various
alimentary principles. The proteids of eggs are egg albumin and globulin,
of which the vitellin of the yolk is most important; nuclein in combination
with iron is also found. In addition to the three common fats there is a yellow
fatty pigment, lutein (lipochrome), lecithin, and cholesterin, a small quantity
of grape-sugar, and inorganic salts, chiefly potassium chloride and phosphates.
TABLE OF THE PERCENTAGE COMPOSITION OF FOWLS' EGGS.
Nitrogenous
Substances. Fats. Salts. Water.
White 20.4 1.6 78
Yolk 16. 30.7 1.3 52
Legumes are used by vegetarians as the principal source of the nitrogen of
the food. Those chiefly used are peas, beans, lentils, etc.; they contain a
nitrogenous substance called legumin, allied to albumin. Legumes contain
300 FOOD AND DIGESTION
about 25.30 per cent of this nitrogenous body, and twice as much nitrogen as
wheat. Nuts also form a very nutritious article of diet.
Carbohydrate Foods. Bread, made from the ground grain ob-
tained from various so-called cereals, viz., wheat, rye, maize, barley, rice,
oats, etc., is the direct form in which the carbo-hydrate is supplied in an
ordinary diet. It contains starch, dextrin, and a little sugar. It also contains
gluten, composed of vegetable proteids, and a small amount of fat.
TABLE OF PERCENTAGE COMPOSITION OF BREAD AND FLOUR.
Nitrogenous Carbo-
matters. hydrates. Fats. Salts. Water.
Bread 8.1 51. 1.6 2.3 37
Flour 10.8 70-85 2 1.7 15
Various articles besides bread are made from flour, e.g., spaghetti, maca-
roni, etc. Dextrin and a small amount of dextrose are present in bread,
particularly in the crust.
Vegetables, especially potatoes. They contain starch and sugar. In cab-
bage, turnips, etc., the salts of potassium are abundant.
Fruits contain sugar, and organic acids, tartaric, malic, citric, and others.
Sugar, chiefly saccharose, used pure or in various sweetmeats.
Oils and Fats. The substances supplying the oils and fats of the
food are chiefly butter, bacon and lard, suet (beef and mutton fat), and vegetable
oils. These contain the fats olein, stearin, and palmitin. Butter contains
others in addition, while vegetable oils, as a rule, contain no stearin.
Mineral or Inorganic Foods. The salts of the food. Nearly all
the substances in the preceding classes contain a greater or less amount of
the salts required in food. Green vegetables and fruit contain certain salts,
chiefly potassium. Sodium chloride is an essential food; it is contained in
nearly all solids, but so much is required that it has also to be taken as a
condiment. Potassium salts are found in muscle, nerve, and in meats gener-
ally, and in potatoes. Calcium salts are contained in eggs, blood of meat,
wheat, and vegetables. Iron is contained in hemoglobin, in milk, eggs, and
vegetables.
Liquid Foods. Water is essential to life, and from two to two and
a half pints a day must be consumed in addition to that taken mixed with
solid food. Of the non-alcoholic substances which may be added to it for
flavoring purposes, such as tea, coffee, cocoa, etc., the last can alone be con-
sidered to have a certain food value, as it contains fats, albuminous material,
and starch, the other constituents of such substances being a volatile oil, an
alkaloid caffeine, and tannic acid. The food value of alcoholic beverages,
which has long been a subject of controversy, as now generally agreed is but
slight. Beer, wines, and spirits contain ethyl alcohol, the amount varying
from 1.5 to 4.5 per cent in beer to 60 to 80 per cent in spirits.
THE PROCESS OF DIGESTION 301
The Effect of Cooking on Foods. In general terms cooking may
be said to render food more easily digestible/ both directly and indirectly,
through increased palatability. Subjecting food to high degrees of heat also
serves to kill parasites, such as trichinae and the various tapeworms, which
may be present and alive in raw meats. In the case of meats various methods
of cooking are employed. In roasting, the meat in bulk is subjected to a
high temperature in an oven for a short time, followed by a somewhat lower
temperature until the cooking is completed, which causes a coagulation of
the outer layers of albumin so that the juices of the meat are retained. In
boiling, the meat is first immersed in boiling water for a time and then the
cooking continues at a lower temperature. If a broth is to be made, the ex-
tractives may be obtained by heating the meat in water for a long period at
a temperature below the coagulation point of albumin. Such a broth con-
tains the flavoring and the stimulating extracts of the meat, but is of only
slight nutritive value. For small pieces of meat, broiling practically serves
the same purpose as does roasting for larger pieces. Frying, as usually em-
ployed, is the least serviceable method of preparation, since the fat or other
oily material used so permeates the food as to render it difficult of penetration
by the digestive juices.
Cooking produces upon vegetables the necessary effect of rendering them
softer, so that they can be more readily broken up in the mouth. It also
causes the starch grains to swell up and burst, and so aids the digestive fluids
in penetrating into their substance. The albuminous matters are coagulated,
and the gummy, saccharine, and saline matters are removed. The conversion
of flour into dough is effected by mixing it with water, and adding a little salt
and a. certain amount of yeast. Yeast consists of the cells of an organized
ferment (Torula cerevisia)', this plant in its growth changes by ferment action
the sugar produced from the starch of the flour, and a quantity of carbon
dioxide and alcohol is formed; the gas together with the action of heat
during baking causes the dough to rise, and the gluten being coagulated, the
bread sets as a perma nently vesiculated mass.
THE PROCESS OF DIGESTION.
The Enzymes. The digestive process involves both mechanical
and chemical changes. The former are secured by the crushing and grinding
in the mouth, together with the mixing and kneading that come from the
peristalses of the stomach and intestine. The chemical changes are the
most important factors of the digestive process. The various secretions that
are poured into the mouth, stomach, and intestines all contain substances
which react on the foods to render the latter more soluble. The special agency
in each secretion is the presence of representatives of the chemical groups
known as enzymes. These enzymes, or unorganized ferments, are the essen-
302 FOOD AND DIGESTION
tial factors in the secretions which produce the chemical changes in the
foods. Their predominant action is one of hydrolytic cleavage; that is,
the substance acted upon takes up water and then splits into two different
substances, usually of the same class. The chemical nature of the en-
zymes is as yet undetermined because of the difficulty of getting absolutely
pure specimens. Their mode of action is at present regarded in the nature
of catalysis. That is to say, the enzymes by their presence facilitate reactions
that would otherwise take place, but very slowly. Practically all are
secreted in the glands as zymogens, which bear the same relation to enzymes
as fibrinogen does to fibrin; they are transformed to enzymes by the proper
stimulus, but never exist as such in the glands.
Each enzyme has a special point of temperature at which it acts best, and
any change in the temperature retards its action; the action is suspended at
a definite point of low temperature, but the enzyme is not destroyed by cold.
The action is suspended at a somewhat higher temperature, and at a still
higher point the enzyme is destroyed. Some enzymes act only in an alka-
line medium, being destroyed in an acid medium, and vice versa. Others
act in either alkaline, or neutral, or acid media. Enzymes are hindered in
their action by the accumulation of the products of their activity. Most of
them cease acting altogether when these products reach a certain concentra-
tion, but will begin acting again on the removal of these products or if the
mixture be simply diluted.
The quantity of the enzyme determines the rapidity of the action, but not
the amount; a small quantity will digest as much as a large quantity, but will
take longer. The enzymes are not used up in the course of their activity,
as far as can be seen, and do not seem to undergo any change in their com-
position.
Enzymes are more or less specific in their action. That is, each enzyme
is supposed to produce its change in only one particular substance, as in
starch, maltose, proteid, fat, etc. An enzyme that can cause cleavage of the
starch molecule will not act on fat or proteid or even on other members of
the starch group. This specific action is doubtless expressive of a definite
relation between the structure of the enzyme and the substance acted on.
An interesting fact as to enzyme action is its reversibility — a phenomenon
now well known and well established for carbohydrates and fats. Kastle and
Lowenhart have shown that lipase, which acts to split neutral fats into
fatty acid and glycerin, will also produce a synthesis, at least of butyric
acid and alcohol into ethylbutyrate. Taylor and Robertson in independ-
ent papers have recently made the far-reaching discovery that the proteid
molecule can be synthesized by the agency (apparent reversible action) of
enzymes.
Enzymes are classified either according to the chemical nature of their
action or according to the class of substances on which they act; the former
DIGESTION IN THE MOUTH 303
classification is more logical, but the latter is more convenient and more gen-
erally used.
TABLE or DIGESTIVE ENZYMES.
Amylolytic.
Ptyalin of saliva, and amylopsin of pancreatic juice, change starch to maltose. Malt-
ase in the saliva, and pancreatic juice in the small intestine, change maltose to dextrose.
Lactase splits lactose to galactose and dextrose, and invertase splits cane-sugar to levulose
and dextrose in the small intestine.
Lipolytic.
Steapsin or lipase, found in the pancreatic juice, splits neutral fats into glycerin and
fatty acid.
Proteolytic.
Pepsin of the gastric secretion, and trypsin of the pancreatic secretion, change pro-
teids to proteoses and peptones, trypsin breaking the proteid down to simpler nitrog-
enous products. Erepsin of the intestine splits peptones to simpler products.
Coagulating.
Rennin of the gastric juice coagulates milk.
Activating.
Enterokinase of the intestinal juice converts trypsinogen to trypsin. (Thrombokin
of the blood is of this class.)
DIGESTION IN THE MOUTH.
The food is received into the mouth, and is subjected to the action of the
teeth and tongue, being at the same time mixed with the first of the digestive
juices, the satvva. It is then swallowed, and, passing through the pharynx
and esophagus into the stomach, is subjected to the action of the gastric
juice, the second digestive juice. Thence it passes into the small intestines,
where it meets with the bile, the pancreatic juice, and the intestinal juices, all
of which exercise a digestive influence upon the portion of the food not already
digested and absorbed. In the large intestine some further digestion and
absorption take place, and the residue of undigested matter leaves the body
in the form of feces.
Mastication. The act of mastication is performed by the biting and
grinding movement of the lower range of teeth against the upper. The
simultaneous movements of the tongue and cheeks assist by crushing the
softer portions of the food against the hard palate and gums, thus supplement-
ing the action of the teeth, and by returning the morsels of food to the action
of the teeth as they are squeezed out from between them until they have been
sufficiently chewed.
The simple up-and-down or biting movements of the lower jaw are per-
formed by the temporal, masseter, and internal pterygoid muscles, the~a<?tioff
of which in closing the jaws alternates with that of the digastric and other
muscles passing from the os hyoides to the lower jaw, which open the jaws.
The grinding or side movements of the lower jaw are performed mainly by
the external pterygoid muscles, the muscle of one side acting alternately with
304
FOOD AND DIGESTION
the other. When both external pterygoids act together, the lower jaw is pulled
directly forward, so that the lower incisor teeth are brought in front of the level
of the upper.
The act of mastication is voluntary. It will suffice here to state that the
afferent nerves chiefly concerned are the sensory branches of the fifth and
tenth or glosso-pharyngeal, and the efferent are the motor branches of the
fifth and the twelfth, or hypoglossal, cerebral nerves.
The act of mastication is much assisted by the saliva, which is secreted by
the salivary glands in largely increased amount during the process. The
intimate incorporation of the saliva with the food is termed insalivation.
The Salivary Glands. The glands which secrete the saliva in
the human subject are the salivary glands proper, the parotid, the submaccil-
lary, and the sublingual, and numerous smaller bodies of similar structure,
and with separate ducts, which are scattered thickly beneath the mucous
membrane of the lips, cheeks, soft palate, and root of the tongue.
FIG. 248.
FIG. 249.
FIG. 248. — Section of the Submaxillary Gland of a Dog, Resting Stage. Most of the Alveolar
cells are large and clear, being filled with the material for secretion (in this case, mucigen), which
obscures their protoplasm; some of the cells, however, are small and protoplasmic, forming the
crescents seen in most of the alveoli. (Ranvier.)
FIG. 249. — Section of a Similar Gland after a Period of Activity. The mucigen has been dis-
charged from the mucin- secreting cells, which consequently appear shrunken and less clear. Both
the cells and the alveoli are much smaller, and the protoplasm of the cells is more apparent. The
crescents of Gianuzzi are enlarged, c, Crescent cells; g, mucus-secreting cells; /, lumen of alveolus.
(Ranvier. )
Histological Structure. The salivary glands are compound tubular
or tubulo-racemose glands. They are made up of lobules. Each lobule con-
sists of the branchings of a division of the main duct of the gland, which
are generally more or less convoluted toward the extremities, that form the
alveoli, or proper secreting parts of the gland. The salivary secreting cells
are of cubical or columnar form and are arranged around a central canal.
The granular appearance frequently seen in the salivary cells is due to the
numerous zymogen granules which they contain.
During the rest period the cells are larger, highly granular, with obscured
NERVOUS MECHANISM OF THE SECRETION OF SALIVA 305
nuclei and smaller lumen. During activity the cells become smaller and
their contents more opaque.
When the mucous type of gland is secreting, or on stimulation of the nerve,
mucigen is converted into mucint the cells swell up, appear more transparent,
and stain deeply in logwood, figure 249. After stimulation, the cells become
smaller, more granular, and more easily stained, from having discharged their
contents, and the nuclei appear more distinct.
Nerves of large size are found in the salivary glands. They are principally
contained in the connective tissue of the alveoli, and certain glands, especially
in the dog, are provided with ganglia. Some nerves have special endings in
Pacinian corpuscles, some supply the blood-vessels, and others penetrate the
basement membrane of the alveoli and end upon, but not in, the salivary cells.
The blood-vessels form a dense capillary network around the ducts of the
alveoli, being carried in by the fibrous trabeculae between the alveoli, in which
also the lymphatics begin by lacunar spaces.
The Nervous Mechanism of the Secretion of Saliva. The secretion
of saliva is under the control of the nervous system. Under ordinary con-
ditions it is excited by the stimulation of the peripheral branches of two
nerves, the gustatory or lingual branch of the inferior maxillary division
of the fifth nerve, and of the glosso-pharyngeal, which are distributed to the
mucous membrane of the tongue and pharynx conjointly. The stimulation
occurs on the introduction of sapid substances into the mouth, and the
secretion is brought about in the following way: From the terminations of
the above-mentioned sensory nerves distributed in the mucous membrane
an impression is conveyed upward (afferent) to the special nerve center
situated in the medulla oblongata which controls the process, and by it is
reflected to certain nerves supplied to the salivary glands, which will be pres-
ently indicated. In other words, the center, when stimulated to action by
the sensory impressions carried to it, sends out impulses along efferent or
secretory nerves supplied to the salivary glands. These cause the saliva to
be secreted by and discharged from the gland cells. Other stimuli, however,
besides that of the food, and other sensory nerves than those mentioned,
may reflexly produce the same effects. For example, saliva may be caused
to flow by irritation of the mucous membrane of the mouth with mechanical,
chemical, electrical, or thermal stimuli, also by the irritation of the mucous
membrane of the stomach in some way, as in nausea which precedes vomiting,
when some of the peripheral fibers of the vagi are irritated. Stimulation of
the olfactory nerves by smell of food, of the optic nerves by the sight of it, and
of the auditory nerves by the sounds which are known by experience to ac-
company the preparation of a meal may also stimulate the nerve center to
action. In addition to these, as a secretion of saliva follows the movement
of the muscles of mastication, it may be assumed that this movement stimu-
lates the secreting nerve fibers of the gland, direct or reflexly. From the fact
20
306 FOOD AND DIGESTION
that the flow of saliva may be increased or diminished by mental states, it
is evident that impressions from the cerebrum also are capable of stimulating
the center to action or of inhibiting its action.
Influence of Nerves on the Submaxillary Gland. The sub maxillary
gland has been the gland chiefly employed for the purpose of experimentally
demonstrating the influence of the nervous system upon the secretion of saliva,
because of the comparative facility with which the gland, with its blood-
vessels and nerves, can be exposed to view in the dog, rabbit, and other
animals.
The chief nerves supplied to the gland are: (i) the chorda tympani, a
branch given off from the facial in the canal through which it passes in the
temporal bone; and (2) branches of the sympathetic nerve from the plexus
around the facial artery and its branches to the gland. The chorda, figure
250, ch. t, passes downward and forward, under cover of the external ptery-
goid muscle, and joins the lingual or gustatory nerve, proceeds with it for a
short distance, and then passes along the submaxillary- gland duct, sm. d,
giving branches to the submaxillary ganglion, sm. gl, and sending others to
terminate in the superficial muscles of the tongue. It consists of fine medul-
lated fibers which lose their medulla in the gland. If this nerve be exposed
and divided anywhere in its course from its exit from the skull to the gland no
immediate result will follow, nor will stimulation either of the lingual or of
the glosso-pharyngeal produce a flow of saliva. But if the peripheral end
of the divided nerve be stimulated, an abundant secretion of saliva ensues,
and the blood supply is enormously increased by dilatation of the arteries. The
veins may even pulsate, and the blood contained within them is more arterial
than venous in character.
When, on the other hand, the stimulus is applied to the sympathetic fila-
ments (mere division producing no apparent effect), the arteries contract,
and the blood stream is in consequence much diminished; and only a sluggish
stream of dark blood escapes from the veins. The saliva, instead of being
abundant and watery, becomes scanty and tenacious. If both chorda tym-
pani and sympathetic branches be divided, the gland, released from nervous
control, may secrete continuously and abundantly (paralytic secretion).
The abundant secretion of saliva which follows stimulation of the chorda
tympani is not merely the result of a filtration of fluid from the blood-vessels,
in consequence of the largely increased circulation through them. This is
proved by the fact that, when the main duct is obstructed, the pressure within
may considerably exceed the blood pressure in the arteries, and also that when
into the veins of the animal experimented upon some atropine has been previ-
ously injected, stimulation of the peripheral end of the divided chorda pro-
duces all the vascular effects as before, without any secretion of saliva accom-
panying them. Again, if an animal's head be cut off, and the chorda be
rapidly exposed and stimulated with an interrupted current, a secretion of
INFLUENCE OF NERVES ON THE SITBMAXILLARY GLAND 307
saliva ensues for a short time, although the blood supply is necessarily absent.
These experiments serve to prove that the chorda contains two sets of nerve
fibers, one set, vaso-dilator, which, when stimulated, act upon a local vaso-
motor center for regulating the blood supply, inhibiting its action, and causing
the vessels to dilate, and so producing an increased supply of blood to the
gland; while another set, which are paralyzed by injection of atropine, directly
stimulate the cells themselves to activity, whereby the cells secrete and dis-
charge the constituents of the saliva which they produce, the secretory nerves.
These latter fibers very possibly terminate on the salivary cells themselves.
If, on the other hand, the sympathetic fibers be divided, stimulation of the
FIG. 250. — Diagrammatic Representation of the Submaxillary Gland of the Dog with its Nerves
and Blood-vessels. (This is not intended to illustrate the exaet anatomical relations of the several
structures.) sm. gld.. The submaxillary gland into the duct (sm. d.) of which a cannula has been
tied. The sublingual gland and duct are not shown, n. I., n. I'., The lingual or gustatory nerve;
ch. t., ch. t'., the chorda tympani proceeding from the facial nerve, becoming conjoined with the
lingual at n. I'., and afterward diverging and passing to the gland along the duct; sm. gl., submax-
illary ganglion with its roots; n. L, the lingual nerve proceeding to the tongue; a. car., the carotid ar-
tery, two branches of which, a. sm. a. and r. sm.p., pass to tljie anterior and posterior parts of the gland;
v. sm., the anterior and posterior veins from the gland ending in v. /., the jugular vein; v. sym., the
conjoined vagus and sympathetic trunks; gl. cer. s., the superior-cervical ganglion, two branches of
which forming a plexus, a. /., over the facial artery, are distributed, n. sym. sm., along the two glan-
dular arteries to the anterior and posterior portion of the gland. The arrows indicate the direction
taken by the nervous impulses; during reflex stimulations of the gland they ascend to the brain
by the lingual and descend by the chorda tympani. (M. Foster.)
tongue by sapid substances, or electrical stimulation of the trunk of the lin-
gual or of the glosso-pharyngeal, continues to produce a flow of saliva. From
these experiments it is evident that the chorda-tympani nerve is the principal
nerve through which efferent impulses proceed from the center to excite the
secretion of this gland.
The sympathetic nerve also contains two sets of fibers, vaso-constrictor
and secretory. But the flow of saliva, upon stimulating the sympathetic, is
scanty, and the saliva itself viscid. At the same time the vessels of the gland
808
FOOD AND DIGESTION
are constricted. The secretory fibers may be paralyzed by the administration
of atropine.
Nerves of the Parotid Gland. The nerves which influence secre-
tion in the parotid gland are branches of the facial (lesser superficial petrosal)
and of the sympathetic. The former nerve, after passing through the otic
ganglion, joins the auriculo-temporal branch of the fifth cerebral nerve, and,
with it, is distributed to the gland. The nerves by which the stimulus ordi-
narily exciting secretion is conveyed to the medulla oblongata, are, as in the
case of the submaxillary gland, the fifth and the glosso-pharyngeal. The
pneumogastric nerves convey a further stimulus to the secretion of saliva when
food has entered the stomach; the nerve center is the same as in the case of
the submaxillary gland.
Changes in the Gland Cells. The method by which the salivary
cells produce the secretion of saliva appears to be divided into two stages,
which differ somewhat according to the class to which the gland belongs, viz.,
whether to (i) the true salivary, or to (2) the mucous type. In the former
case, it has been noticed, as already described, that during the rest which
follows an active secretion the lumen of the alveolus becomes smaller, the
gland cells larger and very granular. During secretion the alveoli and their
cells become smaller, and the granular appearance in the latter to a consider-
able extent disappears, and at the end of secretion the granules are confined
to the inner part of the cell nearest to the lumen, which is now quite distinct,
figure 25 1.
It is supposed from these appearances that the first stage in the act of
secretion consists in the protoplasm of the salivary cell taking up from the
lymph certain materials from which it manufactures the elements of its own
FIG. 251. — Alveoli of True Salivary Gland. A, At rest; B, in the first stage of secretion; C,
after prolonged secretion. (Langley.)
secretion, and which are stored up in the form of granules in the cell during
rest; the second stage consists of the actual discharge of these granules, with
or without previous change. The granules are zymogen granules, and repre-
sent the chief substance of the salivary secretion, ptyalin. In the case of the
submaxillary gland of the dog, at any rate, the sympathetic nerve fibers appear
to have to do with the first stage of the process,, and when stimulated the proto-
SALIVA 309
plasm is extremely active in manufacturing the granules, whereas the chorda
tympani is concerned in the production of the second act, the actual discharge
from the cells of the materials of secretion, together with a considerable
amount of fluid, the latter being an actual secretion by the protoplasm, as
it ceases to occur when atropine has been subcutaneously injected.
In the mucus-secreting gland, the changes in the cells during secretion
have been already spoken of. They consist in the gradual production by the
protoplasm of the cell of a substance called mucigen, which is converted into
mucin, and discharged on secretion into the canal of the alveoli. The mucigen
is, for the most part, collected into the inner part of the cells during rest,
pressing the nucleus and the small portion of the protoplasm which remains,
against the limiting membrane of the alveoli.
The process of secretion in the salivary glands is identical with that of
glands in general. The cells which line the ultimate branches of the ducts
are the agents by which the special constituents of the saliva are formed. The
material which they have incorporated within themselves, which is doubtless
a product of the metabolism of the protoplasm of the cells, is given up again
almost at once in the form of a fluid, secretion, which escapes from the ducts
of the gland. The cells themselves undergo diminution in the mass of their
protoplasm, which is again renewed in the intervals of the active exercise .of
the functions. The source whence the cells obtain the materials for the con-
struction of secretion is the blood-plasma, which is filtered off from the circu-
lating blood into the interstices of the glands, as in all living tissues.
Saliva. Saliva, as it commonly flows from the mouth, is the mixed
secretion of the salivary glands proper and of the glands of the buccal mucous
membrane and tongue. When obtained from parotid ducts, and free from
mucus, saliva is a transparent watery fluid, the specific gravity of which varies
from 1004 to 1008, and in which, when examined with the microscope, are
found floating a number of minute particles, derived from the secreting ducts
and vesicles of the glands. In the impure or mixed saliva are found,' besides
these particles, numerous epithelial scales separated from the surface of the
mucous membrane of the mouth and tongue, and the so-called salivary cor-
puscles, discharged probably from the mucous glands of the mouth and the
tonsils, which subside when the saliva is collected in a deep vessel and left at
rest. They form a white opaque sediment leaving the supernatant fluid trans-
parent and colorless, or with a pale bluish-gray tint. Saliva also contains
various kinds of micro-organisms (bacteria). The saliva, when first secreted,
appears to be always alkaline in reaction; the alkalinity is about equal to .08
per cent of sodium carbonate, and is due to the presence of disodium
phosphate, Na2HPO4.
The mucin is the largest representative of the organic nitrogenous class
of bodies in the saliva. It may be thrown down by addition of acetic acid.
It gives the three chief proteid reactions, and may easily be split up by the
310 FOOD AND DIGESTION
action of a dilute mineral acid into globulin and a carbohydrate whose exact
character has not yet been established, though it resembles a sugar in reducing
copper-sulphate solutions. The presence of potassium sulphocyanide, KCNS,
in saliva may be shown by the blood-red coloration which the fluid gives
with a solution of ferric chloride, Fe2Cl6, and which is bleached on the addition
of a solution of mercuric chloride, HgQ2, but not by hydrochloric acid.
CHEMICAL COMPOSITION OF HUMAN SALIVA. (HAMMERS ACHER.)
In i.ooo Parts.
Water 994-2
Solids 5-8
Mucus and epithelium 2.2
Soluble organic matter (ptyalin) 1.4
Potassium sulphocyanide 0.04
Salts 2.20
Saliva from the parotid is less viscid; less alkaline, the first few drops
discharged in secretion being even acid in reaction; clearer, although it may
become cloudy on standing from the precipitation of calcium carbonate by the
escape of carbon dioxide; and more watery than that from the submaxillary.
It has moreover a less powerful action on starch. Sublingual saliva is the
most viscid, and contains more solids than either of the other two, but has
little diastasic action.
Rate of Secretion and Quantity of Saliva. The rate at which saliva
is secreted is subject to considerable variation. When the tongue and muscles
concerned in mastication are at rest, and the nerves of the mouth are subject
to no unusual stimulus, the quantity secreted is not more than sufficient with
the mucus to keep the mouth moist. During actual secretion the flow is much
accelerated.
The quantity secreted in twenty-four hours varies greatly, but is at least
i liter.
Function of Saliva. The purposes served by saliva are mechanical
and chemical.
Mechanical, (i) It keeps the mouth in a due condition of moisture,
facilitating the movements of the tongue in speaking, and the mastication
of food. (2) It serves also in dissolving sapid substances, and renders them
capable of exciting the nerves of taste. (3) But the principal mechanical
purpose of the saliva is that, by mixing with the food during mastication, it
makes a soft pulpy mass such as may be easily swallowed. To this purpose
the saliva is adapted both by quantity and quality. For, speaking generally,
the quantity secreted during feeding is in direct proportion to the dryness
and hardness of the food.
Chemical. The chemical action which the saliva exerts upon the food in
the mouth is to convert the starchy materials which it contains into soluble
starch and then into sugar. This power the saliva owes to the enzyme ptyalin.
FUNCTION OF SALIVA 311
Certain investigators have of late asserted that saliva contains another enzyme,
known as maltase, which has the power of splitting the disaccharides into
monosaccharides, or maltose into dextrose. The action of this ferment is
certainly very limited. The conversion of the starch under the influence of the
ferment into sugar takes place in several stages, and in order to understand
it a knowledge of the structure and composition of starch granules is neces-
sary. A starch granule consists of two parts: an envelope of cellulose, which
does not give a blue color with iodine except on addition of sulphuric acid,
and of granulose, which is contained within, and which gives a blue color
with iodine alone. Briicke states that a third body is contained in the granule,
which gives a red color with iodine, viz., erythro-granulose. On boiling, the
granulose swells up, bursts the envelope, and the whole granule is more or
less completely converted into a paste or gruel, which is called gelatinous
starch.
When ptyalin acts upon boiled starch, it first changes the latter, by hydro-
lysis, into soluble starch, or amidulin; this is more limpid and more like a true
solution, though it still gives the blue coloration on the addition of iodine.
This stage is very brief, only thirty seconds being sometimes required in labora-
tory experiments to render a stiff starch paste completely fluid when a few
drops of saliva are added at body temperature. This rapidity of action is of
great importance, as under proper conditiqns of mastication practically all
the boiled starch of the food ought to enter the stomach as soluble starch.
When the starch has not been previously boiled, the envelope of cellulose
retards the action of the ptyalin to a very marked degree.
Starch.
I
Soluble starch.
Erythro-dextrin. Maltose and iso-maltose.
I
Achroo-dextrins. Maltose and iso-maltose.
The further stages of hydrolytic cleavage result in the formation of a
variable mixture of maltose and iso-maltose with a series of dextrins, but ap-
parently never result (in laboratory experiments) in the complete conversion
of the dextrins into sugars. Gradually, as the starch is converted, the blue
coloration with iodine is replaced by a purplish-red and finally by a red
color: the latter color is produced by erythro-dextrin (so-called from the
color). In the later stages no coloration is obtained with iodine, and for this
reason the dextrins formed are known as achroo-dextrins; there are probably
several of these, but they have not yet been sufficiently isolated. As sugar
appears very early in the process, even at the stage of erythro-dextrin, and
312 FOOD AND DIGESTION
gradually increases in amount, it is generally concluded that maltose is
formed early in the decomposition of the starch molecule. The process is
usually represented schematically as above.
The sugars formed are maltose (C^H^O^) and a closely allied sugar
known as iso-maltose. A small percentage of dextrose has been found by
some observers, and this is due to the action of maltose. Maltose is allied
to saccharose or cane-sugar more nearly than to glucose; it is crystalline; its
solution has the property of polarizing light to the right to a greater degree
than solutions of glucdse (3 to i); it is not so sweet, and reduces copper sul-
phate less easily. It can be converted into glucose by boiling with dilute
acids and by the action of the enzyme maltase present in saliva.
According to Brown and Heron the reactions may be represented thus:
One molecule of gelatinous starch is converted by the action of an amylolytic ferment into
n molecules of soluble starch.
One molecule of soluble starch = io(Ci2H2oOio) + 8 (HaO), which is further converted
by the ferment into
i. Ery thro -dextrin, 9(Ci2H2oOio) (giving red with iodine) -f- Mal-
tose (CiaHaaOn).
then into 2. Erythro-dextrin 8 (CiaHaoOio) (giving yellow with iodine) -\- Mal-
tose 2 (Ci2H22Ou).
next into 3. Achroo -dextrin 7 (Ci2H20Oio) + Maltose 3 (Ci2H22On).
And so on; the resultant being:
Soluble starch 10 (Ci2H20Oio) + Water 8 (HaO) = Maltose 8 (CiaHaaOn) +
Achroo -dextrin 2 (Ci2H2oOio).
Many observers, however, believe that the maltose simultaneously present
with erythro-dextrin is not actually split off from the starch molecule in the
formation of erythro-dextrin, but that it is the product of more advanced hydrol-
ysis in other starch molecules. They point out that in such a chemical re-
action of considerable time duration, it is improbable that all the starch mole-
cules are attacked at the same rate or are, at any given moment, equally
advanced in cleavage. Their theory is that there is a series of more and more
simple dextrins formed giving rise finally to the disaccharides.
The presence of sugar in such an experiment is at once discovered by the
application of Trommer's test, which consists in the addition of a drop or
two of a solution of copper sulphate, followed by a larger quantity of caustic
potash. When the liquid is boiled, an orange-red precipitate of copper sub-
dxide indicates the presence of sugar.
Influences which Affect the Action of Saliva on Starch. Moderate
heat, about 37.8° to 40° C, is most favorable to the rapid cleavage of starch
by the ptyalin. Cold retards and o° C. suspends the action but does not de-
stroy the ferment. A temperature of 60° C. destroys the ptyalin.
Removal of the products of salivary digestion as they are formed facilitates
the action of the enzyme, as an excess of these products is detrimental to further
action.
The reaction between starch and saliva takes place best in a neutral or
SALIVARY DIGESTION IN THE STOMACH 313
very faintly alkaline medium and is inhibited by strong alkalies and especially
by acids even as weak as the acidity of the gastric juice. This last is of
particular importance since it raises the question as to how long the ptyalin
may act.
The action of saliva on starch is not limited to the brief interval during
which food remains in the mouth, as is now well known, but may continue
for a time in the stomach.
Ptyalin is strictly an amylolytic ferment.
Starch appears to be the only principle of food upon which the saliva acts
chemically. The secretion has no apparent influence on gum, cellulose, or
on fat, and is equally destitute of power over albuminous and gelatinous sub-
stances.
The salivary glands of children do not become functionally active till the
age of 4 to 6 months, and hence the bad effects of feeding them before this
age on starchy food, corn-flour, etc., which they are unable to render soluble
and capable of absorption.
Salivary Digestion in the Stomach. Laboratory experiments
have demonstrated that while the addition of even 0.05 per cent of hydrochloric
acid will inhibit the action of ptyalin on a solution of starch, if any proteids
be present in the solution much more acid must be added before the action
of the ptyalin is stopped. The explanation of the latter fact is that the acid
unites with the proteids in some chemical combination forming "combined
acid," which has little effect, comparatively, on ptyalin. This "combined
acid" gives a red color with litmus, but is distinguished from free acid by
giving a brownish instead of a bluish color with Congo red. When food enters
an empty stomach, as happens at the beginning of a meal the acid first com-
bines with the proteid food stuffs and so does not at once affect the ptyalin.
A still more important fact in its bearing on this subject was recently
discovered by Cannon, who showed experimentally that starchy foods mixed
with weak alkali remain alkaline in the stomach for as much as an hour and
a half. Such foods when swallowed into the stomach are packed away in
that organ in a mass. The secretion of the acid gastric juice comes in contact
only with the outer surface of the mass, which is not materially disturbed by
the stomach peristalses. The center of the mass may, therefore, remain alka-
line until the outer layers are completely eroded away, and the ptyalin may
continue to act on starch during the whole time.
DEGLUTITION.
When properly masticated, the food is transmitted in successive portions
to the stomach by the act of deglutition or swallowing. The following account
of deglutition is based upon the researches of Kronecker and Meltzer, whose
experiments seem to modify in some details the earlier theory of Magendie:
314
FOOD AND DIGESTION
The mouth is closed, and the food after thorough mixing with the saliva
is rolled into a bolus on the dorsum of the tongue. The tip of the tongue is
pressed upward and forward against the hard palate, thus shutting off the
anterior part of the mouth cavity. The mylo-hyoid muscles then suddenly
contract, the bolus of food is put under great pressure and shot backward and
downward through the pharynx and into the esophagus and, if the food be
fluid enough, even to the cardiac orifice of the stomach. Coincidently with
FIG. 252. — Transverse Section of the Human Esophagus, a, Fibrous covering; b, longi-
tudinal muscular fibers; c, transverse muscular fibers; d, areolar or submucous coat; e, muscularis
mucosae; /, mucous membrane, with part of a lymphoid nodule; g, stratified epithelial lining; h,
mucous gland; «, gland duct; m', striated muscle fibers. (V. Horsley.)
the contraction of the mylo-hyoid muscles, the hyoglossi are thrown into
action, drawing the tongue backward and downward, not only increasing
the pressure upon the food, but forcing the epiglottis over the glottis, closing
the larynx.
It has been shown by the Roentgen-ray method that the character of the
food determines somewhat its passage through the esophagus. The dry
and semisolid foods are seized by the musculation of the esophagus and passed
down that organ by a peristaltic wave. The longitudinal muscles contract,
tending to enlarge the diameter of the esophagus in advance of the food, while
contractions of the circular muscles produce pressure on the bolus just
behind, thus forcing it along to the cardia. This wave reaching the
cardiac orifice about six seconds after the commencement of the act of
NERVOUS MECHANISM OF DEGLUTITION 315
deglutition, forces the food into the stomach, the sphincter having previously
relaxed. The interval of time between the commencement of the act of degluti-
tion and the arrival of the more fluid food at the cardiac orifice of the stomach
may not be more than one-tenth second, though it remains at the cardiac
orifice without entering the stomach until the first parts of the act of swal-
lowing is reinforced by the subsequent contraction of the constrictors of the
pharynx and the passage of a peristaltic wave down the esophagus. In
some cases, however, the liquid food is not stopped at the cardiac orifice,
but is sent through the relaxed sphincter by the original force of the
mylo-hyoid contraction.
In man the esophagus was said to contract in three separate segments,
the first segment lying in the neck and being about six centimeters long, the
second being the next ten centimeters of the tube, and the third the remaining
portion to the stomach. But the later Roentgen-ray observations show no
break in the continuous passage of the food, though the movement of the food
is slower in the lower segment of the esophagus.
The act of swallowing consists, then, of the contraction in sequence of
the mylo-hyoids, the constrictors of the pharynx, and the esophagus. The
computed time of contraction is as follows:
Seconds.
Contraction of mylo-hyoids and constrictors of the pharynx 0.3
Contraction of the first part of the esophagus 0.9
Contraction of the second part of the esophagus 1.8.
Contraction of the third part of the esophagus * 3.0
6.0
If a second attempt at swallowing be made before the first has been com-
pleted (that is, before six seconds have elapsed), the remaining portion of the
first act is inhibited, and the contraction wave reaches the stomach six sec-
onds after the commencement of the second act.
During the act of deglutition the posterior nares are closed through the
action of the levator palati and tensor palati muscles, which raise the velum;
the palato-pharyngei, drawing the posterior pillars of the fauces together;
and the azygos uvulae, which raises the uvula — thus forming a complete curtain.
Otherwise the food would pass into the nose, as happens in the case of cleft
palate. At the same time the larynx is closed by the adductor muscles of the
vocal cords and the descent of the epiglottis, the larynx being drawn upward
as a whole through the action of the mylo-hyoid, genio-hyoid, thyro-hyoid,
and digastric muscles. The presence of the epiglottis is not necessary for the
completion of the act of deglitition.
Nervous Mechanism of Deglutition. The sensory nerves engaged
in the reflex act of deglutition are branches of the fifth cerebral supplying the
soft palate; glosso-pharyngeal, supplying the tongue and pharynx; the superior
laryngeal branch of the vagus, supplying the epiglottis and the glottis. The
316 FOOD AND DIGESTION
motor fibers concerned are branches of the fifth, supplying part of the digastric
and mylo-hyoid muscles and the muscles of mastication; the facial, supplying
the levator palati; the glosso-pharyngeal, supplying the muscles of the
pharynx; the vagus, supplying the muscles of the larynx through the in-
ferior laryngeal branch; and the hypoglossal, the muscles of the tongue. The
nerve center by which the muscles are harmonized in their action is situated
in the medulla oblongata. It cannot be definitely circumscribed, but is in
the general level of the vagus origin. The movements of the esophagus are
coordinated by the complex of sensory and motor fibers of the fifth and the
ninth to twelfth cranial nerves, which all take some part in this complicated
reflex.
DIGESTION IN THE STOMACH.
The stomach in man and those mammalia which are provided with a
single stomach consists of a dilatation of the alimentary canal placed between
and continuous with the esophagus, which enters its larger or cardiac end on
the one hand, and the small intestine, which commences at its narrowed end
or pylorus, on the other. It varies in shape and size according to its state of
distention. It is supplied with nerves from the vagus and from the sympa-
thetic and receives a special artery, the gastric artery.
Structure of the Stomach. The stomach is composed of four
coats, called respectively, the external or peritoneal, the muscular, the sub-
mucous, and the mucous coat. Blood-vessels, lymphatics, and nerves are
distributed in and between them.
The muscular coat consists of three separate layers of fibers which, accord-
ing to their several directions, are named the longitudinal, circular, and
oblique. The longitudinal set are the most superficial and are continuous
with the longitudinal fibers of the esophagus and spread out in a diverging
manner over the cardiac end and sides of the stomach to the pylorus. The
circular or transverse coat more or less completely encircles all parts of the
stomach; this coat is thickest at the middle and in the pyloric portion of the
organ, and forms the chief part of the thick ring of the pylorus. The next
and consequently deepest coat, the oblique, is continuous with the circular
muscular fibers of the esophagus at the cardiac orifice of the stomach. This
coat is quite interrupted and more or less incomplete. The muscular fibers
of the stomach and intestinal canal are unstriated.
The mucous membrane of the stomach, which rests upon a layer of loose
cellular membrane, or submucous tissue, is smooth, soft, and velvety. It is
of a pale pink color during life, and in the contracted state is thrown into
numerous longitudinal folds or rugae, which disappear when the organ is
distended. It is composed of a mass of short tubular secreting glands.
The Gastric Glands. The glands of the mucous membrane of the
stomach are of two varieties, Cardiac and Pyloric.
THE GASTRIC GLANDS
317
Cardiac glands arc found throughout the whole of the cardiac end of the
stomach. They are arranged in groups of four or five, which are separated
by a fine connective tissue. Two or three tubes often open into one duct,
-f
FIG. 253. — The Human Stomach and the Vagus Distribution. R. L., Recurrent laryngeal;
Cos, inferior cervical cardiac branch; Ca^, Ca/\, cardiac branches of vagus; A. P. PI., P. P. PL,
anterior and posterior pulmonary plexuses; Oes. PI., esophageal plexus; Cast. R. and L., gastric
branches of vagus, right and left; Coe. PL, coeliac plexus; Hep. PL, hepatic plexus.
figure 254, which forms about a third of the whole length of the tube and
opens on the surface. The ducts and the free surface are lined with columnar
318
FOOD AND DIGESTION
epithelium. The body of the gland is composed of granular secreting cells
called chief cells or peptic cells. Between these cells and the membrana pro-
pria of the tubes are large oval or spherical cells, granular in appearance with
clear oval nuclei; these cells are call oxyntic or parietal cells. They do not
form a continuous layer, figure 254. Intercellular tubules extending from
the duct of the gland between the chief cells and connecting with intracellular
secretory tubules in the parietal cells
have been shown by the Golgi method,
figure 256.
As the pylorus is approached the
gland ducts become longer and the
tube proper becomes shorter, and oc-
casionally branched at the fundus.
The Pyloric Glands. These glands
have much longer ducts and larger
mouths than the peptic glands.
FIG. 254.
FIG. 255.
FIG. 254. — From a Vertical Section through the Mucous Membrane of the Cardiac End of
Stomach. Two peptic glands are shown with a duct common to both, one gland only in part, a,
Duct with columnar epithelium becoming shorter as the cells are traced downward; «, neck of
gland tubes, with central and parietal or so-called peptic cells; h, fundus with curved cecal extrem-
ity— the parietal cells are not so numerous here. X 400. (Klein and Noble Smith.)
FIG. 255. — Cross- sections at Various Levels of Peptic Glands of Stomach. X 400. M,
Section through gastric pit near surface; M'. section through gastric pit near bottom; h, mouth
of gland; k, neck; g, body near fundus; the chief cells are shaded lightly; b, parietal cells.
(Kolliker.)
The parietal cells are absent in the pyloric glands. The pyloric glands be-
come larger as they approach the duodenum, also more convoluted and more
THE GASTRIC GLANDS
819
deeply situated. They are directly continuous with Brunner's glands in the
duodenum (Watney).
Blood-vessels and Lymphatics. The blood-vessels of the stomach first
break up in the submucous tissue and send branches upward between the
closely packed glandular tubes, which anastomose around them by a fine
capillary network with oblong meshes. Contiguous with this deeper plexus,
or prolonged upward from it, so to speak, is a more superficial network of
larger capillaries, which branch densely around the orifices of the tubes and
FIG. 256.
FIG. 257.
FIG. 256. — Longitudinal Section of Fundus of Gland from Dog's Stomach, a, Lumen oi
gland; b, intracellular canals in parietal cells; c, cut-off portion of parietal cell; d, chief cells;
e, intercellular canals leading from lumen of gland to canals in parietal cells. (Bailey.)
FIG. 257. — Tubule of Pyloric Gland of Man. (Highly magnified.) Note the thin basal layer
of cytoplasm; the reticular cell body containing secretion; the subdivision of the latter in some
cells into proximal and distal masses.
form the framework on which are molded the small elevated ridges of mucous
membrane. From this superficial network the veins chiefly take their origin,
pass down between the tubes, with no very free connection with the deeper
intertubular capillary plexus, and open finally into the venous network in
the submucous tissue.
The lymphatic vessels surround the gland tubes with a network. Toward
the fundus of the peptic glands are masses of lymphoid tissue which may
appear as distinct follicles, somewhat like the solitary glands of the small
intestine.
320
POOD AND DIGESTION
Microscopic Changes in the Gastric Glands During Secretion. Lang-
ley has made a study of the histological changes in the glandular tissues
in the fresh state. He finds that during fasting or when the glands are at rest
the chief cells are granular throughout, being crowded with large highly re-
fractive granules. During activity these granules gradually disappear pro-
gressively from the base toward the border of the cell on the lumen of the tube.
They no doubt represent the zymogen substances from which the first discharge
FIG. 258. — Scheme of Blood-vessels and Lymphatics of Stomach. X 70. a, Mucous mem-
brane; b, muscularis mucosae; c, submucosa; d, inner circular muscle layer; e, outer longitudinal
muscle layer; A, blood-vessels; B, structure of coats; C, lymphatics. (Szymonowicz, after Mall.)
of enzyme is derived during the activity of secretion. The parietal cells are
finely granular throughout, though they decrease in size during activity, as in
fact do the chief cells. The pyloric cells do not undergo such marked changes,
and the mucous cells of the more superficial layers of the mucosa cannot be
said to show any special changes at the time of digestional activity of the
other layers. During periods of rest the gastric cells increase in size and
again become charged with granules as before.
The Act of Secretion of Gastric Juice. The gastric glands un-
dergo periods of rest and activity. The active secretion of normal gastric
juice takes place when food is introduced into the mouth, or in fact the
mere sight of appetizing food is followed by an abundant secretion of gastric
juice as shown by Bidder and Schmidt on a dog with a gastric fistula. Such
THE GASTRIC JUICE 321
observations strongly indicate that the act is a nervous phenomenon, at least
under nervous control.
Quite recently Pawlow has proved that secretory fibers are carried
to the gastric glands in the vagus trunk. His experiment consisted in
establishing a gastric fistula, and some days later in dividing the esophagus
in the neck in such a manner that any food swallowed would be diverted
to the exterior through the cut end. A "fictitious meal" could then be given
to the animal, and the effect upon the stomach noted. As long as the vagi
were intact, certain foods (meats) caused a flow of gastric juice, though
none of the food reached the stomach. The secretion of gastric juice con-
tinued for hours with the production of a large quantity of secretion. When
PIG. 259. — Very Diagrammatic Representation of the Nerves of the Alimentary Canal. Oe to
Ret, the various parts of the alimentary canal from esophagus to rectum; L. V., left vagus, ending on
front of stomach; rl, recurrent laryngeal nerve, supplying upper part of esophagus; R. V, right
vagus, joining left vagus in esophageal plexus; oe. pi., supplying the posterior part of stomach, and
continues as R'V to join the solar plexus, here represented by a single ganglion, and connected
with the inferior mesenteric ganglion, m. gl.; a, branches from the solar plexus to stomach and small
intestine, and from the mesenteric ganglia to the large intestine; Spl. maj., large splanchnic nerve,
arising from the thoracic ganglia and rami communicantes; r. c., belonging to dorsal nerves from
the 6th to the gth (or loth); Spl. min., small splanchnic nerve similarly from the icth and nth
dorsal nerves. These both join the solar plexus, and thence make their way to the alimentary
canal; c. r., nerves from the ganglia, etc., belonging to nth and i2th dorsal and ist and zd lum-
bar nerves, proceeding to the inferior mesenteric ganglia (or plexus), m. gl., and thence by the hypo-
gastric nerve, n. hyp., and the hypogastric nerve, n. hyp., and the hypogastric plexus, pi. hyp., to the
circular muscles of the rectum; /, r., nerves from the 2d and 3d sacral nerves, S. 2, S. 3 (nervi
erigentes) proceeding by the hypogastric plexus to the longitudinal muscles of the rectum. (M.
Foster.)
the vagi had been cut, no secretion occurred. Moreover, he found that direct
stimulation of the vagus produced a flow of gastric juice.
Khigine placed foods in an isolated gastric pouch prepared with care to
maintain the nervous relations intact, and it led to secretion of gastric juice
in the main part of the stomach. This is undoubtedly a nervous reflex effect.
21
FOOD AND DIGESTION
Recently observations on a case of stricture of the human esophagus which
prevented food from reaching the stomach have shown that an abundant flow
of gastric juice takes place when food is taken in the mouth.
It seems conclusively established at the present time that the secretion of
gastric juice is a reflex act controlled by a definite nervous mechanism. This
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reflex can be aroused by the sensory stimuli of taste, smell, and even sight.
It can also be initiated by stimuli arising in the stomach itself by the effects
of ingredients of the food or by the products of digestion. Indeed it has been
shown that peptone is a very efficient stimulus for this stomach reflex.
THE GASTRIC JUICE 323
The influence of the higher nerve centers on gastric digestion, as in the
case of emotions, is too well known to need more than a reference.
Immediately on the introduction of food or other stimulating substance,
the mucous membrane, which was previously quite pale, becomes slightly
turgid and reddened with the influx of a larger quantity of blood, and the gas-
tric glands commence actively to secrete. An acid fluid is poured out in minute
drops and the secretion may continue for hours.
The Gastric Juice. The first analysis of gastric juice was made by
Prout on a small and impure specimen. Beaumont made an elaborate and
classic series of observations on the gastric secretion of Alexis St. Martin,
in whom there existed, as the result of a gunshot wound, an opening leading
directly into the stomach near the upper extremity of the great curvature
and three inches from the cardiac orifice. The introduction of any mechan-
ical irritant, such as the bulb of a thermometer, into the stomach through
this artificial opening excited the secretion of gastric fluid. This was drawn
off, and was often obtained to the extent of nearly an ounce.
The chemical composition of human gastric juice has been also investigated
by Schmidt. The fluid in this case was also obtained by means of an accidental
gastric fistula. The mucous membrane was excited to action by the intro-
duction of some hard matter, such as dry peas, and the secretion was removed
by means of an elastic tube. The fluid obtained was found to be acid, limpid,
odorless, with a specific gravity of 1002 to 1010. It contained a few cells and
some fine granular matter. The analysis of the fluid obtained in this way
is given below. Essentially it is a weakly acid fluid containing hydrochloric
acid and two enzymes, pepsin and rennin, with possibly a third, maltase. The
gastric juice of dogs and other animals obtained from gastric fistulas shows
some difference in composition.
CHEMICAL COMPOSITION OF GASTRIC JUICE.
Dogs. Human.
Water 9 7 1 . 1 7 994-4
Solids 28.82 5.60
Solids-
Ferment— Pepsin 17.5 3-19
Hydrochloric acid (free) 2.7 0.2
Salts-
Calcium, sodium, and potassium chlorides; and calcium,
magnesium, and iron phosphates 8.57 2. 19
The quantity of gastric juice secreted daily has been variously estimated;
but the average for a healthy adult may be assumed to range from 2,000 to
3,000 cubic centimeters in the twenty-four hours.
The Acid of Gas'ric Juice. The acidity of the fluid is due to free
hydrochloric acid, although other acids, e.g., lactic, acetic, butyric, are not
infrequently to be found therein as products of gastric digestion or abnormal
324 FOOD AND DIGESTION
fermentation. In healthy gastric juice the amount of free hydrochloric acid
is usually about 0.2 percent, but may be as much as 0.3 per cent. In patho-
logical conditions it may be entirely absent, or may amount to o . 5 per cent, or
even more.
Hydrochloric acid is the proper acid of healthy gastric juice, and various
tests have been used to prove this. The tests depend upon changes produced
in aniline colors by the action of hydrochloric acid even in minute traces,
whereas lactic and other organic acids have no such action.
An aqueous solution of oo-tropeolin, a bright yellow dye, is turned red on
the addition of a minute trace of hydrochloric acid, and aqueous solutions
of methyl violet and gentian violet are turned blue under the same circum-
stances. The lactic acid sometimes present in the contents of the stomach is
derived partly from the sarcolactic acid of muscle and partly from lactic-acid
fermentation of carbohydrates. Lactic acid (C3H6O3), if present, gives the
following test. A solution of 10 cubic centimeters of a 4 per cent aqueous solu-
tion of carbolic acid, 20 cubic centimeters of water, and one drop of ferric
chloride is made; forming a blue-colored mixture. A mere trace of free lactic
acid added to such a solution causes it to become yellow, whereas hydro-
chloric acid even in large amount only bleaches it.
The proteid. matter in the food combines to some extent with the hydro-
chloric acid, which then is known as combined acid and does not redden litmus
paper. As this combination is immediate, it follows that no free acid is found
in the gastric contents until the amount secreted is more than enough to satu-
rate the various albuminous affinities. It is partly for this reason that, as al-
ready mentioned, salivary digestion may continue in the stomach for some
time after the commencement of gastric digestion. According to Ehrlich the
amount necessary to saturate the affinities of 100 grams of various articles
of diet is as follows:
Beef (boiled) 2.0 grams of pure HC1.
Mutton (boiled) 1.9
Veal (boiled) 2.2
Pork (boiled) 1.6
Ham (boiled) 1.8
Sweetbread (boiled) 0.9
Wheat bread 0.3 "
Rye bread 0.5 "
Swiss cheese 2.6 " " "
Milk (100 c.c.) 0.32-0.42 "
The acid is chiefly found at the surface of the mucous membrane, but is
in all probability formed by the parietal cells of the cardiac glands, hence
called oxyntic, for no acid is formed by the pyloric glands in which this
variety of cell is absent. It seems established that the chlorides of the blood
are the source of the hydrochloric acid, for when these chloride salts are
reduced to the point at which they are tenaciously held the hydrochloric
ACTION OF PEPSIN AND HYDROCHLORIC ACID 325
acid is no longer secreted. One can only guess at the detail by which the
parietal cells secrete the acid.
The acid probably results (Maly) from a combination of common salt
with monosodic phosphate, NaH2PO4 + NaCl •= Na2HPO4 + HC1; the
disodic phosphate is then reconverted by the action of carbonic acid and
water, Na2HPO4 + CO2 + H2O = NaH2PO4 + NaHCO3. All these
salts are found in the blood.
The Pepsin. The pepsin of the gastric juice is derived from the
activity of the chief cells of the fundic glands. The zymogen pepsinogen,
which is its immediate precursor, is in all probability represented by the gran-
ules of the resting cells. The ferment pepsin does not exist as such in the cells,
for an extract of peptic glands in 0.2 per cent soda solution kept at 40° C. retains
for hours its power to digest proteid when added to 0.2 per cent hydrochloric
acid. If the extract be first treated with acid till it is active, then neutralized
and kept, it quickly loses its power to digest. The enzyme is destroyed by
the treatment, but the pro-enzyme is not so injured.
Digestive Action of Pepsin and Hydrochloric Acid. The chief func-
tion of gastric juice is to alter the proteid food stuffs so that they may
be readily absorbed. Less important functions are the antiseptic action of
the hydrochloric acid, and the coagulation of milk. The chief digestive power
of the gastric juice depends on the pepsin and acid contained in it, both of
which are necessary for the process in the stomach.
This action on proteids may be shown by adding a little gastric juice
(natural or artificial) to some flakes of fibrin or to diluted egg albumin, and
keeping the mixture at a temperature of about 37.8° C. (100° F.). It is soon
found that the fibrin goes into solution and that the albumin cannot be pre-
cipitated on boiling. If the solution be neutralized with an alkali, a precipitate
of acid albumin is thrown down. After a while the acid albumin disappears,
so that no precipitate results on neutralization, and proper analysis will show
that all the fibrin or albumin has been converted into other proteid substances,
viz., proteases and peptones. The process, as in the case of salivary digestion,
is never complete and the final result is always a mixture of peptones with
proteoses which cannot be further peptonized. The relative proportions, of
course, depend on the duration of the process. A side product is found (as
an insoluble residue) in artificial gastric digestion which gives practically all
the proteid reactions and is soluble in dilute alkali, though insoluble in water,
sodium chloride, or dilute acid. This is known as anti-albumid and may be
changed into peptone by prolonged digestion; it does not occur in physiologi-
cal gastric digestion. The commonest proteose is the one formed from albumin
and is known as albumose, or by the more general name proteose; this name
is used in the subsequent descriptions of the digestive processes.
All classes of proteids are digested by gastric juice, leading to the produc-
tion of proteoses and peptones. The change is indicated best by the characters
326 FOOD AND DIGESTION
of the new proteid formed. Peptones have certain characteristics which
distinguish them from other proteids. They are diffusible, i.e., they possess
the property of passing through animal membranes. In their diffusibility
peptones differ remarkably from egg albumin, and on this diffusibility depends
one of their chief uses. Egg albumin as such, even in a state of solution, would
be of little service as food, inasmuch as its diffusibility renders difficult its
absorption or in the case of insoluble proteids effectually prevents absorption
into the blood-vessels of the digestive canal. When completely changed by
the action of the gastric juice into peptones, albuminous matters diffuse readily,
and are thus quickly absorbed.
Peptones are not found in the blood, even of the vessels immediately con-
cerned in absorption from the stomach and intestines. In their absorption,
therefore, by the epithelial cells, they must undergo a synthetic change, ap-
pearing in the blood as albumins and globulins, which are not readily diffu-
sible and which occupy the same plane as the proteids from which the peptones
were derived. The previous cleavage to proteoses and peptones is in the
nature of preparation for this final act of absorption.
Products at Different Stages of Gastric Digestion. The proteid
is first changed into syntonin, or acid proteid, by the combined action of the
pepsin and acid. Though the acid alone is capable of accomplishing this
step, the fact that it does not do so physiologically is proven by the great length
of time required, in laboratory experiments, for the change.
The next change is the conversion of the syntonin into proteoses which,
according to Neumeister, occurs in two successive stages. The first of these
stages is the conversion of syntonin into the primary proteoses, i.e., proto-
proteose and hetero-proteose. The second is the conversion of both proto-
proteose and hetero-proteose into the secondary proteoses, i.e., deutero-proteose.
The last change is the conversion of the deutero-proteose into the end product
peptone. This last change does not occur completely to any great extent and
the proteoses always predominate in the digesting mass. Schematically the
changes in the proteids may be represented as follows: ,
Proteid.
I
Syntonin (acid proteid).
I I
Proto-proteose. Hetero-proteose.
I I
Deutero-proteose Deutero-proteose.
i I
Peptone. Peptone.
The action of pepsin is one of hydrolysis and the products are hydrated
forms of proteid. The acid is absolutely essential to the action of pepsin, but
it also aids digestion by causing the proteids to absorb water. That this ac-
MOVEMENTS OF THE STOMACH 327
tion is important is proven, in laboratory experiments, by the decreased
length of time required for digestion when fibrin has first been soaked in 0.2
per cent hydrochloric acid and thus caused to swell with the absorption of
water before coming in contract with the pepsin.
Circumstances Influencing Gastric Digestion. A temperature of
about 40° C. is most favorable to gastric digestion. The pepsin is de-
stroyed by a temperature of 55° (neutral) to 65° C. (acid solution) and its
action is retarded and suspended by low temperatures. It is inactive in neutral
or alkaline solution, for an acid medium is necessary. Hydrochloric is the
best acid for the purpose, but nitric acid or the organic acids may be substi-
tuted for the hydrochloric. Excess of peptone delays the action, and the
removal of the products of digestion facilitates the process.
Action of Rennin. Milk is curdled, the casein being precipitated,
and then dissolved. The curdling is due to a special ferment of the gastric
juice, rennin, and is not due to the action of the free acid alone. The effect of
rennin, which is obtained from the fourth stomach of a calf, has long been
known, as it is used extensively to cause precipitation of casein in cheese manu-
facture. The ferment rennin is active in a neutral solution as well as in acid.
Time Occupied in Gastric Digestion. Under ordinary conditions,
from three to four hours may be taken as the average time occupied by the
digestion of a meal in the stomach. But many circumstances wrill modify
the rate of gastric digestion. The chief are: The nature of the food taken and
its quantity (the stomach should be fairly filled, not distended) ; the time that
has elapsed since the last meal, which should be at least enough for the stomach
to be quite clear of food; the amount of exercise previous and subsequent to
a meal (gentle exercise being favorable, over-exertion injurious to digestion);
the state of mind; and the bodily health.
Summary of Changes in the Food in Gastric Digestion. Briefly
summarizing the action of gastric juice, the facts appear as follows: Gastric
juice has a specific digestive action on proteid foods of all kinds, converting
them into the more soluble proteases and peptones. The action is due to an
enzyme, pepsin, acting in and with an acid, hydrochloric acid. Digestion takes
place best at the temperature of the body, is destroyed by high heat and sus-
pended by cold, o° C. Putrefaction is prevented by gastric juice. Milk is
first coagulated by a special enzyme, rennin, and then digested as any other
proteid. Gastric juice dissolves soluble substances like salts, saccharides,
etc. Fats*and carbohydrates are not digested by gastric juice, in fact fats
tend to hinder the action.
MOVEMENTS OF THE STOMACH.
Attention has been called to the fact that the stomach is a muscular sac
capable of holding quite a large mass of food. During a full meal as much
FOOD AND DIGESTION
as one to two liters or more of semi-solid food is packed away in the organ in
a comparatively short space of time. The gastric juice is secreted by the
mucous membrane which surrounds the surface of the food mass. The result
is that the secretion begins to soften and digest the food over its surface, thus
tending to liquefy and erode away layer after layer of the food mass. The pic-
ture is made clearer if one remembers that the food mass is retained almost
wholly in the fundus of the stomach. The pyloric portion of the stomach is
quite strongly muscular and quite definitely marked off by the strong trans-
verse band at its union with the fundus.
The gastric juice is assisted in accomplishing digestion by the movements
of the stomach itself. When digestion is not going on, the stomach is uni-
formly contracted, its orifices not more firmly than the rest of its walls; but,
if examined shortly after the introduction of food, it is found closely encircling
its contents, and its orifices are firmly closed like sphincters. The cardiac
orifice, every time food is swallowed, opens to admit its passage to the stomach,
and immediately closes again. The pyloric orifice, during the taking of food
FIG. 261. — Diagram to Show the Movement of Food in the Pylorus at Times when the Pyloric
Valve is Closed.
and the first part of gastric digestion, is so completely closed that none of the
contents escape.
The character of stomach movements has been admirably determined by
recent observers using the Roentgen-ray method. Thus Cannon working
with cats has shown that in from five to ten minutes after a meal slight rings
or constrictions occur in the pyloric antrum and travel slowly toward the
pyloric valve in the form of a peristaltic wave. Successive waves begin a little
further back toward the fundus each time and follow over the pyloric
antrum with clocklike regularity, in the cat one wave in ten seconds, which
requires in each case about twenty seconds for its completion. In man they
are doubtless slower. These peristalses continue during the whole period of
digestion, for as much as seven or even more hours.
These peristaltic contractions aid the gastric juice in carrying away the
MOVEMENTS OF THE STOMACH
329
softened layers of food by propelling it into the pylorus. There it is thoroughly
mixed with the gastric juice, forming the chyme. Figure 261 gives an idea of
the movement of the food in the antrum. The peristaltic contractions carry
it forward, but if the valve does not open to permit passage to the duodenum,
then the pressure will force the chyme back through the center toward the
fundus. After several minutes the pyloric sphincter will occasionally relax
to allow fluid food to pass to the duodenum, but when more solid particles come
11A.M.
12M.
2RM,
5P.M.
FIG. 262. — Outlines of the Roentgen-ray Shadows of the Stomach Content as Digestion
(Cannon.)
up against the valve the sphincter promptly contracts and remains so for some
time. Toward the completion of digestion even solid undigested particles are
carried on into the intestine.
The movements of the stomach are under nervous regulation. Cannon
found that the peristalses were promptly inhibited in cats by excitement. Stim-
ulation of the vagi leads to contractions of the stomach, wrhile the splanchnics
330
FOOD AND DIGESTION
bring about relaxation or dilatation. It is also demonstrated that afferent
vagus impulses influence the contractions in the stomach.
It seems probable that automatic peristaltic contraction is inherent in the
muscular coat of the stomach, and that the central nervous system is only
employed to regulate it by impulses passing down by the vagi or splanchnic
nerves.
Vomiting. The expulsion of the contents of the stomach in vomit-
ing is preceded by a deep inspiration with closure of the glottis, followed im-
mediately afterward by strong contractions of the muscles of the abdomen,
diaphragm, and stomach. The diaphragm forms an unyielding surf ace against
which the stomach can be pressed. In this way as well as by its own contrac-
tion the diaphragm is fixed, to use a technical phrase. At the same time the
cardiac sphincter muscle is relaxed, and the orifice which it naturally guards is
FIG. 263. — Horizontal Section of a Small Fragment of the Mucous Membrane, including one
entire crypt of Lieberkiihn and parts of several others.
actively dilated. The pylorus is closed, and, the stomach itself also contracting,
;he action of the abdominal muscles produces strong compression which ex-
pels the contents of the organ through the esophagus, pharynx, and mouth.
Reversed peristaltic action of the esophagus probably increases the effect.
It has been frequently stated that the stomach itself is quite passive during
vomiting, and that the expulsion of its contents is effected solely by the pres-
sure exerted upon it when the capacity of the abdomen is diminished by the
contraction of the diaphragm. It is true that facts are wanting to demonstrate
with certainty this action of the stomach in vomiting; but cases of fistulous
opening into the organ appear to support the belief that it does take place; and
the analogy of the case of the stomach with that of the other hollow viscera,
as the rectum and bladder, may also be cited in confirmation.
Vomiting is a reflex act. It can be excited by irritation of the lining of
the stomach which is perhaps the normal stimulus. It is excited by stimula-
tion or irritation of other parts of the alimentary tube, i.e., the pharynx, the
DIGESTION IN THE INTESTINES
331
uvula, the intestine, etc. Vomiting may occur from stimulation of sensory
nerves from many organs, e.g., kidney, testicle, etc., or by impulses arising
in the organs of special sense, the eye, olfactory membrane, etc. The sensory
impulses are coordinated by a nerve center located in the medulla. The
center may also be stimulated by impressions from the cerebrum and cere-
bellum or by changes arising in the center itself, the so-called central vomiting
occurring in disease of those parts. The efferent impulses are carried by the
phrenics and other spinal nerves and by the vagus.
DIGESTION IN THE INTESTINES.
The food that enters the small intestine has already been subjected to two
digestive enzymes. The ptyalin of the saliva and the pepsin of the gastric
juice together with the mechanical processes involved have reduced the food
to a pulpy mass, the chyme. This peptonized food contains most of the total
quantity of food eaten, little having been absorbed as we shall see later, but
much of the starch has been changed to soluble maltose and dextrose and
the proteid to albumoses and peptones. The discharge from the stomach
through the pyloric valve to the duodenum has been going on through three
FIG. 264.
FIG. 265.
FIG. 264. — Piece of Small Intestine (previously distended and hardened by alcohol), Laid
open to Show the Normal Position of the Valvulae Conniventes.
FIG. 265. — Section of the Pancreas of a Dog During Digestion, a, Alveoli lined with cells,
the outer zone of which is well stained with hematoxylin; d, intermediary duct lined with squa-
mous epithelium. X 350. (Klein and Noble Smith.)
or four hours on an average for each full meal. This stream of food passing
down the small intestine, slowly because of the valvulae conniventes, meets
a number of secretions which contain enzymes which act on each of the three
great food principles, proteicte, fats, and carbohydrates. These secretions are
the pancreatic fluid, the succus entericus, and the bile.
332
FOOD AND DIGESTION
The Pancreas. The pancreas is situated within the curve formed
by the duodenum; and its main duct opens into that part of the small intestine
through a duct common to it and to the liver and about two and a half inches
from the pylorus.
The pancreas bears some resemblence in structure to the salivary glands.
Its capsule and septa, as well as the blood-vessels and lymphatics, are similarly
distributed. It is, however, looser, the lobes and lobules being less compactly
arranged.
Heidenhain has observed that the alveolar cells in the pancreas of a fasting
dog consist of two zones, an inner or central zone which is finely granular,
FIG. 266. — Section of the Pancreas of Armadillo, Showing the Two Kinds of Gland- structure.
(V. D. Harris.)
and which stains feebly, and a smaller parietal zone of finely striated proto-
plasm which stains easily. The nucleus is partly in one, partly in the other
zone. During secretion it is found that the outer zone increases in size, and
the central granular zone diminishes, as in the case of the salivary glands.
The pancreatic cell itself becomes smaller from the discharge of the secretion.
During a period of rest the granular zone again increases in size and the
outlines of the cells become full and indistinct. The granules, as in the sali-
vary cells, are the material from which, under certain conditions, the ferments
of the gland are developed, and which are therefore a Zymogen. In addition to
the ordinary alveoli of the pancreas there are distributed irregularly in the
gland other collections of cells of a different character, the Islands oj Lan-
gerhans. These cells are considerably smaller, their protoplasm is more
THE PANCREAS
333
granular and less easily stained with hematoxylin, and their nuclei are small
and stain deeply. The collections of cells vary in size and shape. The
special form of nerve terminations, called Pacinian corpuscles, are often
found in the pancreas. The secretion of the pancreas has been obtained for
purposes of experiment from the lower animals and from man in at least
one case. A pancreatic fistula is established in the dog by opening the
-771
FIG. 267. — Duct with Laterals to the Alveoli. Silver method of Golgi (E. Muller). A, Duct
vrith branches; m, between the cells. B, Laterals more strongly magnified.
abdomen and exposing the duct of the gland which is then made to com-
municate with the exterior. In Pawlow's method a circular bit of the intes-
tinal mucous membrane around the mouth of the duct in the intestine is
brought to the surface and stitched into the wound. The secretion is then
easily collected into a vessel suspended under the opening.
The Pancreatic Juice. Pancreatic juice is colorless, transparent,
slightly viscid, and alkaline in reaction. It varies in specific gravity from
1010 to 1030, according as it is obtained from a permanent fistula — then more
334 FOOD AND DIGESTION
watery, or from a newly opened duct. The solids vary in a temporary fistula
from 80 to 100 parts per thousand, and in a permanent one from 16 to 50 per
thousand. It is characterized by having three distinct and important en-
zymes known as trypsin, amylopsin, and steapsin, whose actions are respect-
ively, proteolytic, amylolytic, and lipolytic (fat-splitting). Maltase, which
inverts the disaccharides, is also present, and some have stated that rennin is
found in pancreatic juice.
CHEMICAL COMPOSITION or PANCREATIC JUICE. (C. SCHMIDT.)
Recent Permanent
From a dog. fistula. fistula.
Water 900.76 980.45
Solids 99-24 19 . 55
Organic substances QO-44 12.71
Ash 8.80 6.84
Sodium carbonate 0.58 3.31
Sodium chloride 7.35 2.50
Calcium, magnesium, and sodium phosphates °-53 0.08
An extract of pancreas made from the gland which has been re-
moved from an animal killed during digestion possesses the active properties
of pancreatic secretion. It is made by first dehydrating in absolute alcohol
the gland which has been cut up into small pieces. After the entire removal
of the alcohol the gland is pulverized and extracted in strong glycerin.
The amount of the ferment greatly increases if the gland be exposed to the
air for three or four hours before placing in alcohol; indeed, a glycerin
extract made from the gland immediately upon the removal from the body
often appears to contain none of the ferments. The conversion of zymogen
in the gland into the ferment takes place only after the gland stands a while.
Dilute acid assists or accelerates the conversion, and if a recent pancreas be
rubbed up with dilute acid before dehydration, a glycerin extract made
afterward, even though the gland may have been only recently removed from
the body, is very active.
Nervous Regulation of the Secretion of the Pancreas. Fibers from
the vagus and from the splanchnics are distributed to the pancreas. In
Pawlow's laboratory it has been found that stimulation of these nerves leads
to the increased secretion of the pancreas. Popielski, in studying the effects
of dilute hydrochloric acid solution in the duodenum, which resulted in a
marked increase of pancreatic secretion, explained the phenomenon as a
local nerve reflex.
Doubt has been cast on the whole question of nervous control by the recent
discovery of the fact that acid (0.4 per cent hydrochloric acid) in the duodenum
results in the production of a chemical substance, secretin, by the duodenal
mucous membrane. This secretin is absorbed into the circulation and acts
specifically on the pancreas to produce increased activity by the pancreatic
cells. Acid extracts of the duodenal mucous membrane produce the same
ACTION OF THE ENZYMES OF PANCREATIC JUICE
335
effects on the pancreas, in fact this is the current method of stimulating
the flow of pancreatic juice at the present time, the secretion being collected
from a tube introduced into the duct
Under the normal stimulus of food, the flow of pancreatic juice is greatly
increased. The increase continues to a maximum in from two to three hours,
after which it gradually decreases through the period of digestion. Pawlow
1.
I.
3.
k.
S.
6.
7.
S.
Ml
/\
\
bo
S
/
\ x
:\
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32
/
/
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y
V
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/ /
\
<U
• /
/ /
\
\
\
•: i
; i
' 1
\
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\
(6
i
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/
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FIG. 268. — Three Curves Showing the Secretion of Pancreatic Juice upon a Diet (i) of 600 c.c.
of milk; (2) of 250 gm. of bread; (3) of too gm. of meat. The divisions along the abscissa repre-
sent hours after the beginning of the meal; the figures along theordinates represent the quantity
of the secretion in cubic centimeters. (Walter.)
has found a certain amount of adaptation not only of the quantity but of
the enzyme composition of the pancreatic secretion to the kind and character
of the food (in dogs).
Action of the Enzymes of Pancreatic Juice. The secretion of the
pancreas accomplishes its digestive action by means of the enzymes given
above, viz., trypsin, amylopsin, steapsin, and maltase.
Trypsin. Trypsin is a proteolytic enzyme. Strange to say it does not exist
in the fresh pancreatic juice as such, but makes its appearance only when there
336 FOOD AND DIGESTION
is an admixture with the secretion of the mucous membrane of the intestine.
The succus entericus contains an activating enzyme, enterokinase, which
converts the inactive and stable trypsinogen of the pancreatic juice into the
active but less stable trypsin. This fact is another of the wonderful series of
contributions to the exact knowledge of the subject of digestion made from
Pawlow's laboratories.
Trypsin converts proteids into proteases and peptones. The process is
both more rapid and more complete than in gastric digestion, so that, in the
final result, the peptones are greatly in excess of the proteoses. The proteids
pass through the same preliminary stages as in gastric digestion, being split
at first into alkali-albumin, then into primary proteoses, both proto-proteose
and hetero-proteose, and then into deutero-proteose. The first stages are so
transient that it is difficult to detect either the alkali-albumin or primary pro-
teose. The deutero-albumoses are easily demonstrated in the earlier stages,
but become very scanty later. Anti-albumid is found as a side product in
artificial digestion, but is not present in normal digestion.
Trypsin also has the power of splitting a certain proportion of peptones,
the hemi-peptones, into simpler bodies such as leucin or amido-caproic acid,
tyrosin or paraoxyphenyl-amido-propionic acid, lysin, lysatinin, tryptophan,
and some other bodies. In the cleavage of the proteid molecule there is prob-
ably left a complex nucleus which may yet serve as a synthetic center for the
rebuilding of the proteid molecule. This nucleus is called a polypeptid.
Leucin and tyrosin have been found in the intestinal contents, so that this
destruction of hemipeptone in artificial tryptic digestion must take place to
a certain extent within the body as well.
In laboratory experiments only about one-half of the peptones can be
changed in this way. The more stable portion which cannot be changed
is usually known as antipeptone. There are several theories as to the reason
or use of this change into leucin, tyrosin, etc. One of the most plausible
is that it saves the body from needless work when too much proteid food has
been taken; the breaking down in the intestine of bodies only slightly removed
from urea relieves the liver and other glandular organs from the strain of
converting an excess of absorbed proteid material into a form in which it can
be excreted. Another theory is that leucin, tyrosin, etc., are essential for
the physiological working of the body in some unknown way, just as are the
products of the thyroid gland. The formation of the decomposition products,
indol and skatol, is caused by the action of bacteria on proteids. The albu-
minous or proteid substances which have not been converted into peptone in
the stomach, and the partially changed substances, i.e., the proteoses, are con-
verted into peptone by the pancreatic juice, and then in part into leucin and
tyrosin, etc.
The ferment trypsin acts best in an alkaline medium, but will act also
in a neutral medium, or in the presence of a small amount of combined acid;
ACTION OF THE ENZYMES OF PANCREATIC JUICE S3?
it will not work in the presence of free acid. It therefore differs from pepsin
in being able to act without the aid of any other substance than water. In
the process of tryptic digestion, proteid matter does not swell up at first, but
seems to be corroded at once.
Amylopsin. Starch is converted into maltose in an exactly similar manner
to that which happens with saliva, erythro-dextrin and one or more achroo-
dextrins being the intermediate products. The amylolytic enzyme of the
pancreatic juice, which cannot be distinguished from ptyalin, is called amyl-
opsin. The maltose thus formed is converted to dextrose by the maltase,
in which form it is ultimately absorbed.
Pancreatic juice, according to certain observers, possesses the property
of curdling milk. It contains a special ferment, rennin, for that purpose.
The ferment is distinct from trypsin, and will act in the presence of an acid
(W. Roberts). The milk-curdling ferment of the pancreas is, in some pan-
creatic extracts, said to be quite powerful, insomuch that i c.c. of a brine ex-
tract will coagulate 50 c.c. of milk in a minute or two.
Steapsin or Lipase. Oils and fats are emulsified and saponified by the pan-
creatic secretion. The terms emulsification and saponification may need a
little explanation. The former is used to signify an important mechanical
change in oils or fats, whereby they are made into an emulsion, or in other
words are minutely subdivided into small particles. If a small drop of an
emulsion be looked at under the microscope it will be seen to be made up of
an immense number of minute rounded particles of oil or fat, of varying
sizes. The more complete the emulsion the smaller are these particles. An
emulsion is formed at once if oil or fat, which when old is slightly acid from the
presence of free fatty acid, is mixed with an alkaline solution. Saponification
signifies a distinct chemical change in the composition of oils and fats. An
oil or a fat being made up chemically of glycerin, a triatomic alcohol, and
one or more fatty-acid radicles, when an alkali (potassium hydrate) is added
to it and heat is applied, two changes take place : first, the oil or fat is split up
into glycerin and its corresponding fatty acid ; second the fatty acid combines
with the alkali to form a soap which is chemically known as stearate, oleate,
or palmitate of potassium. Saponification thus means a chemical splitting
up of oils or fats into new compounds, and emulsification means merely a
mechanical splitting up into minute particles. The pancreatic juice has been
for many years credited with the possession of a special ferment, which was
called by Claude Bernard steapsin, and which is a lipase or fat-splitting fer-
ment. This ferment has not been isolated, but its presence may be demon-
strated by adding portions of the fresh pancreas to butter or other fat and
maintaining the proper temperature. Its action is made manifest by the libera-
tion of butyric acid, which smells like rancid butter.
The generally accepted theory is that only a small portion of the fat which
is eaten is thus changed into soap, and that the function of the saponified fat
22
338 FOOD AND DIGESTION
is to assist in the emulsification of the major part, a process which is favorably
influenced by the bile. The proper emulsification of fat is a necessary pre-
liminary to its absorption, for when in disease the entrance of the pancreatic
juice and of the bile to the intestine is interfered with, the feces contain a
great excess of fat.
Some recent experiments, however, tend to prove that the entire fat of the food is
changed in the intestine into fatty acids and glycerin; that the fatty acids are entirely,
or in part, changed to soaps; and that these soaps, or mixture of soaps and free fatty acids,
are absorbed in solution. The chief facts favoring this view are that: (i) The action of
steapsin is sufficiently rapid to allow the saponification of a full fatty meal within the
ordinary period of digestion; (2) histological examination has never shown that fat par-
ticles can pass into a columnar cell, and none have ever been found in the broad striated
border of the cell; (3) the fat globules found in columnar cells after a fatty meal grow
steadily larger as the period of absorption' progresses, indicating that they are deposited
from solution; (4^ the fatty acids are easily soluble in bile solutions, and the solubility of
the soaps is greatly increased by the presence of bile. The fat constituents, according to
this theory, are recombined in the columnar cells to form neutral fats.
Conditions which Influence the Action of the Pancreatic Enzymes.
The various pancreatic enzymes are influenced by heat, by the presence of
an excess of digestion products, etc., in the same way as ptyalin and pepsin.
Pancreatic enzymes act in a neutral but best in an alkaline solution. The
trypsin, strange to say, is quickly destroyed -by the alkaline solution (Bayliss
and Starling). The pancreatic juice offers the special case of a secretion of
proenzyme which is stable in alkaline solution until acted on by enterokinase,
and the amount of kinase present will, therefore, markedly influence the
amount of digestion of proteid per unit of time.
The Secretions of the Liver. The liver, the largest gland in the
body, situated in the abdomen on the right side chiefly, is an extremely vascu-
lar organ, and receives its supply of blood from two distinct sources, viz.,
44*
L.L.
FIG. 269. — The Liver from Below and Behind. L. S., Spigelian lobe; L. C., caudate lobe;
L. (?., quadrate lobe; R. L., right lobe; L.L., left lobe; g. bl., gall-bladder; v.c.i., inferior vena
cava; u.f., umbilical fissure; f.d.v., fissure of the ductus venosus; p, portal fissure with portal vein,
hepatic artery and bile-duct. (Wesley, from a His model.)
STRUCTURE OF THE LIVER
339
from the portal vein and from the hepatic artery, while the blood is returned
from it into the vena cava inferior by the hepatic veins. Its secretion, the bile,
is conveyed from it by the Hepatic duct, either directly into the intestine, or,
when digestion is not going on, into the cystic duct, and thence into the gall-
FIG. 270. — Portion of a Lobule of Liver, a, Bile capillaries between liver cells, the network in
which is well seen; b, blood capillaries. X 350. (Klein and Noble Smith.)
bladder, where it accumulates until required. The portal vein, hepatic artery,
and hepatic duct branch together throughout the liver, while the hepatic veins
and their tributaries run by themselves. The interstices of these vessels are
filled by the liver cells.
Structure of the Liver. The liver is made up of small roundish
or oval portions called lobules, each of which is about ^V of an inch (about
FIG. 271. — Hepatic Cells and Bile Capillaries, from the Liver of a Child Three Months Old.
Both figures represent fragments of a section carried through the periphery of a lobule. The red
corpuscles of the blood are recognized by their circular contour; vp, corresponds to an interlobular
vein in immediate proximity with which are the epithelial cells of the biliary ducts. (E. Hering.)
i mm.) in diameter, and includes the minute hepatic artery and hepatic
duct. The hepatic cells, which form the glandular or secreting part of the
liver, are of spheroidal form, somewhat polygonal from mutual pressure, about
340
FOOD AND DIGESTION
25 to 30 /j. in diameter, and possess one, sometimes two nuclei. The cell-sub-
stance contains a variable amount of glycogen and often some fatty molecules,
and possibly some granules of bile pigment.
The bile capillaries commence between the hepatic cells, and are bounded
by a delicate membranous wall of their own. They appear to be always
FIG. 272. — Section of Liver. X 80.
P, Portal vein; H, hepatic artery; B, bile-duct,
drickson.)
(Hen-
bounded by hepatic cells on all sides, and are thus separated from the nearest
blood capillary by at least the breadth of one cell, figures 271 and 272.
The gall-bladder, g. bl, figure 269, is a pyriform sac attached to the under
surface of the liver, and supported also by the peritoneum. The larger end,
or fundus, projects beyond the front margin of the liver, while the smaller
end contracts into the cystic duct. It is a muscular walled reservoir covered
with a serous epithelium and lined by mucous membrane. The function
of the gall-bladder is to retain the bile during the interval of digestion.
The Bile. The bile is a somewhat viscid fluid, of a yellow, reddish-
yellow, or green color, a strongly bitter taste, and, when fresh, with a scarcely
perceptible odor; it has a neutral or slightly alkaline reaction, and its specific
gravity is about 1020. Its color and consistency vary much, quite independent
THE BILE 341
of disease; but, as a rule, bile becomes gradually more deeply colored and
thicker as it advances along its ducts, or when it remains long in the gall-
bladder where it becomes more viscid and ropy, darker, and more bitter. This
is on account of its greater degree of concentration, from resorption of its
water, and also from being mixed with mucus.
CHEMICAL COMPOSITION OF HUMAN BILE. (FRERICHS.)
Water 859.2
Solids — Bile salts 91.5
Fat 9.2
Cholesterin 2.6
Mucus and coloring matters 29 .8
Salts 7.7
Bile salts can be obtained as colorless, exceedingly deliquescent crystals,
soluble in water, alcohol, and alkaline solutions, giving to the watery solution
the taste and general characters of bile. They consist of sodium salts of gly-
cocholic and taurocholic acids; the formula of the former being C26H42NaNO6,
and of the latter C26H44NaNO7S.
The bile acids are easily decomposed by the action of dilute acids or alkalies thus:
C26H43NO6 + H2O = C2H5NO2 -f C24H4oO6
Glycocholic Acid. Glycin. Cholic Acid.
and C26H45NO7S + H2O = C2H7NO3S -f C24H4oO5
Taurocholic Acid. Taurin. Cholic Acid.
Glycin is amido-acetic acid, i.e., acetic acid C2H4O2, with one of the atoms of H re-
placed by the radical amidogen NH2C2H3(NH2)O2, C2H5NO2. Taurin likewise is
amido-isethionic acid. Isethionic acid is sulphurous acid H2SO3, in which an atom of
H is replaced by the monatomic radicle oxy-ethylene, C2H4OH, viz., H(C2H4OH)SO3,
and in amido-isethionic acid, the OH hydroxyl in this radicle is replaced by amidogen NH2,
thus H(C2H4NH2)SO3 = C2H7NSO3. The proportion of these two salts in the bile of
different animals varies, e.g., in the ox bile the glycocholate is in great excess, whereas the
bile of the dog, cat, bear, and other carnivora contains taurocholate alone. In human bile
the glycocholate is in excess (4.8 to 1.5).
The yellow coloring matter of the bile of man and the Carnivora is termed
Bilirubin, C16H18N2O3, is crystallizable and insoluble in water, and soluble in
chloroform or carbon disulphide. A green coloring matter, Biliverdin, C16Hlg-
N2O4, which always exists in large amount in the bile of Herbivora, is formed
from bilirubin on exposure to the air, or by subjecting the bile to any other
oxidizing agency, as by adding nitrous acid. Biliverdin is soluble in alcohol,
glacial acetic acid, and strong sulphuric acid, but insoluble in water, in chloro-
form, and ether. It is usually amorphous, but may sometimes crystallize in
green rhombic plates.
There is a close relationship between the coloring matters of the blood
and of the bile, and it may be added, between these and that of the urine,
342 FOOD AND DIGESTION
urobilin, and of the feces, stercobilin. It is probable they are, all of them,
varieties of the same pigment, or derived from the same source. Cholesterin,
C27H45OH, and lecithin, C42H84NPO9 are constant constituents of bile. Iron
is found among the salts of the ash.
FIG. 273. — Crystalline Scales of Cholesterin.
The Role of Bile in Intestinal Digestion. Though it is not a true
digestive fluid, in that it has no ferment and digests nothing itself, yet it must
be regarded as an important aid to digestion for the following reasons: (a) Bile
assists in emulsifying the fats of the food, and thus renders them capable of
passing into the lacteals by absorption. For it has appeared in some experi-
ments in which the common bile-duct was tied, that, although the process
of digestion in the stomach was unaffected, chyle was no longer well formed;
the contents of the lacteals consisting of clear, colorless fluid, instead of being
opaque and white, as they ordinarily are after feeding. It is, however, the
combined action of the bile with the pancreatic juice to which the emulsifica-
tion is due rather than to that of the bile alone. The bile itself has a very
feeble emulsifying power. If the theory be accepted that fats are absorbed
as fatty acids and soaps, in solution, the action of the bile becomes very im-
portant because solutions of bile salts have the power of dissolving the fatty
acids. The moistening of the mucous membrane of the intestines with bile,
for this very reason, facilitates absorption of fatty matters through it.
(b) The bile, like the gastric fluid, has a certain but not very considerable
antiseptic power, and may serve to prevent the decomposition of food during
the time of its sojourn in the intestines. Experiments show that the contents
of the intestines are much more fetid after the common bile-duct has been
tied than at other times. Moreover, it is found that the mixture of bile with
a fermenting fluid stops the process of fermentation.
Bile is also an excretive fluid carrying waste products thrown off by the
liver. The liver during fetal life is proportionately larger than it is after
birth, and the secretion of bile is active, although there is no food in the in-
testinal canal upon which it can exercise any digestive property. At birth,
MODE OF SECRETION AND DISCHARGE OF BILE 343
the intestinal canal is full of concentrated bile, mixed with intestinal secretion,
and this constitutes the meconium, or feces of the fetus. In the fetus, therefore,
the main purpose of the secretion of bile must be directly excretive. Probably
all the bile secreted in fetal life is incorporated in the meconium, and with it
discharged.
Mode of Secretion and Discharge of Bile. The secretion of bile
is continually going on, but is retarded during fasting, and accelerated on
taking food. This is shown by tying the common bile-duct of a dog, and estab-
lishing a fistulous opening between the skin and gall-bladder, whereby all the
bile secreted is discharged at the surface. When the animal is fasting, some-
times not a drop of bile is discharged for several hours. In about ten minutes
after the introduction of food into the stomach, the bile begins to flow abun-
dantly, and continues to do so during the period of digestion.
The bile is constantly being formed in the hepatic cells; thence, being dis-
charged into the minute hepatic ducts, it passes into the larger trunks, and
from the main hepatic duct may be carried at once into the duodenum. This
probably happens only while digestion is going on, i.e., for five to seven hours
after the introduction of food into the stomach. During fasting, it flows from
the common bile-duct through the cystic duct into the gall-bladder, where it
accumulates till, in the next period of digestion, it is discharged into the intes-
tine. The gall-bladder thus acts as a reservoir for the bile during the intervals
when digestion is not in progress.
The mechanism by which the bile passes into the gall-bladder is simple.
The orifice through which the common bile-duct communicates with the
duodenum is narrower than the duct, and appears to be closed, except when
FIG. 274. — Transverse Section through Four Crypts of Lieberkiihn, from the Large Intestine
of the Pig. They are lined by columnar epithelial cells, the nuclei being placed in the outer part
of the cells. The divisions between the cells are seen as lines radiating from L, the lumen of the
crypt; G, epithelial cells, which have become transformed into goblet cells. X 350. (Klein and
Noble Smith.)
there is sufficient pressure behind to force the bile through it. The pressure
exercised upon the bile secreted during the intervals between periods of diges-
tion appears insufficient to overcome the force of the sphincter by which the
orifice of the duct is closed; and the bile in the common duct traverses the
344
FOOD AND DIGESTION
cystic duct and so passes into the gall-bladder, being probably aided in this
retrograde course by the peristaltic action of the ducts. The bile is discharged
from the gall-bladder and enters the duodenum on the introduction of food
into the small intestine. It is pressed on by the contraction of the coats of
the gall-bladder, and of the common bile-duct. Their contraction is excited
by the stimulus of the food in the duodenum acting through a reflex arc to
produce contractions, the force of which is sufficient to open the orifice of the
common bile-duct.
When the discharge of the bile into the intestine is prevented by an ob-
struction of some kind, as by a gall-stone blocking the hepatic duct, it is reab-
FIG. 275. — Longitudinal Section of Fundus of Crypt of Lieberkiihn. b, Goblet cell showing
mitosis; e, epithelial cell; k, cell of Paneth; /, leucocyte in epithelium; m, mitosis in epithelial cell.
Surrounding the crypt is seen the stroma of the mucous membrane. X 530. (Kolliker.)
sorbed in great excess into the blood, and, circulating with it, gives rise to
the well-known phenomena of jaundice. This is explained by the fact that the
pressure of secretion in the ducts, although normally very low, not exceeding
15 millimeters of mercury in the dog, is still higher than that of the portal
veins. If the pressure exceeds 15 mm. the secretion continues to be formed
but passes into the blood-vessels through the lymphatics.
The Intestinal Secretion, or Succus Entericus. It is impossible to
isolate the secretion of the glands of Brunner or of the glands of Lieberkiihn,
but the total secretion of the intestinal mucosa can be secured by isolating a
loop of intestine by the operation known as the Thiry fistula. A few drops
DIGESTIVE CHANGES IN THE SMALL INTESTINE 345
of secretion, the succus entericus, can be obtained by this means. Intestinal
juice is a yellowish alkaline fluid with a specific gravity of ion and con-
tains about 2.5 per cent of solid matters.
Intestinal juice has only slight digestive action. It contains a weak pro-
teolytic enzyme and a weak amylolytic enzyme. Maltase is also present. But
the chief and most profound importance is given to the intestinal juice by the
discovery of the activating enzyme, enterokinase. This specific activating
enzyme for the trypsinogen of the pancreatic juice places the intestinal secre-
tion in the rank of necessary secretion for efficient digestion. Enterokinase
can be prepared by extracting the superficial scrapings of the intestinal mucous
coat. The duodenal region is richest in enterokinase, but the secretion of the
lower intestinal lengths also contains the enzyme.
Extracts of the mucosa of the intestine have been found to contain another
substance which has the specific action of splitting peptones into simpler
amino bodies. This substance has been called erepsin.
There are, therefore, three important new substances in the succus en-
tericus (or in the extract of the glands), secretin, erepsin, and enter -okinase,
in addition to the proteolytic and diastatic enzymes.
Summary of the Digestive Changes in the Small Intestine. The
thin chyme which, during the whole period of gastric digestion, is being con-
stantly squeezed or strained through the pyloric orifice into the duodenum,
consists of albuminous matter that is broken down, dissolving and half dis-
solved; of fatty matter broken down and melted, but not dissolved at all;
of starch in various stages of the process of conversion into sugar, and as
it becomes sugar dissolving in the fluids with which it is mixed; while with
these are mingled gastric juice and fluid that has been swallowed, together
with such portions of the food as are not digestible.
The chyme in the duodenum is subjected to the influence of the bile and
pancreatic juice and also to that of the succus entericus. All these secretions
have a more or less alkaline reaction, and neutralize the acid of the gastric
chyme.
The special digestive changes in the small intestine are: (i) The fats are
changed by the bile and pancreatic juice in two ways, (a) They are chemically
decomposed by the alkaline secretions, and a soap and glycerin are the result.
(b) They are emulsified, i.e., their particles are minutely subdivided and dif-
fused, so that the mixture assumes the condition of a milky fluid or emulsion.
(2) The albuminous substances which have been partly dissolved in the stomach
are subjected chiefly to the action of the pancreatic juice. The pepsin is
rendered inert by the bile. The pancreatic trypsin proceeds with the fur-
ther conversion of the proteoses into peptones, and part of the peptones
(hemipeptones) into leucin, tyrosin, and other amino bodies. (3) The starchy
portions of the food are now acted on briskly by the pancreatic juice and
the succus entericus, and are changed to maltose and dextrose. (4) Salines
346 FOOD AND DIGESTION
and other soluble matters, such as common salt, are usually in a state of
solution before they reach the intestine.
Digestive Changes in the Large Intestine. The changes which take
place in the chyme in the large intestine are probably only the continuation
of the same changes that occur in the course of the food's passage through
the upper part of the intestinal canal. No special enzymes have been clearly
shown for the mucous membrane of the large intestine. The enzymes of the
small intestine may continue their action here, being hindered only by the
acid developed from fermentation processes.
Action of Micro-organisms in the Intestines. Certain changes
take place in the intestinal contents independent of, or at any rate supple-
mental to, the action of the digestive ferments. These changes are brought
about by the action of micro-organisms or bacteria. We have indicated else-
where that the digestive ferments are examples of unorganized ferments, so
bacteria are examples of organized ferments. Organized ferments, of which
& c «
I ' !
o°°,
SJ
0,
FIG. 276. — Types of Micro-organisms, a, Micrococci arranged singly; in tW9s, diplococci —
if all the micrococci at a were grouped together, they would be called staphylococci — and in fours,
sarcinse; b, micrococci in chains, streptococci; c, and d, bacilli of various kinds, one is represented
with flagellum; e, various forms of spirilla; /, spores, either free or in bacilli.
the yeast plant may be taken as a typical example, consist of unicellular vege-
table organisms, which when introduced into a suitable medium grow with re-
markable rapidity. By their growth they produce new substances from those
supplied to them as food. Thus, for example, when the yeast cell is introduced
into a solution of grape-sugar, it grows, and alcohol and carbon dioxide are
produced. These substances probably arise from the formation by the cell ac-
tivity of some chemical substances which are allied to the unorganized ferments
and which greatly increase in amount with the multiplication of the original
cell. In all such fermentative processes organisms analogous to the yeast cell
are present, and it is not strange that if the ferment cell is introduced into a
suitable medium it may by its rapid growth convert an unlimited amount of
one substance into another. Speaking generally, a special variety of cell is
concerned with each ferment action, thus one variety has to do with alcoholic,
another with lactic, and another with acetous fermentation.
THE FECES 347
A considerable number of species of bacteria exist in the body during life,
chiefly in connection with the mucous membranes, particularly of the digestive
tract. Many forms of bacteria have been isolated from the mouth, a few
varieties from the stomach, and a very large number from the intestines. It
is only in the last-named locality that their multiplication has much effect from
a physiological point of view. The normal (hydrochloric-acid) acidity of the
stomach usually destroys all the micro-organisms taken in with the food, but
when the amount of this acid is deficient (and sometimes even when it is nor-
mal) some of the spores may escape. On reaching the small intestine these
spores begin to develop in its alkaline medium, and may increase to such an
extent as to stop all intestinal digestion; the point where this occurs varies
from day to day. The large intestine always swarms with micro-organisms,
though they do not readily pass the ileo-cecal valve into the small intestine.
The bacteria found in the intestine are anaerobic, i.e., they do not develop in
the presence of free oxygen.
The changes induced in the intestine by the activity of micro-organisms
are of two kinds, fermentation and putrefaction; the former of these results
in the breaking down of carbohydrate matter, and the latter in the disintegra-
tion of proteid matter. The process of fermentation is the less complex and
probably occurs normally in the small intestine to a certain extent. The lactic-
acid fermentation is the most important, though the butyric-acid fermentation
is next; under their influence the carbohydrates are broken down into lactic
and butyric acids, and perhaps into acetic acid also. Carbonic acid gas may
be formed at the same time and cause flatulence. Cellulose and other in-
soluble carbohydrates are decomposed, with the formation of marsh gas
and hydrogen, which escape by the rectum.
In putrefaction the process is similar to that in tryptic digestion, the pro-
teids being broken down into peptones, leucin, tyrosin, and a long row of similar
substances. It also results in the production of various gases, such as carbon
dioxide, sulphureted hydrogen, ammonia, hydrogen and methane (marsh
gas), and of a high percentage of the volatile fatty acids, valerianic and butyric.
Of the aromatic substances the most important are indol and skatol, though
their toxicity has been greatly overestimated. Some undergo oxidation, indol
and skatol forming indoxyl and skatoxyl; they are usually carried off in the
feces, but when the bowel is obstructed they are absorbed and eventually
appear in the urine, indoxyl and skatoxyl forming respectively indoxyl- and
skatoxyl-sulphuric acids and their salts. Tyrosin is further broken down
into para-oxy-phenol-propionic acid, paracresol, and phenol; para-oxy-phenol-
acetic acid is also formed. Experiments have been performed to determine
whether or not the intestinal bacteria are neccessary to normal digestion. The
weight of evidence is in favor of the view that they are not.
The Feces. The contents of the large intestine, as they proceed
toward the rectum, become more and more solid, lose more liquid and nutrient
348
FOOD AND DIGESTION
parts, and gradually acquire the odor and consistency characteristic of jeces.
After a sojourn of uncertain duration in the sigmoid flexure of the colon, or
in the rectum, they are finally expelled by the act of defecation. The average
quantity of solid matter evacuated by the human adult in twenty-four hours
is about 200 to 250 grams, but the amount and character vary exceedingly ac-
cording to the food eaten. Vegetable foods contain much indigestible matter,
while meats and meat diets leave very little unabsorbed material to be ex-
pelled in the feces.
TABLE OF COMPOSITION OF FECES.
The amount of water varies considerably, from 68 to 82 per cent and
upward. The following table gives about an average composition:
Water
Solids, comprising:
a. Insoluble residues of the food, uncooked starch, cellulose,
woody fibers, cartilage, horny matter, mucin, seldom mus-
cular fibers and other proteids, fat, and cholesterin ......
b. Certain substances resulting from decomposition of foods,
indol, skatol, fatty and other acids; calcium and mag-
nesium soaps .....................................
c. Special excretions, — Excretin, excretoleic acid (Marcet),
and stercorin (Austin Flint) ..........................
d. Salts, — Chiefly phosphate of magnesium and phosphate
of calcium, with small quantities of iron, soda, lime, and
silica ............................................
e. Insoluble substances accidentally introduced with the food
f. Mucus, epithelium, altered coloring matter of bile, fatty
acids, etc .........................................
g. Varying quantities of other constituents of bile and secre-
tions . . ...............
733-°°
267.00
Intestinal Gases. Under ordinary circumstances, the alimentary ca-
nal contains a considerable quantity of gases. The presence of gas in the
0000006
FIG. 277. — Diagram Illustrating the Segmentation of the Food in the Small Intestine. (Cannon.)
intestines is so constant and the amount in health so uniform that there can
be no doubt that its existence is a normal condition.
The gas contained in the stomach and bowels is from air swallowed with
MOVEMENTS OF THE INTESTINES
349
either food or saliva, gases developed by the decomposition of foods, or of the
secretions and excretions thrown into the intestines. The decomposition of
foods is the chief source. The following table, compiled by Brinton, is a col-
lection of analyses that have been made and is chiefly valuable as showing
the kinds of gases present:
GASES FOUND IN THE ALIMENTARY CANAL.
Composition
by Volume
Whence obtained.
Oxygen.
Nitrog.
Carbon.
Acid.
Hydrog.
Carburet.
Hydrogen.
Sulphuret.
Hydrogen.
Stomach
ii
71
14
4
Small intestines
32
3O
38
"|
Cecum
67
12
8
1 3
1
i
Colon
•} e
r i
6
8
}- Trace.
Rectum
46
42
1 1
1
Expelled per anum. . . .
—
22
40
19
!Q
)
°-5
The amounts of the gases vary with the diet.
An analysis of the intestinal gases (Ruge, copied by Halliburton) in man
is as follows:
Gases.
Milk Diet.
Meat Diet.
Vegetable Diet.
Carbon dioxide .....
9 to 1 6
8 to 13
21 to 34
Hydrogen
43 to ?4
0.7 to •?
1.5 to 4
Carbureted hydrogen
0.9
26 to 37
44 to ZZ
Nitrogen
36 to -?8
45 to 64
10 to 19
The carbon dioxide arises from the carbonates and lactates in food, from
fermentation and putrefaction of carbohydrates and proteids, and from
butyric-acid fermentation.
The hydrogen is derived from butyric- and lactic-acid fermentations, and
carbureted hydrogen comes from the decomposition of acetates and lactates
and from cellulose. The nitrogen is derived from the swallowed air.
MOVEMENTS OF THE INTESTINES.
The muscular activity of the intestines accomplishes two important func-
tions, i.e., it thoroughly mixes the digesting food and secretions and it carries
the content along the tract. Intestinal peristalses have been described for a
long time. These peristalses begin as contractions of the circular muscles,
producing ring-like constrictions that are propagated as waves over the intestine
350 FOOD AND DIGESTION
from above downward. Such constrictions carry the intestinal contents
forward. The longitudinal muscles by their contraction produce pendular
motion of the intestine.
A most instructive contribution to the knowledge of intestinal movements
has been made by Cannon. He fed cats food mixed with 10 to 33 per cent of
subnitrate of bismuth, and observed the shadows of the food when subjected
to the Roentgen rays. A length of food in the intestine was seen to be con-
stricted into a series of oval masses, figure 277. Each of these oval masses is
quickly constricted in the middle, and neighboring halves of adjacent masses
flow together. After this process is repeated a number of times a peristaltic
wave of the type previously described sweeps the whole content of the loop
down the intestinal tract.
Peristaltic contractions of the same general type as in the small intestine
also occur in the large intestine. Cannon has noted a variation here, also. The
ascending and the transverse loops of the colon exhibit rhythmic antiperistalses
which keep the content moving against the ileocecal valve for several minutes
at a time. From time to time strong general contractions, in the cecum and
ascending colon, force some of the food onward. When material has accumu-
lated in the transverse colon, deep successive tonic constrictions appear and
force its contents into the descending colon. When sufficient material has ac-
cumulated here, it is evacuated by strong peristalses combined with compres-
sion by the contracting abdominal muscles.
Reverse or antiperistalsis does not commonly occur in the small intestine,
but large nutrient enemata introduced into the rectum and colon may be forced
by antiperistaltic waves in the large intestine to and through the ileocecal
valve into the small intestine. Here they are treated in the same way as food
which has been introduced in the normal way.
Influence of the Nervous System on Intestinal Peristalsis. As in
the case of the esophagus and stomach, the peristaltic movements of the in-
testines may be directly set up in the muscular fibers by the presence of food
acting as the stimulus. Few or no movements occur when the intestines are
empty. The intestines are connected with the central nervous system both
by the vagi and by the splanchnic nerves, as well as by other branches of the
sympathetic which come to them from the celiac and other abdominal plexuses.
The relations of these nerves respectively to the movements of the intestine
and the secretions are probably the same as in the case of the stomach already
considered.
The vagus fibers are described as the motor fibers for the intestine, while
the sympathetic are said to be at least in part inhibitory. Various states of the
central nervous system, such as fear, anger, etc., inhibit the intestinal move-
ments. The intestine carries out peristalses when isolated from the body so
that the central connections do not originate, but are only regulative. The
intestinal movements are essentially automatic, depending on the rhyth-
SALIVA AND SALIVARY DIGESTION 351
mic property of the muscle itself but coordinated by the complex local nervous
mechanism.
The innervation of the large intestine is also double in character and
the relations are doubtless the same as in the small intestine.
Defecation. The emptying of the rectum is essentially an involun-
tary act which has acquired a certain amount of voluntary regulation. The
act is accomplished wholly reflexly in dogs with isolated lumbar cord, in fact
has been observed when the lumbar spinal a rd was removed. In the latter
case defecation occurs by automatic peristalsis of the rectum, while in the
former cases reflexes through the lumbar cord carry out the act. The stimulus
of the feces against the rectum and the internal sphincter initiate the movement.
Normally in man the rectal stimulus gives rise to the consciousness of
the desire to defecate and the initiation of efferent nerve impulses that may
increase the contraction of the external sphincter and inhibit the act tempo-
rarily. During defecation, however, the voluntary effort leads to relaxation of
the external sphincter, and the normal peristalsis of the rectum is supported
by contractions of the abdominal musculature so as greatly to increase the
abdominal pressure, thus aiding the involuntary reflex.
LABORATORY EXPERIMENTS IN DIGESTION.
I. SALIVA AND SALIVARY DIGESTION.
1. Reflex Salivary Secretion. Saliva, which is the mixed secretion
of the salivary and buccal glands, is produced more or less intermittently. Ex-
amine, taste, or smell appetizing food, for example, an apple, the salivary glands
begin to discharge secretion which is poured into the mouth more rapidly
than under ordinary conditions. This increased activity is a reflex secretion.
It is brought about by the stimulation of sensory structures which lead to
afferent nerve impulses reacting on nerve centers in the medulla to cause
secretory nerve impulses to the glands. The stimulating effect of food in the
mouth causes the most rapid reflex secretion, which may last through several
minutes, or even hours. Especially stimulating substances are, beside food,
such substances as tartaric acid, lemon juice, ether, alcohol, etc., in fact any-
thing that produces strong local irritation will lead to reflex secretion.
2. The Secretory Nerves of the Salivary Glands of the Dog. The
nervous mechanism for the salivary gland is well known, and the anatomical
relations are such as to make this gland a favorable one for studying the nerv-
ous mechanism of glands in general.
Anesthetize a dog and bind it to a suitable holder. Expose the nerves to
the submaxillary gland as follows: cut through the skin of the lower jaw along
the inner border for about 3 inches. Isolate and double ligate the jugular
vein and any other veins in the field except the ones coming from the sub-
352 FOOD AND DIGESTION
maxillary gland. Isolate and cut the digastric muscle, also the mylo-hyoid,
using pains not to injure the duct of the gland or its arteries. When the
muscles are laid back, the artery and accompanying sympathetic nerve
branches, the hypoglossal and the lingual nerves, the submaxillary duct and
the submaxillary gland, will all be exposed. Isolate and introduce a very
fine glass cannula into the submaxillary duct. A small nerve filament
branches from the lingual nerve and runs to the hilus of the gland, the chorda
tympani. Carefully expose the chorda, place a silk ligature under it for con-
venience in handling. Also expose the sympathetic filaments with the artery.
Stimulate the chorda tympani with a mild induction current for a few
minutes at a time at intervals, and note that the secretion which is absent
or forming slowly before stimulation now gathers quickly and leaves the end
of the cannula in a series of drops. Collect the saliva in a small beaker. One
can measure the rate of flow by collecting the saliva in a small graduated
cylinder, or, by changing the beaker every ten minutes, making a record of the
quantity of secretion formed. Stimulate the sympathetic fibers, cutting the
hypoglossal nerve if necessary, and note that the secretion is very slightly in-
creased, but the increase lasts for only a few minutes. If the sympathetic
fibers are stimulated before the chorda, then the sympathetic secretion is
relatively less than if the order of stimulation is reversed.
During stimulation of the nerves, note the relative flow of blood through
the organ. During chorda stimulation the flow is increased; during sympa-
thetic stimulation it is decreased, as these nerves contain vaso-dilator and
vaso-constrictor fibers, respectively.
3. Microscopic Changes in the Gland Cells. Make a histological
preparation (by any standard method of fixing and staining) of the submaxil-
lary gland of the cat, a, taken after a period of several hours' fasting when
the gland cells may be assumed to be at rest; and 5, immediately after a period
of activity (from eating, or activity secured by the stimulation of the chorda
tympani) and note: a, The cells from the resting gland are relatively larger,
the nuclei are pushed back against the basement membrane, they have
sparsely sustaining protoplasm, and the cells are crowded with large gran-
ules, which in a fortunate preparation fill the entire cell. The outlines of the
cells are relatively indistinct and the lumen of the gland is small. Z>, The cells
of the active gland are relatively small, the nuclei are centrally placed, the
protoplasm stains more definitely, the granules are usually present but limited
to the side of the cell next to the lumen, the outlines of the cells are distinct,
and the lumen is often quite large.
4. The Chemical Composition of Saliva. Collect several cubic cen-
timeters of saliva as follows: Wash the mouth thoroughly with water, then
induce secretion of saliva by chewing a bit of paraffin or a piece of thoroughly
washed rubber. The inhalation of ether vapor will often facilitate the reflex
secretion. One should avoid strong acids to induce secretion unless their
DIGESTIVE ACTION OF SALIVA ON STARCH 353
presence is to be taken into consideration afterward. Make the following
tests:
Reaction. A slip of neutral litmus paper when introduced into freshly
collected saliva, or for convenience simply taken into the mouth during sali-
vary secretion, shows an alkaline reaction.
Mucin. To 3 or 4 c.c. of saliva add 2 per cent acetic acid drop by drop
until distinct acidity is obtained. On stirring the saliva with a glass rod a
sticky mucin makes its appearance.
Potassium Sulphocyanide. To 2 c.c. of saliva in a test tube add 2 or 3
drops of ferric-chloride solution, slightly acidulated with hydrochloric acid,
a reddish-brown coloration indicates the presence of potassium sulphocyanide.
One should run a blank test on distilled water for comparison.
Chlorides. Add silver nitrate to 2 c.c. of saliva after first removing the
proteids. A white, cloudy precipitate, which disappears on adding ammonia
and reappears on adding nitric acid, indicates the presence of chlorides.
Proteids. Remove the mucin from a sample of saliva, as above, and test
by the characteristic proteid reactions. A faint trace of proteid can usually
be demonstrated.
5. Digestive Action of Saliva on Starch. Review the test for starch,
dextrin, and dextrose, as preparation for an identification of these prod-
ucts of salivary digestion. To 50 c.c. of i per cent starch paste in the
water bath at 40° C. add 5 c.c. of saliva, and mix thoroughly with a glass rod.
Immediately begin two series of tests: a, for the presence of starch; b, for
the presence of reducing sugar. The tests for starch can be made by adding
to 3 drops of starch, on a porcelain plate, an equal quantity of dilute iodine
in potassium iodide solution. Use a glass rod. Make the tests every 2 minutes
for 20 minutes. The tests for reducing sugar are best made by placing 2 c.c.
of Fehling's solution in each of a series of test tubes and adding, at intervals
of 5 minutes, i c.c. from a dropping-pipet and boiling. If the tests are set
away as fast as they are prepared, a reddish-yellow cuprous oxide will settle
out, and the series will give a rough comparison as to the quantity of reducing
sugar present.
In the first series the deep blue of the starch reaction quickly changes
to a reddish-blue, a red, a reddish-brown, until finally no change in color
other than that produced by the mixture of the iodine occurs, showing that
the starch has passed the second stage of erythro-dextrin in its disappearance.
The indication of reducing sugar in the second series shows that this erythro-
dextrin has been transformed into reducing sugar, and also that the amount
of sugar is greatly increased during the progress of the test.
6. The Influence of Temperature on Salivary Digestion. Prepare
three test tubes, a, b, c, containing 4 c.c. each of saliva. Boil a, place b in
a water bath at 40° C., and place c in ice water. After c has been cooled down
to the temperature of the ice bath add to each 2 c.c. of i per cent starch solu-
23
354
FOOD AND DIGESTION
tion and mix. At intervals of 2 to 5 minutes test these 3 samples for the dis-
appearance of starch and appearance of reducing sugar, as in experiment 5.
No change will take place in a; b will be quickly digested; and the digestion
in c will be slight or suspended. Upon placing c in a warm bath digestion will
quickly occur.
7. Influence of Acids and Alkalies on Salivary Digestion. To
each of 5 test tubes, a, b, c, d, e, add 5 c.c. of saliva. Leave a for the normal;
make b strongly alkaline; c exactly neutral; d acid to the extent of 0.2 to 0.3 per
cent hydrochloric acid; e strongly acid. Place all in the water bath at 40° C.
Add to each 2 c.c. of i per cent starch paste and mix. Test for starch and for
reducing sugar at intervals of 20 minutes and compare, noting the results
in the following table:
A
B
C
D
E
Prepare and set
in water bath
at 40 C.
5 c.c. saliva
5 c.c. saliva
and
i c.c. strong
KOH
5 c.c. saliva
exactly
neutralized
5 c.c. saliva
and
i c.c. 0.2 per
cent hydro-
chloric acid
5 c.c. saliva
and
i c.c. strong
hydrochlo-
ric acid
Then add . ...
2 c.c. i per
2 c.c. i per
2 c.c. i per
2 c.c. i per
2 c.c. i per
cent starch
cent starch
cent starch
cent starch
cent starch
Test for starch
and sugar im-
mediately.
After 20 minutes.
After 40 minutes.
The results obtained in the experiments 5, 6, and 7 show that starch is
converted into reducing sugar, and furthermore that the conditions for its
conversion indicate that the change is accomplished by an amylolytic enzyme
which in this case is called ptyalin.
8. The Action of Ptyalin is Favored by the Removal of the End
Products. Place 50 c.c. of 2 per cent starch paste in a dialyzing tube or
paper, suspend in a beaker of running water. Take 50 c.c. of the same solution
in a beaker, to each add 2 c.c. of saliva and mix thoroughly. Test for the dis-
appearance of starch at intervals of 20 minutes. The starch in the dialyzing
tube will disappear first because the reducing sugar passes out through the
dialyzer, while in the beaker it is retained and hinders the further action of
ptyalin.
GASTRIC DIGESTION
355
II. GASTRIC JUICE AND GASTRIC DIGESTION.
9. The Secretion of Gastric Juice. The conditions which influence
gastric secretion can be readily observed on the dog with a gastric fistula.
Take a dog which has had a gastric fistula prepared some weeks before and
which is in a condition of hunger, place him in a holder with a cup suspended
to collect the gastric juice, and exhibit before the dog some fresh meat or
other food which he enjoys, but do not allow him to eat it. After teasing the
animal for 5 or 10 minutes, an abundant flow of gastric juice will begin. Paw-
low calls this the psychic secretion.
If an esophageal fistula has also been performed on the animal the dog
may be allowed to eat the meat, of course swallowing it out of the esophageal
FIG. 278. — Operation on the Stomach to Form an Isolated Pouch with Nerves Intact. S,
Isolated sac; V, cavity of stomach; A, A, opening at the abdominal wall.
fistula back into the- plate. In this experiment an abundant flow of gastric
secretion takes place and may continue for an hour or more.
If a gastric pouch has been performed by Pawlow's method, the animal
may be allowed to eat the food, swallowing it into the stomach. In this case
the reflex secretion just described takes place as usual, but is followed after
an hour or an hour and a half by a second increase in the quantity of secretion.
This second increase has been ascribed to the reflexes originating in the
stomach, possibly from the reflex stimulating action of the digestive products
themselves.
10. Composition of Gastric Juice. Test a sample of gastric juice
obtained from a gastric fistula, as follows:
Reaction. Gastric juice is strongly acid. Test for free hydrochloric acid
356 FOOD AND DIGESTION
as follows: Gastric juice turns congo-red to a blue color. Organic acids pro-
duce violet. Gastric juice plus 0.5 per cent alcoholic solution of dimethyl-
amido-azobenzol develops a cherry-red color, a reaction that is given by free
hydrochloric acid. Combined hydrochloric acids and organic acids do not give
the color. Giinzburg's reagent, consisting of 2 per cent phloroglucin and i
per cent vanillin in 80 per cent alcohol, produces a rose-colored mirror
on porcelain in the presence of free hydrochloric acid. The test is very
delicate.
Proteids. The usual proteid tests can be applied to gastric juice and show
that it contains small quantities.
11. Artificial Gastric Juice. An active principle, pepsin, of gastric
juice can be obtained by extracting the gastric mucous membrane of the
dog, pig, etc. Scrape off the mucous membrane, grind it to a fine pulp by
repeatedly running it through a sausage machine, or by pounding in a mortar
with clean sand. The mucous membrane should be allowed to stand for
three or four hours before extraction, otherwise the zymogen, and not the
enzyme, will be obtained. Extract a portion of this gastric pulp in water, and
filter. Or extract with glycerin for several weeks and filter. Either of these
extracts contains the enzyme. A solution of the glycerin extract in 0.2 per
cent hydrochloric acid contains all the properties of gastric juice. This is
known as artificial gastric juice.
Commercial pepsin already prepared can be obtained on the market.
Artificial gastric juice is made from commercial pepsin by adding 3 to 5 grams
to a liter of 0.2 per cent hydrochloric acid.
12. Digestive Action of Gastric Juice, or Artificial Gastric Juice.
The digestive action of gastric juice is limited to proteids. Shreds of fibrin
which permit the gastric juice to come in intimate contact with all parts of
the material, form the best proteid for testing the action of this enzyme.
Prepare a series of test tubes, a, b, c, d, each containing 5 c.c. of artificial
gastric juice. Add to a some shreds of fibrin; to b some boiled white of an egg;
to c some fibers of boiled meat; to d some fibers of raw meat; place in a warm
bath at 40° C. and examine at intervals of 20 minutes. Tabulate the results
by the plan indicated in experiment 13, noting particularly the rapidity with
which the proteid goes into solution.
13. Conditions Affecting the Enzyme Action of Gastric Juice.
Prepare a series of test tubes containing 5 c.c. each of gastric juice, according
to the table on the following page. Add a definite quantity of fibrin to each
and note the changes at intervals of 20 minutes.
14. Cleavage Products of Gastric Digestion. Add 5 to 10 grams
of fibrin to 100 c.c. of artificial gastric juice in a flask and place in a
water bath at 40° C. After one hour filter off 40 c.c. Exactly neutralise this
filtrate with i per cent potassium hydrate. A precipitate makes its appearance,
and can be collected on the filter paper, washed with distilled water, and dis-
ACTION OF RENNIN
357
solved in i per cent dilute hydrochloric acid, acid albumin. Test for the pro-
teid reactions.
After two hours filter the remaining 60 c.c., exactly neutralize to remove
any traces of acid albumin, and filter. The filtrate contains proteoses. Con-
centrate the filtrate over a water bath to one-fourth its volume, add an equal
quantity of saturated ammonium-sulphate solution, a sticky precipitate of
primary proteoses separates out. Collect on a filter paper, wash with half-
saturated ammonium sulphate, redissolve in very dilute salt-solution, and
test for proteid reactions. The primary proteoses are precipitated by nitric
acid.
To the filtrate from the half -saturated ammonium sulphate add crystals of
ammonium sulphate until complete saturation with salt. Deutero-albumoses
A
B
C
D
E
Prepare
5 c.c. gas-
tric juice at
5 c.c. neutral
gastric juice
5 c.c. alka-
line gastric
5 c.c. boiled
gastric juice
5 c.c. gastric
40° 'C.
at 40° C.
juice at 40° C.
at 40° C.
juice at o° C.
Then add
Fibrin
Fibrin
Fibrin
Fibrin
Fibrin
Note after 20
minutes.
After 40 minutes.
After 60 minutes.
separate out. Collect on a filter paper, wash, dissolve, and test for proteids.
The secondary proteoses are not precipitated by nitric acid.
Finally the filtrate contains peptone. It can be isolated and tested by
concentrating over the water bath, adding barium hydrate to slight excess
to remove the sulphate, filtering, and precipitating the excess of barium by
exact neutralization with i per cent sulphuric acid. Test for proteid reac-
tions. Peptone gives a rose color in the biuret reaction. The xanthoproteic
reaction gives the color change, but not the usual precipitate. Peptone is re-
dissolved from its alcoholic precipitate without change. It is dialyzable.
15. Action of Rennin. Add a solution of commercial rennin (jun-
ket powder), or of the extract of gastric mucous membrane of the fourth
stomach of a calf, to 5 c.c. of milk and let stand for a few minutes. Repeat
the test with artificial gastric juice. Also with neutral gastric juice. In each
case the milk will form a jelly-like clot, which is firmer in the test tube contain-
ing commercial rennin. In the test tube containing artificial gastric juice,
358 FOOD AND DIGESTION
the milk is first coagulated, then slowly dissolved or digested. This clotting
is due to the special coagulating enzyme, rennin.
III. PANCREATIC JUICE AND PANCREATIC DIGESTION.
1 6. The Secretion of Pancreatic Juice. If a dog containing a pan-
creatic fistula made by Pawlow's method is available, then try the experi-
ment of feeding the animal and noting the rate of secretion of pancreatic
juice through a period of two hours. When the gastric digestion has proceeded
to the point where the acid chyme may be supposed to have entered the duo-
denum, then a sharp increase in the flow of pancreatic juice takes place. This
increased activity will last through a period of two or three hours or more.
It is produced either by nerve reflexes (Pawlow) or by the influence of the
secretion produced by the gastric mucous membrane when stimulated by acid.
17. Influence of Secretin on the Rate of Secretion. Make an ex-
tract of the intestinal mucous membrane, preferably from the duodenum,
by scraping off the membrane, grinding it to a pulp, and extracting it over a
water bath in 0.2 per cent hydrocholoric acid, and filtering.
Anesthetize a large dog, open the abdomen, isolate the pancreatic duct,
introduce a cannula, and arrange for the collection of pancreatic juice. Intro-
duce a cannula into the saphenous vein and connect it with a buret containing
the extract of secretin already prepared. Inject 5~c.c. quantities of the secretin
solution into the vein at intervals of ten minutes. Measure the rate of secretion
of pancreatic juice by counting the drops per minute, or if the secretion is
rapid enough, by collecting it at intervals of five or ten minutes and measuring
it in a graduated pipet.
This method will often yield enough pancreatic juice in the course of a
couple of hours to make the pancreatic experiments which follow. Bayless
and Starling call it secretin juice.
1 8. Chemical Characters of Pancreatic Juice. Test the reaction,
proteid, salt, etc., content of the sample of pancreatic juice collected in the
last experiment.
19. Artifical Pancreatic Juice. Artificial pancreatic juice can be
prepared from the pancreas by grinding and macerating and extracting a
pancreas with water or glycerin, as described for the gastric glands in experi-
ment ii above. Commercial preparations of pancreatic enzyme can be ob-
tained on the market. A solution of glycerin extract of pancreatic gland or
of commerical pancreatin in 0.2 per cent sodium carbonate is known as arti-
ficial pancreatic juice.
20. The Enzymes of Pancreatic Juice. The pancreatic juice con-
tains enzymes which have exerted a digestive action on starches, fats, and
proteids. This fact can be tested as follows : a, To 5"c.c. of artificial pancreatic
juice add 2 c.c. of i percent starch paste, mix and set in the water bath at 40° C.
ACTION OF THE ENZYMES OF PANCREATIC JUICE
359
b, To i c.c. of pancreatic juice (artificial juice is not active), collected in experi-
ment 17, add 0.5 c.c. of neutral olive oil, and place over a water bath, c, To 5 c.c.
of artificial pancreatic juice add a few flocks of fibrin. Test the digestive
action on starch by the iodine test for the disappearance of starch, or by the
copper-reduction test for the presence of reducing sugar. Test the fat by its
reaction, noting that the neutral or slightly alkaline solution has become acid,
also by the fact that an emulsion has been formed. Note that the proteid
has gone into solution.
The digestive action on starch is due to the enzyme amylopsin, or pan-
creatic diastase, as it is sometimes called. The fat-splitting effect is due to the
enzyme lipase, and the solution of the fibrin is accomplished by the proteolytic
enzyme, trypsin.
21. Conditions which Influence the Action of the Enzymes of
Pancreatic Juice. To each of 5 test tubes, a, b, c, d, e, add 5 c.c. of
artificial pancreatic juice. Place a, b, c, d in the water bath at 40° C., and e
into an ice bath. Leave a normal, make b exactly neutral, add to c i c.c. of 2
per cent hydrochloric acid, and boil d. Add to each tube 2 c.c. of i per cent
starch paste. Follow the digestive changes by the tests previously outlined.
Tabulate according to the following scheme:
A
B
C
D
E
Take
5 c.c. pan-
creatic
Neutralize
5 c.c. pan-
5 c.c. pancre-
atic juice and
i c.c. of 2 per
5 c.c. pan-
creatic
5 c.c. pan-
creatic
juice 40° C.
creatic juice
40° C.
cent hydro-
chloric acid
40° C.
juice and
boil.
juice at o° C.
Then add
2 c.c. of
starch
2 C.C. Of
starch
2 C.C. of
starch
2 C.C. Of
starch
2 C.C. Of
starch
Note after 20
minutes.
After 40 min-
utes.
After 60 min-
utes.
-
Repeat this experiment with a second set of test tubes containing fibrin.
Lipase is not very active in artificial pancreatic juice and may be omitted.
If pancreatic juice is available make a third set containing fat.
22. Cleavage Products of Pancreatic Digestion. To 200 c.c. of arti-
360 FOOD AND DIGESTION
ficial pancreatic juice add 25 grams of moist fibrin and place in a water bath
at 40° C., add 7 c.c. of chloroform to prevent putrefactive changes. After three
or four hours filter off 80 c.c. and place the remainder on the water bath for
two or three days. Test the filtrate for alkali albumin, albumoses, and pep-
tones, by the method outlined in experiment 14 above.
Filter the second portion and concentrate to a syrupy mass on the water
bath. Crystals make their appearance. Pour off the fluid, wash the crystals
with cold water, and examine under the microscope for sheaves of tyrosin.
The filtrate contains leucin.
If the digestion had been allowed to proceed without the chloroform,
bacteria would have appeared in the solution, and proteid cleavage products,
due to their action, would be found, notably indol.
IV. BILE AND INTESTINAL JUICE.
23. Bile. Secure bile from the gall-bladder of a pig or dog, or, if
it is possible, a sample of human bile. Test the reaction which, in fresh
bile, is neutral. Test for mucin; albumin; and for iron; hydrochloric acid
and ferrocyanide of potassium give a blue color when iron is present.
Bile Salts. Evaporate 10 c.c. of bile to complete dryness, mix with animal
charcoal, add 50 c.c. of absolute alcohol, filter; add an excess of ether to the
filtrate, which gives a white precipitate of bile salts. Crystals will form on
standing in a well-stoppered flask for a day or two.
Bile Acids. A drop of syrup of cane-sugar in a test tube of bile forms a
deep red-purple color at the line of separation from concentrated sulphuric
acid. Furfur aldehyde with cholalic acid gives the color.
Bile Pigments. With i c.c. of bile in a test tube strong nitroso-nitric
acid produces a play of colors beginning with green, blue, red, and yellow—
Gmelin's test.
Bile does not contain digestive enzymes, but the bile wets the mucous
surface of the intestine and facilitates the solution of fats and fatty acids.
24. Intestinal Juice. The secretion of the mucous membrane
of the small intestine has been proven to have a weak digestive action on pro-
teids and perhaps on starches. It can be obtained from an intestinal fistula.
Its chief digestive importance consists in the presence of the activating enzyme,
enterokinase. Enterokinase can be prepared by extracting the mucous mem-
brane of the small intestine by the method outlined for making a pancreatic
extract.
To two test tubes containing 5 c.c. of artificial pancreatic juice, or pref-
erably containing secretin pancreatic juice, add flocks of fibrin. Keep one
for the control, to the other add 2 c.c. of enterokinase solution. The test tube
containing enterokinase will digest more rapidly and more effectively than
the other.
CHAPTER IX
ABSORPTION
ABSORPTION in its restricted use means the process by which the digested
foods pass through the walls of the alimentary canal and into the circulation.
In its more general meaning absorption is the process by which substances
pass from one part of the body to another by means other than the blood-
and lymph-vessels. Usually the absorption takes place from a free surface,
such as the alimentary canal, the skin, and the lungs.
The alimentary canal is lined throughout with a continuous layer of epi-
thelial tissue. This layer is only a single cell thick in most of its extent,
but nevertheless it effectively separates the food inside the canal from the
lymph in the tissue interspaces on the outside of the mucous membrane.
These spaces are separated from the blood in the adjacent blood-vessels by a
second continuous layer, the endothelial walls of the capillaries. The food,
therefore, in its absorption, must pass through two layers of tissue to reach
the blood stream. But the submucous lymphatic spaces and vessels furnish
channels which may carry substances into the blood by way of the thoracic
duct. The mucous membrane is, therefore, the one strict barrier through
which the food must pass in the act of absorption.
The exact methods by which absorption takes place have long been a
subject of controversy and of research. But this problem is of such diffi-
culty that it is yet, in the main, unsolved. Known physical and chemical
laws were thought to explain the facts of absorption. Some of the known
physical factors concerned in absorption and elimination have already been
considered in a former chapter, osmosis and diffusion, Chapter IV. A third
factor, filtration, consists in the passage of a fluid under pressure through a
membrane. These factors undoubtedly play an important role in the passage
of solutions through the alimentary mucous membrane and the walls of the
blood-vessels. The part which the physical factors play is probably more
pronounced in the absorption of water and crystalloids. The nature of the
fluid within the digestive tract, and the movements of the walls of the stomach
and intestines by means of which the material to be absorbed is brought
into intimate contact with the absorbing membrane, are additional factors
which influence absorption.
But the mechanical and physical factors do not fully explain the observed
facts of absorption. It becomes more and more evident that there is an
361
362 ABSORPTION
unexplained factor bound up in the characteristics of the living protoplasm
of the epithelial cells themselves. When isotonic blood serum is introduced
into the intestine the salts and water are at once absorbed, also the albumins,
but more slowly. In this experiment the osmotic conditions are in balance
and the pressure is greater on the side of the blood-vessels, so that absorption
takes place with the actual expenditure of energy. The important fact
here is that the absorption through a living membrane is influenced by the
membrane in ways that we cannot yet explain. It is this factor which de-
termines the different rate of absorption and the so-called selective absorp-
tion in different regions of the alimentary canal.
As a rule, the current of absorption is from the stomach or intestine into
the blood; but the reversed action may occur, as, for example, when sulphate
of magnesium is taken into the alimentary canal. In this case there is a
rapid discharge of water from the blood-vessels into the canal. The rapidity
with which matters may be absorbed and diffused through the textures of
the body has been found by experiment. It appears that lithium chloride
may be diffused into all the vascular textures of the body, and into some
of the non-vascular, as the cartilage of the hip joint, as well as into the aque-
ous humor of the eye, in a quarter of an hour after being given by way of the
mouth and on an empty stomach. Lithium carbonate, when taken in five-
or ten-grain doses on an empty stomach, may be detected in the urine in
five or ten minutes; or, if the stomach be full at the time of taking the dose,
in twenty minutes.
Absorption in the Mouth. The epithelial lining of the mouth is
of the thicker stratified type and the conditions are otherwise unfavorable
for absorption. Little, if any, absorption normally takes place in the mouth,
and the same is true for the esophagus.
Absorption in the Stomach. The mucous and sub mucous coats of
the stomach, see figure 258, are well supplied with blood-vessels and lym-
phatics. The mucous membrane is, however, so crowded with the peptic
glands that the relative amount of absorbing surface is small. It is limited
to the mucous membrane around the mouths of the glands.
Recent experiments have shown that though absorption does take place
in the stomach, it is not as active as was formerly supposed, even in the case
of water. Von Mering has found that water begins to pass from the stomach
into the intestine almost as soon as it is swallowed, and that very little of it
is absorbed from the stomach. Of 500 c.c. given by the mouth to a large
dog with a duodenal fistula, only 5 c.c. were absorbed in 25 minutes, the
rest having passed into the intestine. Peptones, sugars, and salts are ab-
sorbed in the stomach, but only to a limited extent. Peptones are not ab-
sorbed in appreciable amount unless present to as much as 5 per cent or
more. Examination of the mucous membrane during the stage of active
digestion has revealed the presence of albumoses. Sugars, like peptones, are
ABSORPTION IN THE INTESTINES
absorbed by the stomach only to a slight extent in the weaker solutions,
but are readily absorbed when the more concented solutions are introduced
into the stomach, five per cent and over (von Mehring). Fats are not absorbed
at all in the stomach. Even salts in the stomach are not readily absorbed
until this concentration is from three to four times that of the blood. This
fact is in direct opposition to the popular views on the subject.
While some absorption does take place in the stomach it is evidently not
of any great importance under normal conditions. The presence of alcohol
has been shown to increase the amount of absorption, and pepper, mustard,
and such drugs as produce mild local irritation accomplish the same result.
Absorption in the Intestines. The products of digestion are all
absorbed in the small intestine, as is abundantly shown by experiments.
'•
FIG. 279. — Scheme of Blood-vessels and Lymphatics of Human Small Intestine, a, Central
lacteal of villus; b, lacteal; c, stroma; d, muscularis mucosae; e, submucosa; /, plexus of lymph-
vessels; g, circular muscle layer; h, plexus of lymph- vessels; *', longitudinal muscle layer; /, serous
coat; k, vein; /.artery; m, base of villus; n, crypt; {o, artery of villus; p, vein of villus; g, epithe-
lium. (Mall.)
Absorption from the small intestine has been studied in the human subject
in the case of a patient who had a fistulous opening in the lower part of the
ileum. For example, 85 per cent of the proteid of a test meal was absorbed
before the food reached the fistuh. The food passes slowly down the length
364
ABSORPTION
of the small intestine, and the digestive changes produce a series of cleavages
which have known osmotic and diffusion properties. The question has been
to determine which of the cleavage products are most favorable for absorp-
tion and the details of the mechanism.
The mucous membrane of the small intestine possesses special structures
for absorption, the villi. Each villus projects as a finger-like process into
the lumen of the intestine. Its single-layered covering of epithelial cells
supported by a connective-tissue framework brings a relatively large extent
Lymphatic of head and
neck, right
Right internal jugular vein
Right subclavian vein
Lymphatics of right arm
Receptaculum chyli
Lymphatics of lower extrem-
ities
Lymphatics of head and
neck, left
Toracic duct
Left subclavian vein
Thoracic duct
Lacteals
Lymphatics of lower ex-
tremities
FIG. 280. — Diagram of the Principal Groups of Lymphatic Vessels. (From Quain.)
of surface into contact with the digesting food, which is thus separated from
a loop of capillaries and lymphatic radicals.
The capillaries of the villus are connected with the veins which contribute
to the portal vein, hence carry blood to the liver. The lacteals of the villus
contribute to the mesenteric lacteal system, hence the chyle and lymph pass
through the mesenteric glands and the portal duct to the subclavian vein
in the neck. There are thus two routes by which absorbed foods may reach
the general circulation. These paths can be independently isolated; and a
ABSORPTION OF PROTEIDS FROM THE INTESTINES
365
study of the composition of their discharge during active absorption con-
tributes to our knowledge of the course taken by the different absorption
products.
Absorption of Proteids from the Intestines. Proteid is absorbed
chiefly in the small intestine, though just exactly how cannot at present be
affirmed. In the preceding chapter the cleavage products of proteid diges-
FIG. 281.
FIG. 282.
FIG. 281. — Superficial Lymphatics of the Forearm and, Palm of the Hand, J.— 5; Two small
glands at the bend of the arm; 6, radial lymphatic vessels; 7, ulnar lymphatic vessels; 8, 8,
palmar arch of lymphatics; 9, 9', outer and inner sets of vessels; b, cephalic vein; d, radial
vein; e, median vein; /, ulnar vein. The lymphatics are represented as lying on the deep fascia.
(Mascagni.)
FIG. 282. — Lymphatic Vessels of the Head and Neck and the Upper Part of the Trunk. (Mas-
cagni.) $. — The chest and pericardium have been opened on the left side, and the left mamma de-
tached and thrown outward over the left arm, so as to expose a great part of its deep surface. The
principal lymphatic vessels and glands are shown on the side of the head and face, and in the neck,
axilla, and mediastinum. Between the left internal jugular vein and the common carotid artery,
the upper ascending part of the thoracic duct marked i, and above this, and descending to 2, the
arch and last part of the duct. The termination of the upper lymphatics of the diaphragm in the
mediastinal glands, as well as the cardiac and the deep mammary lymphatics, is also shown.
366
ABSORPTION
tion have been discussed. It was shown there that albumoses, peptones,
peptids, and the amido-acids are derived from the proteids as digestion
products. It has, in the past, been assumed that peptone represents the
form most freely absorbed. No peptone has, however, been isolated from
the blood or lymph on the vascular side of the epithelial membrane. But
the same may be said with equal truth of the other cleavage products. The
present supposition is that the proteids are taken up by the epithelium and
synthesized into other and more complex forms before being discharged
into the blood; or that the digestion cleavages are further broken down in
FIG. 283. — A Small Portion of Medullary Substance from a Mesenteric Gland of the Ox. d, d,
Trabeculae; a, part of a cord of glandular substances from which all but a few of the lymph-cor-
puscles have been washed out to show its supporting meshwork of retiform tissue and its capillary
blood-vessels (which have been injected and are dark in the figure); b, b, lymph-sinus, of which
the retiform tissue is represented only at c, c. X 300. (Kolliker.)
the liver into elimination forms, such as urea, ammonium carbonate, etc.
If the intestinal epithelium produces change in the proteid on its passage
through, then it is evident that absorption of proteids is more than mere
osmosis and filtration. This idea is further strengthened by the known
power of the intestines to absorb certain albumins, egg albumin for example,
which is non-diffusible and non-dialyzable.
In animal foods, such as eggs, meat, etc., it is estimated that about 98 per
cent of the proteid is absorbed; whereas in vegetable foods, where the pro-
teid is often protected from the action of the digestive enzymes, there may
be 10 to 15 per cent loss. Analysis of the total lymph discharge of the thoracic
duct fails to show any increase of proteids during active digestion, from which
it is inferred that proteids pass by way of the liver.
ABSORPTION OF CARBOHYDRATES BY THE INTESTINES 367
From 12 to 15 per cent of the proteid remains in the food as it passes the
ileocecal valve. This amount, less the loss in the feces, is absorbed in the
large intestine.
Absorption of Carbohydrates by the Intestines. Carbohydrates
are broken down to dextrose, levulose, etc., and are absorbed as such. Even
the soluble cane-sugar is split by the invertase of the intestine into the mono-
saccharides, dextrose and levulose. Starch is the source of most of the 500
grams of dextrose absorbed in an average diet per day. During the absorp-
tion of a carbohydrate meal the percentage of dextrose in the blood of the
portal vein is increased over the normal which is o.i to 1.5 per cent. This
excess of dextrose passes through the liver and is temporarily stored in the
FIG. 284. — Section of the Villus of a Rat Killed during Fat Absorption, ep. Epithelium; sir, stri-
ated border; c, lymph-cells; c', lymph-cells in the epithelium; /, central lacteal containing disinte-
grating lymph-corpuscles. (E. A. Schafer.)
liver cells as glycogen. In the case of a fistula in the receptaculum chyli,
the chyle contained less than a half per cent of the total dextrose absorbed.
Experiments on the rate of absorption of the different sugars seem to
indicate that their absorption does not follow known physical laws and that
we must assume an unknown chemical factor in the living protoplasm.
Dextroses are absorbed readily by the large intestine.
Fermentation process from bacterial growth produces certain acids from
the carbohydrates, chiefly in the large intestine. These are readily absorbed.
Absorption of Fats by the Intestines. Fats reach the absorbing
epithelium in two forms, as soluble glycerin and soaps and as finely emulsi-
fied fats. The first two are taken up by the epithelium readily enough,
S68
ABSORPTION
but in the last the process of absorption is not so clear. It is comparatively
easy to demonstrate the presence of microscopic globules of fat, both in the
intercellular substance and in the epithelial cells themselves. But it has
been constantly noticed that there is a clear zone along the free borders of
the cells. Fat drops exist in the adjacent digesting mass, and in the deeper
parts of the cells, but not in this border zone. Since the demonstration of
the reversible action of lipase, the view has been strengthened that in the
very act of absorption the emulsified fats are decomposed and passed through
the cell border only to be resynthesized in the cell protoplasm. This is of
course against the strictly mechanical view. The decreasing efficiency of
fats when the bile, which wets the mucous surface and dissolves the fatty
acids, is withheld from the intestine also supports this view. As absorption
progresses the size of the fat drops in the epithelial cells increases, a fact
FIG. 285. — Mucous Membrane of Frog's Intestine during Fat Absorption, ep, Epithelium;
sir, striated border; C, lymph-corpuscles; /, lacteal. (E. A. Schafer.)
that is readily explained by supposing a continued synthesis and accumula-
tion of fat.
The fat drops are ultimately discharged into the connective-tissue spaces
and finally pass into the lymph channels, the thoracic duct, and into the
blood of the subclavian vein. This is the course taken by the larger per-
centage of the fat. However, some of the fat is absorbed into the capillaries
of the villi and passes through the liver. The presence of fat drops in the
liver cells at certain times can be ascribed to storage of this absorbed fat.
It is said that the more readily emulsified fats, those that melt readily at
the body temperature, are the more completely absorbed. The efficiency
of absorption is as high as 96 to 98 per cent for the oils, and decreases sharply
for such fats as the tallows.
The large intestine is capable of absorbing fats, though not so readily
as the small intestine.
Absorption of Minerals and Water in the Intestines. The salts
common in the foods are most of them readily soluble, dissociate quite com-
pletely in the dilute solutions, and diffuse and dialyze readily. Of the salts
of the foods, the sodium and potassium cations and chlorine anion are the
most readily dissociated and are most diffusible, while the calcium and
ABSORPTION FROM THE SKIN, THE LUNGS, ETC. 369
magnesium cations and the sulphate anion are least diffusible. These sub-
stances pass through the intestinal, epithelial cells and the intercellular sub-
stance; at least salts easily recognized by microchemical means have been
found in both localities during absorption. It seems probable that the
forces concerned are largely osmosis and diffusion.
Yet observers have not been able to show that the rate and character of
the absorption of even the salines obey the known physical laws. In fact
there is evidence that some of the salts, iron for example, are taken up as
organic compounds (hematogens of Bunge). The activity of the epithelial
cells is to be taken into account, even in the absorption of salts.
Water, which we have seen is not absorbed in the stomach, is readily
absorbed in the small intestine. Perhaps the bulk of the water taken into
the system is absorbed in the upper part of the small intestine. In the large
intestine, too, it is absorbed with facility and in considerable quantities.
The content of the bowel is still quite fluid when it enters the ascending colon,
but the feces are quite firm on discharge from the rectum. There are many
analogies by which we may suppose a controlling influence of the epithelium
over the process of water-absorption. Among the fishes there are species,
the salmon for example, in which the blood maintains a relatively constant
osmotic pressure, and therefore salt content. In the salmon this is about
the same as that of human blood. The blood is separated in the gills by
an extremely thin epithelium from the water in which the animals live, yet
these fishes go with impunity from sea water, with two and a half times more
salt than the blood, to fresh water with practically no salt at all. The epi-
thelium of the gills permits the passage of oxygen, but it does not permit
the diffusion or dialysis of the salts or the water in either direction. It is
possible that there is a certain amount of resistance to the passage of water
through the walls of the stomach, while the intestinal epithelium permits
water to pass readily.
The factors active in absorption are under searching investigation at the
present time, so that it is reasonable to hope that the near future will give
a more exact understanding of this intricate subject.
ABSORPTION FROM THE SKIN, THE LUNGS, ETC.
The dry corneous stratified epithelium covering the human body pos-
sesses great resistance to the absorption of most substances. The sebaceous
secretion keeps the surface slightly oily. Watery sclutions do not readily
wet the surface and therefore do not penetrate. There is some absorption
of water on prolonged contact with the skin, but the amount is insignificant.
Medicated baths, especially hot baths, may be accompanied by some slight
absorption of the substances dissolved in the waters; though it must be
confessed that the good effects of such treatment come from other sources.
24
370 ABSORPTION
On the other hand, oily substances come in more intimate contact with
the skin and penetrate deeper and more readily. Therefore lotions con-
taining medicines are occasionally applied to the skin, and slow but gradual
absorption occurs. The volatile oils penetrate the skin readily.
The epithelial lining of the lungs seems peculiarly adapted to the quick
absorption of all gases and volatile substances. This is illustrated by the
rapidity with which anesthesia may be accomplished by breathing the vapors
of ether or chloroform.
Solutions injected into or otherwise brought into contact with the sub-
dermal connective tissue, the body of a muscle, or the peritoneal or thoracic
cavity, very quickly pass into the general circulation. They are practically
injected into the lymphatic intercellular spaces in these instances and, of
course, are very readily carried through the lymphatic vessels, figures 280 and
282, to the thoracic duct and into the blood. -Comparing the rapidity of ab-
sorption in the cases mentioned, that from the muscle is most rapid, a fact
of medical importance in the use of the hypodermic needle for the giving
of medicines in emergency.
CHAPTER X
EXCRETION
EVERY substance taken into the body, in whatever form, must, in the
end, be cast off again, no matter how great the change that may be wrought
during its sojourn. We have already found that in the lungs the expired
air, and in the intestine the feces, carry from the body waste matters of no
further use. We have now to find that the urine separated by the kidney
and the sweat and sebum of the skin are likewise channels by which the
body throws off water, salts, and broken-down organic matters of no further
use to the organism. Of these two organs, the skin and the kidney, the
latter is by far the more important in so far as the quantity and complexity
of its secretion is concerned.
STRUCTURE AND FUNCTION OF THE KIDNEYS.
General Structure. The kidneys are. two in number, and are
situated deeply in the lumbar region of the abdomen on either side of the
spinal column behind the peritoneum. They correspond in position to the
last two dorsal and two upper lumbar vertebrae, the right slightly below
the left in consequence of the position of the liver on the right side of the
abdomen. They are about 4 inches long, 2^ inches broad, and i^ inches
thick. The weight of each kidney is about 4^ ounces, 140 grams.
On dividing the kidney into two equal parts by a section carried through
its long convex border, figure 286, the main part of its substance is seen to
be composed of two chief portions called respectively cortical and medullary,
the latter being also sometimes called pyramidal, from the fact of its being
composed of about a dozen conical bundles of uriniferous tubules, each bun-
dle forming what is called a pyramid. The upper part of the ureter, or duct
of the organ, is dilated into the pelvis ; and this, again, after separating into
two or three principal divisions, is finally subdivided into 8 to 12 smaller
portions, calyces, each of which receives the pointed extremity or papilla of
a pyramid. Sometimes, however, more than one papilla is received by a
calyx.
The kidney is a compound tubular gland. Both its cortical and its medul-
lary portions are composed essentially of numerous tubes, the tubuli urinijerit
371
372
FXCRETION
which begin at the opening on the Malpighian pyramid and, after a devious
course, end in the capsule of the glomerulus.
Tubuli Uriniferi. The tubuli uriniferi, figure 287, are composed
of a nearly homogeneous membrane, and are lined internally by epithelium.
They vary considerably in size in different parts of their course, but are,
on an average, about 40 fj. in diameter, and are found to be made up of several
distinct sections. The first section or part to be identified is the Malpi-
FIG. 286. — Longitudinal Section of Kidney through Hilum. a, Cortical pyramid; b, medullary
ray; c, medulla; d, cortex; e, renal calyx; f, hilum; g, ureter; h, renal artery; *, obliquely cut tubules
of medulla; / and k, renal arches; /, column of Bertini; m, connective tissue and fat surrounding
renal vessels; n, medulla cut obliquely; o, papilla; p, medullary pyramid. (Merkel-Henle.)
ghian, or Bowman's, capsule, figure 287. It is composed of a hyaline membrana
propria, thickened by a varying amount of fibrous tissue, and lined by flattened
nucleated epithelial plates. This capsule is the dilated extremity of the
uriniferous tubule which is invaginated to receive the glomerulus of con-
voluted capillary blood-vessels. The invaginated portion of the tubule is of
particular importance since it is the membrane through which a large part
of the urine is secreted. The glomerulus is connected with an efferent and
an afferent blood-vessel. The Malpighian capsule is connected by a con-
stricted neck, figure 287, N, with the proximal convoluted tubule. This forms
TUBULI URINIFERI
373
several distinct curves and is lined with short columnar cells. The tube
next passes almost vertically downward toward the medulla, forming the
spiral tubule, still within the cortex of the kidney, which is of much the same
diameter. The loop of Henle, L, in the medulla, is a very narrow tube lined
with flattened nucleated cells. Passing vertically upward from the loop of
LABYRINTH \MED.RAY\ LABYR.
Pelvit
FIG. 287. — Scheme of Uriniferous Tubule and of the Blood- vessels of the Kidney, Showing Their
Relation to Each Other and to the Different Parts of the Kidney. G, Glomerulus; BC, Bowman's
capsule; TV, neck, PC, proximal convoluted tubule; S, spiral tubule; D, descending arm of Henle's
loop; L, Henle's loop; A, ascending arm of Henle's loop; IDC, distal convoluted tubule; AC, arched
tubule; SC, straight collecting tubule; ED, duct of Bellini; A, arcuate artery, and V, arcuate vein,
giving off interlobular vessels to corte.x and vasa recta to medulla; a, afferent vessel of glomer-
ulus; e, efferent vessel of glomerulus; c\ capillary network in cortical labyrinth; s, stellate veins; vr,
vasa recta and capillary network of medulla. (Pearsol.)
Henle, the tubule varies somewhat in histological character, but the irregular
tubule and the distal convoluted tube, identical in all respects with the prox-
imal convoluted tube, are to be noted. The proximal convoluted tube
passes into the curved and straight collecting tubes, the latter running
vertically downward to the papillary layer, and, joining with other collecting
tubes, form larger ducts which finally open at the apex of the papilla. These
collecting tubes are lined with nucleated columnar or cubical cells.
374
EXCRETION
Renal Blood Supply. The renal artery divides into several branches
which pass in at the hilus of the kidney and are covered by a fine sheath
of areolar tissue derived from the capsule. They enter the substance of the
organ chiefly in the intervals between the papillae and at the junction between
the cortex and the boundary layer. The main branches then pass almost
horizontally, forming more or less complete arches and giving off branches
upward to the cortex and downward to the medulla. The former are for
the most part straight; they pass almost vertically to the surface of the kidney,
giving off laterally in all directions longer and shorter branches, which ulti-
FIG. 288. — From a Vertical Section through the Kidney of a Dog, the Capsule of which is Sup-
posed to be on the Right, a, The capillaries of the Malpighian capsule, the glomerulus, are arranged
in lobules; n, neck of capsule; c, convoluted tubes cut in various directions; b, irregular tubule:
d, e, and / are straight tubes running toward capsules forming a so-called medullary ray; d, collect-
ing tube; e, spiral tube; f, narrow section of ascending limb. X 380. (Klein and Noble Smith.)]
mately supply the glomerulus. The small afferent artery, figures 287, a,
290, d, which enters the Malpighian capsule, breaks up in the interior into
a dense convoluted and looped capillary plexus, which is ultimately gathered
up again into several small efferent vessels, comparable to minute veins,
which leave the capsule at one or more places near the point at which the
afferent artery enters it. On leaving, they do not immediately join other
small veins as might have been expected, but again break up into a second
set of capillary vessels which form an interlacing network around the urinif-
erous tubules. This second capillary plexus terminates in small veins
which, by union with others, help to form the radicles of the renal vein.
RENAL, BLOOD SUPPLY
375
These form venous arches corresponding to the arterial arches situated
between the medulla and cortex.
Thus, in the kidney, the blood entering by the renal artery traverses
two sets of capillaries before emerging by the renal vein, an arrangement
which may be compared to the portal system.
The tuft of vessels within the Malpighian capsule in the course of de-
velopment has been thrust into the dilated extremity of the urinary tubule,
which finally completely invests it. Thus within the Malpighian capsule
there are two layers of squamous epithelium, a parietal layer lining the cap-
sule proper, and a visceral or reflected layer immediately covering the vas-
cular tuft, figure 290, and sometimes dipping down into its interstices. This
FIG. 289. — Transverse Section of a Renal Papilla, a, Large tubes or papillary ducts; b, c.and
d, smaller tubes of Henle; e, f, blood capillaries, distinguished by their natter epithelium.
(Cadiat.)
reflected layer of epithelium is readily seen in young subjects, but cannot
always be demonstrated in the adult, figures 290 and 291.
The vessels which enter the medullary layer break up into smaller arte-
rioles, which form a fine arterial meshwork around the tubes of the papillary
layer and end in a similar plexus from which the venous radicles arise. The
vessels do not form a double set of capillaries.
Besides the small afferent arteries of the Malpighian bodies there are,
of course, others which are distributed in the ordinary manner, for the nutri-
tion of the different parts of the organ; and there are numerous straight
vessels, the vasa recta, in the pyramids between the tubes. Some of these
are branches of the vasa efferentia from Malpighian bodies, and therefore
comparable to the venous plexus around the tubules in the cortical portion,
while others arise directly as small branches of the renal arteries.
376
EXCRETION
Renal Nerves. Vaso-constrictor and vaso-dilator nerves are sup-
plied to the blood-vessels of the kidney, but no clearly denned secretory
nerves have yet been demonstrated for the organ. The vascular nerves
arise out of the anterior spinal roots (Bradford), chiefly the eleventh to the
FIG. 290.— Malpighian Capsule and Tuft of Capillaries, Injected through the Renal Artery
with Colored Gelatin, a, Glomerular vessels; b, capsule; c, anterior capsule; d, glomerular artery;
e, efferent veins; /, epithelium of tubes. (Cadiat.)
FIG. 291. — Diagrams Illustrating Stages in the Development of the Malpighian Capsule. In i
and 2 the developing blood-vessel is approaching the blind end of the capsule. In 3 the tubule is
beginning to invaginate and enclose the capillary. In 4 and 5 later stages are shown. The cells
forming the two layers of the capsule grow very thin. (Bailey.)
thirteenth dorsal nerves. They reach the kidney by way of the splanchnic
nerves and the renal plexus to the renal artery along which they run into
the substance of the kidney. Berkeley has demonstrated nerve plexuses
about the arterioles and around Bowman's capsule. Terminal knob-like
THE URETERS AND URINARY BLADDER 377
endings of nerve fibrils were shown. Some authors have claimed renal vaso-
constriction following vagus stimulation, but the fact seems not to be uni-
versally admitted.
The Ureters and Urinary Bladder. The duct of each kidney, the
ureter, is a tube about the size of a goose-quill and from twelve to sixteen
inches in length. It is continuous above with the pelvis of the kidney, and
ends below by obliquely perforating the walls of the bladder and opening
on its internal surface. It has three principal coats, an outer fibrous, a
middle muscular, of which the fibers are unstriped and arranged in three
layers. The fibers of the central layer are circular, and those of the other
two layers longitudinal in direction. It has an internal mucous lining con-
tinuous with that of the pelvis of the kidney above and the lining of the urinary
bladder below. The urinary bladder, which forms a receptacle for the tem-
porary lodgment of the urine in the intervals of its expulsion from the body,
is more or less pyriform. Its widest part, which is situated above and be-
hind, is termed the jundus; and the narrow constricted portion in front and
below, by which it becomes continuous with the urethra, is called its cervix
or neck. It is constructed of four principal coats: serous, muscular, areolar
or submucous, and mucous. The fibers of the muscular coat deserve special
mention. They are unstriped, are arranged in three principal layers, of
which the external and internal have a general longitudinal, and the middle
layer a circular, direction. The latter are especially developed around the
cervix of the organ, and are described as forming a sphincter vesicae. The
mucous membrane is provided with mucous glands, which are more numer-
ous near the neck of the bladder.
The bladder is well provided with blood- and lymph-vessels, and with
nerves. The latter are from the sacral plexus (spinal) and hypogastric
plexus (sympathetic). Ganglion-cells are found, here and there, in the
course of the nerve fibers.
THE URINE.
Quantity and General Properties. Healthy urine is a perfectly
transparent amber-colored liquid, with a peculiar but not disagreeable odor,
a bitterish salty taste, and a specific gravity of from 1020 to 1025. The urine
consists of water holding in solution certain organic and saline matters as its
ordinary constituents, and occasionally various other matters. Some of the
latter are indications of diseased states of the system, and others are derived
from unusual articles of food or drugs taken into the stomach.
The total quantity of urine passed in twenty-four hours is influenced
by numerous circumstances. In adults of average size and medium ac-
tivity the daily amount of urine may be given as from 1,200 c.c. to 1,500 c.c.
In Chittenden's recent observations on nine athletic students and on eight
3 78 EXCRETION
soldiers the average daily output of urine through a period of about five
months was for the students 1,215 c-c- witn average specific gravity of 1020,
and for the soldiers 1,042 c.c. with specific gravity of 1023.
GENERAL CHEMICAL COMPOSITION OF THE URINE.
Water 967
Solids:
Urea 14.230
Other nitrogenous crystalline bodies : -^
Uric acid, principally in the form of alkaline Urates, a trace
only free ( fi
Kreatinin, Xanthin, Hypoxanthin f
Hippuric acid
Mucus, Pigments, and ferments J
Salts:
Inorganic:
Principally Sulphates, Phosphates, and Chlorides of So-^j
dium and Potassium, with Phosphates of Magnesium
and Calcium, traces of Silicates ! R
Organic:
Lactates, Hippurates, Oxalates, Acetates, and Formates,
which appear only occasionally . J - 33
Sugar a trace sometimes.
Gases (nitrogen and carbonic acid principally).
Reaction. The normal reaction of the urine is slightly acid. This
acidity is due to carbonic acid and to acid phosphate of sodium, and is less
marked soon after meals. After standing for some time the acidity increases
from a kind of acid fermentation, due in all probability to the presence of
mucus and fungi, and acid urates or free uric acid is deposited. After a
time, varying in length according to the temperature, the reaction becomes
strongly alkaline from the change of urea into ammonium carbonate, due
to the presence of one or more specific micro-organisms (micrococcus urece).
In the process of fermentation the urea takes up two molecules of water, a
strong ammoniacal and fetid odor appears, and there are deposits of triple
phosphates and alkaline urates. This does not occur unless the urine is
freely exposed to the air, or, at least, until air has had access to it.
In most herbivorous animals the urine is alkaline and turbid. The
difference depends not on any peculiarity in the mode of secretion, but on
the difference in the food on which the two classes of animals subsist; for
when carnivorous animals, such as dogs, are restricted to a vegetable diet,
their urine becomes pale, turbid, and alkaline like that of herbivorous
animals, while the urine voided by the Herbivora, e.g., rabbits, fed for
some time exclusively upon animal substances, presents the acid reaction and
other qualities of the urine of Carnivora, and its ordinary alkalinity is again
restored only OP the substitution of a vegetable for the animal diet. Human
urine is not usually rendered alkaline by vegetable diet, but it becomes so
SPECIFIC GRAVITY OF URINE 379
after the free use of alkaline medicines, or of the alkaline salts with carbonic
or vegetable acids; for these latter are changed into alkaline carbonates
previous to elimination by the kidneys.
Specific Gravity of Urine. The average specific gravity of the human
urine is about 1020 to 1025. The relative quantity of water and of solid
constituents of which it is composed is materially influenced by the condition
and occupation of the body during the time at which it is secreted; by the
length cf time which has elapsed since the last meal; by the amount of water
taken; and by several other less important circumstances. The morning
urine is the best adapted for analysis in health, since it represents the simple
secretion unmixed with the elements of food or drink. If it is not used the
whole of the urine passed during a period of twenty-four hours should be
taken. The specific gravity of the urine may thus, consistently with health,
range widely on both sides of the usual average. It may vary from 1015
in the winter to 1025 in the summer; but variations of diet and exercise,
and many other circumstances, may make even greater differences than
these. The variations may be extreme in disease, sometimes decreasing
in albuminuria to 1004, and frequently increasing in diabetes, when the
urine is loaded with sugar, to 1050 or even to 1060.
AVERAGE DAILY QUANTITY OF THE CHIEF URINARY CONSTITUENTS. (MODIFIED FROM
PARKES.)
Per Kilo of
Body Weight.
2 3. oooo grams
0.8800
.5000
.0140
.0084
.0060
.1510
.0480
-0305
.1260
Water
-- 1,500. c.c.
Solids
72. grams
Urea
33 J8o
Kreatinin.
.910
Uric Acid
555
Hippuric
Acid
-400
Pigment and Extractives
IO.OOO
M
Sulphuric
Acid
2.012
'
Phosphoric Acid
3-l64
<
Chlorine. .
7.000
I
Ammonia
77°
1
Potassium
2.500
(
Sodium . .
11.090 "
Calcium. .
.260
1
207 "
Variations in the Constituents of Urine. Most of the constituents
are, even in health, liable to variations from the proportions given in the
above table. The variations of the quantity of water in different seasons,
and according to the quantity of drink and exercise, have just been men-
tioned. The water of the urine is also liable to be influenced by the condi-
tion of the nervous system, being sometimes greatly increased, e.g., in hysteria
and in some other nervous affections, and at other times diminished. The
increase in water may be either attended with an augmented quantity of
solid matter in some diseases, as in ordinary diabetes, or may be nearly the sole
380 EXCRETION
change, as in the affection termed diabetes insipidus. A febrile condition
almost always diminishes the quantity of water; and a like diminution is caused
by any affection which draws off a large quantity of fluid from the body
through any other channel than that of the kidneys, e.g., the bowels or the skin.
In disease or after the ingestion of special foods, various abnormal sub-
stances occur in urine, of which the following may be mentioned. Serum-
albumin, Globulin, Ferments (apparently present in health also), Proteoses,
Blood, Sugar, Bile acids and pigments, Casts, Fats, various Salts taken as
foods or as medicines, Micro-organisms of various kinds.
The Nitrogenous Substances in Urine. The nitrogenous waste prod-
ucts which are formed in the body in the metabolism of the proteid foods
are ultimately eliminated chiefly through the kidney, to some extent through
the bowel, and slightly through the skin. The total nitrogen in the urine
and in the feces multiplied by the factor 6.25 is a measure of the nitrogenous
FIG. 292. — Crystals of Urea.
foods, i.e., proteids, metabolized by the body. The nitrogen excreted in the
urine is in the form of urea 87.5 per cent, ammonia 4.3 per cent, kreatinin
3.6 per cent, uric acid 0.8 per cent, and undetermined forms 3. 73 per cent,
according to Folin. The total quantity of nitrogen eliminated in all these
forms per day is given as about 18 grams. In Chittenden's recent experi-
ments this quantity is reduced to as low as 6 grams or even less per day.
Urea. Urea, CON2H4, is the principal solid constituent of the urine,
forming nearly one-half of the total quantity. It is also the most important
ingredient, since it is the chief form in which the waste nitrogen which is
derived from proteid metabolism is excreted from the body.
Properties. Urea, like other solid constituents of the urine, exists in a
state of solution. When in the solid state, it appears in the form of delicate
silvery acicular crystals, which, under the microscope, are seen as four-
sided prisms, figure 292. It readily combines with some acids, like a weak
base, and may thus be conveniently procured in the form of crystals of nitrate
or oxalate of urea, figures 293 and 294.
THE FORMATION OF UREA 381
Urea is colorless when pure; when impure it may be yellow or brown.
It is without smell and of a cooling niter-like taste. It has neither an acid
nor an alkaline reaction, and deliquesces in a moist and warm atmosphere.
At 15° C. it requires for its solution less than its own weight of water. It is
soluble in all proportions of boiling water, and requires five times its weight
of cold alcohol for its solution. It is insoluble in ether. At 120° C. it melts
without undergoing decomposition; and at a still higher temperature ebulli-
tion takes place, and carbonate of ammonium sublimes.
Urea is decomposed by sodium hypochlorite of hypobromite or by nitrous
acid, with evolution of nitrogen. It forms compounds with acids, of which
the chief are urea hydrochloride, CON2H4.HCL; urea nitrate, CON2H4.-
HNO3; and urea phosphate, CON2H4.H3PO4. It forms compounds with
FIG. 293. — Crystals of Urea Nitrate. FIG. 294. — Crystals of Urea Oxalate.
metals such as HgO.CON2H4, with silver, CON2H2Ag2. Urea is isomeric
with ammonium cyanate, NH4CNO, and was first prepared artificially from
that substance.
The Formation of Urea. Proteids in the body have their nitrog-
enous moiety broken down to ammonia, by what Folin considers essentially
a series of hydrolytic cleavages, which is then built up into urea, as described
more fully in the chapter on Metabolism. This last step is essentially a
synthetic process which, from the fact that ammonium carbonate introduced
into the blood is eliminated as urea, may be supposed to occur as follows:
NH2 NH2
/ /
CO — H2O =CO
\ \
ONH4 NH2
Ammonium
Carbamate Urea
Urea is present in varying amounts in all organs and fluids of the body, as
shown by the following determinations of Schoendorff on the dog:
Per cent of
Organ. Urea.
Blood 0.116
Muscle 0.080
Kidney o. 670
Liver 0.112
Heart o. 173
Brain o. 128
Spleen 0.122
382 EXCRETION
It has been proven that the kidney does not form urea; in fact the kid-
neys may be removed from the body, and urea will continue to accumulate
in the blood. Urea is formed chiefly in the liver, but may in part be con-
structed in other organs, as described more fully on page 411. It follows
that the kidney is only the channel for the elimination of this nitrogenous
compound.
Decomposition of the urea with development of ammonium carbonate
takes place from the action of bacteria (micrococcus ureafi) when urine is
kept for some days after being voided, which explains the ammoniacal odor
then evolved. The urea is sometimes decomposed before it leaves the bladder,
when the mucous membrane is diseased and the mucus secreted by it is
abundant; but decomposition does not occur unless atmospheric germs have
had access to the urine.
Quantity Excreted. The quantity of urea excreted is, like that of the urine
Itself, subject to considerable variation. For a healthy adult about 30 grams
\ er day may be taken as rather a high average. Its percentage in healthy
urine is from 2 to 2.5. Its amount is materially influenced by diet, being
greater on a diet of high proteid content. The quantity of urea excreted
by children, relatively to their body-weight, is much greater than by adults;
thus the quantity of urea execreted per kilogram of weight was found to be,
in a child, 0.8 gram; in an adult only 0.4 gram. Regarded in this way, too,
the excretion of carbonic acid gives similar results, the proportions in the
child and adult being as 82 to 34.
Uric Acid. Uric acid, C5H4N4O3, is rarely absent from the urine
of man or animals, though in the feline tribe it seems to be sometimes entirely
replaced by urea. In birds and reptiles uric acid or its salts is the chief
form in which nitrogen is eliminated from the body.
Properties. Uric acid is a colorless, crystalline compound of the purin
group, figure 295. It is odorless and tasteless. It is very slightly soluble in
water, quite insoluble in alcohol and ether, and freely soluble in solutions
of the alkaline carbonates and other salts.
A study of the elimination of nitrogen in birds, i.e., geese, has shown that
uric acid, like urea in mammals, is formed largely in the liver from antecedent
proteid nitrogen. In man the elimination of uric acid increases or decreases
with the proteid content of the daily diet. It does not, however, follow the
variations of the food nitrogen so closely as in the case of urea. Any food
with a rich nuclein content increases the excretion of uric acid. This ob-
servation has led to the inference that uric-acid nitrogen is derived from
nuclear metabolism, page 413.
Other representatives of the purin group are adenin, guanin, xanthin,
hypoxanthin, etc. Chemically, caffeine from coffee is a trimethyl xanthin.
The most common form in which uric acid is deposited in urine is that
of a brownish or yellowish powdery substance, consisting of granules of
HIPPURIC ACID
ammonium or sodium urate. When deposited in crystals, it is most fre-
quently in rhombic or diamond-shaped laminae, but other forms are not
uncommon, figure 295. When deposited from urine, the crystals are gener-
ally more or less deeply colored, from being combined with the coloring
principles of the urine.
Hippuric Acid. This compound, C9H9NO3, has long been known
to exist in the urine of herbivorous animals in combination with soda. It
also exists naturally in the urine of man, in a quantity equal to or rather ex-
FIG. 295. — Various Forms of Uric Acid Crystals. FIG. 296. — Crystals of Hippuric Acid.
ceeding that of the uric acid. The quantity excreted is increased by a
vegetable diet.
Hippuric acid appears to be formed in the body from benzoic acid or
from some allied substance. The benzoic acid unites with glycin, and hip-
puric acid and water are formed thus:
C6H5.COOH + CH2.NH2.COOH = C6H5.CO.NH.CH2.COOH + H2O.
Benzoic Acid Glycin Hippuric Acid
Hippuric acid is the one substance which has been clearly demonstrated
to be formed by the kidney itself.
Kreatinin. This substance is present in urine in a remarkably
constant quantity, as shown recently by Folin's analyses. Its daily excre-
tion quantity is from i to 15 grams according to the amount of active tissue
in the individual. It is of especial importance as a measure of the metab-
olism of muscle protoplasm.
Ammonia. A considerable daily quantity of ammonia in com-
bination is found in the urine, showing that this is an important method of
nitrogen elimination.
Pigments. The pigments of the urine are the following: i, Uro-
chrome, a yellow coloring matter, giving no absorption band; of which
but little is known. Urine owes its yellow color mainly to the presence of
this body. 2, Urobilin, an orange pigment, of which traces may be found in
nearly all urines, and which is especially abundant in the urines passed by
384
EXCRETION
febrile patients. It is characterized by a well-marked spectroscopic ab-
sorption band at the junction of green and blue. Those who believe urobilin
to be identical with hydrobilirubin suppose that the bilirubin is reduced by
the putrefactive processes in the intestines, and is conveyed in its reduced
form by the blood stream to the kidneys. 3, Uroerythrin, occasionally found.
And, 4, Uromelanin.
Mucus. Mucus sediment in the urine consists principally of the
epithelial debris from the mucous surface of the urinary passages. Parti-
cles of epithelium, in greater or less abundance, may be detected in most
samples of urine, figure 297. As urine cools, the mucus is sometimes seen
suspended in it as a delicate opaque cloud, but generally it falls. In inflam-
FIG. 297.
FIG.
FIG. 297. — Urinary Deposit of Mucus, etc.
FIG. 298.— Urinary Sediment of Triple Phosphates (large prismatic crystals) and Urate of
Amonium, from urine which had undergone alkaline fermentation.
matory affections of the urinary passages, especially of the bladder, mucus
is secreted in large quantities and speedily undergoes decomposition.
Saline Matter. Sulphuric acid, in the form of salts, is taken in
very small quantity with food. Sulphur is also a constituent part of the
proteid molecule; hence its elimination, like that of nitrogen, gives a certain
measure of proteid metabolism. It is excreted as inorganic sulphates of
sodium and potassium, and as ethereal sulphates, compounds of phenol,
cresol, skatol, i.e., cresol sulphuric acid (C7H?OSO2OH), etc.
The phosphoric acid in the urine is combined partly with the alkalies,
partly with the alkaline earths — about four or five times as much with the
former as with the latter. In blood, saliva, and other alkaline fluids of the
body phosphates exist in the form of alkaline, neutral, or acid salts. In the
urine they are acid salts, viz., the sodium, ammonium, calcium, and magne-
sium phosphates, the excess of acid being (Liebig) due to the appropriation
of the alkali with which the phosphoric acid in the blood is combined, by the
several new acids which are formed or discharged at the kidneys, namely the
uric, hippuric and sulphuric acids, all of which are neutralized with soda.
OCCASIONAL CONSTITUENTS OF URINE 385
The phosphates are taken largely in both vegetable and animal food.
Some are excreted at once; others only after being transformed and incor-
porated with the tissues. Calcium and magnesium phosphates form the
principal earthy constituents of bone, and from the decomposition of the
osseous tissue the urine derives a quantity of this salt. The decomposition of
other tissues also furnishes large supplies of phosphorus to the urine, which
phosphorus is supposed, like the sulphur, to be united with oxygen, and then
combined with bases. The quantity is, however, liable to considerable
variation. The earthy phosphates are more abundant after meals, whether
of animal or vegetable food, and are diminished after long fasting. The
alkaline phosphates are increased after animal food, diminished after vegetable
FIG. 299. — Crystals of Cysttn, FIG. 300. — Crystals of Calcium Oxalate.
food. Phosphorus uncombined with oxygen appears, like sulphur, to be ex-
creted in the urine. When the urine undergoes alkaline fermentation phos-
phates are deposited in the form of a urinary sediment, consisting chiefly of
ammonio-magnesium phosphates (triple phosphate), figure 298.
The Chlorine of the urine occurs chiefly in combination with sodium.
Next to urea, sodium chloride is the most abundant solid constituent of the
urine. As the chlorides exist largely in food, and in most of the animal fluids,
their occurrence in the urine is easily understood.
Occasional Constituents of Urine. Cystin, C3H7NSO2, figure 299,
is an occasional constituent of urine. It resembles taurin in containing a
large quantity of sulphur — more than 25 per cent. It does not exist in
healthy urine.
Another common morbid constituent of the urine is Oxalic acid, which is
frequently deposited in combination with calcium, figure 300, as a urinary
sediment. Like cystin, but much more commonly, it is the chief constituent
of certain calculi.
Dextrose and albumin are sometimes present in pathological urine, and are
of particular interest from the clinical point of view. See the subject Gly-
cosuria, page 418.
25
386 EXCRETION
THE METHOD OF EXCRETION OF URINE.
The secretion of urine is an act the complexity of which can be profitably
discussed only after a clear understanding of three main factors which have
already been presented, viz., the chemical composition of the urine secreted,
the structure of the kidney tubule as a secreting organ, and, finally, the chemi-
cal composition of the blood which supplies the materials to the kidney for
the formation of the urine. The substances found in the urine are for the
most part also to be found in the blood-plasma. But the relative percentage
composition is very different. The amount of urea in the blood is only a
fractional part as concentrated as in the urine, while albumins and sugars,
which are so plentiful in the blood, are normally present in the urine only
in traces. The presence of the glomerulus with its special vascular supply,
and the different loops of the tubule, with its gland-like epithelial wall, would,
a priori, lead one to suspect special functions for each.
Theories of the Secretion of Urine. Bowman in 1842, wholly on
structural grounds, advanced a theory of urinary secretion which has more
recently been restated and given an experimental basis by Heidenhain. This
view as given by Heidenhain is as follows:
i, The secretion in the kidney depends upon the physiological activity of
special secreting cells which are of two kinds. 2, The first type of cell is
represented by the single layer of epithelium covering the glomerular capil-
laries. These cells secrete especially water and salts. 3, The second type of
cell is represented by the gland-like epithelial cells which form the convo-
luted tubules and the loop of Henle. These cells secrete the urea, uric acid,
and other specific constituents of the urine. 4, The activity of each kind of
cell is influenced by the chemical composition of the blood and by the flow
of blood through the kidney. 5, The relative secretory activity of the glomer-
ular cells and the tubule cells is sufficient to account for the variation in the
chemical composition of the urine.
Ludwig in 1844 advanced a strictly mechanical theory of urine secretion
based on his own experiments. He considered the glomerulus and Bowman's
capsule as a filtering apparatus in which substances present in the blood are
driven through the epithelium of the capsule into the renal tubule by the
positive pressure of the blood in the glomerular capillaries. This very dilute
urine in the capsule is supposed to be concentrated by the resorption of water
as it flows down the tubule. Ludwig originally considered this resorption of
water an imbibition process in which the greater saturation of salts in the
blood caused water to be taken up through the renal tubule walls, an osmotic
process. At present most observers who accept the view that filtration takes
place at the glomerulus explain the resorption of water down the tubules as
an act of cellular resorption or secretion.
Experimental Observations. There are numerous nerves to the
EXPERIMENTAL OBSERVATIONS 387
kidney, but no proven secretory influence has been shown. The variations
in the secretion of urine that follow nervous stimulation are quite satisfactorily
explained by the changes in the blood flow.
The kidney can be placed in an onkometer and its variation in volume
measured directly, figures 301 and 302. This volume measurement, when
taken with the arterial pressure, gives a very good index of the volume of
blood flowing through the kidney. Now when the kidney is inserted in an
onkometer and the urine collected from the ureter, it is found in general that
the greater the pressure and flow of blood the greater the secretion of urine,
as would follow if the glomerulus were a filtering mechanism. However, if
the renal vein is partially obstructed, even though the blood pressure be in-
creased, the amount of urine secreted is sharply decreased. If the vein is
FIG. 301. — Diagram of Roy's Onkometer. a Represents the kidney enclosed in a metal box,
which opens by hinge /; b, the renal vessels and ducts. Surrounding the kidney are two chambers
formed by membranes, the edges of which are firmly fixed by being clamped between the outside
and inside metal capsules (the latter not represented in the figure), the two being firmly screwed
together by screws at h, and on the opposite side. The membranous chamber below is filled with a
varying amount of warm oil, according to the size of the kidney experimented with, through the
opening then closed with the plug *'. After the kidney has been enclosed in the capsule, the mem-
branous chamber above is filled with warm oil through the tube e, which is then closed by a tap
(not represented in the diagram); the tube d communicates with a recording apparatus, and any
alteration in the volume of the kidney is communicated by the oil in the tube to the chamber d
of the Onkograph, figure 302.
completely occluded, the secretion of urine not only ceases for the time but
does not immediately begin again when the blood pressure and flow are re-
established. The closure of the vein for only one or two minutes is said to
stop the flow of urine for as much as forty-five minutes. This short inter-
ruption of the circulation is sufficient to bring about other changes in the
glomerular epithelium, for it now excretes albumin, which it did not previously
let pass. Therefore, it is not pressure merely that favors the secretion, but
there must be an efficient flow of blood. The secretion is influenced espe-
cially by the amount of blood flowing through the kidney in a given time.
388 EXCRETION
In the frog the kidney has a double blood supply. The renal artery
supplies the glomeruli, while a branch of the renal-portal vein supplies the
tubules. Nussbaum ligated the renal artery in one kidney of the frog, while
leaving the circulation of the other kidney undisturbed. He found that the
operated kidney secreted little or no urine, but that it could be made to secrete
by injections of urea, but not by injections of albumin or sugar as in the nor-
mal kidney. Ligation of the renal-portal vein, which supplies the tubules
in the frog, caused a decrease in the quantity of the secretion, whereas, accord-
ing to Ludwig's view, it ought to have increased the quantity, since obviously
resorption could not take place with any degree of efficiency. In the main,
the evidence is in favor of the view that even the glomerular epithelium does
FIG. 302. — Roy's Onkograph, or Apparatus for Recording Altera^ns in the Volume of the Kid-
ney, etc., as shown by the onkometer. a. Upright, supporting recording lever /, which is raised or
lowered by the needle b, which works through /, and which is attached to the piston e, working in
the chamber d, with which the tube from the onkometer communicates. The oil is prevented from
being squeezed out as the piston descends, by a membrane, which is clamped between the ring-
shaped surfaces of the cylinder by the screw * working upward ; the tube h is for filling the instru-
ment.
not filter merely, but that it, as living protoplasm, regulates and controls
the quantity and kind of material passing through it.
Micro-chemical observations have been enlisted to demonstrate more fully,
if possible, the activity of the differem parts of the epithelial tubule. Heiden-
hain, by injections of indigo-blue into the blood stream, followed by rapid
fixation of the kidney in alcohol at the proper stage of elimination, has de-
monstrated crystals of the pigment in the renal epithelial cells and in the
lumen of the tubule. He concluded that these cells were actively eliminating
the pigment by a secretory process. This observation has been questioned.
But Heidenhain's view is strengthened by Bowman's observation that in birds
crystals of uric acid are to be seen in the cells of the convoluted tubules, and
in the lumen adjacent.
Only traces of the sugars and proteids of the blood are found in normal
urine, but when either cane sugar, peptone, or egg albumin is introduced into
the blood it is rapidly eliminated by the kidney. Egg albumin is not essen-
DIURETICS 389
tially different from the serum albumin of the blood, but the serum albumin
is not excreted. These are both non-dialyzable compounds. Sugar and
urea, both readily dialyzable, present the same comparison, i.e., urea is ex-
creted, while sugar is not. If, however, the percentage of sugar is high, 0.25
per cent or more, it is then eliminated. The excretion of the highly diffusible
sodium chloride bears a similar quantitative relation to excretion. If present
in the blood in relatively low amounts it is not secreted, while if the concentra-
tion is slightly greater it may be quickly eliminated. Other inorganic salts,
present only in traces, are meanwhile rapidly eliminated. Even the rapid
elimination of a slight excess of water in the blood can scarcely be explained
on purely physical grounds. To discharge the water across the glomerulus
from the blood to the urine requires an expenditure of osmotic pressure much
greater than that balanced by the blood pressure. That is, the epithelial cells
must do work, and the energy is dependent on metabolism in the cells. At
FIG. 303. — Curve Taken by Renal Onkometer Compared with that of an Ordinary Blood-
pressure Curve, a, Kidney curve; b. blood -pressure curve. (Roy.)
least one substance, hippuric acid, is built up chemically by the renal cells
and secreted as such.
It would seem, therefore, that the separation of urine in the kidney is a
secretory process dependent on the protoplasmic activity of the living renal
cells, that the apparent selective property of the cells is a manifestation of
such activity, and that even water is secreted.
Diuretics. Certain substances increase the flow of urine and are
called diuretics. They act directly on the renal epithelium, for example,
urea, or indirectly on the circulatory system to increase the flow of blood.
Digitalis is a well-known diuretic which increases the efficiency of the circula-
tion. It also stimulates the renal epithelium with the production of a marked
increase in the flow of urine. Caffeine diuresis can best be explained on an
assumed stimulating action on the renal epithelium. Urea introduced into
the blood produces a copious secretion of urine. Both urea and the saline
diuretics induce a flow of urine out of all proportion to the osmotic changes
produced, and they may be regarded as direct stimulators of the renal epithe-
lium.
390 EXCRETION
THE DISCHARGE OF THE URINE.
As each portion of urine is secreted, it propels that which is already in the
uriniferous tubes onward into the pelvis of the kidney. Thence it passes
through the ureter into the bladder, from which at intervals it is discharged
to the exterior. The rate and mode of entrance of urine into the bladder
has been watched in cases of ectopia vesicae, i.e., cases in which fissures in
the anterior or lower part of the walls of the abdomen and of the front wall
of the bladder expose to view the orifices of the ureters. The urine does not
enter the bladder at any regular rate, nor is there a synchronism in its move-
ment through the two ureters. Ordinarily two or three drops enter the
bladder every minute, each drop as it enters first raising up the little papilla
on which the ureter opens, and then passing through the orifice, which at
once again closes like a sphincter. Its flow is aided by the peristaltic con-
tractions of the ureters, and is increased in deep inspiration or by straining.
The urine collected in the bladder is prevented from regurgitation into the
ureters by the mode in which these pass through the walls of the bladder,
namely, by their lying a half to three-quarters of an inch between the muscu-
lar and mucous coats before they turn rather abruptly forward and open
through the latter into the interior of the bladder.
Micturition. The contraction of the muscular walls of the bladder
may by itself expel the urine with little or no help from other muscles. The
vesicular pressure is increased in the voluntary act by the contraction of
the abdominal and other expiratory muscles which bear on the abdominal
viscera, thus aiding in the expulsion of the contents of the bladder. The
diaphragm is at the same time fixed in contraction and the sphincter of the
bladder relaxes. The pressure within the bladder under the combined con-
tractions of these expulsive muscles sometimes amounts to 8 to 10 cm. of
mercury. The act is completed by the accelerator urinae muscle, which, as
its name implies, quickens the stream and expels the last drop of urine from
the urethra. The act is under the regulative control of a nervous center in
the lumbar spinal cord, through which, as in the case of the similar center for
defecation, the various muscles concerned are coordinated in their action.
It is well known that the act may be reflexly induced, e.g., in children who
suffer from intestinal worms or other such irritation. Generally the afferent
impulses which set up the reflexes leading to the desire to micturate are ex-
cited by overdistention of the bladder, or sometimes by a few drops of urine
passing into the urethra. This impulse passes up to the lumbar center or
centers, and reflexly produces on the one hand inhibition of the sphincter
and on the other contraction of the necessary muscles for the expulsion
of the contents of the bladder. In the voluntary act these motor centers
are stimulated to activity by impulses coming from the higher cerebral
centers.
STRUCTURE AND FUNCTIONS OF THE SKIN
391
THE STRUCTURE AND EXCRETORY FUNCTIONS OF THE SKIN.
The skin serves, i, as an external integument for the protection of the
deeper tissues, and 2, as a sensitive organ in the exercise of touch, a subject
to be considered in the chapter on the Special Senses. It is also, 3, an im-
portant secretory and excretory organ; and 4, an absorbing organ. 5, It
plays an important part in the regulation of the temperature of the body by
controlling the loss of heat, i.e., a temperature-regulating function, discussed
in the chapter on Animal Heat.
Structure. The skin consists principally of a vascular tissue named
the corium, derma, or cutis vera, and of an external covering of epithe-
lium termed the epidermis or cuticle. Within and beneath the corium are
embedded several organs with special functions, namely, sudoriferous glands,
FIG. 304. — Vertical Section of the Epidermis of the Prepuce, a, Stratum corneum, of very few
layers, the stratum lucidum and stratum granulosum not being distinctly represented; b, c, d, and
e, the layers of the stratum Malpighii, a certain number of the cells in layers, d, and e showing signs
of segmentation; layer c , consists chiefly of prickle or ridge and furrow cells; /, basement membrane;
g, cells in cutis vera. (Cadiat.)
sebaceous glands, and hair follicles ; and on its surface are sensitive papilla.
The so-called appendages of the skin — the hair and nails — are modifications
of the epidermis.
The epidermis is composed of several strata of cells of various shapes and
sizes; it closely resembles in its structure the epithelium of the mucous mem-
brane that lines the mouth or covers the cornea. The following four layers
may be distinguished;
392
EXCRETION
The Stratum lucidum, a bright homogeneous membrane, consisting of
squamous cells closely arranged, in some of which a nucleus can be seen.
Stratum granulomm, consisting of one layer of flattened, fusiform, distinctly
nucleated cells. Stratum Malpighii or Rete mucosum consists of many strata
of cells. The deepest cells, placed immediately above the cutis vera, are
columnar with oval nuclei, succeeded by a number of layers of more or less
FIG. 305. — Vertical Section of Skin. A, Sebaceous gland opening into hair follicle; B, mus-
cular fibers; C, sudoriferous or sweat gland; D, subcutaneous fat; E, fundus of hair-follicle,
with hair- papillae. (Klein.)
polyhedral cells with spherical nuclei; the more superficial layers are con-
siderably flattened. The deeper surface of the rete mucosum is accurately
adapted to the papillae of the true skin, being, as it were, moulded on them.
It is very constant in thickness in all parts of the skin. The cells of the middle
layers of the stratum Malpighii are connected by processes, and thus form
prickle cells, figure 28. The pigment of the skin, in the deeper cells of rete
mucosum, causes the various tints observed in different individuals and differ-
ent races. The epidermis maintains its thickness in spite of the constant wear
GLANDS OF THE SKIN 393
and tear to which it is subjected. The columnar cells of the deepest layer
of the rete mucosum elongate, multiply by division, the new cells produced
being pushed toward the free surface of the skin. There is thus a constant
production of fresh cells in the deeper layers, and a constant throwing off of
old ones from the free surface. When these two processes are accurately
balanced, the epidermis maintains its thickness. When by intermittent
pressure a more active cell-growth is stimulated, the production of cells ex-
ceeds their waste and the epidermis increases in thickness, as we see in the
horny hands of the laborer.
The dermis, or cutis vera or true skin, is a dense and tough, but yielding
and highly elastic structure supporting the epidermis. It is composed of
areolar connective tissue interwoven in all directions and forming numerous
spaces by its interlacements. These areolae in the deeper layers of the cutis
are usually filled with little masses of fat, figure 305. Unstriped muscu-
FIG. 306. — Terminal Tubules of Sudoriferous Glands, Cut in Various Directions. From the
skin of the pig's ear. (V. D. Harris.)
lar fibers are also abundantly present, especially in the skin of animals which
erect the hairs with greater ease than is usually the case with man.
There is a rich network of blood-vessels to the dermis. In the dermal
papillcc and about the sweat glands there are special loops of capillaries.
Nerve fibers are also distributed to the papillae.
The special nerve terminations in the skin have been described on page 72.
Glands of the Skin. The skin possesses glands of two kinds:
Sudoriferous or Sweat Glands, and the Sebaceous or Oil Glands.
A Sudoriferous or Sweat Gland consists of a small lobular mass, formed
of a coil of tubular gland-duct, surrounded by blood-vessels, and embedded
in the subcutaneous adipose tissue, figure 305, C. The duct ascends from
this coiled mass for a short distance in a spiral manner through the cutis
and the epidermis, and then opens on the surface of the skin. In the
parts where the epidermis is thin, the ducts themselves are thinner and
more nearly straight in their course,
394 EXCRETION
The duct is lined with a layer of columnar epithelium continuous with
the epidermis. The coiled or secreting portion of the gland is lined with
at least two layers of short columnar cells with very distinct nuclei, figure 306.
The lumen is distinctly bounded by a special lining of cuticle.
The sudoriferous glands are abundantly distributed over the whole sur-
face of the body; but are especially numerous, as well as very large, in the
skin of the palm of the hand and of the sole of the foot. The glands by
which the peculiarly odorous matter of the axillae and groin is secreted form
a nearly complete layer under the cutis, and are like the ordinary sudoriferous
glands, except in being larger and having very short ducts.
The peculiar bitter yellow substance secreted by the skin of the external
auditory passage is named cerumen, and the glands themselves ceruminous
glands; but they do not much differ in structure from the ordinary sudorif-
erous glands.
The sebaceous glands, figures 305 and 306, like sudoriferous glands, are
abundant in most parts of the surface of the body, particularly in parts largely
FIG. 307. — Sebaceous Gland from Human Skin. (Klein and Noble Smith.)
supplied with hair, as the scalp and face. They are thickly distributed about
the entrances of the various passages into the body, as the anus, nose, lips,
and external ear. They are entirely absent from the palmar surface of the
hand and the plantar surface of the foot. They are racemose glands com-
posed of an aggregate of small tubes or sacculi lined with columnar epithelium
EXCRETORY FUNCTION OF THE SKIN 395
and filled with an opaque white substance, like soft ointment, which consists
of broken-up epithelial cells which have undergone fatty degeneration. Mi-
nute capillary vessels overspread them; and their ducts open on either the
surface of the skin, close to the hair, or, which is more usual, directly into
the follicle of the hair. In the latter case, there are generally two or more
glands to each hair, figure 306.
The story of the structure and development of such epithelial struc-
tures as the hair and the nails is best left to the histologist, to whom the
student is referred.
The Excretory Function of the Skin. The function of the skin
which is of special interest to this chapter is that of the excretion of the sweat.
The fluid secreted by the sweat glands is usually formed so gradually that
the watery portion of it escapes by evaporation as fast as it reaches the surface.
But during strong exercise, exposure to great external warmth, in some
diseases, and when evaporation is prevented, the secretion becomes more
sensible and collects on the skin in the form of drops of fluid.
The perspiration, as the term is sometimes employed in physiology, in-
cludes all that portion of the secretions and exudations from the skin which
are thrown on the surface by the sweat glands. As a matter of fact, this is
mingled with various substances lying on the surface of the skin. The con-
tents of the sweat are, in part, matters capable of assuming the form of vapor,
such as carbonic acid and water, and in part other matters which are depos-
ited on the skin, and mixed with the sebaceous secretions.
The secretion of the sebaceous glands and hair-follicles consists of cast-
off epithelium cells, with nuclei and granules, together with an oily matter,
extractive matter, and stearin. In certain parts, also, it is mixed with a
peculiar odorous principle, which contains caproic, butyric, and rutic acids.
It is similar in composition to the unctuous coating, or vernix caseosa, which
is formed on the body of the fetus while in the uterus, and which contains
ordinary fat. This sebaceous secretion serves the purpose of keeping the
skin moist and supple, and, by its oily nature, of both hindering the evapora-
tion from the surface and guarding the skin from the effects of the long-con-
tinued action of moisture. But while it thus serves local purposes, its re-
moval from the body entitles it to be listed among the excretions of the skin.
CHEMICAL COMPOSITION OF SWZAT.
Water 995
Solids: 5
Organic acids (formic, acetic, butyric, propionic,
caproic, caprylic) 0.9
Salts, chiefly sodium chloride - 1.8
Neutral fats and cholesterin 0.7
Extractives (including urea) , with epithelium 1.6
1000
EXCRETION
The sweat* is a colorless, slightly turbid fluid, alkaline, neutral or acid in
reaction, of a saltish taste, and peculiar characteristic odor.
Of the several substances it contains, however, only the carbonic acid and
water need particular consideration.
The quantity of watery vapor excreted from the skin is, on an average,
between 750 and 1,000 cubic centimeters daily. This subject has been very
carefully investigated by La cisier and Sequin. The latter chemist enclosed
his body in an air-tight bag provided with a mouthpiece. The bag was
closed by a strong band above, and the mouthpiece adjusted and gummed
to the skin around the mouth. He was weighed, then remained quiet for
several hours, after which time he was again weighed. The difference in
the two weights indicated the amount of loss by pulmonary exhalation.
Having taken off the air-tight dress, he was immediately weighed again, and
a fourth time after a certain interval. The difference between the two weights
last ascertained gave the amount of the cutaneous and pulmonary exhalation
together; by subtracting from this the loss by pulmonary exhalation alone,
while he was in the air-tight dress, he ascertained the amount of cutaneous
transpiration. The average loss by cutaneous and pulmonary exhalation in
a minute during a state of rest is eighteen grains, — the minimum eleven grains,
the maximum thirty-two grains. Of the eighteen grains, eleven pass off by
the skin and seven by the lungs.
The quantity of watery vapor lost by transpiration is of course influenced
by all external circumstances which affect the exhalation from evaporating
surfaces, such as the temperature, the hygrometric state, and the stillness
of the atmosphere. But, of the variations to which it is subject under the
influence of these conditions, no calculation has been exactly made.
The quantity of carbonic acid exhaled by the skin on an average is said to
be about one-two-hundredth of that eliminated by the pulmonary respiration.
The cutaneous exhalation is most abundant in the lower classes of ani-
mals, more particularly the naked amphibia, as frogs and toads, whose skin
is thin and moist, and readily permits an interchange of gases between the
blood circulating in it, and the surrounding atmosphere. Bischoff found that,
after the lungs of frogs had been tied and cut out, from 3 to 4 c.c. of car-
bonic-acid gas was exhaled by the skin in eight hours. And this quantity
is very large, when it is remembered that a full-sized frog will generate only
about 10 c.c. of carbonic acid by his lungs and skin together in six hours.
The importance of the respiratory function of the skin, which was once
thought to be proved by the speedy death of animals whose skins, after re-
moval of the hair, were covered with an impermeable varnish, has been shown
by further observations to have no foundation in fact. The immediate cause
of death in such cases is the loss of temperature. A varnished animal is
said to have suffered no harm when surrounded by cotton padding, and to
have died when the padding was removed.
INFLUENCE OF THE NERVOUS SYSTEM ON SWEAT SECRETION 3P7
Influence of the Nervous System on Sweat Secretion. The secre-
tion of sweat is closely connected with the quantity of blood flowing through
the cutaneous vessels. The quantity of sweat increases with vaso-dilatation
and diminishes with vaso-constriction. The sweat glands are also under the
control of efferent impulses passing to them from the special sweat centers
in the brain and spinal cord through special sweat nerves. Thus, if the sciatic
nerve be divided in a cat and the peripheral end be stimulated, beads of sweat
are seen to appear upon the pad of the corresponding foot. The sweat ap-
pears even though at the same time the blood-vessels are constricted, or the
blood flow entirely stopped by compression of the aorta, whereas if atropin is
injected previously to the stimulation, no sweat appears, although dilatation of
the vessels may be present. Secretion of sweat, too, may be brought about
reflexly.
The circulation of venous blood in the spinal bulb causes the sweating of
phthisis and of dyspnea generally, by stimulating the sweat center. If the
cat whose sciatic nerve is divided be rendered dyspneic, abundant sweat
occurs upon the foot of the uninjured, and none on the injured, side. The
effect of heat in producing sweating may be both local and general, and, again,
the various drugs which produce an increased secretion of sweat do not all
act in the same way; thus, there is reason for thinking that pilocarpine acts
upon the local apparatus, that strychnine and picrotoxin act upon the sweat
centers, and that nicotine acts both upon the central and upon the local
apparatus.
The special sweat-nerves appear to issue from the spinal cord, in the
case of the hind limb of the cat, by the last two or three dorsal and first
two to four lumbar nerves, pass to the abdominal sympathetic, and from
thence to the sciatic nerve, the general course of the autonomic nerves
for this region. In the case of the fore limb, the nerves leave the cord
by the first to the sixth dorsal nerves, pass into the thoracic sympathetic,
and then join the brachial plexus, reaching the arm through the median and
ulnar nerves.
It will be as well to repeat here the other functions which the skin sub-
serves. In addition to its excretory office, we have seen that it acts as a
channel for absorption. It is also concerned with the special senses, that of
touch and temperature, to the consideration of which as well as to its function
of regulating the temperature of the body we shall presently return. By its
general impermeability it prevents the loss of moisture of the body by direct
evaporation from the tissues. It should be recollected, however, that apart
from these special functions, by means of its toughness, flexibility, and elastic-
ity, the skin is eminently qualified to serve as the general integument of the
body, for defending the internal parts from external violence, while readily
yielding and adapting itself to their various movements and changes of
position.
398 EXCRETION
LABORATORY EXPERIMENTS IN EXCRETION.
PHYSIOLOGICAL REACTIONS
i. The Relation of Blood Flow through the Kidney to the Secre-
tion of Urine. Properly to check this experiment one should make
three determinations: i, the general blood pressure; 2, the volume of the
kidney; 3, the amount of urine secreted. Anesthetize a dog and arrange the
apparatus for taking the blood pressure as directed in experiment 19. Prepare
a renal onkometer, see figures 301 and 302, and an onkograph for recording
the variations in the volume of the kidney. The renal onkometer consists of
a double metal box to fit the form of a kidney. The inner halves of this box
should be covered so loosely with very thin sheet rubber that the rubber can
be fitted into the bottom of the cup without undue tension. The rubber must
be sealed to the outer edges of this inner cup with rubber cement and allowed
to dry. When it is completely dried the inner cup should be adjusted to the
outer, and the spaces enclosed by the rubber sheet filled with water. Or
the onkometer may be closed with parchment and filled with oil as de-
scribed in experiment 23 on the Circulation. The half of the onkometer
that comes against the wall of the body cavity of the animal should be
completely closed with a stopper before the instrument is adjusted to
the kidney. Now adjust the onkometer to the kidney, taking care to
place the renal arteries, veins, and ureter in the tube in such a way as not
to compress them. Fill the outer cup with water and connect this cavity
by a two-way cannula with the recording onkograph. In practice it is more
satisfactory if one introduces between the onkometer and onkograph an over-
flow bottle or bulb, adjusted to maintain the constant pressure on the kidney.
This direction varies from the usual one in that rubber sheeting instead of
parchment is used to cover the inner cup of the onkometer, a method that
permits the use of water instead of oil.
Isolate and insert a small cannula into the ureter. This cannula should
be clamped in a stand at a level as little above that of the kidney as possible.
The urine secreted may be collected in a 10 c.c. graduated cylinder and
measured at intervals of 5 or 10 minutes. Or, if the outflow is scanty, it may
be allowed to drop on a tambour recording apparatus, the rate of dropping
being indicative of the rapidity of secretion.
Determine the normal rate of secretion of a dog under constant anesthesia.
The anesthesia should be medium to light, but should be kept very uni-
form so as to maintain a strong blood pressure. Note the effect on secre-
tion and the corresponding effect on blood pressure and the kidney volume
produced by vagus inhibitions. Section the vagus nerves and produce in-
hibition by stimulating the peripheral end of the vagus. In this instance
there are no reflexes to complicate the experiment, so that the fall in blood
SECRETORY NERVES FOR THE SWEAT GLANDS 399
pressure is a direct cardiac effect. Stimulate the central end of the vagus
which produces a fall of blood pressure through the vaso-motor system.
There should be a normal period of at least ten minutes following each experi-
ment to allow the secretion of the kidney to return to the normal.
Expose the splanchnic nerves at the point where they pass beneath the
diaphragm into the abdominal cavity. Adjust a pair of shielded electrodes,
close the cavity, and, when the animal has returned to the normal uniform
rate of secretion and of blood pressure, stimulate the splanchnic nerves.
The splanchnics contain vaso-constrictor nerves for the kidney. The onkom-
eter experiment should, therefore, demonstrate a sharp decrease in the vol-
ume of the organ, while the blood pressure is only slightly changed. The
rate of secretion should be followed for at least twenty minutes after stimula-
tion of the splanchnics. This test should be repeated two or three times.
In this connection demonstrate the influence of deep chloroform anesthesia
on urinary secretion. The chloroform should be pushed to the danger limit
and maintained there for a couple of minutes or more. Compare the rapidity
of the recovery of blood pressure with the recovery of the rate of secretion.
2. Secretory Nerves for the Sweat Glands. Langley has mapped
out the paths of the secretory nerves for the sweat glands. He has shown
that in the cat these fibers are distributed to the hind limb through the sciatic.
Anesthetize a half -grown cat, isolate the sciatic nerve, cut it and stimulate the
peripheral end with a medium to strong induction current. After a few
moments beads of perspiration will appear on the pads of the foot, which
should therefore be carefully examined before the experiment.
URINE ANALYSIS.
3. Daily Quantity. Determine the total quantity, for 24 hours,
of urine secreted through a period of 3 or 4 days, beginning and ending the
period at a definite hour in the day, preferably on rising in the morning.
The daily secretion varies through wide extremes, depending upon the quan-
tity of liquid taken in the food, the daily exercise, the temperature, etc., etc.
In the analysis of urine it is always better to take a mixed 24-hour sample.
4. Specific Gravity. Determine the specific gravity of 24-hour
urine. This is done by the instrument known as the urinometer which
carries a graduated scale at the neck. Care should be taken to float the
urinometer so that it does not come in contact with the measuring cylinder.
The scale should be read at the bottom of the meniscus.
5. Reaction. Determine the reaction of perfectly fresh urine, using
litmus paper. The normal urine is slightly acid under ordinary conditions,
due to the presence of acid phosphates or perhaps in some cases to traces of
free organic acid.
After standing some time the reaction is usually alkaline, owing to fer-
400
EXCRETION
mentation processes. The reaction may vary also according to the food,
vegetable foods tending to produce alkaline urine, while with animal foods
the reaction is acid.
6. The Total Quantity of Solids. Determine the solids of urine
by evaporating 25 c.c. of a mixed sample of urine to dryness in a weighed
platinum or porcelain dish over a water bath. The
residue should be dried to constant weight in a drying
•oven at 105° C.
A useful rule for approximately estimating the total
solids in any given specimen of healthy urine is to
multiply the last two figures representing the specific
gravity by 2.33. Thus, in urine of specific gravity 1025,
2.33 X 25 = 58.25 grains of solids are contained in
1,000 grains of the urine. Or the total solids are 5.825
per cent. In using this method it must be remembered
that the limits of error are much wider in diseased than
in healthy urine.
The solids of urine consist of inorganic salts of
sodium, potassium, and calcium, and of a long list of
organic compounds, chiefly nitrogenous.
7. Chlorides. Large quantities of sodium chlo-
ride are always present in the normal urine. Add
ammonia to 25 or 50 c.c. of albumin-free urine and heat
to precipitate earthy phosphates, filter. To a sample
of the filtrate add an excess of strong nitric acid and a
few drops of i per cent silver nitrate. A white flocculent precipitate of
silver chloride comes down. This precipitate is soluble in an excess of
ammonia. Reprecipitate by adding nitric acid again. The test may be
made without removing the phosphates, though in this case, upon adding
ammonia, the disappearance of the silver precipitate is complicated by the
appearance of insoluble phosphates.
The chlorides may be estimated quantitatively by Volhard's method, or
some one of its modifications, which depends upon the determination of the
amount of chlorine precipitated by the silver. The student is referred to
chemical text-books for this and other quantitative methods.
8. Sulphates. Sulphates exist in the urine both in inorganic
and organic compounds, chiefly the former. Add a few drops of hydro-
chloric acid to a sample of urine in a test tube, then a solution of barium
chloride, the insoluble barium sulphate settles out. If the test is made on the
normal urine without the addition of the acid, the inorganic sulphate will be
precipitated, while the ethereal or compound sulphate will remain in solution
and can be filtered off. This filtrate, when boiled with strong hydrochloric
acid to 10 per cent over a water bath for a short time, will have the sulphates
FIG. 308. — The
Urinometer.
PHOSPHATES
401
split off from the organic radicle and may be precipitated by the addition
of barium chloride in hot solution.
9. Phosphates. The phosphates of urine consist of the earthy
and alkaline salts, the latter predominating. Take a 50 c.c. sample of urine,
add strong ammonia, and heat. The phosphates of calcium and magnesium
separate out, as they are insoluble in alkaline solution. Filter.
To the filtrate add a solution of magnesium sulphate. This precipitates
the sodium and potassium phosphates as a triple phosphate of magnesium,
which is insoluble. Tests for phosphates in general are:
Add nitric acid to a sample of urine, warm gently, then add a few drops
of 10 per cent ammonium molybdate; a yellow precipitate of ammonium
phospho-molybdate is formed. Or, add acetic acid, then a few drops of
FIG. 309. — Doremus' Ureometer.
uranium acetate; a bright yellow precipitate of uranium ammonium phosphate
is formed. These two reactions are used as the basis for a quantitative de-
termination of phosphorus.
10. The Preparation of Urea. Take zooc.c. of normal urine, evap-
orate to one-half its quantity, and precipitate the phosphates and sulphates
by adding a mixed solution of barium hydrate and nitrate. Filter, evaporate
the filtrate to dryness, take up in warm 95 per cent alcohol, and refilter. Crys-
tals of urea separate out when the alcohol is evaporated off.
Evaporate a large sample, 200 c.c., of urine to a syrupy mass, add nitric
acid. Crystals of urea nitrate are formed. Wash the crystals in dilute nitric
acid, then dissolve in water. The urea is set free by adding barium carbonate
26
402 EXCRETION
until the carbon dioxide ceases to come off. Filter, evaporate over a water
bath to dryness, and dissolve the urea in 95 per cent alcohol; decant, and re-
crystallize by evaporating off the alcohol.
11. Urea Determination by Doremus' Ureometer. Fill the ureo-
meter with hypobromite of sodium solution. Take a sample of urine in
the pipet which accompanies the instrument, drawing it in exactly to the
mark. Insert the pipet past the bend of the ureometer and slowly empty
the urine carefully so as not to lose any of the liberated nitrogen. The instru-
ment is graduated to read off the percentage of urea directly.
12. Uric Acid. Concentrate over a water bath 500 c.c. of urine
to 100 c.c. and boil with 10 c.c. or more of strong hydrochloric acid. Upon
cooling, crystals of uric acid are formed. Decant the supernatant liquid and
wash the crystals with a few cubic centimeters of 10 per cent hydrochloric
acid. . Dissolve the crystals and test.
The Murexide Test. Add to 2 c.c. of uric acid solution in a test tube an
equal quantity of nitric acid. Heat gently, a reddish ring forms at the point
of contact between the nitric acid and uric acid solution. Cool and add
ammonia carefully. The color ring deepens to a purple color. This test
succeeds well by evaporating a few drops of uric acid on a porcelain plate.
Add to the stain a drop of concentrated nitric acid and evaporate. Concen-
tric rings of reddish color will be formed. This color deepens to reddish-
purple when a drop of ammonia is added.
13. Creatinin. Test 20 c.c. of urine in a beaker for creatinin by
adding a cubic centimeter of dilute solution of sodium nitroprusside and then
weak sodium hydrate. A ruby-red color, which quickly turns yellow, indi-
cates the presence of creatinin. (Weyl's reaction.) If the yellow solution
has an excess of acetic acid added and is then boiled, it turns first green and
later blue, forming ultimately a precipitate of Prussian blue.
Urine mixed with picric acid gives a red coloration when made alkaline
with caustic alkali solution.
14. Total Nitrogen in Urine. Determine the total nitrogen in
a sample of urine by the Kjeldahl method. This method depends upon the
conversion of nil the nitrogen to ammonia, the distillation of this ammonia
into a known quantity of sulphuric acid, and the final titration of the excess
of sulphuric acid when the distillation is complete. The computation is
made on the basis that i c.c. of a normal sulphuric acid is equivalent to
i c.c. normal sodium hydrate, and that in turn to i c.c. of ammonium
hydrate. The ammonia neutralizes a portion of the sulphuric acid in the
distillation. One c.c. of normal ammonium hydrate contains 0.014 gram
nitrogen, from which the total nitrogen in the sample used can be readily
computed.
15. Pigments of Urine. The normal color of the urine is due to
the presence of a pigment, urobilin. Prepare urobilin by adding lead acetate
ALBUMIN IN THE
to a 200 c.c. sample of urine. A precipitate forms which carries down the
coloring matter. Filter. Add acid alcohol to the precipitate to extract the
coloring matter, refJter, which gives a deep yellow solution. Shake up with
a few cubic centimeters of chloroform which dissolves the pigment. Draw
off the chloroform solution and allow to evaporate. The residue is a brown-
ish mass of urobilin.
ABNORMAL CONSTITUENTS OF URINE.
Many abnormal constituents may appear in the urine under pathological
conditions, only two of which will be mentioned here.
1 6. Albumin in the Urine. The detection of the presence of albu-
min, albuminuria, is of considerable clinical importance. The following
are the standard tests which present no special difficulty except when traces
only are present.
Heat Coagulation. To a half test tube of urine add a drop of dilute
acetic acid and boil. A white coagulum indicates the presence of albumin.
A faint cloudy appearance indicates traces.
Nitric Acid Test. To 5 c.c. of strong nitric acid in a conical test tube
add 10 or 15 c.c. of urine, pouring it gently down the inclined side of the glass.
Allow the glass to stand for a few minutes, when a white coagulum appears
just above the line of contact of the acid with the urine. This test, known
as Heller's test, will usually indicate the presence of traces of albumin.
Picric Acid Test. Add picric acid to a sample of urine. A whitish
precipitate of albumin will appear at the line of contact, as in the preceding test.
Citric acid two parts and picric acid one part, when boiled with urine
will coagulate minute traces of the proteid.
17. Detection of Sugar in the Urine. Trommers Test. The
presence of sugar in the urine can usually be detected by Trommer's test,
which depends upon the reduction of copper sulphate in the presence of
strong alkali. Boil fresh Fehling's solution and add to it a few cubic centi-^
meters of urine. When sugar is present a reddish-yellow precipitate of copper
oxide comes out. The test should be set away for a few minutes when, if
only traces of the reduction are present, a reddish-brown stain will appear
on the bottom of the test tube. Uric acid, if present in excess, may produce
a slight precipitation of the copper.
Fermentation Test. If sugars are present in the urine, they can be de-
tected by adding yeast to a fermentation tube filled with urine, the liberation
of carbon dioxide indicating the presence of sugar. Cane sugar does not
support the growth of yeast, so it forms an exception by this test.
Phenyl-Hydrazin Crystals. Phenyl-hydrazin forms crystals of phenyl-
glucosazone. To 10 c.c. of urine in a small beaker add o.i of a gram of
phenyl-hydrazin hydrochloride and a double quantity of sodium acetate.
404 EXCRETION
Heat in the water bath for 20 minutes. Upon cooling a deposit of yellow
crystals of phenyl-glucosazone takes place, if glucose is present.
1 8. Quantitative Determination of Sugar in the Urine. Fill a 10-
c.c. graduated pipet with freshly prepared Fehling's solution. Take 10 c.c.
of urine, measured with a dropping-pipet into a small beaker, and boil. While
continuing to boil, add Fehling's solution slowly and cautiously so long as
the color is discharged. The amount of Fehling's required to reduce the sugar
is a measure of the quantity of reducing sugar present — i c.c. of Fehling's
being equivalent to 5 milligrams of dextrose.
For the presence of blood pigments and other abnormal constituents of
the urine, the student is referred to special handbooks on the subject.
CHAPTER XI
METABOLISM, NUTRITION, AND DIET
THE term metabolism means, literally, an exchange of material. In its
broadest physiological sense it includes the study of the exchange of material
between the living tissues of the body and their surrounding media. This
includes the study of the income and outgo of material; the storing of energy-
yielding materials in the body; the transfer of this potential energy into kinetic
energy; and the nutritional processes within the various tissues. The building
up of absorbed food material into the protoplasm of the cell or of simpler com-
pounds into more complex ones, which may be stored in the cell, is known
as anabolism, and the compounds themselves as anabolites. The breaking
down of these substances into simpler forms, whereby the potential energy
of the anabolites is transformed into kinetic energy, is known as catabolism,
and its products as catabolites.
In order to form an estimate of these processes going on in the body, the
amount and nature of the ingested material must be known, as well as the
amount of refuse or unused material that passes out of the alimentary canal
as feces, and the amount of excreted material from the various excretory
organs. It is also necessary to know the potential energy of the ingested
materials, and the possible potential energy must be checked against the ac-
tual energy liberated.
The food is intended to supply the place of the material which has been
utilized by the body, and, in a simpler form, eliminated in the excretions.
But in the choice of a diet this is not enough; the food should be sufficient
to supply such need without waste and without unduly increasing the output
of excreta, while at the same time the body should be maintained in health,
without increase or loss of weight. The food must also supply the energy
liberated without undue waste of the tissues themselves.
These requisites of a diet scale then allow for wide alterations in the
amount of different kinds of foods under different circumstances. Numerous
and most valuable experiments have been performed in recent years to determine
just what each article of the common food materials contributes to the growth
of the tissues and to the kinetic energy liberated by the tissues. The potential
energy of the food can also be checked against the kinetic energy liberated.
A single illustration of this class will serve. In an experiment with mixed food
lasting through four days, on a man with body weight of 64 kilograms, and
doing a minimum amount of work, Atwater made the following determinations :
405 •
406 METABOLISM, NUTRITION, AND DIET
WEIGHT, COMPOSITION, AND HEAT OF COMBUSTION OF FOODS AND EXCRETA PER DAY.
Weight per
day.
Water.
Protein.
2
&
Carbohy-
drates.
%
Carbon.
Hydrogen.
Heat of com-|
bustion.
Food
Beef
Grams.
IOO
Grams.
61.2
Grams.
35.1
Grams.
3.1
Grams.
Grams.
5.62
Grams.
20.0<
Grams.
2.90
Calo-
ries.
227
Butter
25
2.6
.5
21. I
.08
15.77
2.50
194
Whole milk
850
726.8
32-3
45.1
39-9
<C. 10
67.74
9-94
768
Bread . .
300
123.9
22.2
12.0
139.2
3-9°
82.53
12.24
835
Shredded wheat
biscuit
5°
4- !
4.8
.7
30.7
.84
20.46
2.87
204
Ginger snaps . . .
Sugar
5°
20
3-3
2.8
3-6
39-2
20. o
-5°
21.12
8.42
3-°7
i . 30
212
70
Total food per
dav.
1,395
Q2I .9
97-7
8?. 6
278.0
16.04
236.00
34.82
2,<IQ
Average feces
per dav. .
98.8
77-7
7-7
4.0
6.3
1.23
9.98
1.42
1 10
Average urine
per day
1420. 8
1^6^. O
ic.8<?
II. 70
2.08
I ?:
Excretions lungs
and skins
881 o
221 >
23Q7
Total excreta
per day.
2322.6
17.08
243.27
4.40
2642
Balance
— 1.04
-7-l8
-1-30.42
— 123
Careful analyses of the excreta, many of which we have already had oc-
casion to call attention to, show that they are made up, besides water, chiefly
of the chemical elements carbon, hydrogen, oxygen, and nitrogen, but that
they also contain, to a less extent, sulphur, phosphorus, chlorine, potassium,
sodium, calcium, magnesium, iron, and certain other of the elements. Since
this is the case it must be evident that, to balance this waste, foods must be
supplied containing all these elements to a certain degree, and some of
them in large amount, viz., those which take a principal part in forming
the excreta.
The waste products of the body are eliminated through the lungs, the
skin, the alimentary canal, and the kidney. In the lungs the chief waste prod-
uct is water, carbonic-acid gas, and traces of ammonia compounds which
are composed of the elements carbon, oxygen, nitrogen, and hydrogen. Traces
of carbonic-acid gas and small quantities of urea and salts are eliminated
through the skin. From the alimentary canal there are lost, through the feces,
the indigestible and unabsorbed substances from the food, together with
products secreted into the canal by the liver, pancreas, and mucous membrane.
METABOLISM, NUTRITION, AND DIET
407
The secretion lost daily by the kidney, aside from a large quantity of water,
consists of nitrogenous waste products, chiefly urea, and inorganic solids, as
were mentioned in the chapter on Excretion.
The relations between the amounts of the chief elements contained in these
various excreta in twenty-four hours may be thus summarized:
Water.
C.
H.
N.
O.
By the lungs
33O
248 8
6ci ic
By the skin
660
2 6
72
By the urine. . .
1,708
Q 8
3J
i^ 8
II I
By the feces
I2O
20
30
30
12 O
Grams
2 818
28l 2
6 i
18 8
681 AC
From the water in this table should be subtracted the 296 grams of water
which are produced by the union of hydrogen and oxygen in the body during
the process of oxidation, and there should be added to the respective columns
the corresponding amounts of the constituent elements, i.e., 33 grams of hydro-
gen and 262 grams of oxygen. There are 26 grams of salts eliminated through
the urine, and 6 by the feces; a total of 32 grams.
The quantity of carbon daily lost from the body amounts to about 281.2
grams and of nitrogen 18.8 grams, and if a man could be fed by these elements,
as such, the problem would be a very simple one; a corresponding weight
of charcoal and, allowing for the oxygen in it, of atmospheric air would be
all that is necessary. But an animal can live upon these elements only when
they are arranged in a particular manner with others, in the form of such
food stuffs as we have already enumerated, page 297 el seq.; moreover, the
relative proportion of carbon to nitrogen in either of these compounds alone
is by no means the proportion required in the diet of man. Thus, in proteid,
the proportion of carbon to nitrogen is only as 3.5 to i. If , therefore, a man
took into his body, as food, sufficient proteid to supply him with the needed
amount of carbon, he would receive more than four times as much nitrogen
as is needed; and if he took only sufficient to supply him with nitrogen, he
would be starved for want of carbon. It is plain, therefore, that he should
take with the albuminous part of his food, which contains so large an amount
of nitrogen in proportion to the carbon he needs, substances in which the
nitrogen exists in relatively much smaller quantities than the carbon.
It is, therefore, evident that the diet must consist of several compounds,
not of one alone.
Many valuable observations have been made with a view of ascertaining
the effect upon the metabolism of a variation in the amount and nature of
food. These are of great assistance in the consideration of dietetics.
408
METABOLISM, NUTRITION, AND DIET
METABOLISM OF PROTEIDS.
Nitrogenous Equilibrium. Experiments have been made, to a con-
siderable extent upon dogs, which demonstrate the necessity for proteid
food. After a preliminary period without food, during which the output of
nitrogen as shown by the urea has diminished to a comparatively constant
amount, an animal is fed with a diet of lean meat which would suffice to pro-
duce the amount of urea, and so of flesh, which it has been losing during its
starvation period. The effect of this, however, is at once to send up the
amount of urea excreted to a point above that which had been lost previous
to the commencement of the flesh diet. Thus the output of nitrogen still
exceeds its income, and the weight of the animal continues slowly to diminish.
It is only after a considerable increase of the flesh given in the food that a
point is reached where the income and expenditure of nitrogen are equal,
and at which the animal is not using up quickly or slowly the nitrogen of its
own tissue, and is no longer losing flesh. This condition in which the nitro-
gen of the egesta equals the nitrogen of the ingesta is known as nitrog-
enous equilibrium.
EXPERIMENT IN NITROGENOUS EQUILIBRIUM.
DAYS OF EXPERIMENT.
N
Intake.
Grams.
N
Output.
Grams.
JPer cent
Differ-
ence.
S
Intake.
Grams.
S
Output.
Grams.
I. i-c
go OO
89 8l
O 2 I
6-12
131 60
IT.2 ?c;
H-o 88
II 1-2
or go
^6 16
— |- I OO
7— II
144. <O
14.3 1 7
o 86
HI. I-;
154.81
IS3 °2
— o =ci
8-17..
217.72
213.26
O.2I
12-77
12.79
In the dog, according to Waller, nitrogenous equilibrium does not occur
until the amount of flesh of the food is over three times as great as would be
necessary to supply the nitrogen of the urea during a period of starvation.
Thus a dog excretes during a starvation period 0.5 gram of urea per kilo
of body weight; in order to satisfy this waste it would be necessary to ad-
minister 1.5 grams per kilo of meat; this at once increases the urea excreted
to about 0.75 gram per kilo of body weight, and nitrogenous equilibrium
is not attained until over three times, viz., 3 grams per kilo of body weight,
of meat is given. Foster gives even a larger figure. The effect, therefore,
of proteid food is largely to increase the excretion of urea, which indicates
an increase in the metabolism of the tissues.
Studies in nitrogenous equilibrium are based on the fact that when an
THE R6tiE OF PROTEIDS IN METABOLISM 409
animal is given a diet with a constantly increasing amount of proteid food
from day to day, after a few days the total nitrogen found in the excreta
exactly balances that taken in the food. This condition of nitrogenous
equilibrium is established at different levels, varying sometimes according to
the individual and with the kind and quantity of other food principles taken
at the same time as the nitrogenous foods.
Chittenden's latest metabolism experiments have shown that with free
choice, but moderate use, of accessory articles of diet, the human body can
maintain itself in nitrogenous equilibrium for at least several months on an
average of 4 to 10 grams of nitrogen per day, the equivalent of 25 to 62.5
grams of proteid.
The Role of Proteids in Metabolism. The proteids of food are
described by Voit as having two relations to the proteid metabolism and to
outgoing urea; the first part going to maintain the ordinary and quiet metab-
olism of the tissues, for which purpose it is actually built up into the living
protoplasmic molecule, and the second part causing a more rapid formation
of urea, but never becoming a part of the actual protoplasmic molecule. The
former proteids are called mor photic or tissue proteids, the latter circulating
or floating proteids. Normally more proteid is eaten than is needed to sup-
ply proteid to the protoplasm for growth, as has just been stated. Pfliiger
takes the view, however, that the tissues must have an excess of proteid to
destroy in order to perform their metabolic processes normally. This use
of the proteids to form heat by their oxidation, and not to produce tissue, was
looked upon by the older physiologists as a wasteful use of good material,
and was called a luxus consumption.
Folin has recently announced a theory of proteid metabolism in which
he calls special attention to the relation of the nitrogenous excretion products
to the nitrogenous intake. He has shown that the urea contained in the
urine varies almost directly with the quantity of proteid in the food; that
the ammonia varies with the proteid in the food; that the uric acid decreases
(and increases) with the proteid in the food, but not in direct ratio; while the
creatinin excreted is " wholly independent of quantitative changes in the total
amount of nitrogen eliminated."
TABLE SHOWING THE OUTPUT or NITROGEN IN A NORMAL, HEALTHY INDIVIDUAL
ON A FOOD RICH IN NITROGEN, JULY i3TH, AND POOR IN NITROGEN
JULY 20TH (FOLIN).
July i ath. July aoth.
Volume of urine 1,170 c.c. 3850.0.
Total nitrogen 16.08 grams 3. 60 grams
Urea-nitrogen 14-7° ' = 87.5 per cent 22.0 " = 61.7 per cent
Ammonia-nitrogen.... 0.49 =3.0 0.42 =11.3
Uric-acid-nitrogen 0.18 '
Kreatinin-nitrogen 0.58 '
Undetermined nitrogen 0.85 '
= 1.1 " 0.09 " = 2.5
= 3.6 " 0.60
= 4.9 " 0.27
410 METABOLISM, NUTRITION, AND DIET
Folin states this theory as follows: "It is clear that the metabolic proc-
esses resulting in the end products which tend to be constant in quantity
appear to be indispensable for the continuation of life; or, to be more defi-
nite, those metabolic processes probably constitute an essential part of the
activity which distinguishes living cells from dead ones. I would therefore
call the protein metabolism which tends to be constant, tissue metabolism,
or endogenous metabolism; the other, the variable proiem metabolism, I would
call the exogenous or intermediate metabolism.
"The endogenous metabolism sets a limit to the lowrest level of nitrogen
equilibrium attainable. Just where that level is fixed will depend on how
much, if any, urea is derived from the same catabolic processes that produce
the creatinin. If this can be determined, we shall have a formula expressing
more or less definitely the point of lowest attainable protein catabolism,
because at such a point the percentage composition of the urine should be
practically constant. The total nitrogen eliminated when this constant com-
position of the urine has been reached will indicate the lowest attainable
level of nitrogen equilibrium."
The condition of nitrogenous equilibrium, therefore, is one which may
be maintained even if the amount of proteid taken as diet far exceeds the
necessities of the economy, the urea being excreted in excessive amount; and
the wasteful use of proteid food which is so common may not be attended
with harmful consequences, so long as the excreting organs are able to elimi-
nate nitrogen from the body.
It is only in cases of growth, by putting on of flesh, as in growing children,
that nitrogen is retained in the body in health, except to a very small amount.
According to calculations which have been made, it appears that the body
puts on thirty grams of flesh for every gram of nitrogen so retained.
Proteids as Fat- and as Glycogen-Formers. Proteid food is un-
doubtedly a source of energy in the body ; and one can say that such proteid
as is, according to Voit's view, metabolized without becoming part of the
tissue may be considered a source of energy. If this be true, one might ex-
pect that proteids could be metabolized into other forms, such as carbo-
hydrates and fats. Bernard long ago stated that proteid was a glycogen-
former; that abundant glycogen was stored in the liver when flesh diet was
fed, and argued that proteid was the source of the glycogen. The careful
work of a number of investigators has not obtained sufficient evidence to
clear up this question absolutely, but the weight of evidence is in favor of the
view that in the body sugar can be formed from proteids. Whether or not
proteid can be metabolized into fat, and stored as such, seems at present an
open question, notwithstanding the immense amount of work expended in
trying to solve the problem.
Cramer fed 450 grams of lean meat per day to a cat in a respiration cham-
ber for 8 days. The daily excretion of nitrogen was 13 grams, of carbon
THE EFFECT OF AN ALBUMINOID DIET 411
34.3 grams; calculating the amount of carbon in the food as 41.6 grams
daily, this would leave 7.3 grams retained. This carbon might be stored in
the form of glycogen or as fat. Calculated as glycogen, it gives an amount
greater than an animal of that size could retain. Therefore, the probabilities
are that the carbon is deposited in the form of fat.
In the examination of the fat formed in the larvae of blow-flies developing
in a quantity of coagulated blood, Hoffmann found ten times more fat than
existed in the blood. These experiments point in the direction of fat for-
mation from proteid.
The Effect of an Albuminoid Diet. The albuminoid eaten in great-
est quantity is gelatin. Though gelatin closely resembles the proteid mole-
cule chemically, it cannot replace the proteid of the food. In other words,
nitrogenous equilibrium cannot be maintained on a diet consisting of gelatin,
carbohydrates, and fats. Proteid food is absolutely essential to the reconstruc-
tion of the proteid molecule. Gelatin is one of the proteid-like substances
whose food value is comparable to that of carbohydrates and fats, as the
following experiments will prove : On a diet of 500 grams of meat, without any
gelatin, the subject lost nitrogen to the equivalent of 22 grams of proteid, but
when 200 grams of gelatin were added the subject gained 54 grams. In another
experiment, when the diet consisted of 2,000 grams of meat without gelatin,
the gain was the equivalent of 30 grams of proteid, but when 200 grams of
gelatin were added the gain became 376 grams. The lack of real proteid
food value is proven by still a third experiment in which the diet consisted
at first of 200 grams each of meat and of gelatin; here the gain was the equiva-
lent of 25 grams of proteid, but, when the meat was omitted and the gelatin
alone given, there was a loss of 118 grams. In these cases gelatin did not
take the place of proteid in any sense, but rather saved it from oxidation as
a source of energy. The proteid was so protected that, instead of being used
up, it helped to form tissue and increased the body weight. Gelatin, there-
fore, saves proteid material for constructive processes.
Formation of Urea. The nitrogenous fraction of the proteid molecule
is in the end converted largely into urea and is excreted from the body in
that form, as described in the chapter on Excretion. The method of forma-
tion of urea, as well as the place where this occurs, has given rise to great
controversy, while the intermediate products between proteids and urea
have not as yet been fully determined. We can state with certainty that
urea is not formed in the kidneys, since it is not only found in the blood of
the renal artery, but it accumulates in the blood if the kidneys are diseased
or removed and the separation of the urine is interfered with. Circulation
of blood through the kidney does not result in the formation of more urea
than is present in the blood to begin with.
There are a number of experiments that prove that urea is formed in the
liver. The power of the liver cells to form urea is shown by the increase of
412 METABOLISM, NUTRITION, AND DIET
urea in the blood leaving an isolated living liver through which an artificial
circulation is kept up. When ammonium carbamate and other ammonium
salts are added to the blood, the urea increases more rapidly and to a greater
extent. This change occurs even when the living hepatic tissue is chopped
up and simply mixed with the ammonium compounds in a beaker.
If blood from a well-fed animal be circulated through the isolated liver,
there is a distinct increase in the amount of urea it contains. On the other
hand, if the blood be from a fasting animal there is little or no increase of
urea. Evidently, then, the blood from a well-fed animal contains something
which the liver cells are capable of transforming into urea. And, finally, if
the liver be removed and the animal kept alive, as has been done by Pawlow,
there is a marked diminution in the quantity of urea in the urine. The
power of the liver to form urea is thus demonstrated. The question which
now presents itself is, what is this antecedent substance or substances ?
It has already been indicated that urea follows closely the amount of
proteid taken with the food, hence we must look directly to the nitrogenous
fraction of proteid cleavage as the final source of urea. While the different
steps in the process of cleavage, probably hydrolytic (Folin), are yet very
obscure, still it is believed that proteids are first broken down to an ammonia
stage and then again built up into urea by the liver. It is now believed that
ammonium carbamate is at least one true antecedent of urea.
In these experiments the liver is first shut out of the general circulation
by an Eck's fistula connecting the portal vein with the vena cava. This
operation cuts off the chief blood supply of the liver, viz., the portal blood,
but it leaves the small hepatic artery with its oxygen supply to the liver.
When animals survive this operation it is found that they can live only when
fed very carefully on a mixed diet from which proteids are almost entirely
eliminated, and that, if the food contain an excess of proteids, convulsions
ensue with fatal termination. Investigation of the composition of the urine
and of the blood, with the Eck's fistula, shows that the end product of proteid
metabolism is represented by ammonium carbamate and that there is a con-
siderable decrease in urea. If ammonium carbamate is injected into the
blood of normal animals in a larger quantity than the liver can dispose of,
death ensues, following convulsions of the same nature as those produced
by an excess of proteid food in the animals operated on. Ammonium car-
bamate is shown to be, in part at least, the direct antecedent of urea; it is also
shown to be a toxic substance which may cause death by accumulating in
excess. The reaction by which the liver changes it to the inert form of urea
is as follows:
NH2 NH2
/ /
CO — H20 = CO
\ \
OHH4 NH2
Ammonium carbamate. Urea
FORMATION OF URIC ACID 413
The steps by which absorbed proteids are changed to ammonium car-
bamate, etc., are as yet undecided. According to one view, while still in the cir-
culating medium, they are metabolized by direct contact with the living bio-
plasm of the tissues; according to another, they must first be incorporated
into the substance of the body tissues and then changed. The intermediate
steps occur chiefly in the intestinal tract and in muscle tissue, and there is
good reason to suppose that some of the steps are represented by various
extractives which are formed in these regions. 'These substances probably
break down into carbon dioxide, ammonia, and amido-acids, and are then
built up by synthetic processes into ammonium carbamate. Another possible
antecedent is ammonium lactate; this is derived from the lactic acid which
is produced in large quantities in the muscles. The elimination of urea is
increased very slightly by muscular activity. But there is no direct relation-
ship between the amount of work done and the amount of nitrogen excreted
as urea.
There is experimental evidence to show that while the liver produces the
major part of the urea eliminated, other organs or tissues are capable of
forming it to a limited degree.
Formation of Uric Acid. The relations which uric acid and urea bear
to each other in different animals, as we have seen, is still obscure. The
fact that they exist together in the same urine makes it seem probable that
they have different origins. The entire replacement of one by the other, as
of urea by uric acid in the urine of birds, serpents, and many insects, and of
uric acid by urea, in the urine of the feline tribe of mammals, shows their
close relationship. But although it is true that one molecule of uric acid
is capable of splitting up into two molecules of urea and one of mes-oxalic
acid, this is not evidence that uric acid is an antecedent of urea in the
nitrogenous metabolism of the body. The chemical structure of the uric
acid shows it has a nucleus of purin, and therefore is a close relative of
adenin, guanin, hypoxanthin, xanthin, theobromin, caffein, etc. The nucleins
on cleavage yield members of this group, hence may be looked to as the
primary source of uric acid in man. Uric acid, according to Chittenden,
has a double origin — endogenous from nuclear metabolism, and exogenous
from metabolism of foods rich in nuclear and other purin compounds. In
man, at least, the uric acid is to be ascribed to these two sources.
Operative experiments on birds tend to show that the final step in uric-
acid formation takes place chiefly in the liver, for on the removal of this organ
other nitrogenous compounds, i.e., lactates, accumulate in the blood.
Hippuric Acid, Creatinin, etc. The hippuric acid found in the
urine is derived in part from some constituents of vegetable diet, though man
has no hippuric acid, as such, in his food, nor, commonly, any benzoic acid that
might be converted into it. It is derived in part from the natural disintegra-
tion of tissues, independent of vegetable food. Weismann constantly found
414
METABOLISM, NUTRITION, AND DIET
an appreciable quantity, even when living on an exclusively animal diet.
Hippuric acid is formed from the union of benzoic acid with glycin
(C2H5NO2 + C?H6O2 = C9H9 NO3 + H2O), which union takes place under
experimental conditions in the kidneys themselves.
The source of the nitrogenous extractives of the urine is chiefly from the
metabolism of the nitrogenous foods and tissues, but we are unable to say
whether these nitrogenous bodies have merely resisted further decomposition
into urea, or whether they are the representatives of the decomposition of
special tissues, or of special forms of metabolism of the tissues. There is,
however, one exception, and that is in the case of creatinin. This represents
not only the creatinin which enters the body in ordinary flesh food, but is a
nitrogenous v/aste which Folin regards as a measure of muscle metabolism.
The creatinin eliminated is almost a constant quantity in a given individual,
irrespective of the quantity of proteid in the diet. Koch has attempted to
trace a quantitative relation of creatinin excretion to lecithin in the food.
THE METABOLISM OF FATS.
Fats, with carbohydrates, are the direct source of most of the energy
manifested by the body, a fact demonstrated by numerous observations.
The Energy Value of Fats in Metabolism. Fats, in comparison
with other food principles, are of especial value as sources of energy. They
are completely oxidized in the body to carbon dioxide and water, and yield,
therefore, as much energy to the body as they yield upon oxidation outside
the body. The energy equivalent of one gram of fat is 9.3 large Calories,
more than twice that of starch or of proteid, which in the body yield only
4.1 Calories each per gram.
A study of the elimination of nitrogen and of carbon during fasting shows
that the fats contribute to energy formation for many days. This is illus-
trated by the following computation by Voit:
METABOLISM IN A DOG DURING FASTING. (Vorr.)
Loss PER KILOGRAM OF LIVE WEIGHT.
Proteids
in Grams.
Fats
in Grams.
Total
Weight.
Second day
2.21
2.62
72.87
Fifth day
I 1 3
•2 2?
•?! 67
Eighth day
O.o6
3-2c;
3O. <?4
The amount of fat metabolized is sharply influenced by the amount and kind
of other food. For example, if the amount of fat metabolized per day in
fasting is first determined, then a ration of proteid given for a few days,
followed by a second fasting period, it will be found that the metabolism of
SOURCE OF THE BODY FAT
415
body fat is sharply increased in the second period, due to the stimulating
influence of the proteid.
This is demonstrated by the following determination of Rubner:
FOOD OF DOG.
(Rubner.)
Nitrogen of
Food.
Nitrogen
Excreted.
Body Fat
Metabolized.
o. . .
o.
4.38
49-33
4 11) crams lean meat
14. ii
13-72
25.44 average
o
o.
2.80
79-94
760 grams lean meat ....
2< . l6
20. 63
30 . 73 first two days
The fat of the ordinary daily diet is absorbed into the blood and no doubt
contributes directly to oxidation processes. Just the steps in this oxidation
process cannot at present be given. If the fat food is insufficient, then the
body store is drawn upon ; if in excess, then it is stored in the body.
Source of the Body Fat. Excess of fat in the food can be stored
as fat in the body. This fact is demonstrated by Voit, Hoffmann, Rubner,
and others. Rubner states that 82 to 92 per cent of the fat excess can be
stored. The fat stored is of the same kind given in the food, even though
the usual fat of the animal is different. The melting point of dog's fat is
about 20° C., but by feeding an excess of mutton fat the melting point has been
raised to 40° C. The subcutaneous fat of pigs subjected to this experi-
ment is more or less fluid according to the melting point of the fat fed.
The body fat can also be derived from carbohydrate food, a fact which
the practices of the stock feeder and dairyman constantly verify. Two ex-
periments will present the matter more vividly than pages of description.
GAIN IN FAT OF A PIG FED ON RICE. (MEISSL AND STROHMER.)
PIG WEIGHT.
Rice Fed
Daily.
Fat in
Food.
Proteid
in Food.
Proteid
Gain.
Carbon
Gain.
Net Gain
in Carbon.
I4okgm.
2 kgm.
5-3gm-
104 gm.
38 gm-
289 gm.
269 gm.
It is obvious that the 5.3 grams of fat and the 66 grams of proteid cannot
account for the carbon retained, and one must look to the carbohydrate as
the source of the fat.
Jordan placed a Jersey cow on a feed of hay and grain from which the
fat was extracted. The cow in 95 days assimilated 5.7 pounds of fat, in-
creased 47 pounds in weight, and produced 62.9 pounds of fat in the milk.
The nitrogen excreted was the equivalent of 33.3 pounds of proteid. The
non-nitrogenous moiety of the proteid, if its carbon had all gone into fat,
could not have produced over 17 pounds. Summarized, this experiment
416 METABOLISM, NUTRITION, AND DIET
shows conclusively that fat is synthesized from carbohydrate. It requires
about 2.7 grams of dextrose to form i gram of fat, and this condensation
takes place with the formation of carbon dioxide and water and the libera-
tion of about 15 per cent of the available heat of oxidation.
Persistent excess of carbohydrate food produces an accumulation of fat,
which may not only be an inconvenience causing obesity; but may interfere
with the proper nutrition of muscles, produce a feebleness of the action of
the heart, and other troubles.
The formation of fat from proteid is discussed on page 410.
Obesity is a condition of excessive storage' of fats. In many of these
cases there is persistent storing of fat in the presence of a diet of low energy
value and with considerable physical labor. It seems that such persons
must have a very economic protoplasmic metabolism, a biological factor that
lacks sufficient explanation.
THE METABOLISM OF CARBOHYDRATES.
Energy Value. The nutritive function of carbohydrates in the body
is to serve as a source of energy. They are oxidized, with the ultimate pro-
duction of carbon dioxide and water, and must liberate the same amount
of energy as when burned outside the body, i.e., 4.1 Calories. A given
weight of dextrose, therefore, furnishes much less energy than a correspond-
ing weighc of fat.
Carbohydrates are strictly energy-formers and may be regarded as the
immediate source of the energy of oxidations, while fats are reserves drawn
on only after the carbohydrates are used up. Dextrose is a constant constitu-
ent of the blood to the extent of about i to 1.5 per cent. When this percentage
is increased above 2.5, the dextrose is either stored as glycogen, i.e., in the
case of the portal blood during the absorption of a carbohydrate meal, or
eliminated by the kidney, i.e., in diabetes.
The Formation of Glycogen — Glycogenesis. The important fact
that the liver normally forms sugar, or a substance readily convertible
into it, was discovered by Claude Bernard in the following way: He fed a
dog for seven days with food containing a large quantity of sugar and starch;
and, as might be expected, found sugar in both the portal and hepatic blood.
But when the dog was fed with meat only, to his surprise, sugar was still
found in the blood of the hepatic veins. Repeated experiments gave in-
variably the same result. No excess of sugar was found in the portal vein
under a meat diet, if care was taken to prevent reflux of blood from the hepatic
venous system. Bernard found sugar also in the substance of the liver. It
thus seemed certain that the liver formed sugar even when, from the absence
of saccharine and amyloid matters in the food, none could be brought directly
to it from the stomach or intestines.
SOURCE OF GLYCOGEN 417
Bernard subsequently found that a liver removed from the body, and
from which all sugar had been completely washed away by injecting a stream
of water through its blood-vessels, contained sugar in abundance after the
lapse of a few hours. This post-mortem production of sugar was a fact
which could be explained only on the supposition that the liver contained a
substance readily convertible into sugar. This theory was proved correct
by the discovery of a substance in the liver allied to starch, termed glycogen.
Bernard's brilliant researches led him to announce the theory that the
carbohydrate which is periodically absorbed in large amount is stored in the
liver only to be reconverted to dextrose and discharged back into the blood
stream whenever the percentage falls below a certain level. He regarded the
liver as a storehouse which regulated the blood dextrose to a constant level.
This is the glycogenic function of the liver.
Source of Glycogen. The greatest amount of glycogen is produced
by the liver upon a diet of starch or sugar, but a certain quantity is, or at
least may be, produced upon a proteid diet. The glycogen, when stored in
the liver cells, may readily be demonstrated in sections of liver containing it
by its reaction (red or port-wine color) with iodine, and, moreover, when the
hardened sections are so treated that the glycogen is dissolved out, the proto-
plasm of the cell is so vacuolated as to appear little more than a framework.
There is no doubt that in the liver of a hibernating frog the amount of glyco-
gen stored up in the liver cells is very considerable.
AVERAGE AMOUNT OF GLYCOGEN IN THE LIVER OF DOGS UNDER VARIOUS DIETS. (PAVY.)
Diet. Amount of Glycogen in the Liver.
Flesh food 7 . 19 per cent
Flesh food with sugar 14.5
Vegetable diet, i.e., potatoes with bread or barley meal I7-23 "
The dependence of the formation of glycogen on the kind of food taken
is also shown by the following results, obtained by the same experimenter:
AVERAGE QUANTITY OF GLYCOGEN FOUND IN THE LIVER OF RABBITS AFTER FAST-
ING, AND AFTER A DIET OF STARCH AND SUGAR RESPECTIVELY.
After three days' fasting Practically absent
" diet of starch and grape-sugar 15.4 per cent
cane-sugar 16.9 "
Glycogen is also formed from fats in diabetes, but there is no clear proof
that fats increase the amount of glycogen in the cells. Glycerin injected into
the alimentary canal may also increase the glycogen of the liver. The diet
most favorable to the production of a large amount of glycogen is a mixed
diet containing a large amount of carbohydrate, but with some proteid.
Glycogen is stored in other organs of the body. Of these the muscles
are deserving of special mention. The amount of glycogen in the muscles
27
418 METABOLISM, NUTRITION, AND DIET
of young animals is often considerable. The placenta is also a storehouse
of glycogen.
The Destination of Glycogen. The chief theories concerning the
use of glycogen in the organism are advanced by Bernard and by Pavy.
The former considers glycogen as a reserve supply of carbohydrate. When-
ever the glycogen of the blood is reduced below the normal level, i.e., about
o.i to 0.15 per cent, there is a conversion of glycogen into sugar. The sugar
enters the blood and passes to the tissues where its oxidation is a source of
energy. Pavy considers glycogen to be a stage in the synthesis of carbohydrate
to fat and proteid. Bernard's theory is more generally accepted. It ex-
plains more satisfactorily why the sugar content of the blood is so constant.
The conversion of glycogen to sugar takes place by the action of an intracellu-
lar ferment in the glycogenic cells. Such an enzyme has been isolated for
the liver. It is this enzyme that converts the liver glycogen to dextrose after
death, and which is destroyed by boiling in the usual process of isolating
glycogen.
Glycosuria. Sugar may be present to excess not only in the hepatic
veins, but in the systemic blood. When such is the case, the sugar is ex-
creted by the kidneys, and appears in variable quantities in the urine. This
condition is known as glycosuria.
Glycosuria may be experimentally produced by puncture of the medulla
oblongata in the region of the vaso-motor center, puncture diabetes. The
better fed the animal, the larger is the amount of sugar found in the urine
following this operation. In the case of a starving animal no sugar appears.
It is, therefore, highly probable that the sugar comes from the hepatic glyco-
gen, since in the one case glycogen is in excess, and in the other it is almost
absent. The nature of the influence is uncertain. This influence may be
exercised in dilating the hepatic vessels, or possibly may be exerted on the
liver cells themselves.
Many other circumstances will cause glycosuria. It has been observed
after the administration of various drugs, e.g., strychnine; phloridzin, a glu-
coside, and its derivative phloretin, which is not a glucoside; morphine;
adrenalin; nitrite of amyl, etc.; after the injection of curari, poisoning with
carbonic-oxide gas, the inhalation of ether, chloroform, etc., the injection of
oxygenated blood into the portal venous system. Glycosuria has been
observed in man after injuries to the head and in the course of various
diseases. In such cases the glycosuria appears to be due either to some ab-
normal activity of the liver cells themselves or to an interference with the
normal metabolism of the carbohydrate group. In this latter case it is pos-
sible that the usual complete oxidation of carbohydrate is interfered with.
The well-known disease, diabetes mellitus, in which a large quantity of
sugar is persistently excreted daily with the urine, has, doubtless, some close
relation to the normal functions of the pancreas. The nature of the relation-
MINERAL MATTERS, WATER, ETC.
419
ship has not yet been determined, though some recent experiments seem to
be pertinent, page 431.
Mineral Matters, Water, etc. The chief mineral constituents of
the foods are sodium, potassium, calcium, magnesium, and iron, together
with chlorine, sulphur, and phosphorus. The inorganic substances are not
a source of heat. They may supply a certain amount of energy, as osmotic
energy, but this is of no significance as compared with their influence on the
metabolism of organic substances. An animal fed on a normal food deprived
of the mineral constituents survives only a few weeks at most.
The amount of mineral matter in the tissues of the human body, exclusive
of the skeletal parts, is about one per cent. It is safe to say that this is chiefly
in complex organic combination in the body. The daily quantity excreted
is about twenty to thirty grains. This quantity enters the body in the food,
chiefly in combination with complex compounds. It is a question as to what
per cent of inorganic salts, like the calcium, the phosphates, and the iron,
is available when taken into the body in inorganic form.
We have discussed in previous chapters the role of certain salts in
their influence on metabolism; for example, of sodium, potassium, calcium,
iron, etc. Foods like milk and eggs are especially rich in calcium and
phosphorus, and are particularly desirable for young children, the for-
mer for its influence on the growth of the skeleton, the latter for the same
reason and as a stimulator of growth of protoplasm in general. Lack of
mineral constituents, especially calcium compounds, in food shows its in-
fluence on metabolism in the disease known as rickets.
Investigations are in progress at the present time which may demonstrate
more fully the specific influence of phosphorus on animal nutrition and on
growth. Tunnicliff has just demonstrated that an increase of the phos-
NUTRITION EXPERIMENT IN FIVE-MONTHS-OLD PIGS. (E. B. FORBES.)
Rations.
Per cent Gain
in Live Weight
in 60 Days'
Feeding.
Per cent Gain in Certain Tissues
Corresponding to One per Cent
Gain in Live Weight.
Psoas
Muscle.
Ash of
Humerus.
Thickness
of Back Fat.
Hominy ; blood flour; bran ex-
tract. (Phosphorus mostly
as phytin)
69.I
6t.o
41.6
.81
.61
.72
•59
.72
.08
.64
.82
1.04
Hominy; blood flour; bone flour.
(Phosphorus mostly as tri-
calcic phosphate) . ...
Hominy; blood flour. (Low
phosphorus ration)
420
METABOLISM, NUTRITION, AND DIET
phorus content of the food of children, if given in complex organic form,
increases the efficiency of the metabolism of nitrogen by as much as 10 per
cent. If given to children as calcium phosphate it has no beneficial influence
in this regard. Forbes, in his experiments on the nutrition of pigs, shows
that the individuals fed with food to which phosphorus was added, as ground
fresh bone, grew larger and stronger skeletons.
PERCENTAGE OF PHOSPHORIC ACID (P2OB) IN SOME FRESH FOODS. (QUOTED FROM
GlRARD, BY HUTCHINSON, IN " FOOD AND DIETETICS.")
Vegetable. Per cent.
Carrot o . 036
Turnip 0.058
Cabbage 0.089
Potato o . 140
Chestnuts o. 200
Barley meal 0.230
Animal. Per cent.
Pork 0.160
Milk 0.220
Beef -. ... 0.285
Eggs 0.337
White cheese °-374
Mutton °-42S
Salts in the body not only take part in the reactions themselves, but they
stimulate in other substances reactions that are of incalculable benefit to
the body.
The necessity for the taking of water in order to balance the daily excretion,
is sufficiently obvious. Man will live only a few days if deprived of water.
Effects of Deprivation of Food. The animal body deprived of all
food dies from starvation in the course of a variable time. The length of
time that any given animal will live in such a condition depends upon many
circumstances, the chief of which are the nature and activity of the metabolism
of its tissues.
The effect of starvation on the lower animals is, first of all, as might be
expected, a loss of weight. The loss is greatest at the beginning of the de-
privation period, but afterward decreases to a level from which it does not
vary much day by day until death ensues. Chossat found that the ultimate
proportional loss in different animals experimented on was almost exactly
the same, death occurring when the body had lost forty per cent of its original
weight. Different parts of the body lose weight in very different proportions.
The following most noteworthy losses are taken, in round numbers, from
the table given by Chossat:
Per Cent.
Fat
Per Cent.
O1?
Liver
Blood
71?
Spleen
71
Nervous tissues
Pancreas. .
64
These figures are in practical agreement with those of later experimenters.
They show that the chief losses are sustained by the adipose tissue, the mus-
cles and glands.
EFFECTS OF DEPRIVATION OF FOOD
421
The effect of starvation on the temperature of the various animals ex-
perimented on by Chossat was very distinct. For some time the variation
in the daily temperature was more marked than its absolute and continuous
diminution, the daily fluctuation amounting to 3° C. instead of 0.5° to i° C.,
as in health. The temperature fell very rapidly a short time before death,
<n
2
&
(D
<f
DAYS OF FASTING
FIG. 310. — The Elimination of Urea by Dogs during Fasting.
•^^— i Following 2,500 grams of meat in the food.
1,500
minimal amount of proteid in the food.
(Voit.)
and death ensued when the loss had amounted to about 16.2° C. It has been
often said, and with truth, that death by starvation is really death from want
of heat. The effect of the application of external warmth to animals cold
and dying from starvation is more effectual in reviving them than the ad-
ministration of food.
The symptoms produced by starvation in the human subject are hunger, ac-
companied, or it may be replaced, by pain, referred to the region of the stomach;
insatiable thirst; sleeplessness; general weakness, and emaciation. The ex-
halations both from the lungs and from the skin are fetid, indicating the
tendency to decomposition which belongs to badly nourished tissues; and death
METABOLISM, NUTRITION, AND DIET
occurs often with symptoms of nervous disorder, delirium, or convulsions.
Death commonly occurs within from six to ten days after total deprivation
of food. This period may be considerably prolonged by taking a very small
quantity of food, or even by water alone. The cases so frequently related
of survival after many days or even some weeks of abstinence have been due
either to the last-mentioned circumstances, or to other no less effectual con-
ditions which prevented the loss of heat and moisture.
During the starvation period the excretions diminish. The urea, as repre-
senting the nitrogen, falls quickly in amount, reaches a minimum where it
remains constant for several days, then finally falls rapidly immediately
before death. The sulphates and phosphates undergo much the same type
of reduction. The carbon dioxide given out and the oxygen taken in di-
minish. The feces diminish, as well as the bile. It is highly probable
that the greater part of the nitrogen represents the loss of weight of the
muscles.
In starvation, then, we see that the only income consists of water and
the inspired oxygen. The whole of the energy of the body given out in the
form of heat and mechanical labor is obtained at the expense of its own
tissues, there being as a result a constant drain of the nitrogen and carbon,
not to mention the other elements of which the tissues are composed. It is
obvious that such a condition cannot be endured for any, length of time.
REQUISITES OF A NORMAL DIET.
It will be understood from the preceding discussion that it is necessary
that a normal diet should be made up of the various classes of foods in suffi-
cient quantity to supply the same amounts of carbon and nitrogen that are
gotten rid of by the excreta. No doubt these desiderata may be satisfied
by many combinations of foods, and it would be unreasonable to expect the
diet of every adult to be the same. The age, sex, strength, and circum-
stances surrounding each individual must ultimately determine what he
takes as food. A dinner of bread and cheese with an onion contains all the
requisites for a meal, but such diet would be suitable only for those possessing
strong digestive powers. It is a well-known fact that the diet of the con-
tinental nations differs from that of our own country, and that of cold from
that of hot climates, but the same principle underlies all, viz., the replace-
ment of the losses of the body in the most convenient and economical way
possible. Any one in active work requires more food than one at rest, and
growing children require less food than, but a different variety, from adult
men and women.
The chief diet-scales which have been drawn up with the object of supply-
ing the proximate principles in the required proportions are given in the
table below:
REQUISITES OF A NORMAL DIET
STANDARD DIETARIES.
423
AUTHOR.
Proteid.
Fat.
Carbohydrate.
Calories.
Voit
118 gra
127
130
io5
125
119
I25
ms
56 gra
52
40
56
35
5i
I25
ms
500 gra
5°9
550
500
540
531
45°
ms
3,055
3,092
3,160
3,022
3,030
3,J40
3,520
Rubner
Jvloleschott
Munk
Wolff
Playfair . . .
Atwater
Average
121 grams
59 grams
510 grams
3,*35
The basis of these diets is to supply the necessary prdteid nitrogen first
of all, and, second, to supply enough potential energy to balance the energy
expended per day.
The amount of the excreted carbon and nitrogen is not always the same.
It has been proved possible, for example, to subsist on 9 or 10 grams of nitro-
gen and 200 grams of carbon per diem, the ordinary diet for needle-women
in London, and the average of the cotton operatives in Lancashire during the
famine, 1862. The amount of these elements excreted falls to figures cor-
responding to such an income. Of course, upon such a diet the metabolism
is low, and persistent physical weakness must be the result, probably from
insufficient carbon. The 9 or 10 grams of nitrogen in such a semi-starvation
diet would be equivalent to 58.5 to 65 grams of proteid, whereas the amount
of proteid in some diets may be as high as 150 and more grams per day.
Chittenden's nutritional experiments, so often referred to in these pages,
have proven that adult men can subsist in nitrogenous equilibrium, and do
vigorous work and maintain good health, on a proteid diet below that given
in the above example, i.e., on 4 to 10 grams of nitrogen. In such diets a
plentiful supply of carbohydrates is permitted.
Not only the proteids but also the fats may vary. The amount may be
as low as 35 grams and as high as 125 grams. The carbohydrates may vary
from 200 grams to 500 grams and upward. Sometimes, with a small pro-
portion of fat, the carbohydrate may be correspondingly increased to make
up the necessary carbon. A useful table, after Payen, will help to show in
TABLE OF PERCENTAGES OF N AND C IN THE FOLLOWING SUBSTANCES.
N. C.
Beef (without bone) . . 3 . 1 1 .
Roast beef 3.528 17.76
Eggs 1-9 13-5
Cow's milk 0.66 8.
Cheese 2 to 7 35 . to
Beans 4.5 42.
Lentils 4.1 48-
Oatmeal
N. C.
I - Q<? 44 .
Bread
I. 28.
Potatoes
. o. 33 ii .
Eels
2. 3O.
Mackerel
. 3-74 ig.26
Sardines in oil
6. 29.
Butter . .
. o . 64 &3 -
424 METABOLISM, NUTRITION, AND DIET
what ways it is possible to obtain the requisite amount of nitrogen and carbon
from the most common food stuffs.
In order to obtain the amount of proteid present from the proportion of
nitrogen, multiply by 6.25.
From these data, or from the composition of foods on page 298, it is pos-
sible to form various diet-scales which shall supply the needs of different
conditions of growth and decay of the body. Assuming that the average
amount of carbon and nitrogen required is about 300 grams and 20 grams
respectively, this may be obtained as follows:
N. C.
340 grams (12 oz. or f Ib. avoirdupois) lean uncooked meat *. . 10 grams 37 grams
906 " (32 oz. or 2 Ibs. avoirdupois) bread 9 " 252 "
19 grams 289 grams
But this diet is not the usual one; a certain proportion of the carbon is
usually supplied as butter, or bacon, and so if 90 grams of butter or bacon
be used it would supply about 72 grams of carbon, and the carbohydrate
would be diminished nearly one-third; but the nitrogen would also be di-
minished from 9 grams to 6 grams. It would be necessary to supply some
extra nitrogenous principle, which might be done by the addition of eggs,
milk, cheese, beans, or of any of the food-stuffs already enumerated at page
298 et seq.j as supplying nitrogenous food chiefly. For example, 56 grams
(2 oz.) cheese contain, on an average, 3 grams of nitrogen and 20 grams of
carbon; or 28 grams cheese, containing 1.5 grams of nitrogen and about
10 grams carbon, together with 225 grams potatoes and 225 grams carrots,
supplying about i gram of nitrogen and 35 grams of carbon, may be
added. The diet would then read as follows:
c.
37 grams
168 "
72 «
10 "
340 gra
600
90
28
225
225
ms lean uncooked meat
N
IO O Q
rams
«
«
bread
6 o
butter
o <c
cheese
I r
potatoes. . )
I O
carrots... C
19.0 grams 322 grams
The 30 grams of salts necessary to replenish the daily loss by excre-
tion in the urine are contained in the meat 16 grams, the bread 12 grams,
and vegetables about 4 grams.
The fluids should consist of about 2,500 to 2,800 grams, and might be
given as water, with or without tea, coffee, or cacao, which are chiefly
stimulants.
The Energy Requirements of the Body. The food must not only
make up for the substances eliminated from the body but must also supply
the potential energy of heat and motion set free in the living body. The
* As meat loses 23 to 34 per cent in cooking, the weight of cooked meat would be
proportionately less.
THE ENERGY REQUIREMENTS OF THE BODY 425
amount of heat is measured in terms of calories, or more often in large calories.
The work energy may be expressed in gram-centimeters or in kilogrammeters.
The heat-unit calories may be transferred into the work-unit gramcenti-
meters by multiplying by .042, and the converse.
The source of the heat and work energy which is produced in the body is
from the metabolic changes of the tissues, the chief part of which is of the
nature of oxidation, since it may be supposed that the oxygen of the atmos-
phere taken into the system is ultimately combined with carbon and hydrogen.
Any change, indeed, which occurs in the protoplasm of the tissues, resulting
in an exhibition of its function, is attended by the evolution of heat and the
formation of carbon dioxide and water. The more active the changes the
greater is the heat produced. But, in order that the protoplasm may per-
form its function, the waste of its own destructive metabolism must be re-
paired by the due supply of food material to be built up in some way into the
protoplasmic molecule. Food is therefore necessary for the production of
heat. In the tissues, as we have several times remarked, two processes are
continually going on : the building up of the protoplasm from the food, anab-
olism, which is not accompanied by the evolution of heat, and the oxidation
of the protoplastic materials, catabolism, resulting in the production of energy,
by which heat is set free. It is not necessary to assume that the combustion
processes, indeed, are as simple as the bare statement of the fact might seem
to indicate. But complicated as the various stages may be, the ultimate re-
sult is as simple as in ordinary combustion outside the body, and the prod-
ucts are the same.
This theory, that the maintenance of the temperature of the living body
depends on continual chemical change, chiefly by oxidation of combustible
materials in the tissues or by the tissues, has long been established. The
quantity of carbon and hydrogen supplied as food, which, in a given time,
unites in the body with oxygen, is sufficient to account for the amount of heat
generated in the animal within the same period, page 406; an amount capable
of maintaining the temperature of the body at from 36.8° to 38.7° C., not-
withstanding a large loss by radiation and evaporation. This estimation
depends upon the chemical axiom that when a body undergoes a chemical
change the amount of energy set free is the same, supposing the resulting
products are the same, whether the change takes place suddenly or gradually.
If a certain number of grams of different substances are introduced as food,
and if they undergo complete oxidation, the amount of kinetic energy, as
shown in the amount of heat and mechanical work, is the same as would be
developed if the same bodies were completely oxidized outside the body.
If one gram of fat be taken into the body and is completely oxidized, result-
ing in the production of a definite amount of carbon dioxide and water, it
may be supposed to have produced the same amount of heat as it would have
produced outside the body. In the case of proteid food it is a little different,
426 METABOLISM, NUTRITION, AND DIET
since it is never completely oxidized within the body, but may be supposed
to give rise to a definite amount of urea, not a completely oxidized body.
In this case the gram of proteid may be considered to perform the same
amount of heat as the proteid would outside the body minus the amount
which would be obtained from the complete oxidation of the resulting urea.
The actual amount of heat produced per diem has been experimentally
ascertained in the case of man and animals by the aid of an apparatus, the
calorimeter. An animal is enclosed in a metal cage completely contained
in a second cage containing water. Air is led into and out of the inner box
by means of metal tubes so arranged that the inlet tubes maintain a con-
stant temperature and the outlet tubes pass through water between the two
chambers. The heat given out by the animal warms the water in the outside
box, and may be estimated by the rise of its temperature, the amount of which
is known. At the same time the carbon dioxide output is measured.
The amount of heat evolved by the oxidation of various food stuffs has
been carefully measured by numerous observers; the figures calculated by
Rubner being perhaps most satisfactory, which are :
HEAT VALUE TO THE BODY.
i gram carbohydrate 4.1 Calories
i " fat 9.3
i " proteid 4. i
One gram of dry proteid has a total heat value of 5.754 (Rubner), hence
it is obvious that proteid is not completely oxidized by the body. Each
gram of proteid yields at least one-third of a gram of urea, which has a heat
value of 2.5 Calories per gram.
Atwater has checked the energy value of the foods actually consumed
against the actual liberation of heat and work energy of the human body.
He finds a wonderfully close agreement both for periods of rest and for periods
of work. Atwater 's estimate for the energy needs of man are summarized
as follows:
Man without muscular work 2,700 Calories
" with light muscular work 3,ooo "
" " moderate muscular work 3>5°° "
" " severe " 4,500 "
The daily output of energy for the adult man is, according to McKendrick,
as follows:
Kilogrammeters. Calories.
Work of heart per day 88,000
Work of respiratory muscle 14,000
Eight hours' active work 213,344
315,334 or 743
Amount of heat produced in 24 hours 1,582,700 or 3,724
,034 or 4,467
THE INFLUENCE OF THE DUCTLESS GLANDS ON METABOLISM 427
This estimate is relatively high for ordinary activity as determined by
Atwater and others. It is indeed more energy than the standard diets in
the table given on page 423 will yield to the body. For example, Voit's
diet yields 3,055 Calories, and the average of the table is only 3,125 Calories.
THE INFLUENCE OF THE DUCTLESS GLANDS ON METABOLISM.
A further question to be considered is the relationship between the metab-
olism of one tissue and the products of the metabolism of other tissues.
The metabolism of one tissue may produce products, proteid or otherwise,
which when taken up by the blood and carried to other tissues supply ex-
actly what is necessary for their complete anabolism.
The physiology of the internal secretions has revealed a number of such
influences that are best explained on the assumption of the presence of spe-
cial products.
The Thyroid. The thyroid gland is situated in the neck. It con-
sists of two lobes, one on each side of the trachea, extending upward to the
FIG. 311. — Part of a Section of the Human Thyroid, a, Fibrous capsule; b, thyroid vesicles
filled with, e, colloid substances; c, supporting fibrous tissue; d, short columnar cells lining vesicles;
/, arteries; g, veins filled with blood; h, lymphatic vessel filled with colloid substance. (S. K.
Alcock.)
thyroid cartilage, covering its inferior cornu and part of its body; these lobes
are connected across the middle line by a middle lobe or isthmus. The
428 METABOLISM, NUTRITION, AND DIET
thyroid is covered by the muscles of the neck. It is highly vascular, and
varies in size in different individuals.
The gland is encased in a thin transparent layer of dense areolar tissue,
free from fat, containing elastic fibers.
These gland vesicles are each lined with a single layer of cubical cells and
are filled with transparent nucleo-albuminous colloid material.
Accessory Thyroids. The accessory and the parathyroids possess
the structure of the thyroid and apparently perform the same function. The
accessory thyroids undergo hypertrophy when the thyroid has been removed.
The colloid material which is formed within the thyroid vesicles, and is
believed to be their secretion, finally ruptures through their walls into the
lymph channels and thus gains entrance to the circulation. The secretion
of the thyroid falls intq> the class known as internal secretions, and exerts a
profound influence upon the metabolic processes of the body, probably
through its influence on the central nervous system. Complete extirpation
of the thyroid, at least in some animals, produces death, preceded by a group
of characteristic symptoms. In man and the monkey the symptoms after re-
moval come on slowly and resemble the disease known in man as myxedema.
This disease is known definitely to be due to disease of the thyroid, where-
by its function is interfered with. Moreover, if a piece of thyroid of sufficient
size be grafted into an animal from which the glands have been removed,
and the graft takes, the symptoms of thyroid removal are lessened in inten-
sity or disappear altogether. Thyroid feeding or the administration of
thyroid extracts relieves the symptoms of the disease myxedema.
The above facts show that the thyroid gland must perform some im-
portant function in the animal economy, and it is believed that this is accom-
plished by virtue of its internal secretion. The colloid material of the gland
has been submitted to much chemical study, and a substance called iodo-
thyrin has been isolated as its active principle. Baumann and Roos state
that iodothyrin exists in the gland in combination with proteid bodies. lodo-
thyrin relieves the symptoms of thyroid removal much to the same extent
as thyroid feeding. It is a very resistant substance, and is not injured by the
action of the gastric juice or by boiling with 10 per cent sulphuric acid for
a long time.
The Suprarenal Capsules or Adrenals. These are two flattened,
more or less triangular or cocked-hat shaped bodies, resting by their lower
border upon the upper border of the kidneys.
The gland tissue proper consists of an outside firmer cortical portion, and
an inside soft dark medullary portion, figure 312.
The adrenals are very abundantly supplied with nerves, chiefly com-
posed of medullated fibers. These fibers are derived from the solar and renal
plexuses and the vagi, but the method of their termination is unknown.
A vast amount of information has been given concerning the function of
THE SUPRARENAL CAPSULES OR ADRENALS
429
the suprarenal capsules within the last few years by the researches of Schafer
and Oliver, Zyboulski, Abel, and others. Brown-Sequard, it is true, showed
by experiment as early as 1856 that removal of the suprarenals is followed
by the death of the animal, but his experiments were repeated by others who
^L A
FIG. 312. — Vertical Section of Adrenal. A, Capsule; B, cortex; C, medulla; a, glomerular
zone; b, f ascicular zone ; c, reticular zone; v, vein in medulla. (Merkel-Henle.)
did not obtain the same results; and it was concluded that the suprarenal
capsules had no function, or at least that their function was not known.
Death was preceded in the case of Brown-Sequard's animals by symptoms
somewhat analogous to those of the disease of man known as Addison's
disease. The failures to produce symptoms after attempted removal of the
glands have probably resulted from incomplete removal or the presence of
430
METABOLISM, NUTRITION, AND DIET
accessory bodies. Accessory suprarenal capsules are commonly present in
some animals and are sometimes found in man. Further, if one gland is
removed, the other hypertrophies. The experiments of all recent observers
confirm the original experiments of Brown-Se'quard. The presence of the
suprarenal capsules is essential to life.
Schaffer and Oliver found that injections of suprarenal extract produced
marked effects upon the muscular layer of the arteries, the muscular tissue
of the heart, and the skeletal muscles. The muscular layer of the arteries
is markedly contracted, causing vaso-constriction and a rise of blood pressure.
FIG. 313. — Injection of Suprarenal Extract.
pressure, after section of cord and vagi. (Reduced to one-half.)
Effect upon the heart, limb, spleen, and blood
(Schaffer.)
When the heart is freed from nervous control its contractions are increased
both in force and frequency, still further raising blood pressure. If the vagi
are undisturbed the heart beats more slowly, showing an increase of vagus
tone due to stimulation of the vagus center in the medulla. The contraction
of the skeletal muscles in response to a single stimulus is increased.
Very small doses of suprarenal extract are sufficient to produce marked
effects. Thus Schaffer states that less than TTGITO g^111 ("g^ir 8ram) °f tne
desiccated gland is sufficient to produce an effect upon the heart and arter-
ies of an adult man.
It is a curious fact that only extracts of the medullary portion of the gland
THE PITUITARY BODY 431
are active. It has been further shown, by Christian! and others, that if only
small portions of the medulla remain, the animal operated upon survives;
while if all the medullary substance be removed, even though large portions
of the cortex remain, the animal invariably dies.
Abel has succeeded in separating the blood-pressure-raising constituent
of the extract, and calls it epinephrin, C10H13NO3 JH2O. Adrenalin was
isolated by Takamine and assigned the formula C9H13NO3. The hydro-
chloride salt is prepared commercially and produces all the vascular effects
assigned to the gland.
Destruction of the suprarenal capsules through disease in man results in
the production of a group of symptoms known as Addison's disease. The
administration of suprarenal extract to these cases sometimes results bene-
ficially, but not so uniformly as thyroid feeding does in myxedema.
Dreyer has given evidence that the products of this gland are discharged
into the blood of the adrenal vein in increased quantity on splanchnic stim-
ulation.
This gland furnishes, on the whole, very conclusive evidence of the pres-
ence of an internal secretion that is absolutely necessary to the normal metab-
olism of other organs.
The Pituitary Body. This body is a small reddish-gray mass,
occupying the sella turcica of the sphenoid bone.
It consists of two lobes, a small posterior one of nervous tissue, and an
anterior one resembling the thyroid in structure. The gland spaces are oval,
nearly round at the periphery, spherical toward the center of the organ, and
are filled with nucleated cells of various sizes and shapes not unlike gan-
glion cells.
The function of the pituitary body has not yet been fully established.
It has been supposed that the pituitary body has a function associated with
that of the thyroid. On the other hand, tumors or other disease of the pitui-
tary body have been found after death in association with a disease known
as acromegaly, in which the bones and soft parts undergo great hypertrophy.
Howell has found that extracts of the glandular lobe are inactive, but that
extracts of the infundibular lobe, when injected into the circulation, produce
marked rise of blood pressure, increase of vagus tonic ' inhibition, and an
augmentation of the heart's force.
The Internal Secretion of the Pancreas. Minkowski and von
Mering have shown that total extirpation of the pancreas is followed in all
cases by the appearance of sugar in the urine in the course of a few hours.
The amount of sugar which appears is considerable, from 5 to 10 per cent.
This experimental disease is accompanied by an increase in the quantity of
urine and by abnormal thirst and appetite, and proves fatal in fifteen days or
less. These results are obtained only when the entire gland or more than
nine-tenths of it have been removed. If one-tenth or more of the gland be left
432 METABOLISM, NUTRITION, AND DIET
behind, sugar appears in the urine when carbohydrates are eaten, but not
otherwise. Nor is it necessary that the remaining portion of the gland be in
its normal situation. Successful grafts of pancreas under the skin of the
abdomen or elsewhere will prevent the appearance of sugar in the urine and
the other symptoms. If, however, the graft be subsequently removed, the
sugar in the urine and the other symptoms reappear, and the experimental
disease proceeds to a rapidly fatal issue.
The symptoms produced by total extirpation of the pancreas do not de-
pend upon the loss of the pancreatic juice proper to the organism. This
secretion may be diverted from the intestine through a pancreatic fistula
without the production of diabetes. Moreover, Hedon and Thiroloix have
rendered the acini of the gland functionally inactive, and ultimately de-
stroyed them, by the injection of paraffin or other substances into the duct
of Wirsung, without the supervention of diabetes.
These experiments have shown that the ordinary secreting cells degener-
ate and the islands of Langerhans increase in size, leading to the conclusion
that these are the structures that produce a special internal secretion which
influences or controls carbohydrate metabolism in the body. Whether this
hypothetical substance is necessary to the dehydration and synthesis of dex-
trose in the body or whether it is necessary to the complete oxidation of carbo-
hydrate is at present a matter of inference.
The Reproductive Glands. The ovary and the testes are un-
doubtedly concerned with metabolism in the body. It has been shown
repeatedly that extracts of the testes when injected into the system lead to
increased vigor, both of the muscular and of the nervous systems. Ergograms
show an increase in muscular power. Spermin isolated from the testes is
claimed by its discoverer to produce the beneficial effects described. The re-
moval of the testes in domestic animals is followed by an entire change in the
character of the development of the animal, especially in the so-called second-
ary sexual characters. Such animals show less vigor and muscular power.
The removal of the ovaries in women, through surgical operation, has
resulted in very marked nervous symptoms. These symptoms are reduced
or entirely disappear on grafting a portion of the gland, and the disturbed
menstruation following ovariotomy becomes regular again. Experiments by
Loewy and Richter indicate that oxidations in the body are greatly increased
on feeding ovarian extract to ovariotomized animals.
There are other organs whose function is still obscure but in which
the indirect evidence points to an influence on metabolism at one stage or
another of the existence of the animal body. Enough has been given here
to show that the interrelation of the organs is extremely complex in so far as
the metabolism is concerned. It is not enough simply to know the foods and
their composition. The whole complex of intermediary metabolism and
their influence must constantly be taken into consideration.
CHAPTER XII
ANIMAL HEAT
HEAT is produced by the metabolism of the tissues of the body. In man
and in such animals as are called warm-blooded, i.e., only mammals and
birds, there is an average body temperature which is maintained with only
slight variations in spite of changes in their environment. The possible
variations above and below this average are comparatively slight. The
average temperature in all mammals and birds is not the same, for, as we
shall see, the average temperature of man is 37° C. (98.6° F.), in some birds
it is as high as 44° C., while in the wolf it is said to be under 36° C.
The average temperature of the human body in those internal parts which
are most easily accessible, as the mouth and rectum, is from 36.9° to 37.4° C.
(98.5° to 99.5° F.). In different parts of the external surface of the human
body the temperature varies only to the extent of one or two degrees centi-
grade, when all are alike protected from cooling influences; and the differ-
ence which under these circumstances exists depends chiefly upon the
different degrees of blood supply. In the axilla and in the groin, the most
convenient situations, under ordinary circumstances, for examination by the
thermometer, the average temperature is 37° C. (98.6° F.). In different
internal parts, the variation is one or two degrees; those parts and organs
being warmest which contain most blood, and in which there occurs the
greatest amount of chemical change, e.g., the muscles and the glands. The
temperature is highest when they are in a condition of activity. Those tis-
sues which subserve only a mechanical function and are the seat of least ac-
tive circulation and chemical change are the coolest. These differences of
temperature, however, are actually but slight, on account of the provisions
which exist for maintaining uniformity of temperature in different parts.
The average temperature of a healthy body varies somewhat according
to age, sex, time of day, climate, etc. The mean temperature is said to be
slightly higher, 0.5° C., in young children and in old persons than in adults.
It is perhaps very slightly higher in women than in men, in warm climates
than in cold, in winter than in summer. It varies slightly at different times
in the day, especially during sleep when metabolism is at a low ebb.
Heat-producing Organs. Heat is liberated in the body wherever
oxidative metabolism takes place. Of all the tissues of the body muscular
tissue is conspicuous for its mass and for its activity. It is evidently the great
28 433
434 ANIMAL HEAT
heat-producing tissue. The manifestation of muscular energy is always ac-
companied by the evolution of heat and the production of carbon dioxide.
This production of carbon dioxide goes on while the muscles are in mechanical
rest, only in a less degree than that which is noticed during muscular activity,
and so it is certain that an active catabolism is going on in resting as well as
in contracting muscles. This catabolism is a source of much heat, and so
the total amount of heat produced in the muscular tissues per day must be
very great. It has been calculated that, even neglecting the heat produced
by the quiet catabolism of muscular tissue, the amount of heat generated by
muscular activity would supply the principal part of the total heat produced
within the body. The heart, as a special muscle, deserves particular mention
since it is in constant vigorous activity. All its energy is ultimately converted
into heat, accounting for about 5 per cent of the total heat of the body. The
secreting glands, and principally the liver as being the largest and most ac-
tive, come next to the muscles and heart as heat-producing tissues. It has
been found by experiment that the blood leaving the glands is considerably
warmer than that entering them. The metabolism in the glands is very
active; and the more active the catabolism, the greater the heat produced.
It must be remembered, however, that although the organs mentioned are
the chief heat-producing parts of the body, all living tissues contribute their
quota, and this in direct proportion to their activity. The blood itself is also
the seat of catabolism, and, therefore, of the production of heat; but the
share which it takes in this respect, apart from the tissues in which it circu-
lates, is very inconsiderable.
Regulation of the Temperature of the Human Body. The average
temperature of the body is maintained under different conditions of external
circumstance by mechanisms which permit of (i) variation in the loss of heat,
and (2) variations in the production of heat. In healthy warm-blooded ani-
mals the loss and gain of heat are so nearly balanced one by the other that,
under all ordinary circumstances, a uniform temperature, within a degree or
two, is preserved.
Variation in the Loss of Heat. The loss of heat from the human
body is principally regulated by the amount given off by radiation and con-
duction from its surface, by means of the constant evaporation of water from
the same part, heat being thus rendered latent, and to a much less degree by
loss from the air-passages. In each act of respiration, heat is lost to a greater
or less extent according to the temperature of the atmosphere; unless indeed
the temperature of the surrounding air exceeds that of the blood. We must
remember, too, that all food and drink which enter the body at a lower tem-
perature abstract a small measure of heat; while the urine and feces which
leave the body at about its own temperature are also means by which a certain
small amount of heat is lost.
Heat Lost from the Surface of the Body. By far the most impor-
HEAT LOST FROM THE SURFACE OF THE BODY 435
tant loss of heat from the body, probably 90 per cent and upward of the whole
amount, is that which takes place by radiation, conduction, and the evapora-
tion of moisture from the skin. The actual figures are as follows: For every
100 calories of heat produced, 2.6 are lost in heating the food and drink; 2.6
in heating the air inspired; 14.7 in evaporation; and 80.1 by radiation and
conduction. The means by which the skin is able to act as one of the most
important organs for regulating the temperature of the blood, are, i, that
it offers a large surface for radiation, conduction, and evaporation; 2, that it
contains a large but adjustable amount of blood, and the quantity of blood
is greater under those circumstances which demand a loss .of heat from the
body, and vice versa ; 3, that it contains the sweat glands, which discharge a
quantity of moisture to be evaporated from its surface.
The circumstance which directly determines the quantity of blood in the
skin is that which governs the supply of blood to all the tissues and organs
of the body, namely, the power of the vaso-motor nerves to cause a greater
or less tension of the muscular element in the walls of the arteries, and, in
correspondence with this, a lessening or increase of the caliber of the vessel,
accompanied by a less or greater current of blood. A warm or hot atmos-
phere so acts on the sensory nerves of the skin as to lead them reflexly to
cause a relaxation of the muscular fiber of the blood-vessels; as a result,
the skin becomes full-blooded, relatively hot, and moist from sweating; and
much heat is lost. With a low temperature, on the other hand, the blood-
vessels shrink, and with the consequently diminished blood supply, the skin
becomes pale, cold, and dry, an effect produced through the vascular centers
in the medulla and spinal cord.
The activity of the sweat glands of the skin is also regulated reflexly
through the sweat centers. The increased blood supply just described is
favorable to increased production of sweat by the sweat glands. Thus,
by means of the self-regulation the skin becomes the most important of the
means by which the temperature of the body is regulated.
The relative loss of heat by the means given, i.e., radiation, conduction,
and evaporation, will depend on two factors: first, the relative temperature
of the body to the surrounding air; and, second, the humidity of the air. If the
atmospheric temperature is the same as that of the body, of course there will
be no loss of heat by radiation and convection; if the air temperature is
higher, there will be an actual gain. When the humidity of the air is great,
there will be reduced evaporation of perspiration and consequent diminished
heat loss by this means. If we assume a moisture-saturated air at the body
temperature, then heat loss becomes impossible and the temperature of the
body will rise. This is why a hot moist climate is so oppressive, while a
hot but dry atmosphere is readily borne by the human body. The increased
evaporation of perspiration compensates for the decreased loss by radiation
and convection.
436 ANIMAL HEAT
Many examples may be given of the power -which the body possesses of resisting the
effects of a high temperature, in virtue of evaporation from the skin. Blagden and others
supported a temperature varying between 92° to 100° C. (i98°-2i2° F.) in dry air for sev-
eral minutes; and in a subsequent experiment he remained eight minutes in a temperature
of I26.5°C. (260° F.). " The workmen of Sir F. Chantrey were accustomed to enter a furnace,
in which his molds were dried, while the floor was red-hot, and a thermometer in the
air stood at 177.8° C. (350° F.), and Chabert, the fire-king, was in the habit of entering
an oven the temperature of which was from 2O5°-3i5° C. (4oo°-6oo° F.)." (Carpenter.)
But such heats are not tolerable when the air is moist as well as hot, so as to prevent
evaporation from the body. C. James states that in the vapor baths of Nero he was al-
most suffocated in a temperature of 44.5° C. (112° F.), while in the caves of Testaccio, in
which the air is dry, he was but little incommoded by a temperature of 80° C. (176° F.).
In the former, evaporation from the skin was impossible; in the latter it was abundant,
and the layer of vapor which would rise from all the surface of the body would, by its very
slowly conducting power, defend it for a time from the full action of the external heat.
Man is able by suitable clothing to increase or to diminish the amount of
heat lost by the skin. There are baths and other means which man and
animals instinctively adopt for lowering the temperature when necessary.
Although under any ordinary circumstances the external application of cold only
temporarily depresses the temperature to a slight extent, it is otherwise in cases of high
temperature in fever. In these cases a cool bath may reduce the temperature several
degrees, and the effect so produced lasts in some cases for many hours.
Extreme heat and cold produces effects too powerful, either in raising or
lowering the heat of the body, to be controlled by the proper regulating ap-
paratus. Walther found that rabbits and dogs kept exposed to a hot sun,
reached a temperature of 46° C. (114.8° F.), and then died. Cases of sun-
stroke furnish us with several examples in the case of man; for it would seem
that here death ensues chiefly or solely from elevation of the temperature.
The effect of mere loss of bodily temperature in man is less well known
than the effect of heat. From experiments by Walther it appears that rab-
bits can be cooled down to 8.9° C. (48° F.) before they die, if artificial respira-
tion be kept up. Cooled down to 17.8° C. (64° F.), they cannot recover
unless external warmth be applied together with the employment of artificial
respiration. Rabbits not cooled below 25° C. (77° F.) recover by external
warmth alone.
Loss of Heat from the Lungs. The lungs and air-passages are
very inferior to the skin as a means for lowering the temperature. In giving
heat to the air breathed, the lungs stand next to the skin in importance. As
a regulating power, the inferiority is very marked. The air which is ex-
pelled from the lungs leaves the body at about the temperature of the blood,
and is 'always saturated with moisture. No inverse proportion, therefore,
exists, as in the case of the skin, between the loss of heat by radiation and
conduction, on the one hand, and by evaporation, on the other. The colder
the air and the drier, for example, the greater will be the loss in all ways.
Neither is the quantity of blood which is exposed to the cooling influence of
VARIATION IN THE PRODUCTION OF HEAT 437
the air diminished or increased in the lungs, so far as is known, in accordance
with any need in relation to temperature. It is true that by varying the
number and depth of the respirations, the quantity of heat given off by the
lungs may be made to vary also for a few minutes. But the respiratory
passages, while they must be considered important means by which heat is
lost, are altogether subordinate, in the power of actively regulating the tem-
perature.
The loss of heat used to warm foods is an obvious method of expenditure
of heat which may be resorted to, especially in certain fevers. The loss of
heat by the excreta discharged from the body at a high temperature must be
of little use as a means of regulating the temperature, since the amount so
lost must be capable of little variation.
Variation in the Production of Heat. It may seem to have been
assumed, in the foregoing pages, that the only regulating apparatus for tem-
perature required by the human body is one that shall, more or less, produce
a cooling effect; as if the amount of heat produced were always, there-
fore, in excess of that which is required. Such an assumption would be in-
correct. The body has the power of regulating the production of heat, as
well as its loss.
The production of heat in the body is apparently different for each ani-
mal; i.e., the absolute amount of heat set free by different animals in a given
period varies. Each individual has his own coefficient of heat production.
From all that has been said on the subject it will be seen that the amount of
heat for all practical purposes depends upon the metabolism of the tissues of
the body ; everything, therefore, which increases that metabolism will increase
the heat production; so, therefore, the absolute amount of heat produced by a
large animal, having a larger amount of tissues in which metabolism may
go on, will be, c&teris paribus, greater than that of a small animal. But the
activity of the tissue change in a small animal may be greater than in a large
one, as measured per kilo of body-weight, and naturally no strict line can be
drawn between the two.
HEAT PRODUCED PER KILO PER HOUR. (MUNK.)
Man 1.5 calories
Dog (large) 1.7
Dog (small) 3.8
Guinea-pig 7.5
Rat 11.3
Mouse 19.0
Sparrow 35.5
The ingestion of foods increases the metabolism of the tissues. As one
would expect, the rate of heat production is found by experiment upon the
dog to be increased after a meal, reaching its height about six hours after
a meal.
438 ANIMAL HEAT
It has also been experimentally ascertained that the rate of heat produc-
tion varies with the kind of food taken: for example, if sugar be added to the
meal of meat given to the dog, the height of maximum production is reached.
It is often said that the various nations have found by experience what food
is most suitable for the climate in which they live, and that such experience
can be trusted to regulate the quantity consumed. Although there have
been no very conclusive experiments to prove the view, yet it is a matter of
general observation that in northern climates and in colder seasons the quan-
tity of food takerris greater than in warmer climates or in warmer seasons.
Moreover, the kind of food is different. For example, persons living in the
colder climates require much fat in order to produce the requisite amount
of heat.
Influence of the Nervous System on Heat Production. The in-
fluence of the nervous system in modifying the production of heat must be
very important, as upon the nervous influence depends the amount of the metab-
olism of the tissues. The experiments and observations which best illus-
trate it are those showing, first, that, when the supply of nerves to a part is
cut off, the temperature of that part falls below its ordinary degree after a
time; and, second, that when there is severe injury to or removal of the
nervous centers the temperature of the body rapidly falls, even though arti-
ficial respiration be performed, the circulation maintained, and to all appear-
ance the ordinary conditions for chemical changes in the body be com-
pletely maintained.
There is a heat-regulating nervous apparatus closely comparable to that
which regulates the secretion of saliva or of sweat, by means of which the pro-
duction of heat in the warm-blooded animals is increased or diminished, as
occasion requires. This apparatus probably consists of a center or centers
in the brain which may be reflexly stimulated, as, for example, by impulses
from the skin, and which act through special nerves supplied to the various
tissues. The evidence upon which the existence of this regulating appara-
tus depends is the marked effect in the increase of the oxygen consumed by
a warm-blooded animal when exposed to cold, and the corresponding increase
in the output of carbon dioxide, indicating that there is an increase of the
metabolism and so an increased production of heat under such circumstances,
and not a mere diminution of the amount of heat lost by the skin, etc. A
cold-blooded animal reacts very differently to exposure to cold; instead of
increasing the metabolism as in the case of the warm-blooded animal, cold
diminishes the metabolism of its tissues. It is clear, therefore, that in warm-
blooded animals there is some apparatus not possessed by cold-blooded ani-
mals, which counteracts the effects of cold. In warm-blooded animals poi-
soned by curara, or in which section of the medulla has been done, it has been
found that this regulating apparatus is no longer in action, and under such
circumstances no difference appears to exist between such animals and those
INFLUENCE OF NERVOUS SYSTEM ON HEAT PRODUCTION 439
which are naturally cold-blooded. Warmth increases their temperature,
and cold lowers it, and with this there is, of course, evidence of diminished
metabolism.
The explanation of these experiments is that in such animals the connec-
tion between the skin and the muscles through the nervous chain, such as
a thermotaxic nervous apparatus might be supposed to afford, is broken
either at the termination of the nerves in the muscles (curara) or at the sec-
tioned point of the bulb.
The position of these hypothetical centers is a matter of some difference
of opinion. It has been demonstrated that stimulation of certain parts of
the brain may, among other symptoms, produce increased metabolism of the
tissues with increased output of carbon dioxide and a raised temperature:
the parts of which this may be asserted are parts of the corpus striatum and
of the optic thalamus. The general thermogenic centers are probably closely
associated with the motor centers of the cord and brain stem. The thermo-
regulative centers are the nuclei in the corpus striatum and optic thalamus.
Assuming a constant or tonic activity of the thermogenic regulative centers,
it is easy to understand the fall of temperature on their destruction or on the
destruction of the nerve path to the active tissues.
Experimental observations, such as have been made upon animals, receive
confirmation from the observations on patients who suffer from fever or
pyrexia; in them the temperature of the body may be raised several de-
grees, as we have already pointed out. This increase of temperature
might, of course, be due to diminished loss of heat from the skin, but this,
although a factor, is not the only cause. The amount of oxygen taken in
and the amount of carbon dioxide given out are both increased, and with
this there must be increased metabolism of the tissues, and particularly of
the muscular tissues, since at the same time the amount of urea in the urine
is increased. Every one is familiar with the rapid wasting which is such a
characteristic of high fever; it must indicate not only too rapid metabolism
of the body, but also insufficient time for the tissues to build themselves up.
In fever, then, there may be supposed to be some interference with the ordinary
reflex channel by which the skin is able to communicate to the nervous sys-
tem the necessity of an increased or diminished production of heat in the
muscles and other tissues. In consequence of this, and in spite of the con-
dition of increased heat of the body, both at the surface and in the deeper
tissues, the production of heat goes on at an abnormal rate. It is not certain
whether the pathological condition is one which stimulates the thermogenic
center by means of which the metabolism of the tissues is increased, or whether
the normal reflexes which ordinarily inhibit the activity of the center v/hen
the temperature rises fail to bring about their usual reaction. The first is
the probable explanation of the high fevers of certain toxemias,
CHAPTER XIII
MUSCLE-NERVE PHYSIOLOGY
CHEMICAL COMPOSITION OF MUSCLE
Muscle Plasma. The principal substance which can be extracted
from muscle, when examined after death, is the proteid body, myosin, some
of the reactions of which have been already discussed. This body appears to
bear somewhat the same relation to the living muscle that fibrin does to
the living blood, since the coagulation of muscle after death is due to the
formation of myosin. Thus, if coagulation be delayed by removing the
muscles immediately that an animal is killed, and rapidly cooling them to a
temperature below o° C. before the muscles themselves lose their irritability,
it is possible to express from them a viscid fluid of slightly alkaline reaction,
called muscle plasma (Kiihne, Halliburton). Muscle plasma, if exposed to
the ordinary temperature of the air (or more quickly at 37° to4o°C.), undergoes
coagulation much in the same way as does blood plasma under similar cir-
cumstances when separated from the blood-corpuscles at a low temperature.
The appearances presented by the fluid during the process are also very
similar to the phenomena of blood-clotting, viz., first of all an increased
viscidity appears on the surface of the fluid, and at the sides of the containing
vessel, which gradually extends throughout the entire mass, un'il a fine
transparent clot is obtained. In the course of some hours the clot begins
to contract, and to squeeze out of its meshes a fluid corresponding to blood
serum. In the course of coagulation, therefore, muscle plasma separates
into muscle clot and muscle serum. The muscle clot contains the substance
myosin. It differs from fibrin in being easily soluble in a 2 per cent solution
of hydrochloric acid, and in a 10 per cent solution of sodium chloride. It is
insoluble in distilled water, and its solutions coagulate on application of heat;
in short, it is a globulin. During the process of clotting the reaction of the
fluid becomes distinctly acid.
The coagulation of muscle plasma can be prevented not only by cold,
but also, as Halliburton has shown, by the presence of neutral salts in certain
proportions; for example, of sodium chloride, magnesium sulphate, or sodium
sulphate. It will be remembered that this is also the case with blood plasma.
Dilution of the salted muscle plasma will produce its slow coagulation, which
is prevented by the presence of the neutral salts in strong solution.
440
MUSCLE SERUM 441
It is highly probable that the formation of muscle clot is due to the presence
of a ferment, myosin jerment. The antecedent myosin in living muscle has
received the name of myosinogen, in the same way that the fibrin-forming
element in the blood is called fibrinogen. Myosinogen is, however, a mixture
of two globulins which coagulate at the temperatures 47° C. and 56° C. re-
spectively.
Myosin may also be obtained from dead muscle after all the blood, fat, and
fibrous tissue, and substances soluble in water have been removed by subjecting
it to a 10 per cent solution of sodium chloride, or a 5 per cent solution of mag-
nesium sulphate, or a 10 to 15 per cent solution of ammonium chloride,
filtering and allowing the filtrate to drop into a large quantity of water. The
myosin separates out as a white flocculent precipitate. The precipitate gives
all the globulin reactions.
Muscle Serum. Muscle serum is acid in reaction, and almost col-
orless. It contains three proteid bodies, viz.: A globulin (my o globulin),
which can be precipitated by saturation with sodium chloride, or magnesium
sulphate, and which can be coagulated at 63° C.; serum albumin (myo-
albumin), which coagulates at 73° C., but is not precipitated by saturation
with either of those salts ; and myo-albumose, which is neither precipitated by
heat nor by saturation with sodium chloride or magnesium sulphate, but
may be precipitated by saturation with ammonium sulphate. It is closely
connected with, even if it is not itself, myosin ferment. Neither casein nor
peptone has been found by Halliburton in muscle extracts. In extracts of
muscles, especially of red muscles, there is a certain amount of hemoglobin,
and also of a pigment' special to muscle, called by McMunn myo-hematin,
which has a spectrum quite distinct from hemoglobin, viz., a narrow band
just before D, two very narrow bands between D and E, and two other faint
bands, near E b, and between E and F close to F.
Other Constituents of Muscle. In addition to muscle ferments,
already mentioned, muscle extracts contain certain small amounts of pepsin
and fibrin ferment and an amylolytic jerment.
Certain acids are also present, particularly sarco-lactic, as well as traces of
acetic and formic.
Of carbohydrates, glycogen and glucose (or maltose) and inosite are
present. Glycogen is present in considerable amount, especially in the
muscles of well-nourished young animals. The glycogen is converted to mal-
tose in the muscles on standing some hours after death.
Nitrogenous crystalline bodies, such as creatin, creatinin, xanthin, hypo-
xanthin, or carnin, taurin, urea in very small amount, uric acid, and inosinic
acid, are all found on extracting dead muscle.
Salts of potassium and calcium are present in muscle, the chief of which
is potassium phosphate.
442 MUSCLE-NERVE PHYSIOLOGY
THE PROPERTIES OF LIVING MUSCLE.
Elasticity. Muscle has a certain amount of elasticity during rest.
It admits of being considerably stretched, but returns readily and completely
to its normal condition. In the living body the muscles are always stretched
somewhat beyond their natural length, they are always in a condition of
slight tension; an arrangement which enables the whole force of the con-
traction to be utilized in approximating the points of attachment. If the ex-
tensibility of a given muscle be measured by adding to it equal increments
of weight, it will be found that the extension or stretching is considerable at
first, but that the amount decreases with each additional weight. If the
figures obtained be plotted on coordinate paper, a curve approaching a parab-
ola is obtained, whereas a steel spring is perfectly elastic and gives a straight
line. When the weights are removed from a stretched muscle, one by one,
the muscle regains its original length, though slowly. Extreme fatigue
greatly decreases the elasticity, while an increase of temperature increases it.
Cardiac muscle and smooth muscle both manifest elasticity in the same
manner as skeletal muscle. In fact the elasticity of the arterioles is chiefly
due to the smooth muscle in their walls, a fact that is of great importance in the
adaptability of the circulatory apparatus. The flexibility of the stomach,
the urinary bladder, etc., is traceable to the same property of their muscular
walls.
Contractility and Irritability of Muscle. The property of muscular
tissue by which its peculiar functions are exercised is its contractility, which
is excited by all kinds of stimuli applied either directly to the muscles or in-
directly to them through the medium of their motor nerves. The property
of the muscle which enables it to respond to a stimulus is called its irritability.
This property, although commonly brought into action through the nervous
system, is inherent in the muscular tissue. This is proven: i, By the fact
that contractility is manifested in a muscle which is isolated from the influence
of the nervous system by division of the nerves supplying it so long as the natu-
ral tissue of the muscle is duly nourished. 2, It is manifested in a portion of
muscular fiber in which, under the microscope, no nerve fiber can be traced.
3, Substances such as curara, which paralyze the nerve endings in muscles,
do not at ad diminish the irritability of the muscle itself. 4, When a muscle
is fatigued, a local stimulation is followed by a contraction of a small part of
the fiber in the immediate vicinity, without any regard to the distribution of
nerve fibers.
Forms of Stimuli for Muscle or Nerve. The power of contraction
in voluntary muscles is normally called forth in the body by nerve impulses
which reach the muscles over the motor nerves. But a muscle will respond
to stimuli of various kinds, and these stimuli may be applied directly to the
muscle or indirectly to the nerve supplying it. There are distinct advantages,
FORMS OF STIMULI FOR MUSCLE OR NERVE
443
however, in applying the stimulus to the nerve, as it is more convenient, as
well as more potent. The stimuli which will produce contraction in a muscle
are:
1. Mechanical Stimuli. A blow, pinch, prick of the muscle or its nerve
will produce a contraction, repeated on the repetition of the stimulus. If
applied to the same point for a number of times such stimuli will soon destroy
the irritability of the preparation.
2. Thermal Stimuli. If a needle or glass rod be heated and applied to a
muscle or its nerve, the muscle will contract. A temperature of over 45° C.
will cause the muscles of a frog to pass into a condition known as heat rigor.
The sudden change of temperature acts as a stimulus.
3. Chemical Stimuli. A great variety of chemical substances will excite
the contraction of muscles, some substances being more potent in irritating
the muscle itself, and other substances having more effect upon the nerve.
Of the former may be mentioned dilute acids, salts of certain metals, e.g.,
zinc, copper, and iron; to the latter belong strong glycerin, strong acids,
ammonia, bile salts in strong solution, etc.
4. Electrical Stimuli. Any form of electrical current may be employed
to stimulate a muscle to contract, but either galvanism or the induced current
is usually chosen. For experimental purposes electrical stimuli are most
frequently used, as the strength of the stimulus may be conveniently regulated.
In order that a stimulus shall be effective, it must have a certain amount of
energy and the application to the muscle must have a certain abruptness.
For example, a comparatively weak galvanic current suffices to stimulate a
muscle to action when suddenly applied in full force. But if the electric
current be applied very gradually, a current many times stronger will fail to
arouse contraction of a muscle.
Necessary Apparatus used to Produce and Record a Muscle Contraction. Galvanic
currents are usually obtained by the employment of a continuous-current cell such as
that of Daniell, by which an electrical current which varies but little in intensity is obtained.
The cell (figure 314 A) consists of a positive plate of well-amalgamated zinc im-
A B
Fig. 314.— Diagram of a Darnell's Cell A, Dry Cell B,
444
MUSCLE-NERVE PHYSIOLOGY
mersed in a porous cell containing dilute sulphuric acid; and this cell is again contained
within a large copper vessel (forming the negative plate) containing a saturated solution
of copper sulphate. The electrical current is made continuous by the use of the two
fluids in the following manner. The action of the dilute sulphuric acid upon the zinc plate
partly dissolves it, and liberates hydrogen, and this gas passes through the porous vessel, and
decomposes the copper sulphate into copper and sulphuric acid. The former is deposited
upon the copper plate, and the latter passes through the porous vessel to renew the sulphuric
FIG. 315. — Du Bois Raymond's Key.
acid which is being used up. The copper-sulphate solution is renewed by crystals of the
salt, which are kept on a little shelf attached to the copper plate and slightly below the
level of the solution in the vessel. The current of electricity supplied by this cell will
continue without variation for a considerable time. Other cells, such as the dry cell
(which, however, is adapted to open-circuit work) may be used in place of Daniell's. The
FIG. 316. — Mercury Key.
way in which the apparatus is arranged is to attach wires to the copper and zinc plates, and
to bring them to a key, connecting the wires of the battery. One often employed is Du
Bois Reymond's, figure 315. It consists of two pieces of brass about an inch long, in each
of which are two holes for wires and binding-screws, to hold them tightly. These pieces
of brass are fixed upon a vulcanite plate to the under surface of which is attached a screw
APPARATUS USED TO PRODUCE MUSCLE CONTRACTION 445
clamp by which it can be secured to the table. The interval between the pieces of brass
can be bridged over by means of a third thinner piece of similar metal fixed by a screw to
one of the brass pieces, and capable of movement by a handle at right angles, so as to touch
the other piece of brass. If the wires from the battery are brought to the inner binding-
screws, and the bridge connects them, the current passes across it and back to the battery.
Wires are connected with the outer binding-screws, and the other ends are joined together
for about two inches, but, being covered except at their points, are insulated; the un-
covered points are about an eighth of an inch apart. These wires are the electrodes, and the
electrical stimulus is applied to the muscle through them, if they are placed behind its
nerve. When the connection between the two brass plates of the key is broken by depress-
ing the handle of the bridge, the key is then said to be opened.
An induced current is developed by means of an apparatus called an induction coil,
and the one most employed for physiological purposes is Du Bois Reymond's, the one
seen in figure 317.
Wires from a battery are brought to the two binding-screws, d' and d, a key intervening.
These binding-screws are the ends of a coil of coarse covered wire, c, called the primary coil.
FIG. 317. — Du Bois Reymond's Induction Coil.
The ends of a coil of finer covered wire, g, are attached to two binding-screws to the left of
the figure, one only of which is visible. This is the secondary coil, and is capable of being
moved nearer to c along a groove and graduated scale. To the binding-screws to the left
of g, the wires or electrodes used to stimulate the muscle are attached. If the key in the cir-
cuit of wires from the battery to the primary coil (primary circuit) be closed, the current
from the battery passes through the primary coil, and across the key to the battery, and
continues to pass as long as the key continues closed. At the moment of closure of the key,
at the exact instant of the completion of the primary circuit, an instantaneous current of
electricity is induced in the secondary coil, g, if it be sufficiently near and in line with the
primary coil; and the nearer it is to c, the stronger is the current induced. The current
is only momentary in duration and does not continue during the whole of the period while
the primary circuit is complete. When, however, the primary current is broken by open-
ing the key, a second current, also momentary, is induced in g. The former induced cur-
rent is called the making and the latter the breaking shock; the former is in the opposite
direction to, and the latter in the same direction as, the primary current.
The induction coil may be used to produce a rapid series of shocks by means of the
accessory apparatus at the right of the figure, called the magnetic interrupter. If the wires
from a battery are connected with the two pillars by the binding-screws, one below c, and
the other at a, the course of the current is indicated by the arrows in figure 318. The cur-
rent passes up the pillar from e, and along the springs if the end of d' is close to the spring,
446
MUSCLE-NERVE PHYSIOLOGY
then to the primary coil c, and to wires covering two upright pillars of soft iron, b, to the
pillar a, and out by the wires to the battery. In passing along the wire b the soft iron is
converted into a magnet, and so attracts the hammer, /, of the spring, breaks the connection
of the spring with df, and so cuts off the current from the primary coil, and also from the
electro-magnet. As the pillars, b, are no longer magnetized the spring is released, and the
current passes in the first direction, and is in like manner interrupted. At each make and
break of the primary current, currents corresponding are induced in the secondary coil.
These currents are opposite in direction, but are not equal in intensity, the break shock
being greater. In order that the shocks should be nearly equal at the make and break,
a wire, figure 318, e, connects e and d', and the screw d' is raised out of reach of the spring,
and d is raised as in figure 318, so that part of the current always passes through the
primary coil and electro-magnet. When the spring touches d the current in b is diminished,
FIG. 318. — Diagram of the Course of the Current in the Magnetic Interrupter of Du Bois
Reymond's Induction Coil. (Helmholz's modification.)
but never entirely withdrawn, and the primary current is altered in intensity at each con-
tact of the spring with d, but never entirely broken.
Preparation of a Muscle for Contraction under Stimuli. The muscles of the frog
are most convenient for the purpose of recording contractions. The frog is pithed, that
is to say, its central nervous system is entirely destroyed by the insertion of a stout needle
into the spinal cord, and the parts above it. One of its lower extremities is used in the
following manner. The large trunk of the sciatic nerve is dissected out at the back of the
thigh, and a pair of electrodes is inserted behind it. The tendo Achillis is divided from
its attachment to the os calcis, and a ligature tightly tied round it. This is the tendon
of the gastrocnemius, which arises from above the condyles of the femur. The femur is
now fixed to a board covered with cork, and the ligature attached to the tendon is tied to
the upright of the muscle lever, figure 319, B. When the muscle contracts the lever is
raised. It is necessary to attach a small weight to the lever. In this arrangement the
muscle is in situ, and the nerve disturbed from its relations as little as possible.
The muscle may, however, be detached from the body with the lower end of the femur
from which it arises, and the nerve going to it may be taken away with it. The femur
should be divided at about the lower third, and the bone fixed in a firm clamp ; the nerve
is placed upon two electrodes connected with an induction apparatus, and the lower end
of the muscle is connected by its tendon with a lever which can write on a recording
apparatus.
To prevent evaporation this so-called muscle-nerve preparation is placed under a glass
cover (moist chamber, figure 350). The air in the moist chamber is kept moist by means
of water adherent to its sides.
Recording the Effects of a Single Induction Shock. With a muscle-nerve preparation
arranged in either of the above ways, on closing or opening the key in the primary circuit
we obtain and can record a contraction, and if we use the clock-work apparatus revolving
rapidly, a curve is traced such as is shown in figure 320.
CONDUCTIVITY IN MUSCLE 447
Another way of recording the contraction is by use of the pendulum myograph, figure
352. Here the swing of the pendulum along a certain arc is substituted for the clock-
driven movement of the other apparatus. The pendulum carries a smoked-glass plate upon
which the writing lever of a myograph is made to mark. The opening or breaking shock
FIG. 319. — Arrangement of the Apparatus Necessary for Recording Muscle Contractions
with a Revolving Cylinder Carrying Smoked Paper. A, Revolving cylinder; B, the frog arranged
upon a cork-covered board which is capable of being raised or lowered on the upright, which
also can be moved along a solid triangular bar of metal attached to the base of the recording ap-
paratus—the tendon of the gastrocnemius is attached to the writing lever, properly weighted,
by a ligature. The electrodes from the secondary coil pass to the apparatus — being, for the sake
of convenience, first of all brought to a key, D (Du Bois Reymond's); C, the induction coil; F,
the battery (in this figure a bichromate one); E, the key (Morse's) in the primary circuit.
is sent into the nerve-muscle preparation by the pendulum in its swing opening a key,
figure 352, C, in the primary circuit. A muscle or its nerve is more irritable to an opening
shock than it is to a closing shock of the same strength, because the duration of the former
is shorter than that of the latter.
Conductivity in Muscle. In an ameba or other simple undiffer-
entiated contractile protoplasmic unit a stimulus applied at any point is
quickly transmitted throughout the entire mass. Just so is it with differenti-
ated muscle. A stimulus applied at any point of a muscle will quickly be
propagated through the mass as far as there is protoplasmic continuity. In
cardiac muscle and in smooth muscle there is uninterrupted conduction from
cell to cell. But in voluntary muscle each fiber is physiologically isolated from
its neighbors. When a voluntary muscle fiber is stimulated either at the ex-
tremities or at its middle, the effect of the stimulus quickly passes through the
entire fiber, whether it arouses a distinct act of contraction or not.
448 MUSCLE-NERVE PHYSIOLOGY
The rate at which conduction takes place when a contraction accompanies
it has been carefully measured by numerous observers. It varies greatly
in the different kinds of muscle, from two-tenths of a meter per second in the
rabbits' ureter (Engelmann ) to ten meters per second in the voluntary muscles
of man.
SINGLE MUSCLE CONTRACTIONS.
Characteristics of a Single Contraction. The Myogram. The con-
traction of a muscle in response to a single effective stimulus of short
duration is called a simple muscle contraction. A record of such a contraction
is called a myogram. The character of the myogram, and therefore the facts
revealed by it, are dependent on whether or not the record is made on a rapidly
moving recording surface. If the myogram is made on a recording surface
that is standing still, then it shows merely the extent of shortening of the
muscle. The amount of shortening for a given muscle will depend on a series
of conditions, such as nutrition, load, temperature, etc., all of which will
be discussed presently.
When the record is made on a rapidly moving drum or on the pendulum
myograph, it is revealed that the simple contraction occupies a definite period
>f time with well-marked periods or phases. Although the stimulus may be
FIG. 320.— Record of a Simple Contraction of the Gastrocnemius of the Frog. Time in .01
seconds. St, Moment of stimulation. Record taken on a rapid drum that was provided with
an automatic key. -
practically instantaneous, the contraction lasts a considerable fraction of a
second, in the frog's gastrocnemius about o.i of a second.
It will be observed that after the stimulus has been applied, as indicated
by the vertical line St, there is an interval before contraction commences.
This interval, termed the latent period, when measured by the number of vi-
brations of the tuning-fork directly beneath, is found to be about o.oi of a
second. The latent period is longer in some muscles than in others, and
differs also according to the condition of the muscle and the kind of stimulus
employed. During the latent period there is no apparent change in the
CHANGE IN SHAPE DURING MUSCULAR CONTRACTION
449
muscle. The second part of the record shows the contraction phase proper.
The lever is raised by the sudden shortening of the muscle. The contrac-
tion is at first very rapid, but then progresses more slowly to its maximum.
It occupies on an average 0.04 of a second in the frog's gastrocnemius. The
third stage is the relaxation phase. After reaching its highest point, the lever
begins to descend, in consequence of the elongation of the muscle. At first
the fall is rapid, but it then becomes more gradual until the lever reaches the
abscissa or base line, when the muscle has attained its precontraction length.
The stage occupies 0.05 of a second. Usually after the contraction proper
is over the lever oscillates below and above the base line in a series of dimin-
ishing waves, the elastic rebound following movement of the simple contrac-
tion. These are, of course, wholly passive and would occur equally well if
we should lift the weight to the height of the contraction, then simply let it
fall while taking a record.
Change in Shape during Muscular Contraction. There is a consider-
able difference of opinion as to the mode in which the transversely striated mus-
cular fibers contract. The most probable account is that the contraction is
FIG. 321. — The Microscopic Appearances During a Muscular Contraction in the Individual
Fibrillae, after Engelmann. i. A passive muscle-fiber; c to c/=doubly refractive discs, with median
disc a & in it; k and g are lateral discs; f and e are secondary discs, only slightly doubly refractive;
figure on right same fiber in polarized light. The bright part is doubly refracted, black ends not
so. 2. Transition stage. 3. Stage of entire contraction. In each case the right-hand figure repre-
sents the effect of polarized light. (Landois, after Engelmann.)
effected by an approximation of the constituent parts of the fibrils, which, at the
instant of contraction, without any alteration in their general direction, become
closer, flatter, and wider, a condition which is rendered evident by the approxi-
mation of the transverse striae seen on the surface of the fasciculus, and by its in-
creased breadth and thickness. The appearance of the zigzag lines into which
it was supposed the fibers are thrown in contraction is due to the relaxation
of a fiber which has been recently contracted and is not at once stretched again
by some antagonist fiber, or whose extremities are kept close together by the
contractions of other fibers. The contraction is therefore a simple and, ac-
cording to Edward Weber, a uniform, simultaneous, and steady shortening
of each fiber and its contents. What each fibril or fiber loses in length, it gains
in thickness. The contraction is a change of form, not of size; it is, therefore,
not attended with any diminution in bulk from condensation of the tissue.
29
450
MUSCLE-NERVE PHYSIOLOGY
This has been proved for entire muscles, by making a mass of muscles, or many
fibers together, contract in a vessel full of water, with which a fine, perpen-
dicular, graduated tube communicates. Any diminution of the bulk of the
contracting muscle would be attended by a fall of fluid in the tube; but when
m
FIG. 322. — Reflecting Galvanometer. (Thomson.) A, The galvanometer, which consists of
two systems of small astatic needles suspended by a fine hair from a support, so that each set of
needles is within a coil of fine insulated copper wire; that forming the lower coil is wound in an
opposite direction to the upper. Attached to the upper set of needles is a small mirror about
K inch in diameter ; the light from the lamp at B is thrown upon this little mirror, and is reflected
upon the scale on the other side of B, not shown in figure. The coils u are arranged upon brass
uprights, and their ends are carried to the binding-screws. The whole apparatus is placed upon a
vulcanite plate capable of being leveled by the screw supports, and is covered by a brass-bound
glass shade, /, the cover of which is also of brass, and supports a brass rod, b, on which moves a weak
curved magnet, m. C is the shunt by means of which the amount of current sent into the galvanom-
eter may be regulated. When in use, the scale is placed about three feet from the galvanometer,
which is a ranged east and west, the lamp is lighted, the mirror is made to swing, and the light from
the lamp is adjusted to fall upon it, and it is then regulated uncil the reflected spot of light from it
falls upon the zero of the scale. The wires from the non-polarizable electrodes touching the muscle
are attached to the outer binding-screws of the galvanometer, a key intervening for short-circuiting;
or if a portion only of the current is to pass into the galvanometer the shunt should intervene
as well with the appropriate plug in. When a current passes into the galvanometer the needles
and, with them, the mirror are turned to the right or left according to the direction of the cur-
rent. The amount of the deflection of the needle is marked on the scale by the spot of light traveling
along it.
the experiment is carefully performed, the level of the water in the tube re-
mains the same, whether the muscle be contracted or not.
In thus shortening, muscles appear to swell up, becoming rounder, more
prominent, harder, and apparently tougher. But this hardness of muscle in
the state of contraction is not due to increased firmness or condensation of the
CHEMICAL CHANGES IN CONTRACTING MUSCLE 451
muscular tissue, but to the increased tension to which the fibers, as well as their
tendons and other tissues, are subjected from the resistance ordinarily opposed
to their contraction. When no resistance is offered, as when a muscle is cut
off from its tendon, not only is no hardness perceived during contraction, but
the muscular tissue is even softer and more extensible than in its ordinary
uncontracted state. During contraction in each fiber it is said that the aniso-
tropous or doubly refractive elements become less refractive and the singly
refractive more so, figure 321.
Chemical Changes in Contracting Muscle, i. The reaction of the
muscle, which is normally alkaline or neutral, becomes decidedly acid during
contraction, from the development of sarcolactic acid. 2. The muscle gives
out carbon dioxide gas and takes up oxygen. The amount of the carbon dioxide
given out does not appear to be entirely dependent upon the oxygen taken in,
and so doubtless in part arises from some other source. Muscle contracts in
FIG. 323.— Diagram of Du Bois Raymond's Non-polarizable Electrodes, a, Glass tube filled
with a saturated solution of zinc sulphate, in the end, c, of which is china clay drawn out to a
point; in the solution a well-amalgamated zinc rod is immersed and connected, by means of the
wire which passes through a, with the galvanometer. The remainder of the apparatus is simply
for convenience of application. The muscle and the end of the second electrode are to the right
of the figure.
an atmosphere of hydrogen, showing that oxygen is present in fixed combina-
tion. A muscle, however, contracts for a longer time in an atmosphere of
oxygen. 3. Certain imperfectly understood chemical changes occur, in all
probability connected with i and 2, in which glycogen is diminished, and
glucose and muscle sugar, inosite, appear. The nitrogenous extractives are
also increased.
Electrical Changes in Contracting Muscle. Resting muscles un-
injured in the body have a uniform potential, are isoelectric. But when
removed from the body they are more or less injured and, therefore, show
differences of electrical potential between different points on the muscle,
called currents of injury or demarcation currents.
452
MUSCLE-NERVE PHYSIOLOGY
The Demonstration of Muscle Currents. The demonstration of electrical currents
in muscle requires a galvanometer and non-polarizing electrodes. A muscle prism is
insulated, and a pair of non-polarizable electrodes connected with a very delicate galva-
nometer, figure 322, are applied to various points of the prism; and by a deflection of the
needle to a greater or less extent in one direction or another, the strength and direction of
the currents in the piece of muscle can be determined. It is necessary to use non-polariz-
able and not metallic electrodes in this experiment, as otherwise there is no certainty that
the whole of the current observed is communicated from the muscle itself and not derived
from the metallic electrodes and arising in consequence of the action of the saline juices of
the tissues upon them. The form of the non-polarizable electrodes is a modification of Du
Bois Reymond's apparatus, figure 323, which consists of a somewhat flattened glass cyl-
inder, a, drawn abruptly to a point, and fitted to a socket capable of movement, and at-
tached to a stand, A , so that it can be raised or lowered as required. The lower portion of
the cylinder is filled with china clay moistened with saline solution, part of which projects
through its drawn-out point; the rest of the cylinder is filled with a saturated solution of
zinc sulphate into which dips a well -amalgamated piece of zinc connected by means of a wire
with the galvanometer. In this way the zinc sulphate forms a homogeneous and non-
polarizable conductor between the zinc and the china clay. A second electrode of the
same kind is, of course, necessary. Recently Porter has devised a boot-shaped clay
electrode that is burned and hence has the immense advantage of permanency.
Currents of Injury, or Demarcation Currents. If a segment is cut
out of a living gastrocnemius, its cut ends present regions of maximal injury.
Such a preparation is called a muscle prism.
If the points on the surface of a muscle prism be connected with the gal-
vanometer by non-polarizable electrodes, it will be found that the currents
pass from point to point, as shown in the diagram, figure 324.
FIG. 324. — Diagram of the Currents in a Muscle Prism. (Du Bois -Raymond.)
The strongest currents pass from the equator to a point representing the
middle of the cut ends; currents also pass from points nearer the equator to
those more remote, but not from points equally distant, which are isoelectric
points. The cut ends are always negative to the equator. The currents are
in all probability due to chemical changes going on in the muscles at the in-
jured ends.
Action Currents. When a muscle is made to contract the demar-
cation current undergoes a sharp decrease as shown by the deflection of the
galvanometer needle, which swings back in the direction of equilibrium.
HEAT PRODUCED IN A SIMPLE CONTRACTION 453
This deflection, originally called the current of negative variation, has been
shown to be due to the processes going on in the muscle during contraction
and is therefore called the action current. It occurs where no previous demar-
cation current exists.
For the study of the action current the capillary electrometer is very con-
venient. The hearts of cold-blooded animals, because of their slow con-
traction, serve well for demonstration. The muscle contraction passes over
the ventricle in the form of a wave, the electric potential of the muscle changing
as it becomes active or passive. For any two points on the heart muscle,
therefore, there will be two changes of potential, the active part first becom-
ing negative to the inactive, and then, as the wave passes down and the in-
FIG. 325. — Figure for Work Energy, Showing Height of the Contraction of the Gastrocnemius
of the Frog with Loads Increased by Ten Grams at a Time.
active part becomes active, the current is reversed. This is known as a
diphasic current.
In certain fishes definite electrical organs exist, organs which are derived
from muscle-like tissues and which may be regarded morphologically as mus-
cles highly specialized for the production of energy in the form of electricity.
Heat Produced in a Simple Contraction. Becquerel and Breschet
found, with the thermo-multiplier, about 0.5° C. of heat produced by each
forcible contraction of a man's biceps; and when the actions were long con-
tinued, the temperature of the muscle increased i° C. In the frog's muscle
a considerable number of contractions have been found to produce an ele-
vation of temperature equal on an average to less than 0.2° C., while a single
contraction produces, according to R. Heidenhain, from 0.001° to 0.005° C-
One gram of frog's muscle will produce in a single maximal contraction about
0.003 calorie or the equivalent of 126 gramcentimeters of work energy (since
i calorie = o.425 kilogrammeter of work). The cause of the rise of tempera-
ture is the increased chemical activity at the time of 'contraction. As we
have already seen, in the chapter on Animal Heat, muscles have the power of
producing heat even when not contracted.
454 MUSCLE-NERVE PHYSIOLOGY
The amount of heat energy developed during a single contraction will vary
sharply according to the tension under which the muscle contracts. The heat
production follows closely the energy of work produced, and apparently
obeys the same laws.
The Work Energy Liberated by a Simple Muscle Contraction. When
a muscle contracts against a resistance and a load is moved, work
energy is liberated. In fact the liberation of work energy and heat energy
are the specific functions of the muscles among the warm-blooded animals.
A frog's gastrocnemius weighing i gram and loaded with 50 grams will
contract from 0.5 to 0.6 cm, i.e., will do 25 to 30 gramcentimeters of work
for each simple contraction. The amount of work done is intimately associ-
TABLE SHOWING THE RELATION BETWEEN LOAD AND WORK.
Load or Tension. Height Lifted. Work Done.
Grams. Centimeters. Gramcentimeters.
o 1.2 O
40 0.8 32
80 0.5 40
120 O.4 48
160 0.2 32
200 O.I 2O
240 o.o o
ated with the tension under which the muscle contracts. As the tension in-
creases from no load up to 100 or 150 grams (for a i-gram muscle), the work
increases. But as the tension continues to increase, the work "falls off until
a point is reached at which the load is not lifted at all.
CONDITIONS WHICH AFFECT THE IRRITABILITY OF
THE MUSCLE AND THE CHARACTER OF THE
CONTRACTION.
There are a number of conditions which influence both the irritability
of a muscle and the power and character of its contractions. Irritability
and contractility may vary independently, but as a rule any condition which
decreases the one also decreases the other. The most important of these
conditions are: relation of the muscle to the central nervous system, con-
dition of nutrition, stimulus, temperature, fatigue, drugs, disease, etc.
Effect of the Strength of Stimulus. A strength of current that is
just sufficient to give the contraction of a muscle is called a minimal stimulus.
This is a comparatively weak induction current, one which can scarcely be
detected by the tip of the tongue. As the strength of the current is very
gradually increased,' the height of the contraction curve increases until the
maximal stimulus is reached, which produces a contraction of an amplitude
beyond which no increase occurs even though the strength of the stimulus be
THE INFLUENCE OF REPEATED ACTIVITY 455
multiplied many fold. The range between the strengths of the minimal and
maximal stimuli is very restricted indeed. The absolute strength of a mini-
mal stimulus varies exceedingly for a given muscle, depending on its degree
of irritability. This narrow range between minimal and maximal stimuli
serves as a convenient means for detecting the variations in irritability. One
should count on a continued decrease in irritability in isolated muscles, hence
FIG. 326.— Contraction of the Gastrocnemius Under the Influence of Variation of Strength of
Stimulus. The muscle was stimulated by Petr.old's inductorium, graduated to show units of
current. The figures 6, 7, 8, 9, 10, etc., indicate relative strength of stimulus.
should choose a supramaximal stimulus for all such preparations when other
conditions surrounding the muscle are under investigation.
The Influence of Repeated Activity. The irritability of muscle is
decreased by undue functional activity. The cause of the diminished ir-
ritability is twofold: when a muscle contracts, part of its substance is ex-
pended, part of its store of nutriment is exhausted, and it cannot contract so
vigorously again until the loss is made up. To this extent fatigue has much
the same effect as cutting off or diminishing the blood supply. The other
cause for the diminution of irritability is the accumulation of poisonous prod-
ucts in the muscle, substances generated during contraction, probably sar-
colactic acid chiefly. In a living animal these poisonous products exert their
influence not only upon the muscle or muscles immediately concerned in
contraction, but upon the musculature of the body generally, and the effect
remains until they are eliminated from the body. Massage of the muscles
increases the passage of waste products into the general blood stream and the
rapidity of their elimination.
In the first few simple contractions, repeated in series, there is an increase
in the amplitude of the contractions resulting in the phenomenon known
as staircase contractions or "Treppe." This stage is followed by a period
456
MUSCLE-NERVE PHYSIOLOGY
of sustained contractions, and this finally by a diminishing series of amplitudes
until the muscle fails to respond. After a few minutes' rest a muscle will
again give strong contractions, but only for a brief series.
If the time of the simple contractions is measured, it will be found, figure
327, that not only is the amplitude decreased but the duration is greatly
increased as the contractions are repeated. The latent period changes very
little. The contraction phase is considerably prolonged, but the relaxation
phase is very greatly increased. As fatigue progresses, the total time of the
simple contraction may be two or three times longer than the normal. The
FIG. 327. — Contractions of the Gastrocne"mius Muscle to Show Fatigue. The numbers printed
on the figure indicate the contractions in the series which is recorded. (Lee.)
ability of the muscle to do work falls off rapidly, of course; and the greater
the load during the time fatigue is coming on, the more quickly complete
fatigue approaches.
The Influence of Temperature. The irritability of muscle is in-
creased by raising its temperature slightly above that of the animal from
which it has been taken, while it is decreased by cooling. If, however, the
FIG. 328. — Contractions of the Gastrocnemius Muscle to Show the Influence of Temperature
on the Amplitude'of the Contractions. At 40° C. the muscle has begun to pass into rigor mortis,
yet is able to give short contractions. The steps on the curve of rigor at the right occur at tem-
peratures of 41°, 42°, and 43° C.
THE INFLUENCE OF TEMPERATURE 457
temperature be raised too high (40° C. fcr frog, 50° C. for mammal), the
muscle enters into a condition of heat rigor and its irritability is forever lost.
After cooling, unless the cold be too severe and prolonged, the irritability re-
turns as the temperature is raised. A series of vertical records of simple contrac-
tions beginning at room temperature and decreasing with a contraction at each
fall of one degree reveals the fact that the amplitude falls off slowly until a
temperature of 12° to 10° C. is reached, then as gradually increases until 4° to
2° C., after which the amplitude drops off sharply to about — 1° C. However,
this phenomenon is partly one of irritability, since a very strong stimulus will
produce a vigorous contraction until the muscle begins to freeze. If at the
freezing temperature the muscle be slowly and carefully increased in tem-
perature it will recover from the effects of the cooling without apparent injury,
and will give a reverse series to the one obtained by decreasing the temperature.
FIG. 329. — Influence of Temperature on the Duration of the Contraction of the Frog's
Gastrocnemius.
As the increase of temperature is continued above room temperature the
amplitude of the contractions very greatly increases (also the elasticity),
reaching a maximum in the frog's gastrocnemius at about 35° to 36° C. The
amplitude sharply decreases above 35° C. up to 37° to 38° C., where heat
rigor begins and the muscle permanently shortens. Heat rigor is usually
458 MUSCLE-NERVE PHYSIOLOGY
complete at 40° to 41° C. A muscle cannot recover its irritability after heat
rigor has set in strongly.
If the time of the contraction is measured at different temperatures it will
be found to be greatly delayed at 2° to 4° C., and very much quicker than nor-
mal at 33° to 35° C. As in fatigue, the effect falls chiefly on the contraction and
relaxation phases and only slightly on the latent period. The latent period
is more sharply influenced by temperature than by fatigue.
Influence of Blood Supply. In the normal human muscle there
is a delicately balanced vaso-motor mechanism by which the amount of blood
flowing through a muscle is immediately increased when the muscle is in con-
traction. This blood stream is of course carrying nutritive materials to the
muscle and taking away wastes. If the blood supply to a muscle is cut off,
then the muscle can only draw on its stored supply of potential energy, which in
active contraction is sooner or later exhausted. Under such conditions the
muscle increases in irritability for a few minutes and then gradually loses
both its irritability and its power to contract. Even mammalian muscles
have been kept alive and normal in their activity for several hours by irrigat-
ing them with defibrinated and aerated blood (von Frey). Mammalian
muscles will remain irritable for 30 minutes, or longer if cooled, after being
shut off from their blood supply and isolated from the body, but both irrita-
bility and contractility soon disappear entirely.
Effect of Nerve Supply. The voluntary or skeletal muscle normally
contracts in the body only when stimulated through its motor nerve. If the
motor nerve is severed, the muscle is cut off from its normal source of activity,
hence will undergo the changes resulting from disuse, which will be presently
discussed. Aside from this, it is held by most observers that there are dis-
tinct nutritive or trophic nerves which exercise a controlling influence over the
growth, development, and general nutritive processes going on in muscle.
When a motor nerve is cut, the muscle at first exhibits heightened irrita-
bility to all forms of stimuli. In a couple of weeks it decreases in its power
to respond to rapidly changing stimuli like induced currents. It responds
more readily to mechanical shocks and to galvanic currents for six or seven
weeks, then gradually loses the power of contracting through as many months.
The changes are due to protoplasmic degeneration. It is not clear in what
degree these changes are due to loss of trophic nerve influence, to inac-
tivity, and to changes in nutritive conditions. Since degeneration occurs
when the vascular supply is maintained, it would seem that the nutritive con-
dition must be chargeable to one or the other of the first two factors, probably
to both.
Use of muscle increases its power and also its irritability. A properly
regulated exercise is well known to contribute to the health and development
of muscles. In cases of paralysis, mechanical or electrical stimulation is
applied directly to the muscle in an effort to supply artificial exercise until the
THE EFFECT OF DRUGS 459
nerves are regenerated and motor connections reestablished. If such stim-
ulation is not applied, the muscle degenerates from disuse and loses its irri-
tability often before the nerves regenerate.
The Effect of Drugs. Drugs affect the irritability of muscle, some
augmenting, others depressing it. Voluntary muscle, which does not ordina-
rily contract except when stimulated, can be made so irritable by certain
salts that it contracts automatically like heart muscle, and the converse.
Ether, chloroform, etc., anesthetize muscle just as they do nerve, suppressing
both irritability and contractility. Suprarenal extract increases the ampli-
tude of contraction, as do also caffeine, digitalis, nicotine, and others. Ver-
atrine is well known greatly to prolong the relaxation phase of the simple
contraction without materially affecting the contraction phase, or the latent
period.
TETANIC AND VOLUNTARY MUSCULAR CONTRACTIONS.
Effect of Rate of Stimulation. If we stimulate the muscle-nerve
preparation with two induction shocks, one immediately after the other, when
the point of stimulation of the second one corresponds to the crest of the con-
traction of the first, a second curve, figure 330, will occur, which will commence
near the highest point of the first and will rise nearly as much higher, so that
the sum of the height of the two curves almost exactly equals twice the
height of the first. This phenomenon is called summation. If a third
FIG. 330.— Tracing of a Double Muscle-Curve. To be read from left to right. While the
muscle was engaged in the first contraction (whose complete course, had nothing intervened, is
indicated by the dotted line), a second induction shock was thrown in, at such a time that the
second contraction began just as the first was beginning to decline. The second curve is seen to
start from the first, as does the first from the base line. (M. Foster.)
and fourth shock be passed, a similar effect will ensue, and curves one
above the other will be traced, the third being slightly lower than the
second, and the fourth than the third. If a continuous series of shocks
occur, however, the lever after a time ceases to rise any further, and the con-
traction, which has reached its maximum, is maintained. The condition
which ensues is called Tetanus. A tetanus is really a summation of contrac-
460
MUSCLE-NERVE PHYSIOLOGY
tions, but unless the stimuli become very rapid indeed, the muscle will still be
in a condition of vibratory contraction and not of unvarying contraction.
If the shocks, however, be repeated at very short intervals, varying, in the
frog, from eighteen to thirty per second, the muscle contracts to its utmost
at once and continues at its maximum contraction for some time. The
lever rises almost perpendicularly and then describes a straight line, figure
331, c. The rate of stimulation required increases with the rapidity of the
simple contraction. If the stimuli are not so rapid, the line of maximum con-
traction becomes wavy, indicating a tendency of the muscle to relax during
FIG. 331.— a, Frog's gastrocnemius muscle stimulated with four induction shocks per second,
showing complete relaxation between stimuli ; b, same muscle stimulated eight times per
second, showing partial relaxation between stimuli (incomplete tetanus); c, same muscle
stimulated twelve times per second, showing development of an almost complete tetanus.
the intervals between. the stimuli, figure 331, b. As the muscle becomes
fatigued, a less rapid rate of stimulation is required to produce a complete
tetanus, owing to the prolongation of the relaxation period in such a muscle.
The height of the contraction, however, is lessened. This condition of pro-
longed relaxation is known as contracture.
Coordinated Muscular Contractions. In the human body the skel-
etal muscles contract only on stimulation through their motor nerves, i.e.,
under the influence of nerve impulses that have their origin in the central
MUSCLE IN RIGOR MORTIS 461
nervous system. Such motor impulses may arise through reflexes, through
automatic activity of the nerve center, or by higher cerebral origin associated
with conscious psychic effort. In either case the apparatus consists of one
or more central neurones, an anterior-horn motor cell, and the muscle
itself. Conscious or voluntary effort may be taken as a type.
Simple contractions are possible to human muscles, but undoubtedly
tetanic contractions are the rule. If one holds the arm out at right angles to the
trunk, the movement requires the continuous or tetantic contraction of the
deltoid and the series of extensor muscles. If the arm is retained in the
extended position long enough, extreme fatigue is felt and presently one can
no longer maintain the position. Yet, if the muscles involved are immediately
stimulated directly with an electric current, they contract, showing that such
exhaustion as exists is not wholly due to the muscle.
Mosso's ergograph was devised for the specific purpose of studying the
character of fatigue of voluntary effort. This apparatus is adapted to the
study of the fatigue of the flexors of the middle finger, or, in the newer in-
strument devised by Storey, to the abductor of the index finger. Numerous
studies have shown, apparently, that the fatigue of voluntary effort involves,
first, the nervous apparatus and, later, the muscle; that the muscle still retains
a considerable reserve of energy \vhen the apparatus as a whole is exhausted.
Muscle in Rigor Mortis. After the muscles of the dead body have
lost their irritability or capability of being excited to contraction by the ap-
plication of a stimulus, they spontaneously pass into a state of contraction
apparently identical in effect with that which ensues during life. It affects all
the muscles of the body, and, when external circumstances do not. prevent it,
commonly fixes the limbs in that which is their natural posture of equilibrium
or rest. From the simultaneous contraction of all the muscles of the trunk,
a general stiffening of the body is produced, which constitutes the rigor
mortis or post-mortem rigidity.
When this condition has set in, the muscle becomes acid in reaction (due to
development of sarcolactic acid), gives off carbonic acid in great excess,
diminishes in 'volume slightly, becomes shortened and opaque, its substance sets
in a firm coagulatio. Rigor comes on much more rapidly after muscular
activity, and is hastened by warmth.
The immediate cause of rigor seems to be a chemical one, namely, the
coagulation of the muscle plasma. We may distinguish three main stages;
i. Gradual coagulation. 2. Contraction of coagulated muscle clot (myosin),
and 3, squeezing out of muscle serum. During the first stage, restoration is
possible, by the circulation of arterial blood through the muscles;
and even when the second stage has set in, vitality may be restored
by dissolving the coagulum of the muscle in salt solution, and passing arterial
blood through the vessels. After the second stage is advanced, recovery is
impossible.
462 MUSCLE-NERVE PHYSIOLOGY
It has been noticed that the relaxation in muscles after rigor sometimes
occurs too quickly to be caused by putrefaction. The suggestion that in
such cases the relaxation is due to a ferment-action is very plausible.
It is known that pepsin is present in muscles, and that this ferment will
act in an acid medium. The conditions for the solution of the coagulated
myosin are therefore present since the reaction of muscle in rigor is acid.
Subjecting fresh muscle to the action of heat (50° to 60° C.) or immersing
it in distilled water causes a similar coagulation to that of rigor mortis.
The former is known as heat rigor, and the latter as witer rigor.
FIG. 332. — Curve of Shortening of the Gastrocnemius Muscle of the Frog, During Heat Rigor.
The numbers indicate degrees centigrade.
The muscles are not affected simultaneously by rigor mortis. It affects
the neck and lower jaw first; next, the upper extremities, extending from
above downward; and, lastly, reaches the lower limbs. In some rare instances
cnly, it affects the lower extremities before or simultaneously with the upper
extremities. It usually ceases in the order in which it begins: first at the
head, then in the upper extremities, and lastly in the lower extremities. It
never ordinarily commences earlier than ten minutes, and never later than
seven hours after death; and its duration is greater in proportion to the
lateness of its accession. Heat is developed during the passage of a muscular
fiber into the condition of rigor mortis.
Since rigidity does not ensue until muscles have lost the capacity of being
excited by external stimuli, it follows that all circumstances which cause
a speedy exhaustion of muscular irritability induce an early occurrence of the
rigidity, while conditions by which the disappearance of the irritability is
delayed are succeeded by a tardy onset of the rigidity of rigor. This is the
explanation of its speedy occurrence, and equally speedy departure, in the
bodies of persons exhausted by chronic diseases; and its tardy onset and long
MUSCULAR METABOLISM DURING CONTRACTION 463
continuance after sudden death from acute diseases. In some cases of sudden
death from lightning, violent injuries, or paroxysms of passion, rigor mortis has
been said not to occur at all ; but this is not always the case. It may, indeed,
be doubted whether there is really a complete absence of the post-mortem
rigidity in any such cases; for the experiments of Brown-Sequard make it
probable that the rigidity may supervene immediately after death, and then
pass away with such rapidity as to be scarcely observable.
The occurrence of rigor mortis is not prevented by the previous existence
of paralysis in a part, provided the paralysis has not been attended with very
imperfect nutrition of the muscular tissue.
The rigidity affects the involuntary as well as the voluntary musclesr
whether they be constructed of striped or unstriped fibers. The rigidity
of involuntary muscles with striped fibers is shown in the contraction of
the heart after death. The contraction of the muscles with unstriped fibers
is shown by an experiment of Valentin, who found that if a graduated tube
be connected with a portion of intestine taken from a recently killed animal,
and the intestine be tied at the opposite end, and filled with water, the water
will in a few hours rise to a considerable height in the tube, owing to the con-
traction of the intestinal walls. It is still better shown in the arteries, of
which all that have muscular coats contract after death, and thus present the
roundness and cord-like feel of the arteries of a limb lately removed, or those
of a body recently dead. Subsequently they relax, as do all the other mus-
cles, and feel lax and flabby and lie as if flattened, and with their walls nearly
in contact.
Muscular Metabolism During Contraction. The question of the
metabolism of muscle both in a resting and in an active condition has for
many years occupied the attention of physiologists. It cannot be said even
now to be thoroughly understood. Most of the facts with reference to the
subject have been already mentioned. We may shortly recapitulate them
here : First, muscle during rest absorbs oxygen and gives out carbon dioxide.
This has been shown by an analysis of the gases of the blood going to and
leaving muscles. During activity, e.g., during tetanus, the same interchange
of gases takes place, but the quantities of the oxygen absorbed and of the
carbon dioxide given up are increased, and the proportion between them is
altered thus :
Venous Blood.
O2, less than in Arterial
Blood.
CO2, more than in Arterial
Blood.
Of resting muscle
9 per cent
6.71 per cent
Of active muscle
12.26 per cent
10.79 Per cent
464 MUSCLE-NERVE PHYSIOLOGY
There is then a greater proportion of carbon dioxide produced in muscle
during activity than during rest.
During rigor mortis there is also an increased production of carbon dioxide.
Second, muscle during rest produces nitrogenous crystallizable substances,
such as creatin, from the metabolism which is constantly going on in it during
life; in addition there are formed, in all probability, sarcolactic acid and
other non-nitrogenous matters.
During activity the nitrogenous substances, such as creatin, undergo
very slight, if any, increase — about the amount produced during rest — but
the sarcolactic acid is distinctly increased; sugar (glucose) is also increased,
whereas the glycogen is diminished.
During rigor mortis the sarcolactic acid is increased, and in addition
myosin is formed.
From these data it is assumed that the processes which take place in
resting and active muscles are somewhat different, at any rate in degree.
From actively contracting muscle, also, there are obtained an increased
amount of heat and mechanical work; potential energy is converted into
kinetic energy.
Many theories have been proposed to explain the facts of muscular energy.
It has been suggested by Herman that muscular activity depends upon the
splitting up and subsequent re-formation of a complex nitrogenous body,
called by him Inogen. When this body so splits up there result from its
decomposition carbon dioxide, sarcolactic acid, and a gelatino-albuminous
body. Of these the carbon dioxide is carried away by the blood stream; the
albuminous substance and possibly the acid, at any rate in part, go to re-
form the inogen. The other materials of which the inogen is formed are
supplied by the blood; of these* materials we know that some carbohydrate
substance and oxygen form a part. The decomposition, although taking
place in resting muscle, reaches a climax in active muscle, but in that con-
dition the destruction of inogen largely exceeds restoration, and so there must
be a limit to muscular activity. But this is not the only change going on in
muscle, there are others which affect the nitrogenous elements of the tissue,
and from them result the nitrogenous bodies of which creatin is the chief;
these changes may be unusually large during severe exercise.
It has been further suggested as myosin is undoubtedly formed in rigor
mortis when the muscle becomes acid and gives off carbon dioxide, and since
myosin is formed also when muscle contracts, that the phenomenon of
contraction is a condition akin to partial death. The electrical reactions
appear to justify this; both contracted and dead muscle are negative to
living muscle when at rest. What happens to the myosin which is formed
when muscle contracts, if this view be the correct one, is unknown. Halli-
burton suggests that the myosin, which can be made to clot and unclot easily
enough outside the body, is able to do the same thing in the body. It is pos-
CONTRACTION IN INVOLUNTARY MUSCLE AND IN CILIA 465
sible that the clotting of myosinogen which is supposed to occur during con-
traction is not of the same intensity or extent as that which occurs post mortem.
The relation of the hypothetical inogen to the rest of the muscle fiber is unde-
termined. It may be that the inogen is formed by the activity of the muscle-
protoplasm and stored up within itself, and that during rest of muscle it is
gradually used up, whereas in activity it is suddenly and explosively decom-
posed. In the rest of the fiber the nitrogenous metabolism continues much
the same during activity.
THE TYPE OF CONTRACTION IN INVOLUNTARY
MUSCLE AND IN CILIA.
Cardiac Muscle. Some detail concerning the action of cardiac mus-
cle has already been given in connection with the chapter on Circulation.
As compared with the activity of skeletal muscle, cardiac muscle differs
most strikingly in that it is automatic. A strip of heart muscle taken from
any part of the heart, under proper conditions, gives off a series of contrac-
tions, whether it receives any special stimulus or not, whereas we have just
found that skeletal muscle under similar conditions remains quiet unless stimu-
lated in some special way. The fibers of skeletal muscle are more or less
physiologically isolated from each other, and one fiber may contract without
involving contractions of the others. Cardiac muscle, on the other hand,
when stimulated at any point conducts the change produced throughout the
continuity of the mass. Cardiac muscle contractions are influenced by
tension, temperature, fatigue, etc., apparently, in the same way as skeletal
muscle.
When the contraction occurs it is always maximal. The actual am-
plitude of the contraction is dependent on the condition of nutrition of the
cardiac muscle. If the contractions are at a rapid rate they will be relatively
of less amplitude. If an extra contraction is induced in an automatic series,
so that the interval between two contractions is similar, then the amplitude
will be correspondingly reduced. Such an extra contraction is followed by
a delayed automatic contraction, the phenomenon of compensatory pause.
The contractions in cardiac muscle are simple contractions. In fact, it is said
to be impossible to produce a tetanus except in certain invertebrate hearts.
This possibility depends upon the fact that during the time of a single contrac-
tion there is a certain interval between the beginning and the crest of the con-
traction, figure 174, in which the heart muscle is not irritable. This is known
as the refractory phase.
The duration of the contraction of heart muscle is much greater than
the contraction of skeletal muscle. The total time of a contraction in a frog's
gastrocnemius is o.i of a second, while the time of a contraction of the ven-
tricle in the same animal is at least 0.7 to 0.8 of a second. In the terrapin's
30
466
MUSCLE-NERVE PHYSIOLOGY
cardiac muscle the time of a contraction is over a second, but in the warm-
blooded cardiac muscle the time is shorter, perhaps from 0.4 to 0.5 of a
second for the human ventricular muscle.
Smooth Muscle. The physiology of smooth muscle has been given
to some extent in previous chapters, particularly in connection with the move-
ments of the stomach and intestines. As compared with skeletal and cardiac
muscle it is a much more slowly acting contractile tissue. Isolated strips of
smooth muscle, as a rule, contract only when stimulated, though preparations
of certain tissues, like the stomach muscle of the frog, give off rhythmic con-
tractions occasionally. In this regard smooth muscle stands intermediate
between skeletal and cardiac muscle ; the former is normally never automatic,
the latter always.
Smooth muscle requires a different type of stimulus to produce contraction ;
the stimulus must be more prolonged and more intense. For example,
FIG. 333- — Contraction Area in Smooth Muscle. A, Showing the contraction nodes of the
fibers, the deep staining of the nodes, the condensation of surrounding connective tissue; B,
diagrammatic, showing the thickening of the longitudinal fibrillae. Intestine of dog. (Unpub-
lished figure by Caroline McGill.)
smooth muscle is not readily responsive to induction currents of short duration,
but is readily stimulated by galvanic currents or induction currents of longer
duration. The stimulus must be applied through a longer interval of time.
CHANGES DURING THE CONTRACTION OF SMOOTH MUSCLE 4G7
Preparations of the stomach muscle can scarcely be made to contract by a
single induction current, no matter how intense. Such muscle in the body is
always associated with the local nervous apparatus which plays an indeter-
minate part in its activity.
The ureters and gall-bladder are the parts most difficult to excite by stimuli ;
they do not act at all till the stimulus has been long applied, and then con-
tract feebly and to a small extent. The contractions of the cecum and stomach
are quicker, and still quicker those of the iris and of the urinary bladder.
The contractions of the small and large intestines, of the vas deferens, and
of the pregnant uterus, are yet more regular and more sustained.
Changes During the Contraction of Smooth Muscle. The dura-
tion as well as type of contraction in smooth muscle is very markedly differ-
ent from that of voluntary muscle. A contraction in smooth muscle is
i
FIG. 334. — Enlarged Detailed Drawing of the Nucleus of Smooth Muscle in the Relaxed and
in the Contracted State. Intestine of Necturus. Zeissobj. 2, oc. 8. (Unpublishedfigure by Caro-
line McGill.)
characterized by a very long latent period, a slowly developed contraction
phase, and an extremely delayed relaxation, figure 355. The amount and
duration of the contractions are dependent upon the strength and duration of
the stimulus, though the curve of contraction itself does not in other respects
differ sharply from the type of curve of the simple muscle contraction.
Owing to the apparently different structural type of smooth muscle, es-
pecial interest attaches to the changes which occur during its contraction.
Caroline McGill has recently re-examined the histological structure and in-
vestigated the function of this type of muscle, and we are able to present a
figure showing the changes. The longitudinal fibrillae, which are readily
stained with iron hematoxylin, show distinct shortening and thickening at the
468 MUSCLE-NERVE PHYSIOLOGY
nodes of contraction of the muscle, figure 333, B. The whole fiber is thick-
ened at the contraction nodes and stains very readily and usually uniformly.
However, by certain stains the fibrillse can be traced through the node. The
node is an apparent area of chemical differentiation. There is a marked con-
densation of the intermuscular fibrous tissue, which is doubtless purely a
passive phenomenon. The most striking change during contractions is
observed in the nucleus, figure 333, A, and figure 334. The nucleus during
rest is a long slender oval or spindle with a general chromatic network.
"During contraction, the smooth muscle nuclei shorten and thicken by an
active process. The chromatin collects, chiefly at the two ends of the
nucleus, leaving a relatively clear area in the center."
Ciliary Motion. Ciliary motion, which is closely allied to ameboid
and muscular motion, is alike independent of the will, of the direct influ-
ence of the nervous system, and of muscular contraction. It may continue
for several hours after death, or removal of the ciliated tissue, provided the
portion of tissue under examination be kept moist. Its independence of the
nervous system is shown also in its occurrence in the lowest invertebrate
animals which are apparently unprovided with anything analogous to a
nervous system, and in its persistence when the ciliated cells are completely
separated from each other by teasing out in serum or other physiological
solution. The vapor of chloroform arrests the motion; but it is renewed
on the discontinuance of the application of the anesthetic. The movement
ceases when the cilia are deprived of oxygen (although it may continue for
a time in the absence of free oxygen) but is revived on the admission of this
gas. Carbon dioxide also stops the movement. The contact of various
substances, e.g., bile, strong acids, and alkalies, will stop the motion altogether;
but this depends chiefly on destruction of the delicate substance of which the
cilia are composed. Temperatures above 45° C. and below o° C. stop the
movement, whereas moderate heat and faintly alkaline solutions are favorable
to the action and revive the movement after temporary cessation. The exact
explanation of ciliary movement is not known. Whatever may be the exact
explanation, the movement must depend upon some changes going on in the
cells of which the cilia are a part and not on changes limited to the cilia
themselves, since, when the latter are cut off from the cell the movement
ceases, and when severed so that portions of the cilia are left attached to the
cell, the attached and not the severed portions continue the movement. Ciliary
contraction is to be regarded as a type of motor activity carried out in a spe-
cialized form of motor apparatus. The changes going on in the cell must be
classed with similar changes in heart or skeletal muscle. Ciliary tissue is
like cardiac in at least two characteristics: the cells are capable of conducting
a stimulus from cell to cell, and ciliary activity is automatic. As a special
illustration of cilia-like action may be mentioned the motion of spermatozoa,
which are cells with a single cilium.
THE FUNCTION OF NERVE FIBER 469
THE FUNCTION OF NERVE FIBER.
The Nerve Impulse. The motor nerve fibers of the muscle-nerve
preparation are of the medullated type described on page 64. But the es-
sential structure, possessed by all fibers, is the axis cylinder. The peculiar
function of the nerve fiber, i.e., of the axis cylinder, is its power to conduct
a physiological change along its extent, a phenomenon known as a nerve
impulse. A normal nerve impulse in a motor nerve has its origin in the motor
cell of the central nervous system of which the fiber is an outgrowth. The
manner in which such discharge from the cell takes place will be discussed
later. But nerve impulses may be aroused by various artificial means, they
are influenced by certain conditions in the environment, and possess certain
other properties that may be discussed at this point.
Nerve Stimuli. Nerve fibers like skeletal muscle require stimu-
lation before they can manifest any of their properties, since they have no
power of themselves of originating nerve impulses. The stimuli which are
capable of exciting nerves to action are, as in the case of muscle, very diverse.
The mechanical, chemical, thermal, and electrical stimuli which may be used
in the case of muscles are also, with certain differences in the methods em-
ployed, efficacious in stimulating the nerve. The chemical stimuli are chiefly
these: withdrawal of water as by drying; strong solutions of neutral salts of
potassium, sodium, etc.; free inorganic acids, except phosphoric; and some
organic acids. The electrical stimuli employed are the induction and con-
tinuous currents concerning which the observations in reference to muscular
irritability should be consulted. Galvanic currents stimulate nerves only at
the moment of turning on the current and of turning it off. Weaker electrical
stimuli will excite nerves than will excite muscles; the nerve impulse appears
to gain strength as it descends, and a weaker stimulus applied far from the
muscle will have the same effect as a slightly stronger one applied to the nerve
near the muscle.
Characteristics of the Nerve Impulse. When a nerve impulse is
aroused in a motor nerve, as by stimulating a nerve in its course by an induced
current of medium strength, it is propagated along the axis cylinder to the
muscle where it arouses a contraction of the muscle fiber. In the contraction
of the muscle we have indirect but conclusive evidence of the passage of the
nerve impulse, for it can be readily proven that the electrical current does
not escape to the muscle. In this instance it can be shown that there is a
nerve impulse passing from the point of stimulation in the direction away
from the muscle; i.e., the artificially aroused nerve impulse passes over the
entire extent of the fiber stimulated. In fact, a nerve impulse is known to
travel from its point of origin over the entire neurone affected. This antidro-
mal nerve impulse, of course, does not exist in the normal case, since the nor-
470 MUSCLE-NERVE PHYSIOLOGY
mal nerve impulse arises in the nerve-cell body and passes out over the fiber
from its origin to its extremity.
The nerve impulse travels over the nerve fiber with a velocity that was
first determined by Helmholtz. He found that in the sciatic of the frog the
nerve impulse travels at the rate of twenty-seven meters per second. The rate
has been measured in a number of animals and varies between wide limits.
In human nerves the rate is variously given, but thirty meters per second
may be taken as a fair average.
The presence of the nerve impulse can be detected by the action current,
which exists in nerve as in muscle (see page 451 for methods of detecting
the action current).
Rheoscopic Frog. The action current may be demonstrated by means of the follow-
ing experiment:
The muscle current produced by stimulating the nerve of one muscle-nerve preparation
may be used to stimulate the nerve of a second muscle-nerve preparation. The hindleg
of a frog with the nerve going to the gastrocnemius cut long is placed upon a glass plate
and arranged in such way that its nerve touches in two places the gastrocnemius muscle,
exposed but preserved in situ in the opposite thigh of the frog. The electrodes from an
induction coil are placed behind the sciatic nerve of the second preparation, high up.
On stimulating it with a single induction shock, the muscles not only of the same leg are
found to undergo a twitch, but also those of the first preparation, although this is not near
the electrodes. The stimulation cannot be due to an escape of the stimulating current
into the first nerve, but is due to the action current of the second muscle. This experi-
ment is known under the name of the rheoscopic frog.
When the nerve impulse is studied by means of the action current it is
found that a nerve impulse can be aroused by a weaker stimulus than is re-
quired to produce a minimal contraction of a muscle. The response of the
nerve to graduated strengths of the stimulus is increased very rapidly with
slight increase of strength of the stimulus, the augmentation extending through
a somewhat greater range than for muscle. If the stimulus is still further in-
creased there is only slight increase of the resulting nerve impulse.
Fatigue of Nerve Fiber. Many efforts have been made to dis-
cover evidences of fatigue of nerve fiber, with practically complete negative
results. A difficulty has been to secure means of measuring change in intensity
of the nerve impulse. The muscle quickly fatigues so that the character of
the muscle response cannot be taken when measured in the ordinary way.
An effective method used by Howell, Budgett, and Leonard consists in cooling
a segment of nerve to suspend its conductivity, during stimulation of the free
end ; and periodically warming up the cooled segment of nerve to test the
strength of nerve impulse passing through it to the unfatigued muscle beyond.
By this and other methods it has been found that a motor nerve is not fatigued
by at least ten hours' continuous stimulation with induction currents.
One must hesitate to draw the conclusion, however, that the nerve fiber
conducts the nerve impulse without loss of energy. The fiber can be anesthe-
tized, it responds to temperature changes, and gives other evidences of sus-
THE EFFECTS OF BATTERY CURRENTS ON NERVE-FIBER 471
ceptibility to conditions which influence metabolism in other forms of proto-
plasm. Perhaps the nerve fiber is capable of repairing its wastes as rapidly
as they occur.
The Effects of Battery Currents on Nerve Fiber. Galvanic currents
influence nerves in ways that call for special discussion. A constant cur-
rent, say from a Daniell battery, can be introduced into the nerve of a
muscle-nerve preparation by means of a pair of non-polarizable electrodes,
figure 3 2 3, and a convenient key arranged for turning the current on or off the
nerve. It will be found that with a current of moderate strength there will be a
contraction of the muscle, both at the closing and the opening of the key (called
respectively making and breaking contractions), but that during the interval
between these two events the muscle remains flaccid, provided the battery cur-
rent continues of constant intensity. If the current be a very weak or a very
strong one, the effect is not quite the same; one or the other of the contractions
may be absent. Which of these contractions is absent depends upon another
circumstance, viz., the direction of the current. The direction of the current
may be ascending or descending: If ascending, the anode or positive pole is
nearer the muscle than the cathode or negative pole, and the current to return
to the battery has to pass up the nerve; if descending, the position of the elec-
trodes is reversed. It will be necessary before considering this question
further to return to the apparent want of effect of the constant current during
the interval between the make and the break contraction. To all appear-
ances no change is produced, but in reality a very important alteration of
the irritability and conductivity is brought about in the nerve by the passage
of this constant or polarizing current.
A second way of showing the effect of the polarizing current is by stimu-
lating the nerve by a pair of electrodes from an induction coil, while the polar-
izing current from the battery is flowing through the nerve. If the strength of
stimulus required in order that a minimum contraction be obtained by the
induction shock before the polarizing current is applied, and the secondary
coil be removed slightly further from the primary, the induction current
cannot now produce a contraction. If now the polarizing current be sent in a
descending direction, that is to say, with the cathode nearest the muscle, and
the induction current which was before insufficient be applied between the
cathode and the muscle, it will now prove sufficient to cause a contraction.
This indicates that with a descending current the irritability of the nerve is
increased at the cathode. If instead of applying the induction electrodes
below the polarizing electrodes, they are applied above them, the irritability of
the nerve is found to be decreased. If the polarizing current is reversed, i.e.,
made ascending, then the condition of irritability of the nerve is reversed.
Both methods show that the polarization consists in an increase in irritability
at the cathode, called catelectrotonus, and a decrease at the anode called
anelectrotonus. The total change is called by the term electrotonus. As there
472
MUSCLE-NERVE PHYSIOLOGY
is between the electrodes both an increase and a decrease of irritability on the
passage of a polarizing current, it is evident that there must be a neutral point
where there is neither increase nor decrease of irritability. The position of this
neutral point is found to vary with the intensity of the polarizing current ; when
the current is weak the point is nearer the anode, when strong nearer the
FIG. 335- — Diagram Illustrating the Effects of Various Intensities of the Polarizing Currents.
n, n', Nerve; a, anode; k, cathode; the curves above indicate increase, and those below decrease
of irritability, and when the current is small the increase and decrease are both small, with the
neutral point near a, and so on as the current is increased in strength.
cathode, figure 335. When a constant current passes into a nerve, therefore, if a
contraction result, it may be assumed that it is due to the increased irritability
produced in the neighborhood of the cathode, but the breaking contraction
must be produced by a rise in irritability from a lowered state to the normal
in the neighborhood of the anode.
The contractions produced in the muscle of a muscle-nerve preparation
by a constant current have been arranged in a table which is known as Pfluger's
Law of Contractions. It is really only a statement as to when a contrac-
tion may be expected:
DESCENDINC
; CURRENT.
ASCENDING
CURRENT.
STRENGTH OF CURRENT USED.
Make.
Break.
Make.
Break.
Very weak. . ...
Yes
No
No
No
Weak
Yes
No
Yes
No
^Moderate
Yes
Yes
Yes
Yes
Strong
Yes
No
No
Yes
During the passage of a constant current through a nerve and immediately
after its cessation, there is a change in the conductivity as well as of the irri-
tability of the nerve at the anode and cathode, respectively. During the pas-
sage of the current, the conductivity is increased at the cathode and decreased
at the anode. After the passage of the current, the effect is reversed. With
strong currents the area of decreased conductivity may be sufficient to act as a
block, preventing the passage of impulses over it.
EFFECT OF BATTERY CURRENTS ON DEEP-SEATED NERVES 473
The foregoing statements concerning the changes produced in a nerve
by the passage of a constant current may be briefly summarized as follows:
I. A nerve is more irritable to the closing of a constant current than it is to
the opening of a constant current.
II. During the passage of the current through the nerve, both its irrita-
bility and conductivity are increased at the cathode and decreased at the anode.
III. After the passage of the current, the irritability and conductivity are
both decreased at the cathode and increased at the anode.
The Effect of Battery Currents on Deep-Seated Nerves. The follow-
ing account is condensed from Lombard in "An American Text-book of
Physiology."
As an electric current cannot be applied to living human nerves directly,
it is applied to the skin along the course of the nerve. The current passes
from the anode or positive pole through the skin, and spreads out in the
tissues much as the bristles of a brush; it then gradually concentrates and
leaves the skin at the cathode or negative pole.
In addition to the physical anode and cathode of the battery, there are what
are called physiological anodes and cathodes. There is a physiological anode
at every point where the current enters a nerve, and a physiological cathode
at every point where it leaves it.
Generally when the current is applied to nerves through the skin, only part
of it flows longitudinally along the nerves; most of it passes diagonally through
Shin
FIG. 335 A. — Diagram of Skin and Subjacent Nerve. A, the positive electrode or physical
anode; B, the negative electrode or physical cathode. Signs, + physiological anodes; signs-
physiological cathodes. (After Waller.)
them to the tissues below. Thus it happens that in that part of the nerve
beneath either the physical anode or cathode, groups of physiological anodes
and cathodes are found.
The contraction which occurs when the current is closed (closing con-
traction) represents irritation at the physiological cathode, while the opening
contraction represents irritation at the physiological anode. Since there are
physiological anodes and cathodes beneath each electrode, one or more of
four conditions may arise:
i. Anodic closing contraction, i.e., the effect of the change developed at
the physiological cathode, beneath the physical anode (positive pole).
474
MUSCLE-NERVE PHYSIOLOGY
2. Anodic opening contraction, i.e., the effect of the change developed at
the physiological anode, beneath the physical anode (positive pole).
3. Cathodic closing contraction, i.e., the effect of the change developed
at the physiological cathode, beneath the physical cathode (negative pole).
4. Cathodic opening contraction, i.e., the effect of the change developed
at the physiological anode, beneath the physical cathode (negative pole).
The following abbreviations of these contractions are used: ACC, AOC,
KCC, KOC.
The closing contractions, KCC and ACC, are stronger than the opening
contractions, KOC and AOC. Of the closing contractions, KCC is strong-
er than ACC. Of the opening contractions, AOC is stronger than KOC.
These facts are also shown in a table of the effects of gradually increasing the
strength of the current.
Weak Currents.
KCC
Medium Currents.
KCC
ACC
AOC
Strong Currents.
KCC
ACC
AOC
KOC
Sometimes AOC is stronger than ACC.
In diseases which cause degeneration of the nerves going to a muscle,
stimulation causes results different from the above, and we get what is known
as the reaction of degeneration.
r. nervl med. m. pron.
tereti.
m. palmaris longus
m. ulnarls Int.
n. ulnaris
r. vol. prof. n. ulnar.
m. palmar brevis
m. abduc. dig. min.
m. flex. dig. min.
m. oppon. dig. min.
mm, Uimbr. II.,III.,IV.
m. radial. Intern,
m. flex. dig. prof.
m. flex. dig. sublim.
m. flex. poll. long,
m. medianus
•- -S^ m. abduc. poll. brey.
.7 L'. „ .A m. oppon. poll.
m. flex. poll. brev.
m. adduc. poll.
- m. lumbric. I.
FIG. 336. — Figure Showing Motor Points in the Forearm.
LOCOMOTION 475
The intensity of the anodic or cathodic effects is increased by using small
electrodes, and decreased by electrodes of large surface. In fact in practice
it is usual to apply the indifferent electrode to an extended surface, thus re-
ducing its effect below the stimulating intensity. This gives only one active
stimulating electrode and is known as the method of unipolar stimulation.
SOME SPECIAL COORDINATED MOTOR ACTIVITIES.
I. LOCOMOTION.
The greater number of the more important muscular actions of the human
body, those, namely, which are arranged harmoniously so as to subserve some
definite purpose in the animal economy, are described in various parts of this
work in the sections which treat of the physiology of the processes by which
these muscular actions are resisted or carried out. There are, however, some
very important and somewhat complicated muscular acts which may be best
described in this place.
Walking. The coordinated movements of the body are carried out
by the skeletal muscles acting on the skeletal elements as a system of levers.
Even the bones of the skull are levers in so far as their relations to muscles
are concerned.
Examples of the three orders of levers in the Human Body. All levers have been
divided into three kinds, according to the relative position of the power, the weight to be
moved, and the axis oj motion or fulcrum. In a lever of the first kind the power is at one
extremity of the lever, the weight at the other, and the fulcrum between the two. If the
initial letters only of the power, weight, and fulcrum be used, the arrangement will stand
thus: P. F. W. A poker as ordinarily used, or the bar in figure 337, may be cited as an
example of this variety of lever; while, as an instance in which the bones of the human
FIG. 337.
skeleton are used as a lever of the same kind, may be mentioned the act of raising the body
from the stooping posture by means of the hamstring muscles attached to the tuberosity
of the ischium or of the triceps which extends the forearm by action at the elbow,
figure 337.
476
MUSCLE-NERVE PHYSIOLOGY
In a lever of the second kind, the arrangement is thus: P. W. F.; and this leverage
is employed in the act of raising the handles of a wheelbarrow, or in stretching an elastic
band, as in figure 338. In the human body the act of opening the mouth by depressing
the lower jaw is an example of the same kind — the tension of the muscles which close the
jaw representing the weight, figure 338.
In a lever of the third kind the arrangement is, F. P. W., and the act of raising a pole,
as in figure 339, is an example. In the human body there are numerous examples of the
FIG. 338.
employment of this kind of leverage. The act of bending the forearm may be mentioned
as an instance, figure 339. The act of biting is another example.
At the ankle we have examples of all three kinds of lever, ist kind — Extending the
foot. 3d kind — Flexing the foot. In both these cases the foot represents the weight:
the ankle joint the fulcrum, the power being the calf muscles in the first case and the
tibialis anticus in the second case, ad kind — When the body is raised on tiptoe. Here
F 3?
FIG. 339-
the tip of the toe is the fulcrum, the weight of the body acting at the ankle joint the weight,
and the calf muscles the power.
In the human body, levers are most frequently used at a disadvantage as regards power,
the latter being sacrificed for the sake of a greater range of motion. Thus in the diagrams
of the first and third kinds it is evident that the power is so close to the fulcrum that great
force must be exercised in order to produce motion. It is also evident, however, from the
same diagrams, that by the closeness of the power to the fulcrum a great range of move-
ment can be obtained by means of a comparatively slight shortening of the muscular fibers.
In the act of walking, almost every voluntary muscle in the body is brought
into play, either directly for purposes of progression, or indirectly for
the proper balancing of the head and trunk. The muscles of the arms are
LOCOMOTION
477
least concerned; but even these are for the most part instinctively in action
to some extent.
Among the chief muscles engaged directly in the act of walking are those of
the calf, which, by pulling up the heel, pull up also the astragalus, and with it,
of course, the whole body, the weight of which is transmitted through the
tibia to this bone, figure 340. When starting to walk, say with the left leg,
this raising of the body is not entirely dependent on the muscles of the left
calf, but the trunk is thrown forward in such a way that it would fall prostrate
were it not that the right foot is brought forward and planted on the ground to
support it. Thus the muscles of the left calf are assisted in their action by
those muscles on the front of the trunk and legs which, by their contraction,
pull the body forward; and, of course, if the trunk form a slanting line, with
the inclination forward, it is plain that when the heel is raised by the calf
muscles, the whole body will be raised, and pushed obliquely forward and
FIG. 340.
upward. The successive acts in taking the first step in walking are repre-
sented in figure 340, i, 2, 3, etc.
Now it is evident that by the time the body has assumed the position No. 3,
it is time that the right leg should be brought forward to support it and
prevent it from falling prostrate. This advance of the right leg is effected
partly by its mechanically swinging forward, pendulum- wise, and partly by
muscular action; the muscles used being — i, those on the front of the
thigh, which bend the thigh forward on the pelvis, especially the rectus femoris,
with the psoas and the iliacus; 2, the hamstring muscles, which slightly bend
the leg on the thigh; and, 3, the muscles on the front of the leg, which raise
the front of the foot and toes, and so prevent the latter in swinging forward
from striking the ground.
The second part of the act of walking, which has been just described, is
shown in the diagram, 4, figure 340.
When the right foot has reached the ground the action of the left leg has not
ceased. The calf muscles of the latter continue to act, and, by pulling up the
heel, throw the body still more forward over the right leg, now bearing nearly
the whole weight, until the time when the left leg should again swing forward,
and the left foot be planted on the ground to prevent the body from falling
478 MUSCLE-NERVE PHYSIOLOGY
prostrate. As at first, while the calf muscles of one leg and foot are preparing,
so to speak, to push the body forward and upward from behind by raising the
heel, the muscles on the front of the trunk and the same leg (and of the other leg,
except when it is swinging forward (are helping the act by pulling the legs and
trunk, so as to made them incline forward, the rotation in the inclining occur-
ring mainly at the ankle joint. Two main kinds of leverage, are, therefore,
employed in the act of walking, and if this idea be firmly grasped, the details
will be understood with comparative ease. One kind of leverage employed
in walking is essentially the same with that employed in pulling forward the
pole, as in figure 339. And the other, less exactly, is that employed in raising
the handles of a wheelbarrow. Now, supposing the lower end of the pole to be
FIG. 341.
placed in the barrow, we should have a very rough and inelegant, but not
altogether bad representation of the two main levers employed in the act of
walking. The body is pulled forward by the muscles in front, much in the
same way that the pole might be by the force applied at p, while the raising
of the heel and pushing forward of the trunk by the calf muscles are roughly
represented on raising the handles of the barrow. The manner in which these
actions are performed alternately by each leg, so that one after the other is
swung forward to support the trunk, which is at the same time pushed and
pulled forward by the muscles of the other, may be gathered from the previous
description.
There is one more thing to be especially noticed in the act of walking. In-
asmuch as the body is being constantly supported and balanced on each leg
alternately, and therefore on only one at the same moment, it is evident that
there must be some provision made for throwing the center of gravity over the
RUNNING 479
line of support formed by the bones of each leg, as, in its turn, it supports the
weight of the body. This may be done in various ways, and the manner in
which it is effected is one element in the differences which exist in the walk-
ing of different people. Thus it may be done by an instinctive slight rotation
of the pelvis on the head of each femur in turn, in such a manner that the cen-
ter of gravity of the body shall fall over the foot of this side. Thus when the
body is pushed onward and upward by the raising, say, of the right heel, as in
figure 340, 3, the pelvis is instinctively by various muscles made to rotate on the
head of the left femur at the acetabulum, to the left side, so that the weight
may fall over the line of support formed by the left leg at the time that the
right leg is swinging forward, and leaving all the work of support to fall on
its fellow. -Such a "rocking" movement of the trunk and pelvis, however, is
accompanied by a movement of the whole trunk and leg over the foot which
is being planted on the ground, figure 341 , the action being accompanied with
a compensatory outward movement at the hip, more easily appreciated by
looking at the figure (in which this movement is shown exaggerated) than
from the description.
Thus the body in walking is continually rising and swaying alternately
from one side to the other, as its center of gravity has to be brought alternately
over one or the other leg; and the curvatures of the spine are altered in corre-
spondence with the varying position of the weight which it has to support. The
extent to which the body is raised or swayed differs much in different people.
In walking, one foot or the other is always on the ground. The act of leap-
ing or jumping consists in so sudden a raising of the heels by the sharp and
strong contraction of the calf muscles that the body is jerked off the ground.
At the same time the effect is much increased by first bending the thighs on the
pelvis, and the legs on the thighs, and then suddenly straightening out the
angles thus formed. The share which this action has in producing the effect
may be easily known by attempting to leap in the upright posture, with the
legs quite straight.
Running. Running is performed by a series of rapid low jumps pro-
duced by each leg alternately; so that, during each complete muscular act
concerned, there is a moment when both feet are off the ground.
In all these cases, however, the description of the manner in which any
given effect is produced, can give but a very imperfect idea of the infinite
number of combined and harmoniously arranged muscular contractions which
are necessary for even the simplest acts of locomotion.
II. THE PRODUCTION OF THE VOICE.
Before commencing the consideration of the Nervous System and the
special Senses it will be convenient to consider first speech, the production of
the human voice, and the physiology of the larynx as a muscular apparatus.
480 MUSCLE-NERVE PHYSIOLOGY
The Larynx. In nearly all air-breathing vertebrate animals there
are arrangements for the production of sound, or voice, in some parts of the
respiratory apparatus. In many animals, the sound admits of being variously
modified and altered during and after its production; and, in man, one such
modification occurring in obedience to dictates of the cerebrum, is speech.
It has been proven by observations on living subjects, by means of the
laryngoscope, as well as by experiments on the larynx taken from the dead
body, that the sound of the human voice is the result of the vibration of the
inferior laryngeal ligaments, or the true vocal cords which bound the glottis,
caused by currents of expired air impelled over their edges. If a free opening
exists in the trachea, the sound of the voice ceases, but it returns if the opening
is closed. An opening into the air-passages above the glottis, on the con-
trary, does not prevent the voice being produced. By forcing a current of
air through the larynx in the dead subject, clear vocal sounds are elicited,
though the epiglottis, the upper ligaments of the larynx or false vocal cords, the
ventricles between the upper ligaments and the inferior ligaments, and the upper
part of the arytenoid cartilages, be all removed. But the true vocal cords must
remain entire with their points of attachment, and be kept tense and so
approximated that the fissure of the glottis may be narrow.
The vocal ligaments or cords, therefore, are regarded as the proper organs
for the production of vocal sounds. The modifications of these sounds are
effected, as will be presently explained, by other parts, viz., by the tongue,
teeth, lips, etc. The structure of the vocal cords is adapted to enable them to
vibrate like tense membranes, for they are essentially composed of elastic tissue;
and they are so attached to the cartilaginous parts of the larynx that their
position and tension can be variously altered by the contraction of the muscles
which act on these parts.
Thus it will be seen that the larynx is the organ of voice. It may be said
to consist essentially of the two vocal cords and the various cartilaginous,
muscular, and other apparatus by means of which not only can the aperture
of the larynx (rima glottidis) be closed against the entrance and exit of air
to or from the lungs, but also by means of which the cords themselves can be
stretched or relaxed, brought together and separated in accordance with the
conditions that may be necessary for the air in passing over them to set them
vibrating to produce the various sounds. Their action in respiration has been
already referred to.
Anatomy of the Larynx. The principal parts entering into the formation of the larynx,
figures 342 and 343, are — the thyroid cartilage; the cricoid cartilage; the two arytenoid
cartilages; and the two true vocal cords. The epiglottis, figure 343, has but little to do
with the voice, and is chiefly useful in protecting the upper part of the larynx from the
entrance of food and drink in deglutition. The false vocal cords and the ventricle of the
larynx, which is a space between the false and the true cord of either side, need be only
referred to.
Cartilages, a, The thyroid cartilage, figure 342, i to 4, does not form a complete ring
ANATOMY OF THE LARYNX
481
around the larynx, but only covers the front portion, b, The cricoid cartilage, figure 342,
5, 6, on the other hand, is a complete ring; the back part of the ring being much broader
than the front. On the top of this broad portion of the cricoid are, c, the arytenoid car-
tilages, figure 342, 7, the connection between the cricoid below and arytenoid cartilages
FIG. 342. — Cartilages of the Larynx Seen from the Front, i to 4, Thyroid cartilage; T, verti-
cal ridge or pomum Adami; 2, right al&; 3, superior, and 4, inferior cornu of the right side; 5, 6,
cricoid cartilage; 5, inside of the posterior part; 6, anterior narrow part of the ring; 7, arytenoid
cartilages. Xf.
above being a joint with synovial membrane and ligaments, the latter permitting tolerably
free motion between them.
Joints and Ligaments. The thyroid cartilage is also connected with the cricoid, not
only by ligaments, but also by joints with synovial membranes; the lower cornua of the
thyroid clasping the cricoid between them, yet not so tightly but that the thyroid can re-
Caife "Wriabergii
Cart, Santorint
Cart, aryten.
ICroc. itrasciil. „_
Eigs crico-aryten.
Corntcin&E. — —
Cartviracnero
membra*.
FIG, 3 43 . — The Larynx as Seen From Behind after Removal of the Muscles. The cartilages and
ligaments only remain. (Stoerk.)
volve, within a certain range, around an axis passing transversely through the two joints.
The vocal cords are attached behind to the front portion of the base of the arytenoid car-
tilages, and in front to the re-entering angle at the back part of "the thyroid; it is evident,
therefore, that all movements of either of these cartilages must produce an effect on them
of some kind or other. Inasmuch, too, as the arytenoid cartilages rest on the top of the
back portion of the cricoid cartilage, and are connected with it by capsular and other liga-
ments, all movements of the cricoid cartilage must move the arytenoid cartilages, and also
produce an effect on the vocal cords.
31
482
MUSCLE-NERVE PHYSIOLOGY
Intrinsic Muscles. The intrinsic muscles of the larynx are so connected with the
laryngeal cartilages that by their contraction alterations in the condition of the vocal cords
and glottis are produced. They are usually divided into four classes according to their
action, viz., into abductors, adductors, sphincters, and tensors. The Abductors, the crico-
arytenoidei, widen the glottis, by separating the cords; the Adductors, consisting of the
thyro-ary-epiglottici, the arytenoideus posticus seu transversus, the thyro-arytenoidei externi,
FIG. 344. — The Cartilages and Ligaments of the Larynx, Viewed from the Front, a, Epiglottis;
b, hyoid bone; c, cartilage tritica; d, thyro-hyoid membrane; e, superior cornu of thyroid cartilage-
j, thyroid notch; g, pomum Adami; h, crico-thyroid membrane; i, inferior cornu of thyroid cartilage;
/, cricoid cartilage. (Cunningham.)
the crico-arytenoidei later ales, and the thyro-arytenoidei interni, approximate the vocal cords,
diminish the rima glottidis, and act generally as sphincters and supporters of the glottis.
Finally, the tensors of the cords put the cords on the stretch, with or without elongating
them; the tensors are the crico-thyroidei and the thyro-arytenoidei interni.
The attachments and the action of the muscles will be readily understood from the
following table. All the muscles are in pairs except the arytenoideus posticus.
TABLE or THE SEVERAL GROUPS OF THE INTRINSIC MUSCLES OF THE LARYNX AND THEIR
ATTACHMENTS.
GROUP.
MUSCLE.
ATTACHMENTS.
ACTION.
L
Abductors.
Crico-aryte-
This pair of muscles arises, on either
Draw inward and
noidei pos-
side, from the posterior surface of the
backward the out-
tici.
corresponding half of the cricoid car-
er angle of ary-
tilage. From this depression their
tenoid cartilages,
fibers converge on either side upward
and so rotate out-
and outward to be inserted into the
ward the processus
outer angle of the base of the ary-
vocalis and widen
tenoid cartilages behind the crico-
the glottis.
arytenoidei laterales.
ANATOMY OF THE LARYNX
483
GROUP.
MUSCLE.
ATTACHMENTS.
ACTION.
II. and III.
Adductors
and
Sphincters.
D. Middle
layer.
i. A r y t e
n o i d e u s
posticus.
ii. Thyro-
ary tenoi-
dei ex -
terni.
n three lay-
ers:
Outer
layer, Thy-
r o - a r y -
epiglot-
tici.
iii. Crico-
arytenoi
del late
rales.
c. Inner
most layer
Thyro-ar y
tenoidei in
terni.
pair of muscles. Flat and narrow,
which arise on either side from the
processus muscularis of the arytenoid
cartilage, then passing upward and in-
ward cross one another in the middle
line to be inserted into the upper half
of the lateral border of the opposite
arytenoid cartilage and the posterior
border of the cartilage of Santorini.
The lower fibers run forward and
downward to be inserted into the
thyroid cartilage near the commissure.
The fibers attached to the cartilage of
Santorini are continued forward and
upward into the ary-epiglottic fold.
single muscle. Half-quadrilateral,
attached to the borders of the ary-
tenoid cartilages, its fibers running
horizontally between the two.
A pair of muscles. Each of which con-
sists of three chief portions. The
lower and principal fibers arise from
the lower half of the internal surface
of the thyroid cartilage, close to the
angle, and from the fibrous expansion
of the crico-thyroid ligament, and are
inserted into the lateral border of the
arytenoid cartilage. The inner fibers
to the lower half of this border, anc
the outer fibers into the upper half
some pass to the cartilage of Wrisberg
and the ary-epiglottic fold.
A pair of muscles. They arise on eithe:
side from the middle third of the up
per border of the cricoid cartilage anc
are inserted into the whole anterio:
margin of the base of the arytenok
cartilage. Some of their fibers join
the thyroid -ary-epiglottici.
A pair of muscles. They arise on eithe
side, internally from the angle of the
thyroid cartilage, internal to the las
described muscle, b. iii., and running
parallel to and in the substance of the
vocal cords are attached posteriorly to
the processus vocalis and to the oute
surface of the arytenoid cartilages.
lelp to narrow or
close the rima
glottidis.
Oraws together the
arytenoid carti-
lages and also de-
presses them.
When the mus-
cle is paralyzed,
the inter-carti-
laginous part of
the cords cannot
come together.
Approximate the
vocal cords
by drawing the
processus muscu-
laris of the ary-
tenoid cartilages
forward and
downward and so
rotate the pro-
cessus vocalis in-
ward.
Render the vocal
cords tense and
rotate the aryte-
noid cartilages
and approximate
the processus vo-
calis.
484
MUSCLE-NERVE PHYSIOLOGY
GROUP.
MUSCLE.
ATTACHMENTS.
ACTION.
IV.
Tensors.
Crico -thy-
A pair of fan-shaped muscles attached
The thyroid carti-
roidei.
on either side to the cricoid cartilage
lage being fixed
below; from the mesial line in front
by its extrinsic
for nearly one-half of its lateral cir-
muscles, the
cumference backward the fibers pass
front of the cri-
upward and outward to be attached to
coid cartilage is
the lower border of the thyroid carti-
drawn upward,
lage and to the front border of its lower
and its back,
cornea.
with the aryte-
noids attached,
Thyro - ary-
The most posterior part is almost a dis-
is drawn down.
tenoidei
tinct muscle and its fibers are all but
Hence the vocal
interni.
horizontal: sometimes this muscle is
cords are elon-
described as consisting of two layers,
gated a n t e r o -
superficial with cortical fibers, deep
posteriorly and
with oblique fibers, described under
put upon the
Group III.
stretch. Paral-
ysis of these
muscles causes
an inability to
produce high
notes.
Nerve Supply. The sensory filaments of the superior laryngeal branch of the vagus
supply the epithelial lining of the larynx, giving it that acute sensibility by which the glottis
is guarded against the ingress of foreign bodies, or of irrespirable gases. The contact of
these stimulates the nerve endings; and the sensory nerve impulse conveyed to the medulla
oblongata, whether accompanied by sensation or not, arouses motor impulses through
the filaments of the recurrent or inferior laryngeal branch, which excite contraction of the
muscles that close the glottis. Both these branches of the vagi cooperate also in the pro-
Lig. ary-epiglott.
Cart. Wrisbergii
Cart. Santorini
mm. Aryten. obliqu.
m. Crico-arytenoid. post.
Cornu inferior
Lig. cerato-cric.
Pars. post. inf. membrani
Pars, cartilag.
FIG. 345. — The Larynx as Seen from Behind. To show the intrinsic muscles
posteriorly. (Stoerk.)
ANATOMY OF THE LARYNX
485
duction and regulation of the voice. The inferior laryngeal determines the degree of
contraction of the muscles that vary the tension of the vocal cords, and the superior laryn-
geal conveys to the brain the sensation which indicates the state of contraction of these
muscles. Both the branches co-operate also in the actions of the larynx in the ordinary
slight dilatation and contraction of the glottis in the acts of expiration and inspiration,
more evidently in the acts of coughing and other forcible respiratory movements.
The Laryngoscope. This is an instrument employed in investigating the condition of
the pharynx, larynx, and trachea. It consists of a large concave mirror with perforated
center and of a smaller mirror fixed in a long handle. In use the patient is placed in a
chair, a good light (argand burner, or lamp) is arranged on one side of, and a little above
his head. The operator fixes the concave mirror round his head in such a manner that
FIG. 346.— The Parts of the Laryngoscope.
he looks through the central aperture with one eye. He then seats himself opposite the
patient, and so adjusts the position of the mirror, which is for this purpose provided with
a ball and socket joint, that a beam of light is reflected on the lips of the patient.
The patient is now directed to throw his head slightly backward, and to open his mouth ;
the reflection from the mirror lights up the cavity of the mouth, and by a little alteration of
the distance between the operator and the patient the point at which the greatest amount
of light is reflected by the mirror — in other words its focal length — is readily discovered.
The small mirror fixed in the handle is then warmed, either by holding it over the lamp,
or by putting it into a vessel of warm water; this is necessary to prevent the condensation of
breath upon its surface. The degree of heat is regulated by applying the back of the mirror
to the hand or cheek, when it should feel warm without being painful.
After these preliminaries the patient is directed to put out his tongue, which is held
by the left hand of the operator gently but firmly against the lower teeth by means of
a handkerchief. The warm mirror is passed to the back of the mouth, until it rests upon
and slightly raises the base of the uvula, and at the same time the light is directed upon
it: an inverted image of the larynx and trachea will be seen in the mirror. If the dorsum
of the tongue be alone seen, the handle of the mirror must be slightly lowered until the
larynx comes into view; care should be taken, however, not to move the mirror upon the
486
MUSCLE-NERVE PHYSIOLOGY
uvula, as it excites retching. The observation should not be prolonged, but should rather
be repeated at short intervals.
The structures seen will vary somewhat according to the condition of the parts as to
inspiration, expiration, phonation, etc. They are the following: first, and apparently
at the posterior part, the base of the tongue, immediately below which is the accurate out-
line of the epiglottis, with its cushion or tubercle, figure 348. Then are seen in the central
line the true vocal cords, white and shining in their normal condition. In the inverted image
the cords are closer together posteriorly. Between them is left an open slit, narrow while
a high note is being sounded, wide during a deep inspiration. On each side of the true
vocal cords, and on a higher level, are the false vocal cords. Still more externally than the
false vocal cords is the aryteno-epiglottidean fold, in which are situated upon each side
FIG. 347. — To Show the Position of the Operator and Patient when Using the Laryngoscope.
three small elevations; of these the most external is the cartilage of Wrisberg, the interme-
diate is the cartilage of Santorini, while in front and somewhat below the preceding is the
summit of the arytenoid cartilage seen only during deep inspiration. The rings of the
trachea, and even the bifurcation of the trachea itself, if the patient be directed to draw
a deep breath, may be occasionally seen.
Movements of the Vocal Cords. The position of the vocal cords in ordi-
nary tranquil breathing is so adapted by the muscles that the opening of the
glottis is wide and triangular, figure 348, B, becoming a little wider at each
inspiration, and a little narrower at each expiration. On making a rapid
and deep inspiration the opening of the glottis is widely dilated, figure 348, C,
and somewhat lozenge-shaped.
In Vocalization. At the moment of the emission of a note the opening is
narrowed, the margins of the arytenoid cartilages being brought into contact
and the edges of the vocal cords approximated and made parallel at the same
time that their tension is much increased. The higher the note produced, the
tenser do the cords become, figure 348, A; and the range of a voice depends, of
course, in the main, on the extent to which the degree of tension of the vocal
cords can be thus altered. In the production of a high note the vocal cords
are brought well within sight, so as to be plainly visible with the help of the
laryngoscope. In the utterance of low tones, on the other hand, the epiglottis
MOVEMENTS OF THE VOCAL CORDS
487
is depressed and brought over the vocal cords, figure 349. The epiglottis,
by being somewhat pressed down so as to cover the superior cavity of the lar-
ynx, serves to render the notes deeper in tone and at the same time somewhat
duller, just as covering the end of a short tube placed in front of caoutchouc
tongues lowers the tone. In no other respect does the epiglottis appear to have
any effect in modifying the vocal sounds.
The degree of approximation of the vocal cords also usually corresponds
with the height of the note produced; but probably not always, for the width
FIG.
48. — Three Laryngoscopic Views of the Superior Aperture of the Larynx and Surrounding
, in easy and quiet inhalation
r IG. 348. — Three i^aryngoscopic Views ot tne superior Aperture or t)
Parts. A, The glottis during the emission of a high note in singing; B, i
of air; C, in the state of the widest possible dilatation, as in inhaling a very deep breath. The
diagrams A', B' , and C , show in horizontal sections of the glottis the position of the vocal ligaments
and arytenoid cartilages in the three several states represented in the other figures. In all the
figures, so far as marked, the letters indicate the parts as follows, viz.: /, the base of the tongue;
e, the upper free part of the epiglottis; <?', the tubercle or cushion of the epiglottis; ph, part of the
anterior wall of the pharynx behind the larynx; in the margin of the aryteno-epiglottidean fold
w, the swelling of the membrane caused by the cartilages of Wrisberg; s, that of the cartilages
of Santorini; a, the tip or summit of the arytenoi.l cartilages; cv, the true vocal cords or lips of
the rima glottidis; cvs, the superior or false vocal cords; between them the ventricle of the
larynx; inC, tr is placed on the anterior wall of the receding trachea, and b indicates the com-
mencement of the two bronchi beyond the bifurcation which may be brought into view in this
state of extreme dilatation. (Quain, after Czermak.)
of the aperture has no essential influence on the pitch of the note, as long as the
vocal cords have the same tension; only with a wide aperture the tone is more
difficult to produce and is less perfect, the rushing of the air through the aper-
ture being heard at the same time.
488 MUSCLE-NERVE PHYSIOLOGY
No true vocal sound is produced at the posterior part of the aperture
of the glottis, the part of the aperture which is formed by the space between
the arytenoid cartilages. For if the arytenoid cartilages be approximated in
such a manner that their anterior processes touch each other, but yet leave an
opening behind them as well as in front, no second vocal tone is produced by
the passage of the air through the posterior opening, but merely a rustling
sound. The pitch of the note produced is the same whether the posterior
part of the glottis be open or not.
The Voice in Singing. The laryngeal votes may be produced in three
different kinds of sequence. The first is the monotonous, in which the notes
have nearly all the same pitch as in ordinary speaking; the variety of the sounds
of speech being due to articulation in the mouth. In speaking, occasional
syllables receive a higher intonation for the sake of accent. The second mode
of sequence is the successive transition from high to low notes, and vice versa,
FIG. 349. — View of the Upper Part of the Larynx as Seen by Means of the Laryngoscope
during the utterance of a grave note, c, Epiglottis; 5, tubercles of the cartilages of Santorini; a,
arytenoid cartilages; z, base of the tongue; ph, the posterior wall of the pharynx. (Czermak.)
without intervals; such as is heard in the crying in children and in the howling
and whining of dogs. The third mode of sequence of the vocal sounds is the
musical, in which each sound has a determinate number of vibrations, and the
numbers of the vibrations in the successive sounds have the same relative
proportions that characterize the notes of the musical scale.
The different sounds made by the musical voice are characterized by the
three properties of tones in general, viz., the pitch, which is dependent on the
rate of vibration of the vocal cords; the loudness, which depends on the force of
the vibration, and the quality or timber, which is dependent on the resonance of
the cavities of the respiratory apparatus, particularly of the mouth, pharynx,
and nasal cavities.
The Vocal Range of the Voice. In different individuals this com-
prehends one, two, or three octaves. In singers, that is, in persons trained in
singing, it extends to three or more octaves. But the male and female voices
commence and end at different points of the musical scale. The lowest note
of the female voice is about an octave higher than the lowest of the male voice;
the highest note of the female voice about an octave higher than the'highest of
the male. The entire scale of the average human voice includes, from the
lowest male note to the highest female, about three to three and a half octaves.
THE QUALITY OF THE VOICE 489
Some remarkable musical voices have had a range of three and a half octaves.
A principal difference between the male and female voice is, therefore, in their
pitch. But they are also distinguished by the quality of the tone. The voices
of men and of women differ among themselves, both in the general pitch and
in the quality. There are two kinds of male voices, technically called the bass
and tenor, and two of female voices, the contralto and soprano, all differing from
each other in general pitch. The bass voice reaches lower than the tenor,
and its strength lies in the low notes. The contralto voice is lower range than
the soprano, and is strongest in the lower notes of the female voice. The
barytone and mezzo-soprano voices are intermediate in range; the barytone
being intermediate between bass and tenor, the mezzo-soprano between the
contralto and soprano. The difference in the pitch of the male and the female
voices depends primarily on the different size of the larynx and the length of
the vocal cords in the two sexes; their relative lengths in men and women are
as three to two.
The boy's larynx resembles the female larynx. His vocal cords before
puberty are not two-thirds the length of the adult cords; and the angle of the
thyroid cartilage is as little prominent as in the female larynx. Boys' voices are
alto and soprano, resembling in pitch those of women, but louder, and differing
somewhat from them in tone. But, after the larynx has undergone the change
produced during the period of development at puberty, the boy's voice becomes
bass or tenor. While the change of form is taking place the voice becomes im-
perfect, frequently hoarse and crowing, and is unfitted for singing until the
readjustment of the larynx is complete and the muscles which control the vocal
cords are again coordinated. In eunuchs who have been deprived of the testes
before puberty, the voice does not undergo this change. The voice of most
old people is deficient in tone, unsteady, and more restricted in extent. The
first defect is owing to the ossification of the cartilages of the larynx and the
altered condition of the vocal cords; the want of steadiness arises from the
loss of nervous power and command over the muscles, the result of which is
here, as in other parts, a tremulous movement. These two causes combined
render the voices of old people void of tone, unsteady, and weak.
Most persons have the power, if at all capable of singing, of modulating
their voices through a double series of notes of different character: namely, the
notes of the natural voice, or chest-notes, and the falsetto notes. The natural
voice, which alone has been hitherto considered, is fuller, and excites a dis-
tinct sensation of much stronger vibration and resonance than the falsetto
voice, which has mere of a flute-like character.
The Quality of the Voice. The difference in quality of voices,
seen when two or more persons sound the same note, is due to differences in
resonance in the cavities of the mouth and larynx, also of the nose. The
shape of the roof of the mouth, the regularity of the teeth, and the size of the
tongue, and the size and clearness cf the nasopharynx are all factors. The
490 MUSCLE-NERVE PHYSIOLOGY
size and shape of the larynx and mouth cavity which influence the voice
quality can be controlled to some extent during singing, and this is a special
point of training in voice culture.
Speech. Besides the musical tones formed in the larynx a great
number of other sounds can be produced in the vocal tubes, between the
glottis and the external apertures of the air-passages, the combination of which
sounds into different groups to designate objects, properties, actions, etc.,
constitutes language. The languages do not employ all the sounds which can
be produced in this manner, the combination between certain sounds being
often difficult. Those sounds which are easy of combination enter, for the
most part, into the formation of the greater number of languages. Each
language contains a certain number of such sounds, but in no one are all
brought together. On the contrary, different languages are characterized by
the prevalence in them of certain classes of these sounds, while other sounds
are less frequent or altogether absent.
Articulate Sounds. The sounds produced in speech, or the articu-
late sounds, are commonly divided into vowels and consonants: the distinc-
tion between which is that the sounds for the former are generated by the
larynx, while those for the latter are produced by interruption of the current
of air in some part of the air-passages above the larynx. The term consonant
has been given to these because several of them are not properly sounded, ex-
cept consonantly with a vowel. Thus, if it be attempted to pronounce aloud
the consonants b, d, and g, or their modifications, p, t, k, the intonation fol-
lows them only in their combination with a vowel. To recognize the essential
properties of the articulate sounds, it is necessary first to examine them as they
are produced in whispering, and then investigate which of them can also be
uttered in a modified character conjoined with vocal tone. By this procedure
we find two series of sounds: in one the sounds are mute, and cannot be
uttered with a vocal tone; the sounds of the other series can be formed inde-
pendently of voice, but are also capable of being uttered in conjunction with it.
All the vowels can be expressed in a whisper without vocal tone, that is,
mutely. These mute vowel sounds differ, however, in some measure, as to
their mode of production, from the consonants. All the mute consonants are
formed in the vocal tube above the glottis, or in the cavity of the mouth or
nose, by the mere rushing of the air between the surfaces differently modified
in disposition. But the sound of the vowels, even when mute, has its source
in the glottis, though its vocal cords are not thrown into the vibrations necessary
for the production of voice; and the sound seems to be produced by the passage
of the current of air between the relaxed vocal cords. The same vowel-sound
can be produced in the larynx when the mouth is closed, the nostrils being
open, and the utterance of all vocal tone avoided. The sound, when the mouth
is open, is so modified by varied forms of the oral cavity as to assume the
characters of the vowels a, e, i, o, u, in all their modifications
ARTICULATE SOUNDS 491
The cavity of the mouth assumes the same form for the articulation of each
of the mute vowels as for the corresponding vowel when vocalized; the only
difference in the two cases lies in the kind of sound emitted by the larynx.
It has been pointed out that the conditions necessary for changing one and the
same sound into the different vowels are differences in the size of two parts —
the oral canal and the oral opening; and the same is the case with regard to the
mute vowels. By oral canal is meant here the space between the tongue and
palate : for the pronunciation of certain vowels both the opening of the mouth
and the space just mentioned are widened; for the pronunciation of other
vowels both are contracted; and for others one is wide, the other contracted.
Admitting five degrees of size, both of the opening of the mouth and of the
space between the tongue and palate, Kempelen thus states the dimensions of
these parts for the following vowel sounds:
Vowel. Sound. Size of Oral Opening. Size of Oral Canal.
a as in "far" 5 3
a " " name " 4 2
e " "theme" 3 i
O " "go" 2 4
oo " " cool" i 5
Another important distinction in articulate sounds is that the utterance of
some is only of momentary duration, taking place during a sudden change in
the conformation of the mouth, and being incapable of prolongation by a con-
tinued expiration. To this class belong b, p, d, and the hard g. In the
utterance of other consonants the sounds may be continuous; they may be
prolonged, ad libitum, as long as a particular disposition of the mouth and a
constant expiration are maintained. Among these consonants are h, m, n,
f, s, r, 1. Corresponding differences in respect to the time that may be oc-
cupied in their utterance exist in the vowel sounds, and principally constitute
the differences between long and short syllables. Thus the a as in far and
fate, the o as in go and fort, may be indefinitely prolonged; but the same
vowels (or more properly different vowels expressed by the same letters),
as in can and fact, in dog and gotten, cannot be prolonged.
All sounds of the first or explosive kind are insusceptible of combination
with vocal tone (intonation), and are absolutely mute; nearly all the conso-
nants of the second or continuous kind may be attended with intonation.
The tongue, which is usually credited with the power of speech, plays
only a subordinate, although very important, part. This is well shown by cases
in which nearly the whole organ has been removed on account of disease.
Patients who recover from this operation talk imperfectly, and their voices are
considerably modified; but the loss of speech is confined to those letters in the
pronunciation of which the tongue is particularly concerned.
Stammering depends on a want of harmony between the action of the
muscles (chiefly abdominal) which expel air through the larynx, and that of
492 MUSCLE-NERVE PHYSIOLOGY
the muscles which guard the orifice (rima glottidis) by which it escapes, and of
those (of tongue, palate, etc.) which modulate the sound to the form of speech.
Over either of the groups of muscles, by itself, a stammerer may have as much
power as other persons, but he cannot harmoniously arrange their con-
joint actions.
LABORATORY EXPERIMENTS ON MUSCLE AND NERVES.
Physiological experiments on living muscle serve to demonstrate many
of the most fundamental particulars of the subject. The muscles, especially
of cold-blooded animals, when isolated from the body retain their living
attributes for several hours under the ordinary conditions which can be readily
supplied in the laboratory. They, therefore, serve as specially favorable
experimental material.
The muscles of frogs, turtles, and other cold-blooded animals illustrate
practically all the facts which can be shown by the muscles of warm-blooded
animals and are therefore most advantageously used.
1. The Muscle-Nerve Preparation. The classical muscle-nerve prep-
aration is the gastrocnemius muscle and the sciatic nerve. Prepare it
as follows: Kill the frog by pithing. This is done by grasping the frog
firmly in one hand and with the other making a cut with a blunt scalpel
through the cranium just over the medulla, turning the scalpel so as completely
to destroy the medulla. Now take a slender knitting needle, quickly run it
up into the cranial cavity to destroy the brain, and down the spinal canal to
destroy the cord. After a brief spasmodic contraction of the muscles of
practically the entire body, the frog remains limp and motionless. In making
the muscle-nerve preparation it is better to isolate the tendon first, then the
nerve, and finally the femur. The nerve should be prepared as long as possi-
ble and should not be allowed to come in contact with the skin. If the prep-
aration is to be used in a moist chamber, the skin should be entirely re-
moved; if it is to be used in the open air, the skin should be left on. Use
care not to stretch the nerve, and protect it from evaporation.
2. The Irritability of Nerve. Prepare a muscle nerve with its skin
on and do not cut away the foot. Mount it by inserting the femur in a
muscle clamp, letting the leg extend vertically upward, and the foot hang over.
The nerve should lie along the exposed moist femur, one end being slightly
free. Stimulate the nerve in the following ways:
a. Electrical Stimuli. Apply the electrodes from the secondary coil of an
induction apparatus to the tip of the nerve. When an induction current of
sufficient strength is produced, the muscle to which the nerve is attached will
give contractions, thus moving the foot. Notice that contractions occur with
both make and break induction. Apply the electrodes from the two poles of a
IRRITABILITY OF MUSCLE 493
dry battery. When the current of the battery is established a contraction will
occur, but does not continue during the time of the flow of the current. When
the current is stopped a second contraction occurs. The nerve is irritable to
both galvanic and faradic currents.
b. Mechanical Stimuli. Pinch the nerve lightly with forceps, or give it
a sudden stroke with the scalpel handle. With each mechanical impact there
is a single contraction of the muscle.
c. Thermal Stimuli. Touch the end of the nerve with a glass rod heated
in boiling water. At each time the nerve is brought in contact with the rod
there will be muscular contraction, as in the preceding cases. The experi-
ment succeeds better if the nerve comes in contact with the rod for several
millimeters of length. If the tip of the nerve has ceased to respond, then snip
it off with the scissors, and repeat the experiment on the fresh end.
d. Chemical Stimulation. Many chemical substances when brought in
contact with living nerve fiber produce nerve impulses. Try crystals of sodium
chloride, magnesium sulphate, dilute ammonia, acetic acid, 10 per cent nitric
acid, i per cent mercuric chloride.
Tabulate your observations on all the forms of stimulation used above, by
the following outline:
Kind of Stimulation.
Effect Produced.
3. Irritability of Muscle. Repeat the experiments in number 2
above, applying the stimuli, electricity, etc., directly to the muscle substance,
choosing as far as possible portions of muscle which do not exhibit nerve
fiber. The muscle will usually respond by a contraction to each of the above
forms of stimulation.
These tests do not fully demonstrate the direct irritability of muscle sub-
stance, since in each case it is possible that nerves may have been stimulated.
The nerve influences over the muscle can be eliminated by the use of drugs, as
will be shown in the next experiment.
4. Independent Irritability of Muscle. The influence of curara on
the muscle-nerve preparation is demonstrated as follows : Destroy the brain
only of a frog by pithing, taking care not to injure the blood-vessels of the
spinal canal. Place the animal on a glass plate with its back up and dissect out
the sciatic nerve. Use care not to injure in any way the accompanying femoral
artery. Pass a ligature of linen thread under the sciatic and around the mus-
cles and blood-vessels of the leg so as completely to shut off the circulation on
494 MUSCLE-NERVE PHYSIOLOGY
that side. Now inject under the skin of the back three drops of i per cent
curara, allowing twenty to thirty minutes for absorption. When the drug
is completely absorbed, make the following observations:
a. Stimulate the muscles of the ligatured leg, also the muscles of the cura-
rized leg, both will contract.
b. Stimulate the sciatic nerve of the ligated leg below the ligature where
it has not come in contact with the curara; also the sciatic of the opposite
side, which has come in contact with the curara. Stimulation of the first
nerve produces contraction of its muscle; of the second nerve does not pro-
duce contraction of its muscle.
From this experiment of Claude Bernard's it is evident that the curara does
not destroy the irritability of nerve fiber nor the irritability of the muscle
fiber, yet it does destroy the influence of the nerve over the muscle, probably
acting as a specific poison for the motor end-plates. If the motor end-plates
are destroyed, then forms of stimuli which produce contractions of the muscle
must act directly on muscle substance, proving that muscle substance, as such,
is irritable.
5. The Simple Muscle Contraction. Striated muscle responds to
electrical stimuli even of almost instantaneous duration. The response which
the muscle gives to a single stimulus is called a simple muscle contraction,
and is demonstrated as follows:
Make a muscle-nerve preparation with the tendon isolated and the skin
removed, and mount it in a moist chamber, figure 350. Connect the tendon
FIG. 350. — Moist Chamber.
with a recording lever by short copper-wire hooks. Lay the nerve across a
pair of platinum electrodes, shake a little water on the sides of the cover of
the moist chamber, and place it over the preparation so as to prevent drying of
the nerve and of the muscle. Arrange an induction coil with its keys, battery,
THE SIMPLE MUSCLE CONTRACTION
495
and electrodes connected as shown in the diagram, figure 351. Set the second-
ary coil at a position which will give a strong contraction of the muscle, and
record this contraction on the smoked paper of an ordinary recording cylinder.
Whenever the induction shock is sent through the nerve there will be a single
contraction of the muscle. If this contraction is recorded on the drum stand-
ing still, then the record will be a vertical line, the height of which can be
measured. From it and the arms of the lever the exact shortening of the muscle
can be computed. Repeat the stimulus with weaker and weaker currents,
until no contraction is produced. As the stimulus becomes weaker a point
FIG. 351. — Arrangement of Apparatus in the Induction Coil, as Shown for Single Inductions.
is reached at which the contractions rapidly decrease in height and cease
altogether. If, on the other hand, the stimulus is stronger the contractions
only slightly increase.
Arrange the apparatus so as to stimulate the muscle by an automatic key
attached to the recording drum. Adjust the apparatus and lever and revolve
the drum at a rapid rate, allowing the automatic key to be opened while the
drum is turning at a rapid speed. Or take a record on the pendulum myo-
graph, which is especially constructed for this experiment, figure 352. The
muscle contraction now is recorded as a wave which shows some consider-
able duration in t'me. Repeat the experiment, introducing a 100 double
vibration tuning fork to record the speed of the drum, and taking care to
mark the exact point on the record where the automatic key is opened. In
this record the muscle contraction shows three different periods or phases.
The first, a period of no activity, called the latent period, taking about o.oi
of a second; the second, the period of rapid shortening known as the con-
traction phase, taking about 0.04 of a second on the average; and the third,
a period of rapid relaxation or return to the normal, which takes about 0.05
of a second, see figure 353.
The time and character of the simple muscle contraction will be influenced
by: i, load or tension; 2, the exact temperature; 3, by the amount of work
496
MUSCLE-NERVE PHYSIOLOGY
it has previously done, or fatigue ; 4, by the time since it was isolated from the
circulation. Perform a series of experiments varying these effects, and record
the results by the following outline:
Number of
the
Experiment.
Muscle
Used.
Temper-
ature.
Load.
Total Time of
Contraction,
in Seconds.
Latent
Period, in
Seconds.
Contraction
Period, in
Seconds.
Relaxation
Period, in
Seconds.
6. The Relation of the Contraction to the Strength of the Stimu-
lus. Minimal and Maximal Stimuli. Prepare a muscle-nerve of the
frog and mount in the moist chamber and arrange for stimulating the muscle
directly by means of the secondary current of the induction coil, with the ap-
FIG. 352.— Simple Form of Pendulum Myograph and Accessory Parts. A, Pivot upon which
pendulum swings; B, catch on lower end of myograph opening the key, C, in its swing; D, a spring-
catch which retains myograph, as indicated by dotted lines, and on pressing down the handle of
which the pendulum swings along the arc to D on the left of figure, and is caught by its spring.
paratus adjusted as in figure 351. Prepare a recording cylinder for making
vertical records of the contractions. Adjust the writing point of the muscle
lever to the drum and move the drum by hand i cm. after each succeeding
contraction. Set the secondary coil of the induction apparatus so that it will
be too weak to produce a stimulus. Now attempt to stimulate the muscle,
THE EFFECT OF FATIGUE 497
then move the induction coil toward the primary i cm. at a time and repeat
until the first slight contraction appears. Continue to slide the secondary coil
toward the primary, stimulate at each new position, moving the drum forward
FIG. 353- — Record of a Simple Contraction of the Gastrocnemius of the Frog. Time in .01
of a second. 52, Moment of stimulation. Record taken on a rapid drum that was provided with
an automatic key.
for each stimulus as directed, until a series of contractions is obtained
through the range of variation of induction of which the apparatus is capa-
ble, usually twenty to thirty contractions.
A typical tracing, figure 326, shows that as the strength of the stimulus is
increased the amplitude of the contractions quickly mounts from the minimal
to a maximal, after which all further increase in the strength of the stimulus
produces contractions of practically the same height. The first perceptible
contraction is called the minimal contraction, the strength of the current which
produced it a minimal stimulus for that preparation. The contractions of
the greatest amount are called maximal contractions. The weakest stimulus
which produces a maximal contraction is called the maximal stimulus, and
all stronger stimuli supramaximal.
7. The Effect of Fatigue on the Amplitude of the Simple Muscle
Contraction. Prepare a gastrocnemius muscle for direct stimulation
and mount it in a moist chamber. Arrange the induction apparatus for single
stimuli. Adjust the recording lever of the muscle to a smoked-paper kymo-
graph and set the speed of the kymograph to revolve at the rate of i mm. per
second. Now stimulate the muscle with the make induction (short-circuiting
the break) once every two seconds. The contractions will be recorded as vertical
marks on the drum in regular order, at a distance of 2 mm. apart, hence very
slight changes in amplitude are readily detected. The contractions gradually
increase in height for the first ten or twenty, the phenomenon of treppe, then
run for from fifty to one hundred contractions of practically uniform ampli-
tude, after which there is a gradual but sharp decrease known as fatigue.
Repeat the experiment after ten minutes' rest. The former variations occur
now very rapidly, indicating that the fatigue effects are only partially recov-
ered from.
32
498 MUSCLE-NERVE PHYSIOLOGY
8. The Effect of Fatigue on the Time of the Simple Contraction.
Prepare a muscle-nerve and mount it in the moist chamber, arrange for the
record as directed under 5 above. Make a series of records of the simple
contraction when automatically stimulated, recording only every tenth or
twentieth contraction — the intermediate contractions should be shunted and
are used merely to produce fatigue. After a time the contractions will not
only diminish in amplitude, but there will be a gradual increase in the time
consumed by the contraction. This increase in time falls very slightly on
FIG. 354. — Contractions of the Gastrocnemius Muscle to Show Fatigue. The numbers printed
on the figure indicate the contraction in the series which is recorded. (Lee.)
the latent period, is more pronounced in the contraction phase, but is very
marked in the relaxation phase, figure 354.
9. Fatigue of Voluntary Muscular Contraction. The human vol-
untary muscles are used to demonstrate this experiment. Use a Mosso's
ergograph, or any one of its numerous modifications. If the original form is
used, then the muscle should be loaded with about 3 kilos, and contractions
once a second recorded until the muscle can no longer lift the load. The load
may have to be adjusted to the individual, but should be chosen so that ex-
haustion will be obtained with about fifty contractions. This experiment does
not demonstrate complete exhaustion, but merely fatigue down to a certain
level. If an apparatus is previously arranged for direct stimulation of the
muscles by electric currents it will be found that the contractions of the muscles
still occur after the voluntary power is lost, showing that at least a part of
the phenomenon, possibly the chief part, is located in the nervous tissue rather
than in the muscle substance.
10. The Effect of Temperature on Muscle Contractions. Pre-
pare a muscle-nerve and mount it in Porter 's latest form of temperature ap-
paratus. Adjust the levers for vertical records on the smoked paper of the
kymograph. Begin with a temperature of the tap water and gradually lower
the temperature of the preparation by adding small amounts of crushed ice
at first, later ice and some salt crystals, to the external chamber. Take care
THE EFFECT OF TEMPERATURE 499
to lower the external temperature very slowly and gradually, — say about one
degree in two minutes. Stimulate the muscle with a supramaximal stimulus
twice in rapid succession, for i° C. of change. Record these contractions as
pairs of vertical marks on the drum i mm. apart, separating each pair by a
space of i cm. When o° C. is reached, or before if the muscle fails to contract
at a higher temperature, reverse the direction of the temperature change,
gradually but slowly increase it until the muscle goes into heat rigor, which
begins at from 38° to 40° C.
While the muscle is entering rigor, move the drum i cm. for each degree,
as before, so as to record the development of that process.
11. The Effect of Temperature on the Time of the Simple Con-
traction. Repeat the preceding experiment, but record the con-
tractions by the method described in experiment 5 above, recording a con-
traction for every change of 5° C. Measure the time and amplitude of the
different contractions, and the phases of the simple contractions, and tabulate
them as shown in experiment 5.
12. Effect of Load on the Height of the Contraction and on the
Work of Voluntary Muscle. Make a muscle-nerve preparation and
arrange it for stimulation, as in experiment 6 above. Set the induction coil
of the stimulating apparatus for an effective supramaximal stimulus. Re-
cord the contractions as a series of vertical lines on the kymograph, separated
by a distance of i cm. Begin with the load of the lever only for the first
contraction, then increase the load by steps of 20 grams each until the muscle
is no longer able to lift the weight used. Support the lever under a tension
of 20 grams. Use care that no mechanical changes of the apparatus are re-
corded on the smoked cylinder. Repeat the experiment on a fresh muscle,
but do not support the lever.
The amount of work done by the muscle at each contraction is the prod-
uct of the load in grams times the height in centimeters. The height of
the lift can be obtained in this experiment from the height of the record on
the drum and the length of the recording arm and power arm of the lever, in
which the length of the recording lever is to the length of the power lever
as the height of the record obtained is to the actual shortening of the muscle.
Compute the exact amount of work done by each contraction under varying
loads, and tabulate on co-ordinate paper. Compare the variation in work
done with the variation in amplitude of the contraction.
13. Tetanus. A continued contraction of a voluntary muscle can
be shown to be a fusion of simple muscle contractions. This is called a tetanus.
Prepare a muscle -nerve in the moist chamber and arrange the induction coil
for stimulating with a series of rapidly repeated stimuli. The rate of the
stimulation is obtained from the tetanometer, a form of key for rapidly in-
terrupting the current, which should be connected with the primary coil in-
stead of the key, K, figure 351. Stimulate the muscle at a rate of 10 per
500
MUSCLE-NERVE PHYSIOLOGY
second, record the contractions on the drum moving at a speed of about
2 cm. per second. Use care not to overfatigue the muscle, i.e., stimulate
it only 2 or 3 seconds at a time. Repeat this test, increasing the rate of stimu-
lation each time by 5, that is, stimulate at 10, 15, 20, etc., per second. In the
first stimulus there will be a series of simple contractions with almost com-
plete intervening relaxations. As the rate is increased these relaxations be-
come less and less until presently a rate is found which produces continuous,
apparently uninterrupted contraction. This is a tetanus, the others are incom-
plete tetani. The frog's gastrocnemius at a temperature of 20° C. is tetanized
with a stimulation of from 25 to 35 per second.
14. Cardiac Muscle. Cardiac muscle differs from voluntary in
that the contractions occur rhythmically and automatically. This is shown
FIG. 354 A. — Arrangement of Apparatus for Studying the Contractions of the Strip of the Apex
of the Ventricle.
by the isolated frog's heart, which continues to contract when bathed with
blood or salt solution, often for hours. This isolated heart, however, has a
complicated local nervous mechanism. The apex of the ventricle of the
terrapin's heart is practically free from nerve ganglia and may be used to
demonstrate the characteristics of pure cardiac muscle. Cut a strip off the
apex of the terrapin's ventricle, as shown in figure 214, and mount it by means
of light silk-thread ligatures tied around the two ends of a strip and attached
to the apparatus shown in figure 215. When such ventricular strips are
immersed in ordinary 0.7 per cent sodium chloride they will begin contractions
in a few minutes, twenty minutes or so. The contractions will be regular in
rate and will continue through two or three hours, gradually becoming
smaller and smaller until the standstill is reached. If the strip is im-
mersed in its own serum it will give only occasional contractions, but it re-
INVOLUNTARY MUSCLE 501
mains irritable and capable of contracting at any moment. If changed to
salt solution, the salt solution apparently brings out the automatic rhythm
by an increase in its irritability. Portions of the auricle and of the sinus,
especially the latter, are more highly rhythmic than portions of the ventricle,
due to a specific difference in the muscle cells themselves and not to the nervous
mechanism.
Refer to the experiments on cardiac muscle at the end of the chapter on
Circulation.
15. Involuntary Muscle. Strips of smooth or involuntary mus-
cle, cut from the stomach of a frog or terrapin or from the intestine of a frog,
may be used to show the physiology of this character of tissue. Mount a
strip in the moist chamber, or in the apparatus shown in figure 354 A, using
FIG. 355. — Figure Showing the Type of Contraction of a Strip of Muscle from the Stomach of a
Frog. The muscle was stimulated with an interrupted current during the time indicated by the
signal tracing, immediately below the time tracing. Time in seconds.
care not to load it too heavily; the weight of the ordinary muscle lever may
produce too much tension. Stimulate the muscle for one or two seconds with
interrupted induction currents of moderate strength. Contractions will follow,
usually developing very, very slowly as compared with striated muscle, and
lasting through many seconds, from thirty to one hundred seconds. By using
very strong inductions occasionally a contraction may be secured with a
single stimulus, but single-induction currents as a rule do not produce
effective stimuli for smooth muscle, which, requires a more slowly developed
stimulus.
If the stomach muscle of the frog be used and it be handled with extreme
care, it may happen that automatic contractions will develop in the muscle
in the moist chamber. If so, these contractions will be found to be slow and
of varying amplitude. The terrapin's stomach muscle will ordinarily not
show automatic contractions, but by increasing the temperature to about
502 MUSCLE-NERVE PHYSIOLOGY
30° C. automatic contractions will sometimes occur in it. Smooth muscle
responds like voluntary muscle to variations in temperature, to fatigue, strength
of stimulus, etc., etc.
1 6. Ciliary Contractions. Ciliated Epithelium. Make a prepara-
tion of ciliated epithelium by cutting out the esophagus of a terrapin or frog,
slitting it open longitudinally, and smoothing it out on a cork block. The cilia
of this membrane will drive in the direction down the esophagus. Test the
rate at which different loads are moved and measure the distance on the prep-
aration as follows : Cut pieces of clean white paper about 4 and 6 mm. square.
Select a favorable area on the ciliated surface as long as possible, place the 4
mm. square paper at the beginning of the area, and measure the time which it
takes to travel the distance. Measure the speed in terms of seconds per cen-
timeter. Now replace the paper at the point of beginning and load it with
small weighed cubes of paraffin. The rate at which the load is carried will
slightly increase at first as the load is increased, but later will sharply decrease.
Elevate one end of the ciliated membrane and repeat the experiment with
different loads so that the cilia will now carry the load uphill. Calculate the
work done in terms of gramcentimeters of work per square centimeter of
ciliated surface acting on the load.
CHAPTER XIV
THE NERVOUS SYSTEM
THE nervous system consists of an extremely complex anatomical mass
of nerve cells and fibers. It is usually described as made up of two main
divisions, the cerebro-spinal system and the sympathetic. These two divisions
must be regarded as parts of one great whole, and in no sense coordinate.
The gross subdivision of the nervous system may be given as the following:
— first, the cerebro-spinal axis, which consists of matter within the bony
cranium and spinal column, constituting the brain and cord. Second, smaller
masses for the most part in the abdominal and thoracic cavities, also in the
neck and head, and constituting the sympathetic ganglia. Third, the nerves
or bundles of nerve fibers which connect the central nerve axis with the per-
iphery and with the sympathetic ganglia. Fourth, there are special peripheral
organs in connection with the beginnings and endings of the nerve fibers, the
one for receiving nerve stimuli, the other for transmitting stimuli to other tis-
sues. These are properly parts of the nervous system. The peripheral
organs for receiving stimuli constitute the sense organs and will be treated in
a separate chapter.
I. FUNCTION OF THE NERVE CELL.
The Nerve Cell. The nerve cell, the neurone, may be considered
the anatomical and physiological unit of the nervous system. The details
of the structure of the nerve cell, both its body and its processes, have
already been given in chapter II. It is sufficient to recall that the types of
nerve cells found in various parts of the nervous system vary extremely.
The peculiar feature, however, consists in the fact that the cell body has
one or more processes. Sometimes these processes are short but com-
plexly branched, sometimes they are exceedingly long as compared with the
extent of the cell body. The cell processes may or may not be medullated
and subdivided into nodes, but the axis-cylinder process is to be regarded as
a continuity of the protoplasm of the cell body. In recent years the struct-
ure of the cell body and its branches has been very carefully investigated,
with the result that we are finding that the intimate structure is very complex.
Networks of neurofibrillae have been described not only in the cell body, but
extending throughout the course of the processes and, in fact, from cell to cell.
We are not in a position at the present time fully to determine what bearing
503
504
THE NERVOUS SYSTEM
these neurofibrillae have on our accepted theories of nerve function, other than
that they are assumed to be the conducting elements.
The Neurone Theory. Our knowledge of the function of the nerv-
ous system is best explained on the basis of the neurone theory, which
considers the nerve cell as a physiological unit. By this view each gross
division of the nervous system is supposed to consist of a large number of
individual neurones, each of which is a more or less complete morphological
unit capable of carrying on certain functions of its own. Each of these
neurones maintains physiological continuity with its associates, presumably
by protoplasmic contact rather than by continuity; so that well-marked paths
of conduction are possible throughout the extent of the particular mass of
FIG. 356.— Purkinje Cells from the Cerebellum of the Swallow. A, Taken in the morning; B,
taken in the evening. (Hodge.)
which the neurone is a part, and throughout the adjacent masses. By this
view, paths of conduction are made up of series of individual neurones which
are in physiological continuity.
The Characteristics of the Individual Nerve Cell. The function
of the nerve cell may be discussed under two headings: The function of the
cell body, and the function of the cell processes.
The cell body of the nerve cell is the part that contains the nucleus and is
the center of those activities which influence the metabolism of the cell itself.
If the cell body be isolated from its processes, the processes will degenerate,
while the body continues to live. In other words, the cell body may be con-
sidered as the center of those trophic influences which regulate the nutrition
of the processes. Although the nerve cell as a whole is in many, perhap: in
THE CHARACTERISTICS OF THE INDIVIDUAL NERVE CELL
505
most, cases a conducting organ, still those physiological processes which go on
in it produce marked changes in the protoplasm of the cell body. Hodge has
demonstrated that nerve cells which have been active for several hours, in
case of sparrows which have been flying about actively throughout the day, or in
bees after a day's work, show marked evidences of fatigue. These evidences
B
FIG. 356 A. — Spinal Ganglion Cells from the Cat. A, Normal taken before stimulation; B, taken
alter five hours' stimulation. From the right and left, eight tnoracic ganglia. (Hodge.)
consist in the decrease in the size of the nucleus and the appearance of
vacuoles in its structure, also in the shrinking of the protoplasm of the cell,
which, in case of the cells of the spinal ganglia, draws away from its capsule.
If the cells are examined early in the morning, then these fatigue changes will
not be present, the cell having recuperated during the rest of the night. It
506 THE NERVOUS SYSTEM
has also been found that the Nissl granules which are present in the cell body
of resting cells decrease in number and show evidence of disintegration in
cells that have been stimulated for several hours.
The nerve processes or fibers are primarily conducting structures. But
their fibers are susceptible to artificial stimulation, as shown in the previous
chapter, that is, they are irritable. They are influenced by certain changes in
the environment, but they do not show evidence of fatigue upon prolonged
functional activity.
Nutritive Influence of the Cell Body over its Processes— Wallerian
Degeneration. The control of the cell body over the nutrition of the
cell processes is demonstrated by the changes which occur when these proc-
esses are severed from connection with the cell body. Under such conditions
the axis-cylinder process completely degenerates. Ho well and Huber have
followed the degenerative changes in medullated nerve fibers. The medullated
fiber in the course of three or four days, in mammals, breaks up into elliptical
segments of myelin, containing small fragments of the axis-cylinder. These
changes in the cut-off section of nerve occur simultaneously throughout its
whole extent. In the course of a few weeks regenerative changes begin, ap-
parently under trophic influence of the nuclei of the primitive sheath. These
nuclei increase in number and form small masses of protoplasm which ulti-
mately produce a strand of embryonic protoplasm, which is described as the
" band fiber." If the ends of the sectioned nerve have originally been brought
together and sutured in place, then the axis-cylinder processes of the portion of
the nerve fiber still attached to the cell body will grow down into the peripheral
fibers, thus forming new axis-cylinder processes along the course of the band
fiber. If the stumps of the nerves are not so brought together, then apparently
the band fiber again degenerates, especially in adult tissues, though it has been
claimed by Bethe and others that complete regeneration of the peripheral
fiber will take place in very young animals. Even if complete regeneration
takes place in the peripheral fiber, unless connection is established between it
and the central end of the fiber it will ultimately disintegrate and can only
temporarily carry on any physiological function.
The central end of the divided nerve, that is, the part maintaining con-
nection with the cell body, usually degenerates for a few nodes only, then re-
generation and growth of the original stump proceed. Instances are observed
in certain cases where the degeneration of the entire central fiber, including its
cell body, takes place. This happens particularly in those relations where the
original neurone forms a link in a conducting path.
In conclusion, one may infer that the cell body exercises a nutritive or
trophic control over the protoplasm of its branches, just as we have
already seen the neurone as a whole exercises trophic control over
the nutritive processes taking place in the tissue to which its branches are
distributed.
TRANSMISSION OF IMPULSES THROUGH THE NERVE CELL 507
Specific Energy of the Nerve Impulses. We have already discussed
the fact that a nerve fiber, also its cell body, is irritable to various forms of
mechanical, electrical, etc., stimuli. In the complex differentiation of the
nervous system it is found that whatever the form of the external stimulus
applied to a nerve the resulting nerve impulse produces the same effects in the
central nervous system. This idea has been called the specific energy of the
nerve impulse, and was first advanced by Johannes Miiller.
Transmission of Nerve Impulses through the Nerve Cell. The the-
ory has been advanced that in the nerve cell the primary function of some
processes is to carry nerve impulses toward the cell body, and of other processes
to. carry nerve impulses away from the cell body. At the present time this
view is advocated by perhaps the ablest living anatomists and neurologists.
The dendrites conduct toward the cell body, and the axones away from it.
That is, the former are cellulipetal, the latter cellulifugal.
Impressions made upon the terminations or upon the trunk of a cellulifugal
nerve may cause, a, pain or some other kind of general sensation; b, special
sensation; c, reflex action of some kind; or d, inhibition or restraint of action.
Similarly impressions made upon a cellulipetal nerve may cause, a, contraction
of muscle (motor nerve); b, it may influence nutrition (trophic nerve);
c, it may influence secretion (secretory nerve); or d, inhibit, augment, or stop
any other efferent action.
By artificial stimulation nerve impulses can be made to pass in both di-
rections in all classes of nerve processes. That is to say, if a motor axone is
stimulated in the middle of its course it will not only convey a nerve impulse
to its distribution, but also a nerve impulse will pass back over the fiber to
the cell body and out over the dendrites. Normally, in the complex of the
body it is probable that such a neurone will be stimulated only at its points
of contact with other neurones chiefly through its dendrites, and especially
by means of the sensory cells. The dendrites will therefore receive the nerve
stimulus, carry it through the cell body to the axone and its distribution-
In such cells there is isolated, or uninterrupted, conduction throughout the
extent of the neurone. The nerve impulse is able to pass from a given
neurone to adjacent ones only at the termination of the axone or its branches,
which may be considered as special organs for the transference of the nerve
impulses. This activity involves isolated conduction in nerve fibers bound in
a common nerve trunk. It has been supposed that the myelin sheath of a
medullated nerve acts as an insulator of the axis-cylinder, but this can be
only relatively true, for the reason that non-medullated nerves do not possess
the myelin sheath. In non-medullated nerves we must suppose that the
primitive sheath is sufficient to give insulated conduction, or that it is an in-
herent property of the axis-cylinder itself to carry the nerve impulse without
transmission to adjacent fibers.
We have already, page 470, discussed the rate of transmission of the nerve
£08 THE NP:RVOUS SYSTB:M
impulse in motor nerves. In sensory nerves the rate is said to be somewhat
higher; in human nerve from 30 to 42 meters per second.
Physiological Types of Nerve Cells. Many classifications could
be made of nerve cells, based on the differences in their functional relations,
but at this place attention will be called to only one. Nerve cells may be
classified as afferent or sensory, efferent or motor, and connecting or trans-
mitting cells.
Under afferent neurones are classed all those neurones which transmit
the effects of external stimuli received through the sense organs, both general
and special sense organs. These neurones carry nerve impulses toward the
central nervous system, ultimately producing those changes in the cerebral
cortex which are associated with states of consciousness.
Under efferent neurones are included all those which transmit nerve im-
pulses from any part of the central nervous system to the muscles, that is,
motor nerves; or transmit nerve impulses to the glands, secretory nerves; or
that transmit nerve impulse, which inhibit peripheral action, inhibitory nerves.
Under central or transmitting neurones may be included those units which
act as connecting links within the central organ, especially within coordinate
parts of the central nervous system, between the afferent and efferent neurones.
Nerve Centers. Whenever a number of neurones are gathered
in one group to accomplish some specific function it is called a nerve
center. The term usually applies to the aggregation of cell bodies and their
dendritic processes in contradistinction to nerve trunks. There are aggre-
gations of nerve cells into different specific groups, to which we cannot in every
case ascribe a specific function. These groups are not called nerve centers,
but are described by the general anatomical term, ganglia. Such ganglia
are represented by the sympathetic chain, the spinal-root ganglia, the ganglia
of certain cranial nerves, etc. The nerve centers are found in the spinal cord,
the medulla, and the higher cranial groups. The medulla is particularly rich
in nerve centers. The cerebro-spinal axis is in fact an aggregation of nerve
centers of greater or less complexity.
It is by means of the nerve centers that the activities of the differentiated
parts of the human body are brought into intimate correlation. The nerve
centers exercise their influence through the power of inhibiting or decreasing ac-
tivity; or, on the other hand, of augmenting or increasing the activity in the
peripheral tissues or in other parts of the nervous system. For example, the
vagus center regulates the activity of the heart muscle by its power to decrease
or inhibit cardiac contractions. This center, we have already found, is incon-
stant tonic activity; that is to say, in constant regulative control of the heart.
The cardiac augmentory center, on the other hand, produces just the opposite
effect, increasing the activity of the cardiac muscle. What is true for the heart
is likewise true in general for other tissues of the body. The numerous nerve
centers in the central nervous system are brought into correlation through an
NERVE CENTERS 509
exceedingly complex system of communicating fibers. The cerebro-spinal
axis may in fact be regarded as a segmental chain of nerve centers, the com-
plexity increasing from the cord toward the brain, and the coordinating con-
trol culminating in the cerebral cortex.
FIG. 357. — View of the Cerebro-spinal Axis of the Nervous System. The right half of the
cranium and trunk of the body has been removed by a vertical section; the membranes of the
brain and spinal cord have also been removed, and the roots and first part of the fifth and ninth
cranial, and of all spinal nerves of the right side, have been dissected out and laid separately on
the wall of the skull and on the several vertebrae opposite to the place of their natural exit from
the cranio-spinal cavity (After Bourgery.)
510 THE NERVOUS SYSTEM
II. THE STRUCTURE AND FUNCTION OF THE
SPINAL CORD.
STRUCTURE.
The spinal cord is a cylindrical column of nerve-substance connected above
with the brain through the medium of the bulb, and terminating below in a
slender filament of nerve substance, the filum terminate, which lies in the midst
of the roots of the many nerves forming the cauda equina.
General Features. The cord is composed of nerve fibers and nerve
cells. The former are situated externally and constitute the chief portion
of the cord, while the latter occupy its central or axial portion and are so
disposed that on the surface of a transverse section of the cord two somewhat
crescentic grayish masses connected by a narrower portion or isthmus
appear, figure 358. Passing through the center of the cord in a longitudinal
direction is a minute canal, the central canal, which is continued through the
whole length of the cord, opening above into the space at the back of the
medulla oblongata and pons Varolii called the fourth ventricle. The canal
is lined by a layer of columnar ciliated epithelium.
The spinal cord consists of exactly symmetrical halves, separated anteriorly
and posteriorly by vertical fissures (the posterior fissure being deeper but less
wide and distinct than the anterior), and united in the middle by nervous
matter which forms the commissures. The central part, which contains the
central canal, is known as the gray commissure, and is bounded by the anterior
white commissure in front, and the posterior white commissure behind. Each
half of the spinal cord is marked on the sides (obscurely at the lower part, but
distinctly above) by two longitudinal furrows, which divide it into three por-
tions, columns, or tracts — an anterior, lateral, and posterior. From the groove
between the anterior and lateral columns spring the anterior roots of the
spinal nerves; and just in front of the groove between the lateral and
posterior columns arise the posterior roots of the same; a pair of roots on each
side corresponding to each vertebra.
The nerve tracts of the cord are made up of medullated nerve fibers of
different sizes, arranged longitudinally, and of a supporting material of ordi-
nary fibrous connective tissue and neuroglia, figure 105.
The general rule respecting the size of different segments of the cord appears
to be that each is in direct proportion in this respect to the size and number of
nerve roots given off from it, and has but little relation to the size or number
of those given off below it. Thus the cord is very large in the middle and
lower part of its cervical portion, whence arise the large nerve roots for the
formation of the brachial plexuses and the nerve supply of the upper extrem-
ities; and again enlarges at the lowest part of its dorsal portion and the upper
ARRANGEMENT OF NERVE CELLS IN THE SPINAL CORD
511
part of its lumbar, at the origins of the large nerves which, after forming the
lumbar and sacral plexuses, are distributed to the lower extremities. The
chief cause of the greater size at these parts of the spinal cord is increase
in the quantity of the gray matter; for there seems reason to believe that the
white part of the cord becomes gradually and progressively larger from below
upward, doubtless from the addition of a certain number of ascending fibers
from each pair of nerves.
From careful estimates of the number of nerve fibers in a transverse section
of the cord toward its upper end, and the number entering or issuing from it
by the anterior and posterior roots of each pair of nerves, it has been shown
15 iS
FIG. 358. — Horizontal Section of the Cord and its Envelopes, at the Middle of a Vertebral Body
(Schematic), i, Spinal cord with 2, its anterior median fissure; 3, its posterior median fissure;
4, anterior roots; 5, posterior roots; 6, pia mater (in red); 7, ligamentum dentatum; 8, connect-
ing fibers passing from the pia to dura mater; 9, visceral layer, and 9', parietal layer of the arach-
noid (in blue); 10, subarachnoid space; n, arachnoid cavity; 12, dura mater (in yellow); 13,
periosteum; 13,' external periosteum; 14, cellular tissue situated between the dura mater and the
wall of the vertebral canal; 15, common posterior vertebral ligament; 16, intraspinal veins; 17,
vertebra in section. (Testut.)
thjat in the human spinal cord not more than half of the total number of nerve
fibers of all the spinal nerves are contained in a transverse section near its upper
end. It is obvious, therefore, that at least half of the nerve fibers entering
it must terminate somewhere in the cord itself.
The Arrangement of Nerve Cells in the Spinal Cord. The gray mat-
ter of the spinal cord consists of numerous groups of nerve cells and of a
close meshwork of nerve fibers, most of which are very fine and delicate.
Medullated fibers mingled with the small gray fibers about the borders of the
512
THE NERVOUS SYSTEM
gray substance. Mingled with it and supporting it is the meshwork of the
neuroglia.
The multipolar cells of the cord are either scattered singly or arranged in
groups, of which the following are to be distinguished on either side, certain
of the groups being more or less marked in all of the regions of the cord, viz.,
those, a, in the anterior cornu, b, those in the posterior cornu, and c, intrinsic
cells distributed throughout the gray matter.
The cells in the anterior cornu are large and branching, and each gives rise
to an axis-cylinder process which passes out in the anterior nerve root. These
FIG. 359. — From the Lower Lumbar Cord of Man, after a Preparation by Klonne and Miiller,
of Berlin (No. 11,153), stained by Weigert and Pal's method. A portion of the gray substance of
the ventral cornu with the adjoining portions of the lateral column is represented, showing an-
terior-horn cells and the fine medullated fibers which enter the gray substance from the lateral
column and surround the nerve cells, which here are provided with fine pigmented granules. High
power. (Kolliker.)
cells are everywhere conspicuous, but are particularly numerous in the cervi-
cal and lumbar enlargements. In these districts they may be^divided into
several groups: i, A group of large cells close to the tip of the inner part of
the anterior cornu — all the cells of the anterior cornu in the dorsal or thoracic
region are said to belong to this group; 2, several lateral groups, 20,, 2b, and 2C,
figure 360, on the outer side of the gray matter, and a certain number of cells at
the base of the inner part of the anterior cornu particularly well marked in the
thoracic region ; 3, cells of the posterior cornu — these are not numerous. They
ARRANGEMENT OF NERVE CELLS IN THE SPINAL CORD
513
are small and branched, and each has an axis-cylinder process passing cff;
but these processes do not pass into the posterior nerve roots. The groups
are two at least in number, viz., a, in connection with the edge of the gray matter
externally, where it is considerably broken up by the passage of bundles of
fibers through it, and called the lateral reticular formation ; and b, in connection
with a similar reticular formaticn, more at the tip of the gray, known as the
posterior reticular formation.
A group of cells, 3, figure 360, is situated at the base and median side of the
posterior cornu. It is formed of fairly large cells, fusiform in shape, and
constitutes the posterior vesicular column, or Clarke's column. It extends
from the seventh cervical to the third lumbar segment. On the outer por-
tion of the gray matter, midwray between the anterior and posterior cornua,
FIG. 360. — Section of Spinal Cord, One Half of Which (Left) Shows the Tracts of the White
Matter, and the Other Half (Right) Shows the Position of the Nerve Cells in the Gray Matter. 7,
ip, 9, and 3 are tracts of descending degeneration; i, 4, 6 and 8, of ascending degeneration. Semi-
diagrammatic. (After Sherrington.)
is a group of cells, known as the cells of the lateral gray column. These are
small and spindle-shaped, and are more or less marked in the lumbar region,
as well as in the thoracic region, 5, figure 360.
Besides these groups, which have their names largely on account of their
location, there are distributed throughout the gray matter a very large number
of other cells, which are known as intrinsic cells. These send out axones
which pass into the adjacent ground bundles of the same or of the opposite
side, and pass up and down the cord, to enter the gray matter again. They
connect by their end-brushes with cells at different levels of the cord.
The function of these connecting cells, or intrinsic cells, is to unite the pos-
terior and anterior regions of the cord, to serve as conductors between the
lateral halves, or to connect segments at different levels. They are also dis-
33
514
THE NERVOUS SYSTEM
tributing fibers in that they bring a single or at least a small number of pos-
terior neurones into connection with a relatively large number of anterior neu-
rones.
Columns and Tracts in the White Matter of the Spinal Cord. In
addition to the columns of the white matter which are marked out by the
points from which the nerve roots issue, and which are the anterior, the lateral,
and posterior, the posterior is further divided by a septum of the pia mater into
Radix anterior
Fasciculus cerebrospinalis lateralis fpyramidalis lateralis] *
Anterior root fibre
Bundle to anterior funiculus from the formatio reticularis
Fasciculus cerebrospinalis antei
[pyramidalis anterior}
Bundle to anterior funiculus ^
from the formatio reticularis \
Substantia grisea.
Fasciculus
anterolateraUs super-
ficialis fGowersi] and <...
(ascending) bundle from
anterior funiculus to the
formatio reticularis
Substantia alba —
Bundte" to lateral
funiculus from Deiters*
nucleus and from Hhe
red nucleus .
Fasciculus cerebto
spinalis lateralis
(pyramidalis lateral!
Nervus spinalis
Ganglion spinale
Cells of tho spinal ganglion
/ Fasciculus cerebellospinalis
,. Secondary reflex path
, Radix posterior
Collateral
- to the posterior horn
Secondary path of
- posterior funiculus
.Descending posterior
root fibre
Primary reflex path
-•- Ascending posterior
root fibre
Secondary reflex path
. .Descending posterior
root fibre
- Posterior TOO t fibre
Sulcus nietjianv
posterior
--- Posterior root fibre
FIG. 361. — Reconstruction of a Segment of the Spinal Cord Representing Both a Transverse
and Longitudinal Section. (Held, from Spalteholz's Anatomy.)
two almost equal parts, constituting the postero- external column, or column of
Burdach, figure 360, 2, and the posiero-median, or column of Goll. In addition
to these columns, however, it has been shown that the white matter can be still
further subdivided. This subdivision has been accomplished by evidence of
several kinds that the parts or, as they are called, tracts in the white matter
perform different functions in the conduction of impulses.
The methods of observation are the following:
The embryological method. It has been found that, if the development
of the spinal cord be carefully observed at different stages, certain groups of
TRACTS OF DESCENDING DEGENERATION 515
the nerve fibers acquire their myelin sheath at earlier periods than others,
and that the different groups of fibers can therefore be traced in various
directions. This is known as the method of Flechsig.
Wallerian or degeneration method. This method depends upon the fact
already presented that if a nerve fiber is separated from its nerve cell it wastes
or degenerates. It consists in tracing the course of tracts of degenerated
fibers which result from an injury, to any part of the central nervous system.
When fibers degenerate below a lesion the tract is said to be of descending
degeneration, and when the fibers degenerate in the opposite direction the tract
is one of ascending degeneration. By modern methods of staining of the cen-
tral nervous system it has proved comparatively easy to distinguish degener-
ated parts in sections of the cord and of other portions of the central
nervous system. Degenerated fibers have a different staining reaction
when the sections are treated by what are called Weigert's and Marchi's
methods. Accidents to the central nervous system in man have given us much
information as to its organization, but this has of late years been supplemented
and largely extended by the experiments on animals, particularly upon
monkeys. Considerable light has by the method of section and degeneration
been shed upon the path of conduction of impulses to and from the nervous
system. Thus we not only have embryological evidence mapping out different
tracts, but also confirmatory pathological and experimental observations.
The tracts which have been made out are the following:
Tracts of Descending Degeneration. The Crossed Pyramidal Tract.
This tract is situated to the outer side of the posterior cornu of gray
matter, figure 360, 7. It is found throughout the whole length of the spinal
cord; at the lower part it extends to the margin of the cord, but higher
up it becomes displaced inward from this position by the interpolation of
another tract of fibers, the direct cerebellar tract. The crossed pyramidal
tract is large, and may touch the tip of the gray matter of the posterior cornu,
but it is separated from it elsewhere. It is oval in shape on cross-section, and
diminishes in size from the cervical region downward. The tract is particu-
larly well marked out, both by the degeneration and the embryological methods.
The fibers are supposed to pass off as they descend, and to join the various
local nervous mechanisms of nerve cells and their branchings which are rep-
resented in the cord. The tract of degeneration may be traced upward beyond
the cord, in a way to be presently described. The fibers of which this tract
is composed are moderately large, but are mixed with some that are smaller.
The Direct or Uncrossed Pyramidal Tract. This tract is situated in the
anterior column by the sides of the anterior fissure, figure 360, 10. It is smaller
than the crossed tract and is not present in all animals, though conspicuous
in the human cord and in that of the monkey. It can be traced upward to
the cerebral cortex, and downward as far as the mid or lower thoracic region,
where it ends.
516 THE NERVOUS SYSTEM
Antero-lateral Descending Tract. This is an extensive tract, elongated
but narrow, and reaching from the crossed to the direct pyramidal tract. It is
a mixed tract, since not all of its fibers degenerate below the lesions.
Comma Tract. This is a small tract of fibers which degenerate below
the point of section or injury of the cord. Its presence has been demonstrated
in the cervical and thoracic regions. It is supposed to consist of the descending
collaterals of the posterior nerve roots as they pass into the postero-external
columns.
Tracts of Ascending Degeneration. Postero-median Column and
Poster o-lateral Column. These tracts degenerate upward on injury or
on section of the cord, also on section of the posterior nerve roots, figure 360,
i. They exist throughout the whole of the cord from below up , and can be
traced into the bulb. They consist of fine fibers.
Direct Cerebellar Tract. This tract is situated on the outer part of the cord
between the crossed pyramidal tract and the margin. It is found in the cervi-
cal, thoracic, and upper lumbar regions of the cord, and increases in size
from below upward. It degenerates on injury or section of the cord itself,
but not on section of the posterior nerve roots, since its fibers arise from the
cells of Clarke's column. As its name implies, it is believed to pass up into
the cerebellum.
Antero-lateral Ascending Tract, Tract of Gowers, figure 360, 8. This
tract has been shown on injury to the spinal cord; it is situated at the margin
of the cord outside of the corresponding descending tract. It is traceable
throughout the whole length of the cord.
Tract of Lissauer, or Posterior Marginal Zone. A small tract of fine white
fibers, situated at the apex of the posterior horn, is made up of fibers from
the posterior nerve roots which enter the column and pass up and down
for a short distance, finally entering the posterior horn, where they terminate
in fine end-brushes around the cells of the posterior horn.
It will thus be seen that the white matter of the spinal cord has three gen-
eral divisions — into the anterior, the lateral, and posterior columns. These
columns are subdivided into tracts in which the fibers degenerate upward,
those in which the fibers degenerate downward, and others in which the fibers
degenerate neither way except for short distances when the cord is cut across.
These parts cf the cord are composed of commissural fibers which connect
different levels of the cord. The commissural tracts form the antero-lateral
columns and the lateral limiting layer. The arrangement of these tracts is
shown well in figure 360.
The Spinal Nerves. The spinal nerves consist of thirty-one pairs,
from the sides of the whole length of the cord, their number corresponding
with the intervertebral foramina through which they pass. Each nerve arises
by two roots, an anterior and a posterior, the latter being the larger. The roots
emerge through separate apertures of the sheath of dura mater surrounding
COURSE OF THE FIBERS OF THE SPINAL NERVE ROOTS
517
the cord; and directly after their emergence, where the roots lie in the inter-
vertebral foramen, a ganglion is found on the posterior root. The anterior
root lies in contact with the anterior surface of the ganglion, but none of its
fibers intermingle with those in the ganglion, figure 361. But immediately
beyond the ganglion the two roots coalesce, and by the mingling of their fibers
form a compound or mixed spinal nerve, which, after issuing from the inter-
vertebral canal, gives off anterior and posterior (or ventral and dorsal) branches,
each containing fibers from both the roots as well as a third or visceral
branch, ramus communicans, to the sympathetic.
The anterior root of each spinal nerve arises by numerous separate and
converging bundles from the anterior column of the cord; the posterior root
Entering posterior
root
Lissauer's tract
Emc
; anterior root
FIG. 362. — Diagrammatic Transverse Section of the Spinal Cord, Showing the Conduction Paths
and Groups of Cells. (Cunningham.)
by more numerous parallel bundles, from the posterior column, or, rather,
from the posterior part of the lateral column, for if a fissure be directed
inward from the groove between the middle and posterior columns, the pos-
terior roots will remain attached to the former. The anterior roots of each
spinal nerve consist chiefly of efferent fibers; the posterior exclusively of
afferent fibers.
Course of the Fibers of the Spinal Nerve Roots. The Anterior
Roots. The anterior roots leave the cord in several bundles, which may be
called: i, Internal; 2, Middle; 3, External. All have their origin from the
groups of multipolar cells in the anterior cornua. The internal fibers are
originated partly in the internal group of nerve cells of the anterior cornu
518
THE NERVOUS SYSTEM
of the same side; but some fibers can be traced through the anterior com-
missure to cells of the anterior cornu of the opposite side.
The Posterior Roots. The fibers of the posterior roots enter the spinal
cord to the inner or median side of the posterior cornu. The fibers,
as soon as they reach the cord, divide in a fork-like fashion, one branch
passing down a short distance, about three centimeters, the other branch
passing up for a shorter or longer distance. This upper branch some-
times reaches the whole extent of the cord, but generally it extends over
only one or two segments of the cord. The divisions of the posterior root
fibers give off in their course numerous collaterals, figure 368. The fibers
Fl&. 363. — Section of the Spinal Cord, Showing the Grouping of Nerve-Cells and the Course of
Nerve Fibers Entering in Posterior and Anterior Roots. (After Lenhossek.)
of the posterior roots are divided into two sets, an internal or median, an ex-
ternal or lateral group. The lateral set consists mostly of small fibers which
enter the cord opposite the tip of the posterior horn. The fibers pass in part
to the marginal column of Lissauer, where they ascend and descend; in part
they penetrate the posterior horn, and come in relation with its cells. From
the median set some fibers pass to Clarke's column, others pass by way
of the posterior commissure to the median cells of the other side. Others
pass through the gray matter to the anterior horn cells of the same side.
Besides this, they are connected through collaterals with the intrinsic cells of
the gray matter at different levels of the cord. One can realize that each
nerve root has, in this way, an effective grip upon a large extent of the cord.
This is seen well by studying figures 361 and 363.
THE REFLEX ARC AND REFLEX ACTION 519
The Peculiarities of Different Regions of the Spinal Cord. The
outline of the gray matter and the relative proportion of the white matter
vary in different regions of the spinal cord, and it is, therefore, possible to
tell approximately from what region any given transverse section of the
spinal cord has been taken. The white matter increases in amount from
below upward. The amount of gray matter varies; it is greatest in the
cervical and lumbar enlargements, viz., at and about the 5th lumbar and the
6th cervical nerves, and least in the thoracic region. The greatest develop-
ment of gray matter corresponds with greatest number of nerve fibers
passing from the cord.
In the cervical enlargement the gray matter occupies a large proportion of
the section, the gray commissure is short and thick, the anterior horn is blunt,
while the posterior is somewhat tapering. The anterior and posterior roots
run some distance through the white matter before they reach the periphery.
In the dorsal region the gray matter bears only a small relation to the white,
and the posterior roots in particular run a long course through the white matter
before they leave the cord; the gray commissure is thinner and narrower than
in the cervical region.
In the lumbar enlargement the gray matter again bears a very large propor-
tion to the whole size of the transverse section, but its posterior cornua are
shorter and blunter than they are in the cervical region. The gray commissure
is short and extremely narrow.
At the upper part of the conus medullaris, which is the portion of the cord
immediately below the lumbar enlargement, the gray substance occupies nearly
the whole of the transverse section, as it is invested only by a thin layer of
white substance. This thin layer is wanting in the neighborhood of the
posterior nerve roots. The gray commissure is extremely thick.
At the level of the fifth sacral vertebra the gray matter is again in excess, and
the central canal is enlarged, appearing T-shaped in section; while in the
upper portion of the filum terminate the gray is uniform in shape without any
central canal.
The Reflex Arc and Reflex Action. The spinal cord is morpho-
logically a segmental or metameric structure. This is shown both by its
development and by its comparative anatomy. The pairs of nerves are
indicative of the component segments of the cord. The tracts of the cord are
in a sense connectives from segment to segment, connecting the cells of
both adjacent and of widely separated segments. The function of the cord
is comprised in the function of the segments and in the function of the tracts.
From a physiological point of view, it may almost be considered as an
axiom that before a nerve cell can send out a nerve impulse it must first
receive a stimulus of some kind. This stimulus usually consists of an afferent
impulse from the periphery. Its effect upon the receiving cell may be insuf-
ficient to cause any response, or the response may be delayed for a long period
520
THE NERVOUS SYSTEM
and may involve many complicated nervous activities and even psychological
processes. Where the response is approximately immediate, the reaction is
known as a reflex.
A reflex arc, reduced to its simplest terms, consists of the following ele-
ments: a, a sensory surface; b, an afferent neurone; c, an efferent neurone; d,
FIG. 364. — Schematic Sketch of a Reflex Arc. A , With two neurones, an afferent and an efferent;
B, with three neurones, an afferent, efferent, and a connecting or intracentral neurone.
a muscle or gland. The simplest form of reflex arc is schematically shown
in figures 364 and 365.
The gap between the termination of the afferent neurone and the dendron
of the efferent neurone shown in figure 364 is called a synapsis. The reflex arc is
probably seldom as simple as that shown in figure 365, where only two neurones
are involved. More often, three or more
neurones take part, as shown in figures 364 B,
and 366.
The neurone connecting the afferent
neurone with the efferent neurone belongs
to the class of intracentral or connecting
neurones. Since all parts of the cord, in
fact of the entire cerebro-spinal axis, are in-
directly connected with one another by
intracentral neurones, figure 361, the possi-
bility of increasing the number of efferent
limbs of the reflex arc can be readily under-
stood.
A physiological reaction in a tissue pro-
duced by efferent nerve impulses which have
been discharged from a nerve center under
the stimulus of a sensory or afferent nerve
impulse, is called a reflex act. Where the
nervous apparatus involved is of the type
represented in figures 364 and 365, the activ-
ity is called a simple reflex. Most reflexes
FIG. 365. — Sjiowing ^ the Arrangemen t
of a Simple Reflex Mechanism Composed
of a Motor and Sensory Neurone, sg,
Posterior spinal ganglion; s and sth, sen-
sor^ root; m, motor-nerve cell; mw,
motor root. (Kolliker.)
IRRADIATION OF IMPULSES WITHIN THE CORD
521
are more complex in character. The afferent nerve impulse passes through
more than one simple channel in the cord, so that a series of coordinated
acts occurs in what may be called a complex reflex.
The transmission of impulses within the cord occurs over the pathways
of least resistance. Increasing the number of synapses, or the number of
neurone links in the chain of conduction, increases the resistance so that re-
flexes will occur most readily, other conditions being equal, where the least
number of neurones is involved, i.e., in the same segment of the cord in which
the sensory impulse enters, or in immedi-
ately adjacent segments. In addition to the
number of synapses in the reflex arc, other
factors are of importance in determining reflex
reaction; e.g., the intensity of the exciting
stimulus; the quality of the stimulus; the
rapidity of the recurrence of the stimulus;
and the duration of its application. Thus,
a strong stimulus will bring about a reflex
reaction sooner than a weak stimulus of the
same kind. A single weak stimulus which
will cause no reflex may do so if often enough
and rapidly enough repeated, the phenomenon
of summation of stimuli.
A reflex act once started may result in
efferent impulses which continue for some
time after the exciting cause has been removed. The same phenomenon
is observed where groups of nerve cells are stimulated directly. It has been
found, by observing electrical changes in nerve fibers by means of the capillary
electrometer, that when their cells of origin are stimulated they discharge im-
pulses in a rhythmical manner.
Usually, impulses are transmitted to a nerve cell only over its dendrons,
but it must be also assumed that such a conveyance of impulses may take place
over the collaterals of its axone near the cell body, or the cell body may be
stimulated directly by the afferent neurone. The peripheral fiber of the
spinal ganglion cell, although it has the structure of an axone, may be looked
upon physiologically as a dendron, since homologues in lower vertebrates and
in man himself (olfactory-nerve cells) have this structure, the nerve cell body
being situated near the sensory surface from which impressions are received.
Irradiation of Impulses within the Cord. Taking as an example a
frog whose brain has been destroyed, a simple reflex may be demonstrated by
irritating the skin of one foot with a weak stimulus. In response to such a
stimulus the foot is flexed upon the leg, due to a contraction of the muscles of
the reflex arc corresponding to the sensory surface irritated. If the strength or
duration of the stimulus be increased, other groups of muscles are involved
PIG. 366. — Showing the Arrange-
ment of the Reflex Mechanism, with
a Neurone Intercalated between the
Sensory and Motor Neurones.
THE NERVOUS SYSTEM
in the following order: i, Those of the leg and thigh of the same side; 2,
homologous muscles of the opposite side; 3, the arms of the same side and of
the opposite side.
The increasing complexity of the reflexes aroused by stimulation of one and
the same sensory spot is not easy of explanation. We know that there is almost
an infinite number of morphological paths in
the cord, yet the responses are orderly and
observe a certain sequence in their increasing
complexity. The reflexes have a mechanical
definiteness which, in a living structure, seems
almost purposeful, yet there is no conscious-
ness in a frog which has its brain destroyed.
The fact is that in the development of the
nervous system certain physiological paths of
slight resistance have been established between
the sensory areas and the muscles which move
the parts for their protection. Apparently
other physiological nerve pathways exist, but
it requires a stronger sensory stimulus to
arouse nerve impulses along these paths. In
explanation we may suppose that the stronger
afferent impulses are sufficient to overcome
the resistance of increasingly complex paths,
that they diffuse through greater and greater
extents of the cord. But we may repeat that
in the normal state of the cord this diffusion is
in an orderly physiological sequence.
Orderly reflexes can be called forth only
by stimulating sensory nerve endings, the
first of the essential structures of the reflex arc.
If artificial stimuli are applied to a nerve
trunk, as the sciatic, uncoordinated muscular
responses occur because the sensory stimuli
are diffuse and general and are not specific
and local.
An involvement of multiple pathways may
also be accomplished through decreasing the
resistance within the cord, as through the use
of some drug such as strychnine. In the
strychninized frog a slight stimulus brings
about multiple and violent reflex spasms.
These contractions have lost their orderliness and are uncoordinated. The
entire musculature contracts. It is as though the strychnine removed all
FIG. 367. — Scheme of Lower Mo-
tor Neurone. The cell body, proto-
plasmic processes, axone, collaterals,
and terminal arborizations in muscle
are all seen to be parts of a single cell
and together constitute the neurone.
(Barker.) c, Cytoplasm of cell body
containing chrompphilic bodies, neu-
ro fibrils, and perifibrillar substance;
n, nucleus; n', nucleolus; d, den-
drites; ah, axone hill free from chro-
mophilic bodies; ax, axone; sf, side
fibril (collateral); m, medullary
sheath; nR, node of Ranvier where
side branch is given off; si, neu-
rilemma and incisures of Schmidt;
m, striated muscle fiber; tel, motor
end plate.
FUNCTIONS OF THE SPINAL NERVE ROOTS 523
differences in the facility with which afferent stimuli spread through the cord,
and that the resistance was reduced to the minimum. The strychnine effect
is possibly due to a decrease in the resistance at the synapses, and possibly
also to an increase in the irritability of the discharging nerve cells.
We must also suppose that the centers are particularly sensitive to certain
kinds of stimuli, sometimes producing very extensive and violent muscular
actions in response to a slight stimulus of a special kind. Such a condition
is illustrated in the violent and general muscular spasms occurring when a
small particle of food passes into the larynx, violent expiratory spasms ac-
companied by contractions of other muscles taking place.
The time taken in a reflex action for the eye in man has been found to be
0.066 to 0.058 of a second, but this estimate includes the entire time from
the instant of stimulation to the beginning of the contraction of the muscle.
Functions of the Spinal Nerve Roots. The anterior spinal nerve
roots are efferent in function and the posterior are afferent. The fact is
proved in various ways. Division of the anterior roots of one or more nerves
is followed by complete loss of motion in the parts supplied by the fibers of
such roots, but the sensation of the parts remains perfect. Division of the
posterior roots destroys the sensibility of the parts supplied by their fibers,
while the power of motion continues unimpaired. Moreover, stimulation of
the ends of the distal portions of the divided anterior roots of a nerve excites
muscular movements. There are sometimes slight evidences of sensory im-
pulses due to recurrent fibers that are distributed through the anterior root
to the spinal meninges. Stimulation of the proximal ends of the anterior
roots, which are still in connection with the cord, is followed by no appreciable
effect. It must be remembered, however, that in the anterior or efferent nerves
other fibers besides motor are contained, e.g., vaso-motor, secretory, heat fibers,
and when the distal end of a divided nerve is stimulated, the effects are ex-
ercised not only upon muscles, but upon glands, blood-vessels, etc. Stimu-
lation of the distal portions of the divided posterior roots, on the other hand,
produces no muscular movements and no manifestations of pain; for, as al-
ready stated, sensory nerves convey impressions only toward the nerve cen-
ters. Stimulation of the proximal portions of these roots elicits signs of in-
tense suffering. Muscular movements also ensue; but these are the result
of the reflex stimulation of the motor neurones of the anterior horn of the cord
or are movements in response to the afferent impulses passing to higher centers
from the roots stimulated.
Functions of the Ganglia on Posterior Roots. The cells of the posterior
ganglia act as centers for the nutrition of the nerve fibers given off from them.
When these are cut, the parts of the nerves so severed degenerate, while the
parts which remain in connection with the cells of the ganglia do not. Thus
on section of the posterior nerve root beyond the ganglion the peripheral part
degenerates and the central does not, and on section of the root between
524
THE NERVOUS SYSTEM
the ganglion and the cord the central part degenerates and the peripheral
is unaffected.
Spinal Reflexes in Man and Mammals. Much of our knowledge of
the reflexes of the cord is derived from experiments on dogs, though paral-
ysis of the lower extremities in man, by accident or otherwise, has given con-
firmatory information. In man the spinal cord is so much under the control
of the higher nerve centers that its own individual functions in relation to re-
flex action are apt to be overlooked. But if the skin of the foot is stimulated, in
a man whose lumbar cord is completely separated by injury or disease, the
FIG. 368. — Scheme of the Relation of the Posterior Root Fibers upon Entering the Cord. A, The
branch of the dorsal root fibers upon entering cord; B, terminal arborization about cell bodies
of the cord; DR, axones of the dorsal root ; B, their ascending and descending branches; C,
collaterals. (After Cajal.)
foot will be drawn away from the stimulus; or, if the stimulus be strong
enough, the entire leg will be moved. In both cases the movement may be
orderly and well coordinated, and shows that the sensory stimulus has pro-
duced a coordinated reflex through the lumbar cord. The injured person
feels no sensation of pain nor of action, and the phenomenon is independent
of the higher nerve regions. The stimulus that is applied to man must be
carefully graded, since when too intense it calls forth muscular spasms or
convulsive action.
SPINAL REFLEXES IN MAN AND MAMMALS 525
When the cord is first cut, the shock is very great, the lower or isolated
portion of the cord remains for a time quite non-irritable. The vaso-motor and
thermogenic centers are cut off so that there is great vascular dilatation and
marked fall of temperature, the effects of which are likely to lead to death
unless the operated animal is carefully attended. But these effects are slow-
ly recovered from, and man, as well as lower mammals, soon regains the
vascular tone. The general tonus of the muscular system, which is lost at first,
is also regained.
In this partially recovered condition man, and such animals as the cat, the
dog, and the monkey, perform certain of the lowrer functions with a remarkable
degree of perfection. Of course these functions are under constant coordi-
native regulation and control in the normal animal, but experiments and ob-
servation have shown how much of such activity really is a primary function
of the cord. Of these activities the following may be especially mentioned:
Muscular tonus, general reflexes, the special reflexes of micturition, defecation,
erection and the sexual reflex, and parturition, some of which will be briefly
discussed.
The Center of the Tone of Muscles. The tonic influence of the spinal cord
on the sphincter ani and sphincter urethrae will be presently mentioned. The
cord maintains these muscles in permanent tonic contraction. The condition
of the sphincters, however, is not altogether exceptional. Their contraction is
the same in kind, though it exceeds in degree, that condition of muscles which
has been called tone, a condition of slight contraction which they always
maintain during health. This tone of all the muscles of the trunk and limbs
depends on the spinal cord, just as does the contraction of the sphincters.
If an animal be killed by injury or removal of the brain, the muscles retain
their tenseness, but if the spinal cord be destroyed, the sphincter ani relaxes,
and all the muscles become loose, flabby, and atonic, remaining so till rigor
mortis commences.
If an animal, such as the dog, be held off the ground in the erect position
assumed by the human body, when the trunk and hind limb muscles are not
in voluntary contraction the limbs will assume a normal pendular position.
In the pendular position the legs of a dog with cord severed hang more limp
and are more completely extended. The muscles of the former exhibit that
tone which keeps antagonistic muscles always slightly tense, the muscles of the
latter have lost the tenseness.
Whether or not muscular tone is maintained through the constant sub-
minimal action of sensory nerve impulses on the tonic centers of the cord, or
whether these centers are automatic in their action, is a question that can be
answered only by inference. The probability is that tone is a reflex activity,
though it may be contributed to by the normal healthy nutritional condition
of the muscles themselves — a condition which is itself dependent on the
trophic influence of the nerve cells of the cord and brain stem.
526 THE NERVOUS SYSTEM
The Ano-Spinal or Dejecation Center. The mode of action of the ano-
spinal center appears to be this: The mucous membrane of the rectum is
stimulated by the presence of feces or of gas in the large bowel. The stim-
ulus passes up by the afferent nerves of the hemorrhoidal and inferior mesen-
teric plexuses to the center situated in the lumbar enlargement of the cord,
and is reflected through the pudendal plexus to the anal sphincter, and to the
muscular tissue in the wall of the lower bowel. In this way there is produced
a relaxation of the first and a contraction of the second, and expulsion
of the contents of the bowel follows. The center in the spinal cord is
partially under the control of the will, so that its action may be either
inhibited or augmented. The action ma'y be helped by the abdominal
muscles, which are voluntary muscles, but are also stimulated to contract by
reflex action.
The Vesico-Spinal or Micturition Center. The vesico-spinal center acts
in a very similar way to that of the ano-spinal. The center is also in the
lumbar enlargement of the cord. It is stimulated to action reflexly by the
presence of urine in the bladder. The action may be voluntary and is excited
by the sensation of distention of the bladder by the urine. The sensory fibers
concerned are the posterior roots of the lower sacral nerves. The action of the
spinal center is double, or it may be supposed that the center consists of two
parts, one of which is usually in action and maintains the tone of the sphincter,
and the other which causes contraction of the bladder and other muscles.
When evacuation of the bladder occurs impulses pass to that part of the center
which discharges impulses to the bladder and to certain accessory muscles
which cause their contraction; and impulses pass to that part of the center
which inhibits the tonic action on the sphincter urethrae which procures its
relaxation. The way having been opened by the relaxation of the sphincter,
the urine is expelled by the combined action of the bladder and accessory
muscles. The cerebrum may exert its influence on the reflex not only by
stimulating the center to action, but also by inhibiting its action.
The Genito-Spinal Center. The presence of the genito-spinal center is
proven by the fact that dogs, and even man, are known to discharge semen
when the lumbar cord is severed and all voluntary motion and sensibility are
lost. The center situated in the lumbar enlargement of the spinal cord is
stimulated to action by sensory impressions from the glans penis. Efferent
impulses from the center excite the successive and coordinate contractions of
the muscular fibers of the vasa deferentia and vesiculae seminales and of the
accelerator urinae and other muscles of the urethra; and a forcible expulsion
of semen takes place, over which the cerebral centers have little or no control,
and which, in cases of paraplegia, are not felt.
The Erected Center. This center is also situated in the lumbar region and
is a vascular center, already described in the chapter on Circulation. It
is reflexly excited to action by the sensory nerves of the penis, and also in the
CUTANEOUS AND MUSCLE REFLEXES AS DIAGNOSTIC SIGNS 527
normal animal by impulses passing down from the cerebrum. Efferent
impulses produce dilatation of the vessels of the penis.
The Parturition Center. The center for the expulsion of the contents of
the uterus in parturition is situated in the lumbar spinal cord rather higher
up than the other centers already enumerated. The stimulation of the
uterus may, under certain conditions, excite the center to send out impulses
which produce a contraction of the uterine walls and expulsion of the con-
tents of the cavity. The center is independent of the will since delivery
takes place in paraplegic women, and also while a patient is under the influ-
ence of chloroform. Again, as in the cases of defecation and micturition, the
abdominal and thoracic muscles assist; their action being for the most part
reflex and involuntary.
Inhibition of Reflex Actions. Movements such as are produced by stimu-
lating the skin of the lower extremities in the human subject, after division
or disorganization of a part of the spinal cord, do not always occur when the
cerebrum is active and the connection between the cord and the brain is intact.
The reflex which would occur in the animal with spinal cord only is suppressed
or inhibited in the normal animal through the regulative action of the higher
cerebral centers. When one is anxiously thinking, even slight stimuli may
produce involuntary and reflex movements. So, also, during sleep, such reflex
movements may be observed, when the skin is touched or tickled; for example,
when one touches the palm of the hand of a sleeping child, the impression on
the skin of the palm producing a reflex movement of the muscles which
close the hand. But when the individual is awake no such reflex is produced.
Further, many reflex actions are capable of being more or less controlled
or even altogether prevented by the will, of which the following may be quoted
as familiar examples:
When the foot is tickled we can, by an effort of will, prevent the reflex
action of jerking it away. So, too, the involuntary closing of the eyes and
starting back, when a blow is aimed at the head, can be similarly restrained.
Darwin has mentioned an interesting example of the way in which such an
instinctive reflex act may override the strongest effort of the will. He placed
his face close against the glass of the cobra's cage in the Reptile House at
the Zoological Gardens, and, though of course thoroughly convinced of his
perfect security, could not by any effort of the will prevent himself from
starting back when the snake struck with fury at the glass.
It can be readily shown, by comparing a spinal frog and a normal unin-
jured frog, that stimuli which call forth definite reflexes in the one often pro-
duce no movement of the other.
Cutaneous and Muscle Reflexes as Diagnostic Signs. In the hu-
man subject two classes of reflex actions dependent upon the spinal cord are
usually distinguished, the alterations of which, either of increase or of diminu-
tion, are indications of some abnormality, and are used as a means of diag-
528 THE NERVOUS SYSTEM
nosis in nervous and other disorders. They are termed respectively cutaneous
reflexes and muscle reflexes. Cutaneous reflexes are set up by a gentle stimu-
lus applied to the skin. The subjacent muscle or muscles contract in response.
Although these cutaneous reflex actions may be demonstrated almost any-
where, yet certain of such actions as being most characteristic are distinguished,
e.g., plantar reflex; gluteal reflex, i.e., a contraction of the gluteus maximus
when the skin over it is stimulated; cremaster reflex, retraction of the testicle
when the skin of the inside of the thigh is stimulated, and the like. The
ocular reflexes, too, are important. They are contraction of the iris on ex-
posure to light, and its dilatation on stimulating the skin of the cervical region.
All of these cutaneous reflexes are true reflex actions. They differ in different
individuals, and are more esaily elicited in the young.
Muscle reflexes or tendon reflexes consist of a contraction of a muscle
under conditions of more or less tension, when its tendon is sharply tapped.
The so-called patellar-tendon reflex is the best known of this variety of re-
flexes. If one knee be slightly flexed, as by crossing it over the other, so that
the quadriceps femoris is extended to a moderate degree, and the patella tendon
be tapped with the fingers, the muscle contracts and the foot is jerked forward.
Another variety of the same phenomenon is seen if the foot is flexed so
as to stretch the calf muscles, and the tendo Achillis is tapped; the foot is ex-
tended by the contraction of the stretched muscles. It appears, however,
that the tendon reflexes are not exactly wrhat their name implies. The in-
terval between the tap and the contraction is said to be too short for the pro-
duction of a true reflex action. It is suggested that the contraction is caused
by local stimulation of the muscle, but that this would not occur unless the
muscle had previously been stimulated by the tension applied, and placed in
a condition of excessive irritability. It is probable that the condition on which
it depends is a reflex change in the spinal irritability acting on the muscle or
exaggerated muscular tone, which is admitted to be a reflex phenomenon
in the spinal cord.
Conduction in the Spinal Cord. With the differentiation of the
central nerve axis in vertebrates the conduction in the spinal cord becomes
of increasing importance, reaching its maximum in man. It is evident that
the cord is the path by which all nerve impulses arising in the trunk or in the
arms and legs must reach the brain, or vice versa. Impulses of peripheral
origin can and do produce reflexes, but they can arouse sensations and be per-
ceived only after they have been conducted to the cerebral cortex. Motor im-
pulses arising in the brain can reach the anterior-horn cells of the cord only
through the cord as a conducting path. The continuity of the cord, therefore,
while not necessary for the execution of reflexes, is absolutely necessary for
the higher coordinations of the reflexes and for the excitation and controlling
influence of the brain.
Illustrations of this are furnished by various examples of paralysis, but
SENSORY IMPULSES
529
by none better than by the common paraplegia, or loss of sensation and volun-
tary motion in the lower part of the body, in consequence of destructive
disease or injury of a section including the whole thickness of the spinal cord.
Such lesions destroy the communication between the brain and all parts of the
spinal cord below the seat of injury, and consequently cut off from their
connection with the brain the various organs supplied with nerves issuing
from those parts of the cord.
It is not probable that the conduction of motor or sensory impulses is
effected, under ordinary circumstances, to any great extent, as was formerly
supposed, through the gray substance of the cord,
i.e., from cell to cell through the short filaments
lying wholly within the gray substance. But
cells with fibers running for short distances in
the ground bundles are numerous, and these
short connectives are capable of conducting im-
pulses along the cord. All parts of the cord
are not alike able to conduct all impressions;
and as there are separate nerve fibers for motor
and for sensory impressions, so in the cord sepa-
rate and determinate tracts serve to conduct
always the same kind of impressions. The sen-
sations of touch, and perhaps of temperature and
pain, do not appear to have such sharply limited
tracts as do the motor impulses.
Experimental and other observations point
to the following conclusions regarding the con-
duction of sensory and motor impressions through
the spinal cord. Many of these conclusions must,
however, be received with considerable reserve.
Sensory Impulses. The sensory impres-
sions of touch, pain, heat and cold, and of the
muscular sense are conducted to the spinal cord
by the posterior nerve roots. Certain sensory
impressions are then carried directly into the
postero-median column on the same side, and
thence up to the nucleus of this column in
the medulla. It is mainly the impulses of the muscle sense and of the
sense of touch that take this course through the cord, though the sense of
touch is not wholly interrupted upon injury to the posterior columns. In
lower animals it is scarcely interfered with at all. The posterior columns
unquestionably are the primary muscle sensory paths. Visceral sensations
are carried by the posterior root fibers to the cells of the column of Clarke
in the posterior horn, figure 361. From there the impulses pass to the direct
34
FIG. 369. — Diagram to Show
the Manner in Which the Fibers
of the Posterior Nerve Ro9ts
Enter and Ascend the Posterior
Columns of the Cord. (Edin-
ger.)
530 THE NERVOUS SYSTEM
cerebellar tract on the same side, and thence up through the medulla to the
cerebellum, figure 396. The impressions of pain, and of heat and cold, are
conveyed to the nerve cells in the posterior cornua of the same side in part,
and in part to the nerve cells in the posterior cornu and median gray matter
of the opposite side. From this point, the impulses are taken up again by
intermediary neurones and conveyed through the anterior and lateral columns
of the cord to the brain in the ascending tract of Gowers. By reason of the
great number of collaterals and the interpolation in the course of the sensory
impulse of many intermediary neurones, it has been difficult to make out very
sharply defined tracts in the spinal cord for the conduction of the sensations
of temperature, pain, and touch. If one set of fibers is destroyed by disease,
others seem able, through the collaterals, to take up its function. We can say
that injury to the lateral columns has resulted in loss of the sense of pain,
heat and cold, but with only partial disturbance of touch sensations.
It is probable, also, that pain and temperature sensations cross over at once
to a considerable extent and pass up in the opposite side of the cord to which
they enter. Touch and the muscle sense impressions, especially the latter,
pass up largely upon the same side until they reach the medulla or cerebellum.
Motor Impulses. Motor impulses are conveyed downward from
the cerebral cortex of the brain along the pyramidal tracts, viz., the crossed or
lateral, and the direct or anterior, chiefly the former. In the crossed pyr-
amidal tract the impressions pass down chiefly on the sids opposite to which
they originate, having crossed over in the decussation in the medulla. But
some motor impulses do not cross in the medulla, but descend in the direct
pyramidal tract to lower levels of the cord, where they cross in the anterior
commissure. The motor fibers for the legs partially pass downward in the
lateral columns of the same side without decussation. This is also probably
the case with the bilateral muscles, i.e., muscles of the two sides that act
together, such as the intercostal muscles and other muscles of the trunk.
It is quite certain, as was just now pointed out, that the fibers of the anterior
nerve roots are more numerous than the fibers proceeding downward from
the brain in the pyramidal tracts, or the so-called pyramidal fibers. This is
because each pyramidal fiber is really a very long nerve process or axone,
and is supplied in its course with a large number of collaterals, which go off
at different points, and thus put it in relation with different groups of nerve
cells in the anterior cornua at various levels. Each nerve fiber of the pyrami-
dal tract, by means of its collaterals, can control a number of nerve cells, and
can thus coordinate the action of impulses sent out through the anterior roots
to a number of groups of muscles. In other words, the gray matter of the
anterior cornua contains an apparatus with various complicated coordinating
powers, which apparatus is under the regulative control of the neurones whose
cells of origin are in the cortex of the brain. This is the same apparatus that
is also reflexly influenced by sensory impressions passing to the cord.
GENERAL ARRANGEMENT OF PARTS OF THE BRAIN 531
Division of a single anterior pyramid of the medulla at a point just above
the decussation is followed by paralysis of voluntary motions in the muscles of
the opposite side in all parts below. Disease or division of any part of the
cerebro-spinal axis below the seat of decussation of the pyramids is followed
by impairment or loss of voluntary motion on the same side of the body.
The paralysis is never quite complete, and the opposite side usually shows some
slight impairment of function of the muscle.
When one-half of the spinal cord is cut through in monkeys, the results
are as follows (Mott) : Motor paralysis of the muscles of the same side (never
complete paralysis of the muscles used in bilateral associated action), followed
by gradual recovery of muscular movement, except of the finer movements
of the hand and foot; wasting and flabbiness of the muscles; sensory paralysis
of the same side (temperature, touch, pain, and pressure) ; temporary vaso-
motor paralysis on the same side. The temperature of the affected side is
depressed i to 3° F.
III. THE BRAIN STEM.
General Arrangement of Parts of the Brain. The great relative
and absolute size of the cerebral hemispheres in the adult man and in mammals
to a great extent masks the real arrangement of the several parts of the brain.
An examination of the accompanying diagram, figures 370, 371, reveals that
the parts of the brain are disposed in a linear series, as follows (from before
backward): Olfactory lobes, cerebral hemispheres, thalamencephalon (optic
thalami and third ventricle), the mid-brain (corpora quadrigemina and crura
cerebri), medulla oblongata and cerebellum.
This linear arrangement of parts actually occurs in an early stage of the
development of the human fetus, and it is permanent in some of the lower
Vertebrata. In fishes the cerebral hemispheres are represented by a pair
of ganglia intervening between the olfactory and the optic lobes, and con-
siderably smaller than the latter, their adult development is fairly well repre-
sented by the figure 387. In Amphibia the cerebral lobes are further devel-
oped, and are larger than any of the other ganglia.
In reptiles and birds the cerebral ganglia attain a still further development,
and in Mammalia the cerebral hemispheres exceed in weight all the rest of the
brain. As we ascend the scale, the relative size of the cerebrum increases, till
in the higher apes and man the hemispheres, which commenced as two little
lateral buds from the anterior cerebral vesicle, have grown upward and back-
ward, completely covering in and hiding from view practically all the rest of the
brain. At the same time the smooth surface of the cerebral cortex of many
lower mammalia, such as the rabbit, is replaced by the labyrinth of convo-
lutions of the human brain.
When the cerebral hemispheres are removed, several large basal masses of
532 TPIE NERVOUS SYSTEM
nerve substance are revealed: the optic thalami, the corpora quadrigemina,
andthecn/s cerebri. These structures, together with the pons and the medulla,
form a direct continuation forward of the spinal cord and sometimes are desig-
nated under the general term of the brain stem.
For convenience of description, the physiology of the brain will be presented
by discussing the three main subdivisions: the brain stem, the cerebral hemi-
spheres, and the cerebellum.
The human brain on superficial examination does not seem to follow the
general plan outlined above, but when the cerebral hemispheres and the
FIG. 370. — Diagrammatic Horizontal Section of the Vertebrate Brain. The figures serve both
for this and the next diagram. Mb, mid-brain; what lies in front of this is the fore-, and what
lies behind the hind-brain; Lt, lamina terminalis; Olf, olfactory lobes; Hmp, hemispheres;
Th. E, thalamencephalon; Pn, pineal gland; Py, pituitary body; P.M., foramen of Munro; cs,
corpus striatum; Th, optic thalamus; CC, crura cerebri; the mass lying above the canal rep-
resents the corpora quadrigemina; Cb, cerebellum; I-IX, the nine pairs of cranial nerves; i,
olfactory ventricle; 2V lateral ventricle; 3, third ventricle; 4, fourth ventricle; -\-, iter a tertio
ad quartum ventriculum. (Huxley.)
cerebellum are removed then it is found that what remains closely follows
the plan presented. This central axis, or brain stem, is shown in part in
figure 3 7 7.
The morphological parts of the brain usually given are :
1. The /ore-brain, which consists of the corpora striata and the cerebral
hemispheres.
2. The inner-brain, which consists of the optic thalamiand the parts en-
closing the greater part of the third ventricle.
GENERAL ARRANGEMENT OF PARTS OF THE BRAIN
533
3. The mid-brain, which comprises th2 crura cerebri and the corpora
quadrigemina enclosing the aqueduct of Sylvius.
4. The hind-brain, which comprises the pons Varolii, forming the floor
of the fourth ventricle, and the cerebellum, forming the roof.
5. The ajter-b ain, the medulla cblongata or bulb.
FIG. 371. — Longitudinal and Vertical Diagrammatic Section of a Vertebrate Brain. Letters
as before. Lamina terminalis is represented by the strong black line joining Pn and Py. (Huxley.)
PIG. 372. — Base of the Brain, i, Superior longitudinal fissure; 2, 2', 2", anterior cerebral
lobe; 3, fissure of Sylvius, between anterior and 4, 4f, 4", middle cerebral lobe; 5, 5', posterior
lobe; 6, medulla oblongata. The figure is in the right anterior pyramid; 7, 8, 9, 10, the cerebellum;
-K the inferior vermiform process. The figures from I. to IX, are placed against the corresppnding
cerebral nerves; ///. is placed on the right crus cerebri. VI. and VII. on the pons Varolii; X.,
the first cervical or suboccipital nerve. (Allen Thomson.) X £.
534 THE NERVOUS SYSTEM
THE MEDULLA OBLONGATA OR BULB.
Anatomical Structure. The medulla oblongata is continuous with
the spinal cord at its upper end. It lies within the cranial cavity and forms
the first part of the brain stem. The medulla consists of masses of nerve
cells situated in the interior, but pretty generally distributed throughout
the mass. The cell- masses are subdivided by laminae of nsrve fibers into
groups, or nuclei, which give origin to or form the terminations of the various
ranks of nerve fibers.
The nerve fibers are arranged partly in columns and partly in fasciculi
traversing the central cellular matter. The medulla oblongata is larger than
FIG. 373. — Plan in Outline of the Brain as seen from the Right Side. X£. The parts are repre-
sented as separated from one another somewhat more than natural, so as to show their connections.
A, Cerebrum; /, g, h, its anterior, middle, and posterior lobes; e, fissure of Sylvius; B, cerebellum;
C, pons Varolii; D, medulla oblongata; a, peduncles of the cerebrum; b, c, d, superior, middle,
and inferior peduncles of the cerebellum. (From Quain.)
any part of the spinal cord. Its columns are pyriform, enlarging as they pro-
ceed toward the brain, and are continuous with those of the spinal cord. Each
half of the medulla, therefore, may be divided into three columns or tracts of
fibers, continuous with the three columns of which each half of the spinal cord
is made up, but the columns are more prominent than those of the spinal cord,
and are separated from each other by deeper grooves. The anterior, contin-
uous with the anterior columns of the cord, are called the pyramids. The
postero-median and postero-external columns are also represented at the
posterior or dorsal aspect of the cord as the fasciculus gracilis and the fasciculus
cuneatus. The posterior pyramids of the medulla, which include these two
columns of white matter, soon become much increased in width by the addi-
tion of a new column of white matter outside the other two, which is known
ANATOMICAL STRUCTURE
535
as the fasciculus of Rolando. In the upper portion of the medulla the gracile,
cuneati, and Rolandic fasciculi are replaced by the restiform bodies (the in-
ferior peduncles of the cerebellum). The lateral columns of the cord are
scarcely represented as such in the bulb.
It may be said then that the bulb at its commencement differs only slightly
in size from the cord, with which it is continuous. It soon becomes larger
both laterally and antero-posteriorly. It opens out on the dorsal surface into
a space which is known as the fourth ventricle, and from being a cylinder with a
central canal it is flattened out on the dorsal surface by the gradual approach
of the central canal to that surface, where it is directly continuous with the
fourth ventricle.
If the bulb be examined on its anterior or ventral surface, it is found that
the anterior fissure, which is a continuation of the same fissure in the cord, is
FIG. 374.
FIG. 375.
FIG. 374. — Ventral or Anterior Surface of the Pons Varolii and Medulla Oblongata. a, a, An-
terior pyramids; b, their decussation; c, c, olivary bodies; d, d, rjestiform bodies; e, arciform
fibers; f, fibers passing from the anterior column of the cord to the cerebellum; g, anterior col-
umn of the spinal cord; h, lateral column; p, pons Varolii; i, its upper fibers; 5, 5, roots of the
fifth pair of nerves.
FIG. 375. — Dorsal or Posterior Surface of the Pons Varolii, Corpora Quadrigemina, and Me-
dulla Oblongata. The peduncles of the cerebellum are cut short at the side, a, a, the upper
pair of corpora quadrigemina; b, b, the lower; f, f, superior penduncles of the cerebellum; c,
eminence connected with the nucleus of the hypoglossal nerve; e, that of the glosso-pharyngeal
nerve; i, that of the vagus nerve; d, d, restiform bodies; p, p, posterior pyramids; v, v, groove in
the middle of the fourth ventricle, ending below in the calamus scriptorius; 7, 7, roots of the audi-
tory nerves.
occupied at the most posterior part by fibers which are crossing from one side
to the other. This is what is known as the decussation of the pyramids. It is
formed of the fibers which occupy the postero-lateral region in the cord, and
are called the crossed pyramidal fibers. The lateral pyramidal fibers of either
side after crossing the middle line become part of the pyramid of the opposite
side; the rest of the pyramid is made up of the fibers which in the anterior
536
THE NERVOUS SYSTEM
column of the cord are known as the direct or uncrossed pyramidal tract.
These two pyramidal strands of fibers are those which degenerate after lesions
of the parts of the cerebrum known as the motor areas of the cortex. They
can therefore be traced downward after such lesions as tracts of degeneration.
They are the descending fibers of communication between the cerebral motor
cells of the cortex and the different segments of the spinal cord. The outer
borders of the anterior pyramids of the bulb are marked by the exit from that
part of the nervous axis of the twelfth or hypoglossal nerve. Still more later-
ally than this nerve there is on either side a rounded elevation or column which
Optic chiasma
Optic tract
Corpus geniculatum
extern um
Corpus geniculatum
internum
Locus perforatus
posticus
Middle peduncle
cf the cerebellum
Restiform body
Oli
Pyramid
Anterior superfici
arcuate fibres
Decussation of.
pyramids
Optic nerve
Infundibulum
Tuber cinereum
rpora mammillaria
Oculomotor nerve (III.)
Trochlear nerve (IV.)
winding round the crus
cerebri
Trigeminal nerve (V.)
Abducent nerve (VI.)
Facial nerve (VII.)
Auditory nerve (VIII.)
Vago-glossopharyngoal
nerve (IX. and X.)
Hypoglossal
nerve (XII.)
Spinal accessory
nerve (XI.)
First cervical nerve
FIG. 376. — Front View of the Medulla, Pons, and Mesencephalon of a Full-Term Human
Fetus. (Cunningham.)
is known as the olivary body. It begins at a level a little lower than the open-
ing of the fourth ventricle. On the dorsal side of the olivary body is the line
of origin of the eleventh, tenth, and ninth nerves, and from this to the poste-
rior fissure is the posterior pyramid.
The changes in structure which are noticed in a series of sections of the
bulb from below upward may be summarized : In the dorsal or posterior re-
gion, the posterior cornua are pushed more to each side by the large number
of sensory fibers ascending in the posterior columns, and terminating in the
gracile and cuneate nuclei. The substance of Rolando is increased and be-
comes rounded, reaching almost to the surface of the bulb on each side, only a
small tract of longitudinal fibers of the root of the fifth nerve intervening.
ANATOMICAL STRUCTURE
537
I!
538
THE NERVOUS SYSTEM
There is a great increase of the reticular formation around the central canal,
and the lateral approaches the anterior cornu. Then at the ventral or anterior
aspect the decussation of the pyramids begins. By this crossing over of the
fibers, the tip of the gray anterior cornu is cut off from the rest of the gray mat-
ter. The central canal is pushed farther toward the posterior surface, first of
all by the decussation of the anterior pyramids just mentioned, and later on,
i.e., above, by another decussation of more dorsal fibers. These fibers of
the second decussation as they cross form a median raphe and also help to
break up the remaining gray matter into what is called a reticular jormation.
a.m.f.
FIG. 378. — Anterior or Dorsal Section of the Medulla Oblongata in the Region of the Superior
Pyramidal Decussation. a.m.f., Anterior median fissure; f.a., superficial arciform fibers emerg-
ing from the fissure; py, pyramid; n.ar., nuclei of arciform fibers; f.a., deep arciform becom-
ing superficial; o, lower end of olivary nucleus; n.l., nucleus lateralis; f.r., formatio reticularis;
/.a.2, arciform fibers proceeding from the formatio reticularis; g., substantia gelatinosa of Rolando;
a. V., ascending root of fifth nerve; n.c., nucleus cuneatus; n.c.', external cuneate nucleus: n.g.,
nucleus gracilis; f.g., funiculus gracilis; p.m.f., posterior median fissure; c c., central canal surround-
ed by gray matter, in which are n.XL, nucleus of the spinal accessory, and n.XII., nucleus of the
hypoglossal; s.d., superior pyramidal decussation. (Modified from Schwalbe.)
These fibers arise from the nuclei of the fasciculus gracilis and fasciculus
cuneatus of either side, and they are looked upon as a sensory decussation.
There are to be made out various masses of cells in addition to the reticu-
lar formation, viz., the nuclei of the fasciculus gracilis and fasciculus cuneatus,
figure 379, n.g. and n.c.
The olivary bodies extend forward almost to the level of the pons. They
consist of cells and fibers. The cellular matter consists of a plicated thinnish
layer of small nerve-cells, folded upon itself in the form of a loop, with the ends
turned inward and slightly dorsal, figure 379, o. The gray loop is filled with
and covered by white fibers.
Internal to the olivary body on either side are two small masses of gray
TRACTS THROUGH THE MEDULLA 539
matter, one more ventral to the other, called accessory olives, external and
internal, and on the surface of the anterior pyramid on either side a small
mass of gray matter, external arcuate nucleus; laterally another mass of the
same material, the representative of the lateral nucleus of the cord, is seen, viz.,
the antero-lateral nucleus, which gives origin to the spinal accessory nerve.
It will be necessary to follow as shortly as possible the fibers of the spinal
cord upward into the bulb and beyond.
Tracts Through the Medulla. The crossed and direct pyramidal tracts
have already been described. Nothing definite is known of the antero-lateral
descending tracts. The direct cerebellar tracts pass laterally into the restiform
n.am
FIG. 379. — Section of the Medulla Oblongata at about the Middle of the Olivary Body, f.l.a.,
Anterior "median fissure; n.ar., nucleus arciformis; p., pyramid; XII., bundle of hypoglossal
nerve emerging from the surface; at b, it is seen coursing between the pyramid and the olivary
nucleus, o.; f.a.e., external aroiform fibers; n.l., nucleus lateralis; a., arciform fibers passing
toward restiform body, partly through the substantia gelatinosa, g., partly superficial to the
ascending root of the fifth nerve, a. I'.; X., bundle of vagus root emerging; f.r., formatio retic-
ularis; c.r., corpus restiforme, beginning to be formed, chiefly by arciform fibers, superficial and
deep; n.c., nucleus cuneatus; n.g., nucleus gracilis; t, attachment of the ligula; f.s., funiculus
solitarius; n.X., n.X.', two parts of the vagus nucleus; n.XIL, hypoglossal nucleus; n.t., nucleus
of the funiculus teres; n.am., nucleus ambiguus; r., raphe; A., continuation of the anterior column
of cord; o', o", accessory olivary nucleus; P.O., pedunculus olivas. (Modified from Schwalbe.)
bodies and go to the cerebellum. The antero-lateral ascending tracts (Gow-
ers) appear to have the same destination, but pass indirectly into the cere-
bellum by way of the superior medullary velum; some of the fibers probably
pass upward to higher centers. The fibers of the postero-median and postero-
external columns of Goll and Burdach, of the cord, end in the nuclei of the
fasciculus gracilis and cuneatus respectively ; at any rate, ascending degenera-
tion of these columns cannot be traced above these nuclei. The rest of the
fibers of the cord appear to end in the reticular formation of the bulb.
Connections of the Bulb with the Cerebrum and Cerebellum. The
540 THE NERVOUS SYSTEM
pyramidal tracts connect the bulb with the cerebrum ; and the direct cerebellar
and the antero-lateral ascending tract, tract of Gowers, connect it with the
cerebellum. Other connections of the bulb with the cerebrum and with
the cerebellum are:
1. Fibers from the nucleus gracilis and nucleus cuneatus, which, as we
have said, are the endings of the fibers cf the columns of Goll and Burdach
of the cord, pass in sets in the following manner:
a. Internal arcuate fibers pass down and inward to the opposite side in
the reticular formation, composing in part the superior or sensory decussation,
and in the inter-olivary region enter the mesial fillet, which passes upward
through the pons to end about the cells in the mid-brain and in the optic
thalami. These fibers are probably augmented by the addition of fibers from
the anterior columns of the cord, and by fibers arising from cells in the sensory
nuclei of the cranial nerves ending in the bulb.
b. External arcuate fibers, after decussating in the same way, pass outward
superficially over the anterior pyramid and olivary body, reaching the resti-
form body and passing to the side of the cerebellum opposite to their nuclei of
origin. These fibers appear to be interrupted, at least in part, in the external
arcuate nuclei. They connect one side of the spinal cord with the opposite
side of the cerebellum through the gracile and cuneate nuclei.
c. Direct lateral fibers pass to the restiform body and so to the same side
of the cerebellum.
2. Fibers from the olivary body pass to the opposite side of the cerebellum
through the reticular formation and restiform body.
3. Fibers from the vestibular nucleus of the eighth or auditory nerve in
the floor of the fourth ventricle pass to the same side of the cerebellum.
Functions of the Medulla Oblongata. The chief functions of the
medulla are those of carrying impulses, i.e., conduction, between the cord and
brain; of carrying on activities distinctly reflex in character; and of producing
automatic activity.
The Medulla as a Conducting Path. The medulla is the pathway
of all ascending and descending nerve impulses between the spinal cord and
most of the peripheral sensory and motor apparatus on the one hand, and the
cerebellum and the cerebral centers on the other. These conducting paths
are described in the tracts that have already been discussed at some length.
They are represented graphically in the diagrams, figures 380 and 396.
Reflex Centers of the Medulla. The larger number of the cranial
nerves, as we shall presently see, take their origin from the medulla and
pons. Some of these nerves have both sensory and motor roots, while
others are either motor or sensory exclusively. A large percentage of the
afferent or sensory impulses that enter the medulla produce reflex effects
on the motor nuclei so richly represented in the medulla. The nuclei, or
centers, regulating some of the most important functions of the body are
REFLEX CENTERS OF THE MEDULLA
541
among those in this group. When certain of these centers are interfered
with, death follows.
Life may continue when the spinal cord is cut away in successive portions
from below upward as high as the point of origin of the phrenic nerves. In
amphibia, the brain has been all removed from above, and the cord removed as
far as the medulla oblongata from below; yet so long as the medulla oblon-
FIG. 380. — Diagram of Ascending Conduction Paths from the Cord through the Medulla and
the Thalamus to the Cerebral Cortex. (Cunningham.)
gata was left intact, respiration and life were maintained. But if the medulla
oblongata is wounded, particularly if it is wounded in its central part oppo-
site the origin of the vagi, the respiratory movements cease, and the animal
dies from asphyxiation. This effect ensues even when all parts of the nervous
system except the medulla oblongata are left intact.
Injury and disease in men are accompanied by the same nerve disturbances
as are exhibited by these experiments on animals. Numerous instances are
recorded in which injury to the medulla oblongata has produced instantaneous
542 THE NERVOUS SYSTEM
death; and, indeed, it is through injury to it, or of the part of the cord con-
necting it with the origin of the phrenic nerve, that death is commonly pro-
duced in fractures attended by sudden displacement of the upper cervical
vertebrae.
The majority of the medullary centers are reflex centers simply, and are
stimulated by afferent or by voluntary impulses. Some of them are auto-
matic centers and are capable of sending out efferent impulses without pre-
vious stimulation by afferent or by voluntary impulses. The automatic
centers are, however, normally influenced by reflex or by voluntary impulses.
Some of these reflex centers are: i. Bilateral centers for the movements of
deglutition. The medulla oblongata contains in the motor nuclei of the ninth
and tenth nerves the centers whence are derived the motor impulses enabling
the muscles of the palate, pharynx, and esophagus to produce the successive
coordinated and adapted movements necessary to the act of deglutition, page
313. This is proved by the persistence of the act of swallowing in some of
the lower animals after destruction of the cerebral hemispheres and cerebellum;
its existence in anencephalous monsters; and by the complete arrest of the
power of swallowing when the medulla oblongata is injured in experiments.
2. Bilateral centers for the combined muscular movements of sucking, the
nerves concerned being the facial for the lips and mouth, the hypoglossal for
the tongue, and the inferior maxillary division of the fifth for the muscles of the
jaw.
3. Bilateral centers for the secretion 0} saliva, which have been already
mentioned, page 305.
4. Bilateral centers for vomiting, page 330.
5. Bilateral centers for coughing, which is a reflex act quite independent
of the respiratory act. The coughing center is situated above the inspiratory
part of the respiratory center.
6. Bilateral centers for the dilatation of the pupil, the fibers from which
pass out through the spinal cord in the two upper dorsal nerves into the cervi-
cal sympathetic.
7. The respiratory center of the medulla has already been discussed as
regards its automatic action. It is only necessary to repeat here that although
it is automatic in its action, being capable of direct discharge of respiratory
impulses with no other stimulus than the condition of the blood circulating
within it, yet it is constantly reflexly influenced by afferent impulses. The
respiratory center has been proven to be bilateral. It also consists of an
inspiratory part and of an expiratory part. The center is influenced by
voluntary impulses, but one can not voluntarily control this center to the
point of death. The vagus influence is probably the most constant of those
stimulating the respiratory center. But the respiratory reflexes are going on
constantly in response to afferent impulses flowing into the medulla from nu-
merous other sensory nerves over the entire body.
THE PONS VAROLII 543
8. The cardie-inhibitory centers. The medulla contains the centers which
maintain the proper rhythm of the heart, these centers acting through the vagus
fibers. These terminate in a local intrinsic mechanism which has been al-
ready discussed. It is claimed that the center can be stimulated directly, as
by the condition of the blood circulating within it. It is constantly exerting
a tonic influence over the heart, which is the chief reason for considering it
an automatic center. But the cardio-inhibitory center is primarily a re-
flex center. Sensory or afferent impulses arriving over the sensory paths in
the vagus itself, by abdominal paths through the sympathetic, and through
cutaneous nerves, are constantly causing reflex discharges of inhibitory impulses
from this center.
9. Accelerator centers for the heart are present in the medulla. They
are reflexly stimulated by sensory impulses arising from the same general source
as in the preceding center.
10. Vaso-motor centers which control the unstriped muscle ol the arteries,
are also situated in the medulla. The nerve cells constituting the center
are under the constant influence of nerve impulses flowing in from the sensory
and motor structures throughout the whole body. The reflexes produced by
the afferent impulses bring about the variations in vaso-motor tone that not
only regulate the general vascular responses of the body, but control and co-
ordinate the local changes in the size of the blood-vessels.
n. Centers for the secretion of sweat exist in the medulla. The medullary
centers control the subsidiary spinal sweat centers. They may be excited un-
equally so as to produce unilateral sweating.
The reflex medullary centers described above are comparable to the spinal
reflex centers previously described. If the medulla were completely isolated
from the higher cerebral centers, and the spinal cord removed with the ex-
ception of those paths which are necessary to maintain respiration, these medul-
lary reflex centers would be able to coordinate afferent impulses in the same
general way that isolated segments of the cord do. In the living body, however,
the medullary centers are under the influence of changes going on in regions
of the nervous system both above and below, changes which constantly in-
fluence the details of the reactions. The activities are unconscious reflexes
in the same sense that the motor reflexes of the spinal cord are unconscious
and machine-like. The main difference is one of complexity and not of kind.
The Pons Varolii. The pons Varolii is generally spoken of as a
great commissure of fibers; of fibers which connect with the two halves of
the cerebellum and which connect the bulb and spinal cord with the upper
part of the brain. It must not be forgotten that the pons contains several
smaller collections of nerve cells. Sections reveal the following parts or struct-
ures, beginning from the anterior or ventral surface.
i. Transverse or commissural fibers connect one side of the cerebellum
with the other through the middle peduncle. These fibers connect the cere-
544
THE NERVOUS SYSTEM
bellar cortex with the cells of the pontine nuclei; some are afferent, some
efferent; some end in the gray matter of the pons on the same side near the
ventral surface; others cross to the opposite side of the pons and then
become longitudinal, passing on to the tegmentum.
2. Fibers longitudinal in direction are arranged in hrger or smaller bundles
and are separated by gray matter. Most of these fibers are pyramidal fibers
which pass down to the pyramids of the medulla.
3. The dorsal portion of the pons is made up to a considerable extent of the
FIG. 381. — Scheme to Show the Connections of the Posterior Longitudinal Bundle. (Cun-
ningham, modified from Held.)
reticular formation of the tegmental region together with one or two distinct
bundles of longitudinal fibers. The chief longitudinal bundle, situated at the
junction of the ventral two-thirds with the dorsal third, is the fillet, including
a the larger mesial fillet, a sensory tract previously described arising in the
gracile and cuneate nuclei, and by the lateral fillet, an auditory tract. The
second, the posterior longitudinal bundle, is situated on each side of the mid-
line, just internal to the mesial fillet.
4. In the upper part of the pons a mass of gray matter containing pigment,
the locus ceruleus, forming a part of the origin of the fifth nerve and in the
back part a second mass of gray matter, the superior olive.
THE MID-BRAIN
545
THE MID-BRAIN.
The mid-brain includes the crura cerebri, the corpora quadrigemina, and
the geniculate bodies.
The Crura Cerebri. The crura diverge from the anterior edge of the
pons Varolii and pass upward on either side toward the cerebral hemispheres.
At their anterior termination each of them appears to have upon its dorsal
surface, to the inner and outer sides respectively, two large masses of gray
matter which have been already spoken of, viz., the optic thalamus and the
corpus striatum. The crus is made up of two principal parts. Thecrusta
FIG. 382. — Diagram of the Motor Tract as Shown in a Diagrammatic Horizontal Section through
the Cerebral Hemispheres, Crura, Pons, and Medulla. Fr., Frontal lobe; Oc., occipital lobe;
AF., ascending frontal, AP., ascending parietal convolutions; PCF., pre-central fissure, in front
of the ascending frontal convolution; FR., fissure of Rolando; IFF., inter-parietal fissure, a section
of crus is lettered on the left side; SN., substantia nigra; Py., pyramidal motor fiber which on
the right is shown as continuous lines converging to pass through the posterior limb of 1C. , internal
capsule (the knee or elbow of which is shown thus), upward into the hemisphere and downward
through the pons to cross the medulla in the anterior pyramids. (Gowers.)
or pes is in the ventral position, and the tegmentum in the dorsal position. The
two are separated by the substantia nigra.
The pes consists of .longitudinal fibers which pass anteriorly between the
optic thalamus and the posterior part (lenticular nucleus) of the corpus stria-
tum, and also more anteriorly. In this situation the fibers form a compact
mass which spreads out dorsally in the corona radiata. The fibers thus have
the form of a fan bent upon itself as they rise to pass into the cerebral hemi-
sphere. This constitutes the internal capsule, and that portion of it which forms
the angle at which the fibers are bent is called the genu of the capsule. The fibers
of the internal capsule are connected with different districts of the cerebral
cortex. Briefly the connections are, a, the fronto-pontine fibers are in the
« 35
546 THE NERVOUS SYSTEM
anterior limb of the capsule; b, the pyramidal fibers in the genu and the anterior
part of the posterior limb ; c, the temporo-pontine fibers in the posterior part
of the posterior limb. Fibers connecting the optic thalami and corpora
striata with the cerebral cortex run in the capsule. The pes and the corona
radiata form the great sensory and motor highway to and from the cerebral
cortex.
The tegmentum is the continuation anteriorly of the reticular formation of
the medulla. It ends for the most part in the neighborhood of the optic thala-
mus and in the parts beneath. The tegmentum of either side is supposed to
be concerned chiefly with afferent impulses. It is made up to a very consid-
erable extent of collections of gray matter, the most important of which are
the substantia nigra, separating the pes and tegmentum, and the nucleus ruber,
which is a rounded mass situated more toward the aqueduct of Sylvius; it
serves as a way-station in the cerebello-cerebral conduction paths and also
has important connections with the spinal cord. The locus niger extends
back as far as the posterior corpus quadrigeminum. Posteriorly, the teg-
mentum is chiefly reticular in structure.
Corpora Quadrigemina. There are two corpora quadrigemina on
each side, the anterior and posterior. They form prominences on the dorsal
surface of the mid-brain, dorsal to the aqueduct of Sylvius. The posterior
corpora quadrigemina receive through the lateral fillet fibers from the coch-
lear division of the eighth nerve. They are closely associated with the median
corpora geniculata, and, like these, give origin to fibers which continue the
auditory conduction path upward to the auditory center. The anterior
corpora quadrigemina receive fibers from the optic nerve, the mesial fillet,
and also from the occipital cortex, as will be more fully described later. They
are closely associated with the external corpora geniculata. They also form
reflex centers for eye muscles in the ocular adjustments.
Corpora Geniculata. These are two on each side of the brain
stem, the external or outer and the median or inner. The external corpus
geniculatum is at the side of the crus and appears to be a swelling on the lateral
division of the optic tract, and actually receives terminations of the optic fibers,
thus constituting a way-station in the optic conduction paths. Similarly
the median appears to be the termination of the median division of the optic
tract, from which it receives some fibers, figure 416, but it is more intimately
connected with the auditory tracts, forming a way-station between the lateral
fillet and the auditory cortical center, figure 389.
The Optic Thalami. The optic thalami are oval in shape, and rest
upon the crura cerebri. They form part of the floor of the lateral ventricles and
their inner sides bound the third ventricle. They are connected by a trans-
verse tract, the middle commissure.
Each thalamus has several collections of gray matter, forming somewhat
indistinctly defined masses separated by white fibers. These masses of gray
THE OPTIC THALAMI 547
matter are known as the nuclei of the thalamus, and are six in number. They
are called the anterior nucleus, the median nucleus, the lateral nucleus, the
ventral nucleus, the pulvinar, and the posterior nucleus. The corpora geni-
culata are also closely associated with the optic thalamus. The anterior
nucleus is composed of large nerve cells which receive the terminations of
axones of cells of the corpora mammillaria at the base of the brain (bundle of
Vicq d'Azyr). There they meet the fibers of the fornix, which establish
a relation between this tubercle of the thalamus and the hippocampal con-
volutions. The median nucleus is connected by its axones with the cortex
of the island of Reil and the second and third frontal convolutions. The
lateral nucleus is quite large and lies against the internal capsule, into which it
sends fibers. It is connected with the central convolutions. The ventral
nucleus lies beneath the preceding; it is relatively small. It is connected with
the cortex of the frontal lobe and with the operculum, the central convolutions,
and the supramarginal gyrus. The fifth nucleus, known as the pulvinar, forms
the posterior tip of the thalamus, and is connected with the optic tract. The
posterior nucleus, lying just below the pulvinar, is a small mass and is con-
nected with the cortex of the interior parietal convolution. The cells of the
optic thalamus are thus seen to be connected with a large area of the cerebral
cortex. The axones spread out in a great fan in the corona radiata, the
thalamus sending more fibers to the cortex than are received from it.
The collections of nerve cells in the optic thalamus are shown by anatomical
investigations and by methods of physiological degeneration to be on the
pathway of ascending or afferent nerve tracts. Large masses of sensory fibers
pass through the optic thalami, the majority of which form synapses about the
nerve cells in the thalamus. Even in those cases where there is no distinct
ending of the nerve fiber, collaterals are given off which establish physiological
connection with the nuclei.
The optic thalamus is thus closely connected with large areas of the cortex.
It must at least form an important relay in all those activities which involve
the conscious perception of sensory stimuli wherever they may arise. Flechsig
even claims that in the optic thalamus there are definite points of sensory
localization corresponding to every sensory point in the periphery of the body
(including the special senses). The optic thalamus also receives fibers from
various parts of the cerebral cortex, thus establishing a double relation with
this region.
Owing to the difficulty of those operations which establish isolation of the
thalamus, it is not clear to what extent reflex actions may take place through
these nuclei. It is probable, however, that extensive coordinations of afferent
impulses may be mediated by the nuclei of the thalami. Such activities as
walking, riding, writing, speaking, etc., are possibly coordinated reflexes
through the optic thalami, perhaps with the assistance of the medulla in the
case of walking.
548 THE NERVOUS SYSTEM
Corpora Striata. The corpora striata are situated in front and to
the outside of the optic thalami, partly within and partly without the lateral
ventricles.
Each corpus striatum consists of two parts: An intra ventricular portion,
the caudate nucleus, which is conical in shape, with the base of the cone for-
ward-(this consists chiefly of gray matter), and an extraventricular portion, the
lenticular nucleus, separated from the other portion by the internal capsule.
The lenticular nucleus is shown in a horizontal section of the hemisphere to
consist of three parts, the two internal called globus pallidus major and minor,
and the outer called the putamen.
The cells of the corpora striata are somewhat evenly distributed, and not
grouped in nuclei. Their axones pass for the most part into the internal
capsule. It is doubtful if these ganglia have any direct anatomical relations
with the cortex of the brain, but they are intimately connected by fibers to and
from the optic thalami, and are connected with the substantia nigra (Flechsig).
These nuclei are developed from the walls of the embryonic brain tube and
are probably therefore homologous with the areas of the cortex. Their lesion
is said to be accompanied by disturbance in muscular coordination. Lesion
of the left lenticular nucleus is said to cause some disturbance in the power of
speech, though this has not been observed in the case of the right nucleus.
Lesions of the corpora striata produce disturbances in heat regulation, causing
a rise of body temperature, the rise amounting to as much as 2° or 3° C. in
the rabbit. The rise of temperature in man after lesion of the corpus striatum
on one side is said to be chiefly on the opposite side of the body (Kaiser).
THE CRANIAL NERVES.
The cranial nerves consist of twelve pairs; they appear to arise (superficial
origin) from the base of the brain in a double series, which extends from the
under surface of the anterior part of the cerebrum to the lower end of the
medulla oblongata. Traced into the substance of the brain and medulla, the
roots of the nerves are found to take origin from various masses of gray matter.
The roots of the first or olfactory and of the second or optic nerves will be
discussed elsewhere. The third and fourth nerves arise from gray matter
beneath the corpora quadrigemina ; and the roots of origin of the remainder of
the cranial nerves can be traced to gray matter in the floor of the fourth ventri-
cle, and in the more central part of the medulla, around its central canal, as low
down as the decussation of the pyramids.
According to their several functions the cranial nerves may be thus
arranged :
Nerves of special sense. .. . \ Olfactory, Optic Auditory part of the Glosso-
( pharyngeal, and part of the Trigemmal.
Nerves of common sensation. . . The greater portion of the Trigeminal.
THE THIRD NERVE OR MOTOR OCULI
549
Nerves of motion.
Mixed nerves.
\ The Motor Oculi; Trochlearis, lesser division of
( the Trigeminal, Abducens, Facial, and Hypoglossal.
j Facial, Glosso-pharyngeal, Vagus, and Spinal Ac-
( cessory.
The physiology of the first, second, and eighth nerves will be considered
with the Organs of Special Sense.
The Third Nerve or Motor Oculi. Origin. The third nerve arises
in three distinct bands of fibers from the gray nuclei surrounding the aqueduct
of Sylvius near the middle line, but ventral to the canal. The nucleus of origin
consists of large multipolar ganglion cells, and extends to the back part of the
third ventricle as far as the level of the superior corpora quadrigemina. The
FIG. 383. — Section through Anterior Corpus Quadrigeminum and Part of Optic Thalamus. s,
Aqueduct of Sylvius, gr, gray matter of the aqueduct , c.q.s, quadrigeminal eminence; /, stratum
lemnisci; o, stratum opticum, c, stratum cinereum ; Th, pulvinar of optic thalamus: c.g.e, c.g.i,
lateral and median corpora geniculata; br.s, br.t, superior and inferior brachia, f, fillet; p.l,
posterior longitudinal bundle; r, raphe; ///, third nerve, and n.IIl, its nucleus; l.p.p, posterior
perforated space; s.n, substantia nigra — above this is the tegmentum with the circular area of the
red nucleus; cr, crusta; //, optic tract; M, medullary center of hemisphere; n.c, nucleus cau-
datus; st, stria terminalis. (After Quain, from Meynert.)
fibers pass from their origin partly through the red nucleus to their superficial
origin in front of the pons at the median side of each crus. They decussate in
the middle raphe.
Function. The third nerve supplies the levator palpebrae superioris mus-
cle, and all of the muscles of the eyeball, except the superior oblique, to
which the fourth nerve is appropriated, and the rectus externus, which receives
the sixth nerve. Through the medium of the ophthalmic or lenticular ganglion,
of which it forms what is called the short root, it also supplies motor filaments
to the iris and ciliary muscle. The fibers which subserve the three functions,
accommodation, contraction of the pupil, and nerve-supply to the external
ocular muscles, arise from three distinct groups of cells. Optic reflexes in-
volving movements of the eyeballs are through fibers from cells of the superior
corpora quadrigemina (which receive fibers from the optic nerve). These
550
THE NERVOUS SYSTEM
fibers from the corpora quadrigemina descend (chiefly through the posterior
longitudinal bundle) to the nuclei of the third, fourth, and sixth nerves, thus
rendering possible coordinated reflex movements of the eye muscles.
When the third nerve is stimulated within the skull, all those muscles to
which it is distributed are convulsed. When it is paralyzed or divided, the
following effects ensue: i, The upper eyelid can be no longer raised by the
levator palpebrae, but droops, ptosis, and remains gently closed over the eye,
under the unbalanced influence of the orbicularis palpebrarum, which is sup-
FIG. 384. — Fourth Ventricle with the Medulla Oblongata and the Corpora Quadrigemina. The
roman numbers indicate superficial origins of the cranial nerves, while the other numbers in-
dicate their deep origins, or the position of their central nuclei. 8, 8', 8", Auditory nuclei nerves;
t, funiculus teres; A, B, corpora quadrigemina; c.g, corpus geniculatum; p.c, pedunculus cerebri;
m.c.p, middle cerebellar peduncle; s.c.p, superior cerebellar peduncle; i.c.p, inferior cerebellar
peduncle; l.c, locus ceruleus; e.t, eminentia teres; a.c, ala cinerea; a.n, accessory nuleus; 0,
obex; c, clava; f.c, funiculus cuneatus; f.g, funiculus gracilis.
plied by the facial nerve. 2, The eye is turned outward and downward,
external strabismus, by the unbalanced action of the rectus externus and supe-
rior oblique, to which the sixth nerve is appropriated; and hence, from the
irregularity of the axes of the eyes, double sight, diplopia, is often experienced
when a single object is within view of both the eyes. 3, The eye cannot be
moved upward, downward, or inward. 4, The pupil becomes dilated,
mydriasis. 5, The eye cannot accommodate for short distances.
The Fourth Nerve, or Trochlearis. Origin. The fourth nerve
arises from a nucleus consisting of large multipolar ganglion cells situated
THE FIFTH NERVE, OR TRIGEMINAL
551
ventral to the aqueduct of Sylvius, and the inferior corpus quadrigeminum.
The fibers from both sides sweep dorsally around the central gray matter, and
reach the valve of Vieussens, where they decussate in the mid-line of the roof,
then pass forward along the lateral aspect of the crus. The nucleus of the
fourth nerve on either side is connected with those of the third and sixth nerves
and with the optic reflex center previously described.
Functions. The fourth nerve is exclusively motor, and supplies only the
trochlearis or superior oblique muscle of the eyeball.
The Fifth Nerve, or Trigeminal. Origin. The fifth or trigeminal
nerve resembles the spinal nerves in that it has two roots; namely, the larger
nVLK
VJ1I
FIG. 385. — Section Across the Pons, About the Middle of the Fourth Ventricle, py, Pyramidal
bundles; po, transverse fibers passing po\, behind, and pOn, in front of py; r, raphe; o.s, su-
perior olive; a. V, bundles of ascending root of V. nerve enclosed in a prolongation of the sub-
stance of Rolando; VI, the sixth nerve; nVl, its nucleus; VII, facial nerve; VII. a, intermediate
portion, nVIl, its nucleus; VIII, auditory nerve, nVIIl, lateral nucleus of the auditory. (After
Quain.)
or sensory, in connection with which is the Gasserian ganglion, and the small
or motor root, which has no ganglion, and which passes under the ganglion of the
sensory root. The fibers of origin of the fifth nerve come from the floor of the
fourth ventricle. The motor root arises to the inside of the sensory, about the
middle of each lateral half of the fourth ventricle. The sensory fibers,
however, can be traced down in the medulla oblongata as far as the upper part
of the cord. The motor nucleus stretches forward as far as the superior corpus
quadrigeminum, giving rise to a bundle of long fibers termed the descending
root. It is also connected with the locus ceruleus. The sensory nucleus
receives a tract of sensory fibers from the trigeminus extending as low as the
second cervical nerve, and this forms a tract at the tip of the posterior cornu,
between it and the restiform body. The cells of origin of the sensory tract
552
THE NERVOUS SYSTEM
are in the Gasserian ganglion. The nerve appears at the ventral surface of
the pons near its front edge, at some distance from the mid-line.
Motor Functions. The first and second divisions of the nerve, which arise
wholly from the larger root, are purely sensory. The third division is joined
by the motor root of the nerve and is of course both motor and sensory.
Motor branches of the lesser or non-ganglionic portion of the fifth supply
the muscles of mastication, namely, the temporal, masseter, two pterygoid,
anterior part of the digastric, and mylohyoid. Filaments are also said to supply
FIG. 386. — General Plan of the Branches of the Fifth. X J. i, Lesser root of the fifth; 2, greater
root passing forward into the Gasserian ganglion; 3 , placed on the bone above the ophthalmic nerve,
which is seen dividing into the supra-orbital, lachrymal, and nasal branches, the latter connected
with the ophthalmic ganglion; 4, placed on the bone close to the foramen rotundum, marks the
superior maxillary division, which is connected below with the spheno-palatine ganglion, and
passes forward to the infra-orbital foramen; 5, placed on the bone over the foramen ovale, marks
the inferior maxillary nerve, giving off the anterior auricular and muscular Branches, and continued
by the inferior dental to the lower jaw, and by the gustatory to the tongue; a, the submaxillary
gland, the submaxillary ganglion placed above it in connection with the gustatory nerve; 6, the
chorda tympani; 7, the facial nerve issuing from the stylomastoid foramen. (Charles Bell.)
the tensor tympani and tensor palati (Kolliker). The motor function of these
branches is proved by the violent contraction of all the muscles of mastication
in experimental irritation of the third or inferior maxillary division of the fifth
nerve; by paralysis of the same muscles when the nerve is divided or dis-
organized; and by the retention of the power of these muscles when the
facial nerve is paralyzed. Whether the branch of the fifth nerve which is
supplied to the buccinator muscle is entirely sensory, or in part motor also,
must remain for the present doubtful. From the fact that this muscle, besides
THE FIFTH NERVE, OR TRIGEMINAL 553
its other functions, acts in concert or harmony with the muscles of mastication
in keeping the food between the teeth, it might be supposed from analogy
that it would have a motor branch from the same nerve that supplies them.
However, the so-called buccal branch of the fifth is, in the main, sensory.
Sensory Functions. All the anterior and antero-lateral parts of the face
and head, with the exception of the skin of the parotid region, acquire com-
mon sensibility through branches of the ganglionic division of the fifth nerve.
The muscles of the face and lower jaw acquire muscular sensibility through
the filaments of the ganglionic portion of the fifth nerve distributed to them
with their proper motor nerves.
Through its ciliary branches and the branch which forms the long root
of the ciliary or ophthalmic ganglion, it exercises some influence on the move-
ments of the iris. When the trunk of the ophthalmic portion is divided, the
pupil becomes, according to Valentin, contracted in men and rabbits, and
dilated in cats and dogs, but in all cases becomes immovable even under all
the varieties of the stimulus of light. How the fifth nerve affects the iris is
unexplained; it has been suggested the influence of the fifth nerve on the move-
ments of the iris may be ascribed to the affection of vision in consequence of
the disturbed circulation or nutrition in the retina.
Trophic Influence. The morbid effects which division of the fifth nerve
produces in the organs of special sense make it probable that the fifth nerve
exercises some special or trophic influence on the nutrition of all these organs,
although the effects may in part be due to the loss of sensibility which is the
natural protective safeguard. Thus, after such division and within a period
varying from twenty-four hours to a week, the cornea begins to be opaque,
and later it grows completely white. A low destructive inflammatory process
ensues in the conjunctiva, sclerotic coat, and in the interior parts of the eye.
The sense of smell may be at the same time lost or gravely impaired.
Commonly, whenever the fifth nerve is paralyzed, the tongue loses the sense
of taste in its anterior and lateral parts, and according to Gowers in the
posterior part as well.
In Relation to Taste. The tactile sensibility of the tongue is due to the
lingual branch of the fifth nerve, which supplies the anterior and lateral parts
of the tongue. The sense of taste in the lateral and anterior portions of the
tongue have recently been traced back to the pars intermedia and chorda
tympani of the seventh, figures 387 and 388. It forms also one chief sensory
link in the nervous circle .or reflex action in the secretion of saliva. But, de-
ferring this question until the glosso-pharyngeal nerve is to be considered,
it may be observed that in some brief time after complete paralysis or division
of the fifth nerve, the power of all the organs of the special senses may be im-
paired. They may lose not merely their sensibility to common impressions,
for which they all depend directly on the fifth nerve, but also their sensibility
to the special stimuli to which they are adapted.
554
THE NERVOUS SYSTEM
The Sixth Nerve, the Abducens. Origin. The sixth nerve arises
from a compact oval nucleus, situated somewhat deeply at the back part of
the pons near the middle of the floor of the fourth ventricle. The eminentia
teres marks its position. It contains moderately large nerve cells with large
axis-cylinder processes. It is connected, figure 3 7 3 , with the nuclei of the third,
fourth, and seventh nerves, and with reflex centers of the optic tracts, as pre-
viously mentioned. The root is thin, and passes ventrally and laterally through
i.e.
OG.
Sty. hy.
FIG. 387. — The Seventh Nerve and Its Branches.
S.M.
" LM.
Facial nerve; P.I, pars in-
termedia; " VIII, auditory nerve; Aq.Fal, aqueduct of Fallopius; G.G, gemculate ganglion;
E.S.P, external superficial petrosal nerve; MM, middle meningeal artery; G.5.P., great super-
ficial petrosal nerve : G.P.D, great deep petrosal nerve; I.C, internal carotid artery; Via, Vidian
nerve; M.G., Meckel s ganglion: Ty.Pl, tympanic plexus; S.D.P, small deep petrosal nerve; G.Ph,
Glosso-pharyngeal nerve Ty, tympanic branch: S.S.P., small superficial petrosal nerve; U.G,
optic ganglion: Stap, nerve to stapedius1 C.T, chorda tympani nerve; L, lingual nerve; A.Va,
communication with auricular branch of vagus; P. A, posterior auricular nerve- Sty.hy, nerve to
stylo-hyoid; Di, nerve to digastric (posterior belly); T.F, temporal-facial division; C.F, cervico-
facial division; T, temporal M, malar; I.O, infra-orbital; B, buccal. S.M, supra-mandibular ;
LM, infra-mandibular branches. (Cunningham.)
the r^ticular formation, to the surface, which it reaches at the lower edge of
the pons, opposite the front end of the pyramid.
Functions. The sixth nerve is exclusively motor, and supplies only the
rectus externus muscle of the eye. The muscle is paralyzed when the nerve
is divided. In all such cases of paralysis the eye squints inward and cannot
be moved outward.
The Seventh Nerve, or Facial. Origin. The facial or seventh pair of
nerves arises from the floor of the central part of the fourth ventricle, behind
and in line with the motor nucleus of the fifth, to the outside of and deeper
down than the nucleus of the sixth. The nucleus is narrower in front than
behind, and consists of large motor cells with well-marked axis-cylinder proc-
THE SEVENTH NERVE, OR FACIAL 555
esses, which are gathered up at the dorsal surface of the nucleus to form a root.
The root describes a loop around the nucleus of the sixth nerve, running for-
ward for some little distance dorsal to the nucleus, then descending vertically,
passing to the outside of its own nucleus, between it and the descending root
of the fifth nerve. It emerges at the lower margin of the pons, lateral to the
sixth nerve, opposite the front edge of the groove between the olivary and
restiform bodies. There are two roots; the lower and smaller is called the
pars intermedia, and the upper, pars dura.
Functions. The seventh nerve is the motor nerve of all the muscles of
the face, including the platysma, but not including the muscles of mastication,
already enumerated; it supplies, also, the parotid gland, and, through the con-
nection of its trunk with the Vidian nerve, some of the muscles of the soft palate.
It supplies the stapedius, the lingualis and some other muscles of the tongue,
pars interned j
r. auric, vagi
pet rot . 5 up.
. motor's]!.
FIG. 388. — Dissection of the Sensory and Motor Divisions of the Facial in a 2o-cm. Embryo
(Pig). (Streeter.)
and the posterior part of the digastric and stylo-hyoid. Its branches supply
the muscles of the external ear.
Fibers from the chorda tympani are distributed to the submaxillary gland
and produce secretion when stimulated.
When the facial nerve is divided or in any other way paralyzed, the loss of
function in the muscles which it supplies interferes with the perfect exercise
of the organs of the special senses. Thus, in paralysis of the facial nerve .the
orbicularis palpebrarum being powerless, the eye remains open through the
unbalanced action of the levator palpebrae. The conjunctiva is thus contin-
ually exposed to the air and dust and is liable to repeated inflammation, which
may end in thickening and opacity of the cornea.
The sense of taste may be weakened or wholly lost in paralysis of the facial
nerve, which involves the chorda tympani. This result, which has been ob-
served in many instances of disease of the facial nerve in man, appears ex-
plicable on the supposition that the chorda tympani is the nerve of taste to the
anterior two-thirds of the tongue, its fibers being distributed with the so-called
556 THE NERVOUS SYSTEM
gustatory or lingual branch of the fifth. Streeter has just published a
study of the development of the seventh and eighth nerves in which he
traces the chorda tympani through the pars intermedia, as shown in figure
388, thus settling this oft-disputed question.
The Eighth Nerve, or Auditory. The eighth nerve consists of two
divisions, anatomically distinct and functionally independent. These are the
vestibular and the cochlear divisions of the auditory nerve.
The cochlear division arises in the spiral ganglion and passes to the medulla
to establish immediate connections with the ventral cochlear nucleus and the
tuberculum acusticum. The central relations of these nuclei are established
by the striae acusticae, the trapezoideus, and the lateral fillet with the internal
corpus geniculatum and the inferior corpus quadrigeminum of the opposite
side, as told by figure 389. These latter nuclei send tracts to the auditory
center in the superior temporal gyrus.
The vestibular division arises in the vestibular ganglion, which is entirely dis-
tinct from the cochlear ganglion, and enters the medulla, passing to the lateral or
chief auditory nucleus. From this point the relations are not fully established,
but apparently fibers pass to the nucleus fastigii of the opposite side and to the
vermis, where they are brought into relations with motor descending paths.
Functions. The cochlear branch is the auditory nerve proper, and the
vestibular is the nerve of equilibrium.
The Ninth Nerve, or Glosso-pharyngeal. Origin. The glosso-phar-
yngeal nerves, figure 364, IX, arise by nuclei intimately associated with
those of the vagus and spinal accessory nerves. The union of the nuclei is
indeed so intimate that it will be as well to consider the origins of the ninth,
tenth, and eleventh nerves together.
These three nerves emerge from the bulb and spinal cord in their numerical
order from above downward, the bulbar portion from the lateral aspect of
the bulb in a line between the olivary and restiform bodies; and the spinal
portion from a line intermediate between the anterior and posterior nerve roots
as far down as the sixth or seventh cervical spinal nerves.
The combined glosso-pharyngeal-accessory-vagus nucleus appears to con-
sist of two parts, viz., one median or common origin, having conspicuous
nerve cells of moderate size, and three lateral origins, having but few cells of
small size. These are: i, the nucleus ambiguus, which lies on the lateral side
of the reticular formation and is the motor origin of the glosso-pharyngeal,
the vagus, and the spinal accessory; 2, the fasciculus solitarius, situated in
the bulb, ventral and a little lateral to the combined nucleus, is also called the
ascending root of the glosso-pharyngeal nerve or the respiratory bundle; and
3, the spinal portion, which takes origin from a group of cells lying in the ex-
treme lateral margin of the anterior cornu. This is the origin of the spinal
accessory; it corresponds to the antero-lateral nucleus of the bulb, and the
lateral part of the gray matter of the spinal cord.
THE NINTH NERVE, OR GLOSSO-PHARYNGEAL
557
The fibers of the spinal origin of the nerve pass from these cells through
the lateral column to the surface of the cord. The fibers from the median part
pass in a ventral and lateral direction through the reticular formation, th?n
ventral to or through the gelatinous substance and strand of fibers connected
with the fifth nerve, to the surface of the bulb.
The fibers from the nucleus ambiguus join the combined nerve, chiefly
the vagus and glosso-pharyngeal.
The bundles of fibers of the fasciculus solitarius start in the lateral gray
CORPORA QUADRIGEMINA
FIG. 389. — The Nuclei of Origin and Central Connections of the Auditory and Vestibular Nerve.
(Cunningham.)
matter of the cervical cord and higher in the reticular formation of the bulb,
run longitudinally forward, to pass into the roots of the ninth nerve. It is
composed of sensory fibers, chiefly of the glosso-pharyngeal.
The glosso-pharyngeal nerve gives filaments through its tympanic branch
(Jacobson's nerve) , to the fenestra ovalis and fenestra rotunda, and the Eu-
stachian tube; also to the carotid plexus, and through the petrosal nerve, to
558 THE NE'RVOUS SYSTEM
the spheno-palatine ganglion. After communicating with the vagus and,
soon after it leaves the cranium, with the sympathetic, with the digastric
branch of the facial, and the accessory nerve, the glosso-pharyngeal divides
into the two principal divisions indicated by its name, which supply the mucous
membrane of the posterior and lateral walls of the upper part of the pharynx,
the Eustachian tube, the arches of the palate, the tonsils and their mucous
membrane, and the tongue as far forward as the foramen cecum in the middle
line, and to near the tip at the sides and inferior part.
Functions. The glosso-pharyngeal nerve contains some motor fibers,
together with fibers of common sensation and the sense of taste.
Motor fibers are distributed to the palato-pharyngeus, the stylo-pharyngeus,
palato-glossus, and constrictors, of the pharynx.
Sensory fibers of touch and of common sensation are distributed to the
pharynx, the tonsils, and posterior palate. Nerves of taste are supplied to
the taste buds on the posterior third of the tongue and to the fauces.
The Tenth Nerve, Vagus or Pneumogastric Nerve. The origin of the
vagus nerve is, as we have just seen, situated in the lower half of the floor of
the fourth ventricle, figure 374. Its nucleus is said to represent the cells of
Clarke's column of the spinal cord. In origin it is closely connected with
the ninth, eleventh, and the twelfth. The combined glosso-pharyngeal-vago-
accessory nuclei lie outside of, close to, and parallel with the nucleus of the
twelfth. There are two main vagal nuclei: one motor, the other sensory.
Distribution. It has, of all the nerves, the most varied distribution and
functions, either through its own filaments, or through those which, derived
from other nerves, are mingled in its branches. The vagus supplies sensory
branches, which accompany the sympathetic on the middle meningeal artery,
and others which supply the back part of the meatus and the adjoining part
of the external ear. It is connected with the petrous ganglion of the glosso-
pharyngeal, by means of fibers to its jugular ganglion, \vith the spinal acces-
sory, which supplies it with its motor fibers for the larger and upper portion
of the esophagus, and with its inhibitory fibers for the heart; also with the
twelfth; with the superior cervical ganglion of the sympathetic; and with the
cervical plexus. The parts supplied by the branches of the vagus are as
follows:
1 . A large portion of the mucous membrane and probably all the muscles
of the pharynx are supplied by its pharyngeal branches.
2. The mucous membrane of the under surface of the epiglottis, and of
the greater part of the larynx, and the crico-thyroid muscle, by the superior
laryngeal nerve.
3. The mucous membrane and muscular fibers of the trachea, the lower
part of the pharynx and larynx, and all the muscles of the larynx except the
crico-thyroid are supplied by the injerior laryngeal nerve. It also supplies
the first segment of the esophagus.
THE TENTH NERVE, VAGUS OR PNEUMOGASTRIC NERVE 559
-4-
FIG. 390.
FIG.
FIG. 390. — The Distribution of the Tenth or Vagus Nerve. Va.R, Va.L., Right and left vagi; r,
ganglion of the root and connections with Sy., sympathetic, superior cervical ganglion; g.Ph., glosso-
pharyngeal; A cc., spinal accessory nerve; m, meningeal branch; A ur., auricular branch; t, ganglion
of the trunk and connections with Hy., hypoglossal nerve; Ci, €2, loop between the first two cervi-
cal nerves — Sy., sympathetic, Ace., spinal accessory nerve; Ph., pharyngeal branch; Ph.PL,
pharyngeal plexus; S.L., superior laryngeal nerve; I.L., internal laryngeal branch; E.L., external
laryngeal branch ; I. C., internal, and E.G., external carotid arteries; Cai, superior cervical cardiac
branch; Caz, inferior cervical cardiac branch; R.L., recurrent laryngeal nerve; Cas, cardiac
branches of recurrent laryngeal nerve; €0,4, thoracic cardiac branch (right vagus); A. P. PL, an-
terior, and P. P. PL, posterior pulmonary plexuses; Oes.PL, esophageal plexus; Gast.R. and
Gast.L., gastric branches of vagus (right and left) ; Coe.PL, celiac plexus; Hep. PL, hepatic plexus;
PI., splenic plexus; Ren.PL, renal plexus. (Cunningham.)
FIG. 391. — The Constitution of the Cardiac Plexus. Sy., Cervical sympathetic cord; C. i,
superior, C.2, middle, and C.j,, inferior cervical ganglia; Car.i, superior, Car. 2, middle, and
Car. 3, inferior cervical cardiac sympathetic branches; Va., vagus nerve; R.L., recurrent laryngeal
nerve; s, superior, and i, inferior cervical cardiac branches of vagus; D.C.P., deep cardiac plexus;
5. C. P., superficial cardiac plexus; A.P.P., anterior pulmonary plexus; P. P.P., posterior pulmo-
nary plexus; R.Car.P., right, and L.Car.P., left coronary plexuses; Art.PuL, pulmonary artery.
(Cunningham.)
560 THE NERVOUS SYSTEM
4. The mucous membrane and muscular coats of the esophagus receive
fibers from the esophageal branches.
5. The branches of the vagus form the supply of inhibitory nerves to the
heart and the great arteries.
6. The lungs are supplied through the anterior and posterior pulmonary
plexuses.
7. The stomach, the intestines, the spleen, and the liver are supplied by
the gastric, splenic, and hepatic vagus branches.
Functions. Throughout its whole course the vagus contains both sensory
and motor fibers. To summarize the many functions of this nerve, which
have been for the most part considered in the preceding chapters, it may be
said that it supplies, i, motor fibers to the pharynx and esophagus, to the
stomach and intestines, to the larynx, trachea, bronchi, and lungs; 2, sensory
and, in part, 3, vaso-motor fibers to the same regions; 4, inhibitory fibers
to the heart; 5, inhibitory afferent fibers to the vaso-motor center.
Division of both vagi or of both their recurrent branches is often quickly
fatal in young animals; but in old animals the division of the recurrent nerve
is not generally fatal, and that of both the vagi, even, is not always fatal.
The Eleventh Nerve, or Spinal Accessory. This nerve arises by two
nuclei, one the nucleus ambiguus from a center in the floor of the fourth ventri-
cle, partly but chiefly in the medulla and continuous with the glosso-pharyn-
geal-vagus nucleus ; the other, from the outer side of the anterior cornu of the
spinal cord as low down as the fifth or sixth cervical nerve. The fibers from
the two origins come together at the jugular foramen, but separate again into
two branches. The inner arises from the medulla and joins the vagus, to
which it supplies fibers, consisting of small medullated nerve fibers. The
outer consists of large medullated fibers and supplies the trapezius and sterno-
mastoid muscles. The muscles of the larynx, all of which are supplied, ap-
parently, by branches of the vagus, are said to derive their motor nerves from
the accessory; and Vrolik makes the very significant statement that in the
chimpanzee the internal branch of the accessory does not join the vagus at
all, but goes direct to the larynx.
The Twelfth Nerve, or Hypoglossal. Origin and Connections. The
nerve arises from a large-celled and very long nucleus in the bulb, extending
from the floor of the fourth ventricle to the level of the olivary bodies close to the
mid-line and inside the nucleus ambiguus. Fibers from this nucleus run from
the ventral surface through the reticular formation in a series of bundles
passing between the olivary nucleus laterally and the pyramid and accessory
olive medially, to gain the ventral surface. The nerve emerges from a groove
between the pyramid and olivary body. The fibers of origin are continuous
with the anterior roots of the spinal nerves.
This nerve is the motor nerve to the muscles connected with the hyoid bone,
including those of the tongue. It supplies the sterno-hyoid, sterno-thyroid, and
THE CEREBELLUM 561
omo-hyoid through its descending branch, descendens noni; the thyro-hyoid
through a special branch; and the genio-hyoid, stylo-glossus, hyo-glossus,
and genio-hyo-glossus and linguales through its lingual branches.
Functions. The function of the hypoglossal is exclusively motor. In
cases of hemiplegia involving the functions of the hypoglossal nerve the tongue
when protruded deviates toward the paralyzed side, when withdrawn it turns
away from the paralyzed side. Occasionally it is not possible to observe any
deviation in the direction of the protruded tongue; probably because the
tongue is so compact and firm that the muscles on either side can push it
straight forward or turn it for some distance toward either side. In hypo-
glossal paralysis from cerebral lesions or lesions of the peduncles the paralysis
is contralateral.
IV. THE CEREBELLUM.
The cerebellum is a large division of the brain, located just beneath the
cerebrum and behind the medulla and pons. It is connected with the rest
FIG. 392. — Cerebellum in Section and Fourth Ventricle, with the Neighboring Parts, i,
Median groove of fourth ventricle, ending below in the calamus scriptorius, with the longitudinal
eminences formed by the fasciculi teretes, one on each side; 2, the same groove, at the place where
the white streaks of the auditory nerve emerge from it to cross the floor of the ventricle; 3, in-
ferior crus or peduncle of the cerebellum, formed by the restiform body; 4, posterior pyramid;
above this is the calamus scriptorius; 5, superior crus of cerebellum, or processus e cerebello ad
cerebrum (or ad testes) ; 6,6, fillet to the side of the crura cerebri; 7,7, lateral grooves of the crura
cerebri; 8, corpora quadrigemina. (From Sappey, after Hirschfeld and Leveille".)
of the brain by three peduncles on each side: the superior, the middle, and the
inferior peduncle, figure 392.
The cerebellum is composed of white and gray matter, the latter being
external, as in the cerebrum, and like it infolded, so that a larger area may be
contained in a given space. The convolutions of the gray matter, however,
are arranged after a different pattern, as shown in figure 393. Besides the
36
562 THE NERVOUS SYSTEM
gray substance on the surface, there is, near the center of the white substance
of each hemisphere, a small capsule of gray matter called the corpus dentatum,
figure 393, resembling very closely the corpus dentatum of the olivary body of
the medulla oblongata.
If a section be taken through the gray matter of the cerebellum, it will be
found to be composed of two layers, an outer, or molecular, and an inner, or
granular, layer. Each of these layers contains a large number of peculiar-
shaped nerve cells and very rich plexuses of nerve fibers. Recent studies of
the cortex of the cerebellum by modern methods have revealed a most complex
and beautiful arrangement of the parts of the cerebellum.
The General Structure of the Cerebellum. The molecular layer
of the cerebellum contains several peculiar types of nerve cells, of which may be
FIG. 393. — Outline Sketch of a Section of the Cerebellum, Showing the Corpus Dentatum. The
section has been carried through the left lateral part of the pons, so as to divide the superior pe-
duncle and pass nearly through the middle of the left cerebellar hemisphere. The olivary body
has also been divided longitudinally so as to expose in section its corpus dentatum. cr, Crus cerebri ;
f, fillet; q, corpora quadrigemina; sp, superior peduncle of the cerebellum, divided; mp, middle
peduncle or lateral part of the pons Varolii, with fibers passing from it into the white stem; av,
continuation of the white stem radiating toward the arbor vitae of the folia; o, olivary body with
its corpus dentatum; p, anterior pyramid. (Allen Thomson.)
specially mentioned Purkinje's cells and the basket cells. The cells of Pur-
kinje lie along the internal margin of the layer, being, in fact, practically
at the boundary of the molecular and granular layers. They measure 40 to 60 //
in diameter, and have large, round nuclei. Each cell gives off an enormous
number of branching dendrites, which run up toward the surface of the cere-
bellum in the shape of a bush.
The cells of Purkinje give off at their deeper surface an axone which
runs down into the white matter of the cerebellum.
Lying in the molecular layer, somewhat external to the Purkinje cells,
are the cells of the type known as basket cells. These cells have a number of
dendrites, also send out an axone which runs parallel to the surf ace of the cortex,
which gives off numerous collaterals in its course that form baskets around
the cell bodies of the Purkinje cells, figure 394, ZK.
THE GENERAL, STRUCTURE OF THE CEREBELLUM 563
FIG. 394. — Transverse Section Through a Cerebellar Folium (after Kolliker). Treated by the
Golgi method. P, Axone of cell of Purkinje; F, moss fibers; K and K', fibers from white core of
folium ending in molecular layer in conection with the dendrites of the cells of Purkinje; M,
simple cell of the molecular layer; GR, granule cell; GR1, axones of granule cells in molecular layer
cut transversely; M', basket cells; ZK, basket work around the cells of Purkinje; GL, neuroglia
cell; N, axone of an association cell.
molecular
layer
granule
granule
FIG. 305. — A, Afferent fiber to basket (stellate) cell; B, neuraxone of Purkinje cell; C, afferent
fiber to Purkinje cell; D, afferent (mossy) fiber to granule cell.
564 THE NERVOUS SYSTEM
The granular layer contains a large number of very small granule-like
cells that Golgi was the first to show are really nerve cells. They are only
about 5 fji in diameter, and they have a number of short dendrites which end
in clubbed extremities. They give off a very slender axis-cylinder process
or axone which runs up into the superficial part of the molecular layer and
there divides in a T-shaped fashion, the fibers run parallel to the surface of the
convolution and pass in between the branches of the cells of Purkinje.
The white substance of the cerebellum consists of nerve fibers, which are of
three kinds: i, Descending fibers, that are made up of the axis-cylinders
of the cells of Purkinje, carrying impulses down from the cerebellar cortex.
2, Ascending fibers, which pass into the granular layer, and there end in a
number of very short, finely divided brushes of fibers presenting a mossy ap-
pearance, so that these are known as the mossy fibers. These connect with the
granular cells of this layer. 3, Ascending fibers, which pass up through the
granular into the molecular layer and there break up into a fine network which
interlaces with the dendritic branches of the cells of Purkinje.
Paths through the Cerebellar Cortex. It will be seen that the ar-
rangements for the transmission and diffusion of nerve impulses and for the co-
operation of different cells are extremely complicated and delicate. It is not
possible to indicate absolutely by any schema the course of fibers and the
course of impulses through the cerebellum, but approximately it is some-
what like that in the accompanying figure 396.
Impulses pass up along the ascending fibers to the granular cells by way of
the direct cerebellar, the fibers of the gracile and of the cuneatus, from the
restiform body, etc. These cells, being stimulated, send the impulses by their
axis -cylinders to the molecular layer, and through their T-shaped divisions to
the dendrites cf the cells of Purkinje. Thence an impulse is sent out by the
axis-cylinder process of this cell. Other ascending impulses are brought up
by those fibers which pass directly to the molecular layer and send their ter-
minals winding around among the dendrites of the cells of Purkinje. Proba-
bly impulses pass up also through the ascending fibers which affect the
basket cells, and, through them and their basket-like terminals, the cells of
Purkinje. Purkinje cells send cerebellar motor fibers to the nucleus dentatus
cerebelli and through the superior peduncles to the nuclei of the oculo-motor
nerves, and to the ventro-lateral descending tract of the cord, to end about
the anterior-horn cells.
Functions of the Cerebellum. With the exception of its middle
lobe, the cerebellum is itself insensible to irritation and may be all cut away
without eliciting signs of pain (Longet). Its removal or disorganization by
disease is also generally unaccompanied by loss or disorder of sensibility;
animals from which it is removed can smell, see, hear, and feel pain, to all
appearances, as perfectly as before (Flourens; Magendie). It cannot, there-
fore, be regarded as a principal organ of sensation. Yet if any of its crura
FUNCTIONS OF THE CEREBELLUM
565
be touched, pain is indicated; and, if the restiform tracts of the medulla ob-
longata be stimulated, the most acute suffering appears to be produced.
These phenomena may properly be ascribed to the activity of the cerebral
cortex, since the number of collaterals on the fibers that pass to cerebellar tracts
is very great, and impulses arising from their stimulation may reach the sen-
sorium by paths other than through the cerebellum.
Cranial Nerve
Ur )
FIG. 306.— Scheme of Principal Ascending Cerebro- Spinal (black) and Cerebellar (red) Con-
duction Paths. (Modified from Hardesty in Morris Anatomy.)
The experiments of Longet and many others agree in supporting the view
that no stimulation of the cerebellar cortex leads to localized muscular con-
tractions. In other words, there is no localization in the cerebellar cortex
as in the cerebrum, the cerebellum apparently acting as a whole. If the cere-
bellum be removed, as was done by Flourens and numerous later physiologists,
a very profound disturbance in motor functions occurs. With the removal
566
THE NERVOUS SYSTEM
of the superficial layers of the cerebellum, in pigeons particularly, there is
increasing feebleness and lack of harmony of the muscles concerned in lo-
comotion. When the entire organ is cut away in pigeons they lose the power of
walking, flying, and of standing in the usual erect way. Their power of pre-
serving equilibrium is lost, the most characteristic feature. Birds do not
remain in a state of stupor, but attempt to carry out the usual muscular activi-
ties. If a pigeon is laid on its back it cannot recover its erect position, though
it make motions to do so. If set on its feet it will fall to one side or the other,
and is not able to hold its head in the customary position. The endeavors of
the animal to maintain its balance are insecure and uncertain, resembling
the lack of muscular control of a drunken man.
Such an animal does not lose the power of perceiving sensations, nor of
making voluntary efforts, as it will endeavor to avoid the blow that is
threatened.
The experiments afford the same results when repeated on all classes of
animals; and from them and the others before referred to, Flourens inferred
that the cerebellum belongs neither to the sensory nor the intellectual ap-
paratus; and that it is not the source of voluntary movements, although it be-
longs to the motor apparatus, but is the organ for the coordination of the
voluntary movements, or for the excitement of the combined action of muscles.
Such evidence as can be obtained from cases of diseases of this organ
confirms the view taken by Flourens; and, on the whole, it gains support from
comparative anatomy — animals whose natural movements require most
frequent and exact combinations of muscular contractions being those whose
cerebella are most developed in proportion to the spinal cord.
We must remember, too, that the cerebellum is connected with the posterior
columns of the cord through the cuneate and gracile nuclei as well as with the
direct cerebellar tract, all of which probably convey to the middle lobe muscular
sensations. It is also connected with the auditory nerves and bulb by the in-
ternal and external arcuate fibers; and with the tegmentum through the red
nuclei. Its connection with the efferent tracts from the different cerebral
lobes through the pons is also highly important. Movements of the eyes also
occur on direct stimulation of the middle lobe. It seems, therefore, to be
connected in some way with all of the chief sensory impulses which have to do
with the maintenance of the equilibrium, and is generally included in the ner-
vous apparatus which is supposed to govern this function of our bodies.
Foville supposed that the cerebellum is the organ of muscular sense, i.e., the organ
by which the mind acquires that knowledge of the actual state and position of the muscles
which is essential to the exercise of the will upon them; and it must be admitted that all
the facts just referred to are as well explained on this hypothesis as on that of the cerebellum
being the organ for combining movements. A harmonious combination of muscular
actions must depend as much on the capability of appreciating the condition of the muscles
with regard to their tension, and to the force with which they are contracting, as on the
power which any special nerve-center may possess of exciting them to contraction. And
FORCED MOVEMENTS 567
it is because the power of such harmonious movement would be equally lost, whether the
injury to the cerebellum involved injury to the seat of muscular sense or to the center
for combining muscular actions, that experiments on the subject afford no proof in one
direction more than the other.
Forced Movements. The influence of each half of the cerebellum
is directed to muscles on the opposite side of the body; and it would appear
that, for the right ordering of movements, the actions of its two halves must be
always mutually balanced and adjusted. For if one of its crura, or if the
pons on either side of the middle line, be divided, so as to cut off from the
medulla oblongata and spinal cord the influence of one of the hemispheres
of the cerebellum, strangely disordered movements ensue — forced movements.
The animals fall down on the side opposite to that on which the crus cerebelli
has been divided, and then roll over continuously and repeatedly; the rotation
being always round the long axis of their bodies, and generally from the side
on which the injury has been inflicted. The rotations sometimes take place
with much rapidity; as often, according to Magendie, as sixty times in a min-
ute, and may last for several days. Similar movements have been observed
in men; as by Serres in a man in whom there was apoplectic effusion in the
right crus cerebelli; and by Belhomme in a woman in whom an exostosis
pressed on the left crus. They may, perhaps, be explained by assuming that
the division or injury of the crus cerebelli produces paralysis or imperfect and
disorderly movements of the opposite side of the body; the animal falls, and
then, struggling with the disordered side on the ground, and striving to rise
with the other, pushes itself over; and so again and again, with the same act,
rotates itself. Such movements cease when the other crus cerebelli is divided;
but probably only because the paralysis of the body is thus made almost com-
plete. Other varieties of forced movements have been observed, especially
those named "circus movement," when the animal operated upon moves
round and round in a circle; and again those in which the animal turns over
and over in a series of somersaults. Nearly all these movements may result
on section of one or other of the following parts: viz., crura cerebri, medulla,
pons, cerebellum, corpora quadrigemina, corpora striata, optic thalami, and
even, it is said, of the cerebral hemispheres.
V. THE CEREBRUM.
That portion of the brain which is concerned with all intellectual functions
is the cerebrum or, more strictly speaking, the cerebral cortex. The cerebral
cortex is the seat of those activities which we describe as intelligence —
including states of consciousness, acts of idea formation and volition, and
the phenomenon of memory.
The cerebrum includes the cerebral cortex, the mass of fibers connecting
it with lower portions of the brain, the basal nuclei represented by the corpora
568
THE NERVOUS SYSTEM
striata, optic thalami, etc. The structure and function of these basal nuclei
have already been given briefly, so we may turn our attention now to the cere-
bral cortex.
Structure of the Cerebral Cortex. The cerebral cortex forms a large
part of the mass of the cerebrum, in fact of the whole brain. Its superficial
appearance presents a series of ridges and folds, the gyri and sulci. For gen-
eral convenience anatomists have divided the cerebral cortex into five lobes :
the frontal, that portion in front of the fissure of Rolando extending down to the
Sylvian fissure; the parietal, extending from the Sylvian fissure to the parieto-
occipital fissure, and bounded below by the Sylvian fissure; the temporal lobe,
just ventral to the parietal; the central lobe, or island of Reil; and the oc-
cipital lobe, which includes the posterior portion of the cortex behind the
caUoso-Tnarg.
FIG. 397.— Left Hemisphere, from Without. (After Eberstaller.)
parieto-occipital fissure. And, finally, the olfactory and limbic lobes together
make up the olfactory division of the brain. For the detailed arrangements of
the cortex the reader is referred to text-books of anatomy.
In a transverse section of the cerebral cortex there is shown an external
gray layer chiefly composed of nerve cells and an internal white portion of
nerve fibers. The folding of the cortex into convolutions increases the total
mass of gray matter enormously.
The gray or cellular external part of the cerebral cortex has an average
thickness of about 3 mm.; being thin in the occipital and frontal region, 2 mm.,
and thick in the precentral, 4 mm., and postcentral convolutions.
Several types of nerve cells have been described as present in the cortex, the
exact type and relative proportion varying somewhat in different regions.
The typical characteristic cell, however, is the pyramidal cell. The pyramidal
cell, as its name implies, has a pear-shaped cell body with numerous proto-
plasmic processes. The apex of the cell is directed toward the surface of the
STRUCTURE OF THE CEREBRAL CORTEX
569
cortex, and supports numerous branches which extend out into the adjacent
territory, bringing it into contact with a relatively large number of nerve cells.
These processes are dendritic in character. The base of the pyramidal cell
always has a single axis-cylinder process which is directed down into the white
matter, and which in some cases ultimately finds its course through the corona
radiata into the pyramids below. The axis-cylinder processes give off col-
FIG. 398. — The Cerebrum, from Above. (After Eberstaller.)
^— —
medians)
Sale,
extremm:
FIG. 399. — Right Hemisphere, from Within. (After Eberstaller.)
570
THE NERVOUS SYSTEM
laterals both in the immediate neighborhood of the cell and somewhat deeper
along its course.
In the superficial layer of the cortex there is a peculiar type of small cell,
first described by Cajal. Most of these cells are fusiform in shape, with the
long axis parallel to the surface of the convolution. They give off usually two
axones which run along parallel to the surface and send down numerous
r
FIG. 401.
FIG. 400.— Typical Pyramidal Cell from the Human Cortex, a, Cell body; b, main dendrites
with gemmules; c, lateral dendrites; d, axone and collaterals. Only a small part of the axone
is shown. (Bailey.)
FIG. 401. — Showing the Stages in the Development of a Pyramidal Cell. (Ramdn y Cajal.)
fine collaterals at right angles. Another form of Cajal cell, triangular or
quadrangular in shape, is also seen. Both forms have, as a rule, more than
one axone. Their collaterals pass in a horizontal direction, forming a
fine band of fibers, known as tangential fibers. A third type of cell is the
fusiform or polymorphous. Some of these are strictly fusiform in shape and
lie with their axes parallel to the surface of the convolution. They give off
protoplasmic processes which pass down toward the white matter, some of
them turning to run in a horizontal direction. The fusiform and polymorphous
cells are grouped in the same layer.
STRUCTURE OF THE CEREBRAL CORTEX
571
Besides these cells we find scattered through the cortex a considerable
number of the neuroglia cells. The character and position of these are shown
in figure 402.
The general arrangement of the layers of the cortex is described very dif-
ferently by the various authors. It is not uniform in the different parts of the
FIG. 402. — The Principal Constituent Elements of the Gray Cortical Layer of the Anterior
Cerebrum. (After Ram6n y Cajal.)
(After Ram6n y Cajal.)
brain. The simplest and most representative type, however, of the arrangement
is that in which the cortex is divided into four layers. The outermost, or super-
ficial, known as the molecular layer, contains relatively few cells. It is com-
posed of neuroglia tissue, embedded in which are a number of cells of the
Cajal types, which have just been described. There are also in this layer
many neuroglia cells. In the superficial part of the layer of some areas of the
572 THE NERVOUS SYSTEM
cortex are many tangential fibers. The second layer is composed of small
pyramidal cells. In parts of the brain there are here interposed what are
known as the vertical fusiform cells. The third layer is composed of large
pyramidal cells, in which, however, one also sees many small pyramidal cells.
The fourth layer is composed of the fusiform and polymorphous cells, beneath
which is the white substance. This arrangement is shown in the accompanying
figures, 404 and 405. The gray matter of the brain contains, however, not
only these layers and cells, but an infinitely rich mass of fibers, which can be
shown to have a certain definite arrangement. Some of the fibers are vertical,
passing directly up to the most superficial layers of cells; others have a hori-
zontal direction, dividing the gray matter into different layers. These
FIG. 403. — Scheme of Descending Conduction Pathways from the Cerebrum to Lower Nerve
Centers.
layers of fibers have received different names. A typical arrangement is
shown in figure 405. The most conspicuous fibers are those of certain
large triangular or pyramidal cells.
The efferent or axone fibers from the cerebral cortex may be divided into
three classes: i, the projection fibers, which descend through the corona
radiata and internal capsule, to end in lower centers; 2, the commissural
fibers, which cross to the opposite cerebral hemisphere, chiefly through the
corpus callosum; 3, the association fibers, which pass in bundles beneath
the cortex, to end in other regions of the same hemisphere.
It is by means of projection fibers and collaterals that associations are
made with nerve cells in the optic thalamus, tegmentum, and pons, and
through the latter region with tracts going to the cerebellum.
STRUCTURE OF THE CEREBRAL CORTEX
573
H
FIG. 404.
FIG. 405.
..Tangential fibers (Vic
d'Azyr's ribbon)
. .Striae of Bechterew
. . Superradiary network (of
the second and third layers)
. .Striae of Baillarger
..Intermediary network (of
the third and fourth layers)
. .Meynert's intracortical asso-
ciation fibers
. . Subcortical association
fibers
FIG. 404.— Schematic Diagram of the Different Layers of the Cerebral Cortex. (After Ramdn
y Cajal.) I, II, III, and IV, Layers of cortical cells. M, Molecular layer; pPy, layer of small
pyramidal cells; gPy, layer of large pyramidal cells; Pm, layer of polymorphous cells.
FIG. 405. — Schematic Diagram Showing the Arrangement of the Nerve Fibers in the Cerebral
Cortex. The dotted lines separate the four cellular layers of Cajal. 56, White substance.
574
THE NERVOUS SYSTEM
Weight of the Brain and Cord. The brain of an adult man weighs from 48 to 50
oz. about 1,550 grams, or about 2 per cent of the body weight. It exceeds in absolute
weight that of all the lower animals except the elephant and whale. Its weight, relatively
to that of the body, is exceeded only by that of a few small birds, and some of the smaller
monkeys.
In the new-born child the brain (weighing 10 to 14 oz.) is about 10 per cent of the
weight. At the age of 7 years the weight of the brain already averages 40 oz., and about
14 years the brain not infrequently reaches the weight of 48 oz. Beyond the age of forty
years the weight slowly but steadily declines at the rate of about i oz. in 10 years.
The average weight of the female brain is less than the male; and this difference per-
sists from birth throughout life. The difference amounts to about 5 oz. Thus the average
weight of an adult woman's brain is about 44 oz.
The brains of idiots are generally much below the average, some weighing less than 16
oz. Still the facts at present collected do not warrant more than a very general statement,
FIG. 406. — Brain of the Orang, $ Natural Size, Showing the Arrangement of the Convolutions.
Sy, Fissure of Sylvius; R, fissure of Rolando; EP, external perpendicular fissure; Olf, olfactory
lobe; Cb, cerebellum; PV, pons Varolii; MO, medulla oblongata. As contrasted with the
human brain, the frontal lobe is short and small relatively, the fissure of Sylvius is oblique, the
temporo-sphenoidal lobe very prominent, and the external perpendicular fissure very well marked.
(Gratiolet.)
to which there are numerous exceptions, that the brain weight corresponds to some extent
with the degree of intelligence. There can be little doubt that the complexity and depth
of the convolutions, which indicate the area of the gray matter of the cortex, correspond
with the degree of intelligence.
The spinal cord of man weighs from i to ij oz.; its weight relatively to the brain is
about i : 40 in the adult. As we descend the animal scale, this ratio constantly increases
till in the mouse it is i : 4. In cold-blooded animals the relation is reversed, the spinal
cord is the heavier. In the newt, 1 105; and in the lamprey, i : 133.
The most distinctive points in the human brain, as contrasted with that of apes, are:
i. The much greater size and weight of the whole brain. The brain of a full-grown
gorilla weighs only about 15 oz. (450 grms.), which is less than ^ the weight of the human
adult male brain, and barely exceeds that of the human infant at birth. 2. The much
greater complexity of the convolutions, especially the existence in the human brain of
tertiary convolutions in the sides of the fissures. 3. The greater relative size and complex-
ity and the blunted quadrangular contour of the frontal lobes in man, which are relatively
broader, longer, and higher than in apes. In apes the frontal lobes project keel-like
GENERAL FUNCTIONS OF THE CEREBRUM 575
(rostrum) between the olfactory bulbs. 4. The much greater prominence of the temporo-
sphenoidal lobes in apes. 5. The fissure of Sylvius is nearly horizontal in man, while in
apes it slants considerably upward. 6. The distinctness of the fissure of Rolando.
Most of the above points are shown in the accompanying figure of the brain of the
orang.
GENERAL FUNCTIONS OF THE CEREBRUM.
Evidence regarding the physiology of the cerebral hemispheres has
been obtained, as in the case of other parts of the nervous system, from the
study of anatomy, from pathology, and from experiments on the lower animals.
The chief evidences regarding the functions of the cerebral hemispheres de-
rived from these various sources are briefly these: i, Any severe injury of
them, such as a general concussion, or sudden pressure as by apoplexy, may
instantly deprive a man of all power of manifesting externally any mental
faculty. 2, In the same general proportion as the higher mental faculties are
developed in the vertebrates and especially in man at different ages, as well as
in different individuals, the greater is the development of the cerebral hemi-
spheres in comparison with the rest of the cerebro-spinal system. 3, No other
part of the nervous system bears a corresponding proportion to the development
of the mental faculties. 4, Congenital and other morbid defects of the cerebral
hemisphere are, in general, accompanied by corresponding deficiency in the
range or power of the intellectual faculties and the higher instincts. 5, Re-
moval of the cerebral hemispheres in the lower animals produces effects cor-
responding with what might be anticipated from the foregoing facts.
Effects of the Removal of the Cerebrum. The removal of the cere-
brum in the lower animals appears to reduce them to the condition of a
mechanism without spontaneity.
In the case of the frog, when the cerebral lobes have been removed, the ani-
mal appears similarly deprived of all power of spontaneous movement. But
.it sits up in a natural attitude and breathes quietly. When pricked it jumps
away. When thrown into the water it swims. When placed upon a board
it remains motionless, although, if the board be gradually tilted over till the
frog is on the point of losing his balance, he will crawl up till he regains his
equilibrium, and comes to be perched quite on the edge of the board.
If the frog be turned on his back, he regains his normal position. If his
back is stroked gently he will utter the usual croaking sound. These activities
are carried on by the normal frog. There is one striking difference, however,
between the brainless frog and the normal : the former, if placed in a position
and left undisturbed, will remain quietly without moving for an indefinite time.
It has apparently lost the power to initiate movements. Presumably
any memory impressions or effects of former experiences have been lost.
Even the more elemental stimuli, which come from tissue hunger and thirst,
apparently do not affect the brainless frog. In other words, the oper-
576 THE NERVOUS SYSTEM
ation has reduced the animal to the condition of an automaton capable of
carrying on complex activities, but only after receiving some definite stimulus.
This condition contrasts with that resulting from the removal of the entire
brain, leaving only the spinal cord. In this case only the simpler reflex actions
can take place. The frog does not breathe ; he lies flat on the table instead of
sitting up; when thrown into a vessel of water he sinks to the bottom; when
his legs are pinched he kicks out, but does not leap away.
If the cerebrum of the frog be removed, taking special care not to interfere
with the optic nerves or the optic thalami, then he acts somewhat differently.
Whereas with the entire cerebrum removed he makes no effort to take food,
now he will attempt to catch flies or other insects, and will show other signs of
spontaneous activity. He will avoid an object and shows signs of responding
to visual sensations, such as the attempt to feed just mentioned.
The cerebral lobes of the frog, however, are very low in the scale of de-
velopment as compared with other vertebrates. The cortex is a single layer
of rather small cells, and the total volume of the cortex as compared with other
portions of the brain is small.
The case of the pigeon, which represents a higher animal in the scale^
has been extensively studied by Flourens and others. They have shown that
when the cerebrum is carefully removed, leaving the basal nuclei undisturbed,
and the animal has recovered from the immediate effects of the shock, it is
able to carry on many Coordinate activities. In the first place it can stand
or perch without difficulty; if placed on its back it immediately regains its
equilibrium; if tossed in the air it flies until it comes in contact with a firm
support. If disturbed on its perch it will walk away, showing the power
to coordinate not only wing muscles, but the leg muscles. If left undisturbed,
such a pigeon will occasionally make motions, i.e., open its eyes, move its head,
preen its feathers, or even take a step or two. It spends most of its time, how-
ever, sitting quietly as though asleep. If aroused, the animal shows little or no
signs of excitement or fright.
After several months such pigeons are said usually to increase the motions
of spontaneity or take short flights, avoiding obstacles in the way and alighting
definitely on the perch. They will pick around among food for definite articles,
apparently intending to select the food. Early after the operation the pigeon
will pick at objects indiscriminately, but does not take food unless it is placed
in the mouth.
Apparently the main effect produced here is to diminish the complexity and
efficiency of those activities which we call spontaneous. The surprising thing
is that there is as little disturbance among the motor functions as is found.
In mammals it is difficult to remove the cerebral hemispheres, but in those
animals, in which the operation has been carried out, as for example in the rab-
bit and rat, a result very similar to those observed in the case of the frog and
pigeon has been obtained. The animal is able to maintain its equilibrium,
MOTOR FUNCTION OF THE CEREBRAL CORTEX 577
to run or jump, and in fact successfully carry out the most complicated coor-
dinated movements, but it is unable to originate them without stimulation. In
the case of the dog, it has been found impossible to remove the whole brain
at one operation. However, Goltz has succeeded in removing both the
cerebral hemispheres of the dog by doing the operation in successive stages
and taking extraordinary precautions to protect his animal against the great
fall of temperature and the immediate shock of the operation. He kept his
dog alive for some eighteen months and secured a complete recovery from the
series of operations. Goltz 's dog was able to walk about, it responded to a
bright light by closing its eyes, and could be aroused by a sharp, loud sound.
It spent its time lying down in the cage, sleeping rolled up dog-fashion.
When aroused by stimulation of the skin, it would move away from the stim-
ulating object and would sometimes growl and snap at the object. If it snapped
at the object it would do so without going toward it or making the usual effort
to seize the object which we are accustomed to expect of a normal vicious
dog. This dog did not spontaneously feed itself, but had to have food placed
in its mouth before it would swallow. But the animal finally learned to take
food, as in the case of the pigeon. This animal gave very definite responses
to its condition of nourishment; it slept quietly and was peaceful when fully
fed, but was restless and irritable when hungry.
Goltz's dog showed complete absence of those activities which we would
call psychic. That is to say, it showed no memory signs, it was unable
to learn the signal for feeding, it did not manifest any fondness or signs of
pleasure at the presence of its caretaker. In short, there was a complete
loss of memory and intelligence, and the animal, although performing some
activities, was in fact reduced to a mere automaton. It would be difficult to
imagine a more crucial experiment to elucidate the function of the cerebral
cortex.
It is quite evident that the apparatus for carrying out coordinated move-
ments is in these animals not localized either in the cerebrum or in the spinal
cord. It must therefore be connected in some way with the parts of the
brain below the cerebrum and above the cord. There is no reason why such
an arrangement may not be supposed to exist in the human brain, although
we must look upon the cerebrum as the originator of voluntary movements.
LOCALIZATION OF THE MOTOR FUNCTION OF THE CERE-
BRAL CORTEX.
The experiments upon the brains of various animals by means of electrical
stimulation have demonstrated that there are definite regions of the cerebral
cortex the stimulation of which produces definite movements of coordinated
groups of muscles of the opposite side of the body. Fritsch and Hitzig were
the first to show that the cerebral cortex responds to electric irritation. They
37
578
THE NERVOUS SYSTEM
employed a weak constant current in their experiments, applying a pair of
fine electrodes not more than one-twelfth inch apart to different parts of
the cerebral cortex. The results thus obtained have been confirmed and ex-
tended by Ferrier and many others, stimulating chiefly with induction currents.
FIG. 407.
FIG. 408.
FIGS. 407 and 408. — Brain of Dog, Viewed from Above and in Profile. F, Frontal fissure some-
times termed crucial sulcus, corresponding to the fissure of Rolando in man; S, fissure of Sylvius,
around which the four longitudinal convolutions are concentrically arranged; i, flexion of head
on the neck, in the median line; 2, flexion of head on the neck, with rotation toward the side of the
stimulus; 3, 4, flexion and extension of anterior limb; 5, 6, flexion and extension of posterior
limb; 7, 8, 9, contraction of orbicularis oculi and the facial muscles in general. The unshaded part
is that exposed by opening the skull. (Dalton.)
The fundamental phenomena observed in all these cases may be thus
epitomized :
i. Excitation of the same spot on the cortex is always followed by the same
movement in the same animal. 2. The area of excitability for any given
MOTOR FUNCTION OF THE CEREBRAL CORTEX 579
movement is extremely small, and admits of very accurate definition. 3. In
different animals excitations of anatomically corresponding spots produce
contractions in similar or corresponding muscles.
The various definite movements resulting from the electric stimulation
of circumscribed areas of the cerebral cortex are enumerated in the description
of the accompanying figures of the dog's and monkey's brains.
In the case of the dog the results obtamed are summed up as follows by
Hitzig: i, One portion, anterior, of the convexity of the cerebrum is motor;
another portion, posterior, is non-motor. 2, Electric stimulation of the motor
portion produces coordinated muscular contraction on the opposite side of the
body. 3, With very weak currents, the contractions produced are distinctly
limited to particular groups of muscles; with stronger currents the stimulus
is communicated to other muscles of the same or neighboring parts. 4, The
portions of the brain intervening between these motor centers are inexcitable.
Following strong stimulation of cortical motor centers other groups of
muscles than those innervated by the centers stimulated may also take part in
the contractions.
According to the observations of Ferrier, confirmed and extended by later
experimenters, stimulation of various parts of the monkey's brain, as indicated
by the numbers in figures 409, 410, produces movements of definite muscles,
thus: Stimulation of the district marked i causes movement of hind foot;
of 2, chiefly adduction of the foot; of 3, movements of hind foot and tail;
of 4, of latissimus dorsi ; of 5, extension forward of arm; a, b, c, d, movements of
hand and wrist; of 6, supination and flexion of forearm; of 7, elevation of the
upper lip; of 8, conjoint action of elevation of upper lip and depression of
lower; of 9, opening of mouth and protrusion of tongue; of 10, retraction of
tongue; of n, action of platysma; of 12, elevation of eyebrows and eyelids,
dilatation of pupils, and turning head to opposite side; of 13, eyes directed to
opposite side and upward, with usually contraction of the pupils; of 13', similar
action, but eyes usually directed downward; of 14, retraction of opposite ear,
head turns to the opposite side, the eyes widely opened and pupils dilated; of
15, stimulation of this region, which corresponds to the tip of the uncinate
convolution, causes torsion of the lip and nostril of the same side.
It is thus seen that the motor areas chiefly correspond with the ascending
frontal and ascending parietal convolutions, and that the movements of the leg
are represented at the upper part of these convolutions, then follow from above
downward the centers for the arms, the face, the lips, and the tongue.
According to the further researches of Schafer and Horsley, electrical stim-
ulation of the marginal convolution internally at the parts corresponding with
the ascending frontal and parietal convolutions, from the front backward,
produces movements of the arm, of the trunk, and of the leg.
A good deal of doubt was thrown upon the experiments of Ferrier by Goltz
and other observers, from the results of excising the so-called motor areas of
580
THE NERVOUS SYSTEM
the dog's brain. It was found that the part might be sliced away or washed
away with a stream of water, but that no permanent paralysis ensued.
More extensive observations, however, have confirmed Ferrier's original
statement, at any rate with regard to the monkey's brain. Destruction of the
FIG. 410.
FIGS. 409 and 410. — Diagrams of Monkey's Brain to Show the Effects of Electric Stimulation
of Certain Spots. (According to Ferrier.)
motor areas for the arm produces some permanent paralysis of the arm of
the opposite side, and similarly of that for the leg, paralysis of the opppsite
leg. If both areas are destroyed, permanent hemiplegia ensues. Paralysis
of so extensive and permanent a character does not, however, appear the
rule when the brain of a dog is used instead of that of the monkey. It is
suggested that in the animal lower in the scale the functions which in the
MOTOR AREAS OF THE HUMAN BRAIN
581
monkey are discharged by the cortical centers may be subserved to a greater
extent by the basal ganglia.
Motor Areas of the Human Brain. It is naturally of great impor-
tance to discover how far the results of experiments upon the dog and monkey
FIG. 411. — Motor Areas of the Human Brain, Lateral View.
FIG. 412. — Motor Areas of the Human Brain, Median View.
hold good with regard to the human brain. Evidence furnished by diseased
conditions is not wanting to support the general idea of the existence of cortical
motor centers in the human brain, figure 411.
So far, however, it has been possible to localize motor functions in the
precentral and ascending parietal convolutions only; the convolutions which
582
THE NERVOUS SYSTEM
bound the fissure of Rolando and those on the inner side of the hemispheres
which correspond thereto, and possibly the frontal lobe in front of the pre-
central convolution.
The position of the centers is probably much the same as in the monkey's
brain, those for the leg above, those for the arm, face, lips, and tongue from
above downward. Destruction of these parts causes paralysis, corresponding
to the district affected, and irritation causes contractions of the muscles of the
P. CALL O SUM
LOBE-
FIG. 413. — Diagram of Certain Connections of the Frontal, Temporal, and Occipital Lobes.
Founded on the observations of Flechsig, Ferrier, and Turner. (Cunningham.)
same part. Again, a number of cases are on record in which aphasia, or the
loss of power of expressing ideas in words, has been associated with disease of
the posterior part of the lower or third frontal convolution on the left side.
This condition is usually associated with paralysis of the right side, right
hemiplegia.
This district of the brain, particularly the convolutions bounding the
fissure of Rolando, is now generally known as the motor area; and there is no
doubt whatever that from this area pass the nerve fibers which proceed to the
spinal cord, and are there represented as the pyramidal tracts.
MOTOR AREAS OF THE HUMAN BRAIN
This is the reason that movements are produced on stimulation of the white
matter after the superficial gray matter of the animal's brain has been sliced off.
These motor fibers are those which arise from the pyramidal cells of the
cortex. From the motor area of the cortex they converge to the internal cap-
sules, and pass down to the crus. In the internal capsule the fibers which pass
to the pyramidal tracts of the spinal cord occupy that part known as the knee
(genu) and the anterior two-thirds of the posterior limb, figure 414. In this
district the fibers for the face, arm, and leg are in this relation: those for the
face and tongue are just at the knee, and below or behind them come first the
fibers for the arm and then those for the leg.
The more accurately known arrangements of these fibers in the monkey's
brain, named in order, from above down, are those for the eye, head, tongue,
FIG. 414. — Diagram to Show the Relative Positions of the Several Motor Tracts in Their
Course from the Cortex to the Crus. The section through the convolution is vertical; that through
the internal capsule, 1C, horizontal; that through the crus again vertical. CN, caudate nucleus;
O TH, optic thalamus; La and L$, middle and outer part of lenticular nucleus; f, a, I, face, arm,
and leg fibers. The words in italics indicate corresponding cortical centers. (Gowers.)
mouth, shoulder, elbow, digits, abdomen, lip, knee, digits. These fibers come
for the most part from the portion of the cortex on either side of the fissure of
Rolando, but chiefly from the anterior central gyrus, hence called the Rolan-
dic area. But the areas for the head and eyes lie more anteriorly in the
frontal lobe, to the front of the precentral sulcus— that for the head above
that for the eyes, and an area for the trunk (not indicated in the figure 414)
is situated more toward the middle line of the hemisphere, internal to that for
the leg. Those fibers, passing between the occipital lobe and the optic thal-
amus and superior corpora quadrigemina, are concerned with vision, and are
called fibers of the optic radiation. In like manner, from the inferior cor-
pora quadrigemina and the internal geniculate bodies, fibers which make
up the auditory radiation pass to the auditory center.
584
THE NERVOUS SYSTEM
It has already been shown that the motor fibers of the internal capsule of
one side cross over to the opposite side in the decussation of the pyramids in
the medulla. This decussation is not quite complete, as some fibers pass
down on the same side in the direct pyramidal tract. A small portion of these
direct fibers end around the motor neurones of the same side, but the great
majority cross to the opposite side in the anterior commissure at some lower
level of the cord. It follows that the motor areas of the cortex on one side
control the muscular movements of the opposite side of the body, but to a slight
extent those of the same side. Disease in the region of the fissure of Rolando
is usually accompanied by a disturbance of the motor function on the opposite
side of the body, although there is some slight motor disturbance on the same
side.
LOCALIZATION OF SENSORY FUNCTION IN THE CEREBRAL
CORTEX.
There is evidence that fibers from the nerves of special sense are specially
connected with definite and distinct parts of the cerebral cortex.
The fibers from the sensory nerves, we have found, are connected with the
cerebral cortex by a chain of neurones. . These sensory paths, although com-
plex, are definite and distinct. Their cortical connections have been mapped
out with considerable definiteness.
The Body Sensory or Somesthetic Area. The motor function around
the fissure of Rolando for a long time obscured the fact that this region,
FIG. 415-— Diagrams to Show Flechsig's Sensory and Association Areas ont e Surface of the
Cerebral Hemisphere. (From Cunningham, after Flechsig.)
especially the post-central convolution, is intimately connected with the
perception of general body sensations. Physiological and pathological ob-
servations supported this view, and recently Flechsig has much strengthened
the view by his method of studying the progressive development of the brain.
In figure 415 we produce Flechsig's diagram showing the body sensory (som-
esthetic) area. The borders of the area are more or less indefinite and less
VISUAL OR OPTIC CENTER 585
distinct than the main portion. This is indicated by the lighter shading.
Lesions of this area in the cortex lead to loss of sensibility in definite regions of
the opposite side of the body.
Visual or Optic Center. The termination of the optic nerve in each
eye, the retina, to the structure of which we shall return when treating of the
eye, is so arranged that when we look at an object with both eyes, symmetrical
parts of each retina are used. For example, if we look at an object to the left,
an image of that object is focussed upon the right half of both retinae, viz.,
upon the temporal side of the right retina, and upon the nasal side of the left
retina. The optic nerve fibers of these symmetrical parts of the retina are
gathered together behind where the optic nerves decussate, viz., in the optic
chiasma. The fibers which come from the right side of both eyes are contained
in the optic tract of the same side, viz., the right, those from the right eye being
outside of the others. In the same way the left optic tract contains internally
fibers from the left side of the right eye and externally those from the left
side of the left eye. The optic tract thus formed then passes backward and
terminates in three distinct nuclei, viz., the pulvinar of the optic thalamus,
the anterior corpus quadrigeminum, and the lateral corpus geniculatum.
These nuclei atrophy if the eyes are removed from an adult animal; and if
the eyes are removed from a newly born animal, they do not fully develop.
Through the superior corpora quadrigemina the optic tract establishes synap-
ses that bring it into relation with the nucleus of the third nerve, and which
form the basis of the eye reflexes to light stimulation.
It appears that some of the fibers of the optic tract pass directly into the
cerebral cortex without joining with the optic thalamus, corpus quadrigeminum,
or corpus geniculatum.
It was shown above that the fibers of the cerebral cortex, known as the
optic radiation, pass from the occipital region to the three nuclei about
which we are speaking, viz., into the pulvinar of the optic thalamus, the anterior
corpus quadrigeminum, and lateral corpus geniculatum, and it is known that
when the occipital cortex is removed, these three atrophy. It has been further
shown that in a newly born animal the removal of such a region is followed
by imperfect development of the parts in question.
If one optic nerve be divided, blindness of the corresponding eye results ;
but if one optic tract be divided there is a half blindness in both eyes, which is.
called hemianopsia, or hemiopia, right or left, according as the right or left field
of vision is cut off. It is evident that the occipital lobe, figures 412, 413, and
particularly the cuneus, is concerned as a visual center, since not only is it
connected with the optic nerves, as we have seen, but also because the re-
moval of the right occipital lobe in an animal (monkey) is followed by left
hemiopia, removal of the left by right hemiopia, and removal of both occipital
lobes by total blindness.
Olfactory Center in the Cortex. The olfactory nerve differs from
586
THE NERVOUS SYSTEM
the other cranial nerves. In reality it is a representative of the olfactory lobes
of other animals, which are part of the cerebrum. The olfactory lobe origi-
nates as an offshoot from the cerebral vesicle, the front part of which is de-
veloped into the bulb of the olfactory nerve, while the back part forms its
peduncle. The nerve, the cavity of which in man is filled up in the fully de-
veloped condition with neurogliar substance, lies upon the cribriform plate
of the ethmoid bone, and is contained in a groove on the under surface
CORP.
FIG. 416. — Scheme of the Central Connections of the Optic Fibers. (Cunningham.)
of the frontal lobe. On examination of the bulb it is found to be thus made
up: Beneath the neurogliar layer is a layer of longitudinal fibers and a few
nerve cells next ta this is a layer of small cells, nuclear layer, fibers from the
layer of nerve fibers passing through it.
The nuclear layer is also separated into groups of cells by an interlacing
of the fibers. The next layer is thick and is composed of neuroglia and nerve
fibers, some of which are medullated, as well as of cells more or less pyra midal
in shape. Below this layer is the layer of olfactory glomeruli. These glomer-
uli are small synapses of olfactory fibers. The larger also includes small
TASTE CENTER OF THE CORTEX 587
cells and granular matter. A full description of the anatomy of these parts
is given later.
Fibers of the olfactory nerve proper are found below this layer, and pass
through the cribriform plate to be distributed to the olfactory mucous mem-
brane. They arise from cells in the olfactory mucous membrane, and end in
the glomeruli. The peduncle of the nerve or the olfactory tract, as it is some-
times called, is made up of longitudinal fibers originating in the bulb, with
neuroglia and some nerve cells.
The fibers of the olfactory tract have been traced into the nucleus amygdalae
and its junction with the hippocampal gyrus in the temporal lobe, figure 399.
The hippocampus must be in some way connected with smell, since a lesion of
it, leaving the olfactory tract uninjured, seriously interferes with that sense.
Taste Center of the Cortex. It is very uncertain where the taste
center is situated, if such exist. It has been placed in the anterior portion of
the inferior temporal convolution, not far from that of smell, figure 399.
Auditory Center in the Cortex. This center has been localized in
the superior temporal convolution. Experiments have been made which
connect auditory impulses on either side with the inferior corpus quadrige-
minum and the median corpus geniculatum, for when the internal ear is
destroyed there results atrophy of these bodies as well as of the lateral
fillet of the opposite side. On the other hand, destruction of the part of the
temporal lobe above indicated is similarly followed by atrophy of the nuclei
of the same side. These nuclei bear much the same relation to the sense
of hearing as do the anterior corpora quadrigemina and the lateral corpora
geniculata to the sense of sight, figures 389 and 416.
ASSOCIATION CENTERS OF THE CEREBRAL CORTEX.
The theory of localization of the function of different parts of the cerebral
cortex has received substantial support from the study of the motor and the
sensory areas in man and the mammals. But when the exploration of the
cortex is complete and the motor and sensory areas are bounded as definitely
as may be, there still remain great areas in which stimulation is apparently non-
effective so far as our present means of interpretation reveal. Traumatic
and pathological lesions produce no sensory or motor disturbances. The
areas of this class which are most extensive, i.e., which cover the greatest
amount of cortex, are three in number — the frontal lobe, the parietal lobe, and
a large part of the temporal lobe below the superior temporal convolution.
Flechsig has made a study of the development of the human brain, paying
especial attention to the progressive development of the great tracts of fibers.
He has shown that the tracts appear in a certain order of sequence, also that
the myelinization takes place progressively. On the assumption that ef-
fective functionization is acquired with the myelin sheath, he showed a close
THE NERVOUS SYSTEM
correspondence in time between the development of the tracts and the mani-
festation of functions known to involve the tracts in question. The great
somesthetic area and its tracts are first to develop ; then tracts to the occipital or
visual center, to the auditory and other sensory centers, and, finally, to these
great areas whose functions remain obscure.
Basing his deductions on the facts of development, on the isolated cases of
lesion and disease, and on the careful comparative studies of the brains of cer-
tain men of unusual intellectual powers, whose personal characteristics and
FIG. 417. — The Association Fibers in the Centrum Ovale. A, Between adjacent convolutions;
B, between frontal and occipital lobes; C, between frontal and temporal lobes, the cingulum; D,
between temporal and frontal lobes — lesion of this tract causes paraphasia; E, between occipital
and temporal lobes — lesion of this tract causes word -blindness; C.N, caudate nucleus; O.T,
•ptic thalamus.
intellectual genius are known, Flechsig has advanced the hypothesis that the
areas of the cortex not concerned directly with motor or sensory functions are
association areas.
The Association Centers of Flechsig. The great association centers
are the frontal, parietal, and temporal, figure 415. These regions of the cor-
tex are apparently not directly connected with tracts of the brain stem and
cord, but they are richly connected with the areas that do have connection with
the cord. Short association fibers connect neighboring convolutions within
the centers, fibers which are chiefly the axones of the polymorphous cells of the
fourth layer of the cortex. Long association fibers run from one center to
another, such as the cingulum, superior and inferior longitudinal fasciculi,
etc. The longer connectives run from association to association centers,
and from association to sensory and motor centers. Flechsig believes that
the sensory centers are not connected directly with each other, but only in-
directly through the association areas.
Cases of injury and of disease of the human brain in the association areas
are not numerous, but such as there are tend to confirm Flechsig's hypothesis
that the function of these areas is that of the higher psychic activity.
THE ANTERIOR OR FRONTAL ASSOCIATION CENTER 589
The Anterior or Frontal Association Center. The frontal area is
more closely connected with the motor areas and the centers for the somesthetic
sense. With injury to this area the individual shows weakness in attention,
in reflection, and in control over the expressions of anger, self-appreciation,
and other activities that are expressive of personal volitions and emotions.
The American crowbar case is a classical instance of lesion of the frontal
lobe. A young man of twenty-five had an iron bar, an inch and a quarter
in diameter and over three feet long, driven through his skull and brain
by the premature explosion of a blast of powder. He not only recovered,
but lived for twelve years afterward. At the post-mortem examination the
puncture was found to be through the prefrontal lobe, anterior to the coronal
suture.
This man was considered a most efficient workman and foreman before
the injury. After his recovery he was fitful, impatient of restraint, capricious,
obstinate; was most inconsiderate of his associates, profane, passionate;
from a shrewd business man he was changed to the intellectual level of a
child and was regarded by his associates as mentally unbalanced.
A summary of fifty cases of pathological lesions of the prefrontal areas of
the human brain is given by Williamson. The mental traits of thirty-two are
summarized in the following terms: "A condition of mental decadence; a
dull mental state; loss of power of attention; loss of memory; loss of spon-
taneity; the patient takes no heed of his surroundings; sleeping during the
greater part of the da}', or remaining semi-comatose." Yet these patients are
able to walk about and execute well coordinated muscular activities of all
kinds that do not involve complex intellectual activity.
The Parietal Association Centers. Special mention is made of this
association area because there is increasing evidence that it is the parietal
region of the brain, rather than the frontal, as popularly believed, that is
most intimately concerned with acts and powers of imagination, idealization,
and reasoning. It is the region through which the individual maintains his
interests and relations with the external world as against his own body. The
parietal association center is more closely related to the visual, auditory, and
speech centers of the cortex. The great musician Bach had an exception-
ally well developed parietal region.
On the Cortical Centers in General. For purposes of clearness
in presentation, the cortical centers have been discussed one by one, but the
/eader is guarded against the thought that their activities are in any sense
isolated. A motor area does not usually act in the absence of sensory or af-
ferent stimulation in the actual living body, whether it may do so on occasion
or not. Neither do sensory impressions arising in the peripheral sense organ
make their way over definite tracts to the brain and cortex and arouse sensa-
tions alone. Sensations do not occur independent of motor activities on the
one hand, and of intellectual acts through the association centers on the other.
590 THE NERVOUS SYSTEM
The association centers are the highest coordinating regions of the nervous
system. They are to the sensory and motor centers what these latter are to
the reflex centers of the cord, the difference being one of degree and not of
kind. Further, they are probably set into activity by the complex of in-
flowing or afferent impulses in just the same sense that the spinal reflex cen-
ters are set in activity by sensory or afferent stimuli ; the condition is, of course,
a thousand times more complex.
THE PHYSIOLOGY OF SLEEP.
All parts of the body which are the seat of active change require periods of
rest. The alternation of work and rest is a necessary condition of their main-
tenance and of the healthy performance of their functions. These alternating
periods, however, differ much in duration in different cases; but, for any in-
dividual instance, they preserve a general and rather close uniformity. Thus,
the periods of rest and work mentioned, in the case of the heart, occupy, each
of them, about half a second; in the case of the ordinary respiratory muscles
the periods are about four or five times as long. In many cases (as of the
voluntary muscles during violent exercise), while the periods during active
exertion alternate very frequently, yet the expenditure goes far ahead of the
repair, and, to compensate for this, an after-repose of some hours becomes
necessary, the rhythm being less perfect as to time than in the case of the
muscles concerned in circulation and respiration.
Obviously, it would be impossible that, in the case of the brain, there
should be short periods of activity and repose, or, in other words, of conscious-
ness and unconsciousness. The repose must occur at long intervals and must
be proportionately long. Hence the necessity for that condition which we call
Sleep; a condition which, seeming at first sight exceptional, is only an unusually
perfect example of what occurs, at varying intervals, in every actively working
portion of our bodies.
By exposing, at a circumscribed spot, the surface of the brain of a living
animal, and protecting the exposed part by a watch-glass, Durham was able
to prove that the brain becomes visibly paler, anemic, during sleep; and the
anemia of the optic disc during sleep, observed by Hughlings Jackson, may
be taken as a strong confirmation, by analogy, of the same fact.
The Circulation During Sleep. Blood is supplied to the brain in
four distinct but anastomosing arteries. This efficient anatomical arrange-
ment is obviously all the more important when it is remembered that the cir-
culation in the brain has no local device for regulating the blood- flow, but that
it must depend on the variations in general blood pressure. Any variation in
the flow of blood in the brain depends on changes in general blood pressure;
changes which are themselves dependent on variations in the activity of the
heart, the caliber of the blood-vessels, etc., discussed on page 186.
SOMNAMBULISM AND DREAMS 591
Howell and others have studied the circulation by the plethysmographic
method during sleep. The results show that with the loss of consciousness, and
immediately following, there is a sharp dilatation of the blood-vessels of the
arm, probably chiefly of the skin, as shown by the increase in volume. The
vessels remain dilated until the individual begins to awaken, when there is
a rapid constriction with decrease of volume of the organ.
The dilatation of the general blood-vessels draws off the supply of blood
from the brain, and the resulting partial anemia contributes to loss of conscious-
ness. The blood supply is ample for growth and repair and rest of the nervous
system. How efficient this rest period is for the rejuvenation of the nervous
tissue is indicated even by the relatively gross means, figure 356, shown in
the histological preparations of nerve cells.
Somnambulism and Dreams. What we term sleep occurs often in very different
degrees in different parts of the nervous system; and in some parts the expression cannot
be used in the ordinary sense.
The phenomena of dreams and somnambulism are examples of differing degrees of sleep
in different parts of the cerebro-spinal nervous system. In the former case the cerebrum
is still partially active; but the activity is no longer corrected by the reception, on the part
of the sleeping sensorium, of impressions of objects belonging to the outer world; neither
can the cerebrum, in this half-awake condition, act on the centers of reflex action of the vol-
untary muscles, so as to cause the latter to contract — a fact within the painful experience
of all who have suffered from nightmare.
In somnambulism the higher centers are capable of coordinating that train of reflex
nervous action which is necessary for progression, while the nerve center of the muscular
equilibrium sense (in the cerebellum?) is, presumably, fully awake; but the sensorium
is still asleep, and impressions made on it are not sufficiently felt to rouse the cerebrum
to a comparison of the difference between mere ideas or memories and sensations derived
from external objects.
VI. THE SYMPATHETIC SYSTEM.
The fact has already been emphasized that the sympathetic system of
nerves is an organic and constituent part of the nervous system.
Organization and Distribution. The sympathetic system consists
of those collections of nerve cells or ganglia lying outside of the brain and
cord (exclusive of the root ganglia), and the nerve tracts connecting them
with one another and with the cerebro-spinal axis. Its parts that should be
mentioned are : i, a double chain of ganglia and fibers, which extends from the
cranium to the pelvis, along each side of and in front of the vertebral column,
and from which branches are distributed both to the cerebro-spinal system
and to other parts of the sympathetic system. With these may be included the
small ganglia in connection with those branches of the fifth cerebral nerve
which are distributed in the neighborhood of the. organs of special sense,
namely, the ophthalmic, otic, spheno-palatine, and submaxillary ganglia.
2, Various ganglia and plexuses of nerve fibers which give off branches to the
thoracic and abdominal viscera, the chief of such plexuses being the cardiac.
592
THE NERVOUS SYSTEM
solar, and hypogastric; 'but in intimate connection with these are many
secondary plexuses, as the aortic, spermatic, and renal. Fibers pass from
the prevertebral chain of ganglia and from the cerebro-spinal nerves to these
plexuses. 3, Various ganglia and plexuses in the substance of many of the
viscera, as in the stomach, intestines, and urinary bladder. These, which
Gray Ram us
White Ramus
Sy m |\ ath eti c Ga rig I i ort
Recurrent Branc
of Meninges
White
Ramus
GrayRamus
Sympathetic Ganglion.
FIG. 418. — Schematic Representation of the Relation of the Constituents of the Sympathetic
, Chain and the Spinal Nerve. (Modified from Hardesty, in Morris' Anatomy.)
are for the most part microscopic, also freely communicate with other parts
of the system, as well as with the cerebro-spinal axis.
The connections between these parts are as follows: i, The visceral
branch or white ramus, of certain spinal nerves, which passes into the lateral
chain. 2, The gray rami consist of bundles of fibers, usually non-medullated,
which pass from the chain ganglia back into the spinal or cranial nerves, the
ORGANIZATION AND DISTRIBUTION 593
fibers of which they accompany to the periphery. 3, From this chain the
rami efferentes pass into the collateral ganglia, and from these again other
branches pass off into the organs, to end in the terminal ganglia.
The white rami are absent in all the spinal nerves in the regions above
the second (occasionally the first) thoracic nerve root, and below the second
FIG. 419. — Scheme of the Constitution and Connections of Gangliated Cord of the Sympathetic.
The gangliated cord is indicated on the right, with the arrangement of the fibers arising from
ganglion cells. On the left, the roots and trunks of the spinal nerves are shown, with the arrange-
ment of the white ramus communicans above and the gray ramus below. The cells of origin in
the ventral cord of the fibers constituting the white ramus are not shown. (Cunningham.)
lumbar nerve root, with the occasional exception of the roots of the third and
fourth lumbar nerves. This is a rather restricted field of origin for the pregan-
glionic fibers which compose the white rami. These fibers end in adjacent
ganglia of the chain, or pass to higher or lower levels or to more peripheral
ganglia.
A peculiarity in the structure of these white medullated visceral nerves is the
38
594 THE NERVOUS SYSTEM
fineness of their fibers. They are a third or a fourth of the diameter of ordinary
medullated fibers, measuring i.8/,i to 2.7^ instead of 14^ to 19^. Such
fibers are a peculiarity of the spinal nerve roots chiefly in the thoracic region,
but also found in the second and third sacral nerves, and constitute there
the nervi erigentes which pass directly to the hypogastric plexus. From the
hypogastric plexus branches pass upward into the inferior mesenteric ganglia
and downward to the bladder, rectum, and generative organs. These nerves,
called by Gaskell pelvic splanchnic nerves, differ from the rami viscerales of
the thoracic region only in not communicating with the lateral ganglia; the
branches which pass upward from the thoracic region to the neck, he calls
cervical splanchnics, and the splanchnics proper abdominal splanchnics.
Functions. The researches of Gaskell and of Langley have done
much to clear up the former confusion as to the distribution and functions
of the sympathetic. The sympathetic nerve fibers are distributed to smooth
muscle, to gland cells, and to cardiac muscle. These are all organs which
carry on their activities either automatically or reflexly. There is no volun-
tary control of the function of these organs.
The efferent sympathetic fibers supply the muscles of the vascular system, to
which they send the vaso-motor fibers, i.e., vaso-constrictor and cardiac aug-
mentor or accelerator; and vaso-inhibitory fibers, i.e., vaso-dilators. They
supply the muscles of the alimentary canal and of the urinogenital system.
The details of arrangement and functional control of these complex systems
have already been discussed in connection with the function of the organ or
part concerned. They supply the salivary, gastric, and pancreatic glands.
According to Gaskell the functions of the main sympathetic ganglia are the
following: i, They effect the conversion of medullated into non-medullated
fibers. 2, They possess a nutritive influence over the nerves which pass from
them to the periphery. 3, They increase the number of fibers.
The sympathetic ganglia are not nerve centers in the usual sense. It is
better to regard them merely as distributing organs in which reflexes of central
origin and comparatively simple type are distributed over relatively large
areas. These ganglia do not possess the power of reflex function. A type
of pseudo- reflex has been described depending on the law of neurone reaction.
But it is not supposed that such reflexes occur in the normal animal.
Afferent or sensory fibers of the ordinary spinal-root ganglion cells are
present in the sympathetic nerves of the splanchnic region, being distributed
merely to the visceral region. True afferent sympathetic fibers have been
demonstrated. These arise from cells located in the sympathetic ganglia, and
pass through the rami communicantes, to end by terminal arborizations in the
spinal ganglia, chiefly around cells of the Dogiel type. The number and
significance of these afferent neurones are yet uncertain.
CHAPTER XV
THE SENSES
THROUGH the medium of the nervous system man obtains a knowledge
of the existence both of the various parts of his body and of the external
world. This knowledge is based upon sensations resulting from the stimula-
tion of certain centers in the brain by nerve impulses conveyed to them by
afferent nerves. Under normal circumstances the following structures are
necessary for sensation: a, A peripheral organ for the reception of the im-
pression; b, a nerve for conducting it; c, a nerve center for feeling or per-
ceiving it.
Sensations may be conveniently classed as, i, common, and 2, special
sensations.
Common Sensations. Under this head fall all those general sen-
sations which cannot be distinctly localized in any particular part of the body,
such as fatigue, discomfort, faintness, satiety, nausea, together with hunger
and thirst, in which, in addition to a general discomfort, there is in many
persons a distinct sensation referred to the stomach or fauces. In this class
must also be placed the various stimulations of the mucous membrane of
the bronchi, which give rise to coughing, and also the sensations derived from
various viscera, such as the desire to defecate, to urinate, and in the female
the sensations which precede the expulsion of the fetus. It is impossible to
draw a very clear line of demarcation between many of the common sensa-
tions above mentioned and the sense of touch, which forms the connecting
link between the general and special sensations. Touch is classed with the
special senses, and will be considered in the same group with them; yet it
differs from them in its wide distribution over the body. Among common
sensations some would rank the muscle sense, which has been already
alluded to. It is by means of this sense that we become aware of the con-
dition of the muscles, and thus obtain the information necessary for their
adjustment to various purposes — standing, walking, grasping, etc. This
muscular sensibility is shown in our power to estimate the differences between
weights by the different muscular efforts necessary to raise them. It must
be carefully distinguished from the sense of contact and of pressure, of which
the skin is the organ. When standing erect, we can feel the ground contact,
and there is* a sense of pressure, due to our feet being pressed against the
ground by the weight of the body. Both these are derived from the skin
of the sole of the foot. If now we raise the body on the toes, we are con-
595
596 THE SENSES
scious, through the muscular sense, of a muscular effort made by the muscles
of the calf. But the muscle sense will be discussed further, page 603.
Special Sensations. The special senses include Touch, Temper-
ature (Heat and Cold), Taste, Smell, Hearing, Sight.
The most important distinction between common and special sensations
is that by the former we are made aware of certain conditions of various
parts of our bodies, while from the latter is gained a knowledge of the ex-
ternal world. This difference will be clear if we compare the sensations of
pain and touch, the former of which is a common, the latter a special, sensa-
tion. " If we place the edge of a sharp knife on the skin, we feel the edge
by means of our sense of touch; we perceive a sensation, and refer it to the
object which has caused it. But as soon as we cut the skin with the knife,
we feel pain, a feeling which we no longer refer to the cutting knife, but which
we feel within ourselves, and which communicates to us the fact of a change
of condition in our own body. By the sensation of pain we are neither able
to recognize the object which caused it nor its nature."
It is important in studying the phenomena of sensation clearly to under-
stand that the sensorium, or seat of sensation, is in the brain, and not in the
particular organ through which the sensory impression is received. In com-
mon parlance we are said to see with the eye, hear with the ear, etc., but in
reality these organs are only adapted to receive stimuli which produce changes
that are, through their respective nerves, conducted to the sensorium, to give
rise to sensation.
Hence, if the optic nerve is severed, vision is no longer possible. Although
the image falls on the retina as before, the sensory impulse can no longer be
conveyed to the sensorium. When any given sensation is felt, all that we
can with certainty affirm is that some part of the brain is excited. The ex-
citing cause may be some object of the external world, producing an objective
sensation; or the condition of the sensorium may be due to some excitement
within the brain itself, in which case the sensation is termed subjective. The
mind habitually refers sensations to external causes; and hence, whenever
they are subjective we can hardly divest ourselves of the idea of an external
cause, and an illusion is the result.
Sensory Illusions. Numberless examples of such illusions might
be quoted. As familiar cases may be mentioned, humming and buzzing in
the ears caused by some irritation of the auditory nerve or center. These
stimuli may even be interpreted as musical sounds, or voices, sometimes
termed auditory spectra. So-called optical illusions in which objects are
described as seen, although not present, may be caused by changes going
on in some part of the visual apparatus beyond the eye. Such illusions are
most strikingly exemplified in cases of delirium tremens or other forms of
delirium, and may take the form of animals such as cats, rats, or creeping
loathsome forms, etc.
SENSE PERCEPTIONS 597
One uniform internal cause, which may act on all the nerves of the senses
in the same manner, is capillary congestion. This one cause excites in the
retina, while the eyes are closed, the sensations of light and luminous flashes;
in the auditory nerve, the sensation of humming and ringing sounds; in the
olfactory nerve, the sense of odors; and in the nerves of feeling, the sensation
of pain. In the same way a chemical substance introduced into the blood
may excite in the nerves of each sense peculiar symptoms: In the optic nerves,
the appearance of luminous sparks before the eyes; in the auditory nerves,
tinnitus aurium; and in the common sensory nerves, the sensations of creeping
over the surface. So, also, among external causes, the stimulus of electricity,
or the mechanical influence of a blow, concussion, or pressure, excites in the
eye the sensation of light and colors; in the ear, a sense of a loud sound or
of ringing; and in the tongue, a saline or acid taste.
Sense Perceptions. The habit of constantly referring our sensa-
tions to external causes leads us to interpret the various modifications which
external objects produce in our sensations, as properties of the external bodies
themselves. Thus we speak of certain substances as possessing a disagreeable
taste and smell; whereas, the fact is their taste and smell are only disagree-
able to us. It is evident, however, that on this habit of referring our sensa-
tions to causes outside ourselves, perception, depends the reality of the ex-
ternal world to us; and more especially is this the case with the senses of
touch and sight. By the cooperation of these two senses, aided by the others,
we are enabled gradually to attain a knowledge of external objects which
daily experience confirms, until we come to place unbounded confidence in
what is termed the evidence of the senses.
We must draw a distinction between mere sensations, and the judgments
based, often unconsciously, upon them. Thus, in looking at a near object,
we unconsciously estimate its distance and say it seems to be ten or twelve
feet off. But the estimate of its distance is in reality a judgment based on
many things besides the appearance of the object itself; among which may
be mentioned the number of intervening objects, the number of steps which
from past experience we know we must take before we could touch it, and
many others.
\
I. THE SENSES OF TOUCH, PAIN, TEMPERATURE, AND
THE MUSCLE SENSE.
The Sense of Touch. The sense of touch, like all the special
senses, possesses a special end-organ for the initiation of a nerve impulse
through contact with external objects. The sense organ of touch is not con-
fined to particular parts of the body of small extent, like the organ of sight,
for example, but is found in all parts of the skin and its inversions, the stomo-
cleum and proctodeum. The nerves of sensation are contained in the same
598 THE SENSES
trunks with other sensory nerves. They are found in the posterior or sen-
sory roots of the spinal nerves and in the sensory divisions of the cranial
nerves, especially the fifth, seventh, ninth, and tenth.
All parts of the epidermis supplied with sensory nerves are thus, in some
degree, organs of touch, yet the sense is exercised in greatest perfection in
certain parts, the sensibility of which is extremely delicate, e.g., the skin of
the hands, the tongue, and the lips, which are provided with abundant touch
papillae. A peculiar and very acute sense of touch is exercised through the
medium of the nails and teeth, and, to a less extent, the hair may be consid-
ered an organ of touch, as in the case of the eyelashes.
The sense of touch renders us conscious of the presence of a contact
stimulus, from the slightest to the most intense degree of its action. The
FIG. 420. — Touch Corpuscle.
modifications of this sense often depend on the extent of the parts affected.
The sensation of pricking, for example, is produced when the sensitive fibers
are intensely affected in a small extent; the sensation of pressure indicates
a slighter affection of the parts over a greater extent and depth. It is by the
depth to which the parts are affected that the feeling of pressure is dis-
tinguished from that of mere contact.
In almost all parts of the body which have delicate tactile sensibility the
epidermis, immediately over the dermal papillae, is moderately thin. When
its thickness is much increased, as over the heel, the sense of touch is very
much dulled. On the other hand, when it is altogether removed, and the
cutis laid bare, the sensation of contact is replaced by one of pain. Further,
in all highly sensitive parts, the papillae are numerous and highly vascular,
and the sensory nerves are connected with special end-organs which have
been described on page 72 et scq.
ACUTENESS OF THE SENSE 599
The special endings of the nerves which have to do with touch may, how-
ever, be here again mentioned. They are of two kinds, viz., i, Touch cor-
puscles, which are found chiefly in the hands and feet, particularly on the
palmar surface of the hands and fingers, but also on the under surface of the
forearm, on the nipple, eyelids, lips, and the genital organs. Touch corpuscles
are situated in the cutis vera. 2, End bulbs are found in the conjunctiva and
other mucous membranes, the lips, genital organs, tongue, rectum, and else-
where, but not in the skin proper. As regards the Pacinian corpuscles and
similar end-organs, which are so widely distributed, and which may be in some
way connected with the sensation, when they are found in the skin they are situ-
ated very deeply in the cutis vera or in the subcutaneous tissue. They are
extremely numerous on the nerves of the palmar surface of the fingers. In
addition to these special nerve endings, nerve fibers terminate everywhere in
the skin between the cells of the Malpighian stratum of the epidermis.
The acuteness of the sense of touch depends very largely on the cutaneous
circulation, which is of course greatly influenced by external temperature.
Hence the numbness, familiar to every one, produced by the application of
cold to the skin.
Acuteness of the Sense. The perfection of the sense of touch on
different parts of the surface is proportioned to the minimal pressure re-
quired to stimulate the point, i.e., the threshold stimulus. Or it can be
measured by the power which such parts possess of distinguishing and isolat-
ing the sensations produced by two points placed close together. This latter
is a measure of the power of localization in a degree. This power depends,
at least in part, on the number of primitive nerve fibers; for the fewer the
primitive fibers which an organ receives, the more likely is it that several
impressions on different contiguous points will act on only one nervous fiber,
and hence be confounded, and perhaps produce but one sensation. Experi-
ments have been made to determine the tactile properties of different parts
of the skin, as measured by this power of distinguishing distances between
points of simultaneous contact. These consist in touching the skin with the
points of a pair of compasses sheathed with cork, and in ascertaining how
close the points of the compasses might be brought to each other and still
be felt as two bodies.
TABLE or VARIATIONS IN THE TACTILE SENSIBILITY OF THE DIFFERENT PARTS OF
THE SKIN.
The measurement indicates the least distance at which the two blunted points of a pair
of compasses could be separately distinguished. (E. H. Weber.)
Tip of tongue, ........... i mm.
Palmar surface of third phalanx of forefinger, 2
Palmar surface of second phalanges of fingers, ..... 4
Red surface of under-lip, ......... 4
Tip of nose, 6
Middle of dorsum of tongue, ........
600 THE SENSES
Palm of hand, • . . 10
Center of hard palate, . . 12
Dorsal surface of first phalanges of fingers, . 14
Back of hand, . .25
Dorsum of foot near toes, . ..... 37
Gluteal region, . -37
Sacral region, . -37
Upper and lower parts of forearm, . . ... 37
Back of neck near occiput, . - .50
Upper dorsal and mid-lumbar regions, . . . . . . .50
Middle part of forearm, . .. . . . . . . 62
Middle of thigh, . . . * . . ' • 62
Mid-cervical region, . . ...... 62
Mid-dorsal region, . . . . . . . . .62
In the case of the limbs, before the points are recognized as two, they
have to be further separated when the line joining them is in the long axis of
the limb than when in the transverse direction.
According to Weber the mind estimates the distance between two points
by the number of unexcited nerve endings which intervene between the two
points touched. It would appear that a certain number of intervening un-
excited nerve endings is necessary before two points touched can be recognized
as separate, and the greater this number the more clearly are the points of
contact distinguished as separate. The delicacy of the sense of touch may
be very much increased by practice. A familiar illustration occurs in the
case of the blind, who, by constant practice, can acquire the power of reading
raised letters the forms of which are almost, if not quite, undistinguishable by
the sense of touch to an ordinary person.
The different degrees of sensitiveness possessed by different parts may
give rise to errors of judgment in estimating the distance between two points
where the skin is touched. Thus, if blunted points of a pair of compasses
(maintained at a constant distance apart) be slowly drawn over the skin of
the cheek toward the lips, it is almost impossible to resist the conclusion that
the distance between the points is gradually increasing. When they reach
the lips they seem to be considerably farther apart than on the cheek. Thus,
too, our estimate of the size of a cavity in a tooth is usually exaggerated when
based upon sensations derived from the tongue alone. Another curious
illusion may here be mentioned. If we close the eyes, and place a small
marble or pea between the crossed fore and middle fingers, we seem to be
touching two marbles, figure 480. This illusion is due to an error of judg-
ment. The marble is touched by two surfaces which, under ordinary cir-
cumstances, could be touched only by two separate marbles, hence the mind,
taking no cognizance of the fact that the fingers are crossed, forms the con-
clusion that two sensations are due to two marbles.
Sense of Temperature. The whole surface of the body is more or
less sensitive to differences of temperature. The sensation of heat is distinct
SENSE OF TEMPERATURE 601
from that of touch, hence it would seem reasonable to suppose that there are
special nerves and nerve endings for. temperature. At any rate the power of
discriminating temperature may remain unimpaired when the sense of touch
is temporarily in abeyance. Thus if the ulnar nerve be compressed at the
elbow till the sense of touch is very much dulled in the fingers which it sup-
plies, the sense of temperature remains quite unaffected. And in certain
diseases of the cord the sense of touch may be impaired in a part, and tem-
perature remain undisturbed, or the converse.
The mapping of the surface of a part of the skin with reference to its
sensibility to temperature reveals the fact that there are definite heat and
FIG. 421. — Diagram of a Part of the Hand, Showing Distribution of Sense Spots: for touch, A\
for heat, B; and for cold, C. In A the skin is sensitive except at the parts marked with black;
in B and C, the intensity of the shading represents the relative sensitiveness. (Goldscheider.)
cold spots. Furthermore, the areas do not coincide, leading us to conclude
that there are two distinct sense organs concerned, figure 421, B and C.
The sensations of heat and cold are often exceedingly fallacious, and in
many cases are no guide at all to the absolute temperature as indicated by
a thermometer. All that we can with safety infer from our sensations of
temperature is that a given object is warmer or cooler than the skin. Thus
the temperature of our skin is the standard; and as this varies from hour to
hour according to the activity of the cutaneous circulation, our estimate of
the absolute temperature of any body must necessarily vary too. If we put
the left hand into water at 5° C. (40° F.) and the right into water at 45° C.
(110° F.), and then immerse both in water at 27° C. (80° F.), it will feel warm
to the left hand, but cool to the right. Again, a piece of metal which has
really the same temperature as a given piece of wood will feel much colder,
since it conducts away the heat much more rapidly. For the same reason
air in motion feels very much cooler than air of the same temperature at rest.
In some cases we are able to form a fairly accurate estimate of absolute
temperature. Thus, by plunging the elbow into a bath, a practised bath-
attendant can tell the temperature sometimes within half a degree centigrade.
The temperatures which can be readily discriminated are between 10° and
602 THE SENSES
45° C. (50° and 115° F.); very low and very high temperatures alike produce a
burning sensation. A temperature appears higher according to the extent of
cutaneous surface exposed to it. Thus, water of a temperature which can be
readily borne by the hand is quite intolerable if the whole body be immersed.
The delicacy of the sense of temperature coincides in the main with that
of touch, and appears to depend largely on the thickness of the skin; hence,
in the elbow, where the skin is thin, the sense of temperature is delicate,
though that of touch is not remarkably so. Weber has further ascertained
the following facts: two points so near together on the skin that they
produce but a single impression, at once give rise to two sensations, when
one is hotter than the other. Moreover, of two bodies of equal weight, that
which is the colder feels heavier than the other.
As every sensation is attended with a perception and leaves behind it an
idea in the mind which can be reproduced at will, we are enabled to compare
the idea of a past sensation with another sensation really present. Thus we
can compare the weight of one body with another which we had previously
felt, of which the idea is retained in our mind. Weber was indeed able to
distinguish in this manner between temperatures experienced one after
the other, better than between temperatures to which the two hands were
simultaneously subjected. This power of comparing present with past sensa-
tions diminishes, however, in proportion to the time which has elapsed between
them. After-sensations left by impressions on nerves of common sensibility
or touch are very vivid and durable. As long as the condition into which
the stimulus has thrown the organ endures, the sensation also remains, though
the exciting cause should have long ceased to act. Both painful and pleasur-
able sensations afford many examples of this fact.
Sense of Pain. As regards painful sensations, three views can be
taken: i, That it is a special sensation provided with a special conducting
apparatus in each part of the body; 2, that it is produced by an over-stimula-
tion of the special nerves concerned with touch or temperature, or of the
other nerves of special sense; or 3, that it is an over-stimulation of the nerves
of common sensation, which tell us of the condition of our own bodies, both
of the surface and also of the internal organs. There seems to be much in
favor of all of these views. The weight of evidence is, however, rather against
there being any special pain sense with a special end-organ and fibers, though
Barker in his own arm experienced the presence of pain sensations while
there was absence of sensations of touch and temperature. It is, indeed,
certain that, even if any variety of pain be a special sensation, some kind of
pain may be produced by stimulation of the bare sensory nerves apart from
any special form of nerve termination. It is said that the main difference
between the common sensory apparatus which tells us of the condition of all
parts of the body of which thirst and hunger are but examples, and the
special sense of touch and temperature, is that the latter are provided with
THE MUSCULAR SENSE 603
a special local apparatus. By means of this apparatus we are able to local-
ize the sensation. Such a special apparatus is evidently not absolutely es-
sential for the sensation of pain, but this does not exclude the idea that pain
may result from over-stimulation of a nerve of special sense or of its termina-
tion.
The Muscular Sense. The estimate of a weight is usually based
on two sensations: i, of pressure on the skin, and 2, the sense of muscular
resistance.
The estimate of weight derived from a combination of these two sensations
(as in lifting a weight) is more accurate than that derived from the former
alone (as when a weight is laid on the hand) ; thus Weber found that by the
former method he could generally distinguish 19 J oz. from 20 oz., but not
19! oz. from 20, while by the latter he could at most distinguish only 14^ oz.
from 15 oz.
It is not the absolute, but the relative, amount of the difference of weight
which we have thus the faculty of perceiving.
It is not, however, certain, that our idea of the amount of muscular force
used is derived solely from the muscular sense. We have the power of esti-
mating very accurately beforehand, and of regulating, the amount of nervous
influence necessary for the production of a certain degree of movement.
WThen we lift a vessel, with the contents of which we are not acquainted, the
force we employ is determined by the idea we have conceived of its weight.
If it should happen to contain some very heavy substance, as quicksilver,
we shall probably fail in the attempt; the amount of muscular action, or of
nervous energy, which we had exerted being insufficient. It is possible that
in the same way the idea of weight and pressure in raising bodies, or in resist-
ing forces, may in part arise from a consciousness of the amount of nervous
energy transmitted from the brain rather than from a sensation in the muscles
themselves. The mental conviction of the inability longer to support a weight
must also be distinguished from the actual sensation of fatigue in the muscles.
So, with regard to the ideas derived from sensations of touch combined
with movements, it is doubtful how far the consciousness of the extent of
muscular movement is obtained from sensations in the muscles themselves.
The sensation of movement attending the motions of the hand is very slight;
and persons who do not know that the action of particular muscles is necessary
for the production of given movements, do not suspect that the movement
of the fingers, for example, depends on an action in the forearm. The mind
has, nevertheless, a very definite knowledge of the changes of position pro-
duced by movements; and it is on this that the ideas which it conceives of
the extension and form of a body are in great measure founded.
There is no marked development of common sensibility to be made out
in muscles: they may be cut without the production of pain. On the other
hand, there is no doubt that afferent impulses must pass upward from muscles
604 THE SENSES
and tendons acquainting the brain with their condition. This, then, must be
a special sense. It has been suggested that the minute end-bulbs of Golgi
found in tendons, and that the Pacinian corpuscles in the neighborhood of
joints, are the terminal organs of this special sense.
Judgment of the Form and Size of Bodies. By the sense of touch the mind
is made acquainted with the size, form, and other external characters of
bodies. And in order that these characters may be easily ascertained, the
sense of touch is especially developed in those parts which can be readily
moved over thexsurface of bodies. Touch, in its more limited sense, or the
act of examining a body by the touch, consists merely in a voluntary employ-
ment of this sense combined with movement, and stands in the same relation
to the sense of touch, or common sensibility, generally, as the act of seeking,
following, or examining odors does to the sense of smell. The hand is the
best adapted for it, by reason of its peculiarities of structure — namely, its
capability of pronation and supination, \fhich enables it, by the movement
of rotation, to examine the whole circumference of a body; the power it
possesses of opposing the thumb to the rest of the hand, and the relative
mobility of the fingers; and lastly from the abundance of the sensory terminal
organs which it possesses. In forming a conception of the figure and extent
of a surface, the mind multiplies the size of the hand or fingers used in the
inquiry by the number of times which it is contained in the surface traversed;
and, by repeating this process with regard to the different dimensions of a
solid body, acquires a notion of its cubical extent, but, of course, only an im-
perfect notion, as other senses, e.g., the sight, are required to make it complete.
It is impossible in this consideration to say how much of our knowledge
of the thing touched depends upon pressure and how much upon the mus-
cular sense.
II. TASTE AND SMELL.
The special sense organs for taste and smell are stimulated by chemical
substances, the former by chemicals in solution, the latter by volatile materials.
They are also closely associated in action and we do not always differentiate
between the two.
THE SENSE OF TASTE.
The conditions for the perceptions of taste are: i, the presence of a sense
organ, a nerve, and a nerve center with special endowments; 2, the excitation
of the sense organ by the sapid matters, which for this purpose must be in a
state of solution; 3, a temperature of about 37° to 40° C. (98° to 100° F.).
The Nerves and Organs of Taste. The principal organ of the sense
of taste is the tongue. But the soft palate and its arches, the uvula, tonsils,
THE NERVES AND ORGANS OF TASTE
605
and probably the upper part of the pharynx, are also endowed with taste.
These parts, together with the base and posterior parts of the tongue, are
supplied with branches of the glosso-pharyngeal nerve, and evidence has
been already adduced that this is the principal nerve of the sense of taste.
The anterior parts of the tongue, especially the edges and tip, are innervated
FIG. 422. — Papillar Surface of the Tongue, with the Fauces and Tonsils, i, Circurnvallate
papillae, in front of 2 , the foramen cecum ; 3, fungiform papillae; 4, filiform and conical papillae; 5,
transverse and oblique rugae; 6, mucous glands at the base of the tongue and in the fauces; 7,
tonsils; 8, part of the epiglottis; 9, median glosso-epiglottidean fold (frenum epiglottidis). (From
Sappey.)
by fibers from the lingual branch of the fifth, but which arise in the ganglion
of the pars intermedia and are distributed in the chorda tympani, figures 387
and 388.
The mucous membrane in the regions just mentioned possesses special
epithelial structures called taste buds. The taste buds are very abundant
606 THE SENSES
in the side walls of the circumvallate papillae. They are also present in the
fungiform papillae, in the foliate papillae, and in the mucous membrane.
The taste bud is located at the deeper part of the stratified epithelium, is
ovoid in shape, and its free end abuts on the surface or opens to the surface
by a short canal. It is composed of two kinds of modified epithelial cells —
the supporting cells, which are long, spindle-shaped cells that form a sheath
around the special gustatory cells; and the taste cells, which are neuro-epithe-
lial cells that are found in the center of the taste bud. They are very slen-
der cells that project on the surface by a delicate process. A bundle of nerve
fibrils enters the base of each taste bud and forms a net about the taste cells.
The circumvallate, the fungiform, and the filiform papillae, shown in
figure 422, are special structures that facilitate the stimulation of the taste
FIG. 423. FIG. 424.
FIG. 423. — Taste-Bud from Side Wall of Circumvallate Papillae. (Merkel-Henle.) a, Taste-
pore; b, nerve fibers, some of which enter the taste bud, intrageminal fibers, while others end freely
in the surrounding epithelium, intergeminal fibers.
FIG. 424. — Vertical Section of a Circumvallate Papilla of the Calf, i and 3, Epithelial layers
covering it; 2, taste goblets; 4, and 4' , duct of serous gland opening out into the pit in which the
papilla is situated; 5 and 6, nerves ramifying within the papilla. (Engelmann.)
buds by sapid substances. They are all formed by a projection of the mucous
membrane, and contain special branches of blood-vessels and nerves. In
details of structure, however, they differ considerably one from another.
Circumvallate Papillce. These papillae, figure 424, eight or ten in number,
are situated in tv*o V-shaped lines on the base of the tongue. They are
circular elevations from i to 2 mm. in diameter each, with a central depres-
sion, and surrounded by a circular fissure, at the outside of which is a
slightly elevated ring. Both the central elevation and the ring are formed
of close set simple papillae.
Fungiform Papillce. The fungiform papillae are scattered chiefly over
the sides and tip, and sparingly over the middle of the dorsum, of the tongue;
the name is deri ed from their being usually narrower at the base than at
the summit. They also are supplied with loops of capillary blood-vessels,
and nerve fibers.
TASTE SENSATIONS 607
Conical or Filiform Papillce. These, which are the most abundant
papillae, are scattered over the whole surface of the tongue, but especially
over the middle of the dorsum. They vary in shape somewhat, but for the
most part are conical.
Taste Sensations. The occurrence of two kinds of special sensi-
bility, i.e., touch and taste in the same part, makes it sometimes difficult to
determine whether the impression produced by a substance is perceived
through the ordinary tactile sensitive fibers, or through those of the sense of
taste. In many cases, indeed, it is probable that both sets of nerve fibers
are concerned, as when irritating acrid substances are introduced into the
mouth.
Many of the so-called tastes are due to the sapid substances being also
odorous, and exciting the simultaneous action of the sense of smell. This is
shown by the insipid tastes of certain substances when their action on the
olfactory nerves is prevented by closing the nostrils. Many of the popular
drinks lose much of their apparent excellence if the nostrils are held close
while they are drunk.
When these accessory sensations are taken into account it is found that
the clearly defined tastes are reduced to four: sweet, bitter, acid, and salt.
These taste sensations are produced by the respective substances when in
solution. If dry salt or quinine is placed on the surface of the tongue, no
taste appears until solution takes place in the secretions of the tongue. A
piece of metal, as a silver coin, gives rise to a seemingly distinct taste sensa-
tion, called metallic, but it is probably not to be accepted as coordinate with
the others. The acid taste may be excited by electricity. If a piece of zinc
be placed beneath and a piece of copper above the tongue, and their ends
brought into contact, an acid taste (due to the feeble galvanic current) is
produced. The delicacy of the sense of taste is sufficient to discern one part
of sulphuric acid in 10,000 of water, or one part of quinine in 200,000 of water.
But it is far surpassed in acuteness by the sense of smell.
ACUTENESS OF THE SENSE OF TASTE. (HALL.)
The average of 10 individuals.
Sugar i part to 520
Quinine i " " 444,000
Acetic Acid i " " 5,640
Salt i " " 469
Exploration of the taste areas reveals the fact that regions of the tongue
and mouth are not equally sensitive to the sapid substances. Sweet tastes
are especially developed at the tip and sides of the tongue, while bitter tastes
are almost absent in the front, but especially developed on the basal region,
and in the fauces and pharynx. Salts are more stimulating to the tip of the
608
THE SENSES
tongue, and acids along the sides. Individual tests of the fungiform papillae
by Oehrwall showed that about half the papillae reacted to sweet, bitter,
and acid, but that certain ones reacted only to sweet, or to sweet and bitter,
or to acid and bitter. This suggests the specific nature of the taste sensa-
tions and tends to prove that there may be a special organ for each kind of
stimulus. Experiments have also shown that it is possible to do away with
the power of tasting bitters and sweets while the taste for acids and salts
remains. This is done by chewing the leaves of an Indian plant, Gymnema
sylvestre. It has also been shown that the power of tasting sweet substances
disappears before that of tasting bitter. Other experiments have shown that
the mechanisms for salt and acid tastes are distinct.
After-tastes and Contrasts. Verv distinct sensations of taste are
FIG. 425. — Localization of Taste. Bitter ; acid ; salt, ; sweet ; T, tonsils;
FC, foramen cecum; CF, circumvallate papillae; FP, fungiform papillae. (Hall.)
frequently left after the substances which excited them have ceased to act
on the nerve, as the after-taste of metallic bitter, which remains after breaking
the stimulating current. Such sensations often endure for a long time, and
modify the taste of other substances applied to the tongue. Thus, the taste
of swv^et substances is intensified after the tasting of common salt. After
rinsing the mouth with water containing salt, it is said that sweet solutions
are perceived that are too dilute to be detected ordinarily. Many other
chemicals produce similar results. The application of a sapid substance,
acid for example, to one side of the tongue intensifies the sensation produced
by a sapid substance applied to the other side. There is a simultaneous con-
trast which suggests that the same relation exists between tastes as between
colors, of which those that are opposed, i.e., complementary, render each
THE SENSE OF SMELL, 609
other more vivid, though no general principles governing this relation have
been discovered in the case of tastes. In the art of cooking, however, atten-
tion has at all times been paid to the consonance or harmony of flavors in
their combination or order of succession, just as in painting and music the
fundamental principles of harmony have been employed empirically while
the theoretical laws were unknown.
Frequent and continued repetitions of the same taste render the perception
of it less and less distinct, in the same way that a color becomes more and
more dull and indistinct the longer the eye is fixed upon it. There is fatigue
of the taste organ at some point.
THE SENSE OF SMELL.
The sensation of smell is produced by the action of odorous particles on a
special end-apparatus, which in turn causes nerve impulses that arouse changes
in a special area in the sensorium. The stimulating cause is the direct action
of chemical substances as in the sense of taste. In this case, however, the
substances must reach the sensory membrane in a gaseous state, or in ex-
FIG. 426.— Nerves of the Septum Nasi, Seen from the Right Side. Xf .— /, The olfactory bulb;
i, the olfactory nerves passing through the foramina of the cribriform plate, and descending to
be distributed on the septum; 2, the internal or septal twig of the nasal branch ot the opntnai-
mic nerve; 3, naso-palatine nerves. (From Sappey, after Hirschfeld and Leveille.)
tremely fine division so that it can quickly enter into solution in the moisture
on the sensitive mucous surface. The odorous particles are carried to the
membrane by inspiratory currents of air.
The Olfactory Apparatus. The essential parts of the olfactory ap-
paratus are the nasal sensory or olfactory membrane to receive the special
stimuli, and the nervous apparatus to conduct the olfactory nerve-impulse to
the sensory area in the cortex cerebri for its perception.
The nose is not entirely an organ for the seat of smell. In fact the nasal
39
610 TJIK SENSES
cavities are divided into three districts called respectively: Regio vestibularis,
which is the entrance to the cavity. It is lined with a mucous membrane very
closely resembling the skin, and guarded by hairs and by sebaceous glands.
2, Regio respiratoria, which includes the lower and middle meatus of the
nose. It is covered with mucous membrane of stratified columnar ciliated
FIG. 427. — Nerves of the Outer Walls of the Nasal Fossae, i, Network of the branches of
the olfactory nerve, descending upon the region of the superior and middle turbinated bones;
2, external twig of the ethmoidal branch of the nasal nerves; 3, sphenq-palatine ganglion; 4,
ramification of the anterior palatine nerves; 5, posterior, and 6, middle divisions of the palatine
nerves; 7, branch to the region of the inferior turbinated bone; 8, branch to the region of the
superior and middle turbinated bones; 9, naso-palatine branch to the septum cut short. (From
Sappey, after Hirschfeld and Leveille".)
epithelium. The mucosa is thick and consists of fibrous connective tissue;
it contains a certain number of tubular mucous and serous glands, 3, Regio
oljactoria. This includes the anterior two-thirds of the superior meatus, the
middle meatus, and the upper half of the septum nasi, figures 427 and 428.
It is of a yellowish color. It consists of a thicker mucous membrane than
in 2, made up of loose, areolar connective tissue covered by epithelium of a
special variety, resting upon a basement membrane. The cells of the epithe-
lium are of two principal kinds: a, columnar epithelial cells whose function
is to support b, the bipolar olfactory cells. The epithelial cells are prismatic
in shape and have upon their surfaces facets into which the olfactory cells
fit themselves, figure 428, e. They are thus analogous to the cells of Miiller
of the retina. The olfactory cells have an oblong or fusiform shape, which
is mainly determined by the large nucleus. The thin protoplasmic body has
two processes, an external and an internal. The external is large and passes
up to the free surface, to end in a small bunch of fibrils that are not vibratile.
The internal process is very fine, often varicose, and passes through the
cribriform plate to form a glomerular basket with the branches of the mitral
cells of the olfactory bulb.
THE OLFACTORY Al'PAltATUS
611
The olfactory bulb must be studied in relation with the nerve fibers and
olfactory cells with which it is connected. These parts together form a sen-
sory end-organ which resembles in many respects the retina. The discovery
of its true structure has thrown a flood of light on the architecture of the nerve
centers as a whole.
The olfactory bulb is not a nerve, but a modification of the brain cortex.
A transection shows it to be made up of four layers: i, Peripheral fibers. 2,
Olfactory glomerules. 3, Layer of mitral cells.
4, Layer of granular cells and deep nerve fibers.
The first and external layer is composed of
the fine nerve fibrils of the olfactory nerves.
They pass through the cribriform plate of the
ethmoid, arising from the olfactory cells of which
they are processes.
The glomerular layer contains numbers of
small round bodies whose structure shows that
they are made up of the interlocking expansions
of the olfactory fibers, on the one hand, and of
the branches of the " mitral " cells, on the other.
These are mingled in a close network, but do not
anastomose. It was by the study of these bodies
in part that the fact of the non-continuity of the
neurones was demonstrated, figure 429. This
layer also contains small fusiform cells with
branching dendrites that extend outward to the
glomeruli. Each has an axis-cylinder process
which passes inward to join the fibers of the
internal olfactory nerves.
The layer of mitral cells contains large
cells, some of them triangular and some in the
shape of a miter. They have numerous den-
drites, one of which passes into a glomerulus and
then breaks up in a fine arborization. An axis-
cylinder process passes off from the inner surface
and is continued as an internal olfactory nerve fiber in the olfactory tract.
The layer of granules and central fibers contains a large number of very
small nerve cells, which are peculiar in that they have no axis-cylinder.
Their dendrites extend chiefly into the layer of mitral cells. They resemble
the spongioblasts of the retina and probably have commissural functions.
This layer has also some small star-shaped cells whose dendrites end in the
mitral-cell layer. Among these cells run numerous fibers, chiefly from the
mitral cells and the fusiform cells of the glomerular layer. The general ar-
rangement is shown in figure 429.
FIG. 428. — Bipolar Olfactory
Cells from the Nasal Fossae of
the Rat (Full-term Fetus). A,
Epithelium of the olfactory
mucosa; e, epithelial cells; /, f,
nerve cells; i, nerve fibers ter-
minating freely on the epithelial
surface; h, olfactory nerve fibers;
g, sensory nerve derived from the
trigeminus. (Cajal.)
612
THE SENSES
The Stimulation of the Olfactory Membrane. The extent of the
nasal mucous surfaces, and of the frontal and antral sinuses connected with
them, might suggest that the sensory olfactory surface is widely distributed,
but such is not the case. Air impregnated with vapor of camphor has been
injected into the frontal sinus through a fistulous opening, and odorous sub-
stances have been injected into the antrum of Highmore; but in neither case
was any odor perceived by the patient. All parts of the nasal cavities are
endowed with cutaneous sensibility by the nasal branches of the first and
FIG. 429-— Principal Constituent Elements of the Olfactory Bulb of a Mammal. (Van Gehuch-
ten.)
second divisions of the fifth nerve, hence the sensations of cold, heat, itching,
tickling, and pain, and the sensation of tension or pressure in the nostrils.
That these nerves cannot perform the functions of the olfactory nerves is
proved by cases in which the sense of smell is lost, while the mucous mem-
brane of the nose remains susceptible to the various modifications of the
sense of touch. But it is often difficult to distinguish the sensation of smell
from that of mere feeling, and to ascertain what belongs to each separately.
This is true particularly of the sensations excited by acrid vapors in the nose,
as of ammonia, horse-radish, mustard, etc., and the difficulty is the greater
when it is remembered that these acrid vapors have nearly the same action
upon the mucous membrane of the eyelids.
THE STIMULATION OF THE OLFACTORY MEMBRANE 613
The true olfactory membrane is limited to the small area on either side
of the superior meatus and supplied by the olfactory nerve. It is stimulated
by odorous substances when they penetrate the upper chamber of the nose.
Currents of air can be drawn over this membrane more certainly and effect-
ively by sniffing the air, as noticed in the acts of a dog following the trail.
The odorous particles must come into contact with the olfactory cells when
in solution in the moisture over the surface and produce its stimulus by chemi-
cal change. Mere presence in solution is not always adequate to a stimula-
tion. It seems that movement over the surface is necessary, at least to effective
stimulation. Haycraft has repeated some of the older experiments and finds
that eau de Cologne can be introduced into the nasal cavity in warm saline
solutions without producing a sensation of smell even when 10 per cent solu-
tions are used. He also showed that Cologne, bergamot, etc., can be slowly
diffused into the nasal cavity without producing a stimulus. If, while the
vapor is thus in the nasal cavity, the nostril be closed and the person goes
into pure air and breathes, then an odorous sensation is at once experienced.
This shows that even odorous gases "must be moved over the olfactory
surface" in order to produce a stimulus.
The presence of bodies in quantities so minute as to be undiscernible
even by spectrum analysis, 0.00000003 of a grain of musk, can be distinctly
smelt (Valentin). Opposed to the sensation of an agreeable odor is that of
a disagreeable or disgusting odor, which corresponds to the sensations of pain,
dazzling and disharmony of colors, and dissonance in the other senses. The
cause of this difference in the effect of different odors is unknown; but this
much is certain, that odors are pleasant or offensive in a relative sense only,
for many animals pass their existence in the midst of odors which to us are
highly disagreeable. A great difference in this respect is, indeed, observed
among men. Many odors, generally thought agreeable, are to some per-
sons intolerable; and different persons describe differently the sensations
that they severally derive from the same odorous substances. There seems
also to be in some persons an insensibility to certain odors, comparable with
that of the eye to certain colors; and among different persons, as great a
difference in the acuteness of the sense of smell as among others in the acute-
ness of sight. We have no exact proof that a relation of harmony exists /
between odors as between colors and sounds, though it is probable that such
is the case, since it certainly is so with regard to the sense of taste. Such a
relation would account in some measure for the different degrees of perceptive
power in different persons; for as some have no ear for music, so others have
no clear appreciation of the relation of odors, and therefore little pleasure
in them.
Most of the substances taken as foods into the mouth give off odorous
particles that stimulate the olfactory .membrane. In fact, the chief elements
in food flavors are not tastes, but smells, or combinations of the two. This
614 THE SENSES
is particularly true of meats. Meats are especially prized for their delicate
flavors, and cooking Is performed to bring out these flavors. Yet meat has
little taste other than salt; the so-called tastes are due to odorous particles
entering the nostril and stimulating the olfactory membrane at the same
moment the taste buds of the mouth are stimulated.
Subjective sensations occur frequently in connection with the sense of
smell. Often a person smells something which is not present, and which
other persons cannot smell; this is very frequent with nervous persons
but it occasionally happens to every one. In a man who was conscious of a
bad odor, the arachnoid was found after death to be beset with deposits of
bone, and a lesion in the middle of the cerebral hemispheres was also dis-
covered. Dubois was acquainted with a man who, ever after a fall from
his horse, which occurred several years before his death, believed that he
smelt a bad odor.
III. HEARING AND EQUILIBRATION.
THE ANATOMY OF THE EAR.
For descriptive purposes, the Ear, or Organ of Hearing, is divided into
three parts, i, the external, 2, the middle, and 3, the internal ear. The first
two are only accessory structures to the third, which contains the essential
parts of the organ of hearing. The accompanying figure, 430, shows very
well the relation of these divisions to each other.
The External Ear. The external ear consists of the pinna or
auricle and the external auditory canal or meatus.
The principal parts of the pinna, figure 430, are two prominent rims en-
closed one within the other, the helix and antihelix, and inclosing a central
hollow named the concha; in front of the concha, a prominence directed
backward, the tragus, and opposite to this one directed forward, the anti-
tragus. From the concha, the auditory canal passes inward and a little
forward to the membrana tympani, to which it thus serves to convey the
vibrations of the air. It consists of a fibre-cartilage tube lined by skin con-
tinuous with that of the pinna, and extending over the outer part of the mem-
brana tympani. Fine hairs and sebaceous glands are present toward the
outer part of the canal, while deeper in the canal are small glands, resembling
the sweat glands in structure, which secrete the cerumen.
Regarding the external ear, therefore, as a collector and conductor of
sonorous vibrations, all its inequalities, elevations, and depressions become
of evident importance; for those elevations and depressions upon which the
undulations fall will tend to intensify certain sound waves while not affecting
others. It is thought that this forms at least an aid in determining the direc-
tion whence a sound comes.
THE MIDDLE EAR OR TYMPANUM
615
The Middle Ear or Tympanum. The middle ear, or tympanum,
3, figure 430, is separated by the membrana tympani from the external auditory
canal. It is a cavity in the temporal bone, opening through its anterior and
inner wall into the Eustachian tube.
The Eustachian canal establishes communication between the tympanic
cavity and pharynx, thus equalizing the air pressure on the sides of the
FIG. 430. — Diagrammatic View from Before of the Parts Composing the Organ of Hearing of
the Left Side. The temporal bone 9f the left side, with the acc9mpanying soft parts, has been
detached from the head, and a section has been carried through it transversely, so as to remove
the front of the meatus externus, half the tympanic membrane, the upper and anterior wall of
the tympanum and Eustachian tube. The meatus internus has also been opened, and the bony
labyrinth exposed by the removal of the surrounding parts of the petrous bone, i, The pinna
and lobe; 2, 2', meatus externus; 2', membrana tympani; 3, cavity of the tympanum; 3', its
opening backward into the mastoid cells; between 3 and 3', the chain of small bones; 4, Eusta-
chian tube; 5, meatus internus, containing the facial (uppermost) and the auditory nerves; 6,
placed on the vestibule of the labyrinth above the fenestra ovalis; a, apex of the petrous bone;
b, internal carotid artery; c, styloid process; d, facial nerve issuing from the stylo-mastoid foramen;
e, mastoid process; /, squamous part of the bone covered by integument, etc. (Arnold.)
surface for incus; 5, head, 6, neck; 7, processus brevis; 8, manubrium; 9, body; 10, short proc-
ess; IT, long process; 12, processus longus; 13, head; 14, facet for incus; 15, manubrium, 16^
head; 17, neck; 18, crus anterius; 19, crus posterius; 20, foot plate.
616
THE SENSES
tympanic membrane, serving the same mechanical purpose as the vent-hole
in a snare or bass drum. The cavity of the tympanum communicates pos-
teriorly with air cavities, the mastoid cells, in the mastoid process of the tem-
poral bone; but its only opening to the external air is through the Eustachian
tube. The cavity of the tympanum is lined with mucous membrane, the
Recessus epitympanicus
Body of incus
Short process of incus
Ligament of incus
Chorda tympani nerve
Pyramid, with tendon
of stapedius muscle
jssviing from it
•Superfor'ligament of malleus
•Head of malleus
•Anterior ligament of malleus
-Handle of malleus
Foot of stapes
fij^- — Tensor tympani muscle
Osseous part of
Eustachian tubfl
FIG. 432. — Left Membrana Tympani and Chain of Tympanic Ossicles (Seen from Inner
Aspect). (Cunningham.)
epithelium of which is ciliated and continuous with that of the pharynx. It
contains a chain of small bones, ossicula auditus, which extends from the
membrana tympani to the fenestra ovalis.
The Membrana Tympani. The tympanic membrane is placed in a slant-
ing direction at the bottom of the external canal, its plane being at an angle
of about forty-five degrees with the lower wall of the canal. It is formed
chiefly of a tough and tense fibrous membrane, the edges of which are set
in a bony groove. Its outer surface is covered by a continuation of the epithe-
lial lining of the auditory canal, its inner surface with part of the mucous
membrane of the middle ear.
The Tympanic Ossicles. The ear bones, or ossicles, are named the
malleus, incus, and stapes. The malleus is attached by a long slightly curved
process, called its handle, to the membrana tympani, the line of attachment
being vertical, including the whole length of the handle, and extending from
the upper border to the center of the membrane. The head of the malleus
is irregularly rounded; its neck, or the line of boundary between it and the
handle, supports a short conical process which receives the insertion of the
tensor tympani muscle. The incus, shaped like a bicuspid molar tooth, is
articulated by its broader part to the malleus. Of its two fang-like processes,
one directed backward has a free end lodged in a depression in the mastoid
bone; the other, curved downward and more pointed, articulates by means
THE INTERNAL EAR (J17
of a roundish tubercle with the stapes. The stapes is a little bone shaped
exactly like a stirrup, of which the base or bar fits into the fenestra ovalis.
The stapedius muscle is attached to the neck of the stapes.
The bones of the ear are covered with mucous membrane reflected over
them from the wall of the tympanum. They are movable both altogether
and one upon the other. The malleus moves and vibrates with every move-
ment and vibration of the membrana tympani, and its movements are com-
municated through the incus to the stapes, and through the stapes to the
membrane closing the fenestra ovalis. The malleus, also, is movable in its
articulation with the incus. The membrana tympani which moves the long
process of the malleus is altered in its degree of tension by the degree of con-
traction of the tensor tympani muscles. The stapes is movable on the process
of the incus, the contractions of the stapedius muscle draws it outward. The
axis round which the malleus and incus rotate is the line joining the pro-
cessus gracilis of the malleus and the posterior process of the incus.
The Internal Ear. The internal ear, or labyrinth, constitutes the
proper organ of hearing. It contains special epithelial structures to which
arc distributed the auditory nerve. The organ is located in a cavity in the
petrous bone, called the osseus labyrinth. The auditory organ within is
FIG. 433. FIG. 434-
FIG. 433 . — Right Bony Labyrinth, Viewed from the Outer Side. The specimen here represented
is prepared by separating piecemeal the looser substance of the petrous bone from the dense walls
which immediately enclose the labyrinth, i, The vestibule; 2, fenestra ovalis; 3, superior semi-
circular canal; 4, horizontal or external canal; 5, posterior canal; *, ampullae of the semicircular
canals; 6, first turn of the cochlea; 7, second turn; 8, apex; 9, fenestra rotunda. The smaller
figure in outline below shows the natural size. X 2.5. (Sommering.)
FIG. 434. — View of the Interior of the Left Labyrinth. The bony wall of the labyrinth is re-
moved superiorly and externally, i, Fovea hemielliptica; 2, fovea hemispherica; 3, common
opening of the superior and posterior semicircular canals; 4, opening of the aqueduct of the
vestibule; 5, the superior, 6, the posterior, and 7, the external semicircula- canals; 8, spiral tube
of the cochlea (scala tympani) ; 9, opening of the aqueduct of the cochlea; 10, placed on the lamina
spiralis in the scala vestibuli. Xa.s. (Sommering.)
called the membranous labyrinth. The membranous labyrinth contains a
fluid called endolymph; while outside it, between it and the osseous labyrinth,
is a fluid called perilymph. This is not a pure lymph, as it contains mucin.
618
THE SENSES
The osseous labyrinth consists of three principal parts, namely the vesti-
bule, the cochlea, and the semicircular canals, containing the respective divisions
of the membranous labyrinth. The osseous labyrinth possesses openings on
its inner wall for the entrance of the divisions of the auditory nerve from the
cranial cavity, in its outer wall the jenestra ovalis, 2, figure 433, an opening
filled by the base of the stapes, and the fenestra rotunda. The vestibule
also presents an opening, the orifice of the aqueductus vestibuli,
The Membranous Labyrinth. The membranous labyrinth cor-
FIG. 435- — Membranous Labyrinth of a 30 mm. Human Fetus. A, Viewed from its Lateral
Aspect; B, viewed from the mesial aspect. (Streeter.)
responds generally with the form of the osseous labyrinth, so far as regards
the vestibule and semicircular canals, but is separated from the walls of these
parts by perilymph, except where the nerves enter into connection within it.
The labyrinth is a closed membrane containing endolymph.
The Utriculus and the Sacculus. The vestibular portion of the inner ear
consists of membranous sacs, the upper, the utriculus, the lower called the
sacculus. The former is connected with the semicircular canals, the latter
with the cochlea by the cochlear canal. The utriculus and the sacculus have
on their floors a special patch of sensory epithelium called the macula. The
fibers of the vestibular divisions of the auditory nerve end in the maculae,
THE COCHLEA AND THE ORGAN OF CORTI 619
figure 435. In the cavities of the sacculus and utriculus are small masses of
calcareous particles called otoliths.
The Semicircular Canals. There are three semicircular canals for each
ear, one horizontal and two vertical ones placed almost at right angles to
each other. The three canals, therefore, occupy the three planes of space.
Each has a considerable enlargement or swelling, called an ampulla. The
epithelium of the ampulla is modified at the point of entrance of the nerve
into a thickened hillock called the crista acustica. This epithelium is com-
posed of rod cells or supporting cells which extend the full thickness of the
crista, and of hair cells, which occupy the inner or free half of the crista.
The hair cells are the sensory cells. They have hair-like processes which
project from the free ends of the cells out
into the endolymph of the cavity. Nerve
fibrils run up into the crista and apparently
form terminal arborizations about the hair
cells, or, according to some observers, end
in the cells.
The Cochlea and the Organ of Corti.
The membranous cochlea is located in
the spiral canal in the petrous bone, called
the cochlear canal. It is attached to the paP; 4- scfit vestj^u: s, porous
substance of the modiolus near one of
wall of the cavity between the fenestra modioeiitioixs°f (Arnold")*1'8 spiralis
ovalis and the fenestra rotunda, and to the
outer wall of the canal and the free border of the lamina spiralis almost, but
not quite, to its summit. A small cavity is thus left around the upper end
of the cochlea connecting the scala vestibuli above with the scala tympani
below. A cross-section through the cochlear canal shows the relations of
the cochlear canal which was named scala media by the earlier anatomists.
The free portion of the membranous wall above is called the membrane of
Reisner, while that below is called the basilar membrane. The basilar mem-
brane supports the special sensory apparatus for the reception of stimuli
of sound waves.
Organ of Corti. The basilar membrane supports cells of several types.
About midway between the outer edge of the lamina spiralis and the outer
wall of the cochlea are situated the rods of Corti. Viewed sideways, they are
seen to consist of an external and internal pillar, each rising from an expanded
foot or base on the basilar membrane, figure 438. They slant inward
toward each other, and each ends in a swelling termed the head, the head of
the inner pillar overlying that of the outer, figure 438. Each pair of pillars
forms, as it were, a pointed roof arching over a space, and by a succession
of them a little tunnel is formed. It has been estimated that there are about
three thousand of these pairs of rods of Corti between the base of the cochlea
and its apex. They are found progressively to increase in length, and be-
THE SENSES
come more oblique; in other words, the tunnel becomes wider, but diminishes
in height as we approach the apex of the cochlea.
Leaning against the rods of Corti and apparently supported by them
are sensory cells or hair cells. The hair cells are in two series, the inner and
the outer hair cells. The former consist of a single layer, the latter of three
or four layers, figure 438. There are two additional types of supporting cells,
the cells of Deiters and of Hensen. The whole structure when viewed from
above bears a remarkable resemblance to the keyboard of a piano.
The cochlear division of the auditory nerve enters the base of the modiolus
and sends a spiral whorl of fibers out under the spiral lamina The gan-
FIG. 437- — Semidiagrammatic Section of a Cochlear Whorl. (After Heitemann.)
glionic cells of the cochlear division of the auditory nerve are located in the
base of the lamina where they form the spiral ganglion. The nerve fibers
from the ganglion cells pass out through small holes in the periphery of the
spiral plate of bone, to enter the organ of Corti. Here they form small longi-
tudinal bundles that quickly end about the hair cells.
THE PHYSIOLOGY OF HEARING.
All the acoustic contrivances of the organ of hearing are means for con-
ducting sound. Since all matter is capable of propagating sonorous vibra-
tions, the simplest conditions must be sufficient for mere hearing; since all
substances surrounding the auditory apparatus would stimulate it. The com-
plex development of the organ of hearing, therefore, must have for its object
THE PHYSIOLOGY OF HEARING
621
the more effective propagation of the sonorous vibrations and their intensi-
fication by resonance; and, in fact, the whole of the acoustic apparatus may
be shown to have reference to these principles.
The external ear and the auditory passages influence the propagation of
sound to the tympanum by collecting from the atmosphere the sonorous undu-
lations that strike against the external ear and by transmitting them by the
air in the passage to the membrana tympani.
In animals living in the atmosphere, the sonorous vibrations are con-
veyed to the auditory epithelium through three different media in series;
membrana tectoria,
outer hair-cells
inner rod vas basilar outer ceils of Deiten
membrane rod
FIG. 438. — Semidiagrammatic Representation of the Organ of Corti and Adjacent Structures.
(Merkel-Henle.) a. Cells of Hensen; b, cells of Claudius; c, internal spiral sulcus; x, Nuel's space.
The nerve fibers (dendrites of cells of the spinal ganglion) are seen passing to Corti's organ through
openings (foramina nervosa) in the bony spiral lamina. The black dots represent longitudinally
running branches, one bundle lying to the inner side of the inner pillar, a second just to the outer
side of the inner pillar within Corti's tunnel, the third beneath the outer hair cells.
namely, the air of the external ear and meatus, which sets in vibration the
tympanic membrane, the solid chain of auditory ossicles, and the fluid of the
labyrinth. Sonorous vibrations are imparted too imperfectly from air to
the solid structures of the body as a whole for the propagation of sound to
the internal ear to be adequately effected by that means alone. In passing
from air directly into water, sonorous vibrations suffer also a considerable
diminution of their strength; but if a tense membrane exists between the
air and the water, the sonorous vibrations are communicated from the former
to the latter medium with very great intensity, This fact, of which Miiller
gives experimental proof, furnishes at once an explanation of the use of the
fenestra ovalis and of the membrane closing it. It is the means of com-
municating, in full intensity, the vibrations of the ear bones, or, in their absence,
of the air in the tympanum, to the fluid of the labyrinth. The vibration of
the fluid, the perilymph and endolymph, of the internal ear, sets the basilar
membrane in vibration and in consequence stimulates the sensory apparatus
SL'iNSKS
resting upon it. This last is the essential stimulating act, while all that pre-
cedes is more or less accessory or contributory to this act. Just what the
accessory apparatus contributes can best be understood by an examination
of the stimulus and the sensation which results from its action.
Sound. Any elastic body, e.g., air, a membrane, or a string, per-
forming a certain number of regular vibrations per second, gives rise to
what is termed a musical sound or tone. We must, however, distinguish
between a musical sound and a mere noise; the latter being due to irregular
vibrations.
Musical sounds are distinguished from each other by three qualities:
i, Strength or Intensity, which is due to the amplitude or length of the wave
of vibrations. 2, Rate, the number of vibrations in a second. 3, Quality,
or Timbre, the peculiar property by which we distinguish the same note
sounded on two instruments, e.g., a piano and a flute. It has been proved
by Helmholtz to depend on the number of secondary tones, termed harmonics,
which are present with the predominating or fundamental tone. That is,
rhythmic vibrations are either simple in form, like the vibrations of a reed
or tuning fork, or compound, like the vibrations of a violin or piano string.
If the string of a violin is plucked it not only vibrates as a whole, but in seg-
ments in the ratio of one, two, three, etc. The form of air wave that is pro-
duced by several such vibrating bodies is very complex indeed, as, for example,
when an orchestra is playing.
The compound wave can be analyzed into its constituent elements by a
system of resonators, on the principle of sympathetic vibration. If one
sounds a series of musical notes before such a system of resonators it will be
found that the tones and overtones are selected by the resonators and made
more prominent so that they can be identified.
The sensation of sound has in it certain elements that correspond closely
with the physical properties of sound, i.e., loudness, pitch, and quality. Loud-
ness is dependent merely on the intensity of the stimulation. A sound wave
of great energy, for example, produces a larger movement of the tympanic
membrane, and it, through the chain of bones and the fluid of the internal
ear, a larger swing of the basilar membrane, hence a more intense stimulus
of the organ of Corti.
Function of the External and Middle Ears. It has already been
stated that the external ear collects the sound waves and conducts them
against the membrana tympani. This membrane vibrates as a whole to
the compound waves that impinge upon it, and thus serves for the trans-
mission of sound from the air to the chain of ossicles of the middle ear. It is
often compared to the membrane of a drum, but there are fundamental
differences.
When a drum is struck, a certain definite fundamental tone is elicited;
similarly a drum is thrown into vibration when certain tones are sounded in
FUNCTION" OF TIIK KXTKKXAL AM) M1DDLIO EARS (W.'J
its neighborhood, while it is quite unaffected by others. In other words, it
can take up and vibrate in response only to those tones whose vibrations
nearly correspond in number with those of its own fundamental tone. The
tympanic membrane can take up an immense range of tones produced by
vibrations ranging from 30 to 4,000 or 5,000 per second. This would be clearly,
impossible if it were an evenly stretched membrane. The fact is that the
membrana tympani is by no means evenly stretched, and this is due partly
to its slightly funnel-like form, and partly to its being connected with the
chain of auditory ossicles. Further, if the membrane were quite free in its
center, it would go on vibrating as a drum does some time after it is struck;
each sound would be prolonged, leading to considerable confusion. This
B
fie. 439- — Showing A and B, Simple Pendular Vibrations, Separated by One Octave. C,
The form of the curve produced by the combination of A and B.
evil is obviated by the ear bones, which check the continuance of the vibra-
tions like the "dampers" in a piano.
The vibrations of the membrana tympani are transmitted by the chain
of ossicles to the fenestra ovalis and fluid of the labyrinth, their dispersion
in the tympanum being prevented by the difficulty of the transition of vibra-
tions from solid to gaseous bodies. The necessity of the presence of air on
the inner side of the membrana tympani, in order to enable it and the auditory
ossicles to fulfil the objects just described, is obvious. Without this pro-
vision, neither would the vibrations of the membrane be free nor the chain
of bones isolated, so as to propagate the sonorous undulations with con-
centration of their intensity. But while the oscillations of the membrana
tympani are readily communicated to the air in the cavity of the tympanum,
those of the solid ossicles will not be conducted away by the air, but will
be propagated to the labyrinth without being dispersed in the tympanum.
The propagation of sound through the auditory ossicles to the labyrinth
must be effected by oscillations of the bones as a whole.
The existence of the membrane over the fenestra rotunda permits approxi-
624
THE SENSES
mation and removal of the stapes to and from the labyrinth. When the
membrane of the fenestra ovalis is pressed toward the labyrinth by the stapes,
the membrane of the fenestra rotunda may, by the pressure communicated
through the fluid of the labyrinth, be pressed toward the cavity of the tym-
panum. The long process of the malleus receives the undulations of the
membrana tympani, figure 440, a, a, and of the air in a direction indicated
by the arrows, nearly perpendicular to itself. From the long process of the
malleus they are propagated to its head, b; thence into the incus, c, the
long process of which is parallel with the long process of the malleus. From
the long process of the incus the undulations are
communicated to the stapes, d, which is united
to the incus at right angles. The several changes
in the direction of the chain of bones have, how-
ever, no influence in changing the character of
the undulations, which remain the same as in
the meatus externus. From the long process
of the malleus the undulations are communi-
cated by the stapes to the fenestra ovalis in a
perpendicular direction. Increasing tension of
the membrana tympani diminishes the facility of
transmission of sonorous undulations from the
air to it. It has been inferred, therefore, that
hearing is rendered less acute by increasing the
tension of the membrana tympani. This is ac-
complished by the contractions of the tensor
tympani muscle. The exact influence of the
stapedius muscle in the act of hearing is un-
known. It acts upon the stapes in such a
manner as to make it rest obliquely in the fenestra ovalis, depressing that
side of the stapes on which it is attached and elevating the other side to
the same extent. It seems to prevent too great a movement of the bone.
The pharyngeal orifice of the Eustachian tube is usually shut. During
swallowing, however, it is opened; which may be shown as follows: If the
nose and mouth be closed and the cheeks blown out, a sense of pressure is
produced in both ears the moment we swallow. This is due, doubtless, to
the bulging out of the tympanic membrane by the compressed air, which at
that moment enters the Eustachian tube. The principal office of the Eusta-
chian tube has relation to the prevention of the effects of increased tension of
the membrana tympani. Its existence and openness will provide for the
maintenance of the equilibrium between the air within the tympanum and
the external air, so as to prevent the inordinate tension of the membrana
tympani which would be produced by too great or too little pressure on either
side. While discharging this office it serves as an outlet for mucus. If the
FIG. 440. — Diagram to Illus-
trate the Action of the Ossicles
of the Middle Ear in the Conduc-
tion of Sound to the Internal
Ear.
THE FUNCTION OF THE INTERNAL EAR 625
tube were permanently open, the sound of one's own voice would probably
be greatly intensified, a condition which would of course interfere with the
perception of other sounds. At any rate, it is certain that sonorous vibra-
tions can be propagated up the tube to the tympanum by means of a catheter
inserted into the pharyngeal orifice of the Eustachian tube.
The Function of the Internal Ear. The fluids of the labyrinth re-
ceive the sonorous vibrations at the fenestra ovalis and, we must assume,
conduct the same throughout the cavity. In all forms of organs of hearing
even to the simplest, liquid is the medium through which the auditory sen-
sory epithelium is stimulated. We have already seen that in the mammalian
ear there is a special mechanical arrangement to intensify the vibrations of
the fluid in the cochlear canal.
The utriculus, sacculus, and semicircular canals are probably not concerned
with auditory function, but with the sense of equilibrium; hence they will
be discussed separately a little later.
The cochlea is the special organ of hearing. When it is set in vibrations
the movement stimulates the sensory hair cells on the basement membrane,
producing a sensory impulse which is transmitted along the paths to the brain
and there produces an auditory sensation. If the stimulus results from a
disturbance of an explosive or non-harmonic nature, the sensation is inter-
preted as a noise. If the disturbance is rhythmic or harmonic and repeated
in sequence within certain limits of rate, then a tone is perceived.
The intensity of sound, the energy of the disturbance, affects the basilar
membrane by producing motion of varying amplitude. This stimulates the
hair cells with greater or less intensity, which can be detected by the sensorium
as loudness. Loudness of the sound sensation is interpreted as intensity of
sound wave.
The interpretation of pitch is accomplished by the ear through a wide
range of rates of vibration that produce sensations of tone. The average
person can perceive musical tones over a range of vibration of from sixty-four
double vibrations per second for the lower notes, to four thousand and ninety-
six for the higher notes. These limits may be extended to thirty per second
and forty thousand per second, respectively, but only a small number of
tones can be perceived outside of the narrower limits given above. This
extraordinary range of tone is conceivable only on the supposition of local-
ization of the stimulus in some part of the organ. Most physiologists look
to the basilar membrane and the organ of Corti for the localization.
Suppose a simple tuning fork to be vibrating with a frequency of sixty-
four per second, then these waves will be conducted through the auditory
apparatus until they fall on the basilar membrane, and will set it in vibration
at the same rate. The exact type of the vibration is at present a matter of
inference. The piano theory of Helmholtz is probably the most satisfactory.
It assumes that the basilar membrane vibrates as would a number of strings
40
626 THE SENSES
set in the transverse dimension. In support of this assumption it is asserted
that the membrane is taut in the transverse and loose in the longitudinal
plane. Retzius has estimated that it contains about 24,000 fibers, and that
it measures in width at the base 0.135 mm. and at the apex 0.234 mm. In
the above illustration the vibration frequency of sixty-four would supposedly
set in sympathetic vibration that part of the apex of the basilar membrane
which vibrated in the same frequency, and the sensory cells of the organ of
Corti, located over the vibrating fiber, would be stimulated accordingly. In
the same way notes of medium and of high frequency stimulate localized
areas of sensory cells in the middle and basal parts of the organ of Corti and
produce sensations of corresponding pitch.
This idea of localization of auditory sensory stimulation makes it easier
to understand the analysis by the ear of compound sonorous waves. Such
waves impinge on the membrana tympani and are transmitted through the
conducting media unanalyzed, and may be supposed to fall on the basilar
membrane as compound waves. The basilar fibers acting like so many
resonators, take up the constituent sonorous elements in sympathetic vibra-
tion. In short, the basilar membrane is an analyzer in which the compound
wave is reduced to its simple components, each of which stimulates its cor-
responding portion of the organ of Corti. The auditory nerve impulses are
conducted through the cochlear nerves to the sensorium where they produce
auditory sensations with the same definiteness of pattern as cutaneous or
optical stimuli produce sensations that correspond to the patterns of stimula-
tion. The audition is so definite that one can consciously pick out one or
the other of the constituent stimulating elements and follow and examine
the same to the exclusion of the others, as when one follows a single instru-
ment in an orchestra or a single voice in a group of chattering children.
Bernstein says of this wonderful organ :
" In the cochlea we have to do with a series of apparatus adapted for per-
forming sympathetic vibrations with wonderful exactness. We have here
before us a musical instrument which is designed, not to create musical
sounds, but to render them perceptible, and which is similar in construction
to artificial musical instruments, but which far surpasses them in the delicacy
as well as the simplicity of its execution. For, while in a piano every string
must have a separate hammer by means of which it is sounded, the ear pos-
sesses a single hammer of an ingenious form in its ear bones, which can make
every string of the organ of Corti sound separately."
Auditory Judgments. Direction. The power of perceiving the
direction of sounds is not a faculty of the sense of hearing itself, but is an act
of the mind judging on experience previously acquired. From the modifica-
tions which the sensation of sound undergoes according to the direction in
which the sound reaches us, the mind infers the position of the sounding
body. The only true guide for this inference is the more intense action of the
AUDITORY JUDGMENTS 627
sound upon one than upon the other ear. But even here there is room for
much deception, by the influence of reflexion or resonance, and by the propaga-
tion of sound from a distance, without loss of intensity, through curved con-
ducting tubes filled with air. By means of such tubes, or of solid conductors,
which convey the sonorous vibrations from their source to a distant resonant
body, sounds may be made to appear to originate in a new situation. The
direction of sound may also be judged of by means of one ear only; the position
of the ear and head being varied, so that the sonorous undulations at one
moment fall upon the ear in a perpendicular direction, at another moment
obliquely. But when neither of these circumstances can guide us in dis-
tinguishing the direction of sound, as when it falls equally upon both ears,
its source being, for example, either directly in front or behind us, it becomes
impossible to determine whence the sound comes.
Distance. The judgment of the distance of the source of sounds is in-
ferred from their intensity. The sound is interpreted as coming from an
exterior sonorous body. When the intensity of the voice is modified in imita-
tion of the effect of distance, it excites the idea of its originating at a distance
Ventriloquists take advantage of the difficulty with which the direction of
sound is recognized, and also the influence of the imagination over our judg-
ment, when they modulate the voices, and at the same time pretend, them-
selves, to hear sounds as coming from a certain direction.
Duration of the Auditory Stimulus. By removing one or several teeth
from the toothed wheel of a vibrator, the fact has been demonstrated that in
the case of the auditory organ, as in that of the eye, the sensation continues
longer than the impression which causes it; for a removal of the tooth pro-
duced no interruption of the sound. The gradual cessation of the sensation
of sound renders it difficult to determine its exact duration beyond tha-t of
the impression of the sonorous impulses.
Binaural Sensations. Corresponding to the double vision of the same
object with the two eyes is the double hearing with the two ears; and analo-
gous to the double vision with one eye, dependent on unequal refraction, is
the double hearing of a single sound with one ear, owing to the sound coming
to the ear through media of unequal conducting power. The first kind of
double hearing is very rare; instances of it, however, have been recorded.
The second kind, which depends on the unequal conducting power of two
media through which the same sound is transmitted to the ear, may easily
be experienced. If a small bell be sounded in water, while the ears are closed
by plugs, and a solid conductor be interposed between the water and one
ear, two sounds will be heard differing in intensity and tone ; one being con-
veyed to the ear through the medium of the atmosphere, the other through
the conducting-rod.
Subjective Sensations. Subjective sounds are the result of a state of irri-
tation or excitement of the auditory nerve produced by other causes than
628 THE SENSES
sonorous impulses. A state of excitement of this nerve, however induced,
gives rise to the sensation of sound. Hence the ringing and buzzing in the
ears heard by persons of irritable and exhausted nervous system, and by
patients with cerebral disease, or disease of the auditory nerve itself; hence
also the noise in the ears heard for some time after a long journey in a rattling,
noisy vehicle. Ritter found that electric currents also excite sounds in the
ears. From the above truly subjective sound we must distinguish those
dependent, not on a state of the auditory nerve itself merely, but on sonorous
vibrations excited in the auditory apparatus. Such are the buzzing sounds
attendant on vascular congestion of the head and ear or on aneurismal dilata-
tion of the vessels. Frequently even the simple pulsatory circulation of the
blood in the ear is heard. To the sounds "of this class belong also the buzz
or hum, heard during the contraction of the palatine muscles in the act of yawn-
ing, during the forcing of air into the tympanum so as to make tense the
membrana tympani.
Irritation or excitement of the auditory nerve is capable of giving rise to
movements in the body and to sensations in other organs of sense. In both
cases it is probable that the laws of reflex action, through the medium of the
brain, come into play. An intense and sudden noise excites, in every person,
closure of the eyelids, and, in nervous individuals, a start of the whole body
or an unpleasant sensation throughout the body like that produced by an
electric shock.
THE SENSE OF EQUILIBRIUM.
Although the utriculus, sacculus, and semicircular canals form the major
part of the labyrinth and are closely associated with the cochlea in develop-
ment, there is increasing evidence that these structures are not concerned
with hearing, but rather with a sense of equilibrium. This view has been
strengthened by recent investigations into the anatomical relations of the
different elements in the auditory nerve, figure 435.
These structures have each a special modification of the sensory epithelium
which receives the vestibular branch of the eighth nerve. These epithelial
areas are differentiations of the embryonic ear pit, which is derived from the
epiblast. In fishes which have well-developed semicircular canals and vesti-
bule, this sensory epithelium has a common origin from the embryonic anlage
which gives rise to the ear, the branchial sense organ, and the lateral line
organs, all of which probably have static functions.
The Semicircular Canals. The semicircular canals are connected
with the utriculus, are three in number on each side, and have been already
shown to lie in space practically at right angles to one another. Each is
filled with endolymph, and each has a special organ, the crista acustica,
which receives a division of the vestibular branch of the eighth nerve.
THE SEMICIRCULAR CANALS 629
The function of the semicircular canals is believed to be to give rise to
sensations by which we determine the motion of the body in space. It was
shown long ago that if one closes his eyes and turns rapidly around the vertical
axis, then suddenly stops and opens the eyes, surrounding objects seem to
be rotating around this same vertical axis. If the head be inclined so that
the face is in the horizontal plane and the rotation around the vertical axis
be repeated, then, upon suddenly raising the head into the ordinary position
and opening the eyes, objects seem to be moving about the head around the
horizontal axis. In both these cases the direction of the apparent motion
of objects depends upon the actual motion of the body that preceded it and
is in the opposite direction. In the first case the rotation is in the plane of
the horizontal circular canal. It is assumed here that, at the beginning of
such a movement, the endolymph, being fluid and inert, tends to remain still
for a moment and the canal to move over it so as to produce pressure in the
funnel of the ampulla. That is, it has the same effect as though the endo-
lymph moved in the canal. This relative motion bends the hairs of the hair
cells of the crista acustica, thus stimulating the hair cells and giving rise to
sensory nerve impulses. When the head suddenly stops rotating the situa-
tion is just reversed and there will be a second stimulation, but in the opposite
direction. When one considers the position of the three semicircular canals,
it will be seen that movement of the head in any direction will stimulate one
or more of the cristae, giving rise to either simple or complex sensory impulses.
This theory is borne out by the effects of operation on the semicir-
cular canals. By the observations of Flourens, injury to the semicircular
canals causes disturbances in muscular coordination, especially in move-
ments that take place in the plane of the injured canal. If a horizontal canal
in a pigeon be sectioned, the animal supports its head in the vertical position
very well, but is unable to coordinate its horizontal movements. It tends to
produce rotary motions around the vertical axis. If a vertical canal is sec-
tioned, the head falls to one or the other side according to the canal, and the
animal shows instability of position in that plane. It has been shown that
stimulation of a sectioned canal produced reflex movements in that plane.
Muscular coordination is a complex phenomenon and involves operation
of numerous sensory impulses from other organs of the body, especially from
the eye and general skin. Some confusion has arisen from the fact that there
are associated with the disturbance in the semicircular canals movements
of the eyes and head in higher animals, and of the eyes, head, and fins in such
animals as fishes — the so-called compensatory movements. Without going
into details, it is sufficient to state that the sense organs of the semicircular
canals probably form only one of the series of sensory structures concerned
in the coordination of movements.
The Utriculus and Sacculus. The utriculus and sacculus each have
a sensory area, the maculae, over which there rests in the human ear
630 THE SENSES
and in most animals small particles of calcareous matter, otoliths. These
otoliths, therefore, lie among the projecting hairs of the sensory cells. This
is characteristic of these sensory areas and differentiates them from the
arrangement present in the cristae. There would seem to be close agree-
ment in function between the maculae and cristae, and we naturally look to
the influence of the otoliths on the processes which result in the stimulation
of the maculae. Attempts have been made to remove the otoliths, with the
result that in such animals there Is apparent inability to maintain a constant
position in space. The experiments have been performed which have sug-
gested the theory that the otoliths take an active part in stimulating the sen-
sory cells, probably by their mere pressure. If the head is inclined in one
or the other direction, the pressure of the otoliths will shift on the hair cells,
and that is sufficient to stimulate them. If this view is correct, then we may
regard these structures as static in function as compared with the semicircular
canals, which are dynamic. The anatomical separation of the nerves for the
cochlea from the division for the utriculus, sacculus, and semicircular canals
itself suggests isolation in function, figures 389 and 435. It is conceivable
that loud noises of an explosive nature may cause sufficient vibration of the
endolymph to affect the otoliths and thus stimulate the cristae. Yet, if such
stimulation takes place it is probably only of secondary importance.
IV. THE SENSE OF SIGHT.
THE EYE.
The eye, the organ of vision, is the most complex and most highly devel-
oped of the organs of special sense. It consists not only of a special sen-
sory epithelium, the retina, sensitive to light stimulation, but of a series of
special structures which intensify and localize the stimulus. There are also
accessory organs for the protection of the eye.
The Eyelids and Lachrymal Apparatus. The eyeball is kept
moist over its free surface and protected from external injury by the eyelids,
by the glands that secrete the lachrymal fluid to moisten the surface of the
cornea, and by the oil glands that secrete oil on the margins of the lids.
The conjunctiva , or lining membrane of the lids, which is reflected on to
the free surface of the eyeball, protects the eye from injury by its extraor-
dinary sensitiveness to irritation by dust or other external substance. Its
stimulation produces reflex secretion of the lachrymal fluid that flows over
the surface of the eye, and tends to wash away the stimulating substance.
The Eyeball and its Parts. The detail of the structure of the eye-
ball is too complex to be given here except in so far as seems necessary for a
clearer presentation of the physiological facts. A gross dissection reveals
THE CORNEA
631
the tough, white, sclerotic coat; the intermediate thin, vascular, pigmented
choroid coat; and the inner nervous coat, the retina.
The section also shows that the eyeball is specialized in structure in its
anterior region and that its contained cavity is divided into two parts, viz.,
Posterior chamber
Canal of Schlemro
Suspensory liga!
Equator
FIG. 441. — Section of the Eyeball.
the anterior and posterior chambers are filled with the transparent aqueous
fluid. This fluid is like lymph in its composition. The vitreous chamber
between the lens and the retina is filled with the clear jelly-like vitreous
substance.
The Cornea. The sclerotic coat is continuous with the cornea in
front of the eyeball, but the cornea is transparent and its radius of curvature
FIG. 442.— Vertical Section of Rabbit's Cornea, a, Anterior epithelium, showing the different
shapes of the cells at various depths from the free surface; b, portion of the substance of cornea.
(Klein.)
is less than that of the main portion of the eye. It is composed of strati-
fied epithelial cells, and is richly supplied with sensory nerves that form
an intra -epithelial plexus of delicate varicose fibrils. The cornea has no blood-
vessels, but has a rich network of lymphatic spaces.
632 THE SENSES
The Lens. The lens is a special modification composed of highly
refractive material, situated just behind the iris. It is enclosed in a capsule
and supported in its place by the suspensory ligament, which is fused into
the capsule around its equator. The lens is a biconvex structure composed
of transparent fibers which are arranged in concentric layers. Its posterior
curvature is greater than the anterior, the radii being 6 and 10 mm. respectively.
The Ciliary Apparatus and the Iris. These structures are a con-
tinuation and modification of the choroid coat in' the anterior portion of the
eye. Around the circumference of the cornea the choroid coat is consider-
ably thickened and folded in the modification known as the ciliary apparatus.
A radial layer of muscle, figure 445, is knitted into the base of the cornea, on
the one hand, and extends back into the choroid, on the other. Thick bundles
of the circular fibers are also present in this mass of muscle. From the ciliary
FIG. 443- FlG- 444.
FIG. 443. — Ciliary Processes, as Seen from Behind, i, Posterior surface of the iris, with the
sphincter muscle of the pupil; 2, anterior part of the choroid coat; 3, one of the ciliary processes,
of which about seventy are represented. Xi.
FIG. 444. — Laminated Structure of the Crystalline Lens. The laminae are split up after hard-
ening in alcohol, i, The denser central part or nucleus; 2, the successive external layers. X4.
(Arnold.)
processes, extending over the lens, is the iris. It is a sheet of connective tissue
and muscle lined with epithelium and highly pigmented.
In the middle anterior portion is a round aperture, the pupil. The mus-
cle fibers are arranged circularly and radially and are of the unstriated muscle
type. Contractions of the circular muscles of the iris produce constriction
of the pupil, while contractions of the radial fibers produce dilatation. Both
the ciliary apparatus and the iris are supplied with motor nerves.
Fibers of the third cranial nerve are distributed to the ciliary muscles,
apparently to both radial and circular muscles, and when these nerves are
stimulating the resulting contractions of the muscles tend to remove the tension
from the capsule of the lens. These nerve fibers pass through the ciliary
ganglion where they form a synapsis with ganglionic cells. Motor fibers
from the third cranial nerve also supply the circular muscles of the iris, which
produce constriction of the pupil through the motor nerves by way of the
STRUCTURE OF THE RETINA
633
cervical sympathetic and superior cervical ganglion, and the ophthalmic branch
of the fifth cranial nerve.
Structure of the Retina. The retina occupies the deeper half of the
cup of the eyeball. It extends forward as far as the ora serrata, where its
complex structure changes the form to a simple epithelial layer, which lines
the anterior portion of the eyeball and the ciliary processes. In the center
of the retina is a round yellowish spot having a minute depression in its center,
called the yellow spot of Sommering. The depression in its center is the
anterior ciliary arteries and
greater arterial circle
angle of the iris
meridional fibres
ciliary muscle
llmbus of cornea
anterior chamber
«pithelium
anterior limiting!
membrane I
mlar spaces
posterior chamber
epithelium of lei
capsule of lens
posterior limiting membrane
stroma of iris
posterior surface of iris
sphincter of pupil
FIG. 44S-— Meridional Section of a Portion of the Anterior Part of the Eyeball. (Toldt.)
fovea centralis. About 2.5 mm. to the inner side of the yellow spot is the
point at which the optic nerve enters and spreads out its fibers into the retina.
The optic nerve arises from the base of the brain and passes forward
toward the orbit, being covered by the membranes which cover the brain.
The fibers of the optic nerve are exceedingly fine, and are surrounded by the
myelin sheath, but do not possess the ordinary external nerve sheath. As
they pass into the retina they lose their myelin sheaths and proceed as axis-
cylinders (the cells of origin of these fibers are in the retina). Neuroglia
supports the nerve fibers in the optic nerve trunk. In the center of the nerve
is a small artery, the arteria centralis retina. The number of fibers in the
634
THE SENSES
optic nerve is said to be upward of 500,000. The fibers of the optic nerve
spread out over the inner surface of the retina as far as the ora serrata.
The retina itself consists of layers of nerve elements supported by deli-
cate connective tissue. The older descriptions recognize some eight or ten
layers in the retina, but the newer investigations of Cajal, Golgi, Retzius,
and others have shown that the retina is a much simpler structure than hereto-
fore described. The retina is formed of essentially three layers of nerve cells.
Stratum
pigment!
1 Stratum
opticurii
Membrana limitans interna
FIG. 446. — Section of Human Retina. (Cunningham, modified from Schulze.)
Naming from the center of the eye outward, they are: The ganglionic layer;
the layer of bipolar cells; and the layer of rods and cones, figure 447. The
cells of these layers have numerous fibrous processes which interlock in such a
way that they seem to form different areas when studied in cross-section. If
we recognize the strata of interlacing fibers, then the following may be
made out:
The layer of ganglion cells.
The layer of bipolar cells . .
The layer of visual cells. . .
. Ganglionic layer, with the fibers of the optic nerve.
. Internal molecular layer,
j 3. Internal granular layer.
I 4. The external molecular layer.
( 5. The external granular layer.
| 6. The layer of rods and cones.
STRUCTURE OF THE RETINA
635
The Nerve Fiber and Nerve Cell Layers. The inside of the retina is
formed of a layer of nerve fibers which have their origin in the adjacent large
nerve cells and run toward the exit of the optic nerve. Externally the gan-
H
FIG. 447. — Transverse Section of a Mammalian Retina. A, Layer of rods and cones; B, bodies
of visual cells (external granular) ; C, external molecular layer; E, layer of bipolar cells (internal
granular); F, internal molecular layer; G, layer of ganglionic cells; H, layer of optic-nerve fibers;
a, rod; b, cone; c, body of the cone cell; d, body of the rod cell; e, bipolar rod cells: /, bipolar cone
cells; g, h, i, j, k, ganglionic cells ramifying in the various strata of the internal molecular zone;
r, inferior arborization of the bipolar rod cells, connecting with the ganglionic cells; r, inferior
arborization of the bipolar cone cells; t, epithelial or Miiller cells; x, point of contact between the
rods and their bipolar cells; z, point of contact between the cones and their bipolar cells; s, centrif-
ugal nerve fiber. (Cajal.)
glionic cells send up numerous processes, or dendrites, which interlace with
the fibers of the bipolar cells of the second layer.
The Middle Layer. The middle layer consists of bipolar cells which send
one process toward the ganglionic layer to interlace with the dendrites of the
FIG. 448.— Perpendicular Section of the Retina of a Mammal. A, External grains or bodies of
rods; B, bodies of cones; a, horizontal external or small cell; b, horizontal internal or large cell; c,
horizontal internal cell with descending protoplasmic appendages; e, flattened arborization of one
of the large cells; f, g, h, j, I, spongioblasts ramifying in the various strata of the internal m< lec:
ularzone; ra, n, diffuse spongioblasts; o, ganglionic cell; i, external
molecular zone. (Cajal.)
molecular zone; 2, internal
636
THE SENSES
ganglionic cells, and one process externally. This process is often divided
into many branches, which separate out into a horizontal brush, interlacing
with the processes of the rods and cones. Special cells have been described
for this layer of the retina, as, for example, the spongioblasts of Cajal.
The External Layer of Rods and Cones. The rod cells are composed of
two parts quite different in structure, known as the outer and inner limbs.
The outer limb is a cylindrical rod about 30 /j. long by 2 p. in diameter. It is
transparent and composed of doubly refractive material. The inner limb
of the cell is about the same length as the outer, is similar, and is longitudinally
striated, and contains a nucleus on its course, figure 447, d.
The cone cells are also made up of two limbs, the outer of which is conical
instead of cylindrical as in the case of the rods. In other respects they are
similar to the rods in structure, with the exception that the inner limb ends
in a brush of fibrils which interlace with the bipolar cells of the middle layer.
FIG. 449. — Distribution of the Rods and Cones. A, In the peripheral part of the retina;
B, from the region of the macula lutea.
In man and mammals the number of rod cells are much greater than the cones,
but it is said that in birds cones predominate. Even in man the center of the
fovea centralis is devoid of rods and consists of cones only, figure 450.
All the elements of the retina are sustained and isolated by large cells
lying vertically which are known as the -fibers of Mutter. The nucleus of the
fiber of Miiller is found at the level of the internal granular layer, and the
two extremities of the protoplasm or cell body are condensed in two homo-
geneous layers, known as the external and the internal limiting layer. The
external limiting layer is placed just between the two segments of the rod
and cone cells. The internal limiting layer is situated upon the internal
surface of the retina.
At the ora serrata the layers are not perfect and disappear in this order:
nerve fibers and ganglion cells, then the rods, leaving only the inner limbs of
the cones, these cease, then the inner molecular layer. The Mlillerian fibers
persist.
STRUCTURE OF THE RETINA
637
At the pars ciliaris retinae, the retina
is represented by a layer of columnar
cells, derived from the fusion of the
nuclear layers which are in contact with
the pigment layers of the retina and con-
tinued over the ciliary processes.
Pigment Layer. This layer, which
was formerly considered part of the
choroid, consists of cells which cover
and entirely surround the outer limbs
of the rods and cones.
Blood-vessels oj the Eyeball. The
eye is very richly supplied with blood-
vessels. In addition to the conjunc-
tival vessels, which are derived from the
palpebral and lachrymal arteries, there
are at least two other distinct sets
of vessels supplying the tunics of the
eyeball, i, The vessels of the sclerotic,
choroid, and iris, and 2, the vessels of
the retina. The first are the short and
long posterior ciliary arteries which
pierce the sclerotic in the posterior half
of the eyeball, and the anterior ciliary
which enter near the insertions of the
recti. These vessels anastomose and
form a very rich choroidal plexus;
they also supply the iris and ciliary
processes, forming a very highly vas-
cular circle round the outer margin
of the iris and adjoining portion of
the sclerotic. The distinctness of
these vessels from those of the con-
junctiva is well seen in the difference
between the bright red of blood-shot
eyes (conjunctival congestion), and the
pink zone surrounding the cornea
which indicates deep-seated ciliary con-
gestion.
The central artery of the optic nerve
enters the retina from the center of
the optic disc and sends out branches
over the retinal cup lying in the nerve
FIG. 450. — Diagrammatic Section of the
Macula Lutea and Fovea Centralis. 2,
Layer of nerve fibers; 3, layer of multi-
polar cells; 4, internal molecular layer,
composed of intertwining arborescent proc-
esses; 5, layer of bipolar cells, or internal
granular layer; 6, external molecular layer,
composed of intertwining arborescent proc-
esses; 7, nuclei of epithelial cells, or ex-
ernal granular layer; 8, frillwork formed
by processes from fibers of Miiller, often
called the "external limiting membrane ";
9, layer of rods and cones; 10, layer of
pigment epithelium.
638
THE SENSES
fiber layer, figure 451. These blood-vessels, however, are absent from the
fovea centralis and reduced in size in the macula lutea, figures 451 and 452.
FIG. 451. — Diagram of the Blood-vessels of the Human Retina. (Leber, after Jaeger.) ans,
vns, Superior nasal artery and vein; ats, vts, superior temporal artery and vein; ani, vni, inferior
nasal artery and vein; ati, vti, inferior temporal artery and vein; am, vm, macular artery and vein;
ane, vme, median artery and vein.
FIG. 452. — Blood-vessels of the Macula Lutea. The part that is totally free from vessels is
the fovea centralis.
THE OPTICAL APPARATUS.
The optical apparatus may be supposed, for the sake of description, to
consist of several parts; i, A system of transparent refracting surfaces and
media by means of which images of external objects are brought to a focus
upon the back of the eye; 2, a sensitive screen, the retina, which is a special-
ized sensory apparatus in connection with the terminations of the optic nerve,
and capable of being stimulated by luminous objects, and of sending such
impressions as to produce in the brain visual sensations. To these main
REFRACTIVE MEDIA AND SURFACES 639
parts may be added, 3, an apparatus for focussing light from objects at differ-
ent distances from the eye; and 4, since both eyes are usually employed in
vision, an arrangement by means of which the eyes may be turned in the
same direction so that binocular vision is possible. The arrangement of
the optic nerve fibers, and of the continuation of these backward in the optic
chiasma, and thence to special districts of the brain have already been dis-
cussed.
The eye may be compared to a photographic camera, and the transparent
refracting media correspond to the photographic lens. In a camera images
of external objects are thrown upon a screen, the sensitive plate, at the back
of the camera box. In the eye, the camera proper is represented by the eye-
ball with its choroidal pigment, the sensitive screen by the retina, and the
lens by the refracting media. In the case of the camera, the screen is adjusted
to receive clear images of objects at different distances by an apparatus for
focussing. The corresponding adjustment in the eye is accomplished by
the accommodating apparatus.
Refractive Media and Surfaces. At first sight it would seem as if
the refracting apparatus of the eye were very complicated, since it consists
of so many parts. These parts are: the anterior surface of the cornea itself,
the posterior surface of the cornea, the aqueous humor, the anterior surface
of the lens, the substance of the lens itself (which is unequally refractive),
the posterior surface of the lens, and the vitreous humor. Thus there are
four surfaces, and at least, including the air, five media. For all practical
purposes, however, we may leave out of consideration all but three refracting
surfaces and their adjacent media. These are: the anterior surface of the
cornea, separating the air and the corneal substance; the anterior surface
of the lens, separating the aqueous humor and the lens substance; and the
posterior surface of the lens, separating the lens surface from the vitreous
humor.
Image Formation. In the refraction through a simple transparent
spherical surface there are certain cardinal points to be considered. The
rays of light which fall perpendicularly on such a surface pass through with-
out refraction. All such rays cut the center of the radius of curvature of the
lens, called the nodal point. A line that passes through the center of curva-
ture of a lens and thus pierces the nodal point is called the optical axis, and
the point on the surface pierced by the optical axis is the principal point.
In every optical system there are certain other cardinal facts to be considered.
All rays which do not strike vertical to the curved surface are refracted
toward the optical axis. Rays which impinge upon the spherical surface of
a lens parallel to the optical axis will meet at a point upon the axis called the
posterior principal focus, figure 453, F. The posterior principal focus is
outside of the nodal point. Again, there is a point in the optical axis in front
of the surface, rays of light from which strike the surface so that they are
640
THE SENSES
refracted in a line parallel with the axis, df; such a point, F2, is called the
anterior principal focus.
In any given system the principal foci can be found by erecting verticals
at the nodal and principal points of the optical axis and laying off lengths
on each, a and Z>, proportional to the refractive indices of the media. A line
drawn through a on the principal vertical and b on the nodal vertical will cut
the optical axis at the posterior principal focus, and vice versa.
FIG. 453. — Diagram of a Simple Optical System. (Foster.) The curved surface, bd, is sup-
posed to separate a less refractive medium toward the left from a more refractive medium toward
the right.
If a luminous point outside the anterior principal focus is considered,
it is obvious that rays from it will be so refracted when they enter the convex
surface that they will become converging and will ultimately meet again in
a point or focus. Two such points form conjugate foci, figure 454. If the
anterior focus of a conjugate is moved away from the anterior principal focus,
then the posterior conjugate will move toward the posterior principal focus,
and the converse. If one conjugate is known, the other can be found as
FIG. 454.— Diagram to Show the Relations of Conjugate Foci, cd. Refracting surface; AB
and ba, conjugate foci; o, nodal point; F", posterior principal focus.
follows: From a point in the plane of the known conjugate, but outside the
principal axis, draw two rays, one perpendicular to the refracting surface
which will pass through the nodal point, the other parallel to the principal
axis. The latter will be refracted through the posterior principal focus and
when prolonged will meet the first ray in the plane of the second conjugate,
figure 454, a. This relationship between conjugate foci is played upon in the
focussing of a camera.
IMAGE FORMATION 641
It is quite obvious that the eye, even considering only the three surfaces
above indicated, is a much more complicated optical apparatus than the one
described in the figure. It is, however, possible to reduce the refractive
surfaces and media to a simpler form when the refractive indices of the dif-
ferent media and the curvature of each surface are known. All of these
data have been very carefully collected. They are as follows :
Index of refraction of aqueous and vitreous, ....
" " " " the lens, ....'..
Radius of curvature of cornea,
" anterior surface of lens,
" " " posterior " " ...
Distance from anterior surface of cornea and anterior surface of lens
Distance from posterior surface of cornea and posterior surface of lens
I-336S
I-4371
7.829 mm.
10. o
6.0
3-6
7-2
With these data it has been found comparatively easy by mathematical
calculation to reduce the different refractive surfaces of the different curva-
tures into one mean curved surface of known curvature, and the differently
refracting media into one mean medium the refractive power of which is
known.
The simplified or so-called schematic eye, formed upon this principle,
suggested by Listing as the reduced eye, has the following dimensions:
From the anterior surface of the cornea to the principal point, . = 2.3448 mm
From the nodal point to the posterior surface of lens, . . . = 0.4764 "
Posterior chief focus lies behind cornea, . . . . . = 22.8237 *'
Anterior chief focus in front of cornea, . . . . . = 12.8326 '
Radius of curvature of ideal surface, . . . . . . = 5.1248 '
In this reduced or simplified eye the principal posterior focus, about
23 mm. behind the spherical surface, would correspond to the position of
the retina behind the anterior surface of the cornea. The refracting surface
would be situated about midway between the posterior surface of the cornea
and the anterior surface of the lens.
The optical axis of the eye is a line drawn through the centers of curva-
ture of the cornea and lens, and when prolonged backward it cuts the retina
between the optic disc and the fovea centralis. This differs somewhat from
the visual axis which passes through the nodal point of the reduced eye to
the fovea centralis, and forms an angle of five degrees with the optical axis.
The visual or optical angle is the angle included between the lines drawn
from the borders of any object through the nodal point. It has been shown
by Helmholtz that the smallest angular distance between two points which
can be appreciated is fifty seconds, the size of the retinal image being 3.65 /*;
this practically corresponds to the diameter of the cones at the fovea centralis
which is 3 /*, the distance between the centers of two adjacent cones being 4 /*.
The image of an object formed upon the retina may be considered as a
series of points, from each of which a pencil of light diverges to the eye, and
41
642
THE SENSES
this pencil has for its center or axis a ray which impinging upon the refrac-
tive surface perpendicularly to the surface is not refracted, but passes through
the nodal point and is prolonged backward to the retina, whereas the diverging
rays are also made to converge to a principal posterior focus behind the lens,
FIG. 455. — Diagram of the Method of the Formation of an Inverted Image Exactly Focussed
upon the Retina. The dotted line is the ideal surface of curvature.
or the chief axis of the pencil of light proceeding from the point in question,
and this focus, if the image is to be clear, should fall on the retina.
Thus from each point of an object a corresponding image is formed on
the retina, so that an image of the distant object is produced. It is an inverted
image. Whether the image is blurred or not depends upon the refractive
power of the media, and upon the distance of the anterior surface of the cornea
from the retina. If the refractive media are too powerful, or the eye too long,
the image is formed in front of the retina, figure 456 ; if the reverse, the image
FIG. 456. — Diagram of the Course of a Ray of Light, to Show how a Blurred or Indistinct Image
is Formed if the Object be not Exactly Focussed upon Retina. The surface CC should be supposed
to represent the ideal curvature. The nodal point should be nearer the posterior surface of lens
as in figure 455.
is formed behind the retina, and in both cases an indistinct and blurred image
is the result.
Accommodation. The distinctness of the image formed upon the
retina is mainly dependent on the perfection with which the rays emitted
by each luminous point of the object are brought to a focus upon the retina.
ACCOMMODATION 643
If this focus occurs at a point either in front of or behind the retina, indis-
tinctness of vision ensues, in the way we have just described, with the pro-
duction of a halo. The focal distance, i.e., the distance of the point at
which the luminous rays are collected from a lens, besides being regulated
by the degree of convexity and density of the lens, varies with the distance
of the object from the lens, being greater as this is shorter, and vice versa.
In other words, the luminous points on the object and the focal points on the
retina are conjugate foci. Hence, since objects placed at various distances
from the eye can within certain limits be seen with almost equal distinctness,
there must be some provision by which the eye is enabled to adapt itself, so
that, at whatever distance the luminous object may be, the focal point may
always fall exactly upon the retina.
Accommodation is the act of adapting the eye to vision at different distances.
It is obvious that the effect might be produced in either of two ways, viz.,
i, by altering the convexity, and thus the re-
fracting powrer, either of the cornea or of the
lens; or 2, by changing the position of the
lens relative to the retina, as in the focussing
of a camera, so that whether the object be
near or distant, the focal points to which the
rays are converged by the lens may always
fall exactly on the retina. The amount of
either of these changes which is required
in even the widest range of vision is ex-
tremely small, for from the refractive powers
of the media of the eye the difference be- °{J^-ot
tween the focal distances of the images *£?$?&
of an object at a distance and of one at
four inches is only about 3.5 mm. On
this calculation the change in the distance of the retina from the lens re-
quired for vision at all distances, supposing the cornea and lens to remain
the same, would not be more than about one line. Beer has shown that the
second method is indeed the type of accommodative apparatus in fishes.
But in man and the higher animals accommodation occurs by the first
method, i.e., by changing the convexity of the refracting surface.
The accommodation of the human eye for objects at different distances is
primarily due to a varying shape of the lens, its front surface becoming more
or less convex, according as the distance of the object looked at is near or
far. The nearer the object, the more convex the front surface of the lens,
up to a certain limit, and vice versa ; the back surface takes little or no share
in accommodation. The following simple experiment illustrates this point:
If a lighted candle be held a little to one side of a person's eye, an observer
looking at the eye from the other side sees three distinct images of the flame,
644
THE SENSES
figure 457. The first and brightest is, i, a small erect image formed by the
anterior convex surface of the cornea; the second, 2, is also erect, but larger
and less distinct than the preceding, and is formed at the anterior convex
surface of the lens; the third, 3, is smaller, inverted, and indistinct; it is
formed at the posterior surface of the lens, which is concave forward, and
FIG. 459.
FIG. 458. — Diagram of Sanson's Images. A, When the eyes are focussed for far objects, and
B, when they are focussed for near objects. The figure to the right in A and B is the inverted
image from the posterior surface of the lens.
FIG. 459. — Phakoscope of Helmholtz. At B, B', are two prisms, by which the light of a candle
is concentrated on the eye of the person experimented with at C. A is the aperture for the eye
of the observer. The observer notices three double images, as in figures 457 and 458, reflected from
the eye under examination when the eye is fixed upon a distant object; the position of the images
having been noticed, the observed eye is then focussed on a near object, such as a reed pushed up
by C; the images from the anterior surface of the lens will be observed to move toward each other,
in consequence of the lens becoming more convex.
therefore, like all concave mirrors, gives an inverted image. If now the eye
under observation be made to look at a near object, the second image be-
comes smaller, clearer, and approaches the first. If the eye be now adjusted
for a far point, the second image enlarges again, becomes less distinct, and
recedes from the first. In both cases alike the first and third images remain
unaltered in size, distinctness, and relative position. This proves that during
accommodation for near objects the curvature of the cornea, and that of the
posterior surface of the lens, remain unaltered, while the anterior surface of
the lens becomes more convex and approaches the cornea.
The experiment, figure 458, is more striking when the two prisms of the
phakoscope which form two images of the candle are used. The pair of
images of the candle from the front surface of the lens not only approach
those from the cornea during accommodation, but also approach one another,
and become somewhat smaller, Sanson's images.
THE MECHANISM OF ACCOMMODATION 645
The Mechanism of Accommodation. The mechanism of accommo-
dation depends primarily upon the inherent tendency of the lens to approxi-
mate the shape of a sphere. When the eye is at rest the intra -ocular tension
is such as to put stress on the suspensory ligament around its equator, which
compresses the elastic lens in its antero-posterior dimension. The elasticity
of the lens can make itself apparent when the tension of the suspensory liga-
ment is relaxed. This takes place completely after a division of the fibers
of the zonula. When we remove the lens from the eye of a young person,
we see it assume the spherical shape immediately upon the division of its
connections. In life this slackening of the tension of the suspensory liga-
ment of the lens is brought about by the contraction of the fibers of the ciliary
body. This allows the anterior surface of the lens to become more convex,
by its own elastic powers, thus focussing entering rays of light from a near
object upon the retina, figure 460. It therefore appears that when the eye
is at rest it is focussed for distant objects, inasmuch as the suspensory liga-
ment is taut and the anterior surface of the lens more flattened. The normal
eye is passive when in focus for distant objects. It is the active contraction
of the muscles of accommodation that focusses for near objects. The iris
acts in coordination with the accommodative contractions of the ciliary mus-
cles. In viewing near objects the pupil contracts, and upon viewing distant
ones it dilates.
Range of Distinct Vision. Near-point. In every eye there is a limit to
the power of accommodation. If a book be brought nearer and nearer to the
FIG. 460.— Diagram Representing by Dotted Lines the Alteration in the Shape of the Lens on
Accommodation for Near Objects. (E. Landolt.)
eye, the type at last becomes indistinct, and cannot be brought into focus
by any effort of accommodation, however strong. This limit, which is termed
the near-point, can be determined by the experiment of Scheiner. Two
small holes not more than 2 mm. apart are pricked in a card with a pin; at
any rate their distance from each other must not exceed the diameter of the
pupil. The card is held close in front of the eye, and a small needle viewed
646
THE SENSES
through the pin-holes. At a moderate distance it can be. clearly focussed,
but when brought nearer, beyond a certain point, the image appears double
and more or less blurred. This point where the needle ceases to appear single
is the near-point of vision. Its distance from the eye can of course be readily
FIG. 461. — Diagram of Experiment to Ascertain the Minimum Distance of Distinct Vision.
measured. It is usually about five or six inches, 12 to 15 cm. In the accom-
panying figure, 461, the lensfr represents the eye; «,/, the two pin-holes in the
card, nn the retina ; a represents the position of the needle. When the needle
is at a moderate distance, the two pencils of light coming from e and / are
focussed at a single point on the retina nn. If the needle be brought nearer
FIG. 462. — Diagram of the Axes of Rotation of the Eye. The thin lines indicate axes of
rotation, the thick the position of muscular attachment.
than the near-point, the strongest effort of accommodation is not sufficient
to focus the two pencils, they meet at a point behind the retina. The effect
is the same as if the retina were shifted forward to mm. Two images h, g, are
formed, one from each hole. It is interesting to note that when in this way
REFLEXES OF THE PUPIL
647
two images are produced, the lower one g really appears in the position Q,
while the upper one appears in the position P. This may be readily verified
by covering the holes in succession.
During accommodation two other changes take place in the eyes. The
eyes converge by the action of the extra-ocular muscles, chiefly by the internal
and inferior recti or internal and superior recti. The pupils contract.
Movements of the Eye. The eyeball possesses movement around three axes indicated
in figure 462, viz., an antero-posterior, a vertical, and a transverse, passing through a
center of rotation a little behind the centre of the optic axis. The movements are ac-
complished by pairs of muscles.
Direction of Movement.
Inward, ....
Outward, ....
Upward,
Downward, ....
Inward and upward,
Inward and downward, .
Outward and upward,
Outward and downward,
By what muscles accomplished.
Internal rectus.
External rectus.
( Superior rectus.
| Inferior oblique.
j Inferior rectus.
/ Superior oblique.
Internal and superior rectus.
Inferior oblique.
j Internal and inferior rectus.
( Superior oblique,
j External and superior rectus.
\ Inferior oblique,
j External and inferior rectus.
( Superior oblique.
The contraction of all of the muscles during the act of accommodation, viz.,
of the ciliary muscle, of the recti muscles, and of the sphincter pupillae, is
under the control of the fibers of the third nerve. But the superior oblique
may also be employed, in which case the fourth nerve is concerned.
Reflexes of the Pupil. Contraction of the iris may occur under the
following circumstances: i, On exposure of the eye to a bright light; 2, On
the local application of eserine (active principle of Calabar bean); 3, On the
administration internally of opium, aconite, and in the early stages of chloro-
form and alcohol poisoning; 4, On division of the cervical sympathetic or of
stimulation of the third nerve. Dilatation of the pupil occurs, i, in a dim
light; 2, when the eye is focussed for distant objects; 3, on the local applica-
tion of atropine and its allied alkaloids; 4, on the internal administration of
atropine and its allies; 5, in the later stages of poisoning by chloroform,
opium, and other drugs; 6, on paralysis of the third nerve; 7, on stimulation
of the cervical sympathetic, or of its center in the floor of the front of the
aqueduct of Sylvius. The contraction of the pupil is under the control of
a center in the floor of the aqueduct beneath the anterior corpora quadri-
gemina. This center is reflexly stimulated by a bright light, and the dilata-
tion when the center is not in action is due to the stimulation of the radial
fibers of the iris by sympathet* nerves. In addition, it appears that both
648 THE SENSES
contraction and dilatation may be produced by a local action of certain drugs
which is independent of and probably often antagonistic to the action of the
central apparatus of the third and sympathetic nerves.
The close coordination between the two eyes is nowhere better shown
than by the condition of the pupil. If one eye be shaded by the hand its
pupil will of course dilate; the pupil of the other eye will also dilate, though
unshaded, due to crossed reflex action.
Defects in the Optical Apparatus. Under this head we may con-
sider the defects known as: i, Spherical Aberration; 2, Chromatic Aberra-
tion; 3, Astigmatism; 4, Myopia; 5, Hypermetropia.
The normal or emmetropic eye is so perfect that parallel rays are brought
exactly to a focus on the retina without any effort of accommodation, figure
466. Hence all objects except near ones (in practice all objects at a distance
of twenty feet or more) are seen without any effort of accommodation; in
other words, the far-point of the normal eye at rest is at an infinite distance.
In viewing near objects we are conscious of the effort (the contraction of
the ciliary muscle) by which the anterior surface of the lens is rendered
more convex, and rays which would otherwise be focussed behind the retina
are converged upon the retina.
Spherical Aberration. The rays of a cone of light from an object situated
in the field of vision do not all meet in the same point, owing to the greater
refraction of the rays which pass through the circumference of a lens than
that of those traversing its central portion. This defect is known as spherical
aberration. In the camera, telescope, microscope, and other optical instru-
ments it is remedied by the interposition of a screen with a circular aperture
in the path of the rays of light, cutting off all the marginal rays and allow-
ing the passage only of those near the center. Such correction is effected
in the eye by the iris, which forms a diaphragm to cover the circumference of
the lens, and prevents the rays from passing through any part of the lens
but its center, which corresponds to the pupil. The iris is pigmented to pre-
vent the passage of rays of light through its substance. The image of an
object will be most defined and distinct when the pupil is small, if the light
is abundant; so that, while a sufficient number of rays are admitted, the
narrowness of the pupil may prevent the production of indistinctness of the
image by spherical aberration. But even the image formed by the rays passing
through the circumference of the lens, when the pupil is much dilated, as in
the dark, or in a feeble light, may, under certain circumstances, be well defined.
Distinctness of vision is further secured by the pigment of the outer sur-
face of the retina and of the posterior surface of the iris and the ciliary proc-
esses, which absorbs any rays of light that may be reflected within the eye,
and prevents their being thrown again upon the retina so as to interfere
with the images formed there. The pigment of the retina is especially im-
portant in this respect; for with the exception of its outer layer the retina is
DEFECTS IN THE OPTICAL APPARATUS 649
very transparent; and if the surface behind it were not of a dark color, but
capable of reflecting the light, the luminous rays which had already acted
on the retina would be reflected again and would fall upon other parts of
the same membrane, producing indistinctness of the images.
Chromatic Aberration. In the passage of light through the periphery of
an ordinary convex lens, decomposition of each ray into its elementary colored
parts commonly ensues, and a colored margin appears around the image,
owing to the unequal refraction which the elementary colors undergo. This
is termed chromatic aberration. It is corrected by the use of lenses constructed
of alternate layers of glass of different refractive indices so ground that they
produce chromatic dispersion in opposite directions and thus mutually correct
any chromatic aberration which may have resulted. The human eye has
considerable chromatic aberration, as may readily be demonstrated, experi-
ment 13, page 673.
An ordinary ray of white light in passing through a prism has its con-
stituent rays refracted in unequal degrees, and therefore appears as colored
bands fading off into each other, known as the spectrum. The colors of the
spectrum are arranged as follows: red, orange, yellow, green, blue, indigo,
violet; of these the red ray is the least, and the violet the most, refracted.
Hence, as Helmholtz has shown, the rays from a white point cannot be ac-
curately focussed on the retina, for if we focus for the red rays, the violet are
out of focus, and vice versa: such objects, if not exactly focussed, are often
seen surrounded by a pale yellowish or bluish fringe.
For similar reasons a red surface looks nearer than a blue one at an equal
distance, because, the red rays being less refrangible, a stronger effort of
accommodation is necessary to focus them, and the eye is adjusted as if for
a nearer object, and therefore the red surface appears nearer, experiment 13.
Astigmatism. This defect, which was first discovered by Airy, is due to
a greater curvature of the refractive surfaces of the eye in certain meridians
than in others. Thus vertical and horizontal lines crossing each other can-
not both be focussed on one plane; one set stands out clearly, and the others
are blurred and indistinct. This defect, which is generally present in a slight
degree in all eyes, is usually seated in the cornea, but occasionally in the
lens as well.
The plane of greatest curvature in the cornea is usually in the vertical
meridian, a fact which doubtless comes from the pressure of the eyelids during
development. If one looks at figure 463, A or B, with one eye, the three lines
in the radii of the figure will be seen with unequal distinctness. Certain
sets will stand out sharp and black and others dim and with indistinct out-
lines, and if the astigmatism is great enough the three lines may not be dis-
tinguished. Figures C and D of this series enable one to detect minute traces
of astigmatism with great accuracy.
It is somewhat difficult to picture the rays from a luminous point in their
650
THE SENSES
courses through eyes which have this defect, but an examination of figure
464 will show their refraction. In this figure four rays coming from the
point L in the arrows are represented as striking on the refractive surface
of the eye atA,B, C, D, and being converged toward a focus. The rays A, C,
separated by vertical line on the refractive surface, are focussed at flt while the
lines A, B, separated by the horizontal distance on the refractive surface, are
ABC
FIG. 463. — Astigmatic Charts.
brought to a focus at /2. The point L, therefore, has two apparent focal points,
one point composed of the rays that strike in a horizontal plane, /2, the other
of rays that strike in a vertical plane, /r If the retina of the eye be placed
at /! it will see an image of a point with indistinct horizontal rays. If placed
at the position /2 it will see a luminous point with indistinct rays in the
vertical plane* If the series of points in the arrow MN be considered,
it is evident that at the position fl the rays which fall in the vertical plane
will form distinct foci, while those that fall in the horizontal plane will form
overlapping diffuse images in that plane. Since they are overlapping, they
will not appear separate except at the ends of the image of the arrow, and the
arrow will therefore be seen distinctly. If the position /2 is considered
where the rays of the horizontal plane are focussed, then it is evident that
FIG. 464. — The Unequal Refraction of Rays in an Astigmatic Eye. (John Green.)
the points in the arrow MN will present a series cf rays or halos in the
vertical plane, thus rendering its outline very dim or indistinct. The condi-
tion with the arrow OP is exactly the reverse. Hence, in the astigmatic
eye the images of the horizontal arrow MN will be distinct at the focus }ly
while the image of the vertical arrow OP will be distinct in the focus /2, and
the eye cannot see the two lines distinctly at the same time. This condition is
DEFECTS IN THE OPTICAL APPARATUS 651
further illustrated in figure 465 which represents the position /t shown in
figure 464.
Myopia. This is that refractive condition of the eye in which parallel
rays are brought to a focus in front of the retina, 4, figure 466. It is due
either to an abnormal elongation of the eyeball, antero-posteriorly, or to an
increase in the convexity of the refracting surfaces, or to both of these con-
ditions. Parallel rays are focussed in front of the retina, and, crossing,
form circles on the retina. Thus, the images of distant objects are blurred
and indistinct. The eye is, as it were, permanently adjusted for a near point.
Rays from a point near the eye are exactly focussed on the retina. But those
which issue from any object beyond a slight distance, the myopic jar-point,
which is less than twenty feet, cannot be distinctly focussed. This defect
is corrected by concave glasses, which cause parallel rays entering the eye
FIG. 465. — Diagram of Character of Retinal Images in Astigmatism. (John Green.)
to diverge. Such glasses of course are needed only to give a clear vision of
distant objects. For near objects they are not required.
Hypermetropia. This is that refractive condition of the eye in which
parallel rays are brought to a focus behind the retina, 3, figure 466. It is the
opposite of myopia, and is due either to an abnormal shortening of the eye-
ball, antero-posteriorly, or to a decrease in the convexity of the refracting
surfaces, or both. Parallel rays entering the eye at rest are focussed behind
the retina. An effort of accommodation is therefore required to focus parallel
rays on the retina. When the rays are sharply divergent, as in viewing a very
near object, the accommodation is insufficient to focus them. Thus, both
ne2r and distant objects require an effort of accommodation, and the eye
is under a constant strain which produces in the end various nervous, as well
as ocular, disorders. This defect is obviated by the use of convex glasses,
which render the pencils of light more convergent. Such glasses are espe-
cially needed for near objects, as in reading, etc. They are also required for
distant vision to rest the eye by relieving the ciliary muscle from constant work.
Presbyopia. Presbyopia is a condition of diminished range of accom-
modation. It takes place with considerable uniformity from youth to old age.
652 THE SENSES
It is not a disease, but a physiological process which every eye undergoes as
its owner grows older. It is due to a gradual diminution of elasticity of the
lens by a sort of sclerosis from the center toward the periphery. It begins
even in childhood, but advances so slowly that it is not until the age of
twenty-five or so that a distinct, though small, nucleus is present. With
advancing years the process goes on until finally the lens becomes inelastic
FIG. 466. — Diagram Showing: i, Normal or emmetropic eye bringing parallel rays exactly to a
focus on the retina; 2, normal eye at rest, showing that light from a near point is focussed behind the
retina, but by increasing the curvature of the anterior surface of the lens (shown by dotted lines)
the rays are focussed on the retina; 3, hypermetropic eye. In this case the axis of the eye is shorter,
and the lens normal (or the lens may be flatter than normal and the eyeball normal); parallel
rays are focussed behind the retina; 4, myopic eye. In this case the lens is too convex (or the
axis of the eye is abnormally long) ; parallel rays are focussed in front of the retina.
and is unable to assume a shape convex enough to focus rays from a near
object upon the retina, as in reading. The defect is remedied by the use
of convex lenses equivalent to the loss in accommodation.
Visual Sensations, from Excitation of the Retina. Light is the
normal agent in the excitation of the retina. The only portion of the retina
capable of reacting to the stimulus is the rod and cone layer. The proofs of
this statement may be summed up thus: i. The point of entrance of the optic
VISUAL SENSATIONS, FROM EXCITATION OF THE RETINA 653
nerve into the retina, where the rods and cones are absent, is insensitive to
light and is called the blind spot. The phenomenon itself is very readily
demonstrated. If we close one eye, and direct the other upon a point at
such a distance to the side of any object that the image of the latter must
fall upon the retina at the point of entrance of the optic nerve, its image is
lost. If, for example, we close the left eye, and direct the axis of the right
eye steadily toward the circular spot in figure 467, while the page is held at
a distance of about six inches from the eye, both dot and cross are visible.
On gradually increasing the distance between the eye and the object, by
removing the book farther and farther from the face, keeping the right eye
steadily on the dot, it will be found that suddenly the cross disappears from
view, while on removing the book still farther it suddenly comes into view
again. The cause of this phenomenon is simply that the portion of retina
which is occupied by the entrance of the optic nerve is quite blind; and there-
fore that when it alone occupies the field of vision objects cease to be visible.
• -I-
FIG. 467. — Diagram for Demonstrating the Blind Spot-
2. In the fovea centralis and macula lutea, which contain rods and cones but
no optic-nerve fibers, light produces the greatest effect. In the latter, cones
occur in large numbers, and in the former cones without rods are found,
whereas in the rest of the retina, which is not so sensitive to light, there are
fewer cones than rods. We may conclude, therefore, that cones are even
more important to vision than rods. 3. If a small lighted candle be moved
to and fro at the side of and close to one eye in a dark room while the eyes
look steadily forward into the darkness, a remarkable branching figure,
Purkinje's figures, is seen floating before the eye, consisting of dark lines on
a reddish ground. As the candle moves, the figure moves in the opposite
direction, and from its whole appearance there can be no doubt that it is a
reversed picture of the retinal vessels projected before the eye. The two
large branching arteries passing up and down from the optic disc are clearly
visible, together with their minutest branches. A little to one side of the disc,
in a part free from vessels, is seen the yellow spot in the form of a slight de-
pression. This remarkable appearance is due to shadows of the retinal
vessels cast by the candle. The branches of these vessels are chiefly dis-
tributed in the nerve fibers and ganglionic layers; and since the light of the
candle falls on the retinal vessels from in front, the shadow is cast behind
them, and hence those elements of the retina which perceive the shadows
must also lie behind the vessels. Here, then, we have a clear proof that the
light-perceiving elements of the retina are not the fibers of the optic nerve
forming the innermost layer of the retina, but the external layers of the retina,
the rods and cones.
654 THE SENSES
When light falls on the rods and cones it produces changes which develop
nerve impulses that are transmitted by the chain of neurones extending
through the retina, the optic nerve and chiasma, the geniculate bodies, etc.,
to the cerebral cortex of the occipital lobe, which is the sensorium for visual
sensations. We have already seen that the eye possesses a wonderful me-
chanical perfection for receiving and focussing light on definite parts of the
retina. A comparison of visual sensations shows that there are corresponding
qualities in the sensation, as, for example, its intensity, duration, localiza-
tion, complexity, etc.
Duration of Visual Sensations. The duration of the sensation pro-
duced by a luminous impression on the retina is always greater than that
of the stimulus which produces it. However brief the luminous impression,
the effect on the retina always lasts for about one-twentieth of a second.
Thus, suppose an object in motion, say a horse, to be revealed on a dark
night by a flash of lightning, the image remaining on the retina during the
time of the flash. The object is really revealed for such an extremely short
period (a flash of lightning being almost instantaneous) that no appreciable
movement could have taken place in the period during which the stimulus
was produced on the retina of the observer. The horse would appear stand-
ing in the position of motion for about a twentieth of a second, though he
would not be seen to make any motions. And the same fact is proved in a
reverse way. The spokes of a rapidly revolving wheel are not seen as dis-
tinct objects, because at every point of the field of vision over which the re-
volving spokes pass, a given impression has not faded before another comes
to replace it. Thus every part of the interior of the wheel appears filled.
The duration of the ajter-sensation produced by an object is greater in a
ratio proportionate to the duration of the impression which caused it. Hence,
the image of a bright object, as of the light of a window, may be perceived in
the retina for a brief period, the positive after-image. If, however, the primary
stimulation is sharp and intense there will follow presently an appearance of
the window in which all the contrasted lights are reversed, the negative after-
image.
Intensity of Visual Sensations. It is quite evident that the more
luminous a body the more intense is the stimulus it produces. But the in-
tensity of the sensation is not directly proportional to the intensity of the
luminosity of the object. It is necessary for light to have a certain intensity
before it can excite the retina, but it is impossible to fix an arbitrary limit
to the power of excitability. As in other sensations, so also in visual sensa-
tions, a stimulus may be too feeble to produce a sensation. If it be increased
in amount sufficiently, it reaches a point that is intense enough to produce an
effect; this is a minimal or threshold stimulus. The amount of increase in
the stimulus that produces a perceptible change in the sensation is at
first very slight, but later quite great. It dees not depend on the absolute
INTENSITY OF VISUAL SENSATIONS
655
change of intensity of the stimulus, but is proportional to the intensity of the
stimulus already acting, Weber's law.
This law, which is true only within certain limits, may be best under-
stood by an example. When the retina has been stimulated by the light of
one candle, the light of two candles will produce a difference in sensation
which can be easily and distinctly felt. If, however, the first stimulus is that
of an electric arc -light, the addition of the light of a candle will make no dif-
ference in the sensation. So, generally, for an additional stimulus to be felt,
it may be proportionately small if the original stimulus is small, and must
be greater if the original stimulus is great. The stimulus increases as the
numbers expressing its strength, while the sensation increases as the
logarithms.
Every one is familiar with the fact that it is quite impossible to see
the jundus or back of another person's eye by simply looking into it. The
interior of the eye forms a perfectly black background to the pupil. The same
FIG. 468. — Diagram to Illustrate the Action of the Ophthalmoscope when a Plane Concave
Glass is Used, c, Observer's eye. The light reflected from any point, d, on retina of a, would
naturally be focussed at e; if the lens b is used it would be focussed at i, in other words, at back
of c. The image would be enlarged, as though of g, and would be inverted. (After McGregor Rob-
ertson.)
remark applies to an ordinary photographic camera, and may be illustrated
by the difficulty we experience in seeing into a room from the street through
the window, unless the room be lighted from within. In the case of the
eye this fact is partly due to the feebleness of the light reflected from the
retina, most of it being absorbed by the retinal pigment. But the difficulty
is due more to the fact that every such ray is reflected back to the source of
light and cannot be seen by the unaided eye without intercepting the in-
cident light as well as the reflected rays from the retina. This difficulty is
surmounted by the use of the ophthalmoscope.
The ophthalmoscope, brought into use by Helmholtz, consists in its simplest form
of a concave mirror with a hole in it. The one described is one of the less intricate of the
modern instruments. It consists of, a, a slightly concave mirror of metal or silvered glass
perforated in the center, and fixed into a handle; and 6, a biconvex lens of 6 to 8 cm.
focal length. Two methods of examining the eye with this instrument are in common use
— the direct and the indirect : both methods of investigation should be employed. A nor-
mal eye should be examined. A drop of a solution of atropine (two grains to the ounce)
or of homatropine hydrobromate should be dropped into the right eye only about twenty
minutes before the examination is commenced; the ciliary muscle is thereby paralyzed,
656
THE SENSES
the power of accommodation is abolished, and the pupil is dilated. This will materially
facilitate the examination; but it is quite possible to observe all the details to be presently
described without the use of this drug. The room being now darkened, the observer seats
himself in front of the person whose eye he is about to examine, placing himself upon a
FIG. 469. — Diagram to Illustrate Action of Ophthalmoscope when a Biconvex Glass is Used.
The figure d on retina of a is under ordinary conditions focussed at / and inverted. If the lens
b be placed between eyes, the image h is seen by the eye c as an enlarged image. (After Mc-
Gregor Robertson.)
somewhat higher level. A subdued but steady light is placed close to the left ear of the
patient in the examination of the right eye. Guiding the mirror in his right hand, and
looking through the central hole, the operator directs a beam of light into the eye of the
patient. A red glare, called in practice the reflex, due to the illumination of the retina, is
seen. The patient is then told to look at the little finger
of the observer's right hand as he holds the mirror; to
effect this the eye is rotated somewhat inward, and at the
same time the reflex changes from red to a lighter color,
owing to the reflection from the optic disc. The observer
now approximates the mirror, and with it his eye to the
eye of the patient, taking care to keep the light fixed upon
the pupil, so as not to lose the reflex. At a certain dis-
tance, which varies with the refractive power in different
eyes, but is usually an interval of about two or three
inches between the observed and the observing eye, the
vessels of the retina will become visible as lines running in
different directions. The smaller and brighter red arteries
can be distinguished from the larger and darker colored
veins. An examination of the fundus of the eye reveals
the optic disc and the entrance of the blood-vessels, the
macula lutea, and the fovea centralis. No blood-vessels
are seen in the fovea. This constitutes the direct method
of examination, figure 468; by it the various details of
the fundus are seen as they really exist, and it is this
method which should be adopted for ordinary use.
If the observer is ametropic, i.e., is myopic or hyper-
metropic, he will be unable to employ the direct method
of examination until he has remedied his defective vision
by the use of proper glasses.
In the indirect method, figure 469, the patient is
placed as before, and the operator holds the mirror in
his right hand at a distance of 30 to 40 cm. from the
patient's right eye. At the same time he rests his left
little finger lightly upon the patient's right temple, and
holding the lens between his thumb and forefinger, two
or three inches in front of the patient's eye, directs the
light through the lens into the eye. The red reflex, and subsequently the white one,
having been gained, the operator slowly moves his mirror, and with it his eye, toward or
away from the face of the patient, until the outline of one of the retinal vessels becomes
visible, when very slight movements on the part of the operator will suffice to bring into
FIG. 470. — The Ophthalmo-
scope. The small upper mir-
ror is for direct, the larger for
indirect, illumination.
THE FIELD OF VISION
657
view the details of the fundus above described, but the image will be much smaller and in-
verted. The lens should be kept at a fixed distance of two or three inches, the mirror
being alone moved until the disc becomes visible: should the image of the mirror obscure
the disc, the lens may be slightly tilted.
The Field of Vision. The field of vision of an eye is that part
of the external world which can be seen by it when the eye is fixed. Under
such circumstances objects near the axis of vision stimulate points in the retina
near the fovea or on it, while objects at an angle of 60° to 90° from the axis
105
60*
180
10,
S10
225
21*0
255
FIG. 471. — Perimeter Chart, Showing Extent of Field of Vision for White Light and to the
.Colors Red, Green, Yellow, and Blue. (Krapart.)
of vision stimulate regions of the opposite side o"f the retinal cup, i.e., the
retinal field is inverted.
The perimeter is an instrument for measuring the field of vision in terms
of angular measure. When a field is charted by means of the perimeter it
is revealed that objects can be seen further out in the field in some directions
than in others. For example, objects in the temporal field can be seen at
an angle of 90° to 100°, while on the nasal side they are seefi only 60° to 70°.
If the head is turned to the right or the left while keeping the eye fixed, it is
found that objects are seen at a greater angle. This shows that the limita-
tions are due to the facial boundaries of the eye preventing the light from
entering the eye and not from lack of sensitiveness of the retina. In fact
the retina is sensitive to light out to the ora serrata.
Localization in the Retina. Careful exploration of the retina with
the perimeter gives a measure not only of the extent of the visual field but of
42
658 THE SENSES
its acuteness and localization in different areas toward the periphery. Con-
sidering the minimal distance apart which two luminous points must be to
be distinguished as two, it is found that when the image falls on the fovea
the two points may be very near together, as little as one minute or even less.
Two stars can be seen only at a somewhat greater angular distance, two to
three minutes. One minute angular measure covers an area on the retina of
a trifle over 4 /*. The diameter of the cones is about 2 /*, so that the stimuli in
the fovea fall on at least two separate cones. The inference seems reasonable
that the retina in its most sensitive part can localize stimuli that fall on ad-
jacent cones.
The area of the fovea centralis is small, from 0.5 to 1.5 mm. Outside of
its area the acuteness of vision quickly falls off. The fact is roughly estimated
by fixing the vision on a letter in the printed line in the book before the
reader and then determining the number of letters to either side that can be
identified. The height of these letters is 1.5 mm. ; by measuring the distance
of the page from the eye one can quickly calculate the area of distinct vision
on the retina. Test types are printed on the basis of an angle of five minutes.
In the outer limits of the retina the power of localizing stimuli is very
slight; in fact, in the extreme borders of the field it is difficult to determine
other than general form.
Visual Purple. The method by which a ray of light is able to
stimulate the endings of the optic nerve in the retina is not yet understood.
It is supposed that the change effected by the agency of the light which falls
upon the retina is in fact a chemical alteration in the protoplasm, and that
this change initiates a nerve impulse that is transferred to the optic nerve
endings. The discovery of a certain temporary reddish-purple pigmenta-
tion of the outer limbs of the retinal rods in certain animals, e.g., frogs, which
had been killed in the dark, forming the so-called rhodopsin or visual purple,
appeared likely to offer some explanation of the matter, especially as it was
also found that the pigmentation disappeared when the retina was exposed
to light, and reappeared when the light was removed, and that it underwent
distinct changes of color when other than white light was used. It was also
found that if the operation were performed quickly enough and in the dark,
the image of an object, optogram, might be fixed in the pigment on the retina
by soaking the retina of an animal in alum solution.
The visual purple cannot, however, be absolutely essential to the due pro-
duction of visual sensations, as it is absent from the retinal cones, and from
the macula lutea and fovea centralis of the human retina, and does not appear
to exist at all in the retinae of some animals, e.g., bat, dove, and hen, which
are, nevertheless, possessed of good vision.
However, the fact remains that light falling upon the retina bleaches the
visual purple, and this must be considered as one of its effects. It has been
found that certain pigments, also sensitive to light, are contained in the inner
VISUAL PURPLE
659
segments of the cones. These colored bodies are said to be oil globules of
various colors — red, green, and yellow — called chromophanes, and are found
only in the retinae of animals other than mammals. The rhodopsin at any
rate appears to be derived in some way from the retinal pigment, since the
color is not renewed after bleaching if the retina be detached from its pig-
ment layer. The second change produced by the action of light upon the
retina is the movement of the pigment cells. On the stimulation by light
the granules of pigment in the cells which overlie the outer part of the rod
and cone layer of the retina become diffused into the parts of the cells be-
tween the rods and cones, the melanin granules, as they are called, passing
FIG. 472. — Sections of Frog's Retina Showing the Action of Light upon the Pigment Cells and
upon the Rods and Cones, (von Gendesen-Stort.) A, From a frog which had been kept in the
dark for some hours before death; B, from a frog which had been exposed to light just before being
killed. Three pigment cells are shown in each section. In A the pigment is collected toward the
nucleated part of the cell, in B it extends nearly to the basis of the rods. In A the rods, outer
segments, were colored red (the detached one green) ; in B they had become bleached. In A the
cones, which in the frog are much smaller than the rods, are mostly elongated ; in B they are all con-
tracted.
down into tne processes of the pigment cells. A movement of the cones and
possibly of the rods is also said to occur, as has been already incidentally
mentioned. Under the influence of the stimulus of light the outer parts of
the cones, which in an eye protected from light extend to the pigment layer,
are retracted. It is even thought by some that the contraction is under
the control of the nervous system. Finally, according to the careful researches
of Dewar and McKendrick, and of Holmgren, it appears that the stimulus of
light is able to produce an action current in the retina. McKendrick believes
that this is the electrical expression of those chemical changes in the retina
of which we have already spoken.
Color Sensations. When a ray of sunlight enters the eye it pro-
660 THE SENSES
duces a sensation of white light. But if the ray first passes through a prism,
then it produces sensations corresponding to the colors of the spectrum. As
is well known, white light is produced by vibrations of the luminiferous ether
through a wide range of vibration rates. When a beam of white light is
passed through a dispersing prism those vibration rates of low frequency
are refracted less than those of higher frequency, giving rise to the
spectrum. Vibrations of the luminiferous ether of rates just outside of the
spectral rates exist, those which have a lower rate giving rise to heat rays,
and those of higher rate to the so-called actinic or chemical rays, because
they exert a powerful chemical action. Those spectral colors which stimu-
late the retina to produce sensations of color presumably affect the retinal
elements through chemical changes which they produce there. But this
matter will be discussed under theories of color vision.
The examination of color sensations reveals certain correspondences be-
tween the physical color of the stimulus and the resulting color perception.
If a pure spectral color be allowed to fall on the retina, a corresponding simple
sensation is produced. If two colors fall on the same portion of the retina
at the same time, a sensation is produced that is different from that which
occurs when either color alone stimulates. The same fact holds true for
three colors or more. In fact, three spectral colors can be selected which
by proper combination can be used to produce sensations of all the colors of
the spectrum. Such colors are called the fundamental colors, and while
the choice is more or less arbitrary, red, green, and violet are the colors usu-
ally considered.
Extent of the Visual Field for Color. The retina is most sensitive
to color in the region of the macula lutea. If by means of the perimeter one
explores the retina to spectral red, for example, it is found that the color can
be identified only at a distance of from 30° to 50° from the macula; the
limits extending out somewhat farther on the nasal side of the retina, that
is, the part corresponding to the temporal visual field. In the same way yel-
low can be identified for from 40° to 70°, blue from 40° to 50°. The visual
field for green is quite restricted, usually extending only from 20° to 30°.
The extent of the color visual field varies greatly in different individuals.
Complemental Colors, and After-images of Color. Certain colors,
when allowed to stimulate the retina at the same time, tend to neutralize each
other. That is, they produce sensations approaching white, usually some
shade of gray, which will have a tinge of one or the other primary colors
according to the proportion of stimulation. These pairs of colors are called
complemental colors. Each spectral color has its complemental color, a fact
that is represented in figure 473. The complemental colors of greatest physi-
cal significance are red and green (greenish blue), yellow and deep blue
(indigo blue), green (greenish yellow), and violet.
Positive after-images of color exist for a brief moment, but the greatest
COLOR-BLINDNESS 661
significance attaches to the negative after-images. The negative after-images
of color following the stimulus of colored light upon the .retina are not the
sensation of color produced by the color of an object, but are the opposite
or complemental color. The after-image of red is, therefore, green, and
that of green, red; that of violet, yellow and of yellow, violet, etc. The
same relation holds with the other colors. A condition for the development
of a strong after-image is that the primary image shall have continued to a
certain degree of fatigue. The colors which reciprocally excite each other
Green
MMM
FIG. 473. — Geometrical Color Table for Determining the Complemental Colors.
in the retina are those placed at opposite points in the color table, figure 473.
The after-images of color are most intense in the axis of the visual field and
are not always present in the periphery of the retina, as can readily be seen
by examining the chart, figure 471.
Color sensations may also be produced by contrast. Thus, a very small
dull gray strip of paper, lying upon an extensive surface of any bright color,
does not appear gray, but has a faint tint of the color which is the comple-
ment of that of the surrounding surface. A strip of gray paper upon a green
field, for example, appears to have a tint of red, and when lying upon a red
surface, a greenish tint; it has an orange-colored tint upon a bright blue
surface, and a bluish tint upon an orange-colored surface; a yellowish color
upon a bright violet, and a violet tint upon a bright yellow surface. The
color excited thus must arise as an opposite or antagonistic condition of the
retina, and the opposite conditions of which it thus becomes the subject,
would seem to balance each other by their reciprocal reaction. A necessary
condition for the production of the contrast colors is that the part of the
retina in which the new color is to be excited shall be in a state of compara-
tive repose; hence the small object itself must be gray. A second condition
is that the color of the surrounding surface shall be very bright.
Color-Blindness. Many persons are unable to distinguish one or
more of the fundamental colors, and therefore have different perceptions
THE SENSES
of the color combination from that of the normal individual. It is said that
from 4 to 5 per cent of men and about E per cent of women are defective in
color vision. This defect is called color-blindness.
In very rare cases complete color-blindness exists. Such individuals
distinguish lights and shades only, that is, form. A more common defect,
however, is the absence of one or more of the fundamental color sensations,
the most common of all being the red-blind, or the red-green blind. The red-
green blind individual cannot distinguish red and green colored yarns from
each other or from shades of gray which reflect light with the same intensity.
When they are given the color test by the Holmgren yarns, they indiscrim-
inately mix the reds, greens, and grays. Cases have been described in which
the individual was red-blind alone, or green-blind alone. A less common color
defect is the inability to distinguish yellows and blues, yellow-blue blindness.
Color-blindness may occasionally arise from disease or accident, but it
is usually congenital. The individual often does not discover his defect until
examined especially for his color vision. He may have learned to apply
the terms green and red to surrounding objects, such as the grass, bricks, etc.,
but he distinguishes these objects by slight differences in intensity of lumi-
nation, form, etc., and not by the sensations of color which the normal
individual experiences.
Theories of Color Vision. We have no way of determining the
method by which the colors stimulate the retina other than our inferences
from indirect evidence. It is probable that the energy of light vibration
is transformed in the retinal structures into either physical or chemical change,
perhaps the latter. Those interested in the phenomena of color vision gener-
ally accept one of two theories, or their modifications, in explanation of
the facts.
The Young-Helmholtz Theory of Color Vision. This theory assumes
that there are three fundamental sensory elements in the retina which cor-
respond to and are stimulated primarily by the three primary colors — red,
green, and violet. The theory in its present form further assumes that each
color-perceiving element is slightly stimulated by others of the spectral rays,
as shown in figure 474. When red rays fall upon the retina, they stimulate
the red-perceiving elements strongly and the green and violet very feebly.
The resulting sensation is that of red. So also is it with green and violet rays.
When the retina is stimulated by both red and green rays, the two correspond-
ing color-perceiving elements are strongly stimulated. The resulting color
perception, however, is a combination of the two sensations and corresponds
to some region of the spectrum between the red and green, according to the
relative intensity of the two stimuli. When all three color-perceiving ele-
ments are stimulated at the same time, this theory assumes that white light
will be perceived. In a similar manner all the various color sensations are
arrived at.
THEORIES OF COLOR VISION
663
Bering's Theory of Color Vision. This theory is based on the assump-
tion that there are chemical substances in the retina, photogenic substances,
which are stimulated by the colors of the spectrum. It assumes three photo-
genic substances which are called the red-green, the yellow-blue, and the
FIG. 474. — Diagram to Illustrate the Stimulating Effects of the Three Primary Colors. (Young-
Helmholtz theory.) i is the red; 2, green, and 3, violet, primary color sensations. The lettering
indicates the colors of the spectrum. The diagram indicates by the height of the curve to what
extent the several primary sensations ef color are excited by vibrations of different wave lengths.
(Helmholtz.)
white-black substances. By the theory, when the red-green substance is
stimulated by red or green light, respectively, the former produces destruc-
tive or catabolic changes, the latter constructive or anabolic changes, in the
substance. When red light falls upon the retina, it produces catabolism in
the red-green substance, which in turn develops a nerve impulse that arouses
FIG. 475.— Diagram to Illustrate the Reactions of the Three Photogenic Substances, according
to Hering's Theory. (Foster.)
the sensation of red. When green light, on the other hand, stimulates the
retina, it produces anabolism of the red-green substance and the sensation of
green. The same rule holds with the other two substances. It will be
noticed that this theory is based on the complemental colors.
THE SENSES
^hen we apply the theories mentioned above to the phenomena of color-
contrast and color-blindness, we find that each is defective in some point.
By the Young-Helmholtz theory it is difficult to understand the perception
of the sensation black, for by the theory black could be perceived only as
the absence of all colors, and it is generally granted that there is a distinct
black sensation other than and different from mere darkness. This theory
explains those cases of blindness to one color, as red-blindness, for example.
The Hering theory, on the other hand, gives us a rational explanation for
positive black sensation, and is particularly applicable to the observed facts
of color-contrast and negative color after-images.
Color after-images, as for instance the after-images of green following
stimulation by red light, are readily explained by Bering's theory, since the
strong catabolism in the red-green substance will be followed immediately
by anabolism to bring this substance up to its normal in the eye, thus pro-
ducing the after-image. This phenomenon can be explained by the Young-
Helmholtz theory only by assuming that following the stimulation by red
light and the consequent fatigue of red-perceiving elements there is sufficient
light entering the eye to stimulate the relatively sensitive green and violet
perceiving elements, thus producing an after-image. Strong after-images
are perceived in the dark room, so that the Hering theory is most applicable
in the explanation of these cases.
Binocular Vision. When one looks at an object with a single eye,
the eye is so adjusted that the axis of vision is directed toward the object
investigated. This is called ocular fixation. The ocular fixation is accom-
plished by the coordinated contractions of the six pairs of ocular muscles.
Its purpose is to bring the image of the object examined in the external visual
field as nearly as possible upon the macula lutea. In binocular vision both
eyes are fixed on the same pofnt in the visual field. A projection of the
visual axis of each eye will pierce the point of fixation in the external object.
It is evident that objects to either side of the point of fixation will give off
rays which will enter the eyes, stimulating fields in the retina on the opposite
side of the visual axis. An examination of figure 476 will show that each
point in the visual field, A, B, C, D, stimulates corresponding points, a, b, c, d,
a', b', c', d', in the retinas of the two eyes, a, b, c, d, and a', V, c', d', are corre-
sponding points in the two retinas. When a and a' are stimulated at one
and the same time, the resulting sensation is attributed to one object in the
visual field, A, and these are corresponding points. This can be shown
by pressing one eye out of its normal fixation so that the axes of the two eyes
are not directed toward the same point. If one eye is pressed lightly by the
thumb while examining a given object, as soon as, the pressure is applied
two objects will appear. This phenomenon is known as diplopia. Diplopia
is due to the fact that the images of visual objects do not fall on correspond-
ing points in the two retinae.
BINOCULAR VISION
665
The parts of the retinae in the two eyes which thus correspond to each
other in the property of referring the images which affect them simulta-
neously to the same spot in the field of vision, are, in man, just those parts
which would correspond to each other if one retina were placed exactly in
front of and over the other, as in figure 477. Thus, as we have noticed in
speaking of the distribution of the optic nerve fibers, the temporal portion
of one eye corresponds to or is identical with the nasal portion of the other
eye. The upper part of one retina is also identical with the upper part of
FIG. 476. — Diagram Showing the Symmetrical Correspondence of the Retinal Fields. N,
Nodal point; F, fovea cen trails. The observer is supposed to be looking down upon the optical
apparatus from above. Note that the line CD, which is on the lower side of the object, is the
upper side of the image; and that the line BD, which is the right side of the object, is the left side
of the image, which brings it at the inner segment of the right retina and the outer segment of the
left retina.
the other; and the lower parts of the two eyes are identical with each other.
The distribution of the optic nerve fibers corresponds with the distribution
of the identical points. The identical points on the upper and lower parts
of the retinae may also be shown by the following simple experiment.
Pressure upon any part of the ball of the eye, so as to affect the retina,
produces a luminous circle, seen at the opposite side of the field of vision to
that on which the pressure is made. If, now, in a dark room, we press with
the finger at the upper part of one eye, and at the lower part of the other,
two luminous circles are seen, one above the other; so, also, two figures are
666
THE SENSES
seen when pressure is made simultaneously on the outer or the inner sides
of both eyes. But if pressure be made with the fingers upon both eyes
simultaneously at their lower part, one luminous ring is seen at the middle
of the upper part of the field of vision. If the pressure be applied to the upper
part of both eyes, a single luminous circle is seen in the middle of the field of
vision below. So, also, if we press upon the outer side of one eye and upon
the inner side of the other eye, a single luminous spot is produced, and is appar-
A jb
FIG. 478.
FIG. 477. — Diagram to Show the Corresponding Parts of the Retinae.
FIG. 478. — Diagram to Show the Simultaneous Action of the Eyes in Viewing Objects in Dif-
ferent Directions.
ent at the extreme right of the field of vision. The hemispheres of the two
retinae may, therefore, be regarded as lying one over the other, as in C, figure
477; so that the left portion of one eye lies over the identical left portion of
the other eye, the right portion of one eye over the identical right portion of
the other eye; and with the upper and lower portions of the two eyes, a lies
over a', b over b', and c over c'. The points of the one retina intermediate
between a and c are again identical with the corresponding points of the other
retina between a' and c'; those between b and c of the one retina, with those
between V and c' of the other. If the axes of the eyes, A and B, figure 478,
be so directed that they meet at a, an object at a will be seen singly, for the
point a of the one retina and a' of the other are identical. So, also, if the
object ft be so situated that its image falls in both eyes at the same distance
from the central point of the retina— namely, at b in the one eye and at b' in
the other— ft will be seen single, for it affects identical parts of the two retinae.
The same will apply to the object y.
The reason why the impressions on the identical points of the two retinae
give rise to but one sensation, and the perception of but a single image,
must either lie in the structural organization of the deeper or cerebral por-
tions of the visual apparatus, or it must be the result of a mental operation;
VISUAL JUDGMENTS 667
for in no other case is it the property of corresponding nerves of the two
sides of the body to refer their sensations to one spot.
Many attempts have been made to explain this remarkable relation be-
tween the eyes, by referring it to anatomical relation between the optic nerves.
The circumstance of the inner portion of the fibers of the two optic nerves
decussating at the commissure, and passing to the eye of the opposite side,
while the outer portion of the fibers continue their course to the eye of the
same side, so that the left side of both retinae is formed from one root of the
nerves, and the right side from the other root, naturally led to an attempt
to explain the phenomenon by this distribution of the fibers of the nerves.
And this explanation is favored by cases in which the entire half of one
side of the retina sometimes becomes insensible.
Visual Judgments. Form and Solidity. The estimation of the
form of bodies by sight is the result partly of the visual sensation and partly
of the association of ideas. The form of the image perceived by the retina
depends wholly on the outline of the part of the retina affected; the sensa-
tion alone is adequate only to the distinction of superficial forms from each
other which lie in one plane, as of a square from a circle. But the idea of a
solid body, as a sphere, or a body of three or more surfaces, e.g., a cube,
can be attained only by the action of the mind in constructing it from the dif-
ferent superficial images seen in different positions of the eye with regard
to the object, and (as shown by Wheatstone and illustrated in the stereoscope),
from two different perspective projections of the body being presented simul-
taneously to the mind by the two eyes. Hence, when, in adult age, sight is
suddenly restored to persons blind from infancy, all objects in the field of
vision appear at first as if painted flat on one surface; and no idea of solidity
is formed until after long exercise of the sense of vision combined with that
of touch. The clearness with which an object is perceived, irrespective of
accommodation, would appear to depend largely on the definiteness of stimu-
lation of the rods and cones which its retinal image covers. Hence, the nearer
an object is to the eye, within the limits of vision, the more clearly are all
its details seen. Moreover, if we want carefully to examine any object, we
always direct the eyes straight toward it, so that its image shall fall on the
yellow spot, which has already been shown to be the area of most acute vision.
In binocular vision the images of an object, while they fall in approxi-
mately corresponding points on the two retinae, are never absolutely the same.
When an object is placed so near the eyes that to view it the optic axes
must converge, a different perspective projection of it is seen by each eye,
these perspectives being more dissimilar as the convergence of the optic axes
becomes greater. Thus, if any figure of three dimensions, an outline cube,
for example, be held at a moderate distance before the eyes, and viewed with
each eye successively while the head is kept perfectly steady, A, figure 479>
will be the picture presented to the right eye, and B that seen by the left eye.
668
THE SENSES
Wheatstone has shown that on this circumstance depends in a great measure
our conviction of the solidity of an object, or of its projection in relief. If
different perspective drawings of a solid body, one representing the image
seen by the right eye, the other that seen by the left, for example, the drawing
of a cube, A, B, figure 479, be presented to corresponding parts of the two
retinae, as may readily be done by means of the stereoscope, the mind will
perceive not merely a single representation of the object, but a body pro-
jecting in relief, the exact counterpart of that from which the drawings were
made.
Size and Distance. The estimation of the size of an object and its distance
away from the observer is based in part upon the visual image and in part
upon judgments due to past experience. The two elements are inseparable
and mutually dependent. Thus, a lofty mountain many miles away may
subtend the same visual angle as a small hill near at hand. While the size
\
FIG. 479. — Diagrams to Illustrate how a Judgment of a Figure of Three Dimensions is Obtained.
and shape of the two images may be identical, yet the image of the hill near
at hand is more distinct, its details are perceived, and its outlines are sharper
than in the image of the mountain. If the atmosphere be charged with
moisture or with dust, the image of the mountain will be still more indistinct
and dim. From previous experiences we have learned that the dimness and
indistinctness of the one and the definiteness of the other are associated with
distance.
If two objects are very near at hand then there will be a difference in
the convergence of the two eyes in binocular vision. It is now well known
that the ocular muscles are possessed of a very delicate muscle sense. This
muscle sense leaves the impression which enables us to judge that the one
object is nearer and the other farther. In the common and familiar objects
about us we have from long experience and intimate contact learned their
actual size and the character of the retinal image formed at definite, but known
distances. When such an object forms an image of the common size and
usual distinctness on the retina, the judgment as to its distance is quickly
made.
In the case of unknown objects which are associated with known ob-
jects, the judgment of the size and distance, of the latter is used in forming
LABORATORY EXPERIMENTS ON THE SENSE ORGANS
669
a judgment of the size and distance of the former by comparison. Many
visual deceptions are based on these comparisons, a fact that is often taken
advantage of by photographers. It is also well known that people living in
a moist, hazy climate are utterly unable accurately to estimate distances
when suddenly transferred to a clear mountain climate.
LABORATORY DIRECTIONS FOR EXPERIMENTS ON THE
SENSE ORGANS.
i. Touch. Use the small compasses with rounded tips provided
for the purpose, and determine the power of localization of the sense of touch
as follows: Have the person observed close his eyes, then touch different
parts of the skin, of the hand, arm, face, neck, etc., and let the observed one
announce the exact point touched.
The localization can also be determined by touching two points 6n the
skin with the points of the compasses separated by varying distances. Ex-
amine especially the skin on the forearm, on the back of the hand, on the
palm of the hand, the tips of the fingers, and at different points on the face,
including the lips and tip of the tongue. Touch these regions of the skin
FIG. 480. — Aristotle's Experiment.
with either one or with two points of the compasses, and allow the person
observed to announce results, drawing your conclusions according to the
principle of trial and error. Make a table showing the power of local dis-
crimination in the different regions.
2. Aristotle's Touch Experiment. Roll the tips of the middle and
index fingers over a marble and note that the sensation from the two fingers
is interpreted as that of a single object. Now cross the fingers and repeat
the experiment. This time there is the sensation of touching two spheres.
3. Temperature Sensations. It is a common experience that the
hand brought in the neighborhood of a warm or a cold object develops the
670 THE SENSES
sensation of warmth or cold. Examine a given small area of the back of
the hand with the thermoesthesiometer. Certain points will give stronger
sensation of heat than others. Map these out carefully. Examine the same
area for the cold. A large number of cold spots will be found and they will
not coincide with the warm spots, figure 421.
The stimulation for the hot and cold spots does not depend upon the
absolute temperature, but on the relative temperature. Insert the hand in
fp.
FIG. 481. — Localization of Taste. Bitter ; acid ....; salt, ; sweet ; T, tonsils;
FC, foramen cecum; CF, circumvallate papillae; FP, fungiform papillae. (Hall.)
water that feels lukewarm. Place the same hand in a cup of quite warm water
for a moment, then reinsert it in the lukewarm water. This will now feel cold.
4. Sensations of Taste. The distribution of taste organs in the
tongue is shown in figure 481. Examine your own tongue for organs of
sweet, acid, saline, and bitter, using solutions of i to 2 per cent salt, 10 per
cent sugar, 2 to 5 per cent acid, 5 per cent acetic acid, and o.i per cent quinine.
Wipe the tongue dry and apply the solution named from the tip of a glass
rod. The best form of rod is about 15 cm. long by 0.5 cm. in diameter, and
has one end drawn out to a slender pencil-shaped tip and of a size which
will suspend a very small drop. Too large a drop diffuses over too great an
area of the tongue. Occasionally small crystals of sugar, salt, etc., give more
satisfactory results.
Perform the experiments on yourself before a mirror and map the re-
sults as shown in figure 481.
If the experiments are done with care certain papillae will be found which
give one or two of the taste sensations, but not all.
5. Sensations of Smell. Quantitative experiments on the sense
THE LIMITS OF THE SENSE OF HEARING 671
of smell are difficult to determine. Inhale vapor of ammonia so dilute that
it can just be detected. Note that the sensation is strongest at the moment
of drawing the vapor into the nostril. Fill the nostrils with the diluted vapor
and close the external opening; the sensation quickly disappears. Keeping
the nostrils closed, walk into the open air, then inhale fresh air. At the
moment of the inhalation of fresh air the ammonia is again per-eptible.
Repeat with bergamot, rose water, etc.
6. The Limits of the Sense of Hearing. Use a set of tuning forks
for the purpose, and determine the lowest vibration per second which can be
perceived as sound. Determine the highest limits in the same way.
7. Acuteness of the Sense of Hearing. Listen to the vibrations,
of a tuning fork, or, better, to the ticking of a watch which is moved back and
forth from the ear. Measure the distance at which it can just be distinguished.
This experiment should be performed with the person blindfolded, and ex-
traneous noise should, of course, be suppressed.
8. Refraction. Light passes out from a luminous point in straight
lines so long as the line of propagation is in a medium of uniform density.
If the rays pass form a transparent medium of one density into a second
medium of different density, they will usually be turned out of their course, or
refracted. If the rays enter the second medium at right angles to its surface,
they will continue in straight lines, but if they enter at any other angle they
will be refracted. If the second medium is denser than the first, the rays will
be refracted toward the perpendicular; if it is less dense, away from the per-
pendicular.
Use a Hall's refraction-measuring apparatus (constructed of a carpenter's
try square). Adjust it in a water-pan, and fill to the exact level with clear water.
Clamp a rule to the vertical limb of the apparatus at an angle with the axial
point of the instrument. Read the horizontal scale of the instrument along the
edge of the clamped rule. Remove the instrument from the pan, using care
not to disturb the adjustment of the ruler, and construct the angle of refrac-
tion on coordinate paper. Determine the relation of the angle of incidence
and of refraction, and compute the refractive index of the water, the air
having a refractive index of one.
Repeat the determination using a block of glass.
9. To Determine the Refractive Power of a Convex Lens. Use a
meter stick which is provided with a movable diaphragm or screen, and a
holder for a lens. Measure the focal distance of lens number i as furnished
from the optical set. Put the lens in its holder and focus the image of the
sun or. of an electric bulb on the screen, moving the screen back and forth
until the sharp focus is determined. If the lens is accurately ground, the
focus will be at a distance of one meter, which is the refractive power of a
one-diopter lens, by definition. In the same way determine the refractive
power of Jenses numbers 2, 3, and 4.
THE SENSES
Construct the path of the light in the formation of the image in these cases.
If the measurement in the above case is made through two parallel open-
ings or diaphragms about 5 mm. in diameter each, and separated by 4 or
5 mm., the point of focus can be more accurately determined (see Schemer's
experiment, No. 14.) Construct the mathematical figure showing the
course of both cones of rays in this test.
10. Determination of Near and Far Limits of Vision. Support a
meter stick in a horizontal position at a comfortable level for the eye. Mount
a needle in a cork and set it on the meter stick about 25 cm. in front of the
eye. Make two pin-holes in a card at a distance of about 2 mm. from each
other. Hold this card with the pin-holes close in front of one eye, and bring
the eye up to the end of the meter stick; cover the other eye. Observe that
when the needle is brought nearer and nearer to the eye, at a certain distance
it becomes double. Determine this distance very accurately. It is the near-
point of accommodation for the right eve. Make the same determination for
the left eye.
Hold the punctured card in front of the right eye, and move the needle
(it is better to use something larger) farther and farther away until it becomes
FIG. 482. — Diagram of Experiment to Ascertain the Minimum Distance of Distinct Vision.
again double, if it does so. This is the far-point of accommodation. In
normal eyes there is no far limit. In practice an eye that has no far limit
under twenty feet is considered normal. This test should be made on each
eye.
11. Inverted Image on the Retina. Dissect off a segment of the
sclerotic of a fresh ox eye, or use a fresh eye from an albino rabbit. Make
a tube of black paper of the size of the eye, and insert the eye in one end,
with the cornea directed into the tube. In the dark room examine the image
of the candle flame as formed on the retina of the eye in the tube. In a
favorable experiment, a clear inverted image of the candle can be seen on
the retina through the semi-transparent membranes of the eye. The same
experiment can be demonstrated with the camera, or with a small lens, using
a ground-glass plate to make the image more apparent.
12. Spherical Aberration. In physical optics it is found that it is
difficult to grind lenses so that they will refract equally in the center or
CHROMATIC ABERRATION 673
optical axis and in the periphery. Unequal refraction of these two regions
is called spherical aberration. It is corrected in optics by diaphragms which
shut out the light, either from the borders of the lens or from its center. The
former method is used in the eye. To demonstrate Spherical Aberration, look
at an object two meters from the eye, such as part of the window. Pass a
card across the eye until the light enters only at the margin of the pupil,
i.e., the borders of the lens. It will be found that the object is no longer in
focus and the outlines are dim and diffused. Normal eyes are near-sighted
for the rays that are refracted by the borders of the lens.
13. Chromatic Aberration. Look toward the borders between the
sash and the bright light of an open window, at a distance of twenty feet or
more. Use the right eye only. Bring a card across the pupil approaching
from the side of the light until the eye is almost covered with the card.
The window sash will seem to have a blue-violet fringe. If the card is
brought across from the opposite side, the sash will have a reddish-yellow
fringe.
Make a cross of two strips of Bradley's pure color paper, one red and the
other blue, on a black surface. When held at the proper distance the red
appears nearer than the blue. This phenomenon is brought out more strongly
by covering the colored papers with very thin white tissue paper. The
judgment of distance is based on the effort of accommodation which is
greater for the red than for the blue and violet rays.
14. Schemer's Experiment. Use two needles on corks, the method
described in experiment i, placing one at a distance of 20 cm., and the other
about 60 cm. from the eye. Use only the right eye, look through two pin-
holes in a card at the far needle. The near needle will appear double, but
the images will be somewhat blurred. While looking at the far needle, bring
a cardboard across the right hole, note that the left image of the near needle
disappears, and vice versa. If one accommodates for the near needle, the far
needle appears double, and upon covering the right hole with the card the
right image of the far needle disappears. This is known as Scheiner's Ex-
periment. Construct a diagram to explain these phenomena.
15. Purkinje-Sanson's Images. Examine the eye of another person in
a dark room as follows : With the observing eye focus for a far object, let the
observer hold a candle slightly to one side of the axis of vision and about
one foot from the eye. If the observer looks into the other eye from the side
opposite the candle, he will be able to see three reflected images, figures 457
and 458. One, from the anterior surface of the cornea, is bright and dis-
tinct, and of medium size and erect. In the middle of the pupil there will be
a second image, larger and quite dim. This is a reflection from the front
of the lens. The third image, reflected from the posterior surface of the lens,
will seem to be farther back in the eye, quite small and inverted. These
images can all three be seen at once with careful adjustment of the relative
43
674
THE SENSES
positions of the candle and the observer, with reference to the axis of
vision of the eye observed.
If the observer protects his own eye from the direct light of the candle
by a blackened cardboard between his eye and the candle, and asks the
observed person to accommodate now for near objects, now for far, keeping
the axis of vision constant, he will be able to note that the middle image,
i,e., the one from the anterior surface of the lens, changes in size and in relative
position with reference to the other two, which are essentially constant. With
near accommodation this image becomes smaller and seems to move toward
the image from the cornea; with far accommodation it becomes larger and
appears to move to the image reflected from the posterior surface of the lens.
This shows that the act of accommodation consists in a change in the con-
vexity of the front of the lens.
1 6. The Phakoscope of Helmholtz. This classical instrument was
invented by Helmholtz to demonstrate the act of accommodation, as out-
FIG. 483. — Disc of Concentric Lines for the Astigmatic Test.
lined in the second paragraph of the preceding experiment. Repeat the
preceding experiment, using this instrument in a dark room.
17. Astigmatism. Astigmatism is a term used to describe the con-
dition of unequal curvature of the refracting surfaces of the eye in the
different meridia. The cornea is the surface which usually shows the greatest
astigmatism. This defect is demonstrated by numerous forms of astigmatic
charts, the most serviceable of which are the barred-letter test type, the clock
dial, or the dials shown in figure 463 or 483. Hang an astigmatic dial at a
distance of six meters and test the right and left eyes separately, as follows:
When the vision is focussed on the center of the dial, if the eye is normal,
the three bars in each radius of the clock dial will be seen with equal distinct-
ness and have sharp black lines. In an astigmatic eye one or more of these
radii will appear sharp and distinct, while the other will appear dim and
THE BLIND SPOT 675
indistinct, the relative difference depending upon the degree of astigmatism.
Note the meridian of astigmatism in the right and left eyes separately. Use
the test set, and find the cylinder necessary to correct the astigmatism in each
eye and determine its meridian.
Astigmatism is commonly shown by the presence of radii when one looks
at the stars at night, or by the ragged outline of a pin-hole in a card, when
held at arm's length against a white sky. In extreme cases outlines like
FIG. 484. — Diagram for Demonstrating the Blind Spot.
the bars in the window sash or checks in clothing may be distorted, or some
of the lines may not even be seen.
1 8. The Blind Spot. Look with the right eye at the spot in the ac-
companying figure at a distance of about 20 to 25 cm., covering the left eye.
Hold the spot in the line of direct vision and move the book to and from
the eye; in some cases it is necessary to rotate the book slightly. It will be
found that the cross to the right will, at a certain position, completely disappear.
This happens when its image falls on the retina directly over the entrance of
the optic nerve, which has no visual cells, and is, therefore, the blind spot.
FIG. 485. — The Blind Spot with the Eye 30 cm. from the Paper.
This area is large enough to cause a man completely to disappear at a dis-
tance of about one hundred meters.
Place a sheet of white paper at a distance of 30 cm. in front of the eye,
holding the head in a fixed position by some support; look with the right eye
at the top of the cross made on the left of the sheet of paper. Covering the
sharpened portion of a lead pencil with white paper, leaving the black tip
exposed, move this pencil across the paper from the visual center to the
right. At a certain distance the black lead will suddenly disappear.
676 THE SENSES
Mark this point. Continue to move the pencil until the lead reappears.
Mark this point. These two points represent the limits of the blind spot in
the horizontal plane, as magnified by the conditions of the experiment. Mark
the limits in the other meridians in the same manner. Compute from the
figures obtained the exact size of the blind spot in your right eye, figure 485.
Repeat on the left eye. Usually these areas are not symmetrical. The com-
putation may be based on the following proportion: a, the diameter of the
mapped blind spot is to the distance of the map from the nodal point of the
eye, x, as c, the distance from the nodal point to the retina, which is 1.5 cm.,
is to x, the diameter of the actual blind spot in the retina, x varies from
1.5 to 3 or more mm. a : b : : c : x.
19. Relations of the Size of the Retinal Image to Distance. Com-
pute the size of the retinal images of familiar objects by the equation given
in the last experiment. Compute the size of the image formed on the,, retina
by a man six feet tall at a distance of 100 feet. Compute the size of the
image formed by a tower 125 feet tall at a distance of 575 feet.
20. Purkinje's Shadows. Stand in front of a blackened wall in
the dark room. While looking toward the wall with the right eye accom-
modated for distant objects, move a lighted candle back and forth about
10 to 20 cm. to the right of the eye and a little below its level. Presently
many branching shadows will be seen as though they stood in space in front
of the individual. These are the shadows of the blood-vessels cast upon the
retina. A careful examination will show that these shadows seem to con-
verge to a point to the right of the center of vision of the right eye. By moving
the candle up and down or from side to side, the shadows seem also to move
slightly. Many persons can readily see Purkinje's figures by looking through
the narrow spaces between the fingers of the hand moved close in front of
the eye, when the vision is directed toward a bright sky. One can demonstrate
by this means that the macula is free from blood-vessels, since the pattern
of the blood-vessels around the borders of the macula is very readily de-
termined. This is especially true if there is slight retinal congestion.
21. Duration of the Retinal Image. When a beam of light falls
upon the retina for an instant it produces a stimulus which endures for a
time after the stimulus is removed. This interval can be measured by the proper
mechanical device. Place on the color wheel a disc, which has a small seg-
ment cut out at one point on the periphery. Put a printed page behind the
segment with the observer standing in front. Rotate the segment faster and
faster until the printed page is seen continuously. At this point the visual
image made at one revolution of the disc lasts until the next impression on
the same spot. The speed of the revolution of the color wheel can be measured
by attaching an electric contact key and signal magnet to the disc wheel and
measuring the rate of interruptions against the known vibrations of a tuning
fork. The same phenomenon may be determined by placing on the disc
LIMITS OF THE FIELD OF VISION 677
two complemental colors and judging the speed of revolution required for
complete fusion.
22. Limits of the Field of Vision. The limits of the visual field are
determined by direct measurement with the perimeter. Set the person whose
retina is to be measured in a comfortable erect position, with one eye at the
center of the arc of the perimeter and the other covered by an eye-shade.
The observed eye must be fixed on the center of the field of vision, and care
must be used to prevent obstruction of the field. The examination is made
with greatest accuracy by bringing an object into the field of vision from behind
the person observed. When the individual examined first detects the presence
of the object, he announces it and the angle is read off from the arc of the
perimeter and recorded on the chart for the purpose. These readings should
be made in about twelve radii. They should be made for each eye.
23. Limits for the Field of Vision for Color. To measure the limits
of the field of vision for colors one should proceed as in the preceding experi-
ment, except that small squares of colored papers are brought into the field
from the rear. The retina should be mapped for red, green, yellow, and blue.
Use Bradley's pure color papers. Take four penholders and mount on the
end of one a centimeter square of red paper, on the others green, yellow, and
blue. To make a determination bring the color up from behind and, as soon
as it is certainly detected and announced, remove it from the field of vision.
Examine the eye for all four colors at one sitting, mixing them indeterminately
in the individual tests. Occasionally an eye will be found which exhibits a
well-marked restriction of the color field, though the individual himself may
not be completely color-blind.
24. Color-Blindness. Make an examination for color-blindness,
using Holmgren's colored yarns. Spread the yarns out on a table in the best
of light. Place the three confusion skeins in front of the individual to be ex-
amined and ask him to match them quickly from the skeins on the table,
paying no attention to lights and shades of the same color. A color-blind
individual will confuse colored skeins, most usually the reds, greens, and grays.
25. Color Mixing. Use Bradley's color wheel and test the effect
of simultaneous stimulation of the retina with two or more colors, by placing
on the wheel two or more colored discs, rotating the wheel at a speed sufficient
to cause complete fusion. The sensation produced by two colors applied
simultaneously will be entirely different from that produced by either alone.
Red and green (or greenish blue), when mixed in the proper proportion, pro-
duce a sensation of gray. The same effect may be had from yellow and blue,
orange and violet, or any of the complementary colors chosen according to
the geometrical color table, figure 473. By mixing three colors, red, green,
and violet, in the proper proportion one can produce a sensation almost the
same as that produced by white light.
26. Color After-images. Color after-images can be demonstrated
678 THE SENSES
by looking continuously at the center of one of the primary colors of Bradley's
color charts against a white or gray wall until there is apparent fatigue,
then suddenly removing the chart. An after-image of approximately the
complementary color will appear in the course of a few seconds. Occasionally
these images are very vivid. The experiments are brilliant if performed in
the dark room, using colored gelatin screens through which an intense light
shines. When the light is turned off, a brilliant after-image of the comple-
mentary color appears.
27. Retinoscopy. Use the ordinary small ophthalmoscope and ex-
amine the retina of the eye of a cat or rabbit. Dilate the eye by the use of
atropine. Place the animal whose eye is to be examined on a support in
front of a bright but uniform light (an Argand burner). Reflect the light
from the mirror of the ophthalmoscope through the pupil into the retinal cup
of the animal. Usually the ophthalmoscope has to be focussed for a cat's
retina. When a good light is secured, the retinal cup will appear as a bril-
liantly colored disc, with the branching blood-vessels, and usually with some
brilliant bluish-green pigment in the lower portions of the retinal disc.
After some practice on the cat or the rabbit, the student should examine
the retina of one of his mates, preferably an eye that has an unusually wide
pupil. In some cases a light dosage of homatropine may be used on one eye.
This will dilate the pupil and the examination will be much easier.
Students are not recommended to use atropine unless under conditions
which permit the eye to rest for two or three days following.
28. Visual Acuity. The visual acuity of the eye should be tested
first for the right eye, then for the left. Hang a test chart at a distance of
twenty feet, so that its disc is well illuminated, and allow the individual tested
to read off the letters on the chart, beginning with the larger ones at the top.
The letters on this chart are constructed on the basis of a visual angle of five
degrees. When the letters marked "twenty feet" or "six meters " represent
the limit of accurate identification, the visual acuity is said to be i, or
normal. If the line marked "thirty feet" is the limit, then the acuity is one
and a half; if "fifteen feet," then the visual acuity is three-fourths, etc.
If the eyes tested are astigmatic, or have other optical defects, these must
first be corrected before testing for visual acuity.
29. The Test Set. The student is recommended to close the ex-
periments on the eye by fitting glasses for himself and at least two others.
He should correct for the defects that have been revealed in the preceding
experiments, especially for astigmatism; myopia, or hypermetropia ; and
presbyopia. Of course each eye must be tested and fitted separately.
CHAPTER XVI
THE REPRODUCTIVE ORGANS
THE REPRODUCTIVE ORGANS OF THE MALE.
THE male reproductive organs comprise the Testes, the Vas Deferens,
the Vesicula Seminalis, the Prostate Gland, and the Penis.
The Testes. The testes consist of two parts, i, the testicle, which
is covered by the tunica vaginalis and secretes the germinal cells, and 2, the
conducting tubules, which compose the epididymis and vas deferens.
The testicle is divided by connective-tissue septa into lobules, the tubuli
semi ni jeri. Each tubule is limited by a membrana propria on which rests
the germinal epithelium.
On the approach of sexual maturity the process of spermatogenesis begins.
\
FIG. 486. FIG. 487.
FIG. 486.— Plan of a Vertical Section of the Testicle, Showing the Arrangement of the Ducts.
The true length and diameter of the ducts have been disregarded, a, a, Tubuli seminiferi coiled
up in the separate lobes; b, tubuli recti or vasa recta; c, rete testis; d, vasa deferentia ending in
the coni vasculosi; /, e, g, convoluted canal of the epididymis; h, vas deferens; /, section of
the back part of the tunica albuginea; i, i, fibrous processes running between the lobes; s, me-
diastinum.
FIG. 487.— Vertical Section through the Wall of the Tubules of Epididymis. X 700 (Kol-
liker.) b, Connective tissue and smooth muscle cells; e, basal layer of epithelial cells; f, high
columnar cells; p, pigment granules in columnar cells; c, cuticula; h, cilia.
The germinal cells multiply rapidly, and, by a complex series of mi totic divisions
or stages, form ultimately the male reproductive cells, or sperm cells.
The important stages in order are: archispermiocyte, spermatogonia,
primary and secondary spermatocytes, spermatids, and spermatozoa. The
spermatogonia stage is the stage of rapid multiplication; the spermatocyte,
that of maturation, comparable to the maturation stage of the ovum.
679
680
THE REPRODUCTIVE ORGANS
The sperm cells are the essential male reproductive cells. Each sperma-
tozoan consists of a minute oval head, a middle piece, and a tail. The head
is 4 /* by 2.5 P. The middle piece and tail are about 50 to 60 M long.
Sperm cells possess the power of flagellate movement.
The Vas Deferens. This is the single duct proceeding from each
testicle to join its fellow at the base of the bladder. Each has an ampulla or
spc.i
FIG. 488. — Later Stages in Spermatogenesis of the Bull, spg.r, Reserve spermatogonium;
spg, spermatogonium; spc.g, spermatocyte in late synapsis stage; spc.i, spermacyte in stage just
preceding the maturation divisions; spd, spermatids in advanced stage of histogenesis, with
heads deeply embedded in Sertoli cell. Highly magnified. (After Schoenfeld.)
enlargement just before it unites with its fellow. The vas deferens has muscu-
lar walls and is lined with ciliated epithelial cells.
The Vesiculae Seminales. The seminal vesicles have the appear-
ance of outgrowths from the base of the vasa deferentia. Each vas deferens,
just before it enters the prostate gland, through part of which it passes to
terminate in the urethra, gives off a side branch which bends back from it at
an acute angle. This branch, dilating, variously branching, and pursuing in
THE PENIS
681
both itself and its branches a tortuous course, forms the vesicula seminalis.
Each vesicula is a single-branching convoluted and sacculated tube.
The structure resembles closely that of the vasa deferentia.
The Penis. The penis is attached to the symphysis pubis by its
root. It is composed of three long, more or less cylindrical masses enclosed
PIG. 489. — Section of a Tubule of the Testicle of a Rat, to Show the Formation of the Sperma-
tozoa, a, Spermatozoa; b, seminal cells; c, spermatoblasts, to which the spermatozoa are still
adherent; d, aaembrana propria; e, fibro-plastic elements of the connective tissue. (Cadiat.)
FIG. 400 — Dissection of the Base of the Bladder and Prostate Gland, Showing the Vesiculae
Seminales and Vasa Deferentia. a, Lower surface of the bladder at the place of reflection of the
peritoneum; b, the part above covered by the peritoneum; i, left vas deferens, ending in e, the
ejaculatory duct; the vas deferens has been divided near i, and all except the vesical portion
has been taken away; s, left vesicula seminalis joining the same duct; s,s, the right vas deferens
and right vesicula seminalis. which has been unraveled; p, under side or the prostate gland; m,
part of the urethra; u, u, the ureters (cut short), the right one turned aside. (Waller.)
682
THE REPRODUCTIVE ORGANS
in remarkably firm fibrous sheaths. Two, the corpora cavernosa, are alike
and are firmly joined together. They receive below and between them the
third part, or corpus spongiosum. The urethra passes through the corpus
spongiosum. The enlarged extremity, or glans penis, is continuous with the
corpus spongiosum. Cowpcr's glands are at its base, and their ducts open
into the base of the urethra.
The Prostate Gland. The prostate is situated at the neck of the
urinary bladder, and encloses the base of the urethra. The prostate is made
up of small compound tubular glands embedded in an abundance of mus-
FIG. 491. — Human Spermatozoa (after Retzius). A, Side view; B, front view.
cular fibers and connective tissue. The glandular substance consists of
numerous small saccules, opening into elongated ducts, which unite into a
smaller number of excretory ducts. The acini of the upper part of the prostate
are small and hemispherical, in the middle and lower parts the tubes are
longer and more convoluted. The ducts, twelve to twenty in number, open
into the urethra. They are lined by a layer of columnar cells, beneath which
is a layer of small polyhedral cells.
The muscular tissue of the prostate not only forms the chief part of the
stroma of the gland, but also forms a continuous layer inside the fibrous sheath,
as well as a layer surrounding the urethra continuous with the sphincter of
the bladder.
The Seminal Fluid. The sperm cells of the testes are joined on their
way to the exterior by the fluids secreted by the mucous lining of the various
tubules and glands. Of the fluids the chief ones are the secretions of the
THE REPRODUCTIVE ORGANS OF THE FEMALE 683
seminal vesicles, of the prostate gland, and of Cowper's glands. The sperm
cells and the secretions together constitute the seminal fluid.
After the period of puberty the seminal fluid is secreted constantly but
slowly, except under sexual excitement. It is ordinarily received into the
seminal vesicles, whence it is expelled at the time of coitus. In celibates the
seminal fluid may at times escape in small quantity into the urethra to be
washed away by the urine, or periodic reflex emissions may occur. The
seminal vesicles contribute a secretion, as well as a vesicle to receive the sperm.
The secretion of the seminal vesicles and that of the prostate gland are
in some way concerned in maintaining the activity and prolonging the life of
the spermatozoa. These cells remain alive in the fluid for as much as forty-
eight hours after removal from the body, and remain alive quite indefinitely
in the vesicles in the body. The secretions have been proven necessary to
the life and function of the spermatozoa by the results of operations in which
the seminal vesicles and the prostate were removed, whereby the animal be-
came sterile.
THE REPRODUCTIVE ORGANS OF THE FEMALE.
The female genital organs consist of the ovaries, the Fallopian tubes, the
uterus, and the vagina.
The Ovaries. The ovaries are paired bodies, situated in the cav-
FIG 492.— Diagrammatic View of the Uterus and Its Appendages, .as Seen from Behind. The
uterus and upper part of the vagina have been laid open by removing the posterior wall; the
Fallopian tube, round liagment, and ovarian ligament have been cut short, and the broad liga-
ment removed on the left side. «, The upper part of the uterus; c, the cervix opposite the os m-
SSSTtte triangular shape of the uterine cavity is shown, and the dilatation of the cervical
cavity with the rug* termed arbor vite; v, upper part of the vagina; od Fallopian tube -or ovi-
duct • the narrow communication of its cavity with that of the cornu of the uterus on each side is
seen- /, round ligament; lo, ligament of the ovary; o, ovary; «, wide outer part of the right Fal-
lopian tube; fi, its fimbriated extremity; po, parovarium; h. one of the hydatids frequently found
connected with the broad ligament, i. (Allen Thomson.)
ity of the pelvis, and adherent to the posterior surface of the broad ligament.
The border of the ovary is called the hilum, and it is at this point that the
684
THE REPRODUCTIVE ORGANS
blood-vessels and nerves enter it. Each ovary is about 4 cm. long, 2 cm. wide,
and 1.25 cm. thick. It is supported by the suspensory ligament.
The internal structure of the ovary consists of a peculiar soft fibrous con-
nective tissue, stroma, abundantly supplied with blood-vessels. The surface
of the ovary is covered with cubical epithelium. Embedded in the stroma in
various stages of development are numerous minute follicles cr vesicles, the
Graafian follicles, containing the ova, figure 494. They are small and numer-
ous near the surface of the ovary, either arranged as a continuous layer, as
in the cat or rabbit, or in groups, as in the human ovary. Nearer the center
are large and fully developed follicles.
Each follicle has an external membranous envelope, or membrana propria,
which is lined with a layer of nucleated cells, forming a kind of epithelium
FIG. 493 . — Diagrammatic Section of the Ovary, Showing its Cortical or Ovigenous Layer, Formed
of Ovisacs in Various Stages of Evolution. (Duval.) A, A, A, Primordial ovisacs; B, B, B, ovisacs
further developed; C, ovisac approaching maturity; D, ripe ovisac with its proligerous disc (DP)
containing the ovum; MG, membrana granulosa; H, hilum of ovary.
or internal tunic, and named the membrana granulosa. The cavity of the
follicle contains the ovum enclosed in a very delicate membrane. The large
spherical nucleus contains one or more nucleoli. The nucleus is known as
the germinal vesicle, and the nucleolus as the germinal spot.
The human ovum measures about 0.2 mm. in diameter. Its external
investment, or the zona pellucida, or vitelline membrane, is a transparent
membrane, about 10 ^ in thickness, which under the microscope appears
as a bright ring, figure 495. The ovum itself has the characteristic structure
of the typical cell, with the exception that its cytoplasm is filled with numerous
yolk granules. The larger granules cr globules, which have the aspect of
fat-globules, are in greatest number at the periphery of the yolk.
The nucleus, or germinal vesicle, is about 0.05 mm. in diameter. The
vesicle is of greatest relative size in the smallest ova.
The Graafian follicles are formed in the following manner: The em-
THE OVARIES
685
bryonic ovary is covered with short columnar cells, or the so-called germinal
epithelium. The cells of this layer undergo proliferation so as to form several
strata, and grow into the ovarian stroma as longer or shorter columns or tubes.
By degrees these tubes become cut off from the surface epithelium, and form
cell nests, small if near the surface, larger if in the depth of the stroma. The
nests increase in size from multiplication of their cells. , Certain cells of the
germinal epithelium enlarge, and form ova; and the formation of ova takes
place in the nests within the stroma. The small cells of a nest surround
the ova, and form their membrana granulosa, and the stroma growing up
separates the surrounded ova into so many Graafian follicles.
The smallest follicles are formed at the surface, and make up the cortical
Downgrowths of epith^Hum
Germinal epithelium
Ovum with its investing cells
Stratum grajmlosom
epithelial cells Ovarian strorna
Graafian follicle
Ovum
uorfolliculi
Discus proligerus
FIG. 494. — A, Diagrammatic Representation of the Manner in which the Graafian Follicles
Arise During the Development of the Ovary. B, Diagram Illustrating the Structure of a Ripe
Graafian Follicle. (Cunningham.)
layer. It is said by some that the superficial follicles as they ripen become
more deeply placed in the ovarian stroma; and, again, that as they increase
in size, they make their way toward the surface.
When the Graafian follicles mature, they form little prominences on the
exterior of the ovary covered only by a thin layer of condensed fibrous tissue
and epithelium. From the earliest infancy, and through the whole fruitful
period of life, there appears to be a constant formation, development, and
maturation of Graafian vesicles, with their contained ova. Until the period
of puberty, however, the process is comparatively inactive. But, coincident
with the other changes which occur in the body at the time of puberty, the
ovaries enlarge and become very vascular, the formation of Graafian vesicles
is more abundant, the size and degree of development attained by them are
greater, and the ova are capable of being fertilized.
THE REPRODUCTIVE ORGANS
The Fallopian Tubes, or Oviducts. The Fallopian tubes are about
10 cm. in length and extend between the ovaries and the upper angles of the
uterus. At the point of attachment to the uterus, each tube is very narrow;
but in its course to the ovary it increases to about 3 mm. in thickness. At
its distal extremity, which is free and floating, it bears a number of fimbria,
one of which is longer than the rest and is attached to the ovary. The canal
FIG. 495. — Diagrammatic Representation of a Human Ovum and Its Coverings. (Cunning-
ham.)
The corona radiata, which completely surrounds the ovum, is represented only in the lower
part of the figure.
1, Corona radiata; 5, vi tell us or yolk;
2, granular layer; 6, germinal vesicle (nucleus);
3, vitelline membrane; 7, germinal spot (nucleolus);
4, zona pellucida (oolemma) ; 8, nuclear membrane.
of the tube is narrow, especially at its point of entrance into the uterus. Its
other extremity is wider and opens into the cavity of the abdomen by the
fimbriae. The Fallopian tube is invested with peritoneum, and its canal is
lined with ciliated epithelium.
The Uterus. The uterus, u, c, figure 492, is a somewhat pyriform
organ, and is about 7.5 cm. in length, 5 cm. in breadth at its upper part
or fundus, but at the neck or cervix only about 1.25 cm. The part be-
tween the fundus and neck is termed the body of the uterus; it is about
2.5 cm. in thickness.
The uterus is constructed of three principal layers, or coats: serous,
fibrous and muscular, and mucous. The serous coat, which has the same
general structure as the peritoneum, covers the organ except the front surface
of the neck. The middle coat is a thick mass of unstriped muscle. The
muscle fibers become enormously developed during pregnancy. The arteries
THE VAGINA 687
and veins are found in large numbers in the outer part so as to form almost a
special vascular coat. The mucous membrane of the uterus is composed of col-
umnar ciliated epithelium, which extends also to the interior of the tubular
glands, of which the mucous membrane is largely made up. In the cervix of
the uterus the mucous membrane is arranged in permanent longitudinal folds,
palma plicatce. The glands of this part branch repeatedly, and extend deeply
into the substance of the cervix. The body has numerous simpler tubular
glands. The glands are also lined with ciliated epithelium. They secrete a
thick glairy mucus, resembling white of egg.
The Vagina. The vagina is a membranous canal 8 to 10 cm. long,
extending obliquely downward and forward from the neck of the uterus,
which it embraces, to the external organs of generation. It is lined with
mucous membrane, covered with stratified squamous epithelium, which in
the ordinary contracted state of the canal is thrown into transverse folds.
External to the mucous membrane, the walls of the vagina are constructed
of unstriped muscle and fibrous tissue, within which in the submucosa,
especially around the lower part of the tube, is a layer of erectile tissue. The
lower extremity of the vagina is embraced by an orbicular muscle, the sphincter
vagina. The external organs of generation are the clitoris, the labia interna
or nymphce; and, the labia externa or pudenda, formed of the external integu-
ment, and lined internally by mucous membrane. Numerous mucous follicles
are scattered beneath the mucous membrane of the external organs of genera-
tion; and two larger lobulated glands, the glands of Bartholin, analogous to
Cowper's glands in the male, are located at the sides of the lower part of the
vagina. The ducts of these glands are about 1 2 mm. long and open immediately
external to the hymen at the mid-point of the lateral wall of the vaginal orifice.
Ovulation and Menstruation. In the process of development in the
ovary, the individual Graafian follicle increases in size and gradually ap-
proaches the surface of the ovary. When fully ripe or mature, it forms a
little projection on the exterior. Coincident with the increase in size, which
is caused by the augmentation of its liquid contents, the external envelope
of the distended vesicle becomes very thin and eventually bursts. The ovum
and fluid contents of the vesicle escape on the exterior of the ovary, whence
they pass into the Fallopian tube.
In man and mammals ovulation apparently occurs only at certain periods.
These periods seem to precede or occur during the changes in the woman
that constitute the phenomenon of menstruation, or, in the lower mammals,
of heat.
That ovulation and discharge occur periodically, and only during the
phenomenon of heat, in the lower mammalia, is made probable by the facts
that, in all instances in which Graafian vesicles have been found presenting
the appearance of recent rupture, the animals were at the time or had recently
been in heat. There are few authentic and detailed accounts of Graafian
688
THE REPRODUCTIVE ORGANS
vesicles being found ruptured in the intervals of heat; and females do not ad-
mit the males, and never become impregnated, except at those periods. Al-
though conception is not confined to the periods of menstruation, yet it is
more likely to occur about a menstrual epoch than at other times.
The exact relation between the discharge of ova and menstruation is not
very clear. It was formerly believed that menstruation was the result of
a congestion of the uterus arising in association with the enlargement and
rupture of a Graafian follicle; but though a Graafian follicle is, as a rule,
ruptured at each menstrual epoch, yet instances are recorded in which men-
struation has occurred where no Graafian follicle can have been ruptured, and
FIG. 496.
FIG. 497-
FIG. 498.
FIG. 496. — Diagram of Uterus just Before Menstruation. The shaded portion represents the
thickened mucous membrane.
FIG. 497. — Diagram of Uterus when Menstruation has just Ceased, Showing the Cavity of the
Uterus Deprived of Mucous Membrane.
FIG. 498.— Diagram of Uterus a Week After the Menstrual Flux has Ceased. The shaded por-
tion represents renewed mucous membrane. (J. Williams.)
cases where ova have been discharged in amenorrheic women. It must
therefore be admitted that menstruation is not dependent on the matura-
tion and discharge of ova.
Observations made after death, and facts obtained by clinical investiga-
tion, support the view that rupture of a Graafian follicle does not happen on
the same day of the monthly period in all women. In the minority of cases
it may occur toward the close or soon after the cessation of a flow. On the
other hand, in almost all subjects examined after death, of which there is
record, rupture of the follicle appears to have taken place before the com-
mencement of the menstrual flow.
SOURCE AND CHARACTER OF MENSTRUAL CHANGES
However, the presence of the ovaries seems necessary for the performance
of the menstrual function; for women do not menstruate when both ovaries
have been removed by operation. (See page 432 for a discussion of the
functional effects of removal of the ovary.)
Source and Character of Menstrual Changes. The menstrual periods
usually occur at intervals of a lunar month, the duration of each being from
three to six days. In some women the intervals are so short as three weeks
or even less; while in others they are longer than a month. The periodical
return is usually attended by pains in the loins, a sense of fatigue in the
lower limbs, and other symptoms, which vary extremely in different individuals.
The menstrual discharge is a thin sanguineous fluid, and consists of blood,
epithelium, and mucus from the uterus and vagina. The menstrual flow is
preceded by a general engorgement of all the pelvic organs with blood. The
cervix and vagina become darker in color and softer in texture, and the quantity
of mucus secreted by the glands of the cervix and body is increased. The
uterine mucous membrane is swollen and the glands are enlarged. The dis-
charge of blood, the source of which is the mucous membrane of the body
of the uterus, is probably associated with uterine contractions. There is
great difference of opinion as to whether or not any of the uterine mucous
membrane is normally shed during the process of menstruation. John
Williams believes that the whole of the mucous membrane of the body of
the uterus is thrown off at each monthly period, forming a true decidua men-
strualis, figure 496, while Moricke and others believe that the mucous mem-
brane remains intact. Leopold believes that red blood-corpuscles escape
from the congested capillaries and undermine the superficial epithelium, and
that in this way the superficial layer of the mucous membrane is eroded and
subsequently regenerated. There is a period of regeneration followed by a
period of rest before the next repetition. Minot distributes the variations in
time as follows :
Tumefaction 5 da7s
Menstrual discharge 4
Restoration of mucosa 7
Period of rest 12
The menstrual period is often accompanied by profound disturbances in
other parts of the body, especially of the vascular and of the nervous systems
and of the nutritive processes.
Corpus Luteum. Immediately before, as well as subsequent to, the rupture
of a Graafian follicle and the escape of its ovum, changes ensue in the interior
of the follicle, which result in the production of a yellowish mass, termed a
Corpus luteum.
When fully formed, the corpus luteum of mammals is a roundish solid
body, of a yellowish or orange color, and composed of a number of lobules,
44
gg0 THE REPRODUCTIVE ORGANS
which surround, sometimes a small cavity, but more frequently a small stelli-
form mass of substance, from which delicate processes pass as septa between
the several lobules. The processes gradually change till they nearly fill the
cavity of the follicle, and even protrude from the orifice in the external cover-
ing of the ovary. Subsequently this orifice closes, but the fleshy growth within
still increases during the earlier period of pregnancy, the color of the substance
gradually changing to yellow, and its consistence becoming firmer. After
the orifice of the follicle has closed, the growth of the yellow substance con-
tinues during the first half of pregnancy, till the cavity is reduced to a com-
paratively small size or is obliterated; in the latter case, merely a white stelli-
form cicatrix remains in the center of the corpus luteum.
The first changes of the internal coat of the Graafian follicle in the proc-
ess of formation of a corpus luteum seem to occur in every case in which an
ovum escapes. If the ovum is impregnated, the growth of the yellow sub-
stance continues during nearly the whole period of gestation and forms the
large corpus luteum commonly described as a characteristic mark of impreg-
nation.
The significance of the corpus luteum is found in the belief that it is the
portion of the ovary especially concerned in the production of an internal
secretion that affects the uterus, especially stimulating it at and before the
menstrual period.
Menstrual Life. The occurrence of a menstrual discharge is one
of the most prominent indications of the commencement of puberty^ in the
female sex; though its absence even for several years is not necessarily at-
tended with arrest of the other characters of this period of life or incapability
of impregnation. The average time of its first appearance in females of this
country and others of about the same latitude is from fourteen to fifteen:
but it is much influenced by the kind of life to which girls are subjected, being
accelerated by habits of luxury and indolence, and retarded by contrary con-
ditions. Its appearance may be slightly earlier in persons dwelling in warm
climates than in those inhabiting colder latitudes. The menstrual functions
continue through the whole fruitful period of a woman's life, and usually
cease between the forty-fifth and fiftieth years, which time is known as the
climacteric. Menstruation does not usually occur in pregnant women.
CHAPTER XVII
DEVELOPMENT
Changes Which Occur in the Ovum Prior to Impregnation. The
ovum when ripe and detached from the ovary is a single cell enclosed within
the zona pellucida, and containing the germinal vesicle and germinal spot.
The ovum undergoes a series of changes preparatory to fertilization, known
as maturation, the general effect of which is to reduce the chromatin in anticipa-
FIG. 499. — The Maturation of the Ovum; Extrusion of the "Polar Bodies." (Diagrammatic.)
A, An ovum at the commencement of the process; B, after the formation of the spindle. The
chromosomes are gathered at the equator of the spindle. C, One apex of the spindle has pro-
jecteJ into a bud on the surface, and half of the divided dyads have passed to each pole; D, the
separation of the first polar body; E, the commencement of the second polar body; F, the comple-
tion of the second polar body. (Cunningham.)
tion of the added chromatin from the sperm nucleus. The primary change
observed in the ovum consists in the migration of the germinal vesicle or nucleus
to the surface, and the disappearance of its nuclear membrane, with a con-
sequent indistinctness of its outline. Its protoplasm becomes to a consider-
able extent confounded with the yolk substance, and its germinal spot dis-
appears. The next step in the process is the appearance in the yolk of two
691
692
DEVELOPMENT
centrosomes in a clear space near the poles of the elongated vesicle, and the
formation of a nuclear spindle, with the aster at either end lying near the sur-
face of the yolk. The nucleus now divides
into two parts, and that nearer the surface
is extruded from the ovum enveloped in a
very small amount of protoplasm. This
forms the first polar body. The nucleus
again divides by mitosis, one-half of the
chromatin is extruded from the ovum,
forming a second polar cell; the chro-
matin that remains behind constitutes the
female pronucleus. The centrosome has
disappeared and the ovum undergoes no
further changes unless fertilized by the
sperm.
Changes Following Impregnation.
The process of impregnation of the ovum
has been observed most accurately in the
lower types. The process is as follows:
The head of a single spermatozoon joins
with an elevation of the yolk substance, the
tail remaining motionless and then disap-
pearing. The head enveloped in the proto-
plasm then sinks into the yolk and becomes
a nucleus, from which the yolk substance
is arranged in radiating lines. This is the
male pronucleus. The middle piece of the
sperm is believed to furnish a new centro-
some to the ovum. The centrosome now
divides and moves to either side the two
pronuclei, a segmentation spindle is formed,
and the egg undergoes its first segmen-
tation.
The process of segmentation begins
almost immediately in each half of the yolk,
and cuts it also in two. The process is
repeated until at last by continued cleav-
ages the whole yolk is changed into a mul-
berry-like mass, still enclosed by the zona
pellucida, figure 500. Fertilization prob-
ably takes place in the Fallopian tubes, and
segmentation of the fertilized ovum occurs
on its passage to the uterus.
PIG. 500. — Conversion of the Mo-
rula to the Blastula. Formation of
Blastodermic Vesicle and Membrane.
A, Appearance of segmentation cavity
and attachment of inner cell- mass to
ectoderm at upper pole of ovum; B1,
extension and flattening of inner cell-
mass as it oc urs in rabbits and some
other mammals; B2, extension of en-
toderm as it occurs in insectivora,
monkeys, apes, and man; C, comple-
tion of bilaminar blastodermic vesi-
cle; BC, blastodermic cavity; EC,
ectoderm; EE, embryonic ectoderm;
EN, entoderm; 7, inner cell-mass;
SC, segmentation cavity; ZP, zona
pellucida. (Cunningham.)
CHANGES FOLLOWING IMPREGNATION
The passage of the ovum from the ovary to the uterus occupies probably
eight or ten days in the human.
The peripheral cells, which are formed first, arrange themselves at the sur-
face of the yolk into a membrane, the ectoderm. The deeper cells of the in-
terior pass gradually toward the surface, thus increasing the thickness of the
membrane already formed by a second, or entoderm, layer of cells, while the
central part of the yolk, the blastoderm cavity, remains filled only with a clear
fluid. By this means the yolk is shortly converted into a kind of secondary
vesicle, the walls of which are composed externally of the original vitelline
membrane, and within by the newly formed cellular layer, the blastoderm or
germinal membrane, as it is called.
Important changes occur in the structure of the mucous membrane of
the uterus. The epithelium and subepithelial connective tissue, together
with the tubular glands, increase rapidly, and there is a greatly increased
vascularity of the whole mucous membrane, while a substance composed
PIG. 501. — Section of the Lining Membrane of a Human Uterus at the Period of Commencing
Pregnancy, Showing the Arrangement and Other Peculiarities of the Glands, d, d, d, with Their
Orifices, a, a, a, on the Internal Surface of the Organ. Twice the natural size.
chiefly of nucleated cells fills up the interfollicular spaces in which the blood-
vessels are contained. The effect of these changes is an increased thickness,
softness, and vascularity of the mucous membrane, the superficial part of
which itself forms the membrana decidua.
The object of this increased development is the production of nutritive
materials for the ovum; for the cavity of the uterus shortly becomes filled
with secreted fluid, consisting almost entirely of nucleated cells in which the
chorion villi are embedded.
When the ovum first enters the uterus it becomes embedded in the structure
of the decidua, which is yet quite soft, and in which soon afterward three
portions are distinguishable. These have been named the decidua vera, the
decidua basalis, and the decidua capsularis.
In connection with these villous processes of the chorion, there are de-
veloped depressions or crypts in the decidua vera, which correspond in shape
to the villi they are to lodge; and thus the chorionic villi become more or
less embedded in the maternal structures. These uterine crypts, it is im-
694
DEVELOPMENT
portant to note, are not, as was once supposed, merely the open mouths of
the uterine follicles.
The Placenta. During these changes the deeper part of the mucous
membrane of the uterus, at and near the region where the placenta is
placed, becomes hollowed out by sinuses, or cavernous spaces, which com-
municate on the one hand with arteries and on the other with veins of the
uterus. Into hese sinuses the villi of the chorion protrude, pushing the thin
Pecidua basalis
Unchanged layer Maternal vessel
Stratum spongiosum
Stratum compactum
Placontal villus.
Primitive streak
Mesoderm
Placental villus
Cavity wind
becomes cud on
Decidua vera/
Decidua vera
FIG. 502. — Diagram of the Early Stage of Human Embryo in Relation to the Uterus.
(Cunningham.)
walls of the sinuses before them, and so come into intimate relation with the
blood contained in them. There is no direct communication between the blood-
vessels of the mother and those of the fetus; but the layer or layers of membrane
intervening between the blood of the one and of the other offer no obstacle to
a free interchange of matters between them by diffusion and osmosis. Thus
the villi of the chorion, containing fetal blood, are bathed or soaked in maternal
blood contained in the uterine sinuses.
The placenta, therefore, of the human subject is composed of a fetal part
and a maternal part — the term placenta properly including all that entangle-
ment of fetal villi and maternal sinuses, by means of which the blood of the
fetus is enriched and purified after the fashion necessary for the proper growth
and development of those parts which it is designed to nourish.
The whole of this structure is not, as might be imagined, thrown off
immediately after birth. The greater part, indeed, comes away at that time,
as the after-birth; and the separation of this portion takes place by a rending
CIRCULATION OF BLOOD IN THE FETUS
695
or crushing through of that part at which its cohesion is least strong, namely,
where it is most burrowed and undermined by the cavernous spaces before
referred to. In this way it is cast off with the fetal membrane. The remain-
ing portion is either gradually absorbed, or thrown off in the uterine dis-
charges which occur at this period. A new mucous membrane is of course
gradually developed.
Circulation of Blood in the Fetus. The circulation of blood in
the fetus differs considerably from that of the adult.
Returning from the placenta by the umbilical vein the blood is first con-
veyed to the under surface of the liver, where the stream is divided— a part of
the blood passing straight on to the inferior vena cava through a venous canal
FIG. 503. — Diagrammatic View of a Vertical Transverse Section of the Uterus at the Seventh
or Eighth Week of Pregnancy, c, c, c', Cavity of uterus, which becomes the cavity of the decidua,
opening at c, c, the cornua, into the Fallopian tubes, and at cf into the cavity of the cervix, which
is closed by a plug of mucus; dv, decidua vera; dr, decidua reflexa, with the sparser villi embedded
in its substance; ds, decidua serotina, involving the more developed chorionic villi of the commenc-
ing placenta. The fetus is seen lying in the amniotic sac. The umbilical cord and its vessels
pass up from the umbilicus to the distribution of the blood-vessels in the villi of th chorion-
and the pedicle of the yolk-sac the cavity between the amnion and chorion. (Allen Thomson.)
called the ductus venosus, while the remainder passes into the portal vein and
reaches the inferior vena cava only after circulating through the liver. It is
carried by the vena cava to the right auricle of the heart, into which cavity the
blood is also pouring that has circulated in the head and neck and arms, and
has been brought to the auricle by the superior vena cava. It might be
DEVELOPMENT
naturally expected that the two streams of blood would be mingled in the
right auricle, but such is the case only to a slight extent. The blood from the
superior vena cava— the less pure fluid of the two— passes almost exclusively
into the right ventricle, through the auriculo-ventricular opening, just as it
does in the adult. The blood of the inferior vena cava is directed by a fold
FIG. 504. — Diagram of the Fetal Circulation.
of the lining membrane of the heart, called the Eustachian valve, through the
foramen ovale into the left auricle and into the left ventricle, and out of this
into the aorta, and thence to all the body, but chiefly to the head and neck.
The blood of the right ventricle is sent out in small amount through the pul-
monary artery to the lungs, and thence to the left auricle, as in the adult,
but the greater part by far passes through a canal, the ductus arteriosus, lead-
ing from the pulmonary artery into the aorta just below the origin of the three
PARTURITION
697
great vessels which supply the upper parts of the body, and is distributed to
the trunk and lower parts of the body. A large portion passes out by way
of the two umbilical arteries to the placenta. From the placenta it is returned
by the umbilical vein to the under surface of the liver, from which the de-
scription started.
After birth the foramen ovale, the ductus arteriosus, and ductus venosus
all close, and the umbilical vessels are tied off, so that the two streams of blood
which arrive at the right auricle by the superior and inferior vena cava, re-
spectively, thenceforth mingle in this cavity of the heart, and pass into the
FIG. 505. — Dissection of the Lower Half of the Female Mamma During the Period of Lactation,
f. — In the left-hand side of the dissected part the glandular lobes are exposed and partially un-
ravelled, and on the right-hand side the glandular substance has been removed to show the
reticular loculi of the connective tissue in which the glandular lobules are placed, i , Upper part
of the mammilla or nipple; 2, areola; 3, subcutaneous masses of fat; 4, reticular loculi of the con-
nective tissue which support the glandular substance and contain the fatty masses; 5, one of
three lactiferous ducts shown passing toward the mammilla, where they open; 6, one of the sinus
lactei or reservoirs; 7, some of the glandular lobules which have been unravelled; 7', others massed
together. (Luschka.)
right ventricle, by way of the pulmonary artery to the lungs, and through
these, after aeration, to the left auricle and ventricle, to be distributed over
the body.
Parturition. With the implantation of the embryo and the devel-
opment of the placenta, the uterus grows rapidly until the end of preg-
nancy. The muscles of its walls increase enormously in volume, appar-
ently by an increase in the size of the fibers, and the whole structure may
become thirty or forty times its size in the resting period. Many changes
take place also in other parts of the body, changes which are dependent on
the presence of the fetus. Full-term pregnancy occurs when the uterus is
698
DEVELOPMENT
isolated from the nervous system, hence it has been inferred that there is some
sort of special secretion, possibly of the embryo itself, that makes its way into
the blood and influences the organs of the mother.
At the end of the period of pregnancy the strong4jterine walls begin periodic
contractions which ultimately result in the delivery of the fetus. These con-
tractions are at first weak and at long intervals, but later become very strong
and follow each other in rapid succession. The uterine contractions are sup-
ported by reflex contractions of the abdominal and thoracic muscles. After
the fetus is delivered the uterine contractions become milder, but still continue
until the placenta is finally expelled.
The initiation of the contractions of the uterus at delivery probably de-
pends on the chemical stimulation of some substance or substances produced
in the uterus itself or in the fetus; substances that react on the nervous mech-
anism and on the uterine muscles themselves. This view cannot be said to
be proven, but it is supported by certain observed facts and experiments.
Lactation. There is a marked development of the mammary glands
especially in the later part of the period of gestation. Upon delivery of the
fetus the gland enlarges very sharply and an abundant secretion is formed.
FIG. 506.
FIG. 507.
FIG. 506. — Section of Mammary Gland of Bitch, Showing Acini, Lined with Epithelial Ce-lls of
a Polyhedral or Short Columnar Form. Xzoo. (V. D. Harris.)
FIG. 507. — Globules and Molecules of Cow's Milk. X4oo.
The secretion of the first few days is called the colostrum. It contains a
larger per cent of solids, has the large granular colostral corpuscles, is more
alkaline than ordinary milk, and has a specific gravity of 1040 to 1046.
The mammary glands have been isolated from the nervous system to
determine whether or not the association in time between their changes and
the changes in the uterus were of a nervous nature. The isolated mammae
develop and begin lactation at parturition as in the normal. It would seem
that here, too, there is some special form of stimulation through the medium
of the blood. Yet one must not draw the conclusion that the nervous system
THE COMPOSITION OF MILK 699
exerts no influence on the mammary gland. Stimulation of the nerves to the
gland produces vascular changes that increase or decrease the quantity of
secretion. Many observations have been noted in women, which show that
the secretion of milk is sharply influenced by, or even completely suppressed
by, nervous states.
The Composition of Milk. Milk has a specific gravity of 1028
to 1034. Its fat is held in emulsion. Under the microscope, it is found that
the milk globules vary in size, the majority being from 2 to 3 p. in diameter.
The old view that they have an investing membrane of albuminous mate-
rial is now generally discarded.
COMPOSITION OF COLOSTRUM (PFEIFFER).
Proteids 5.71
Fat i 2 . 04
Sugar 3.74
Salts 0.28
Water 88.23
100.00
SALTS IN WOMAN'S MILK (ROTCH).
Calcium phosphate 23.87
Calcium silicate 1.27
Calcium sulphate 2.25
Calcium carbonate 2 . 85
Magnesium carbonate 3-77
Potassium carbonate 23 .47
Potassium sulphate 8.33
Potassium chloride 12 .05
Sodium chloride 21 . 77
Iron oxide and alumina °-37
100. oo
In addition to the oil or butter fat, milk contains certain proteids, milk-
sugar, and several salts. Its percentage composition is given in the tables
appended.
CHEMICAL COMPOSITION OF MI-LK. (AFTER FOSTER, HARRINGTON, et a/.)
Human. Cow. Mare. Bitch.
Water 87.30 87 90 76
Solids 12.70 13 10 24
Fats 4-oo 4-0 2.0 10.0
Proteids i-S° 4-Q 2.5 10.0
Sugar 7-0° 4-3 5-°
Salts.. o-20 °-7 °-5 °-5
INDEX
ABDOMINAL viscera, vascular nerves
for, 223
Abducens nerve, 554
Absorption, 361
conditions for, 362
methods of, 361, 364
places for, 362, 370
rapidity of, 362, 370
through the intestines, 363
the lungs, 370
the mouth, 362
the skin, 369
the stomach, 362
Accelerator centers for heart, 183
Accessory olives, 539
thyroids, 428
Accommodation of vision, 642, 645
Achromatic layer, 17
spindle, 19
Achromatin, 18
AchroSdextrin, 311
Acid albumin, 82
Acromegaly, 431
Activating ferments, 303
Adamkiewicz reaction, 196
Addison's disease, 429, 431
Adenoid tissue, 35
Adipose tissue, 37, 38
Adrenalin, 431
Adrenals, 428
After-birth, 694
-images, 654, 660, 677
-sensations, 602
Agglutinative substances, 129
Air cells, 250
changes in, during respiration, 263
composition of, 263
diffusion of, 267
pressure of, 267, 285
quantity breathed, 259, 284
volume breathed, 284
Albumin, acid, 82
alkali, 83
Albumin, egg, 81
native, 80, 8 1
serum, 81
Albuminates, 82
reactions of, 97
Albuminoids, 86
effect of diet of, 411
Albumins, 81
reactions of, 97
Albumoses, reactions of, 97
Alcohol as a food, 300
Alkali albumin, 83
Ameba, 3
Ameboid movement, 3
Amido-acids, 89
Amitosis, 10, 19
Ammonia, effect of breathing, 279
in the urine, 383
Ammonium carbamate, 412
Amylolytic ferments, 303
Amylopsin, 303, 334, 337
Anabolism, 6, 405
Anabolites, 405
Anacrotic limb, 206
wave, 207, 208
Anaphase, 20
Anelectrotonus, 471
Animal heat, 433
Animals differentiated from plants, 10
Anode, 471, 473
Ano-spinal center, 526
Anterior association center, 589
Antipeptone, 336
Antiperistalsis, 350
Apnea, 277, 289
Arborization, interepithelial, 72
Archispermiocyte, 679
Archoplasm, 18
Areolar tissue, 34
Aristotle's experiment, 669
Arterial flow, 196, 198
rhythmic, 198
velocity of, 199
701
702
INDEX
Arterial pulse, 237
blood-pressure and nervous reg-
ulation in, 239, 240
Arteries, 149
blood-pressure in, 187
nerves of, 151
Arterioles, 149
Articulate sounds, 490
Asphyxia, 278, 290
Assimilation, 6
Association centers of brain, 587
Aster, 19
Astigmatism, 649, 674
Atmosphere, composition of, 263
Attraction sphere, 18
Auditory center, 587
judgments, 626
nerve, 556
Auricles, action of, 155
Auriculo-ventricular valves, action
of, 156
Autolytic substances, 129
Axis cylinder, 65
Axone, 64
BACTERIA in digestive tract, 347
Basement membrane, 22
Basket cells, 562
Basophile, 113
Bezold's ganglia, 175
Bidder's ganglia, 175
Bile, 340, 360
acids, 341, 360
capillaries, 340
coloring matter of, 341
chemical composition of, 341
discharge of, 343
functions of, 342
mode of discharge of, 343
mode of secretion of, 343
pigments of, 360
salts, 341, 360
Bilirubin, 90, 341
Biliverdin, 90, 341
Binaural sensations, 627
Binocular vision, 664
Bioplasm, 2
Biuret reaction, 96
Bladder, urinary, 377
Blastema, 2
Blastoderm, 14
Blind spot, 653, 675
Blood, 10 1
arterial flow, 196
buffy coat, 103
capillary flow, 199
carbon dioxide of, 271
chemical composition of, 115
circulation of, 141, 186
experiments on, 226
in fetus, 695
coagulation of, 102, 137
calcium in, 106
conditions affecting, 106
fibrin in, 103
theories of, 105
corpuscles of, 107
chemical composition of, 139
colorless, 112
ameboid movement of,
113, 201
chemical composition of,
117
number of, 112
phagocytosis, 134
varieties of, 113
enumeration of, 134
percentage of, 135
red, 107
action of reagents on, 133
characters of, 108
chemical composition of,
118
development of, no
number of, 108
origin of, 1 10
varieties of, no
defibrination of, 104
differences between arterial and
venous, 127
elimination of carbon dioxide by,
271
examination of, 132
ferments in, 117
flow, arterial, 196
capillary, 199
regulation of, 209
velocity of, 203
in arteries, 199
in capillaries, 201
in veins, 203
venous, 202
INDEX
703
Blood, gases of, 267
hemoglobin, 118
isotonicity of, 136
laboratory experiments on, 132
laking of, 128
microscopical examination of, 132
morphology of, 107
oxygen of, 269
plasma, 101
chemistry of, 139
composition of, 115
percentage of, 135
reaction of, 136
plates, 115
portal, 127
pressure, 186
arterial, 187, 234, 239, 240
capillary, 195, 238
in man, 192
model, 236
respiratory undulations of,
191
variations in, 195
venous, 195
production of heat by the, 434
quantity of, 101
influence on secretion, 295
respiratory changes in, 267
serum, 102
chemistry of, 139
composition of, 117
globulicidal properties of , 128
specific gravity of, 136
uses of, 10 1
variations in composition of, 126
velocity of flow, 203
venous flow, 202
whipped, 138
Blushing, 215
Body, chemical composition of, 78
energy requirements of, 425
experiments on the chemistry of,
95
Bone, 41
blood-vessels of, 42
canaliculi of, 43
cells, 44
development of, 45
growth of, 50
Haversian canals of, 44
lacunae of, 43, 44
Bone, lamellae of, 43, 44
marrow, 41
microscopic structure of, 43
ossification in cartilage, 46
in membrane, 46
periosteum of, 42
Bowman's sarcous elements, 60
theory of urinary secretion, 386
Brain, 531
after-, 533
arrangement of different parts,
531
association centers of, 587
distinctive characters of human,
532. 574
fore-, 532
gray matter in, 568
hind-, 533
inner-, 532
mid-, 533
motor areas of, 577, 582
of human, 581
tracts in, 583
Rolandic area of, 583
sensory areas of, 584
stem, 531, 532
vascular nerve-supply cf, 220
weight of* 574
Bronchi, 245
Buffy coat, 103
Bulb, the, 534, and see Medulla
centers in, 540
connections with cerebrum and
cerebellum, 539
functions of, 540
Bundle of Vicq d'Azyr, 547
Burdach, column of, 514
CAJAL, cells of, 570
Calcification, 47, 50
Calcium salts in the body, 94
in coagulation of the blood,
106
tests for, 99
Calorimeter, 290, 426
Calorimetry, 290
Canaliculi, 43
Cane sugar, 92
Capillaries, 151
blood -pressure in, 195
structure of, 152
704
INDEX
Capillary circulation, 238
flow, 199
velocity of, 20 1
Carbohydrates, 91
absorption of, by intestines, 367
as foods, 297, 300
chemical reactions of, 98
metabolism of, 416
Carbon, amount excreted, 407
dioxide, determination of, 286, 287
elimination of, 263, 264, 271,
396
monoxide, effect of breathing, 279
hemoglobin, 140
Carbonates, 94
Carboxy hemoglobin, 121
Cardiac action, force of, 169
contractions, automatic, 231
experiments on, 227, 228
maximal, 174
cycle, 155, 1 68
impulse, 160
muscle, 61, 465, 500
action of, 465
compared with other
muscles, 466, 500
automatic contractions of,
231
development of, 63
properties of, 170
refractory phase, 465
nerves, 232
Cardio-accelerator centers, 183, 543
Cardiogram, 161, 226, 228
Cardiograph, 161
Cardio-inhibitory centers, 181, 543
Cartilage, 38
development of, 41
elastic, 41
hyaline, 38
temporary, 40
white fibro-, 41
Casein, 85
Caseinogen, 85
Catabolism, 6, 405
Catabolites, 405
Catacrotic limb, 206
wave, 207
Catelectrotonus, 471
Cathode, 471, 473
Caudate nucleus, 548
Cell, i, 8, 17, 18
body, 17
difference between plant and ani-
mal, 10
differentiation, 14, 17
division of, 10, 18
functions of, 1 1 , 14
growth, 7, 10
multiplication, 18
nucleus of, 9, 17
reticulum of, 8
structure of, 8, 17
Cells, decay and death of, 22
derived elements of, 22
modes of connection, 21
origin of, 2 1
shapes of, 21
types of, 21
Cellulose, 13, 91
Center for muscle tone, 525
Centers, motor, 577, 581
sensory, 584
spinal, 526
Centrosome, 18
Cerebellar cortex, paths through, 564
Cerebellum, 561
connection with bulb, 539
functions of, 564
general structure of, 562
Cerebral cortex, fibers from, 572
structure of, 568
Cerebrum, 567
arrangement of parts, 568
connection with bulb, 509
effects of removal of, 575
functions of, 575
motor areas of cortex, 577, 582
sensory areas of, 584
weight of, 574
Cerumen, 394
Ceruminous glands, 394
Chemical composition of the body,
78
elements in the body, 78
Chemistry of the body, experiments
on, 95
Chest, changes in diameter of, during
respiration, 284
Cheyne-Stokes breathing, 278
Chlorides in the body, 94
in the urine, 385
INDEX
705
Chlorides, tests for, 99
Chlorine, effect of breathing, 279
Chlorophyll, 12
Chondrigen, 87
Chondrin, 87
Chorda tympani, 306, 352, 355
Chordae tendineae, 148
Chromatic aberration, 649, 673
Chromatin, 18
Chromophanes, 659
Chromoplasm, 17
Chromo-proteids, 84
Chromosome, 19
Chyme, 329
Cilia, 30
Ciliary apparatus, 632
contraction, 468, 502
epithelium, 502
motion, 468
Circulation, coronary, 183
during sleep, 590
effect of respiration on, 280
in brain, 220
in erectile structures, 224
laboratory experiments on, 226
local peculiarities of, 220
of blood, 141
regulation of flow, 209
time of, 236
through blood-vessels, 186
velocity of, 203
vegetable, 4
Coagulated proteids, 83
Coagulating ferments, 303
Coagulation of blood, 102, 137
calcium salts, in 106
conditions affecting, 106, 138
theories of, 105
Cochlea, 619
Cohnheim's areas, 61
Cold, influence of extreme, 436
Collagen, 86
Collaterals, 68
Colloids, 129
Color, after-images, 654, 660, 677
-blindness, 66 1, 677
complemental, 660
extent of visual field for, 660
Bering's theory of, 663
limits of field of vision for, 677
-mixing, 677
Color, sensations of, 659, 66 1
Young's and Helmholtz's theory
of, 662
Colorless corpuscles, 112
Colostrum, 698
Column of Burdach, 514
of Goll, 514
Columnae carneae, 145, 148
Comma tract, 516
Common sensations, 595
Complemental air, 259, 285
Compound proteids, 81, 84
Conductivity of muscle, 447
Conjunctiva, 630
Connective tissues, 31
adenoid, 35
adipose, 37
areolar, 34, 36
cells of, 31
development of, 36
fibrous, 36
gelatinous, 34
general structure of, 31
intercellular substance of, 32
lymphoid, 35
retiform, 35
varieties of, 32
white fibrous, 33, 36
yellow elastic, 33, 36
Consonants, 490
Contractility of muscle, 442
Contraction phase of muscle, 449
Contracture, 460
Convoluted tubule, 372
Cooking, effects of, 301
Cornea, 631
Corona radiata, 545, 546
Coronary circulation, 183
Corpora cavernosa, 224
geniculata, 546
quadrigemina, 546
striata, 548
Corpus Arantii, 148
dentatum, 562
luteum, 689
spongiosum, 224
Corpuscles, blood, 107
Malpighian, 372
of Bowman, 372
of Golgi, 76
of Krause, 74
706
INDEX
Corpuscles of Meissner, 74
of Pacini, 73
Coughing, center for, 542
Cranial nerves, 548
Crassamentum, 102
Creatinin, 383, 402, 413, 414
Crura cerebri, 545
Crusta, 545
petrosa, 52
phlogistica, 103
Crystalloids, 129
Cutis vera, 393
Cystin in urine, 385
Cytolysis, 128
Cytoplasm, 17
DEATH, 7
Decay, 7
Decidua basalis, 693
capsularis, 693
menstrualis, 689
vera, 693
Decussation of the pyramids, 535
Defecation, 351
center for, 526
Degeneration in spinal cord, 515
reaction of, 474
Wallerian, 506
Deglutition, 313
center for, 316, 542
nervous mechanism of, 315
time occupied in, 315
Demarcation currents, 451, 452
Dendrites, 64
Dental papilla, 55
Dentine, 52
Depressor nerve, 215
Dermis, 393
Development, 691
Dextrin, 92
tests for, 98
Dextrose, 92
tests for, 98
Diabetes mellitus, 418
Dialysis, 129
Diapedesis, 201
Diaphragm in respiration, 254, 256
Diaster, 20
Diastole of heart, 154, 156
Dicrotic notch, 207
pulse, 208
Dicrotic wave, 207, 208
Diet, normal, requisites of, 405, 442
tables, 423
Diffusion, 129
Digestion, 297, 301
enzymes in, 301, 303
experiments in, 351
in intestines, 331, 345, 346
in mouth, 303, 353, 354
in stomach, 316
Digestive ferments, 303
Diphasic current, 453
Diplopia, 550, 664
Disassimilation, 6
Distance, estimation of, 668
Diuretics, action of, 389
Dogiel's cells, 175
Dreams, 591
Du Bois-Reymond's induction coil, 445
key, 444
Ductless glands, influence on metabo-
lism, 427
Ductus arteriosus, 696
venosus, 695
Dyspnea, 278, 290
EAR, cochlea of, 619
external, 614
function of, 622
internal, 617
function of, 625
membranous labyrinth, 618
middle, 615
function of, 622
organ of Corti, 619
ossicles of, 616
tympanum, 615
Eck's fistula, 412
Edestine, 82
Egg albumin, 81
Eggs, composition of, 299
Eighth nerve, 556
Elasticity of muscle, 442
Elastin, 87
Electrodes, 445
Elect rotonus, 471
Elements, chemical, in body, 78
Eleventh nerve, 560
Emission of semen center, 526
Emulsification, 99, 337, 342
Enamel, 53
INDEX
707
Enamel cap, 56
germ, 55
organ, 55
papilla, 55
End -brushes, 68
-bulbs, 74
-plates, 62
Endocardiac pressure, 162
Endocardium, 143
Endomysium 59
Endoneurium, 68
Endothelium, 24
Energy, income and output of, 426
requirements for body, 425
Enterokinase, 303, -345, 360
Enzymes, 301
action of, on pancreatic juice, 359
activating, 303
amylolytic, 303
classification of, 302
coagulating, 303
t digestive, 303
lipolytic, 303
proteolytic, 303
Eosinophile, 100, 113
Epiblast, 14
Epidermis, 391
Epiglottis, 245
Epinephrin, 431
Epineurium, 68
Epithelial tissues, 22
Epithelium, 22
ciliated, 29, 31
classification of, 23
columnar, 23, 24, 28
cubical, 23
functions of, 24, 31
glandular, 29
simple, 23
situations of, 23, 31
specialized, 29
squamous, 23, 27
stratified, 23, 27
transitional, 28
Equilibrium, sense of, 628
Erectile tissue, 224
Erection center, 526
Erepsin, 303, 345
Ergograph, 461
Erythroblasts, 112
Erythrocytes, 107
Erythrodextrin, 311
Eustachian tube, 615, 624
valve, 143, 696
Excreta, analysis of, 406, 407
channels of elimination of, 407
quantity of, 406
Excretion, 291, 371, 398
during starvation, 422
from skin, 395
laboratory experiments in, 398
Expiration, forced, 256
muscles of, force of, 262
quiet, 256
relative time of, 258
Expired air, oarbon dioxide of, 263,
286, 287
changes in, 263
External genitals, vascular nerves
for, 224
Eye, 630
anatomy of, 630
astigmatism, 649, 674
chromatic aberration of, 649, 673
image formation, 639
movements of, 647
muscles concerned in, 647
optical apparatus, 638
axis, 641
refractive surfaces and media, 639
schematic, 641
spherical aberration of, 648, 672
Eyeball, 630
blood-vessels of, 637
ciliary apparatus, 632
cornea, 631
iris, 632
lens, 632
retina, 633
Eyelids, 630
FACIAL nerve, 554
function of, 555
paralysis of, 555
relation to taste, 555
secretory, 555
Fallopian tubes, 686
Falsetto voice, 489
Far-point, 672
Fasciculus cuneatus, 534
gracilis,. 534
of Rolando, 535
708
INDEX
Fasciculus solitarius. 556
Fasting, 420, 421
metabolism during, 414
Fatigue, effect on muscular contrac-
tion, 497, 49 8
Fats, 90, 98
absorption of, by intestines, 367
as food, 297, 300
chemical reactions of, 98
digestion of, 337, 338
emulsification of, 99, 337, 342
energy value of, 414
metabolism of, 414
saponification of, 99, 337
source of, in body, 415
Fatty acids, 91
tests for, 99
Feces, 347
composition of, 348
excretion by, 407
Fermentation in intestine, 347
Ferments, 97
chemical reactions of, 97
in the blood, 117
unorganized, 301, and see En-
zymes
Fetus, circulation of blood in, 695
Fibers of Remak, 66
Fibrin, 83
. ferment, 105
Fibrinogen, 82, 105
Fictitious feeding, 321
Fifth nerve, 551
-Fillet, 544
Filtration, 361
Finger, vasomotor changes in, 241
Fish, composition of, 299
Fission, 7
Food, and digestion, 297
effects of deprivation of, 420
mastication of, 303
-principles, 297
salts of, 300
Foods, 297
carbohydrates, 297, 300
classification of, 297
effect of cooking, 301
fats, 297, 300
heat production from, 426, 437
income and output of. energy, 406
inorganic, 297, 300
Foods, liquid, 300
mineral, 297, 300
nitrogenous, 297
percentage composition of, 298
proteids, 297
salts, 300
water, 297
Forced movements, 567
Fore-brain, 532
Form, estimation of, 667
Fossa ovalis, 143
Fourth nerve, 550
Fovea centralis, 633
Frontal association center, 589
GALACTOSE, 93
Gall-bladder, 340
Galvanic currents, 443
Ganglia, 508
spinal, functions of, 523
Gases in alimentary canal, 348
Gastric digestion, 316, 355
changes in food in, 327
circumstances influencing,
327
cleavage products of, 356
products of, 326
time of, 327
juice, 321, 355
acid of, 323
'action on milk, 327
on proteids, 326
artificial, 356
chemical composition of, 323,
355
digestive action of, 356
enzyme action of, 356
fictitious meals, action on,
321
hydrochloric acid in, 324
pepsin in, 325
psychic secretion of, 355
quantity of, 323
secretion of, 320, 355
secretion, changes in glands dur-
ing, 320
nervous mechanism of, 322
Gelatin, 86
Gelatinous tissue, 34
Gemmation, 7
Genito-spinal center, 526
INDEX
709
Germinal epithelium, 685
matter, 9
spot, 684
vesicle, 684
Giant cells, 42
Glands, cardiac, 317
ceruminous, 394
gastric, 316
mammary, 698
pyloric, 318
reproductive, relation to metabo-
lism, 432
salivary, 304
sebaceous, 395
secreting, 293
sudoriferous, 393
types of, 293
Globulin, serum, 82
Globulins, 81
reactions of, 97
Globus pallidus, 548
Glomerulus, 374
Glosso-pharyngeal nerve, 556
in respiration, 274
Glottis, respiratory movements of, 257
Glucoproteids, 85
Glucose, 92
Glycin, 341
Glycogen, 92, 417
destination of, 418
formation of, 416
relation to metabolism, 416
sources of, 417
tests for, 98
Glycogenesis, 416
Glycoproteids, 85
Glycosuria, 418
Goblet cells, 26
Golgi, corpuscles of, 76
Goll, column of, 514
Gowers' tract, 516
Graafian follicles, 684
Granulose, 91
HAVERSIAN canals, 44
Head, vascular nerve supply of, 220
Hearing, acuteness of, 671
limits of, 671
physiology of, 620
Heart, 142
action of, 154
Heart, anatomy of, 142
automaticity of, 178
-beat, 1 60
rate of, 226, 227
sequence, 227
theories of, 174
-block, 176
capacity of, 146
chambers of, 143
character of contraction, 170, 174
coronary circulation of , 183;
cycle of, 155, 1 68
depressor nerve of, 215
development of, 146
endocardiac pressure, 162
excised, experiments on, 228, 229
force of action, 169
frequency of action, 154, 185
ganglia of, 175
impulse of, 160
influence of accelerator nerve on,
182, 543
of coronary circulation on, 1 83
of drugs on, 185
of inhibitory nerves on, 179,
543
of mechanical tension on, 184
of nervous system on, 179
of nutrient fluids on, 229
of sympathetic system on,
211
of temperature on, 184
of vagus on, 179
irritability of, 172
isolated, 230
metabolism oft 178
methods of investigating beat, 226
muscle, 61, 500
properties of, 170
nerves of, 179
production of heat by, 434
regulation of force and frequency
of contraction, 179
relation of rhythm to nutrition,
178
rhythmic contraction of, 1 70, 1 78
size of, 146
sounds of, 158
causes of, 159
structure of, 146
tonicity of, 172
710
INDEX
Heart, valves of, 148
action of, 156
volume of, 229
weight of, 146
work per diem, 426
Heat, animal, 433
dissipation of, 434
from lungs, 436
from skin, 434
influence of extreme, 436
of nervous system on pro-
duction of, 438
produced in muscular contrac-
tion, 453
-producing tissues, 433
production of body-, 425, 433, 437
regulation of body-, 434, 438
centers for, 439
-rigor, 462
variations in loss of, 434
in production of, 437
Heidenhain's experiments on urine
secretion, 386
Hemachromogen, 124
Hemacytometer, 135
Hematin, 124, 125
Hematoblasts, no
Hematoidin, 125
Hematoporphyrin, 124
Hemianopsia, 585
Hemin, 125
Hemiopia, 585
Hemoglobin, 118, 140, 269
action on gases, 121
combining power with oxygen, 269
derivatives of, 124, 140
estimation of , 122, 136
reduced, 121
Hemoglobinometer, 122, 136
Hemolysis, 128
Hemometer, 136
Henle's membrane, 150
loop, 373
Hepatolytic sera, 128
Hind -brain, 533
Hippuric acid, 383
formation of, 383, 413
Histons, 84
Hyaline cartilage, 38
cells, 113
leucocytes, 113
Hyaloplasm, 8, 17
Hydrochloric acid, 324, 325
combined, 324
digestive action of, 325
test for free, 324
Hydrogen, amount excreted, 407
effect of breathing, 279
Hyperisotonic solutions, 130
Hypermetropia, 651
Hyperpnea, 278, 289
Hypertonic solutions, 130
Hypoblast, 14
Hypoglossal nerve, 560
Hypoisotonic solutions, 130
Hypotonic solutions, 130
INCOME of energy, 425
Indol, 360 %
Induced currents, 445
Induction coil, 445
Infundibulum, 144
Inhibition, function of nerve centers
in, 527
Inogen, 464
Inorganic foods, 300
principles, 93
Inosite, 93
Insalivation, 304
Inspiration, 253
forced, 256
muscles of, 253
force of, 262
quiet, 253
relative time of, 258
Inspired air, 263, 286
Intercellular substance, 21, 32
Interepithelial arborizations, 72
Internal capsule, 545
secretions, 291, 427, 431
Intestinal digestion, 331
r61e of bile in, 342
gases, 348
juices, 344, 360
secretion, 344
functions of, 345
Intestines, absorption in, 363
action of microorganisms in, 346
defecation, 351
digestion in, 331
feces in, 347
fermentation in, 347
INDEX
711
Intestines, gases in, 348
large, summary of digestive
changes in, 346
movements of, 349
influence of nervous system
on, 350
putrefaction in, 347
small, summary of digestive
changes in, 345
vascular nerves for, 224
Intonation, 491
Invertase, 303
Involuntary muscle, 501
lodothyrin, 428
Iris, 632
contraction of, 647
Iron, 94
tests for, 99
Irritability, 5
of heart-muscle, 172
of muscle, 442
Islands of Langerhans, 332
Isotonic solutions, 130
Isotonicity of blood, 136
Ivory, 52
JUDGMENT of form and size of bodies,
604
of form and solidity, 667
of size and distance, 668
Jumping, 479
KARYOKINESIS, 10. 19
Karyolymph, 17
Karyoplasm, 17
Karyosomes, 18
Keratin, 87
Kidneys, 371
action of diuretics on, 389
blood supply of, 374
effect of blood pressure on, 398
factors affecting secretion from
386
function of, 371
glomeruli of, 374
Malpighian bodies of, 372
nerves of, 376, 387
structure of, 371
tubuli uriniferi of, 372
vasa efferentia of, 375
recta of, 375
Kidneys, vascular nerves of, 224
volume of, 387
Krause, corpuscles of, 74
membrane of, 60
Kronecker-Meltzer theory of deglu-
tition, 313
Kymograph, 188
LABYRINTH, 618
Lachrymal apparatus, 630
Lactalbumin, 81
Lactase, 303
Lactation, 698
Laekeals, 364
Lactic acid, test for, 324
Lactose, 92
Lacunae, 43
Laky blood, 128
Langerhans, islands of, 332
Large intestine, summary of digestive
changes in, 346
Laryngoscope, 485
Larynx, 245, 480
Latent period of muscle, 448, 495
Leaping, 479
Legumes, composition of, 299
Lens of eye, 632
Lenticular nucleus, 548
Leucocytes, 112
Leucolytic sera, 128
Levers, action of, in the body, 475
Levulose, 93
Life, phenomena of, i
Limbs, vascular nerves for, 225
Linin, 18
Lipase, 303, 337
Lipochromes, 90
Lipolytic ferments, 303
Liquid foods, 300
Liquor sanguinis, 101
Lissauer, tract of, 516
Liver, 338
glycogenic function of, 416
secretions of, 338
structure of, 339
urea formation in, 411
vascular nerves for, 224
Localization, cerebral, 577, 584
Locomotion, 475
Locus ceruleus, 544
Lud wig's theory ot urine secretion, 386
712
INDEX
Lungs, 248
absorption from, 370
blood supply of, 252
excretion by, 407
interchange of gases in, 272
loss of heat from, 436
lymphatics of, 252
nerves of, 252
structure of, 249
Luxus consumption, 409
Lymph, 131
chemical composition of, 131
flow, 132
formation of, 131
Lymphatic sheaths, peri vascular, 154
spaces, in blood-vessels, 154
Lymphocyte, 100, 113
Lymphoid tissue, 35
Lytic substances, 128
MAGNESIUM salts in the body, 94
Malpighian bodies, 372
Maltase, 303, 311, 334
Maltose, 92, 312
Mammary glands, 698
Manometer, 188
Marrow, bone, 41
Mastication, 303
muscles of, 303
nervous mechanism of, 304
Maximal stimulus, 454
Meat, composition of, 298
Meconium, 343
Medulla oblongata, 534, 537, and see
Bulb
as a conducting path, 540
functions of, 540
reflex centers of, 540
section of, 531
Medullary sheath, 65
Meissner's corpuscles, 74
Melanin, 90
Membrana decidua, 693
tympani, 616 '
Membranous labyrinth, 618
Menstrual discharge, 689
life, 690
Menstruation, 687
Mesoblast, 14
Mesothelium, 24
Metabolism, 6, 405
Metabolism, constructive, 6
destructive, 6
during fasting, 414
endogenous, 410
exogenous, 410
influence of ductless glands on,
427
reproductive glands on, 432
intermediate, 410
nutrition and diet, 405
tissue, 410
Metaphase, 19
Metaplasm, 17
Methemoglobin, 122
Microcytes, no
Micro-organisms, action of, in intes-
tine*,^ 46
Microsomes, 8
Micturition, 390
center for, 526
Mid-brain, 545
Milk, composition of, 299, 699
Millon's reaction, 96
Mineral foods, 300, 419
absorption of, in intestines, 368
Minimal stimulus, 454
Mitosis, 10, 19
Monaster, 19
Motor activities, coordinated, 475
areas of cortex, 577, 582
of human brain, 581
end-plates, 62
impressions, 530
-oculi nerve, 549
tracts in human brain, 583
Mouth, absorption in, 362
digestion in, 303
in speech, 491
Movement, ameboid, 3
gliding, 4
streaming, 4
Movements, circus, 567
forced, 567
Mucigen, 309
Mucin, 85, 309
Mucous membranes, 292
Mucus in urine, 384
Murexide test, 402
Muscle, blood supply of, 62
cardiac, 61, 465, 500
chemical changes of, 451
INDEX
713
Muscle, chemical composition of, 440,
441
clot, 440
coagulation of, 440
conditions affecting irritability of,
454
conductivity of, 447
contractility of, 442
contraction of, 443, 467
contracture, 460
currents, demonstration of, 452
development of, 62
effect of blood supply on, 458
of drugs on, 459
of nerve supply, 458
of single induction shocks on,
446
of temperature on, 456
of use on, 458
elasticity of, 442
electrical phenomena of, 451
end-plates, 62
experiments in, 492
ferments, 441
heart, 61, 465, 500
in rigor mortis, 461
involuntary, 57, 466, 501
compared with skeletal and
cardiac, 466
irritability of, 442, 493
-nerve preparation, 492
nerve supply of, 62
non-striated, 57
plain, 57
plasma, 440
properties of, 442
record of contraction of, 443
serum, 440, 441
skeletal, 59
stimuli, 442, 496
striated, 58
tetanus, 459
-tone, center of, 525
voluntary, 58
Muscular action as heat producer, 433
activity, 464
center for tone of, 525
contraction, 443, 465
action currents, 452
apparatus for producing and
recording, 443
Muscular contraction, changes in shape
during, 449
characteristics of single, 448
chemical changes during, 451
conditions affecting character
of, 454
co-ordinated, 460
differences between volun-
tary and involuntary, 466
effect of blood supply on, 458
of drugs on, 459
of fatigue on, 497, 498
of load on, 499
of nerve supply on, 458
of rate of stimulation on,
459
of repeated activity on,
455
of strength of stimulus
on, 454, 496
of temperature on, 456,
498, 499
of use on, 458
electrical changes during, 451
energy liberated during, 454
heat produced during, 453
latent period of, 448, 495
metabolism during, 463
preparation for, 446
record of, 443, 447
recording, 446
refractory phase of, 465
response to stimuli in volun-
tary and involuntary, 466
simple, 448, 494
single twitch, 448
summation of contractions,
459
tetanic, 459, 499
voluntary, 459
co-ordination, 460, 629
energy, 464
tissue, 56
Musculi pectinati, 144
Mydriasis, 550
Myelin sheath, 65
Myelocyte, 100, 113
Myeloplaxes, 42
Myoalbumin, 441
Myoalbumose, 441
Myoglobulin, 44-
714
INDEX
Myogram, 448
Myograph, pendulum, 448
Myohematin, 441
Myopia, 651
Myosin, 82, 44.1, 464
ferment, 441
Myosinogen, 441, 465
Myxedema, 428
NASAL region, smell, 610
Near-point, 645, 672
Nephrolytic sera, 128
Nerve cells, 70, 503
arrangement of, in spinal
cord, 511
body, 70
characteristic of individual,
5°4
functions of, 503, 504
neurone theory, 504
nutritive influence of, 506
transmission of impulses
through, 507
types of, 508
centers, 508
functions of, 508
collaterals, 68
end-brushes, 68
fibers, 64, 72
effect of battery current on,
471, 473
fatigue of, 470
functions of, 469
medullated, 64
non-medullated, 66
impulses, 469
cellulifugal, 507
cellulipetal, 507
character of, 469
specific energy of, 507
transmission through cells,
507
velocity of, 470
stimuli, 442, 469, 492
terminations, 72
tissue, 64, 66
trunks, 67
Nerves, cardiac, 232
cranial, 548
functions of, 548
depressor, 215
Nerves, effect of currents on human,
471. 473
experiments on, 492
irritability of, 492
spinal, 516
vasomotor, 211, 213, 217, 219
Nervous system, 503
functions of, 504
influence on secretion, 295
sympathetic, 591
tissues, 64, 66
axones of, 64, 507
dendrites of, 64, 507
ganglia of, 508
neuroglia of, 64, 77
Pacinian corpuscles, 73
Neuraxone, 64
Neurilemma, 64
Neuroglia, 64, 77
Neurokeratin, 87
Neurone, 64, 503
theory, 504
varieties, 508
Neutrophile, 100, 113
Ninth nerve, 556
Nitrogen in proteids, 88
Nitrogenous bodies, 79
equilibrium, 408
foods, 297
output, 409
Nitrous oxide, effect of breathing, 279
Nodes of Ranvier, 65
Nceud vital, 272
Nostrils, respiratory movements of , 2 5 7
Nuclear matrix, 1 7
Nuclei of optic thalamus, 546
Nucleic acid, 85
Nucleins, 85
Nucleoli, 1 8
Nucleoplasm, 17
Nucleoproteids, 84, 85
Nucleus, 9, 17
ambiguus, 556
ruber, 546
structure of, 17
OBESITY, 416
Ocular fixation, 664
Odontoblasts,.52, 55
Oils, 90
as food, 300
INDEX
715
Olein, 90
Olfactory apparatus, 609
bulb, 611
center, 585
glomeruli, 586
membrane, 613
nerve, 586
tract, 587
Olivary bodies, 536, 538
Olive, accessory, 539
superior, 544
Onkograph, 388
Onkometer, 388
Ophthalmoscope, 655
Optic center, 585
nerve, 633
thalami, 546
Optical apparatus, 638
defects in, 648
Organ of Corti, 619
Organized ferments, 346
Osmosis, 129
Osmotic pressure, 130
Ossein, 86
Osseous labyrinth, 618
Ossicles of ear, 616
Ossification, 45
center of, 46
in cartilage, 46
in membrane, 46
Osteoblasts, 46
Osteoclasts, 48
Osteogenetic fibers, 46
Output of energy, 426
Ovaries, 683
relation to metabolism, 432
Oviducts, 686
Ovulation, 687
Ovum, 684, 686
changes in, following impregna-
tion, 692
prior to impregnation, 691
Oxalic acid in urine, 385
Oxygen, amount excreted, 40 /
in expired air, 265
in tissues, 270
determination of, in air, 286
Oxyphile, 113
PACINIAN corpuscles, 73
Pain, sense of, 602
Pancreas, 332
enzymes of, 334
extirpation of, 431
extract of, 334
internal secretion of, 43 1
islands of Langerhans in, 332
secretion of, 333
structure of, 332
Pancreatic digestion, 358
cleavage products of, 359
fistula, 333
juice, 333, 358
artificial, 358
chemical characters of, 358
composition of, 334
conditions influencing action
of, 338
enzymes of, 334, 358
action of, 335, 338, 359
secretion of, 358
action of nerves on, 334
action of secretin on,
334, 358,
Papillae of skin, 392
of tongue, 606
Paralytic secretion of saliva, 306
Paranucleoproteids, 84
Parathyroid glands, 428
Parietal association center, 589
Parotid gland, 304
nerves of, 308
Parturition, 697
center, 527
Pelvic viscera, vascular nerves for, 224
Penis, 68 1
Pepsin, 303
action of, 325
in gastric juice, 325
Pepsinogen, 325
Peptone plasma, 107
Peptones, 84, 325
characteristics of, 326
reactions of, 97
Perforating fibers of Sharpey, 45
Pericardium, 142
Perichondrium, 38, 46
Perimysium, 59
Perineurium, 68
Periosteum, 42
Peripheral resistance, 186, 210
Peristalsis, intestinal, 349
716
INDEX
Peristalsis, reversed, 350
Peri vascular lymphatic sheaths, 154
Perspiration, 395
Pfliiger's law of contractions, 472
Phagocytes, 134
Phagocytosis, 134
Phakoscope of Helmholtz, 674
Phenomena of life, i
Phenomenon of treppe, 497
Phosphates, 94
tests for, 90
Phosphoric acid in urine, 384
Phosphorus in foods, 420
Phrenic nerve, influence on respira-
tion, 289
Physiological material, source of, 1 5
utilization of, 15
Physiology, i
Pigment cells, 32
Pigments, 90
bile, 360
Pituitary body, 431
Placenta, 694
Plants differentiated from animals, 10
Plasma, 101, 115
chemistry of, 139
composition of, 115
percentage of, in blood, 135
reaction of, 136
Plasmosomes, 18
Plethysmogram, 241
Pleurae, 248
Pneumogastric nerve, 558, and see
Vagus
Pneumograph, 258
Pons Varolii, 543
Postdicrotic wave, 207
Posterior longitudinal bundle, 544
marginal zone, 516
pyramids, 534
roots of spinal nerves, 518, 523
Potassium salts in the body, 94
Poultry, composition of, 299
Precipitins, 129
Predicrotic wave, 207
Presbyopia, 651
Pressor nerves, 216
Pressure, endocardiac, 162
Prickle cells, 27
Pronucleus, female, 692
male, 692
Prophase, 19
Prostate gland, 682
Protamin, 84, 89
Proteids, 79
absorption of, from intestines, 365
action of trypsin on, 336
as fat formers, 410
as glycogen formers, 410
circulating, 409
coagulated, 83, 97
color reactions of, 96
compound, 81, 84
classes of, 80
decomposition products, 87
digestion of, 325
floating, 409
metabolism of, 408, 409
morphotic, 409
nitrogen in, 88
precipitations, 96
properties of, 79"
reactions of, 95
simple, 80, 8 1
sulphur in, 89
tissue, 409
Proteolytic ferments, 303
Proteoses, 84, 325
Prothrombin, 106
Protoplasm, i, 2
chemistry of, 3
definition of, 2
effect of stimuli on, 5
growth of, 7
irritability of, 5
movement of, 3
physiological characteristics of, 3
properties of, 2
reproduction of, 7
structure of, 8
Pseudo-nucleoproteids, 84
Ptosis, 550
Ptyalin, 303, 310
action of, 303, 311, 354
Pulse, 2t>4
arterial, 237
dicrotic, 208
variations in rate of, 185
-wave, rate of propagation of, 237
Pulvinar, 547
Pupil, 632
contraction of, 647
INDEX
717
Pupil, dilatation of, 647
center for, 542
reflexes, 647
Purkinje's cells, 562
figures, 653
shadows, 676
Purkinje-Sanson's images, 673
Putamen, 548
Putrefaction in intestines, 347
Pyramids, 534
decussation of, 535
RACEMOSE glands, 294
Ranvier, nodes of, 65
Reaction of degeneration, 474
Red corpuscles, 107
action of reagents on, 133
chemical composition of, 118
, development of , no
origin of, no
varieties of, no
nucleus, 546
Reflex action, 519
time of, 523
arc, 519
centers in medulla, 540
Reflexes, complex, 521
cutaneous, 528
inhibition of, 527
morbid, 527
muscle, 528
simple, 520
special centers for, 526
spinal, 524
tendon, 528
Refraction, 671
Refractory period, 172
phase, 465
Relaxation phase of muscle, 449
Remak's fibers, 66
ganglia, 175
Rennin, 303, 334
action of, 327, 337, 357
reproductive organs, 679
of female, 683
of male, 679
Reserve air, 260, 285
Residual air, 260
Respiration, 243
changes in diameter of chest,
during, 284
Respiration, effect of altitude on, 280
of, on circulation, 280
of various gases on, 279
of vitiated air on, 279
expiration, 256
influence of cutaneous nerves on,
288
of general sensory nerves on,
274, 288
of glosso-pharyngeal on, 274
of phrenic on, 289
of superior laryngeal on, 274
of vagus on, 273, 289
inspiration, 253
internal, 244
laboratory experiments in, 283
mechanism of, 253
nervous apparatus of, 272, 288
rhythm of, 258
special types of, 277
tissue, 244
volume of air breathed, 284
Respirations, number of, 262, 283
Respiratory apparatus, 244
elimination of carbon diox-
ide by, 271
nervous regulation of, 272
capacity, 260, 285
circumstances affecting, 261
center, 272, 542
automatic action of, 275
stimulation of, 275
changes in air breathed, 263
in the blood, 267
in the tissues, 270
interchange, 290
movements, 253
character of, 283
establishment of, at birth,
277
nervous mechanism of, 288
rate and character of, 287
recording of, 257, 283
relative time of, 258
of nostrils and glottis, 257
murmur, 259
muscles, force of, 262
pressure, 267, 285
quotient, 266
rate, 262, 283
rhythm, 258
718
INDEX
Respiratory rhythm, action of stimuli
on, 273
terms for quantity of air breathed,
259
Rete mucosum, 392
Reticular formation in medulla, 538
Reticulum, 8, 17
Retiform tissue, 35
Retina, 633
cones of, 636
inverted image on, 672
layers of, 634
localization in, 657
movement of pigment cells, 659
rods of, 636
Retinal image, duration of, 676
relation of size to distance,
676
Retinoscopy, 678
Rheoscopic frog, 470
Rhodopsin, 658
Rhythmical contractility, 170
Rhythmicity of arterial flow, 198
Ribs, movement of, in respiration,
255
Rigor mortis, 461
cause of, 461
heat, 462
order of occurrence, 462
water, 462
Rima glottidis, 245
Rolandic area, 583
Running, 479
SACCHAROSE, 92
Sacculus, 6 1 8, 629
Saliva, 309
action of, on starch, 311, 312, 353
chemical compositipn of, 310, 352
function of, 310
properties of, 310
ptyalinin, 303, 310, 311
quantity of, 310
secretion of, center for, 305
mechanism of, 305
rate of, 310
Salivary digestion in stomach, 313
influence of acids and alkalies
on, 354
of temperature on, 353
glands, 304
Salivary glands, changes in, during
secretion, 308, 352
nerves of, 351
structure of, 304
secretion, 308
reflex, 351
Salts, absorption of, by intestines, 368
as foods, 300
bile, 341, 360
in the body, 93
tests for, 99
Sanson's images, 644
Saponification, 99, 337
Sarcode, 2
Sarcolemma, 59
Sarcoplasm, 61
Sarcostyles, 59
Sarcous elements of Bowman, 60
ScKeiner's experiment, 673
Schwann, sheath of, 65
Sebaceous glands, 394
Secretin, 334, 345
influence on pancreatic secretion,
334, 358
Secreting glands, 293
production of heat by, 434
types of, 293
organs, types of, 292
Secretion, 291
circumstances influencing, 295
discharge of, 295
external, 291
internal, 291, 427, 431
organs and tissues of, 292
process of, 294
psychic, 355
true, 291
Segmentation, 692
Semicircular canals, 619, 628
Semilunar valves, 148
action of, 157
Seminal fluid, 682
Sensations, binaural, 627
common, 595
objective, 596
of color, 659
special, 596
subjective, 596
Sense, hearing, 614
muscular, 595, 603
of equilibrium, 628
INDEX
719
Sense of pain, 602
of sight, 630
of smell, 609
of taste, 604
of temperature, 600
of touch, 597
organs, directions for experiments
on, 669
perceptions, 597
Senses, the 595
special, 597
Sensorium, 596
Sensory areas of brain, 584
illusions, 596
impressions, 529
Serous membranes, 292
Serum, 102
agglutinative substances, 129
albumin, 81
blood, 102, 117
chemistry of, 139
composition of, 117
globulicidal action of, 128
globulin, 82
hemolytic action of, 128
precipitins of, 129
Seventh nerve, 554
Sharpey's fibers, 45
Sight, 630
Silicon, 94
Sixth nerve, 554
Size, estimation of, 668
Skein, 19
Skin, absorption from, 369
amount of carbon dioxide ex-
haled by, 396
excretion by, 407
excretory functions of, 391, 395
exhalation from, 396
functions of, 391, 397
glands of, 393
loss of heat from, 434
papillae of, 392
respiratory functions of, 396
structure of, 391
Sleep, 590
Small intestine, digestion in, 345
mucosa of, 364
villi of, 364
Smell, center for, 585
sensation of, 670
Smell, sense of, 609
Soaps, 91
Sodium salts in the body, 94
Solidity, judgment of, 667
Somesthetic area of brain, 584
Somnambulism, 591
Sound, 622
Sounds, articulate, 488, 490
localization of, 626
of the heart, 158
pitch of, 625
Special centers in bulb, 540
sensations, 596
Speech, 480, 490
action of tongue in, 491
mouth in, 491
Spermatids, 679
Spermatocytes, 679
Spermatogonia, 679
Spermatozoa, 679, 680, 682
Spermin, 432
Spherical aberration, 648, 672
Sphygmogram, 206
Sphygmograph, 205
Sphygmomanometer, 194
Sphygmometer, 206
Spinal accessory nerve, 1 560
bulb, 534
centers, 525, 526
cord, 510
antero-lateral ascending tract;
5i6
descending tract, 516
arrangement of nerve cells in,
5ii
ascending degeneration of,
5i6
columns of, 514
comma tract of, 516
conduction in, 528
course of motor impulses in,
53<>
of sensory impulses in,
529
crossed pyramidal tract, 515
descending degeneration of,
5*5
direct cerebellar tract, 516
pyramidal tract, 515
functions of, 510, 513
Gowers' tract, 516
720
INDEX
Spinal cord, hemisection of, 531
intrinsic cells in, 513
irradiation of impulses in,
521
Lissauer's tract, 516
peculiarities of different re-
gions, 519
postero-lateral column, 516
postero-marginal zone, 516
postero-median column, 516
reflex action in, 519, 524
reticular formation, 513
tracts of, 514
weight of, 574
nerve-roots, functions of, 523
nerves, 516
anterior roots, 517, 523
course of fibers, 517
posterior roots, 518, 523
reflexes, 524
Spirem, 19
Spleen, vascular nerves for, 224*
Spongioplasm, 8, 17
Staircase contractions, 455
Stammering, 491
Starch, 91
action of amylopsin on, 337
of ptyalin on, 311, 312, 353
chemical reactions of, 98
hydrolysis of, 98
Starvation, 420
death from, 420
effect on body temperature, 421
symptoms of, 420, 421
Steapsin, 303, 334, 337
Stercobilin, 90, 342
Stereoscope, 667
Stethograph, 258
Stethometer, 257
Stimuli, forms of, 442
maximal, 454
minimal, 454
Stokes' fluid, 121
Stomach, 316
absorption from, 362
action of pylorus, 328
blood-vessels of, 319
changes in glands during secre-
tion, 320
digestion in, 313, 316
gases in, 349
Stomach, glands of, 316
lymphatics of, 319
movements of, 327
nerves of, 316
nervous control of movements of,
329
secretion in, 320
structure of, 316
vascular nerves for, 224
Stomata, 25
Strabismus, 550
Stratum granulosum, 392
lucidum, 392
Malpighii, 392
Striated muscle, 58
development of, 62
Submaxillary gland, action of atro-
pine on, 306
paralytic secretion of, 306
secretion of, 306
Substantia nigra, 545, 546
Succus eritericus, 344
Sucking, center for, 542
Sudoriferous glands, 393
Sugar, test for, in urine, 403
Sulphates, 94
tests for, 94
Sulphur in proteids, 89
Sulphuretted hydrogen, effect of
breathing, 279
Sulphuric acid in urine, 384
Sulphurous acid, effect of breathing,
279
Summation, 459
of stimuli, 521
Superior laryngeal nerve in respira-
tion, 274
Supplemental air, 260
Suprarenal capsules, 428
active principle of, 430
functions of, 428
internal secretion, 431
nerves of, 428
relation to Addison's dis-
ease, 429, 431
extract, 430
Swallowing, 313
Sweat, 395
centers, 543
chemical composition of, 395
glands, 393
INDEX
721
Sweat, influence of nervous system
on secretion of, 397, 399
Sympathetic ganglia, functions and
structure, 591, 594
nervous system, 591
functions, 594
organization and distribu-
tion, 591
Synapsis, 520
Synovial membranes, 292
Systole of heart, 154, 156
TACTILE corpuscles, 74, 599
of Meissner, 74
menisques, 75
Taste, 604
after-, 608
buds, 605
center, 587
influence of fifth nerve on,
553
seat of, 604, 607
sensation of, 670
varieties of, 607
Taurin, 341
Teeth, 50
dentine of, 52
development of, 54
enamel of, 53
ivory of, 52
permanent, 51
structure of, 51
temporary, 50
Tegmentum, 544, 545, 546
Telophase, 20
Temperature, body, 433
dissipation of, 435
influence of extreme heat and
cold on, 436
regulation of, 434
sense of, 600, 669
variations in, 433
influence of, on muscular con-
tractic.i, 456
Tenth nerve, 558
Testes, 679
relation to metabolism, 432
Tetanometer, 499
Tetanus, 459, 499
Thermogenic centers, 439
Third nerve, 549
46
Thoracic viscera, vascular nerves for,
222
Thorax, respiratory changes in diam-
eter, 284
Thrombin, 105
, Thrombocytes, 115
Thrombogen, 106
Thrombokinase, 106, 139
Thyroid gland, 427
accessory, 428
functions of, 428
Tidal air, 259, 285
Tissues, connective, 31
elementary, 22
epithelial, 22
interchange of gases in, 272
muscular, 56
nervous, 64
Tone, of artery, 212
of muscle, 172, 525
Tongue, 604
action of, in speech, 491
papillae of, 606
Tonicity of heart muscle, 172
Tooth-pulp, 51
Touch corpuscles, 599
sense of, 597, 669
acuteness of, 599
Tract of Gowers, 516
of Lissauer, 516
Traube-Hering curves, 216
Treppe, phenomenon of, 497
Trigeminus nerve, 551
functions of, 552
Triolein, 90
Tripalmitin, 90
Tristearin, 90
Trochlearis nerve, 550
Trommer's test, 403
Trunk, vascular nerves for, 225
Trypsin, 303, 335
action of, 336
Tubular glands, 293
Tubuli seminiferi, 679
uriniferi, 372
Twelfth nerve, 560
Tympanum, 615
UNORGANIZED ferments, 301, and see
Enzymes
Unstriped muscle. 57
722
INDEX
Urea, 380
amount in tissues of body, 381
antecedents of, 412
determination of, 402
formation of, 381, 411
preparation of, 401
properties of, 380
quantity excreted, 382
Ureters, 377
Uric acid, 382, 402
condition of, in urine, 382
formation of, 413
properties of, 382
tests for, 402
Urinary bladder, 377
Urine, 377
abnormal constituents of, 403
albumin in, 385, 403
ammonia in, 383
analysis of, 399
average daily quantity of con-
stituents, 379
chlorides in, 385, 400
creatinin in, 383, 402
cystin in, 385
dextrose in, 385, 403, 404
discharge of, 390
diuretics, action of, 389
excretion by, 407
of, experiments on, 386
factors affecting secretion of, 386
nitration theory of secretion, 386
general properties of, 377
hippuric acid in, 383, 413
method of excretion of, 386
mucus in, 384
nitrogenous substances in, 380
occasional constituents of, 385
oxalic acid in, 385
phosphates in, 384, 401
pigments in, 383, 402
• quantity of , 377, 399
reaction of, 378, 399
relation of blood pressure to secre-
tion of, 398
saline matter in, 384
secretion of, theories of, 386
solids of, 400
specific gravity of, 379, 399
sugar in, 403, 404
sulphates in, 384, 400
Urine, urea in, 380, 401
uric acid in, 382, 402
variations in quantity of con-
stituents, 379
in specific gravity, 379
Uriniferous tubules, 372
Urobilin, 90, 342, 383, 402
Urochrome, 90, 383
Uroerythrin, 90, 384
Uromelanin, 384
Uterus, 686
Utriculus, 6 1 8, 629
VAGINA, 687
Vagus nerve, 558
effects of section, 560
functions of, 560
relation to deglutition, 315
to gastric secretion, 321
to heart's action, 179
to respiration, 273, 289
Valves of heart, 148
action of, 156
of veins, 154
Vas deferens, 680
Vasoconstrictor ac.tivity, 219
center, 214
nerves, 213, 219, 226
reflexes, 215
Vasodilator activity, 219
center, 218
nerves, 217, 219
reflexes, 218
Vasomotor centers, 543
changes, 241
nerves, 211, 220
tone, 214
Veins, 152
blood pressure in, 195
. . structure of, 152
valves of, 154
vasoconstrictor nerves in, 226
Venous flow, 202
velocity of, 203
Ventilation, 279
Ventricles of heart, action of, 155
Vesico-spinal center, 526
Vesiculae seminales, 680
Vesicular breathing, 259-
Vicq d'Azyr,* bundle of, 547
Villi, 361
INDEX
723
Visceral sensations, 529
Vision, accommodation of, 642, 645
binocular, 664
field of, 657
limits of, 660, 672, 677
localization of, 657
' mechanism of accommodation,
645
range of distinct, 645
Visual acuity, 678
center, 585
judgments, 667
purple, 658
sensations, 652
after-images, 654
intensity of, 654
sense, 630
Vital capacity, 260, 285
phenomena, i
Vitellin, 86
Vitiated air, effects of, 279
Vocal cords, 245, 480
movements of, 486
Voice, 480
• difference between male and fe-
male, 488, 489
in singing and speaking, 488
production of, 479
quality of, 489
Voice, vocal range of, 488
Vomiting, 330
action of abdominal muscles, 330
of diaphragm, 330
of pylorus, 330
center for, 331
nervous mechanism of, 331
Vowels, 490
WALKING, 475
Wallerian degeneration, 506, 515
Water, 95
absorption of, in intestines, 368
amount excreted, 396, 407
in expired air, 266
in the body, 95
as food, 300
rigor, 462
Weyl's reaction, 402
White fibrous tissue, 33
development of, 36
Wreath, 19
XANTHO-PROTEIC reaction, 96
YELLOW elastic tissue, 33
development of, 36
ZYMOGENS, 302
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