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LIPPriVCOTT'S PHrSIOLOGTES

THE THIRD BOOK

OF

ANATOMY, PHYSIOLOGY

AND

HYGIENE

OF THE HUMAN BODY

BY
J. A. CULLER, Ph.D.

PROFESSOR OK PHYSICS IN MIAMI UNIVERSITY, OXFORD, OHIO

PHILADELPHIA AND LONDON
J. B. LIPPINCOTT COMPANY

Copyright, 1904, by J. B. Lippincott Company

Copyright, 1905, by J. B. Lippincott Company

We, the undersigned, have carefully read Book III. of the Lippin-
cott Physiologies, and are happy to note the full and adequate teaching
of the physiological reasons for obeying the laws of health, including
those that relate to the nature and effect of alcoholic drinks and other
narcotics upon the human system which this book contains.

The truths taught are well told in language adapted to pupils in
elementary and secondary schools, for which we heartily recommend
the book.

Mary H. Hunt,

Life Director of National Educational
Association ; National Director of Bu-
reau of Scientific Temperance Investi-
gation, and World and National Super-
intendent of Department of Scientific
Temperance Instruction of the Wom-
an's Christian Temperance Union.

Members of the Text-Book Covunittce
of the Advisory Board

George W. Webster, M.D.,

President of Illinois State Board of
Health.

Lewis D. Mason, INLD.,
T. D. Crothers, M.D.,

Professor of Diseases of the Brain
and Nervous Sj'stem, the New York
School of Clinical Medicine.

Rev. Albert H. Plumb, D.D.
William A. Mowry, Ph.D.

Electrotyped and Printed by
J. B. Lippincott Company, Philadelphia, U. S. A,

PREFACE

This is the last book of a series of three. It is the
most advanced of the tliree, and is complete within
itself. It is intended to embrace the facts in anatomy,
physiology, and hygien*e which every man and woman
shonld know.

Every effort has been put forth to make the subject
plain to the reader. This is important in a subject of this
kind. A lack of interest very frequently arises from the
inability to grasp an idea as it is presented, though it
may be simple enough when presented in a different way.

The body is treated as an organized unit, each part
having a function, and all parts being related to the
others and dependent upon the harmonious operation of
all. The division of labor among the organs of the body
is often so sharp that a derangement of one tends to a
disorganization of the whole body. This furnishes a
strong basis for rules of hygiene and the consideration
of the alcohol problem.

This book contains not only general statements, but
exact information as far as possible. Technicalities may
seem to be avoided by general statements, but the subject
is thus often robbed of its interest and value. The red
corpuscles are the carriers of oxygen, but in a book of
this kind the function of the hemoglobin and its affinity

iii

iv PREFACE

for oxygen should be explained. Otherwise the pupil
may get the idea, as in cases known, that the gas is
carried in the concave depression of the corpuscle. This
is an illustration of the many peculiar ideas which pupils
form fi'om only general statements.

Questions are appended at the end of each chapter.
These are mainly topical. It is i^resumed that the
teacher will add numerous questions in the nature of
quizzes, as conditions may demand, but the best recita-
tion is one in which a pupil discusses a topic in a con-
nected discourse.

A list of experiments, such as may be performed in
any school where this book is used, is found at the end
of each chapter. The experiments are i^urposely few in
number, being selected with the intention that not one
of them need be omitted. It is better to give them from
time to time during the study of the text, rather than all
at once. The teacher will find it profitable to supple-
ment the list with others when time and conditions per-
mit. Nothing is so great an aid in making this subject
interesting as ex|3eriments which are performed by
teacher and pupils. Many experiments may be per-
formed at home, and will be performed with zest by
most of the class after they have had proper direction.

The subject of alcohol and its effect on the body has
been treated in the light of modern investigation. The
statements in regard to its effect are based upon a knowl-
edge of the nature of the human organism, reliable
experiments which have been made, and the experiences
of the past.

PREPArn^: V

The writer acknowledjj^es his iiulel)tedness to tlie J. B.
Lippincott Company for many courtesies, and permission
to use a number of cuts belonging to tliem. Also te
S. II. Williams, professor of biology in Miami Univer-
sity, for many valuable suggestions and reading of man-
uscript, and to G. W. Hoke, professor of natural history
in Miami University, for many helps and suggestions.

By permission of Ginn & Co. two cuts from BlaisdelPs
physiology are used in this text.

TABLE OF CONTENTS

Cn.vrTER PAGE

I. (Jeneraf, \'iew of the Subject 5

II. The Cells of the' Body l-*^

III. The Skeletox 3^

IV. Structure and Nourish :sient of Bones 45

V. Joints -^'^

VI. -Motion ''^^'

VII. Foods '^

VIII. Digestion ^'^

IX. Wholesome and Unwholesome Drinks 118

X. Circulation 1-^

XI. Respiration ^^'"-^

XII. Bacteria ^^-^

XIII. The Skin 207

XTV. Excretion --^

XV. The Xervous System 231

XVI. Physiology of the Xervous System 258

XVII. Hygiene of the Xervous System 271

XVIII. The Special Senses 293

Vll

LIST OF ILLUSTRATIONS

¥

FIG. PAGE

1. Typical coll \:i

2. Collection of plant-cells 14

3. kSection of twig of basswood 14

4. Section of pinewood !.">

5. Stomata of leaf 13

6. Bone-cells 10

7. Multiplication of cells from a single cell 17

8. Cell under a strong microscope 17

9. Protozoa . 19

10-15. Stages of cell division 20

16. The amoeba radiosa 22

17. Pavement epithelium 24

18. Columnar epithelium 24

19. Ciliated epithelium 2.5

20. Tvpe of gland 29

21. Human skeleton 34

22. Longitudinal section of bone 37

23. The cranium 38

24. A vertebra 39

2.5. The atlas 39

26. The axis 40

27. The sacrum and coccyx 40

28. The spinal column 41

29. Tlie ribs 42

30. The forearm and lower leg 43

31. Section of flat bone 45

32. ^klagnified .section of bone 46

33. Bone tied in knot 48

ix

X LIST OF ILLUSTRATIONS

FIU. PAGE

34. The hip-joint oo

35. Pivot-joint 5G

3G. Muscular movement 60

37. Bones of arm and biceps muscle 61

38. Levers of first class 62

39. Levers of second class 64

40. Lever of third class 64

41. Shape of muscle 66

42. Fascia of muscle 67

43. Muscles of forearm 68

44. Striated muscle fibres 69

45. Involuntary muscle fibres 69

46. Exercisers 72

47. Trichinae in pork 90

48. Osmosis of liquids 95

49. Permanent teeth 98

50. Section of tooth 99

51. Magnified section of tooth 99

52. Racemose gland 100

53. Stomach and intestines 103

54. ^lucous coat of stomach 104

55. Section small intestine of cat 107

56. Microphotograph of villi 107

57. Diagram of villus 108

58. External view of liver 109

59. Lobule of liver 109

60. Shallow wells 125

61. External view of heart 131

62. Cavities of heart 132

63. Auriculo-ventricular valves 133

64. Section of heart 133

65. Semilunar valves 134

66. Showing course of blood through heart 135

67. Section of artery and vein 136

LIST or IFJJ'S'njATIoNS xi

fl»'- PACK

(is. ( iipilliirics \im

(59. C'apillaiit's in miisclc i;jS

70. IJrd l»l(i<t(lc((||)uscl('s I j;;

71. Microphotoj^rapli of red coi pii^clcs 1 i;;

72. Scctidi) llirouiili vent ri('lf'.> of licail 140

7.*{. Selii'iiu' showiii^^ circulation of blood 14S

74. The fluco envelopes of the eartli liiJ

1'}. Tlie laiyiix 100

70. The vocal cords 100

77. The trachea and bronchi. 107

78. Infundibiila and air-sacs 108

79. The lungs 109

80. The pleura 170

81. Illustration of action of ribs 172

82. Illustration of action of diaphragm 17.3

8.3. Illustration of the combustion of iron 17.3

84. Illustration of changes in a leaf 177

8,1. Ivxchanges in the lungs 178

SO. Dillusion of gases 178

87. Window arranged for ventilation 182

SS. Particles of dust 184

89. Action of intercostal muscles 190

90. Bacteria 192

91. Multiplication of bacteria 193

92. Yeast-plants 193

93. Bacteria of diphtheria 198

94. Bacteria of lock-jaw 199

9.5. Bacteria of tuberculosis 200

9G. Bacteria of typhoid fever 201

97. Cross-section of skin of monkey's linger 207

98. Magnified cross-section of skin 209

99. Surface of palm of hand 210

100. Sweat-glands -H

101. Hair-follicle 213

xii LIST OF ILLUSTKATIONS

^I<5. PAGE

102. Cross-section of kidney 224

103. Section of cortex of kidney 22.j

104. Malpighian body 220

105. Malpighian bodies 227

lOG. Neurons 234

107. A neuron 230

108. Medullated nerve-fibre 230

109. Neuralgia cells 237

110. Brain on right side 239

111. Top of cerebrum 240

112. Section of brain, left half 241

113. Convolutions 242

114. Section of nerve 244

115. Section of spinal cord 248

IIG. A piece of spinal cord 249

117. Cervical nerves 250

118. Relation of nerves from spinal cord 251

119. Communication of neurons 252

120. End plate 252

121. Connection of nerve and muscle 253

122. Branching of nerves 254

123. Motor and sensory areas of brain 2G0

124. The supply of blood to the brain 274

125. Fatigued cells 275

126. Section of the eye 297

127. Illustrations of refraction 299

128. Influence of cornea 300

129. Function of iris 301

130. Attachment of lens 303

131. Focal distance 304

132. Convexity of lens 304

133. Emmetropic eye 305

134. Myopic eye 306

135. Hypermetropic eye 307

LIST or ILf.rSTIJATIoXS xiii

rir.. PACK

l:{t>. .Musflfs t)l ryt' :iOS

1.57. Nerve elements of retina ;ilO

13S. Rod and cone 311

130. Retina 312

140. Optic nerves :;14

141. Tear f,'lan(Is 317

142. Sound-waves 320

143. Pinna of ear . 322

144. Drum-head and ossicles of ear 323

145. Mechanical action of tympanum 32.j

14G. Section of ear 32S

147. Labyrinth of ear 329

148. The cochlea 331

140. The membranous labyrinth 332

150. Acoustic epithelium 333

151. Canals of the cochlea 334

152. Corti's organ 335

153. Tactile papillae 340

154. Pacinian corpuscles 341

155. Olfaotory bulb 343

156. The tongue 340

157. Circumvallate papillae 347

THIRD BOOK OF PHYSIOLOGY

CHAPTEK I

0

A GENERAL VIEAV OF THE SUBJECT

Matter and life. — 3Iau hiis always been interested
in the study of his own body. It is natural for liim to
look about and make comparisons between other objects
aud himself. He observes that every known form of
matter is either an inert, lifeless substance, as stone,
iron, water, and air, or is organized and endowed with
life, as in vegetables and animals.

The great bulk of matter is lifeless, but the small part
that is endowed with life is of greatest interest and im-
portance.

We do not know what life is, but we do know that it
has a wonderful influence upon matter that is taken into
the bodies of plants and animals.

We know that vegetables and animals are alive for
three reasons : (1) They can take up lifeless matter called
their food and can change it in such a way that it builds
up and strengthens their own bodies. Only a live body
can do this. (2) They can reproduce their own kind.
They are both made up of small bodies called cells, and
the cells can produce others just like themselves. The

6

G THIRD BOOK OF PHYSIOLOGY

cells of a live body only can do this. (3) They can move.
It is true a tree cannot move about bodily, but there is a
constant movement within ite cells, as will be explained
in the next chapter.

Any body that can do these three things is alive.

Animals and vegetables. — Some minute organ-
isms are of such a low order that it is not possible to tell
whether they are animals or plants. In all the higher
orders, however, there is a clear distinction between the
animals and the plants.

(1) Animals have the power of voluntary motion of
the whole body, while plants are fixed to one place.

(2) Animals feed on complex foods that have been
prepared by plants, while plants feed on simple foods,
such as minerals, water, and carbon dioxide.

(3) Animals have a distinct digestive tract within the
body, while plant food is prepared in the green leaves.

(4) Animals are endowed with a distinct nervous sys-
tem, to which plants have nothing to correspond. Mail
is an Animal.

Classes of animals. — The animal kingdom is di-
vided in modei'n zoologies into twelve branches. The
lowest branch includes the Protozoa. This word means
Jirst life, and is a general name for a group of the lowest
kind of animals. All these are of very simple structure,
and so small that they can be seen only by aid of the
microscope. They may be found wherever there is water.
During their lifetime they are composed of but a single

A <;RNK^^\L v.ifw of tiik sriuKcT 7

cell, aii.l yet they eat, breathe, move, feel, and reproduce
like utluT animals, oiilv in a verv simiile wav.

From thest* lowest foiins of the animal kinjjjdom there
is a gradual rise to higher and more complex forms.
Many cells unite to form one lx)dy, and different kinds
of cells form organs with special functions.

The highest branch of the animal kingdom is the IV/-
tebratf's. This includes all animals that have a backbone.
Mtin is a Veiiehrate AnhnAl.

The vertebrates. — Vertebrate animals are of six
kinds. (1) The Cyclosiomata. a kind of eel without true
bones, and with only a trace of a backlx)ne. It gets its
name from the fact that its mouth is circular and always
stands open. The lamprey is an example of this class.
(2) The Fishes. (3) The Amphibia, vertebrates which
spend the early part of their life as tadpoles in water,
such as toads and frogs. (^4; The Beptiles. (5) The
Birds. (6) The Mammals.

Mammals are distincruished bv the hair on the IhxIv
and by the mamumry gland that secretes milk for the
nourishment of their joung. They also differ from

the other vertebrates in having a midriff, or diaphragm,
that separates the chest from the abdomen. Man is a
Mamma2.

The study of man. — We are about to study the
wonderful structure and oi)eration of the highest and
most complex organism in wliich life resides, — the hu-
man bodv.

8 THIRD BOOK OF PHYSIOLOGY

. Scientists have investigated and experimented for many-
years to find out how the body is made and how it oper-
ates. While many things are yet without a satisfactory
exi^lanation, much is known with certainty, and with
these things all should be familiar.

The more one knows the more he can do, and the
greater is his pleasure, whether he reads, travels, works,
converses, or communes with his own thoughts.

The chief object in this stud\', however, is that it may
lead to the development of a sound and skilful body.

Man is capable of high development of both mind and
body, but those who are ignorant of the principles of
physiology and hygiene are apt to follow instincts, appe-
tites, and passions rather than intelligence and reason.
Although knowledge alone will not produce a sound body
or a sound mind, yet the practice which should accom-
pany knowledge is much more likely to follow when
there is an intelligent basis for the manner and purpose
of eating, breathing, sleei)ing, working, and study.

A healthy body and a vigorous mind are, as a rule,
found together.

The great advantages of good health should furnish a
sufficiently strong motive for understanding the condi-
tions by which it can be secured.

The three divisions of the subject.— When a
machinist undertakes to operate a machine with which
he is not familiar, he first makes a study of it and tries
to answer three questions :

(1) How is it constructed?

A (iFA'F.K'AI. VIKW OF TIM-: sril.IKC.T [)

(2) What is tlic use nf cadi part, and how (hx'S it
()|K'rat(' ?

(3) How can it 1m' iiia(h' !(► operate most enicit'iitly and
k(M'}) ill i;()o(l runnini;' order?

Tilt' liunian body is a machine more complex and intri-
cate than anything the mind lias hoxm able to devise.
Mduy of its operations are automatic, but the whole body,
cither directly or indirectly, is placed under the control of
the mind which resides within it. The freedom of choice
makes each one responsible for his physical condition.

The three divisions of this subject are :

(1) Anatomy, a description of the construction of the
body.

(2) Physiology, a description of the use and. operations
of the various parts of the body.

(3) Hygiene, a description of the conditions and laws
of good health.

Anatomy. — The word anatomy is from two Greek
words which mean, to cut apart. The act of cutting a
body apart to determine the structure of its parts is called
dissection. What we learn about the situation, structure,
and adaptability of the various parts of the body is
called the anatomy of those parts. For example, in giving
the anatomy of the stomach we would tell its location in
the body, its shape and size, its openings, its linings, and
its relation to other organs.

Physiology. — The word physiology is made up of two
Greek words which together mean, a discourse on nature.

10 THIHD BOOK OF PHYSIOLOGY

The woi'd is now applied to nature only as it is seen
in animals and plants. In this book we shall studj^
nature only as it is seen in man. The proper title of
this book, then, is, The Physiology of the Human Body.

Physiology proper deals only with the activities of the
various parts of the body. In giving the physiology of
the stomach, we describe its movements and the effect
of its secretions upon the food within it.

The term is also used in a broad sense including both
anatomy and hygiene. In this sense it is used as a title
of this book.

Hygiene. — The word hygiene is from a Greek word
which means health. The name of the goddess of health
in mythology is Hygeia Hygiene treats of the principles
and rules which have for their object the promotion of
good health.

Aids to the study of physiology.— All the
sciences are very closely related, and each one helps to
explain the others. Progress in the study of physiology
has been possible only in proportion as the other great
sciences have advanced.

The chemist can analyze the matter of the body and
determine its composition. He can also determine the
composition of foods and their adaptability to the needs
of the body. He can follow the food in its circuit through
the body and can note the changes it undergoes, thus de-
termining the chemical function of the organ through
which it passes.

A GENERAL VIKW OF TlIK SUIUKCT 11

Physics throws lit;hl \\\u)\\ Ihc study of i)hysioh>gy in
funiisliino- ;i cN^nr know i<'(lu<. ,,i" jj,,. ukm li;niic:ii juiiici-
pU'S omi)U)y(Hl in the body, tlic ciK'rjry valiH' <>{' foods,
and ill sliowiiio- Miat th(5 body is a true machine.

^rodorn biolo.cjy h;is been, probably more than any
other science, n ,ii:rent source of information in re^^ard to
living nature in motion. The biologist is not satisfied
with snperficial knowledge, but searches for the basis of
even life itself. The microscope has been a powerful in-
strument in his hands, and has opened to his view the
structure and activity of the living cell. The subject
of physiology cannot be clearly understood without a
knowledge of the activities within the cell. For this
reason the next chapter is devoted to a study of the cell.

REVIEW QUESTIONS.
These and similar sets of questions at the end of chapters should
be assigned as definite lessons to be carefully prepared. The pupil
is not ready to recite the review lesson until he can answer each
question without turning to the text. It is a good plan in this sub-
ject, as in most others, to insist on having the first lessons very
thoroughly prepared and understood. Successful preparation of
the first lessons is sure to result in an interest in the subject and
greater effort in the lessons that follow. Each succeeding chapter
is written on the assumption that the preceding one has been mas-
tered.

1. What are the proofs of life?

2. Is it proper to use the expression 'Mive coal" or ''live
wire"?

3. How can you distinguish between animals and plants?

4. Is a dead ox an animal ? What is it ?

12 THIRD BOOK OF PHYSIOLOGY

5. "What is the lowest branch of the animal kingdom ? What
is their manner of life?

6. What is the highest branch ?

7. Give in order the six kinds of vertebrates.

8. Give an example of each kind.

9. "What does the word amphibia mean? (See dictionary. )

10. Xame three things that distinguish mammals.

11. How does an animal differ from a brute?

12. What is man's position in the animal kingdom?

13. Of what advantage is a knowledge of physiology ?

14. Does a body need to be large in order to be healthy?

15. AVhat would you say of a strong body that was unskillful?

16. What are the three things a machinist must know about his
machine ?

17. What are the three divisions of physiology?

18. Define anatomy.

19. Define physiology.

20. Define hygiene.

21. In what broad sense is the term physiology often used ?

22. AMiat other sciences aid in the study of physiology ?

23. Of what use is the microscope in this study?

24. W^hat is biology ? ( See dictionary. )

('II A VTKU n

THE ('p:lls of the body

What the cell is.— ^lost cells are too small to be
seen by the naked eye, but the microscope reveals not
only the cell, but the minute parts of which it is com-
posed. Fig. 1 represents a cell which may be taken as
a type of all cells. On the out-
side is the cell-wall, which may
be thin or thick, circular or ir-
regular in shape, or may be want-
ing altogether. The cell-wall is
not alive, but is the material
which has been secreted by the
live material within the cell.
Within the walls is the cell-sub-
stance, or protoplasm. This sub-
stance makes up the most of the cell and is found alike
in cells of j^lants and animals. It is a somewhat trans-
parent mass, in some cases a thin liquid, and in others
thick like jelly.

Lying within the protoplasm is the nucleus. This is
a small body surrounded by a membrane and having
within it several smaller bodies called nucleoli. The
nucleus is an essential part of the cell, as will be shown
later.

13

Fig. 1.— Typical cell. C,
cell-wall ; ^V, nucleus ; n,
nucleolus ; P, protoplasm.

14

TIIIED BOOK Ot^ PHYSIOLOGY

Cellular structures.— AH living bodies are made
up uf cells. Some very small animals consist of only-
one cell, but all higher animals
and plants are composed of many
thousands of them. Plant- cells
are usually enclosed in heavy
walls, and when they are crowded
one against another they are
forced to assume a shaj^e best
suited to the space they occupy,
as shown in Fig. 2. In Fig. 3
is shown the arrangement of cells
in a twig of basswood as seen

Fig. 2. — Diagram of a col-
lection of plant-cells.

Fig. 3. — Microphotograph uf a cro-=s--eciion of a twig of basswood.

through a low-power microscope. The outline of the
cell-walls can be plainly seen arranged in rows radiating

Tin: CIILLS OF TIIK I'.ohV i:.

from the ce'iitic. Dry wood, in fact, is oiil\ a collection
of cell-walls. riie slreii^rth of wood depends on the kind
and anioiiiil of material «leposited in the walls of the
cells. Fig. 4 gives the appeanince of a cross-section of
pine wood.

Fig. 4. — Cross-section of pine wood.

In i:)lants as in animals there is a division of work
among the cells. Some assume the office of protection
of the others. Some collect and prepare the plant food.
A great variety of work is performed by the various
tissues of which tlie plant is composed. Fig. 5 shows

Fig. 5.— Surface of leaf showing stomata.

the microscopic appearance of the surface of a leaf.
The large flat cells are plainly seen, but the points of
chief interest are the modified cells about the stomata ^ or

16 THIRD BOOK OF PHYSIOLOGY

mouths. These are a good example of special functions
of cells. Their office is to regulate the transpiration of
water from the leaves. When water in the leaves is
scant, these cells close the stoma and prevent its escape,
but when water is present in excess the cells open the
stoma and permit it to freely evaporate.

The cells of plants have many characteristics in com-
mon with those of animals, though the latter are often
less clearly defined and more difficult
to study. In the tissues of animals
a distinction should be made between
the cell proper and the material which
Fig. 6.— Bone-cells. ^^^^ cells collect about themselves. In
Fig. 6 is a representation of three
bone-cells highly magnified. The spaces between the'
cells are filled in with bone material which may be
considered the walls of the cells.

In the same way the muscle, nerves, cartilage, and
other tissues are largely composed of material which the
cells have built np about themselves and which may be
considered a cell-wall modified to suit the special pur-
pose of the tissue.

The origin of cells.— The body of man, as well
as the bodies of all higher animals and plants, begins as
a single cell, or egg. The egg, A, Fig. 7, divides into
halves forming two complete cells. Each of the halves,
in turn, divides into two, making four, then eight, six-
teen, thirty-two, and so on. Several stages in the divi-
sion of the egg are illustrated in Fig. 7. The last, U,

THE TRLLS OF TIIF. P.oDV

has the appeiirance of a l>eiry, and is Ciilled the imilherry
stage of develo])iiient. This Imudh' of cells is closely
bound together, and continues to grow by a multiplica-

rion of cells and an accumulation
of cell material. The bodies of man
and all higher animals are formed
out of such bundles of cells. All
start as a single cell, which by di-
viding and subdividing results in
the growth of the body. The body
of a full-grown man is composed of
many millions of cells.

Parts of a cell. — Microscopes
have been very much improved, and

Fig. 7. — Diagram il-
lustrating the multipli-
cation of cells from a
sintrle cell.

Fig. 8. — Appearance of a cell under a
strong microscope.

scientists have learned much better ways of using them,
so that now they can see many things which before es-
caped their notice. In Fig. 8 is shown a cell as it ap-

18 THIRD BOOK OF PHYSIOLOGY

pears under a modern microscox^e. The protoplasm, F,
has the appearance of a mass of foam. ]S[ear the centre
of the cell is the nucleus surrounded by a membrane, m.
Within the membrane appear two different kinds of sub-
stances. One is like the protoplasm in the body of the
cell, and the other is represented in the figure by the
heavy lines, ch. This latter substance is called chromatin,
and is one of the most interesting and important parts
of the cell. Just above the nucleus aj)pear two aster-like
bodies, c These are called centrosomes. At first only a
very small dot appears, but soon it divides into two,
which are later surrounded by the radiating fibres as
shown.

The other marks are not essential i)arts of the cell.
An empty space is seen at v, and d is only a speck of
lifeless matter.

The nucleus. — All cells have a nucleus in some
form. It is the most essential part of the cell. Without
the nucleus a cell cannot assimilate food or reproduce
itself. Some interesting experiments have been per-
formed to demonstrate the importance of this part of the
cell. Certain small animals are made of only one cell,
but are large enough so that they may be cut into parts
and the action of the parts observed through a micro-
scope. In Fig. 9 is a representation of such an animal.
A bead-like string of nuclei extends through its body.
If it be cut into parts as shown at B, the two ux)i)er
pieces will contain nuclei, but the lowest one will not.
It would then be observed that the two nucleated pieces

TiiK cKi.Ls or 'rill-: r.oDv

i:»

live on as tliou^'^li iiothin*:^ liiid happened to them, and
each ill time wouUl take on the sjime form as the origi-
nal. The otlier piece would be observed to move abont

,■#■

,.Al!;'!"'/;".;^:^

3^-

.///?'/'/f/^>j?^

dCimCi^^cW?p^^,

?

^/~<

m

B

Flo. 0. — .1, protozoa ; 5, same out into three parts, the
being without nuclei ; C, the two nucleated pieces regaini

lowest
nir the

form of the original.

for a short time, but it would not assimilate food or
change its form, and soon its life would cease. Such ex-
periments show that the nucleus is a vital part of the cell.

How new cells are formed. — This is a subject of
great importance in biology and i^hysiology. We here
give the ijrincipal steps by which one cell becomes two.
The diagrams show only the i^art of the cell to which
attention is particularly directed. A cell at rest is repre-
sented in Fig. 10. The nucleus is filled with a net-work
of fibres, and just above it are the two dots called centro-
somes. Sometimes only one dot is seen, but it soon divides

20

TIIIED BOOK OF PHYSIOLOGY

into two. These soon begin to change in a very interest-
ing \vay.

The first change noticed is in tlie nucleus. Here the
fibres form into a thread and then break up into a num-
ber of pieces called cliromoHomes. The number of chromo-
somes is always the same for animals of the same species.
In this cell there are four.

Fig. 10.

Fig. 11.

Fig. 12.

Fig. 13.

Fig. 14.

Fig. 15.

The next change is seen in the centrosomes. They
assume a star-like appearance and begin to move from
each other, as shown in Fig. 12. though they are still con-
nected by fibres running from one to the other.

The membrane about the nucleus now disappears, and
the centrosomes continue to separate until one is on each
side of the cell with the chromosomes between them, as
shown in Fig. 13.

TllK (MOI.I.S OK 'rilK lioDV L>i

Tlir ('li:iiin<' wliicli iinw follows is iiiosl woii<l<'iful of all.
Tln' cliiomosoinos Splil Icii^tliwiso iiiln f wo <mju;i1 pints,
i'oui- of tliese, in this pailiciilaf ccli. iiionc to our cimiI i(>-
soiiie und foiii- lo 111*' ol her. The <li\ ision of I he, clii-oino-
soiiies into iMiual parts insures tha-t the new eell will lu*
just like its parent.

Tlie last step in the division is represented in Fi<;. j5.
A partition grows thi-ough the body of the cell dividin*^
it into two parts. A ni(*nibrane suriounds each set of
chromosomes, which now become the nuclei of the \u)w
cells. A centrosome remains with each nucleus. Th(^
cells separate, and each takes up its i^articular woik in
the body until again they undertake the process of
division just described.

The single cell. — Manj^ very small animals are com-
posed of only one cell. When they divide and become
two, each lives independent of the other. The amoeba^
shown in Fig. 16, is such an animal. When at rest it
may be sj^herical in form, and is then only about y^Vo ^^
an inch in diameter and looks like a lump of clear jelly.
It contains a nucleus, but the parts of its body are all
alike. It has no feet, mouth, stomach, or lungs, and yet
it moves, eats, digests its food, and breathes. It can i)ut
forth a projection from its body on any side and then
cause the rest of the body to flow into it. In that way it
moves about. It may wrap its body about other very
small animals or i^articles of food, and digest them. In
that way its whole body becomes, for a time, a stomach.
At any point of its body it takes in oxygen from the

22

THIRD BOOK OF PHYSIOLOGY

air in water and gives out carbon dioxide just as other
animals do. Thus it can turn any part of its body to a

B

EiG. 16. — The amoeba radiosa. A, B. C, and D are views of the
same amoeba, showing how it changed its shape within a few minutes.
One of the circles within the body represents the nucleus and the other
two are particles of food
shown in this cut.

The amoeba itself is only 3!^ as large as

variety of uses, but no one part has any special duty to
perform.

THE ("RLLS OF TlIK IU)I)Y 2:{

A k\u)\v\i'{h^v of tlie jimoeba is important in a study of
])]iysiolo«iy, because a <j^reat nunilxT of one-eel led struc-
tures of this kind are found within llie liuniini body.
Tliey are called irJiitr corpx-sclrs, and are of llu^ <;reatest
service to the body, as will later be shown.

A collection of cells. — It is jdain that an animal
of only one cell can never grow very lar<:;e oi* accom]>lish
very much alone. In all liiiiher animals, including man,
a great number of cells are joined together forming one
bodj^, and the work of the body is divided among them.
Some cells are concerned only in building up a bony
framework for the body ; some secrete fluids needed for
the digestion of food ; some form the protecting layer on
the outside of the l^ody. Just as in a large factory there
is a division of labor, and each workman is an expert in
some i)articular process or operation, so there is a di-
vision of labor among the cells of the body. Thus each
cell becomes specially fitted for doing some particular
thing necessary to the welfare of the whole body.

Tissue. — A number of cells of similar origin grouped
together and having a special work to do in any part of
the body constitute a tissue.

Each cell is alive and to some extent is independent
of the other cells, but, as already shown, a single cell is
so small that it is a very helpless creature when alone.
We have to use a good microscope to even see it. A
single cell of muscle can contract, but its etfort is very
feeble. When^ however, thousands of them act together,

24

THIJRD BOOK OF PHYSIOLOGY

the bundle of muscle is able to lift beavy weights and
perform hard labor.

There are in the body six different kinds of tissue :
(1) Epithelium 5 (2) Connective ; (3) Adipose ; (4) Os-
seous ; (5) Muscular ; (6) Nervous.

Epithelium. — Epithelium is the name of the layers
of cells that cover the whole outside of the body and line
all the vessels within that communicate with the outside.

Epithelium is a very common and a \'ery important
tissue.

Fig. 17. — Pjivement epithelium. Fig. 18. — Columnar epithelium.

- Its chief use on the surface of the skin is to i^rotect^the
parts beneath it. Here the cells are flat, and are fitted to-
gether at their edges much like the tile in a pavement,
and so it is called pavement epithelium^ Fig. 17. The nails
and hair, also the claws and horns of animals, are made
of this kind of tissue.

Another kind is called columnar epithelium, for, as seen
in Fig. 18, the cells are set on end and have the appear-
ance of columns. This kind of bells lines the stomach and
intestines.

Still another kind, shown in Fig. 19, is called ciliated
epithelium because the cells have projections at the top

TIIK (TJ.LS or TIIR r.oDV

25

that look like eyelnslies (ciliaj. Wliile the cells are alive
tlu' cilia ;in' in coiistnnt motion. iMshini:- back and forth.

Fig. 19. — Ciliated epithelium.

Snch cells line the air-x^assage of the nose, windpipe, and
lungs. They are also found in various other parts of the
bodv.

Connective tissue. — Connective tissue is distrib-
uted throughout the body, and its duty is to bind to-
gether and sui)port the various parts.

One kind is called white fibrous tissue. It forms the
ligaments which bind the bones together at the joints.
It is the tissue of the tendons that connect muscle to bone.
It serves as a tough membrane to cover various organs of
the body. In nearly every organ of the body it is an in-
dispensable connecting tissue. When seen under the
microscope it has the appearance of silvery white waving
bands. It is not elastic, but is very strong. Even the
bone to which it is attached will break before the white
tissue will give way.

An example of its strength may be seen in a butcher-

2G THTKD BOOK OF PHYSIOLOGY

shoj) where a beef or pork is hung from a peg by the ten-
don of the hind leg.

Another kind of connective tissue is called the yellow
elastic tissue. It differs from the white fibrous tissue in
color and also in the fact that it is elastic. It can be
stretched, and will return to its original condition as soon
as the stretching force is removed. It is found in various
places in the body where such a tissue is needed, as in the
skin, vocal cords, and arteries.

A third kind is called areolar tissue because its fibres
are lax and the spaces between them may be easily filled
up with air or a liquid. This tissue is very abundant in
the body. It binds parts together, but allows them to
move freely on each other. It is found, for example,
just under the skin, all over the body. It is this tissue
which allows the skin to have such great freedom of
movement. When the hide is removed from a dead ox
it is only the areolar tissue that needs to be severed.

Adipose tissue. — -Adipose tissue is a collection of
cells that contain fat. Each cell has a nucleus and is
alive like other cells, but is degenerate and soon to die.
This tissue is found in many parts of the body within the
areolar tissue. It is often abundant beneath the skin
and around the heart and kidneys. The fat of the cell is
a liquid while the animal is alive but becomes solid after
death. Lard is obtained from the adipose tissue of the
hog, and tallow from that of beef.

Fat is also found in the body outside of adipose tissue.
It is not part of a cell, but consists of little globules of

TIIR CELLS OF TIIK liohV 27

fjit sueli as are roniul in tlio blood. The usa of Hit will \hi
ih'scvihoi] under llu' subject of food.

Osseous tissue. -^>^w'>"s' fi-ssnf is the name ai)|)li«'d
to tlu^ collection of cells thai bnild np llie l)one of Ihii
body. Three such cells are shown in Fig. 0. Their
function is to j»ather from the blood the material they
need, and to Imild up around themselves the hard and
strong substance called bene. Bone is made hard by the
lime compounds — calcium phosphate and calcium car-
bonate— which the cells secrete.

In some parts of the body these cells do not secrete
lime, and then the tissue is called cartilage. Such is the
nature of the pads between bones at the joints, and many
other parts of the body. If the cartilage of the external
ear were as inflexible as bcme, there would be great danger
that it might be broken off by accident. Cartilage, how-
ever, is classed with the osseous tissue.

Muscular tissue. — Muscular tissue is the name of a
very abundant collection of cells which form a material
called muscle. This tissue can contract under the in-
fluence of the cell. It thus pulls upon the bodies to
which its ends are attached and draws the bodies closer
together. This tissue is used in every motion that is
made by the body.

Nervous tissue. — Nervous tissue is a collection of
cells that form the brain, the spinal cord, the nerves, and
the ganglia. These cells are provided with long thread-

2S THIRD BOOK OF PHYSIOLOGY

like projections that run out to the cells of other tissues.
In this way the nerve-cells have a directing and controll-
ing influence over all parts of the body.

Organs. — A collection of cells having similar work
to perform is called a tissue.

A collection of several kinds of tissue all working to
the same purpose is called an organ. The ear, for ex-
ample, is made up of manj^ different tissues, which to-
gether form the organ of hearing. The lungs are the
organs of respiration. The stomach, intestines, liver,
and pancreas are organs of digestion. The eye is the
organ of sight, and the brain of thought.

Systems. — A system includes several organs working
together to the same end. The circulatory system would
include all organs that have to do with the circulation
of blood or other fluids. These would be the heart, arte-
ries, capillaries, veins, and lymphatics.

Six important systems may be named : digestive^ circula-
tory, respiratory, nervous, excretory, and motor.

The excretory system includes all those organs that are
concerned in getting rid of the waste products or other
substances that would be injurious if retained in the
body.

The motor system includes the muscles, bones, ten-
dons, and motor nerves as far as they are concerned in
giving to the body its variety of motions.

Many organs belong to two or more systems. The
lungs, for example, are organs of respiration, but in ex-

Tin: CKLLS OF TJIK HuDY

29

piralioii tlicy an' also oriians of excretion, sinee earlxm
dioxide and otlier waste matter thus escape into the air.

Glands. — In many i)laces in the body it is necessary
to secrete Irom the blood certain liqnids wbicli are needed
in the economy of the body. Examples of such secre-
tions are the juices needed to digest food, and the sweat
which is poured out on the skin.

At otlier places it is necessary to excrete matter for
which the body no longer has any need, or matter which
would be harmful if not j^romptly thrown off. An ex-
ample of this is the urea which is excreted by the
kidneys.

Secretion and excretion are accomplished by organs
called glands. A simple form of gland is represented in
Fig. 20. It consists of a layer of epi-
thelial cells built U2^ in connective
tissue around a cavity and having an
outlet called a duct. A net-work of
blood capillaries lies close to these cells
on the outside. The cells take from
the blood the material suited to the
special purpose of the gland. For
example, the glands of the mouth will
secrete saliva and those in the stom-
ach will secrete gastric juice.

Fig. 20.— Type of
gland. C, cavity
surrounded with epi-
thelial cells ; d, duct.

Serous and mucous membranes.— The two
principal lining membranes of the cavities of the body
are the serous and mucous membranes. The serous mem-

30 THIED BOOK OF PHYSIOLOGY

brane lines all cavities that are closed, that is, having
no communication with the outside of the body. This
membrane lines the cavities of the abdomen, and is there
called the peritoneum ; it covers the lungs, and is there
called the pleura ; it surrounds the heart, and is there
known as the pericardium.

Serous membrane is thin and glistening and always
moist in a healthy body. It is a protection and support
to the body it surrounds.

The mucous membraiie lines all cavities that communi-
cate with the outside.

It may be considered as a continuation of the skin
which covers the outer surface of the body. It is com-
posed of layers of epithelial cells, and contains, in many
places, small glands which secrete fluids suited to the
purpose of the organ which they line.

The two cavities of the trunk. — The trunk of
the body is divided into two main cavities. The upper
one is called the thorax and the lower one the abdomen.
They are separated by the diaphragm, which is a parti-
tion between them. The lungs, heart, and large blood-
vessels are the principal organs in the thorax.

In the abdomen are the stomach, small and large in-
testines, liver, kidneys, spleen, pancreas, and numerous
blood-vessels.

THE CELLS OF THE BODY 31

QUESTIONS FOR REVIEW.

1. What lire f(»ur i)arts of a typical c«'H ?

2. What is protoplasm ? (Consult also the dictionary and cyclo-
pa'dia. )

3. What is wood?

4. What are stoniata, and how d(j they operate?

5. What distinction is made between the cell and the cell mate-
rial ?

6. Make a drawing of seve/al bone-cells,

7. How do cells originate?

8. What is the unit in the animal body?

9. Make a drawing to illustrate the appearance of a cell under
a strong microscope.

10. l)escribe the several parts that may be yeen.

11. Describe an experiment showing the importance of the
nucleus.

12. Describe six steps in the formation of new cells from old
ones.

13. What is karyokinesis ? (See dictionary. )

14. What part of the process makes it almost certain that the
new cells will be like the old?

15. Describe the amteba.

16. How is it different from other animals?

17. What cells of similar kind are in the body?

18. What is meant by a division of labor?

19. What is the advantage of a collection of cells ?

20. What is a tissue ?

21. How many kinds of tissue in the body? Name them.

22. Define epithelium.

23. Describe and make drawings of three different kinds of
epithelium.

24. Why should there be different kinds?,

25. What is the function of connective tissue ?

32 THIRD BOOK OF PHYSIOLOGY

20. Describe and give examples of three kinds of connective
tissue.

27. Describe adipose tissue.

28. What is osseous tissue ?

29. What is the function of muscular tissue ?

30. What is the relation between the nervous tissue and the
other tissues ?

31. What is an organ ? Give examples.

32. What is a system ? Name six.

33. Define the duty of each system.

34. What is secretion and excretion ?

35. Describe the structure of a simple gland.

36. Of what use are glands ?

37. What is serous membrane, and where is it found in the body?

38. What kind of organs are lined with mucous membrane ?

39. What kind of fluids do glands secrete ?

40. What are the two main cavities in the trunk of the body,
and what are the chief organs in each?

CnAPTEK III
THE SKELETON

The skeleton of the human body is made of bonevS,
with pa<ls of cartilage at the joints and strong ligaments
holding the joints in place.'

Use of bones. — Bones are of great use to the body
in four dififerent ways. (1) They determine the general
figure and shape of the body. (2) They protect the
delicate and vital parts. (3) They furnish support for
the softer parts. (4) Many of them can be used as levers,
so that the muscles can give to the various parts of the
body the kind of motion best suited to our needs.

Number and names of bones.— In the adult
human body there are two hundred and six different
bones, with thirty-nine different names.

(The common names of bones are in constant use, and
are a part of the vocabulary of every intelligent person.
For this reason the student is urged to make himself
familiar with the names given below.

Another reason for committing these terms and others
that follow is that any science can be clearly understood
only when the terms in which it is expressed are clearly
defined in the mind of the reader. The student is ex-
pected not onh' to give the names, but to locate the

3 33

THIRD BOOK Ot PHYSIOLOGSf

Fig. 21. — The human skeleton.
After a study of the following pages on the skeleton, the student
will be expected to rapidly name all the parts here shown without
reference to other pages.

THE SKELETON

35

The skill 1—8 bones. . .

The face— 14 bones . . ^

hones either by reference to bis own body or by reference
to the cut on the oj)posite page or on a physiological
chart.)

BONKS OF THK HUMAN SKELETON.

1 Frontal, forehead.

2 Temporal, temples.
2 Parietal, sides uf head.
1 Occipital, back of head.
1 SpHenoid, base of skull.

1 Ethmoid, front of skull.

2 Xasal bones, bridge of nose.
2 Malar hones, cheek.
2 Lachrijmal bones, at inner part of the

orbit of the eye.
2 Turbinated bones, in nostrils.

1 Vomer, between nostrils.

2 Palate bo7ie.^, in back part of roof of
mouth.

2 Upper maxillary, upper jaw.

1 Loner maxillary, lower jaw.

2 Malleus, the hammer.
2 J)icus. the anvil.
2 Stapes, the stirrup.
7 Cervical vertebrse, in neck.
12 Dorsal vertebrse, in back.
5 Lumbar vcrtehrx, in small of back.
1 Sacrum, at lower end of vertebral col-
umn.

1 Coccyx, below sacrum.
The ribs— 24: bones ... 12 ribs on each side of thorax.
The sternum— 1 bone . . breast-bone.
The OS innominatum —

2 bones the hip-bones.

The ear— 6 bones

The vertebral column
— 26 bones ....

36

THIRD BOOK OF PHYSIOLOGY

The hyoid — 1 bone

The upper limbs — 64
bones

The lower Hmbn-
bones ....

-(50

. at base of tongue.
2 Clavicle, collar-bone, at top of chest, in

front.
2 Scapula, shoulder-blade, back of

shoulder.
2 Humerus, arm.
2 Radius, forearm, on same side as the

thumb.
2 Ulna, forearm, by the side of the radius.
16 Carpal bones, wrist-bones.
10 Metacarpal bones, in body of hand.
28 Phalanges, 3 in each, finger and 2 in

each thumb.
2 Femur, thigh-bone from hip to knee.
2 Patella, knee-pan.
2 Tibia, shin-bone.
2 Fibula, by shin-bone on outer side.
14 Tarsal bones, ankle-bones.
10 Metatarsal bones, in the body of foot.
28 Phalanges, 3 in each toe and 2 in each

great toe.

Classes of bones. Long bones.— As to their
structure and use, bones may be classified as long, short,
Jlat, and irregular. The Jong hones are the humerus,
radius, ulna, femur, tibia, fibula, metatarsal and meta-
carpal bones, the phalanges, and the clavicle.

Long bones are not always of great length. The bones
of the fingers are short, and yet they are classed with the
long bones. A long bone may be described as a hollow
cylinder, having thick and very compact bony tissue at
its middle but expanded at its extremities, where the

TUK SKKLETON

bone is of a spongy cliaiadi r. 1*^1,^. 22 shows part of a
long bone that h;is been cut in t\v«> lengthwise.

Fio. 22. — Longitudinal section of upper end of femur. 1, 2, compact
bone ; 3, cancellated bone.

Short bones. — The short bones are such as those of
the carpus and tarsus. Thej^ are made of spongy bone,
and covered with a thin crust of hard, compact bone.

Flat bones. — The flat bones are used to protect other
parts of the body and to furnish a broad surface for the
attachment of muscle. They are made of two plates of
hard bone, quite close together, with spongy bone be-
tween.

The flat bones are the frontal, parietal, occipital, nasal,
lachrymal, vomer, scapula, hip-bones, sternum, ribs, and
patella.

38

THIRD BOOK OF PHYSIOLOGY

Irregular bones.— The irregular bones are so called
because of their form. They are all bones of the skele-
ton not included in the other three classes. They all
have a hard, bony shell on the outside with spongy bone
tissue within.

The cranium. — The cranium is a strong bony box
which supports and protects the most delicate and most
important organ of the body, — the brain. In the cranium
of the adult, as shown in Fig. 23, the flat bones are joined

Fig. 23. — Cranium.

edge to edge h\ a kind of joint called a suture. The
edires ""row into each other and form a solid union. The
cranium of the infant is soft and easily distorted, because
the bones are not yet hardened with lime.

All the other bones of the skull articulate with the
sphenoid, which, like a wedge, holds them firmly to-
gether.

TIIH SKKLKTON

?,'.)

The vertebral COlunm. — Tho vertebral column is
coiupusod of o.i vertcbnc (Latin, vcrtere, to turn) placed
one on top of tlie otlier. The cliaracteristic parts of a
vertebra are the Vmdj', several processes, and a perfora-
tion just back of the body. These an^ shown in Fig. 24.

..s

i#^^

Fig. 24. — Vei'tebra. B, body; T^ transverse process ; S, spinous

process.

The vertebrae are piled up in the manner shown in
Fig. 28, and serve as a strong pillar to hold up the head
and the trunk of the body. The holes together form a
tube for the protection of the spinal cord.

Fig. 2.5. — Atlas.

The atlas. — The topmost vertebra is called the atlas,
because the head rests upon it (see Atlas in dictionary).

40

THIRD BOOK OF PHYSIOLOGY

It differs in shape from the other vertebrae, as may be
seen in Fig. 25. It articulates with the base of the skull,
and when the head is turned it turns with it.

Fk;. 2*;.— Axis.

Axis. — The rsecond vertebra is called the axi.s, because
it forms a pivot uj^on which the atlas rotates. The pecu-
liaritj^ in the shape of the axis is the tooth-like projection
called the odontoid process. The atlas fits over this x^ro-
cess and rotates about it when the head is turned from
side to side.

Fig. 27. — Sacrum and coccyx.

Sacrum and coccyx. — At the lowest point of the
backbone is the coccyx. In early life it consists of four

TIIK SKFJJ«:T()X

41

separate bones, but later tliey grow t<>j;elh<*i- and fm m
one solid bone, ft is called the
coceyx because it looks like the
beak of a euekoo.

Just above the coccyx is the
sacrum, or sacred bone. It is so
called because it was once used in
sacrifices. In early life it is com-
posed of five separate bones, but
later they grow together.

The sacrum and coccyx, to-
gether with the two large hip-
bones, form a strong basin at the
base of the trunk of the body. It
is called the jx'his, l>ecause lyelvin
in the Latin language means basin
(see skeleton on page 34).

Flexibility of the back-
bone.— The bod}' of each vertebra
is about one inch thick. AVhen
they are placed one on top of the
other thay form a cobimn that is
slightly curved like the letter S.
The bony i:)art of the vertebraj do
not touch each other. There is a
pad of elastic cartilage between
them, and all are bound firmlj'
together by strong ligaments.

Both the shajje of the column and the pads of cartilage

Fig. 28. — Showing curves
of spinal column.

42

THIRD BOOK OF PHYSIOLOGY

prevent sudden jars from walking, jumping, or a slight
fall. The cartilage also permits great freedom of move-
ment in all directions.

The ribs. — The ribs are flat, elastic l)ones surround-
ing the chest. They are twenty-four in number, twelve

Fig. 29.— The ribs.

on each side. The u^^per seven on each side are true
ribs, and the lower five are false ribs. All articulate
with the backbone by a true joint, two to each dorsal
vertebra. In the front the seven true ribs are joined
to the sternum by means of cartilage. The fii^t three
false ribs are joined in front to the cartilage of the
lowest ti^ue rib. and the two remaining ones have no
attachment in front, and so are QduW^d floating ribs. The

THE SKKLKTON

4:j

ribs do not pass strai^lit aiouiid the chest, but are lower
ill front, and also sa^ in llie niiddlo. Tlie advantage of
this will be apparent when we come to the study of
breathing.

The extremities. — There are many points of simi-
larity between the bones of the arms and legs. The

tei

Fig. 30. — Forearm and lower leg.

femur is the largest bone in the body, and the corre-
sponding bone in the arm is the humerus. The tibia is
the next longest, and is on the same side as the great toe.
The radius of the arm is a corresponding bone on the
same side as the thumb. The fibula of the leg has its

44 THIRD BOOK OF PHYSIOLOGY

counterpart in the ulna of the arm. The tarsus is similar
to the carpus. The metatarsus and metacarpus are much
alike, and both the feet and the hands end in phalanges.

QUESTIONS FOR REVIEW.

1. Give four uses for bones.

2. How many bones in the human body?

3. Give good reasons for learning their names.

4. Name and locate the bones of the skull.

5. Point out and name the bones of the face.

6. Define the names of the ear bones.

7. What are the three classes of vertebrae? Locate them.

8. What are the three kinds of ribs?

9. Where is the sternum? The os innominatum? The hyoid?

10. Name all bones of the upper limbs.

11. Name all bones of the lower limbs.

12. Name together the corresponding bones of the arms and legs.

13. Point out on the chart all the bones of the body, giving
names.

14. How are bones classified as to their structure?

15. Define a long hone. Name all the long bones.

16. AVhat is the structure of short hones? Oijiat hones f

17. To which of the four classes do the ribs belong?

18. Locate the sphenoid.

19. How many vertebrae are there, and why are they so called?

20. Which vertebra is called the atlas ? Why so called?

21. What is the use of the odontoid process?

22. What is the pelvis f

23. What provision is made to relieve the brain from sudden
jars ?

24. What is the difference between the true, the false, and the
floating ribs ?

25. How can you tell which of the two bones in the forearm is
the radius ?

CHAPTEE IV

STRUCTURE AND NOURISHMENT OF BONE

Strength of bones.— Bones which are to serve as
a framework of the bodies of animals should be strong
and at the same time light. This condition is brought
about by making all long bones in the form of tubes, as
shown in Fig. 22. A tube will support much more

Fig. 31. — Cross-section of a flat bone.

weight than the same amount of material in form of a
solid rod. This principle is utilized in the use of hollow
iron pillars for the sujjport of buildings and in the
hollow stalks of grasses and grains. In the middle of
the shaft of the long bone the tube is smaller, but the
walls are thicker and almost as compact iis ivory. To-
wards the ends the walls are thinner and the shaft
larger. The exi^anded ends are filled with spongy bone
which looks something like lattice work, and so is called
cancellous bony tissue. The strength and lightness of flat
bones are secured by having two plates of compact bone
with cancellous tissue between them. The shai)e and
structure of a bone depend upon the nature of its ser
vice to the body.

45

46 THIED BOOK OF PHYSIOLOGY

Microscopical examination of bone.— When

we look through the inicroscoj^e at a very thin slice of
bone it is seen to have a very definite and interesting
structure which can never be seen with the naked eye.
Fig. 32 ilhistrates the appearance of such a cross-section.

r^^:r^iM^^^U:.-^^Q,

tm.

.. .J ' - :-'-~.^~'- 9- ;.

Fig. o2. — Cross-section of hone, highly magnified.

The lioles at the centres of the circles are only about sk
of an inch across, some being larger and some smaller.
These holes are tubes cut across. The tubes run length-
wise with the bone and are called Haversian canals, from
the name of the discoverer. Dr. Havers. The bone-cells
are arranged in circles around the canals. Their loca-
tion may be determined by the black, irregular spots
called lacunce where the living cell resides. Very fine
tubes, called canaUculi, ladiate from each lacunae, con-
necting them one to another and with the central Haver-
sian canal. Each canal with its concentric layers of

STRUCTrUK OK IloXK 47

lacnnii' jukI caiialiculi form a ll<(rrr.sian si/shni. IIi<^ljly
maunilied Ixnw cells arc I'cprcsciilcii in Vi*!;. <!.

How bone is nourished, rin- hone-cells, like
most cells of the body, arc lixcd to one i^lace. Their
food must be brought to them or tliey will starve. The
bones that are usually picked up for examination are dead
bones. They are no more like the live bone than a dead
twig on the ground is like a live one on a tree. When a
live bone is cut, blood will ooze from its numerous canals.
It is plain that the blood here, as elsewhere, is the agent
by which food is brought to the cells. All bones are sur-
rounded by a membrane called the periosteiun (around the
bone). In this membrane are numerous blood-vessels
that enter the bone in many places and traverse the
Haversian canals. The hollow bones are lined on the
inside with a similar membrane called the endosieum. An
arter}^ enters the long bone usually through a foramen at
about the middle of the shaft. It distributes itself in
the endosteum. From this source the marrow which fills
the hollow of the bone receives its nourishment, and also
the inner layers of bone are supplied with bone material
from the same source.

Composition of bone. — A chemical examination
shows that bone is composed of two kinds of substances
closely mixed together. One of these is called animal
matter and the other earthy ^natter, — about one-third of the
former and two-thirds of the latter. The earthy matter
may easily be removed from bone by submersion for a

48 THIHD BOOK OF PHYSIOLOGY

time ill dilute muriatic acid. (See directions at end of
this chapter.) The acid readily combines with the lime
compounds, so that in the course of a day only the ani-
mal matter of bone remains in place. This is now
so flexible that it may be tied into a knot, as shown
in Fig. 33.

A piece of fresh bone i:)ut into a hot fire for an hour or
two will lose all its animal matter, and onh^ the hard
part, which is largely the phosphate and carbonate of
lime, will remain un burned.

The bones of young children are quite soft, because
they are composed of a large proportion of animal matter.

Fig. 33. — Bone tied in knot.

As the child grows older, more and more lime is de-
posited about the cells, and so the bones grow harder and
more brittle. Ossification begins at the middle of a bone
and extends out to the joints.

The shafts of the long bones are filled with a yellowish
fatty substance called marrow. The cancellous tissue is
filled in with a thin reddish liquid, which is sometimes
called marrow, though it contains very little fat, while
true marrow contains 96 per cent. fat.

This red liquid is intimately connected with the for
mation of new red blood-corpuscles.

Health of bone. — Bone has but few nerves distrib-
uted to it, and so we feel but little pain from any wound

STRUCT UEE OF BONE 49

which it receives. It iiuiy Imm-oiho diseased, however,
just like any other part of the body. (Jood bone can be
built up by the cells only when the necessary material is
furnished to them in the blood. Bone is formed fiom
the materials in the food which we eat.

There is a disease called rickets^ which is common
with children who live on scant and poor food. The
backbone and legs are often bent and distorted, because
the bone-cells are poorly^ fed and do not build up a
sufficiently rigid tissue.

A man does not leach his full height until about the
age of twenty-five years ; and, although the bones may
have been perfectly healthy, yet they have been soft and
flexible. The hardening of bone continues even long
after full growth has been attained. The bones of chil-
dren may be made to take on a variety of shapes and
positions which, if allowed to remain so, will become
fixed in later life.

Bow-legs are quite a common misfortune, but in most
cases the deformity could have been prevented by proper
care in the early life of the child, or by proper appliances
while the bone was still soft.

Stoojjing shoulders and a contracted chest are a result
of careless habits of posture w^hile the bones are soft.
The fault cannot be corrected in later life. The head
should be carried erect (not thrown back), the chest ex-
panded forward, and the proper curve of the backbone
maintained.

Tight shoes deform the bones of the feet, produce an

50 THIRD BOOK OF PHYSIOLOGY

awkward and unsteady gait, and make walking a painful
exercise.

A firm and graceful walk is much more to be admired
than a small shoe.

Tight clothing about the waist is sure to deform and
displace the lower ribs. The vital organs within the
chest and abdomen are seriously hindered in their work
by such compression.

Those who sit long in one place should be careful of
their posture. School seats should be of such a height
that the feet of the pupils may rest squarely on the floor.

Older pupils should have desks of such size that they
are never forced into a cramped i:)Osition. All desks
should be close enough together to permit pupils to sit
up while they write or do other desk work.

Fracture of bone. — A broken bone is said to be
fractured; (1) when it is a clean break it is called a sim^Ze
fracture ; (2) when the soft parts about a break are lace-
rated, so that there is an opening from the skin into the
bone, it is called a comjwund fracture.

It is a wise provision of nature that the bones of the
young are soft and flexible 5 otherwise, the numerous
bumps and falls to which a child is liable would be ac-
companied by serious results. As the child grows older
he becomes more skilful in his movements, and learns
how to avoid accidents. The bones become harder and
stronger, but also more liable to fracture.

When bone is broken nature sets about at once to heal
the fracture. At first a watery fluid is poured out around

STKUCTTRK or I'.oXE 51

the broken ends, and lliis in course of a fow days will
heconir tiiick like jcllx . In t liis a <leposit of lime is made
until it is almost as liaid as hone its<'lf. Thus a natural
splint is formed about tiie fracture, and the ends of the
bones are hold more firmly in place. It requires five or
six weeks for healthy bone to unite, and several months
may elapse before union is complete.

It sometimes happens that bones will not readily unite.
This is called iMayed union. The delay may be for
months, or may even be permanent.

If the parts of a broken bone remain in their proper place^
and are kept quiet for five or six weeks, nature alone will
repair the fracture in a very satisfactory manner. In
nearly all cases, however, a broken bone is also displaced,
and in that position will not unite at all, or, if it does,
will be weak and crooked.

For these reasons the services of a surgeon should
always be secured at once.

QUESTIONS FOR REVIEW.

1. How are bones made both strong and light?

2. How is this principle utilized in nature and architecture?

3. What determines the shape and character of a bone? Give
examples.

4. What is a Haversian canal? How large are they? What is
their use ?

5. What are lacuruc, and how are they connected ?

6. Where are the bone-cells?

7. What constitutes a Haversian system?

8. How do bone-cells get their food?

9. What is the periosteum f The endosteum ?
10. What is inside the long bones?

52 THIRD BOOK OF PHYSIOLOGY

11. What is the composition of bone?

12. AVhat kind of substance fills the spaces of the cancellous
tissue ?

13. What is the cause of rickets?

14. Why should young people be careful of their posture in sit-
ting and walking?

15. What is the jjroper posture ?

16. What deformities are caused by tight clothing?

17. What is a simple fracture f A compound fractured

18. How are flexible bones an advantage to children ?

19. How does nature try to repair a fracture?

20. Why is a surgeon needed when a bone is broken?

21. Why is a horse usually shot when one of his legs is broken?

EXPERIMENTS.

Animal matter in bone.— Secure from the butcher a clean fresli rib of
a lamb or sheep. Place it in a bottle or dish of such shape that the bone mas-
be completely covered with about one pint of water. Pour into the water alx»ut
three ounces of hydrochloric acid and set it aside for twelve hours or more. The
acid will dissolve the lime, leaving only the animal matter, which is now so
soft and pliable it can be tied into a knot.

Earthy matter in bone.— Place a piece of fresh bone in the hot coals of
a stove or furnace for two or three hours. The animal matter will all burn
away, leaving only the mineral matter, which may now be broken with a
hammer.

Weigh the bone Ijefore and after burning. The difference in weight is the
weight of the animal matter burned away.

Examination of a bone.— Secure a fresh bone of the lower leg of a
sheep or beef and make the following observations :

1. The smooth cartilage at the ends.

2. Try the strength of it.

3. Peel off some of the periosteum.

4. Look for au opening in the side of the bone.

5. Saw the bone in two lengthwise and note the thickness of the bony walls.

6. Examine the marrow.

7. Look for cancellous tissue.

8. Find the endostemn.

9. Secure any bone that is not a lon^ bone, saw it iu two, and closely examine.

CHAPTER V

JOINTS

Use of joints. — A stone pillar which has been
chiselled into the likeness of a man has no need of joints,
for it will not need to change its position.

A tree needs no joints, for it is by nature stationary.
Joints would be a source of weakness to a tree.

Man and all the higher animals, however, must be
capable of a great variety of motions and movements,
and for that purpose they are supplied with numerous
joints. When a man loses the use of a single important
joint he is at a disadvantage in the activities of the
world, and is considered a cripple.

The structure of joints. — In all joints of the
body where one bone glides on another, three important
provisions are made. (1) The surfaces are made smooth.
(2) A lubricating fluid is supplied as needed. (3) The
bones are bound firmly in place.

These are just the conditions we try to secure in the
machines which we build, wherever one jyart must bear
uj^on another while in motion, and where friction is to
be avoided.

Articular cartilage. — The smooth surface of joints
is secured by a layer of cartilage on the articulating

54 THIED BOOK OF PHYSIOLOGY

ends of bones. This is the only part of a bone that is
not covered with periosteum.

The smoothness of the cartilage affords ease of move-
ment and its elasticity helps to break the force of any
concussion. The cartilage varies greatly in thickness,
being thickest at points where the greatest pressure is
received, — the middle of the convex surfaces and the
edges of concave surfaces.

Synovia. — The joint, however, would soon become
stiff or could be moved only with great difficulty with-
out a lubricating fluid ready at any time it is needed.
Such a fluid is supplied to all the movable joints. It is
called the synovial fluid because of its likeness to the
white of an e^gg (see the word in the dictionary). The
fluid is secreted by the synovial membrane and poured
out on the joint.

How joints are held in place. — The ends of bones
at a joint must be held to their proper places, and at the
same time there must be freedom of movement. These
conditions are secured in a variety of ways. Strong liga-
ments consisting mainly of bundles of white fibrous tissue
(see page 25) are fastened to the bones aboA^e and below
the joint. The hip-joint, for example, is enclosed by a
set of ligaments which form a capsule or box about the
joint. Such ligaments are very strong, and will resist
even violent attempts to pull the joint apart.

Air-pressure also helps to keep some of our joints in
place. This is particularly true of such joints as that in

.TOTNTS

55

the liip, where the ball of llir rnnni- fits into the deep
socket of tlie lii{»-l)OTie. Any attempt to laill tlie ])all
from its socket would Im* lesisted by the pressure of the
air because of the vacuum produci-d in the socket. Since
the diameter of the socket is nearly two inches, the air-

FiG. 34. — The hip-joint. Capsular ligaments stripped back to show

the ball and socket.

pressure which would resist any attempt to suddenly
pull the bones apart would be about fifty pounds.

Kinds of joints. — Mature tries to make each organ
of the body most efficient in its particular kind of work.
We would expect to find that the joints in the various
parts of the body would be of a kind best suited to the
work which that part of the body has to do. Joints may
be classified as immovable and movable^ the latter being of
greatest interest and importance.

56

THIRD BOOK OF PHYSIOLOGY

The immovable joints are those where the bones are
almost in direct contact, with only a thin layer of con-
nective tissue between them, and without any motion of
one upon the other. Such joints connect the bones of
the cranium. The bones of the face, except the lower
jaw, are also bound together by immovable articulations.

There are three important kinds of movable joints, —
pivot-jomts. hinge-joints, and ball-and-socket joints.

The pivot-joint permits only the motion of rotation. A

Fig. 35. — Example of pivot-joint. Atlas on axis.

good example is found in the motion of the atlas on the
axis when the head is turned from side to side. The
relation of these two bones is shown in Fig. 35. Across
the ring of the atlas is a strong ligament which holds
the atlas in place and yet permits it to rotate about the
odontoid process.

The hinge-joint is common in the human body and in
the bodies of all higher animals. Onh' a forward and
backward motion in one plane is permitted by a joint of
this kind. The motion is like that of a door on its

JOINTS :)7

hinjjfcs. A good example is louiid in (lie last two joints
of the fingers. Those joints permit the fingers to be
closed and opened, l)ul do not admit of any latei-al
motion. The elbow and knee are also exami)les of
hinge-joints.

The haU-and-socket joint allows greater freedom of
movement than is i)0ssible with any other kind of joint.
The best example of such a joint is found in the hip. l>y
reference to Fig. 34 it is j51ain that, within certain limits,
the leg can be moved in auy direction desired.

In the shoulder, where the humerus articulates with
the scapula, is also a joint of this kind. The socket here
is not so deep as that at the hip. As a result of the shal-
low socket the arms have a greater range of motion than
the legs, but the shoulder-joint is more liable to dislo-
cation.

Another kind of joints, called gliding joints, may also
be mentioned. Examples may be found in the bones of
the carpus and tarsus, which maj^ glide slightly upon
each other.

Health of joints. — Joints are delicate in struc-
ture, and so are liable to disorder unless they receive
proper care. A diseased condition of the joints, called
gout, is common with those who drink strong wine and
other alcoholic liquors. The tendency to gout is also
often inherited.

Another serious disease, often located in joints, is rheu-
matism. It is frequently the result of negligence in the
niattei: of clothing suited to changes in the weather. It

58 THIED BOOK OF PHYSIOLOGY

may be caused by sitting in damp places, or by neglect-
ing to cliange clotliing after exposure to wet. Eheuma-
tism is the cause of a great deal of pain and discomfort,
and yields very slowly to any treatment now known.

Joints are liable to sprains and dislocations. When
the ligaments about a joint are torn or unduly stretched,
the joint is said to be sj) rained. Even slight sprains
should receive immediate attention, for neglect may, as
has often been the case, result in stiff joints.

When the bones of a joint are forced out of place it is
called a dislocation. When this occurs, no time should
be lost in calling a surgeon to put the bones in place again.

QUESTIONS FOR EEVIEAV.

1. Of what use are joints in the human skeleton ?

2. What are the three conditions of a good movable joint?

3. How do joints of the body compare with joints of a machine?

4. Describe the use of articular cartilage.

5. How is a joint lubricated ?

6. What provision is made for keeping joints in place?

7. Give examples of immovable joints.

8. What kind of joints in the bones of the face?

9. Name three important kinds of movable joints.

10. Describe the motion of the atlas on the axis.

11. What kind of motion in a hinge-joint?

12. Of what advantage is a ball-and-socket joint?

13. What kind of joints are in the tarsus and carpus?

14. What is gout f what is one of its causes?

15. What are some of the causes of rheumatism in the joints ?

16. What is a sprain ?

17. What is a dislocation ?

18. Point out and name each kind of movable joint seen in skele-
ton on page 34.

CHAPTER VI

MOTION

Motion a test of life. — Animals have the power of
vohintary inoveiiieiit. Our common test of life is the
ability to move. Some motion, such as the beating of the
heart or the act of breathing, is going on in the body at
all times. The power of voluntary movement, however,
is one of the chief distinguishing marks between the
higher animals and the higher plants.

Movement within the cells. — Beside the com-
monly observed motions of the body, there are also many
delicate motions which are never seen except by aid of
a strong microscope.

The motion within the cell, as in case of cell division
described on page 20, is an evidence of the life of the
cell.

The white corpuscle is capable of independent move-
ment, and goes about from j)lace to place within the
body.

Another examjDle of cellular movement is found in cer-
tain of the epithelial cells which are provided with cilia
(Fig. 19). These cilia, some thirty to each cell, are in
constant motion, lashing back and forth. This motion is
produced by the cell, and continues long after the body
as a whole has ceased to live.

59

60 THIRD BOOK OF PHYSIOLOGY

Motion by means of muscles. — The principal
bodih- motions are accomplished by the action of the
muscles upon the bones. One important use of the skel-
eton and its joints is to give the body agility and facility
of motion.

The skeleton alone, however, has no power of motion.
The power to produce motion resides chiefly in the
muscles, which are attached to the bones. They are
called skeletal muscles. There are also other kinds of
muscle, such as those of the heart and arteries, which
will be described later.

The two ends of a skeletal muscle are attached to two
different bones, which have a movable joint between
them. When the muscle contracts, the positions of the
bones are changed in their relation to each other. In

Fig. 36. — Diagram showing how motion is produced by contraction of

muscle.

the diagram (Fig. 36) the muscle is attached at O and I.
The joint is at J. AVhen the muscle shortens, the lines
A J and B J will be drawn towards each other. If the
point O is immovable, all the motion will be made by
A J. Such is the plan of most skeletal muscles. It is
plain that if the two ends of the muscle were attached

MOTIOX

Gl

to the Siime bone its contractions wonld only tend to
stniin the bone and tear the mnscle.

Shape and attachment of muscles. — Skeletal
muscles consist of a soft. red. central part, which tapers
off at each end into cords of white fibrous tissue. The
coitls are called tendons, and they .serve as a convenient
means for the attachment of muscles to bones. Some
muscles, however, are attacheil directly, without the in-
tervciition of tendons.

Fig. oT. — Showing bones of the arm and biceps muscle.

In Fig. 37. O is called the origin of the muscle and
/the insertion. The origin is the end nearest the centre
of the body, and which usually moves the least. In the
Fig. is a representation of the muscle called the biceps.
It is the large muscle of the arm. to which men and l>oys
often point as an evidence of their muscular ability.

62

TITTPJ) P,O0K OF PHYSIOLOGY

It has its origin in the shoulder-blade at 0, and its in-
sertion at I. When it contracts, the forearm and hand
are raised.

Mechanical principles in the motions of the
skeleton.— The lever is the chief mechanical con-
trivance for i^roducing the motions of the body: Levers
are usually classed as three kinds, the difference depend-
ing on the point of attachment of the iceiffht. the powet',

W

©

^

w

©

w

@

■^

u

Fig. 38.— Levers of the first class.

and the fulcrum . Tlie fulcrum is alwaj'S the still place,
or the axis upon which the lever rotates. Fig. 38 shows
three levers of the first class. The bolts show the posi-
tions of the fulcrums. The hand shows the point where
the power is applied, and the weight or resistance to the
power is at the other end.

Mot I ox 03

Tn the topmost lrv<'r Mh' Iwo aims ai<' ('(iiuil, and so
there is no a(hantaj;:(^ except that wlien tlie liand i)uslie8
down the weight goes up.

In the second lever the weight end is niucli lonj^'cr
tlian tlie hand end, and so, wlien tlie hand moves down
and up, the weight will move u]) and down, but much
farther and faster. With this arrangement the hand can
move only a light weight, but it can move it rapidly.

Tn the third one the hand has the long arm of th«i
lever. The weight may now be heavy, but it can be
moved up and dow^n only slowly.

Not much use is made in the body of this first class of
levers. An example of it is found in the backward move-
ment of the head. Here the fulcrum is the point where
the skull articulates with the atlas. The front part of
the head is heavier than the part back of this fulcrum,
and so the head will fall forward of itself But a back-
ward motion is produced by the contraction of muscles
which are attached to the backbone below and to the
occipital bone above.

In the second class of levers the fulcrum is at one end
and the powder at the other, with the weight between
them. In this arrangement there is a gain in power, and
the closer the weight is to the fulcrum the heavier it may
be for the same power exerted by the hand, but the weight
will move through a smaller distance and less rapidly
than the hand does. A good example of this kind of
lever is found in the foot. It is used in rising on the toes.
Here the toes are the fulcrum, the power is applied at the
heel, and the weight of the body is between.

64

THIED BOOK OF PHYSIOLOGY

When the strong muscle of the calf contracts, it pulls
upon the tendons which are attached to the heel and the
body is raised.

W

©

Fig. 39. — Levers of the .«ecoiid cla.ss.

Every step we take in walking and running involves
the use of this muscle and lever.

W

Fig. 40.— Lever of the third claas.

Levers of the third class are most common in the body.
Here the power is applied between the fulcrum and the
weight. The power, in this kind of lever, must always

MOTION 65

bo j^rciitcr tliiiii {\w wci^lil, or rcsistiiiici', but tliero is ;i
^SLin in (hr vclointy with wliich tiic \v(^ii;lit is moved.
The; niovi'mcnt by wliicii Die liiiud is raised to Iheinouth
is accomplished by a ]vv(iv of this kind.

By reference to Fijj^. M it is seen that tlie fulcrum is the
elbow, the weij^ht is the foi-earm, the hand, and what-
ever the hand contains, and the power is applied to the
radius a little way below the elbow at the point of inser-
tion of the biceps.

Voluntary muscles. — Muscles are of two kinds,
the voluntary and the involuntary. The voluntary^ as the
word would indicate, are those which are under the con-
trol of the mind and can be operated at will.

When you nod in response to an inquiry, we know you
mean yes, because the muscles that produce that motion
are voluntary'. All the skeletal muscles are volun-
tary.

Each bundle of muscle, as we shall see later, is made
up of a great number of cells with the cell material about
them. Each cell is connected by a nerve-thread to the
nervous centre, — the brain. When we wish any voluntary
muscle to do work, a message is sent out along the nerve
from the brain to the muscle. The muscle is thus stimu-
lated to activity. Each cell of the muscle contains a
store of energy which it gets from the food we eat. When
the food material unites with the oxygen which we
breathe, the energy is changed to heat and work.

The energy is all in the cell, and the message from the
brain only excites the cell to activity. It is not like ring-

66

THIED BOOK OF PHYSIOLOGY

ing an electric bell by pressing a button, for in that case
all the energy passes over the wire to the bell.

The relation of a general to his army is a good illustra-
tion of the relation of the brain to the muscle. The
energy is in the army, but it may remain perfectly passive
until orders are received from the general. The order

Fig. 41. — Showing the shape of a muscle before and after contraction.

may set the whole army in motion. Only the stimulus
and not the energy came from the general.

Involuntary muscles. — Involuntary muscles are
those over which the mind has no direct control. They
are such muscles as are found in the walls of the gullet,
and which by contractions force the food down into the
stomach. The muscles in the coats of the stomach are of
this kind, and after a meal they contract on the food,
moving it about and mixing it with the digestive juices.
The intestines by a contraction of the muscles in their
walls move the food along without any voluntary atten-
tion on our part. The action of the heart is beyond the

MOMMON

67

control of the will. Its muscles are therefore involuntary.
The muscles which are concerned in the operation of
breathing may be called semi-voluntary, for they can, to
some extent, be controlled by the will, but breathing will
continue while we are asleep, or while we are completely
absorbed in other matters.

It must not be thought that these cells move purely of
their own accord. They, too, are stimulated by nerves
which come from nerve-centres,
as will be exj^lained under the
discussion of the nervous system.

Structure of voluntary
muscle. — The voluntary mus-
cles are put up in bundles called
fascicc. The fascice are bound
with connective tissue, and are
in turn made up of smaller bun-
dles called fasciculi, five of which
are shown in Fig. 42. The fas-
ciculi are composed of fibres,
which are the cells and cell mate-
rial of muscle.

The fibres are composed of a
soft substance enclosed in a sheath called the sarco-
lemma. The fibres are small, having an average diameter
of about ^U of an inch, while their length varies from i
to 1\ inches.

A bundle of muscle may be a foot or more long, so that
a fibre cannot always reach from end to end of the mus-

FiG. 42.— Portion of fas-
cia showing live fasciculi
and their component fibres.

68

THIRD BOOK OF PHYSIOLOGY

cle. In that case the end of one lies between two others
that follow, and to which they are cemented by means

of the sarcolemma.

At the ends of skeletal mus-
cles the fibres blend into the
tendons, or, if there be no ten-
dons, they connect to the bone.

When the fibre is examined
by a strong microscope, it is seen
to be marked across by very fine
alternating bands of dark and
light. A bundle of this kind of
fibres is called striped or striated
muscle.

Each fibre contains a nucleus,
and is connected by a nerve to
the brain so that it can be made
to contract at will.

Structure of involuntary
muscle. — The involuntary mus-
cles are made wp of spindle-
shaped fibres Avhich are about
43 0 of an inch iu length and
about 4oW inch in breadth. Each contains an elongated
nucleus.

This kind of muscle is used to surround cavities of the
bodj^, cliiefly the digestive tract and blood-vessels. As
they are not attached to bones, they have no origin or in-
sertion.

Pig. 43. — Showing- iiuis-
cles of the forearm and
their tendons.

MOTION

C9

The fibros are not striated ;is in voluntary muscles.
They slowly contract uiulcr proper stimulus, becoming
shorter, and thus cliauging the capacity <►(" tlu^ cavity
which thev surround.

Fir,. 44. — Striated muscular fibres.

The fibres of the heart partake of the structure of both
kinds of muscle. Its flattened fibres are laced together

Ftg. 45. — Fibres of iuvuluntury muscles.

and are without a sarcolemma, as is the case with invol-
untary muscles, but the fibres are striped as in voluntary
muscles, though not so distinctly.

The development of muscle.— Muscle is capable
of high development. Our bodies are made in such a

70 THIRD BOOK OF PHYSIOLOGY

way that when any organ or part of the body is called
upon for greater and greater service an effort is made to
meet the demand.

When a muscle has been unused for a long time, it
degenerates, until but little is left of it, except the con-
nective tissue.

After a broken arm or leg has been in the splints for
several weeks, the muscles become so weak that it requires
long and careful exercise to bring them back to their
former strength.

The brawny arm of the blacksmith, on the other hand,
shows the effect of vigorous daily exercise. Exercise is
a call for power which nature tries to furnish.

Food of rauscle. — Each muscular fibre or cell, as
we have alread}^ explained, is a little engine capable of
converting food into heat and motion. Just like other
engines, however, they cannot give out any energy until
they first receive it. Good air and good food are neces-
sary to the development of strong and healthy muscle.
Without these, exercise is worse than useless.

Development gradual.— Many young people try
to develop the muscle too rapidly. They sometimes
choose large dumb-bells for their gymnastic exercises and
expect to see great results in a few days or weeks. This
is a mistaken notion. The true development of either
body or mind comes gradually.

Those who are experienced in this matter give more
attention to the regularity and persistence in their practice

MOTION 71

than to tlie intensity ol' it. A strong man can profitably
use only a two-pound (hinib-bell, but lie must piactisi* a
certain len<;th of time every day and then rest.

When exercise is carried too far, the muscle becomes
exhausted and weakened.

Clothing during exercise.— In a later chapter we
shall see that one office of the skin is to throw otl" wavSte
matter which, if retained in the circulation, would be a
poison to the blood. During vigorous exercise the quan-
tity of waste thrown off is nuich greater than at other
times, and for this reason the clothing should be loose
and light. The same kind of clothing is also necessary
for the freedom of the nuiscles and to i^ermit the escape
of the excess of heat which is always developed by ex-
ercise.

Kinds of exercise. — There are a great many kinds
of good exercises. The kind, however, is not always so
important as the way it is done.

As a rule, it may be said that outdoor exercises are
good for bodily development because of the wholesome
air and sunshine.

Also those exercises which call into use many muscles
of the body are preferable.

Walking is good, inasmuch as it takes one into the
open, fresh air ; but if the Avalk is onl}- a stroll about
the streets it fails to call into use many parts of the
body. The best kind of a walk is one up and down
hills and over fields and fences. A dress parade is of
little value.

72

THIRD BOOK OF PHYSIOLOGY

Those who live near a body of water have at hand a
most beneficial kind of exercise in rowing, which should

call into full use the muscles of
tlie arms, legs, and back.

Lawn tennis is among the
best of outdoor exercises.

Base-ball and foot-ball under
a proper director are good kinds
of sport, not only for the exer-
cise in the game itself, but also
because success comes only to
those who take good care of
their general health at all times.

Physical culture.— In re-
cent times there is a demand
for physical culture apart from
any games. This can be se-
cured, under the guidance of a
competent director, in the gym-
nasia of the best schools and
colleges.

In any game there are some
parts of the body which receive
an undue amount of exercise,
and other parts which receive
none, or not enough for their proper development.

In physical training the development progresses in a
systematic and natural manner. The action of the heart,
lungs, and muscles are all strengthened. Those who are

Fig. 46. — Exercisers

MOTION 73

MCiik can tluis !)(' made (it locngaji^ti in streniioiis athletic
sport without haini to themselves. Thii general health is
improved by sucii culture, and the chances of disejuse and
sickness are much reduced.

One Diay obtain such culture at home by use of dumb-
bells, Indian clubs, and exercisers such as shown in
Fig. 4(>.

iMore important than the apparatus, however, is the
will-power needed to persist in taking the regular daily
exercise.

It is best always to first consult one who is competent
to instruct in this art, that the many errors which the un-
aided novice is sure to make may be avoided.

Whatever the nature of the exercise is, the conditions
that should prevail are : good air, many muscles in use,
moderation, rest, persistency in effort, and regularity in
time.

Skilful muscles. — The development of a strong and
healthy body is desirable for several reasons. Such a
condition has associated with it a good appetite for food
and ability to assimilate it ; a vigorous circulation of
blood ; and deep breathing. Such a condition of body
furnishes a good foundation for a vigorous and sustained
action of mind. "A sound mind in a sound body" is a
true maxim. It is not necessary for this purpose that the
muscles be highly developed, ^but that they should receive
sufficient exercise to keep them in a healthy and vigorous
condition.

A large and strong muscle, however, is, to most people.

74 THIRD BOOK OF PHYSIOLOGY

of no advantage in itself. Such a muscle may strike a
heavy blow or lift a great weight, but such things can be
done by the brutes, which have still stronger muscles.
Man's object must be to acquire skill in the use of his
muscle.

A strong muscle that is trained to move the arms,
hands, legs, and body in a skilful manner is worth all
the time and effort which such training requires.

Effect of alcohol on the muscles. — At one time
it was thought that alcohol would add strength to the
muscles. Its true nature and effect upon the body were
not then known. In these later years a close study
of the subject has been made by able scientists and
physicians who were interested only in finding out the
truth. The evidence in all cases is that the use of
alcoholic drinks will lessen the ability of the muscles for
sustained work, and the man who relies upon the use of
his muscles for a living, cuts down the soui'ce of his
strength by the use of alcohol.

Of course, other evil effects follow the use of alcohol,
but onlv the effect on muscle is beins^ considered here.

Experiments with the ergograph. — The ergo-
graph is an instrument by which it is possible to tell
quite exactly any change in the ability of muscles to do
work. Experiments with this instrument have shown
that with doses as small as one and one-half teaspoonful
of alcohol there was at fi.rst, for a short time, an increase
in work. But soon there was a rai^id drop m the scale.

MOTION 75

so that llic total work done was less than without jilco-
hol. Many experiments of this kind indicate that alco-
hol has a depressinjr effect ujmmi the nmscles.

Experiments with armies. — Tt was once custom-
ary to deal out to soldiers rations of strong drink, such
as whiskey, rum, and brandy. This was done because it
was believed that the soldier could then endure a longer
march and greater fatigue and hardshii). Trial has been
made with soldiers in the armies of the United States,
England, Germany, and other nations, with the use of
alcohol and without it.

The results clearly showed that the soldiers without
alcohol were in much better physical condition at the
end of a hard contest or long march. Those who had
taken alcohol would start out more briskly, but would
sooner fall by the way.

Alcohol and the railroads.— All good railroads
seek to do business on an economical and efficient
basis. To do this they must have efficient men. They
have found that alcohol, even in moderate quantities,
will sooner or later lessen a man's efficiency for service.
The officials of a good railroad will not accept the ser-
vices of a man who is known to drink any kind of alco-
holic liquors. Some will not even permit their em-
ployees to lodge or board at a hotel which has a bar
attached. Similar precautions are taken by all large
business firms.

This is not so much because these corporations are

7G THTHD BOOK OF PHYSIOLOGY

interested in the temperance problem, but they want
those men who can l3est do their work. They know from
experience that a good man will l>e better if he is a total
abstainer from alcoholic liquors.

Athletics and alcohol. — Those who train for ath-
letic contests, where they will need all the strength and
power of endurance they can muster, are required to
totally abstain from the use of tobacco and alcohol. Ex-
perience has shown the trainers that these two poisons
are destructive, and tend to tear down and not to
build up.

Even those who follow the ignoble calling of prize
fighting are compelled to be total abstainers, at least
during their period of training.

A young man who belongs to the boat-crew or foot-
ball team of one of the great colleges could not more
efFectivel}' disgrace himself in the eyes of his fellow-
students than by using alcohol or tobacco on the eve
of an important contest.

Effect of alcohol on skill. — Most people are not
directly concerned in athletic sports, but the same prin-
ciple that makes it advisable to refrain from alcohol in
that case will more forcibly apply in the serious contests
of life. The degree of skill needed to make one a suc-
cess in any art is acquired only by long practice under
favorable physical conditions. Alcohol so affects the
nerves and muscles that the nerve is not able to deliver
a clear-cut order to the muscular cell, or the cell is not

MOTION 77

a])l(' to execute the order. The result is an uiistrady
aud clunisy motion.

It is claiiiM'd on <^ood authority that the present com-
mercial supnunacy of the United States is in good part
due to the fact that there is less drinking among our
workmen than among those of European countries.
The result must be the acquisition and retention of an
artistic skill which results in a better and larger output
of goods. The Labor Bureau of the United States shows
iu its report that a large per cent, of the employers of
skilled and unskilled labor require total abstinence on
the part of their employees. They are not even willing
that their men should drink after their day's work is
done, for both experience and exact experimentation
have shown that alcoholic drinks taken at night impair
working ability the following day.

QUESTIONS FOR REVIEW.

1. What is our common test of life?

2. Describe some movements in the body which we do not
ordinarily observe.

3. How are nuiscles attached in reference to joints? Why?

4. What is meant by origin and insertion of muscle ? Illustrate
by reference to the biceps.

5. Show the advantages and disadvantages of levers of the first
class. Where in the body is this lever used?

6. What is the position of fulcrum, power, and xceight in levers
of the second class? Give example of its use in the body.

7. When is a lever of the third class ? Give example of its use
in the body.

8. Which kind of lever is most used in the body? What is tlie
effect on bodilv motions ?

78 THIED BOOK OF PHYSIOLOGY

9. What are voluntary muscles ? AVhere are they located ?

10. How are muscles stimulated to activity?

11. Is the energy in the nerves or in the muscles? Illustrate by
the relation of a general to his army.

12. AVhere are the involuntary muscles ? Why so called?

13. Explain the structure of voluntary muscles.

14. Explain the structure of involuntary muscles.

15. What is peculiar about the structure of heart muscle?

16. How can muscle be developed ?

17. Why do working muscles need food?

18. Why cannot muscle be developed rapidly?

19. What kind of clothing is best during exercise? Why?

20. Name some good exercises. Give reasons.

21. How does physical culture differ from exercise in games ?

22. AVhy is skill desirable ?

23. What is the effect of alcohol on muscle ?

24. What is shown by the ergograph ?

25. What has been the experience with armies?

26. What is the action of railroad officials in regard to alcohol?
Why?

27. Wh}' do those who train for athletic contests not drink
alcohol ?

28. What is the effect of alcohol on skill?

CHAPTER VII

FOODS

The use of food. — Our l)Oflies need food for two
purposes, first, to build up and maintain the tissues of
the body, and, second, to furnish the energj^ needed for
the ivork we have to perform and the heat which must be
maintained in the body.

Nature has given to all animals the sensations of
hnnger and thirst, and an appetite for those things
which the tissues need. A perfectly healthy appetite
should be a' safe guide in choosing food. Most appetites,
however, are not reliable, and for this reason, among
others, food is a proper subject for intelligent study both
as to its nature and its use in the body.

Constant loss of material from the body. —
There is constantly being thrown off from the body in
various ways a quantity of matter which would be in-
jurious if retained in the body, or which is no longer of
any use. Every breath from the lungs carries out con-
siderable water and carbon dioxide : by perspiration the
skin is constantly giving off water and waste ; a large
amount of water and urea is excreted by the kidneys ;
the undigestible parts of food as well as the undigestible
matter which is eaten with food are daily thrown off'
from the body ; and the surface epithelium is constantly

79

80 THIRD BOOK OF PHYSIOLOGY

wearing away and falling off. From all such causes the
body loses on an average about nine ijounds each day.

It is plain that at this rate the l)ody would soon waste
away unless food be supplied at the same rate.

The nine pounds a day is for the average healthy body
at work at its full capacity. When food is not sufiQcient
to supply the loss, the waste will be less, but the body
will be less efficient in the same proportion.

Loss of energy. — The old idea of food was that it
was only for the purpose of supplying the tissues with
material for their growth and repair, and to lubricate
the moving parts. The real nature of food was not un-
derstood. We now know that the chief function of food
is to supxjly energy. Every motion and action of the
body, even thinking itself, is a use of energy which was
in the food. When the body does any work it must
lose a certain amount of energy, and is to that extent less
able to do other work.

When the body does very little work, not so much
food need be eaten, for the energy from the food last
taken has not yet been expended. When much work -is
done the energy is soon exhausted, and we are made
aware of the fact by the sensation of hunger.

Two kinds of energy. — There are two kinds of
energy, called the potential and the l-lnetic. The water
in a dam has potential energy because it would flow
down the valley if the dam were removed. A weight
on a shelf has potential energy because it will fall if the

FOODS 81

shelf is removed. Coal has a p<>teiitial enerj]:y bc^caiise it
h;us a strong allinity for uxyg<Mi and w ill unite with it,
producing the intense heat of combustion. Material
bodies in general possess potential energy by virtue of
their position ur chemical character. Food contains
potential energy because in the body it combines with
oxygen and is changed to other substances.

The result of all such changes is the energy of motion
which is called kinetic energy.

The main purpose of food is that we may take into
our bodies potential energy, which may there be con-
verted into kinetic or moving energy by means of which
we move, work, think, and keep warm.

There is a large amount of energy in the world, and the
amount never grows any larger or smaller as a result of
any changes which we can bring about.

Our chief concern must be to keep the body in such
a state of health that the necessary amount of energy
may be appropriated by it and made to do useful work.

Comparison with steam-engine. — The relation
of coal to the steam-engine may serve in part as an illus-
tration of how food is converted into ability to do work.
The fuel — coal, wood, or gas — is made to unite with
oxygen under the boiler. An intense heat is generated,
which is carried by the steam to the engines, and there
converted into the motions of the machines of the mills
and factories.

After the fire is once started, the boilers and engine,

if kept in repair, will continue to do the work to which

6

82 THIED BOOK OF PHYSIOLOGY

they are adapted as long as they receive their proper food,
which is coal or some form of carbon.

AVhen the fireman cuts off the supply of fuel, the en-
gine runs slower and slower, and finally becomes still and
cold.

While the engine is running, its whole operation con-
sists in getting energy from the fuel and passing it on in
some form to other objects upon which it does work.

The coal is the source of the energy of the engine in
about the same way that food is the source of the energy
of the human body. The method by which the change is
brought about, however, is different in many particulars.

Oxidation in the human body.— The one im
portant particular in which the coal of the engine and
the food of the body are exactly alike is the strong af&nity
of both for oxygen. Their potential energy consists in
the fact that they can be oxidized, that is, thej" will com-
bine with oxygen, or burn. By this process the energy
is made available.

In the case of the engine the fuel is all oxidized rapidly
and with intense heat at one place, that is, in the fire-box.
In the body oxidation takes place slowly and in all parts
of the body. Food is carried in the stream of blood to
all the cells and there, for the most part, it is burned, and
its potential energy becomes kinetic or moving energy.
The most of the oxidation occurs in those cells which are
most concerned in the performance of work, as in the
muscles.

Oxidation within the body does not result in a high

FOODS 83

temperature like that from hmiiiiig wood or (M»al. In
fact, it is quite certain thai much of the energy of food is
converted into the energy of motion without any heating.
Some of it is converted into lieat energy, and thus the
temperature at which the body can best live is main-
tained.

The difference in the rapidity of oxidation, such as
occurs in a stove, and that within the body, may be ill us-
trated by use of a magnesium ribbon. When a piece is
lighted in the open air it will rapidly oxidize, that is,
burn. A piece of the same material placed in a bottle
and moistened with a few drops of water will also com-
pletely oxidize, but will require several days to do so.
The total amount of heat produced is the same in both
cases if the same amount of material is used.

Composition of the body. — The tissues of the
body are found to be composed mainly of four elements,
— carbon, hydrogen, oxygen, and nitrogen. In addition to
these a number of other elements are also found, thousrh
in less quantity. They are sulphur, phosphorus, chlorine,
sodium, potassium, calcium, magnesium, and iron.

The three main compounds in the body.—

The elements named above do not exist separately in the
tissues, but are united in a variety of ways forming com-
pounds. The most important compound is proieid. It
is found only in live matter of animals and plants, and
is composed of carbon, oxygen, nitrogen, hydrogen, and
sulphur. A good examj)le of a proteid is the white of

84 THIRD BOOK OF PHYSIOLOGY

an egg. It is imi)ortaut to notice that proteid contains
nitrogen.

The second class of imi^ortant compounds in the body
are the carbohydrates. These are composed of carbo7i,
hydrogen^ and oxygen, but no nitrogen. One important
carbohydrate is glycogen, which is found in large quanti-
ties in the liver. Others are grape sugar, muscle sugar,
and milk sugar. These are all closely related to starch,
from which they can be made.

The third important comx:>ound is fat. This substance,
like the carbohydrates, is composed only of carbon,
hydrogen, and oxygen, but in different proportion. The
quantity of fat in the body varies greatly in different in-
dividuals and in the same individual at different times,
but the average quantity in a man is about six pounds.

Other substances in the body. — The three classes
of substances just named are the important organic com-
pounds of the body. There are also several other sub-
stances which are not important in themselves, but which
are indispensable because of the assistance they give in
the processes of life.

Water constitutes about two-thirds of the weight of
the body. If a man weighs one hundred and fifty pounds,
one hundred i^ounds are water. Every tissue of the body
contains some water. Even the enamel of the teeth, the
hardest substance in the body, is 2 per cent, water.
Muscle is three- fourths water. Bone is about 22 per
cent, water, and saliva is almost -pure water.

Salt is found in all tissues of the body.

FOODS 8.1

Phosphate and carbonate of lime are tlie chief constitu-
ents of the bones and the teeth.

A number of either compounds are also found in the
body.

What is a food. — Foods should l>e such sul:)stances
as will sup])ly the material of which we find the body is
composed. A sutetance is not a foo<l simply Ijecause it
contains elements which* are found in the bo<ly. but it
must be of such a character that it can be digested and
made a part of the body. A food is anything ichich, when
taken into the blood, will supply the needs of the body without
doing it harm.

Food of the body a complex compound. — Car-
bon is an important element in food, but carbon alone is
not a food. Charcoal is almost pure carbon, but it can-
not be digested or in any way l^ecome a part of the body.
Neither can the body make any use of hydrogen or nitro-
gen as foods. Oxygen is the only element which, when
uncombineil with other elements, may be considered
a food.

The chemist writes CeHioOe as the symbol for grape
sugar. When the carbon, hydrogen, and oxygen are
united in this kind of a complex compound, the body
can use them as food. In the body the sugar unites with
the oxygen which we breathe, and the result is a breaking
down of the sugar compound into the simpler substances,
water and carbon dioxide. In this way the energy which
was in the sugar is set free for work or heat

86 THIRD BOOK OF PPIYSIOLOGY

The compounds of fats and proteids are still more
complex than that of sugar, but they, too, unite with
oxygen, and are broken up into simpler compounds with
the like result of a liberation of energy.

Three classes of foods. — Froteid is an essential
food. It alone contains the nitrogen of food, and is the
chief source of supply of that element to the body.
Proteid is built up by vegetables. From this source
animals obtain it. Lean meat is rich in proteid. Since
man's food consists of both meat and vegetables, he gets
proteid from both sources.

The chief sources of i^roteid are meat, milk, eggs, and
vegetables, — principall}^ wheat.

The carbohydrates of food are chiefly obtained direct
from the starch and sugar which are stored up in vege-
tables. The chief sources are wheat, rice, and other
cereals, potatoes, fruit, cane sugar and grape sugar.

The/«/s of food are obtained from a variety of sources,
such as fat meats, butter, cream, and oils.

Wheat as a food. — Bread is often called ''the staff
of life.'* An examination of a grain of wheat shows
that it is rich in the foods just described. It contains
about 14 per cent, of i^roteids, 57 per cent, of starch, 5
per cent, of grape sugar, 2 per cent, of fats, and many
other substances in small quantity.

The proteid of wheat is mainly the gluten. It is this
which makes the dough sticky and tenacious.

When yeast is added to the mass of dough it begins to

FOODS 87

ferment iind ronii alcohol and carbon dioxide. In this
way bubbles of yas ar(^ formed in every part of the
douj^h and are held in by the tenacious gluten. The
formation of the gas causes the bread to '^ rise." In the
hot oven the bread rises rapidly because the heat causes
a rapid expansion of the ga«. When it is baked the gas
can escape, but the bread retains the light and porous
character given to it by the bubbles of gas.

Wheat contains more gluten than any other cereal, and
consequently its flour can be most easily made into light
bread.

Corn. — Corn contains only a little more than half as
much of the proteids as compared with wheat, but a
greater per cent, of starch, and it is the richest of all
cereals in fats. Corn holds a place along with wheat as
one of the valuable vegetable foods.

Some other vegetables. — Peas and beans are about
half starch, but they are rich in proteids, containing about
25 per cent.

Eice is about four-fifths starch, but is poor in proteids.
Rice alone is a poor diet.

Potatoes are poor in both proteids and starch.

Many fresh vegetables are valuable articles of diet,
though they are mainly composed of water and salts.
That the body needs them is shown by the fact that a dis-
ease called scurvy will break out among those who are
compelled to eat only meats. Such has often been the
case with sailors on a long voyage, or men in other situa-
tions where they cannot get fresh vegetables.

88 THIED BOOK OF PHYSIOLOGY

Animal food.— A very common food is the flesh of
animals. This consists of muscles, fat, and the various
other tissues mingled with them. Flesh is rich in proteid
of various kinds, the chief one being myosin. Gelatin is
derived from the white fibrous tissue. Several mineral
foods are also obtained from meats.

Good meat that is well cooked is a valuable food for
adults, particularly^ for those engaged in heavy work or
severe exercise.

Eggs are rich in proteid, both the "white" and the
"yellow." All the food material necessary for starting
the chick are in the egg.

Milk is nature's food-mixture, and is a comj)lete food
for infants. For adults it is not a complete food, as it
does not contain the various kinds of food in the proper
proportion. From milk we get cream and butter, which
are the fats ; milk sugar, which is a carbohydrate 5 and
casein, or cheese, which is the proteid.

The need of a mixed food. — Some foods contain
all the different kinds needed by the body, but not in the
right proportion. Xo one food makes a complete diet,
except milk for infants. It is estimated that a man doing
a moderate amount of work will use up about 4000 grains
of carbon and 300 grains of nitrogen each day. He will
then need food which contains this amount of these ele-
ments. If he takes more carbon or nitrogen than the
body needs, the excess will not only do the body no good,
but will add to the labor of the various organs to get rid
of it.

FOODS 89

For exanii^lc, meat alone in sufTioiont quantity to yield
the necessary amount of carbon would also yield three
times the amount of nitroj^cn needed. When uieat is
eaten with bread and other ve*^etables the proper propor-
tion of the food elements may l>e supplied without the
excess of any one.

Amount of food. — ^lost food is eaten for the en-
ergy it contains, and the' work which it enables a man to
do. It is evident, then, that a man needs more food when
he is hard at work than when he is at rest or engaged
only in mild forms of exercise.

As to how much food the body needs, it is not yet pos-
sible to give a definite answer. The authointies do not
agree on this matter. It is quite certain, however, that
most people err in eating too much rather than too little.
According to a standard which has been largely followed,
it is assumed that a man doing moderate work would
need 118 grams of proteid, 56 grams of fat, and 500 grams
of carbohydrates per day.

The total fuel value of this amount of food is 3055 large
calories.'-'

Recent exxjeriments would indicate that an amount of
food whose fuel value is only 1600 large calories is, when
properly digested and assimilated, better both for health
and ability to do strenuous work.

If excess of food were only so much matter to be re-

* A large calorie is the amount of lieat needed to raise the tem-
perature of one kilogram of water one degree centigrade.

90 THIED BOOK OF PHYSIOLOGY

fused and cast off by tlie body, it would not be a matter
of particular concern. But the organs of digestion and
excretion make an effort to handle all of it. They are
overtaxed, and none of their work is done well. Such
ill-13repared food may even be a poison to the tissues and
work great evil to the health of the body.

The cooking of foods. — Cooking is practised bv all
civilized peox^le. and is indispensable in the preparation
of certain kinds of food. The carbohydrates, which are
mainlv starch, form tlie laro'er bulk of foods. AVhen the

Fig. 47. — Triehinfe in pork.

Starch is cooked, it is much more readily soluble in the
juices employed in its digestion.

Meats are not only more palatable when properly jjre-
pai'cd in the kitchen, but the tissues are softened, and
can be more finely divided by mastication, and more
readily dissolved by the gastric juice in the stomach.

Another good reason for cooking some foods is that any
minute living organisms which might be present may be
destroyed by the intense heat. This is particularly true
of i^ork. lu Fig. 47 is a specimen of diseased pork, as it
appears under the microscope, showing trichinae coiled
up in the tissue. These, if eaten, may lodge in the tissues
of the body. Thorough cooking will kill them.

FOODS 01

Rules and methods of cooking cannot be given in a
book of this character. Many books are written and
schools established for instruction in this useful art. A
general knowledge of the best ways to prepare food would
be of the jrreatest vahie to tho human nice.

Is alcohol a food ? — Any substance which at first
seems to supply the body's needs, but which in time
works a serious injuiy, is not a food.

The sj'mbol which the chemist uses for alcohol is
CJIgO. Since carbon, hydrogen, and oxygen are essen-
tial parts of the tissues of the body and of our foods, it
might at first appear that alcohol would be a desirable
food.

^Mleu we consider a number of other compounds, how-
ev^er, which also contain elements found in the body, but
which we know to be poisonous, we see that our inference
in regard to alcohol is not correct. Hydrocyanic acid,
for example, is a deadly poison. A very small quantity
of it will kill almost instantly, and yet it is made up of
hydrogen, carlxm. and nitrogen, its symbol being HCX.

Again, we know that alcohol will oxidize. — that is. it
will burn and yield heat and energy.

Alcohol will also oxidize in the human body and yield
a certain amount of heat and energy. Since this is one
of the most important functions of food, it would appear
that alcohol would be a food.

A true food, however, will yield heat and energy with-
out doing any harm to the organs and tissues of the bodj*.
Alcohol, while it yields heat and energy, acts at the same

92 THIED BOOK OF PHYSIOLOGY

time as a poison. For this reason alcohol cannot be
classified as a food.

This may be illustrated in this way : It is vrell known
that when sulphuric acid and water are mixed together
in about equal parts, the mixture will become very hot.
This acid will also corrode and "eat up" iron. Suppose
now that an engineer sliould adopt the plan of mixing
sulphuric acid witli the water in the boiler when he
wanted to "get ui>" steam. The water would be rapidly
heated, and, to an ignorant person, this would seem to
be a good plan. It would soon be found, however, that
the material of the engine was being rapidh^ destroyed
by the acid, and either this method of getting energy
would have to be discontinued or the boiler would soon
need to go to the shop for repairs or be abandoned alto-
gether.

QUESTIONS FOR REVIP:W.

1. State the two chief purposes of food.

2. "What are some of the ways by which the body loses in weight?

3. AVhat was an old idea about the purpose of food ?

4. AVhy does a man get hungr}- sooner when he works tlian
when he is idle ?

5. What are the two kinds of energy?

6. Explain what is meant by potential energy.

7. How does a steam-engine get its energy ?

8. AVhat difference in the use of food in a steam-engine and in
man ?

9. How does the body get energy from food?

10. Where did the food get its energy ?

11. What difference in the kind of oxidation in an engine and
in a human body?

F()OJ)S ^''*

12. Name the four elements of which the body is largely com-
p<^tHl. Name i?everal others.

l.S. What are the three chief comiMumd.s of the binly ? What is
their composition?

14. How much of the body is water?

15. Define a foinl.

10. Why must the food of the body be complex compounds?

17. What element of food is found only in ])roteid?

18. How are proteids formed?

19. What kinds of foods ftirnish us with proteids?

20. What kind of foods furnish carbohydrates?

21. What is the source of fats?

22. What makes wheat a good food?

23. Explain the rising of bread.

24. How does corn differ from wheat as a foo<l ?

25. What shows that the body needs fresh vegetable food?
2G. Name and tell the value of several animal foocLs.

27. Why is a mixed diet necessary?

28. How much should one eat?

29. What evil results follow from excessive eating?

30. What is the use of cooking?

31. How can proper methods of cooking be learned?

32. What are trichime?

33. Is alcohol a food? What makes it seem to be a food? Why
is it not a food ?

34. What will a good food do for a body?

35. How does alcohol differ from a food ?

36. Illustrate by the action of sulphuric acid on the boiler of an
engine.

EXPERIMENTS.

Test for proteid.— The white of an egg is nearly pure proteid. Stir the
white of an egg into about one-half pint of water, and tilter. Put some of the
solution into a test-tube or bottle and add to it some nitric acid. Note the change
to a yellow color. Add ammonia and the color will change to an orange.

94 THIED BOOK OF PHYSIOLOGY

This test for proteid can be applied to meats, wheat, corn, and other sub-
stances.

Test for carbohydrates.— Prepare some starch paste by boiling a little
corn-.starch in water. Add a little of the starch to a test-tube full of water and
shake well. Add to this a drop of the tincture of iodine and the liquid will turn
blue. This is a test for starch, and may be applied to i:)otato, flour, and other
substances containing starch.

Slow and rapid oxidation.— The experiment alluded to in the text of
burning magnesium ribbon is performed by holding a piece of the ribbon, one
or two inches in length, with pliers, and lighting it with a match. The light is
brilliant, but the combustion is quiet and safe. The slow combustion is similar
to what is called rust in case of iron, and may require a week or two.

Heat from a mixture of sulphuric acid and water.— Fill a test-
tube or small bottle half full of water and j:)Our into it slowly about the same
amount of strong sulphuric acid. The bottle will become so hot that it cannot
be held in the hand. This acid must be handled with care. To carry out the
illustration suggested in the last paragraph of this chapter, add some carpet-
tacks or small pieces of iron to the mixture and note the rapid corrosion of the
iron.

CHAPTER VTTI

DIGESTION

What digestion is. -Digestion of food is a process
by which food is so chang^ed that it can be taken into the
blood-vessels of the bodj^ For
example, we eat a great deal of
starch, bnt, although it may be in
the stomach or intestines, it will be
of no benefit to the body as long
as it is starch.

The starch must be changed to
sugar by certain juices that are
poured out upon it in the intes-
tines, and the sugar is then easily
dissolved and can be passed through
the cells in the wall of the intes- b

tines and into the blood-vessels
close by. Such a change in the
character of food is called diges-
tion.

Why digestion is neces

sary.-Food must not only be in j,^^ 48.-Apparatus to
solution, as just explained, but the show osmosis of liquids,
solution must be of a certain kind.

Most of it gets through the walls of the intestines by a
process called osmosis. In Fig. 48 is shown a simple
apparatus to illustrate this principle.

95

96 THIRD BOOK OF PHYSIOLOGY

A is a vessel partly filled with water. B is a thistle
tube, over the bottom of which is tied a jjiece of any
animal membrane, such as bladder or the cjising taken
from bologna. B is then partly filled with, say, a strong
solution of salt and suspended in the water. After a
time the liquid in B will rise in lieight and the water in
A will become slightly salt. This shows that there is a
movement of the liquids through the membrane in both
directions, but more rapidly into B. In the apparatus
shown, copper sulphate was used in the tube, and the
liquid raised from the point .c to I and flowed over the
top.

Any solutions that will diffuse into each other will pass
through such a partition, when placed between them,
even more readily than without it.

While the food is in the intestine, a thin sejjta of this
kind is between it and the blood. The food passes through
bj" osmosis.

After the food is carried by the blood-vessels to the
various i)arts of the body, it passes out to the cells by a
similar process. Digestion must change foods to a solu-
tion which is capable of this kind of diffusion.

The fats are not digested in this manner, but they get
into the blood by being passed in fine droplets through
the body of the cells that line the intestines, — a process
not yet understood.

The alimentary tract. — The alimentary or digest-
ive tract may be considered a long tube through which
the food is made to pass. As the food is pushed along, it is

DICKS'HON 97

acted upon by tlie various dij^estive lliiids, wliicli change
it to a condition suitable for intro(hiction into the body.
While tlie food is in the tube it is still on the outside of
the body i)ro])er, for the tube is only an op(uiing through
the body. Food is not in the Inxly until it is taken up
by the blood.

Tlie entire tract is lined with nuicous membrane.

The parts of the alimentary tract are the mouth, fauces^
phanjnx\ oesophagus, sfonlach, small intestines, and large
intestines.

The mouth. — The mouth may be considered the
gateway to the digestive tract. It is here that we can
exercise our will as to the kind and character of the food
which we will take.

After food is swallowed, digestion is carried on without
any attention on our part. In the mouth occur the first
two acts of digestion. These are mastication and insali-
vation.

Mastication. The teeth. — The part of the mouth
concerned in the first step in digestion is the teeth. The
front teeth bite off morsels of food and the back teeth
grind the food into fine bits.

Since the proper food for infants is milk, teeth do not

appear until about the age of six months. At that age

a temporary set of teeth begin to cut through the gums

one after another, until at about two years of age there

are ten teeth in each jaw.

These do not last long, for soon a permanent set starts

7

98

THIRD BOOK OF PHYSIOLOGY

beneath tbeni, and at the age of five or six years l>egin to
push out the first set and to take their phices. At the
age of twelve or thirteen years all the permanent teeth
have appeared except the back ones, which are called
wisdom teeth, and which do not come till the age of
twenty or twenty -five yeais.

Fig. 49. — -Permanent teeth of the right side. (Gray.) 1, 2, and 3,
molars ; 4 and o, bicuspids ; 6, canine ; 7 and 8, incisors.

The full set numbers sixteen in each jaw, making thirty-
two in all. In each jaw the four front teeth are called
incisors ; the next two, one on each side, are the canines ;
the next two on each side are hicuspids ; the last three on
each side are the molars.

Composition of teeth. — Teeth are made of a hard
material similar to bone. They are composed of a
crown, which is that part extending beyond the gums ;

DIGESTION

99

the neck, which is surrouiKh'd by the <^uins ; and the yoot,
which is einbe(hhMl in Ww, hour of tlic jaw iind liniily
fixed with cement.

A cross- sec Mo 11 of a tooth shows that it is composed of
three parts. In the centre is the i)iilp-cavity, wliicli is
filled with a nct-woi'k of blood-vessels and nerves.

Fig. 50. — Longi-
tudinal section of
tooth. E, enamel ;
D, dentine; P, pulp.

Fig. 51. — Cross-section of tooth,
masrnified, sliowinsr enamel.

Surrounding the pulj) is the dentine, which is very
hard, and yet is alive and composed of fibres radiating
from the pulp and receiving nourishment from the blood
that circulates through the pulp-cavity.

Enamel covers the crown of the tooth and is thickest
on the grinding surface. It is the hardest substance in
the body, and can withstand a great deal of grinding
without wearing away. Fig. 51 shows a very thin sec-
tion of tooth as it appeared under the microscope.

100 THIRD BOOK OF PHYSIOLOGY

Salivary glands. — The process of griDding the food
between the teeth is called mastication. While food is
being masticated, a fluid called saliva is poured out into
the mouth through ducts from the salivary glands.

There are three sets of these glands. They are the
parotid, submaxillary, and subungual, — two of each kind.

The parotid glands are situated just
below and in front of the ears, and
the ducts from them open into the
mouth on the inner surface of the
cheek, near the second molar tooth
of the upper jaw. The submaxillary
\J^ ^ and sublingual glands are situated

Fig. 52.— Racemose beneath the tongue, and empty into
^ ■ the mouth just under the tongue.

These are called racemose glands, because they consist
of sacks all connected together and giving the whole
the appearance of a bunch of grapes, as shown in
Fig. 52.

The purpose and nature of saliva. — The office
of saliva is, first, to keep the mouth moist at all times ;
second, to moisten the food so that it may be more thor-
oughly masticated and afterwards swallowed ; third, to
dissolve some of the foods that are already soluble ; and,
fourth, to begin the change of starch to sugar.

Saliva is almost pure water, but it contains a ferment
called ptyaliHj which causes the change of starch to
sugar.

Ptyalin is not a living organism, like a yeast ferment.

DIGESTION 101

It can chan<i:e an indefinite quantity of starch to sugar
without itself wasting away, and so only a small quan-
tity is needed.

The "ropy" cliaracter of the saliva in the mouth is
due to the secretions of the mucous membrane which
lines the mouth.

The fauces. — After the food has been masticated
and mixed with saliva, it is pushed by the tongue
through the fauces, — an opening in the back part of the
mouth. The fauces is surrounded by the soft palate and
umda above, the base of the tongue below, and pillars of
muscles and the tonsils at the sides.

The uvula is at the centre above and hangs lower than
the soft palate.

The tonsils are small glands that secrete mucus.

The pharynx. — After i)assing the fauces the food
reaches the pharynx. The pharynx is a centre for a
number of passages which radiate from it. It is some-
what conical in shape, with the small end downward.

From it are seven openings : one into the larynx,
leading to the lungs ; one into the gullet, leading to the
stomach ; one into the mouth : two into the nostrils ;
two into the Eustachian tubes, communicating with the
drums of the ears.

At the top of the windpipe is a plate of cartilage
called the epiglottis. This is raised during breathing,
but shuts down like a lid when food is being swallowed.

102 THIRD BOOK OF PHYSIOLOGY

The epiglottis can be seen if the mouth be widely
opened and the tongue pressed down.

The oesophagus. Deglutition.— The oesophagus
is a tube leading from the pharynx down through the
chest to the stomach. It lies near the spinal column, and
at its lower end it pierces the diaphragm and enters the
stomach just beneath. It is composed of two layers of
muscle, the fibres of one running lengthwise, and of the
other around the tube. It is lined with mucous mem-
brane.

After food has once entered the oesophagus it is forced
down by an involuntary contraction of the muscles just
above it. It is not possible to perform the act of swal-
lowing unless there is something to swallow, as may be
shown by swallowing three or four times in quick suc-
cession, until all saliva is removed from the mouth.

The act of swallowing is called deglutition.

The stomach. — The stomach may be considered a
place where the alimentary tract is expanded into a
pouch. Here the food is, for a time, arrested in its
progress along the tract.

The stomach is situated on the left side of the body,
just beneath the heart. When fairly well filled it is
about ten inches long and five inches through its widest
part. It has two openings. One is called the cardiac
orifice, where the food enters, Fig. 53, c. The other is
called the xyyloruH, ]). A ring of muscle about the pylorus
keeps it closed except when food is ready to pass through

hlCKS'PIoN

103

it. Tlio stoiuacli lias foiir <'();its, ('all('(l Uk^ srrons (see
page 20), the musculcir, tlic (trcolar (see page 2()), and the
viucoun. The bust naiiKMl is the coat next to the; contents
of th(; slomacli.

Fig. 53. — Stomach and intestines.

The mnscular coat is composed of three layers. In
the outside one the fibres run lengthwise, in the next
they pass around the stomach, in the third the fibres
radiate obliquely from the cardiac orifice, but do not
form a complete layer.

The peritoneum (see page 30) suspends the stomach as

104 THIED BOOK OF PHYSIOLOGY

in a sling, and between its folds blood-vessels run to the
stoniacli.

The mucous coat. — ^The mucous coat is the most
important of the four coats of the stomach. When ex-
amined with a microscope of only moderate power it is
seen to have a honeycomb appearance, caused bj' the

Fig. 54. — Mucous coat of stomach, epithelial layer removed, showing
the openings of the gastric glands.

minute shallow pits that cover its surface. In each pit
is the mouth of a gastric gland. These glands are minute
tubes, packed in between the columnar epithelium cells.
(See page 24.) They secrete the gastric juice which
effects the stomach digestion.

Digestion in the stomach.— While the food is
being masticated the gastric juice is being secreted and
poured out into the stomach, ready for the food when it
arrives. Secretion of gastric juice continues during di-

DKJESTIOX 105

gestion. The saliva is an alkaline substance, but gjistiic
juice is str()ni::ly acid in its reaction, so that the conver-
sion of starch to sujjjar by the saliva ceases while the
food is in the stomach.

Gastric juice is composed of pepsin, rennin, coaler, and
about .2 per cent, of hydrochloric acid.

The pepsin converts the proteids mto peptones, and in
that condition they can pass by osmosis through the
membranes that line th^ alimentary tract.

The rennin coagulates the casein of milk and the pep-
sin then converts it also to peptone.

The starches are not changed in the stomach.

The albuminous walls of the fat cells are dissolved
away, but the fat is not changed.

The presence of food stimulates the muscular walls of
the stomach to action. By their alternate contraction
and relaxation they i^roduce a movement called peri-
staltic motion. By this means the contents of the stomach
are moved about and thoroughly mixed together.

The mass of food, after it has been digested in the
stomach for some time, is of about the consistency of
thick cream, and is called chyme.

From time to time, as the digestion of the proteids
is completed, the pylorus opens and lets the chyme
through. In from two to four hours the stomach is
empty again.

The small intestine. — The small intestine is about
twenty feet in length, though varying considerably in
different persons. It begins at the pyloric orifice of the

106 THIRD BOOK OP PHYSIOLOGY

stomach, wheie it is largest, and ends at the large intes-
tine. The first ten inches of it is called the duodenum
(twelve) because it is about as long as twelve fingers
placed side by side. The next eight feet of it is called
the jejunum (emptjO- The remainder is called the ileum
(twisted) because of its many folds.

Like the stomach, the small intestine is composed of
four coats, — the serous^ muscular, areolar, and mucous.

The serous coat is formed by folds of the j)eritoneum.
These folds are called the mesentery, and they serve both
to support the intestines and to conduct the blood-vessels
to them.

The muscular coat has two layers, one running length-
wise and the other being circular. The circular is
stronger and of more importance.

The mucous coat. — The mucous coat of the small
intestine lies in the permanent folds or ridges called
valvulce conniventes which pass transversely around the in-
testines. They prevent a too rapid passage of food along
the intestine and present a larger surface for absorption.

On the inner surface of the mucous coat are small pro-
jections called villi. These are only about tV of an inch
long, but they stand close together, giving the surface a
velvety appearance. In Fig. 55 is shown a section of
the small intestine of a cat. As the section is very thin
and is magnified, the villi do not have their natural,
crowded appearance.

In Fig. 56 is shown a few villi of the same specimen
as above, but more highly magnified. The dark lines

DK.'KSTION^

lo:

show th»* blood-vessels, wliicli ure liere filled with a
colored sui)stunce.

j^

''>

/

Fio. 5-3. — Section of smaii mrostine of cat.

A^Tien a villus is clos^^ly examined, it is fonnd to be
covered with a layer of epithelial cells as shown in Fig. 57.

FiG. 56. — Micn)photograph of villi.

Within is a net-work of ves.sels to receive and carry away
the liquids that pass through the layer of cells. In the

108

THIRD BOOK OF PHYSIOLOGY

centre, L, is a tube called a lacteal, which, during diges-
tion, is filled with a milky white liquid. About the
lacteal are the capillary blood-vessels.

Here and there between the villi are the mouths of
glands called the crypts of Lieberkiihn.

Fig. 57. — Diagram of villus. E, layer of epithelial cells ; yl, artery

F, vein : L, lacteal.

The liver. — Two large glands concerned in intestinal
digestion are set off from the alimentary tract, but con-
nect with it by means of ducts, through which they pour
their secretions into the small intestine. These glands
are the liver and the pancreas.

The liver is the largest gland in the body and weighs
from three to four pounds. It is situated on the right
side of the abdomen, just below the diaphragm, and
consists of five lobes. It contains a net-work of tubes,
through which the blood and other liquids circulate.

DKiKSTloX

100

Fig. 58.— External view of liver. 1, riglit Icbe ; 2, left lobe; ^,
portal vein; 4, hepatic artery; o, bile duc-t ; 6, gall-bladder; 7, in-
ferior vena cava.

Fig. 59.— Lobule of the liver. Blood is brought by portal vein to
outer surface of the lobule and flows through the lobule to its centre,
where it is collected by the hepatic vein and conducted to the inferior
vena cava.

110 THIRD BOOK OF PHYSIOLOGY

On close examination it is seen that the liver is made
up of a great number of masses called lobules. Each
lobule consists of hepatic or liver cells, between which
run numerous fine blood-tubes. The work of the liver
is done by these cells. In Fig. 59 is seen a cross-section
or a lobule highly magnified.

The liver is of great service to the body in sevei'al
ways. In this chapter we are interested in its ability
to produce bile. This substance is gathered up by nu-
merous hepatic ducts, which finally unite and pour the
bile into the duodenum.

Beneath the liver is a gall-bladder, in which the gall is
stored when not needed for digestion.

The pancreas. — The other large gland concerned in
digestion is the pancreas. It is situated in the abdomen
back of the stomach. It is a racemose gland and re-
sembles those that secrete saliva. It is six to eight
inches long, but quite narrow and thin, weighing only
from two to four ounces.

Its function is to secrete pancreatic juice, which is
poured through a duct that opens into the bile duct just
before it reaches the duodenum.

Digestion in the small intestine.— While the
food is passing through the process of gastric digestion,
the glands concerned in intestinal digestion secrete their
juices and pour them into the small intestine. When
the chyme passes through the pj^lorus into the duo-
denum, digestive juices are there ready to receive it.

DIGESTION 111

These are the pancreatic juice, the bile, ami the secre-
tions from the small glantLs embedded in the niucx)us
coat of the intestine.

These, when mingled with tln' food nuuss, change the
acid chyme to tlic iilkaliiR' chiile.

Action of the pancreatic juice.— The secretion
of the paucrea^s is the most important of the intestinal
juices. It is a clear, alkaline liquid, and is capable of
doing three things : First, it rapidly converts starch into
sugar. This action was begun by the saliva, but was
stopped by the acid in the gastric juice of the stomach.

Second, it digests any proteids that escaped digestion
in the stomach.

Third, it changes some of the fats to soap, in which
form it is soluble in water, and so can be absorbed.
Most of the fats, however, lue only emulsified, and are
passeil as small droplets through the bodies of the epi-
thelial cells.

The action of bile. — The human bil«.' i.s a brownish
liquid, but will, if kept for a time, turn green. Its use
is not fully known, but it is certain, from the bad etfects
which follow when the supply is shut off, that bile has
an important office in digestion.

It is alkaline, and helps to neutralize the acid of the
chyme. It excites the muscular coat to action, and tlius
is a means of moving the food along the intestine.

It also facilitates the absorption of fats.

Intestinal juice. — The juice secreted by glands in
the mucous coat of the intestine is, like the other two,

112 THIRD BOOK OF PHYSIOLOGY

alkaline. It converts the sugars which we eat into a
kind which can be more readily absorbed by the villi.

The large intestine. — The final portion of the ali-
mentary tract is called the large intestine. It is but five
feet in length, but is called ''large" because it will aver-
age about two inches in diameter. The area of its cross-
section, then, is nearly four times as great as that of the
small intestine.

It begins on the right side of the abdomen and ex-
tends up along that side, forming the ascending colon;
then across, forming the transverse colon; then down on
the left side, forming the descending colon. (See Fig. 53.)

The small intestine opens into the side of the colon
some distance from the end. At this opening there are
folds of the mucous membrane which form a valve
called the ileocolic valve. By this arrangement the con-
tents of the small intestine may easily pass into the
colon, but cannot return.

The part of the colon below the ileocolic valve is
called the cwcum (blind), because it is closed at the lower
end. From the caecum hangs the vermiform appendix.
This is a slender tube about four inches long, and is the
seat of a common inflammation called apx^endicitis .

The coats of the large intestine are the same as in the
small, except that the mucous coat is not supplied with
villi. It is furnished, however, with numerous glands.

Action of the large intestine.— By the time the
food mass has reached the ileocolic valve its valuable

DKiESTION 113

food contents have been largely absorbed. Tliat which
enters the colon is mostly water, some food, and wiuste
products. In the large intestine a great deal of water is
absorbed, and the digestion of the remnants of fo(Kl will
continue and the food will be absorbed.
The residue is cast from the body.

Hygiene of Nutrition. Mastication.— Thor-
ough mastication is a hiatter of real importance in the
preparation of the food for digestion. Foods must be
chewed until they are thorough!}^ ground up. Experi-
ments show that those who insist on thorough mastication
ha\e fewer ailments of their digestive organs and are
stronger with a less quantity of food.

Even when food is quite soft, it is necessary to chew it
until it is well mixed with saliva, for the ferment in
saliva continues its effect on starch throughout the diges-
tive tract, except in the acid contents of the stomach.

Care of teeth. — Mastication will not be well done
unless the teeth are good. Teeth will readily decay.
Particles of foreign matter allowed to remain between
the teeth is the cause of much of the decay.

After each meal a w^ooden toothpick should be used,
and the teeth washed with brush and water. Since the
material of the teeth is chiefly phosphate of lime, acid
will dissolve them. For this reason it is well to use often
a mild soap in washing the teeth to neutralize any acid.

Teeth which are neglected are apt to become covered
with a coating called tartar. This is not only injurious

114 TIIIED BOOK OF PHYSIOLOGY

to the teeth, but objectionable in appearance, and should
be removed by a dentist.

Decay begins at a small spot on a tooth and extends
in to the pulp. The beginning of decay may escape at-
tention for a long time, and after toothache begins it is
often too late to save the tooth.

It is a good plan to consult a dentist two or three
times a year, if only to be assured that the teeth are in a
sound condition.

A healthy stomach. — As long as the stomach is in
a healthy state one is seldom conscious that he has such
an organ. When it is disordered, however, it is the
cause of a great deal of suffering, and the whole body
must suffer with it.

Some practices which produce a disordered condition
of the stomach, and which are to be avoided, are : (1)
Eating too much ; (2) forcing food into the stomach be-
fore it is properl}' masticated ; (3) eating too often, thus
keeping the stomach constantly excited to action with-
out periods of rest ; (4) doing vigorous work either
directly before or after a meal ; (5) the use of alcoholic
drinks.

When proper care is taken with respect to gastric
digestion, the proper conditions for the best intestinal
digestion will be provided at the same time.

Alcohol and digestion. — It was once customary to
take at meals some drink containing alcohol. Some
people still continue the custom. It was supposed to aid

DKIKSTKJxN 115

digestion, but tests nuidc, in i-et^ent years sliow that it
retards rather than promotes digestion. Food w.ill re-
main longer in tlie stomacli when alcohol is taken with
it. Many drinkers are troubled with catarrli of the
stomacli. The mucous membrane becomes inflanu^d and
unhealthy. The freedom from i)ain which the dyspeptic
experiences after a drink of alcoholic liquor is not a
result of the curative power of the alcohol, but of its
deadening eft'ect upon th'e sensory nerves.

The strong appetite which some have for strong drink
is an indication of a disordered condition of the stomach.
Appetite for bread is satisfied whenever enough is eaten,
but that for alcohol may increase eveu beyond the con-
trol of the drinker.

QUESTIONS FOR REVIEW.

1 . What is digestion ? Illustrate.

2. Why is digestion necessary,?

3. Describe an experiment showing the action in osmosis.

4. Have ?/0M tried the experiment?

5. How do fats get into the blood ?

6. When food is in the stomach, is it inside or outside the
body ? Explain.

7. What are the parts of the alimentary tract?

8. What are the first two acts of digestion ?

9. Describe the temporary set of teeth.

10. Classify the permanent teeth.

11. What is the crown of a tooth? Name the other parts.

12. AVhat three parts are observed in a cross-section of a tooth ?

13. Describe the enamel. The pulp. The dentine.

14. How is saliva secreted ?

15. What is a racemose gland ?

116 THIED BOOK OF PHYSIOLOGY

16. What are four uses of saliva?

17. Whatisptyalin?

18. "What makes saliva *' ropy " ?

19. Bound the fauces.

20. What is the uvula ? What are tonsils ?

21. What is the pharynx ? Name the openings from it.

22. What is the epiglottis ? What is its use ?

23. What is deglutition ?

24. Describe the cesophagus.

25. Locate and describe the stomach.

26. Describe the muscular coats of the stomach.

27. How is the stomach held in place?

28. Describe the mucous coat of the stomach.

29. What are the digestive juices of the stomach ? What is the
action of each ?

30. What kind of food is digested in the stomach ?

31. What changes are made on fats in the stomach ?

32. AVhat is the use of the muscular coats on the stomach ?

33. What is chyme?

34. Describe the small intestine. Name its parts.

35. What is the mesentery ?

36. What are valvulse conniventes? What their use?

37. What is a villus ?

38. Describe the structure of a villus.

39. Describe the liver. What part does it have in digestion ?

40. Describe a liver lobule.

41. Describe the pancreas.

42. What three juices act upon the food in the small intestine?

43. What is the effect of the pancreatic juice ?

44. What is the use of the bile?

45. Describe the large intestine.

46. What is the use of the ileocolic valve?

47. Describe the vermiform appendix.

48. What is the coecum ?

DKiKSTION 117

49. Describe the coats of the colon.

50. "What are the changes on the food in the colon ?

51. AVliy is thorough mastication necessary?

52. What causes teeth to decay?

53. "What are some ways of caring for the teeth?

54. State several ways by which the stomach maybe disordered.

55. What effect does cheerfulness at the table have on digestion?
50. What effect does alcohol have on digestion?

57. Will alcohol cure the cause of pain?

58. Why does appetite for* alcohol become so strong?

59. What is a beverage? (See English dictionary. )

EXPERIMENTS.

To illustrate action of gastric juice.— Prepare an artificial gastric
juice by mixing together pepsin 5 parts, hydrochloric acid 3 parts, and water 500
parts. Put into this liquid some pieces of hard-boiled egg, and keep at about the
same temperature as the body. After a time the egg will be dissolved, or digested.
This ilhistrates digestion of proteids.

Action of saliva. — Collect one-half test-tube full of saliva from the
mouth. Put iuto it a little cooked starch and keep warm. In a short time make
a test for sugar as follows :

Add to the contents of the tube a few drops of dilute copper sulphate. Then
add caustic soda in excess until the liquid becomes a clear blue. Now boil the
liquid in the upper part of the tube, and if grape sugar be present it will turn red.

Emulsion of fats. — Shake up some olive oil and a solution of caustic
soda. The mixture becomes milky in appearance. The oil is divided into very
fine drops, which do not collect together. This is called an emulsion.

CHAPTER IX

WHOLESOME AND UNWHOLESOME DRINKS

Much of the ill-healtli of the human race comes from
not knowing what is good and what is not good for the
body. Untold suffering has thus resulted from ignorance
concerning the nature and effects of alcoholic drinks.
Many false suppositions concerning their origin have led
to mistaken ideas of their value. It is very important
that such false opinions should be corrected.

It is well known that ripe fruit in its season is a whole-
some part of a healthy person's diet ; but the fruit season
in the temperate zone is short, hence men have tried
various means of preserving fruits beyond their ripening
time. Drying is an old method of preserving fruit. In
drying, the water of the fruit evaporates, and, if care is
taken, the fruit is otherwise not much changed.

Another way of preserving fruit is to boil it with sugar
and seal it while boiling hot in air-tight cans. If this is
well done, the fruit does not lose its wholesomeness. But
if the cans are not perfectly tight, or the fruit not suffi-
ciently heated, germs of mould or other minute organ-
isms get inside and cause the fruit to spoil. When this
happens the fruit becomes unfit to eat, because the fer-
mentation has changed its nature. It is apt to contain
poisons which may cause illness if it is eaten.
118

wir()M-:s()Mi<: and rx\\Mi()r;i<:s()MK dimxks no

Sometimes people wish to pieserve only the juice of
fruit and use it iis n drink. If tlie juice is pressed out
and at once heated and sealed in air-tight cans or bottles,
while boiling hot, it can be kept from changing, just as
fruit can by canning. If the juice is not thus heated and
bottled, but is allowed to stand after it is pressed out, it
will soon ferment and change. During the fermentation
a poison is developed which makes the fermented liquid
unhealthful.

The cause of fermentation in expressed fruit juice is a
small germ, invisible except under a microscope ; but it
is not the same kind of a germ that causes whole or
stewed fruit to spoil. The germ that sets up fermenta-
tion in expressed fruit j nice is a species of yeast. Similar
germs can be seen in common yeast by soaking it and ex-
amining it under a microscoi^e. The wild yeast germs
float in the air, in a dry state, settle upon the skins and
stems of fruit, and from there are washed into the juice
when it is expressed from the fruit. In a few hours,
under the right conditions of moderate warmth, they
begin to change the fruit juice. This change is called
alcoholic fermentation, because the sugar of the fruit
juice is thereby changed, in whole or in part, to alcohol
and carbon dioxide gas. Every fermentation changes
the nature of the substance fermented.

Fermented fruit juices are unhealthful^ because they con-
tain alcohol, which is a poison to the human system.

A poison is any substance whose nature it is when
absorbed into the blood to injure health or destroy life.
It is not necessary that a substance cause sickness or

120 THIED BOOK OF PHYSIOLOGY

death at once, in order to be a poison ; its injurious
effects may follow so slowly and subtly that they do not
show plainly at first.

Poisons are classified by authorities on this subject
according to their characteristic effects upon the body,
or its various i)arts. A narcotic poison is one that dulls
or deadens the brain. Alcohol is classed by writers on
poisons among the narcotics, because its most important
effect is to dull the nervous system. It is similar in this
respect to opium, ether, and chloroform, all of which
belong to the same class, i.e., narcotic poisons.

The most common drinks made in this country by fer-
menting fruit juices are cider, made from the juice of
apples, and wine, made usually from the juice of grapes,
occasionally from currants, elderberries, and some other
fruits.

Wine has been much used as a promoter of social
intercourse. The narcotic effect of the alcohol in the
wine, when only a small quantity is taken, dulls the
nerves enough to take the edge off of the understanding
and weaken the self-control. In this condition a person
says and does things which he would be ashamed of
in his right senses. A companj-, after the effect of wine
begins to show itself, will laugh at silly speeches which
at other times would seem pitiable instead of funny. It
is a poor compliment to civilization to assume that people
must be slightly narcotized before they can be agreeable
companions.

One danger in social wine drinking, in some classes of

WIIOLKSOME AND UNWHOLESOME DRINKS 121

society, is that wine lias been used as a means of admin-
istering drugs, which still further stupefy the iniud and
thus quickly i^repare the way for crime. But the great-
est danger in wine is the power of the alcohol it contains
to make the drinker want more, while it destroys the
power of his will to control the desire for more. It is
futile to urge self-control in the use of a substance whose
nature it is to destroy self-control. The best way of
exercising self-control in regard to alcoholic drinks is to
refuse the invitation to take them. The wine drinker
may intend to be moderate ; but it is the nature of the
alcohol in his wine to weaken his self-control and make
him immoderate.

Light wines, such as are ordinarily used as beverages,
contain 10 per cent, of alcohol, but more is often added
to wines till it may reach as much as 35 per cent.

Cider or fermented apple juice. The juice of
apples when pressed out and fermented makes a liquid
called cider. The yeast germs which are on the surface
of the api^les when they are ground and crushed grow
and multiply so rapidly in the exi^ressed juice that in a
few hours much of the sugar of the juice may be changed
to alcohol.

Cider-making is a common way of disposing of small
and unsound apples ; but it has been a sad economy for
many farmers whose promising sons have acquired at
the cider-barrel the craving for alcohol that has led to
their destruction. Hard cider contains more alcohol than
most malt liquors. When alcoholic fermentation has

122 TIIIKD BOOK OF PIITSTOLOGY

gone on until about 14 per cent, of the fermenting liquid
is alcohol, the yeast germs can no longer continue their
work. Another fermentation, however, the acetic, takes
place in this liquid and changes the alcohol to acetic acid,
by which process hard cider is turned into vinegar.

Beer. — A large percentage of alcoholic liquors is
made from grain = These are the malt liquors, such as
beer, ale, and porter, which may contain from 2 or 3 to
10 per cent, of alcohol. The most common of these is
beer.

One of the x^rincipal food elements in grain is starch.
When grains are ground and made into flour or meal,
and then into bread or other cereal food, the starch re-
mains largely unchanged, except such i^arts as are turned
into dextrine, which is a kind of sugar and a good food.
When grain is used for making beer, the starch is first
changed to sugar by sprouting the grain, and the sugar
is then soaked out with water. Thus is obtained a sweet
liquid called wort, the sugar of which can be changed to
alcohol by fermentation. Yeast is added to the wort.
Alcoholic fermentation takes place and changes the sugar
of the wort to alcohol, and the result is beer.

Beer, like all alcoholic liquors, is a dangerous drink
because it contains alcohol.

The false idea that beer is harmless because there is not
much alcohol in it and that a little will not do a man any
harm, is a cause of much mischief. It makes the drinker
careless about the amount he drinks. Even if he takes
but little, that little has the power to set up a craving

wrror.KsoMK axd t'xwitolesome drinks 123

for more that leads liim to make uj) for tlie weakness of
his drink bj' the quantity lie takes. Thus the beer
drinker often gets as much alcohol as if he took whiskey
or brandy.

The narcotic effect of the alcohol further deadens the
drinker's sensibilities, making him careless, not only
about his own welfare but that of others. Judges in
criminal courts have again and again called attention to
the frequent association of beer drinking with the com-
mission of crime. Their testimony strengthens the evi-
dence that beer is a demoralizing drink.

At the present time there is special need that boys be
warned against the offer of free beer. Accepting such
offers may fasten upon them the craving for alcohol that
will lead to their spending the most of their future earn-
ings for beer or other alcoholic drink. The effort to
teach a boy to drink beer is not made for the benefit of
the boy, but to swell the number of beer customers.
Such attempts to mortgage a boy's future money-earning
power to drink are as inhuman as the bygone i)ractice of
slave- catching in Africa.

The distilled liquors, gin, whiskey, rum, brandy, con-
tain more alcohol than the fermented drinks. Gin con-
tains 38 per cent.; whiskey, 45 per cent.; rum, 48 per
cent.; brandj', 50 per cent. These are all injurious in
proportion to the amount of alcohol they contain.

Drinking water. — It is of the utmost importance
to the health of the people in any community that
only good drinking water be used. Water is the only

124 THIRD BOOK OF PHYSIOLOGY

drink needed by man. and he should have plenty of it
and have it free from impurities. A man needs about
three quarts of water every day. A part of this is already
in the foods eaten, so that a pint or more of water as such
may satisfy the body's needs. There is very little danger
that any one will drink too much pure water. A gi'eat
deal is needed for proper digestion, absorption, secretion,
and excretion. If water is drunk in excess, it is easily
eliminated. Most people drink too little water. It should
not be taken, however, to moisten the food in the mouth
during a meal. The saliva alone must do that.

Sources of water. — All land water comes from rain.
Part of it remains on the surface in rivers, brooks, pools,
and cisterns, and is called surface water.

Part runs down through the ground and rocks, thus
supplying the springs and deep wells. Another part is
just beneath the surface and supplies the shallow wells.

Impurities in water. — Water is nature's great sol-
vent, and also a universal culture medium for all kinds
of minute organic life. While it slowly percolates
through the soil and rock, it takes up in solution many
mineral substances. These in a moderate quantity are
not objectionable. Such water is found in most deep
wells and springs.

Surface water may be good for drinking, but it is
always to be suspected.

The rain falling upon the land carries to the streams
any decaying matter which may be Wiished along, and

WIloT.FSO.MI-: AND IN W IIoI.ESOME DRINKS 125

the sewage of a city, if allowed to emptj' into a stream,
may contaminate the water with germs of disease.

Water is safe only when free from decaying matter.
Shallow wells are the greatest source of impure water.
Decaying matter from barn-yards or out-houses may easily
have a shallow underground i:)iissage to the well.

Fig. 60. — A shallow woll, such as are always to be suspected.

Such wells have often started an epidemic of typhoid
fever. A painted pumj:) and neat lawn and curb about
such a well do not purify the water, for the poison is
seeping in beneath the surface.

A well deep down into the rock, with water-tight iron
casing, will, as a rule, contain good water.

126 TIIirvD BOOK OF PHYSIOLOGY

Means of purifying water.— Good water will be
without color, odor, or organic matter of any kind.
Effort is often made to provide such water by the use of
small house-filters. These may make the water clear, but
may not take out the germs of disease which are the most
objectionable. In fact, an old filter often contaminates
more water than it ever purified.

Nature's way is to filter water through thick layers of
clean sand, gravel, earth, and rock, thus supplying the
deep wells with pure water. This cannot be done for
shallow wells, nor can man imitate this method on a
small scale.

Organic matter in water may not of itself be injurious,
but may be a food for certain classes of germs which then
grow and thrive there.

If water is suspected, it should be boiled (not warmed)
for twenty minutes. This will efifectuallj' destroy all bac-
terial life and make the water free at least from that
danger.

Ice water. — The custom of placing ice in the water
to be drunk is a wrong practice for two reasons.

First, if the water was impure from which the ice was
taken, the ice will be impure. Germs of disease in water
are not killed by freezing the water.

Second, much water at such a temperature interferes
with digestion and may produce a disordered condition
of the stomach.

Water may be cooled by ice, but the melted ice should
never form part of the drinking water.

WIIOLKSOMI-: AND T N W IIOLKSO.M M DIMNKS 127

QUESTIONS FOIl KKVIKW.

1. lIoNv may fruit be presorvcd?

2. What is the cause of feriiieiitatic.n?

8. Why are fermented fruit juices unliealthful?

4. What is a poison ?

5. "What kind of a poison is alcoliol?

0. State some evil effects of wine drinking.

7. How docs the juice in the apple differ from hard cider?

8. How is beer made ?

9. State some of the evil effects of beer drinking.

10. What are distilled liquors?

11. How much water does a man need in a day ?

12. What is the effect of drinking more water than is needed?
i:]. Why should water not be taken along with foods?

14. What becomes of the water which falls as rain?

15. What causes water to be " hard" ?

16. W' hy is rain water " soft" ?

17. What is the source of impurities in water?

18. When is drinking-water safe?

19. Explain how shallow wells are liable to contain impure water.

20. Why is a deep well better ?

21. What is the use of filters?

22. How may impure water be made fit to drink?

23. State some evil results that may follow the use of ice water.

CHAPTEE X

CIRCULATION

Why circulation is necessary.— We have seen
that the body is made up of a g^reat many cells, each
having a life of its own, but all working together to
serve the purpose of the bodj^ as a whole. All the cells,
however, except the white corpuscle, are fixed in posi-
tion and incapable of moving from their place.

The cells cannot live without food, but they cannot go
after it. Circulation of the fluid food is necessary to carry
nourishment to the cells.

The cell cannot perform its functions without pro-
ducing waste products, which must be carried away.
Circulation is necessary to carry off waste products and other
objectionable substances, and transport them to organs of ex-
cretion, such as the lungs, liver, hidneys, and skin, ichere they
may be taken out of the circulating fluid and cast from the
body.

How the food gets into the stream of blood.—

Under the subject of digestion the food was followed
until it was in a liquid form and had passed through the
walls of the villi into the vessels within.

At this point was found a net-work of fine tubes.
These are a part of the general circulating system, and
here the food is taken into the stream of blood. Part
128

CIL'CCLA'no.V 129

of the tubes j^ather u}) all the food, except the fats, and
convey it to the liver. Other tubes, calle<l lacteals, collect
the fats and convey them up throuj^h a tube called the
thoracic duct to a vein in the left shoulder, whence it s<j(tn
reaches the heart.

The blood that wius carried i'roni the stomach and
intestines to the liver was there changed and purified by
the action of the hepatic cells, and thus made fit to be
sent out to the other cells of the body.

The proteid food, as has been explained, was changed
by digestion to peptone so that it would dialyze through
to the blood-vessels in the villi. In this form it would
be a poison to the body, and must be changed back to
proteid again. This is done by the epithelial cells that
cover the villi, so that peptone in a healthy body does
not get into the circulation.

Action of the liver. — The structure of the liver
and its office in the secretion of bile has been described
on page 108. It would seem strange, however, that such
a large gland should have nothing to do but to secrete
bile. It appears that the liver has another duty of much
greater importance. Its chief work is to store up
glycogen and deal it out to the current of blood as it
is needed.

Glycogen is a kind of sugar which the liver is able to
make from the sugars that are eaten and the starch which
was converted to sugar in digestion. The quantity of
glycogen in the liver is greatest just after the digestion
of a meal and decreases during starvation until none

130 THIRD BOOK OF PHYSIOLOGY

remains. Thus tlie liver acts as a storehouse of this
important food.

The liver is also a door-keeper guaiding the entrance
of food into the circulation, and, within the limit of its
ability, will take out substances that would be harmful
to the system.

After food passes the liver it is carried by a larj^e vein
to the heart.

The organs of circulation. — The circulation of
the blood is accomplished by means of the heart., arteries.,
capillaries., veins., and lymphatics. The heart is the central
organ of the system, and from it pass tubes, through some
of which blood is sent out. and through others blood is
received back again to the heart.

The whole system of tubes through which the blood
circulates is closed except at two points, where the lym-
phatic ducts enter the subclavian veins, — one on each
side under the clavicle. These two points are guarded
by valves which close whenever blood would flow out
into the ducts.

There is no place, then, where the blood can flow out
of its channel to other tissues, except in the spleen (see
spleen), and so the food can get to the cells only by oozing
through the walls of the blood-vessels.

This occurs only in the capillaries. The jiurpose of the
heart, arteries, and veins is to keep the capillaries sup-
plied with a fresh current of blood.

The heart. — The heart is a large hollow bundle of
muscular fibres. It weighs ten or twelve ounces. It is

CIlJCrLATION

131

located in (lie thorax jnst above tlie (liaplinjj^nn, and
midway l)etween tlic rij^^ht and left sides. It is conieal
in shape, witli its point downward, forward, and to the
left. The b;ise of the heart wonld then be towards the
right shonUler.

^tT

rr

Fig. 61. — External view of the heart. 1, right auricle; 2, right
ventricle; 3, pulmonary artery; 4, left auricle; 5, left ventricle; 6,
aorta ; 7, subclavian veins ; 8, carotid arteries ; 9, superior vena
cava ; 10. inferior vena cava ; 11, descending aorta.

It is enclosed in a loose bag, which is attached to the
diaphragm. The bag, called the pericardium^ is lined
with a moist and very smooth serons coat, so that there
is very little friction between it and the heart proper.

132

THIRD BOOK OF PHYSIOLOGY

The cavities of the heart are also lined with a coat
called the endocardiuni.

Divisions of the heart.— The heart is double.
The two halves are bound together, but have no opening

between them. They are
often called the rigid and
left hearts. The only way
blood can get from one side
of the heart to the other is
by going out in a circuit
through the arteries, capil-
laries, and veins, and then
back to the other side.

Each side of the heart
contains two cavities. The
upper ones are called auri-
cles and the lower ones ven-
tricles. So there is a right auricle and a right ventricle and
a left auricle and left ventricle::

The left side of the heart is larger and stronger than
the right.

The muscular walls of the left ventricle are thick and
strong because they have the most of the heart's work to
do, — that of forcing blood out to even the farthest ex-
tremity of the body.

Fig. 62 — Diagram showing
cavities of the heart. RA^ right
auricle ; R F, right ventricle ; LA^
left auricle ; L F, left ventricle. *

Valves of the heart. — ^Yhen the muscular walls
of the heart contract they will make the cavity smaller
and the blood will be forced out. There would be no

riKrr'L ATiox

13.3

advantajxc in tliis if tlie blood could go back throun^h the
sjuiu' tulM' in wbicli it oiitcrod ; so valves are needed to

Open

Closed

Fio. 63. — Diagruiii illustruting the action oi the- auiiculu-veiitricular

valves.

Fig. 64. — Section of the right auricle and right ventricle of the heart.

keep the blood alwaj^s flowinfij in the same direction.
Between the auricles and ventricles are valves having
the common name auriculo-ventricular valves. The one

134

THIRD BOOK OF PHYSIOLOGY

between the right auricle and ventricle is called the tri-
cuspid valve, while the corresponding one in the left heart
is called the mitral valve. These valves are simply flaps
of the endocardium, the tricuspid having three flaps or
cusps, as the name indicates, and the mitral, two. These
offer no resistance to blood flowing from the auricles
into the ventricles, but any attempt of blood to flow in
the opposite direction would push one flap against the
other and thus close the opening.

Strong cords of connective tissue are fastened to the
edge of the flaps and to the walls of the ventricle.

These permit the valves to close,
but prevent their going any far-

ther. The arrangement is sim-
ilar to that of double swinging
doors which open in only one
direction.

At the point where the blood
is forced from the left ventricle
into the large artery, called the
aorta, are three semilunar valves.
They get their name from their

half-moon shape, as seen in Fig. 65. They open to blood

flowing out, but are closed by any movement of blood in

the opposite direction.

The same arrangement is found at the point where

blood is driven from the right ventricle into the artery

leading to the lungs.

Semilunar valves

Course of the blood in the heart.— The blood
enters the right auricle of the heart and flows on

CIRCULATION

135

Uiroii<^li the ti'icuspid valve into the rij^ht ventricle.
Wlieii the rij^^ht veiitride is filled its muscles contract
and squeeze upon tiic hhMxl. tlius closing the tricuspid
valve and forcing the blood through the semilunar
valves, m (Fig. 66), into the artery, S, which leads to
the lungs.

Fig. go. — Diat!;rain showing the course ot the blood through the
heart, c, superior vena cava ; />, inferior vena cava ; Z), right auricle ;
e, tricuspid valve ; G right ventricle ; w, semilunar valve ; S, pulmo-
nary artery ; /j, />, />, j), pulmonary veins ; A", left auricle ; /f, left ven-
tricle ; ?2, semilunar valve ; A, aorta.

When the blood returns from the lungs it enters the
auricle on the left side, K, and passes on into the left
ventricle, H. The contraction of the strong muscles of
the left ventricle closes the mitral valve, i, and forces
the blood out into the great artery. A, which carries it
to all parts of the system.

13G

THIED BOOK OF PHYSIOLOGY

Thus the auricles act as reservoirs to hold the blood
while the valves are closed, and the valves act like the
valves of a pump, opeuing only to a flow in one di-
rection.

The arteries. — Arteries are tubes through which
blood is forced out to the various tissues of the body.
The arteries stand open like a heavy rubber tube,
whether they are filled with blood or not.

Fig. 67. — Section of arterv and vein. A, arterv ; V. vein.

The walls of arteries are composed of three coats.
The inner one is thin and transparent, being a continua-
tion of the inner lining of the heart. The middle coat
is quite thick in the larger arteries, and is composed of
muscular fibres and yellow, elastic tissue arranged in
rinsrs around the tube. The outer coat is composed of

(MIJCrrvATlOX 137

layei's of wliitc, fibrous tissiu', and so is very stroii<^ siiul
U)Uii;h.

Distribution of arteries. — The arteries arise from
the iH'art, one from each ventricle.

The one from the right ventricle carries the impure
blood to the lungs. It is called the pulmonary artery.

The one from the left ventricle carries the pure red
blood out to all parts of the body. It is called the aorta.

The aorta arches up over the heart, sending off
branches to the heart itself the head, and the arms.
Then it descends, close to the backbone, through the
thorax, sending off numerous small branches to nourish
the tissues in that region. Then it passes through
the diaphragm into the abdomen, where many large
branches are distributed to the important organs located
there.

Near the base of the abdomen the aorta divides, one
branch passing down each leg.

Each of these numerous branches also divides in a
similar manner until the tubes are so small they cannot
be traced except by the aid of a microscope. At the
ends of the numerous fine arteries the capillaries begin.

Capillaries. — The capillaries are very fine tubes that
pervade nearly every tissue of the body. They are in-
terposed between the ends of an artery and the begin-
ning of a vein.

The walls of the capillary tubes are an extension of
only the thin inner layer of the artery, and so the food

138

THIRD BOOK OF PHYSIOLOGY

contents of tlie blood can easily transfuse to the cells just
outside.

The average size of the capillaries is about xsVo of an
inch, but they lie so close together and are so numerous

Fig. 68. — Capillaries. A, terminal of fine artery ; V, origin of vein.

that it is hardly possible to prick the skin with a fine
needle without puncturing some of them and letting out
some blood.

The capillaries are the most essential part of the
whole system of circulation, for it is from them alone

that the cells are fed. In Fig.
69 is a representation of the
relation of the capillaries to a
bundle of muscle-fibres.

The cells of the muscle are
surrounded by a liquid called
lymph. As the blood passes
through the capillaries the
cell-food transfuses through into the lymph. Both the
cells and the capillaries are bathed in lymph, and the
exchange takes place according to the principle of os-
mosis explained on page 95.

The cell then takes its food from the lymph.

Blood moves very slowly in the capillaries, — only

Fig. 69. — Diagram showing
muscle-cells and blood capil-
laries.

CIRCULATION 139

about one iiicli in ii ininulc, — and so there is time lor the
osiiiot i(- act ion.

Veins. — Tlic arteries lM'<xin as a sinnle laryc I nix*,
which (livi(h\s and snhdivides until the hranclies are
exceedin<;iy nnincrons and minute, when they pass into
the capillaries.

At the other end of each capillary is a minute vein
which now receiv(is the blood.

These fine veins unite to form a larger tube, which in-
cre;uses in size as it approaches the heart.

Thus the blood flows from the large artery out to its
branches ; while in a vein it starts at the branches and
is collected into a large vein.

The arteries distribute blood, the veins collect it and
bring it back to the heart again.

Two large veins return the blood from the system to
the heart. One, called the superior vena cava, collects all
blood from parts above the heart, and another, called the
inferior vena cava, collects all blood from regions below
the heart.

Structure of veins. — The walls of veins are com-
posed of three coats similar in structure to those of ar-
teries, but the middle one is not uearly so thick. Veins
do not stand open except when filled with blood.

In the veins at intervals are placed semilunar, or half-
moon, valves, at some points one, and at others two or
three, together. They are pockets fastened to the walls
of the vein so that blood may floM' past them towards

140 THIRD BOOK OF PHYSIOLOGY

tlie heart: but if it flows in the opposite direction the
pockets will fill with blood and press a^^ainst each other,
thus closing the vein. The semilunar valves of the heart
operate in the same way. (See Fig. 65.)

Veins are slightly enlarged at the points where valves
are placed. If the flow of blood in a surface vein be
stopped by pressure, the position of the valves can be
located by the ••knots" seen here and there along the
vein.

Lymphatics. — As explained above, the active tissue-
cells are constantly bathed in lymph, which is constantly
supplied from the blood. When the lymph has served
its purpose it must bediained off. This, however, is not
done by the veins, but by a special system of tubes called
lymphatics. These begin as very small tubes which unite,
forming two ducts that convey the lymph to the right
and left subclavian veins.

The ducts are supplied with valves similar to those in
veins.

The two ducts are called the thoracic duct and the right
lymphatic duct.

The thoracic duct collects the lymph from the lower
extremities, the abdominal organs, the left side of the
head and thorax, and the left arm. and empties into the
left subclavian vein.

The right lymphatic duct collects from the right side
of the head and thorax and the right arm, emptying into
the right subclavian vein.

The thoracic duct also receives the emulsified fats

riRcri-ATION 141

whicli were coUccUmI hy the lacteals in the villi of tlie
iiitesliiies-

Lympliatic nodes. At many points alonj^ tlie
lymphatic ducts arc iMxh's or knots. Tli(iy arc imincrous
in the ji;roins, iicck, anii[)its, and mesentery. When for
any reason they are inflamed, th^y are spoken of as
'•waxen kernels." They are made up of interlacing
connective tissue packed with cells which are \'(;ry much
like white corpuscles.

The lymph filters through the nodes, carrying witii it
some of the cells, which become white corpuscles in the
blood.

The spleen. — The spleen may be considered a large
lymph-node. It lies just below the stomach on the left
side. It is a dark red body about five inches long and
weighs about six ounces. It is spongy in texture, and its
meshes are filled in with a soft substance called spleen-
ptdp.

The pulp consists largely of red and white blood-
corpuscles.

The blood brought by the splenic artery is poured
directly into the spleen-pulp and comes directly in con-
tact with the cells and tissues there.

The spleen appears to be concerned in the production
of white corpuscles and in the elimination of worn-out
red ones.

The exact function of the spleen is not yet fully
known.

142 TIIIED BOOK OF PHYSIOLOGY

Blood. — Blood is a liquid which is composed of all
the substances needed to nourish and maintain the life
of the cells. It constitutes about one-thirteenth of the
weight of the body.

Blood has three great duties to perform : (1) to carry
to the cells of the body the food which is taken up from
the alimentary canal ; (2) to take oxygen from the air
which we breathe and distribute it to the cells ; (3) to
gather up waste matter, such as carbon dioxide, water,
and urea, and carry them to the excretory organs, where
they are cast out.

Blood is composed of blood-plasma, red, corpuscles, and
white corpuscles.

Blood-plasma. — Blood-plasma is the purely liquid
pait of the blood. About 90 per cent, of it is water.
In solution in the water are the proteids, which consti-
tute about 8 or 9 per cent, of the plasma, and the carbo-
hydrates, fats, and minerals, which form about 2 per
cent.

In addition to these is a small quantity of another
substance called fibrinogen, which causes blood to clot.

Red corpuscles. — After blood has passed through
the capillaries of the lungs it has a bright red coloi-.
The only part of the blood having this color, however,
is the red corj)uscle.

Red corpuscles are very small, circular discs, whicli
are concave on both sides. They are about saVo i'^^'l^ ^^
diameter and one-fourth as thick. It has been calcu-

CIKCULATIO.N

14:5

lated that tliere are 5,000,000 of Uhmh in a drop of blood
as larj;:e lus a ])inhrad. When only a lew are s(M'n lliey
are faintly red, but a great number
tojjether give a deep- red coh)r.

Fig. 71 shows the appearance of
human bhxxl when it is spread ex-
ceedingly thin under a compound
microscope.

Hemoglobin. — The function Fig. to— Red eor-
of the red corpuscle is to carry P"^^^^^- «, «, ;^ ""'nber

joined ; 6, 6, side view ;

oxygen out from the lungs to the ^^ ^iew of edi^e.
tissues of the body. It is made up

of a fine, spongy framework called the stroma, in the
meshes of which is a substance called hemoglobin.

Fig. 71. — lilnod .-i.-t-u uudfi a luicrctsuupe.

This substance is the most important part of the cor-
puscle. It is a proteid substance and contains iron. Its
great value lies in the fact that it will readily combine
with oxygen \n the lungs, and then, floating in the

144 THIET) BOOK OF PHYSIOLOGY

plasma, will carry the oxygen uiit to the tissues aud give
it up to them.

The hemoglobin is red when it is oxidized, but as soon
as it loses the oxygen it turns purple. Hence the differ-
ence in the color of blood before and after passing
through the capillaries of tissues.

Origin of red corpuscles. — Red corpuscles per-
form their part for a certain length of time, and when
worn out are brought, it is thought, to the spleen, where
they are disintegrated. Xew ones must then he set
adoat at some point in the body. This appears to be
done in the red marrow of the bones, for at that place
are found colored cells with a nucleus, and from them
appear to come the unnucleated discs called the red
corpuscles.

White corpuscles. — White cori^uscles are masses
of protoplasm with one or more nuclei. They are usu-
ally larger than red corpuscles, but are not nearly so
numerous. When at rest they are sx^herical in form, but
are capable of assuming a great variety of shapes, very
much like the amoeba described on page 21.

White corpuscles are carried along by the blood, but
are not confined by the blood-vessels, for they can jDass
out through the walls into the tissues when necessary.

Function of white corpuscles. — White cor-
puscles move about in the blood and through the tissues
of the body, apparently without anything to do, but
alwavs on the lookout for somethins: to do.

CiUCULATloX 145

They have l)eeii called the scavengers of the lK)dy, be-
cause if they meet any foreign substance they at once set
a]>out to remove it.

The foreign matter is taken into their own bodies and
dissolved or carried out to the surface. This is often
done at the sacrifice of their own lives to save the
body.

When tht* skin or mucous lining is cut or l^roken,
germs of disease will lo^ige there and begin to multiply
and feed on the tissues. When this happens, the white
corpuscles collect about the spot in great numljers and
attack the invading germs.

In such a case the white corpuscles are like a standing
army called upon to repel an invasion. If the army is
strong, a.s it is in good health, it usually comes off victo-
rious. Many of the corpuscles, however, must sacrifice
themselves in the contiict, and the pus in a wound i» a
mass of their dead bodies.

Blood-clots. — While the blood is in the living body
it is a thin liquid. But as soon as any is allowed to
escape it becomes thick, and forms the blood-clot. After
blood has stood for an hour or more the clot shrinks
in size, and a yellow liquid called serum runs from it.
Serum is just like plasma, except that the fibrinogen is
wanting. (See page 142.)

The clotting is due to the fibrinogen, which, for some
cause unknown, is changed into a great number of inter-
lacing fibres (fnWedJibrin.

The threads of fibrin gradually contract and gather

10

146

THIED BOOK OF PHYSIOLOGY

up, as in a net, all tlie corpuscles and squeeze out the
serum. This operation is called coagulation.

Fibrin can easily be separated if some fresh blood,
secured at the slaughter-house, be whipped with a bun-
dle of twigs. The fibrin will adhere to the twigs, and
can then be washed and examined.

The circuit of the blood. — After this study of the
various organs of circulation and their function, we are

ready to follow the blood

A

B

in its circuit through the
body.

Since only pure blood
is ready for distribution,
and the left ventricle of
the heart is the chief
agent in sending it out,
the proper place to begin
the circuit is at the left
ventricle of the heart.
This cavity, as we have
learned, is surrounded by very heavy muscular walls
capable of hard work. When filled with red blood, the
muscle-fibres shorten, thus closing the cavity and forcing
the blood out through the semilunar valves into the
aorta. This great artery communicates by numerous
branches to every tissue of the body.

Fig. 72. — Section through the
ventricles of the heart. A^ when
ventricles are filled with blood ; B^
just after contraction.

In the arteries. — The walls of the arteries are com-
posed in part of elastic tissue. The left ventricle forces

CIRCULATION 147

a quantity of blood into them at every beat. Thus the
arteries are kept so full that their elastic walls are
stretched. We can now s«*e the use of the semilunar
valves to keep the blood in the aorta until the left ven-
tricle can fill up again. The arti^ries thus exert a steady
pressure upon the blood within them.

Pulse. — New blood is forced into the aorta, which is
already full and distended. This causes a wave or j;w/«e
to pass over it. The pulse may be felt at 5iny point
where the artery comes close to the surface. Blood
passes through the large arteries at the rate of about one
foot per second ; but it is not the rush of blood that causes
the pulse.

The fresh ventricle-full of blood causes a sudden en-
largement of the aorta at the point where it enters, and
it is this distention which travels as a wave, or i^ulse,
along the artery.

Control of quantity of blood in an artery. —

One of the coats of the wall of an artery is composed of
muscular fibres which pass around the artery. When
these contract they make the artery smaller, and when
they relax they j)ermit the elastic tissue to stretch, and
the artery may become larger. In this way the quantity
of blood which may flow to any part of the body can be
regulated.

The action of these muscles is under the control of the
sympathetic nervous system, as will be explained later.

The flow of blood is not under control of the will, but

148 THIED BOOK OF PHYSIOLOGY

Fig. 73. — Scheme showing the circulation of the hlood. RA^ right
auricle; BV, right ventricle; PA, pulmonary artery; L, capillaries
of lungs ; PV, pulmonary vein ; LA, left auricle ; LV, left ventricle ;
AO, aorta; Sc, Sc, subclavian arteries; c,c, carotid arteries; A, A,
capillaries of arms ; 77, capillaries of head ; CA, coeliac artery ; HA,
hepatic artery ; SA, splenic artery ; GA, gastric artery ; G, capillaries
of stomach ; Sp, capillaries of spleen ; PV, portal vein ; Li, capil-
laries of liver; HV, hepatic vein; MA, mesenteric artery; I, capil-
laries of intestines ; MV, mesenteric vein ; RA, renal artery ; K, 1,
capillaries of Malpighian bodies of the kidneys ; K, 2, capillaries about
the tubules of kidneys ; RV, renal vein ; LE, capillaries of lower ex-
tremities ; A VC\ ascending vena cava ; D VC, descending vena cava.

ClJiCULATlOI^

149

150 THIRD BOOK OF PHYSIOLOGY

certain kinds of emotion may result in such a contraction
of the arteries carrying blood to the head that the face
may become very pale, and fainting may result from lack
of blood.

Other kinds of emotion may cause the muscles to relax
and a large quantity of blood will come to the face,
causing blushing.

Exposure to cold will cause the arteries near the sur-
face to contract, and so the skin becomes white. Warmth
will relax them, and a ruddy color comes with an in
creased supply of blood.

Blood in the capillaries.— The arteries have di-
vided into countless small branches, and the blood in a
steady stream, and without any pulse, now leaves them
and enters the capillaries. Here the exchange takes place
between the blood and the tissues. The nature of the
exchange will depend on the contents of the blood and
the nature of the tissue through which the capillaries
pass. In the liver one kind of exchange will occur ; in
the kidneys, another kind ; in the villi, the lungs, the
muscle, the bone, and the skin, still other kinds. In all
cases, however, the exchange occurs through the walls
of capillaries.

Systems of circulation. — There is but one great
system of circulation, for the blood which leaves the left
ventricle of the heart will return to the same point again.

For convenience, however, the circuit may be divided
into several systems depending on certain marked

CIIM'IU.ATTON 151

changers effected in llic blood at various points in its
ciiTuit.

The most important divisions are tlie systeviic, the
poriol, the renal, and the pulmonary.

Systemic circulation. — Blood is supplied by the
arteries to the cells of every tissue of the body. This is
the general or si/stemic circulation. By this system blood
is carried to the capillaries about the cells of muscle,
bone, nerve, and all other tissues. In these capillaries
the blood loses the materials needed for the repair and
growth of the cell, and for energy. These pavSs by os-
mosis into the lymph about the cell. At the same time
the blood gains, by osmosis into the capillaries, carbon
dioxide, water, and urea.

Distinction must be made between the systemic circu-
lation, where blood is supplied for the benefit of the cells,
and the other kinds of circulation, where blood is forced
through capillaries of various organs that it may be
modified or purified. All these latter changes are for
the benefit of the systemic circulation.

The portal circulation. — The blood which is
furnished by the systemic circulation to the stomach,
intestines, pancreas, and spleen supplies the needs of
the cells of those organs, and also furnishes materials
needed for the juices used in digestion. In exchange for
these, the blood takes up a supply of food which has
passed from the digestive tract into the capillaries of the
stomach and intestines.

152 THIED BOOK OF PHYSIOLOGY

The blood is now gathered up from these four organs
by minute veins which unite into one large one called
the portal vein. Through it this blood is conducted to
the liver, where it passes through a second set of capil-
laries and is changed 1u a manner explained on page 129.

This is the only place in the body where a vein sup-
plies blood to capillaries.

Renal circulation. — Two branches of the ab-
dominal aorta carry blood to the kidneys. Some small
branches of these are made to supply blood to the tissues
of the kidneys, but most of the blood passes through
another system of bodies, to be described later. The
blood here loses a great deal of water and urea. Just
after the blood passes through the kidneys it is probably
purer than at any other point in its circuit.

In the veins. — After any portion of blood has
fulfilled its purpose in circulation, it is gathered up and
brought back to the heart by the regular system of veins.
The color of the blood is now a purple, because that is
the color of hemoglobin when it loses its oxygen.

Pulmonary circulation. — Although the blood

has returned to the heart, it is bj^ no means back to our
starting- place at the left ventricle. It has only reached
the right heart.

The superior and inferior vena cava now pour the blood
into the right auricle, whence it flows into the right ven-
tricle. The walls of the right ventricle now close in

CIRCULATION 153

upon it, slnittiii^^ tlic Iricnspid valve and forcing it out
into thvi puhnonari/ aftcnj and on to the lungs.

When the blood started out. from the left ventricle it
was a bright red, showing that the red corpuscles were
loaded with oxygen. When it passed through the capil-
laries of the systemic system the oxygen was given up to
the cells there, and the color of the corpuscles changed to
purple.

The pulmonary artery is the only artery that carries
purple blood.

In the lungs an important exchange is made. Blood
gives up carbon dioxide, water, and certain organic im-
purities to the air in the air-sacs, and takes in return a
fresh supply of oxygen.

The blood is now a bright red again and is conducted
by the pulmonary veins to the left auricle. Thence it
flows into the left ventricle. The circuit is now com-
plete.

Heart-beats. — ^The two auricles contract and relax
together. Likewise the two ventricles. While the ven-
tricles are contracting the auricles are filling, and as
soon as the ventricles relax the auricles contract.

As explained before, the auricles are hardly more
tlian small reservoirs to hold blood while the valves
below them are closed. Their contraction is but feeble.

The alternate contraction and relaxation of the ven-
tricles may be felt at a point where the apex of the
heart is close to the chest-wall. This point is to the left
of the sternum, between the fifth and sixth ribs.

154 THIRD BOOK OF PHYSIOLOGY

Sounds of the heart. — If the ear be pressed tightly
upon the point directly over the apex of the heart, two
distinct sounds are heard during each beat. They are
similar to the sounds made in pronouncing the syllables
loob dup. The sounds are caused by the action of the
valves. The mitral and tricuspid valves close at the
same time, producing the sound loob. When the ven-
tricles relax, the l)ack pressure of the elastic aorta sud-
denly closes the semilunar valves, causing the sound
(iTq).

Work of the heart. — The heart of an adult beats
about seventy-two times every minute. The ventricles
have to force the blood into the arteries against a strong
back pressure, and they must continue to do this about
sevent^^-two times a minute during life.

As a consequence the heart is the hardast- worked
organ in the body. If a strong man would carry upon
his shoulder a weight of 200 i^ounds to the top of a
mountain 2000 feet high, he would have done no more
work upon the weight than the heart does every day
upon the blood.

Rest and nourishment of the heart. — After
each contraction of the heart there is a period of relaxa-
tion and rest which is even longer than the time of
contraction.

Thus the heart rests more than half the time, though
each period of rest is short.

The muscles of the heart are well supplied with blood.

CIRCULATION 155

The first branch from the aorta, just above the heart, is
the coronary artcrii, which carries blood directly to the
imiscles of the heart and supplies the cells with food.
The heart gets no nourishment from the blood while it is
in the auricles and ventricles.

Hygiene of circulation. — A x^igorous circulation
oi good blood is sure to result in good health and a rapid
recovery from temporary illness or accidental injury.
But good blood is possible only under the four con-
ditions already pointed out. (1) A plentiful supply of
nourishing food must be taken into the blood-current
from the alimentary tract. (2) The blood must be sup-
plied with an abundance of oxygen from the air in the
lungs. (3) The kidneys, liver, lungs, and other excre-
tory organs must take from the blood the waste products
and other substances no longer of use in the blood. (4)
The nervous system must be able to control the tlow of
blood and to direct it to the point where it is most
needed.

Effect of exercise on the circulation. — It is
observed that exercise increases the rapidity of the
heart-beats. This results in a more rapid flow of blood,
deeper breathing, and, in time, hunger. Blood is sup-
plied in larger quantity to any part of the body that is
active. An exercise that calls into action every part of
the body will quicken the flow of blood through the en-
tire system. Such exercise frequently repeated tends to
build up a stronger body.

156 THIED BOOK OF PHYSIOLOGY

Contraction of the muscles and movements of the
body also assist circulation in a mechanical way. The
veins and lymphatics are supplied with numerous
valves, so that any pressure upon them will always push
the liquid within them towards the heart, for the valves
will prevent any movement in the opposite direction.

Since many veins and lymphatics lie near the surface,
any tight bands or clothing will seriously impede the cir-
culation at any time, but particularly during exercise.

Colds. — The cause of ^^ colds" is not certainly known,
but they appear to be closely connected in some way with
the circulation of the blood.

An exposure to cold weather, to wet, or to drafts of
air may contract the blood-vessels on the surface of the
body and bring about a condition called a cold. What-
ever may be the exact cause, it is known from expe-
rience that colds may be avoided by maintaining a vigor-
ous circulation by exercise and deep breathing. ^Yoolen
clotliing assists in preventing sudden changes in surface
temperature.

Bleeding from a wound.— Y^^hen a vein is punc-
tured, the blood oozes out in a steady stream because it is
not under pressure. The bleeding may be stopped by a
bandage on the side of the wound farthest from the
heart.

When an artery is severed, the blood issues in a stream
with considerable force, which increases with each beat
of the heart. Such a wound needs immediate attention.

riRCULATloN 157

The bleeding may be temporarily checked by a tight
bandage on the side of the wound towards the heart.
The bandage must be tight, as the arteries usually lie
deep in the tlesh.

Effect of alcohol on the heart.— Under some
conditions the heart may beat faster after a person takes
an alcoholic drink, but such quickened action is not due
to any strengthening action of alcohol on the heart itself,
as was once supjiosed. It is due rather to distuibance
of the nerves in other parts of the bod}-.

The mere act of swallowing or sipping cold water will
increase the beating of the heart, and so will swallowing
anj' hot, biting substance, as pepper or ginger tea, be-
cause of the sensitiveness and complex relations of the
nervous system. AVhen the heart beats faster after taking
an alcoholic drink, the result is chiefly due to such dis-
turbance of the nerves, for when care Ls taken to avoid
all irritation of the throat and stomach in giving an alco-
holic drink, little or no change in the heart-beat occurs.
Muscular action also makes the heart beat faster, and so
in all exact tests of this kind the person taking the alco-
hol is kept quiet and away from the company of others.
Under such precautions it is seldom that any change in
the heart's action occurs, showing that the old notion
that alcohol is a stimulant or a source of strength for the
heart is false.

Instead of being a benefit to the heart, alcoholic drinks
are a fruitful source of heart disease. German physicians
have begun to observe that in cities where the most beer

158 THIRD BOOK OF PHYSIOLOGY

is drunk they have the largest number of cases of heart
disease.

Alcohol and the arteries. — It has been explained
that the supply of blood through the arteries is regu-
lated by muscles under control of the nervous system.
A large dose of alcohol, such as is contained in a drink
of whiskey, will disturb the controlling power of the
nervous system and allow the arteries to relax, and warm
blood flows freely out to the surface of the body.

Thus the heat can rapidly radiate and the tempera-
ture of the whole body is reduced.

For this reason those who drink alcoholic liquoi^s suffer
more and will be more quickly frozen from long exposui^e
to cold.

Alcohol and oxygen. — The oxygen forms only a
loose chemical combination with the hemoglobin of the
red corpuscle. Alcohol has a strong afl&nity for oxygen,
and. when mingled with the blood, robs the corpuscles
of the oxygen which should go to the tissues.

YThile the oxidation of the alcohol will produce heat,
it is at the expense of the bodily health and vigor.

Tobacco and the circulation. — Experience shows
that the nicotine of tobacco is injurious to the organs of
circulation, particularly to the heart.

The heart-beat often becomes irregular and spasmodic.
It is claimed by reputable physicians that much of the
heart- trouble and heart-failure is caused by the use of
tobacco.

CIRCULATION 15!)

Tobacco is particularly harniful lo voulli uiidri- lliirty
years of a«;e.

QUESTIONS FOR KEVIKW.

1. Why is circuhition lu'ct'ssary?

2. How (Iocs food get from the stomach and iuteHtiiU'H into the
blood ?

3. What is tlic use of glycogen?

4. Give three functions of the liver.

5. Name the organs of circulation.

6. What is the heart? Its size, shape, and position.

7. Describe the pericardium.

8. Describe the cavities of the heart.

9. Name and locate the valves of the heart.

10. Make drawings to show the manner of action of the valves.

11. IMake drawing and trace the course of the blood in the heart.

12. What are arteries ? Describe their coats.

13. What is the function of the pulmonary artery ?

14. Describe the course of the aorta.

15. What are capillaries? What does the word mean?

16. What is the location and size of capillaries?

17. What is the function of the capillaries?

18. How does food get from the capillaries to the cells?

19. How is the blood collected again ?

20. Describe the structure of a vein.

21. What kind of valves in veins? How may their location be
observed in surface veins?

22. What is the function of the lymphatics ?

23. Describe the two large lymphatic ducts.

24. What are " waxen kernels" ?

25. What is the construction of the lymphatic nodes? What
their function?

26. Describe the spleen.

27. How much blood in a man who weighs 200 ptjunds?

28. State three important uses of blood.

160 THIED BOOK OF PHYSIOLOGY

29. What is the composition of blood ?

30. Describe blood-plaaraa.

31. Give a full account of the red corpuscles.

32. What is the function of hemoglobin ?

33. What is the origin of the red corpuscle ?

34. Describe the white corpuscle. AVhat is its origin ?

35. Of what use is the white corpuscle?
35. What is fibrin ? How is it formed ?

37. Beginning at the left ventricle, trace the blood in a complete
circuit through the body. (It will take some time to prepare and
answer this question, but it should be done. The answer will in-
clude all matter from page 146 to 153, and should be prepared by
each pupil for one continuous recitation.)

38. Explain the beating of the heart.

39. Describe the sounds of the heart.

40. How much work does the heart do?

41. What is the coronarv artery?

42. What four conditions will supply good blood?

43. How does exercise affect circulation?

44. What is the effect of alcohol on circulation ?

45. How does blood flow from a cut in an artery? How from a
vein*? Why?

40. What should be done when an art«ry is severed?
47. On which side of an artery must pressure be applied to stop
bleeding? Why? How in case of a vein ? Why?

EXPERIMENTS.
Fibrin. — Secure a quart of fresh blood at the slaughter-house. Take a
stock of broom or a bundle of fine twigs and beat it in the manner of beating
eggs. The fibrin will cling to the broom, and the red corpuscles adhering to it
can be rinsed off with water. After the fibrin i.> taken out, the remaining part
will not coagulate, however long it may stand.

Serum. — Allow some fresh blood to stand for a time in a glass jar. A clot
will form in the centre, and a yellowish liquid, the serum, will .separate from it.

("IKcn.A'noN h;i

To show the pulee at the wrist. -Secure u .small piccr (if mirror
alHuit V| inch s(iiuire, iiiul fa.sten it with wax <»iito the point in the wri.st where
the i>ulse i.s mo.st plainly felt. Re.st the hand near a window in such j>osition
that the sunlight will be reflecte<l to the ceiling of the room. At every beat of
the heart the bright spot on the celling will move back and forth through a ff)ot
or more.

To illustrate the principle of the pulse.— Connect one end (..f a
heavy rubber tube to a water-tap. Turn the water on, and then close the other
end of the tube until water i.s.sues in a .«<mall stream under pressure. The tube
will be stretched and rigid like a large artery. Now suddenly open and close the
water-faucet, and the i>ulse aloyg the rubber tube may be felt each time fre-sh
water is admitted.

Examination of the heart.— Secure from the butcher an ox heart.
Carefully examine the exterior and the number of tubes. Dissect and examine
the cavities. Search for the valve.<;. Notice the thickness of the walls.

To examine red corpuscles.-Puncture the skin of the thumb with a
needle and let out a small drop of blood. Spread the blood on a slip of glass,
and examine under a compound microscope. The blood must be only a very
thin smear on the glass, or the separate corpuscles will not be seen.

11

CHAPTER XI

RESPIRATION

The ocean of air. — The air is a great ocean of gas
which forms the outer layer of the earth. Air moves with
the earth, and is a part of it. Nothing is outside the

Fig. 74. — The three envelopes of the earth. Man's abode i= at the
bottom of the outer haver.

earth unless it is beyond this layer of air. Man, properly
speaking, lives beneath the surface of the earth. His
natural place is in the plane where the ocean of air rests
upon the oceans of water and the land.

162

RRSPI RATION 163

Tlie deptli of tlw mimmhI ocean is not known, for it luis
no definite snrface at tlie top, but shades off into lighter
and ligliter air until none exists. It is very probable
that some air exists as hi«j:h as 1000 miles al)ove the lands
and watei*.

Since air has weight, tin; layer next to the land is
pressed upon with considerable force. At sea level tlie
pressure is about 14.7 jKninds on every square inch of
surface. Since air, like all gases, is very compressible, it
is quite dense at the bottom. Each cubic foot of air at
sea level will weigh 1.28 ounces.

Man and other land animals are fitted to live in this
lower dense layer of air.

The air is composed of several gases which are mixed
together by diffusion.

The most important one is oxygen. Oxj^gen is the
breath of life, and man is dependent upon it for every
minute of his existence.

The relation of man to this medium in which he must
live, forms the topic of discussion in this chapter.

What respiration is. — Eespi ration is a process by
which an exchange of gases takes place between the air
and the tissues of the body. The oxygen, taken from the
air in the lungs, is carried by the red corpuscles to the
cells of the bod}'. The blood takes up in exchange the
carbon dioxide and other tissue waste, and convej^s them
back to the lungs, where they are given out to the air.

This broad definition would necessitate oui' tracing the
air from the nostrils to the cells of the body and back again.

164 THIRD BOOK OF PHYSIOLOGY

The part of the process from the lungs to the cells is
called internal respiration, and is tieated here under the
subject of the circulation of the blood.

The first part of the process — from the nostrils to the
lungs and return — is called external respiration, and is the
proper subject of this chapter.

Why respiration is necessary.— Many very
small animals have no lungs and no blood, and yet their
life, like that (»f man, depends on their taking food and
having it combine with oxygen of the air. They are so
small, however, that they do not need special organs.
They absorb their food and air through the surface of
their bodies.

In man and all higher animals the body is large, and
most of the cells lie far beneath the surface. For this
reason man needs special apparatus to carrj^ both the
food and the oxygen to the cells.

What oxygen does for the ceUs. — Roughly
speaking, it may be said that oxygen does for the body
what a draft of air does for the steam-engine.

In the boiler of the engine the oxygen combines with
the burning coal, producing heat and energy, while
carbon dioxide and water pass up the chimney as waste
products of combustion.

In the body the oxygen combines with the food in the
cell, producing heat and energy, while carbon dioxide
and water pass out at the lungs as waste products of
combustion.

RESPIRATION 1(;5

Th<' cell a|)p«':iis to liave tlie ability to ston* uj) hotli
food aiul oxygen to a limited extent, and tln-n have
them unite in combustion when eni^-oy and lieat are
needed. Practically all such combustion takes place hi
the cells and under the control of tlie nervous system.

Organs concerned in external respiration. —

The respiratory tract, through which air is brought into
close contact with the blood in the luugs, consists of the
nostrils, i)liarijnx^ Jaryrix, trachea, bronchi, bronchial tabes,
infundihula, and air-sacs. The i^assage of air in and out
through this tract is brought about chiefly by movement
of the rihs and diaphragm.

The nostrils. — -The nostrils are lined with a mucous
membrane, which is always kept moist with a secretion
of uiucus.

Particles of dust and minute germs are lodged on the
sticky mucus, and thus the air is strained on its entrance
to the respiratory tract. The mucous lining is under-
laid with a net-work of blood-vessels, and by this means
the air is also warmed in the nostrils.

Larynx. — From the nostrils the air passes into the
pharynx, wliicli has already been described as a box
with seven openings.

One of these openings is the voice-box, at the top of
the windpipe. It is called the larynx.

Across the top of the larynx are stretched the mem-
branes called the vocal cords. The opening between the
vocal cords is the glottis. The epiglottis stands ready to

166

THIRD BOOK OF PHYSIOLOGY

close the glottis whenever anything is swallowed, but at
all other times the glottis is open. The larynx is con-

FiG. 75.— The larynx. E, epiglottis; A, " Adam's apple. "

A

B

Fig. TG. — Vocal cords. V F, true vocal cords ; P F, false vocal
cords; L, epiglottis. A^ cords open, as in breathing ; B, cords drawn
close together, as in speaking and singing.

structed of cartilage. '^Adam's apple" is a projection
of one of the cartilages of the larynx.

RESPIRATION

167

The trachea. — The trachea, or windpipe, is a tube
about one inch in diameter and extendin^^ from tlie
larynx downward for a distance of al)out four and one-
half inches, when' it divides into two l)ranches called
the bronchi.

Fig. 77. — Tracheu and bronchi showing the rings of cartilage. T to T,
trachea ; LB, left bronchus ; RB, right bronchus.

The trachea is kept open by some sixteen to twenty
incomplete rings of cartilage of about the shape of a
horse-shoe. The incomplete part of the rings is on the
posterior side, where the tube is completed bj^ a connec-

168

THIED BOOK OF PHYSIOLOGY

tive tissue. Against this part lies the oesophagus.
While food is being swallowed, the windpipe is more
or less closed by the pressure upon its soft side.

The whole tube is lined with mucous mem])rane whose
surface-cells are ciliated epithelium, (See page 25.)
The cilia are an interesting example of provisions within
the body for the care and protection of important or-
gans. Cilia line nearly the whole respiratory tract, be-

FiG. 78. — Tiifundilmla and air-sacs.

ginning in the nostrils. Xone are found in the air-sacs.
They are not hairs, but minute projections of the cell
material which wave constantly back and forth. Their
movement is more rapid in a direction towards the outlet
of the air-passages, and thus any objectionable sub-
stance in the lungs or windpipe is slowly pushed up to
the throat, where it may be coughed up.

The bronchi have a structure similar to that of th^

RKSIM RATION

169

windpipe, and in fact are onlj- a continuation of the
windpipe in two branches.

The right bronchus is about one inch long, and the
left one twice as long, but of smaller diameter.

Bronchial tubes. — At'ier the bronchi enter the
lungs they are called bronchial tubes. These tubes divide
into smaller and smaller branches, and are distributed to
every part of the lung tissue. They finally end in coni-
cal expansions called infundibula, which are covered with

Fig. 79.— The lungs.

clustei"S of air-sac6 having somewhat the appearance
shown in Fig. 78.

The lungs. — The lungs are the most important or-
gan of respiration. They are two in number, the right
and left, and they occupy most of the space within the
walls of the thorax. The weight of the two lungs to-
gether is about forty to fifty ounces, the right one being
somewhat heavier and larger thau the left one.

170

THIRD BOOK OF PHYSIOLOGY

Lung tissue is composed of the numerous bronchial
tubes with their terminal air-sacs ; a net- work of ar-
teries, capillaries, veins, and lymphatics ; and an abun-
dance of elastic tissue binding all together. It is the
least dense of all the tissues of the body, being only
about one-half as heavy as the same volume of water.

The walls of the air-sacs are very thin, and blood

Fig. 80. — Diagram showing pleura. i2, right lung; X, left lung;
e, entrance of bronchi and blood-vessels ; i, part of pleura which ad-
heres closely to surface of the lung ; o, part of pleura which adheres
to chest' wall. The space between i and o is called the pleural cavity,
though the two are in contact ; D, diaphragm.

capillaries lie just outside. The sacs are very small, but
exceedingly numerous. The total number has been esti-
mated at between five and six millions, and their total
area as twenty square feet. When thej^ are filled with
air the exchange of gases readily occurs.

The pleura. — Each lung is enclosed in a serous
membrane called the pleura. The pleura adheres tightly
to the lung, and completely covers it except at the point

RESPIF^\TION 171

where the bronchi and blfKul tnbes ont^r it. At this
point the pleura turns back, iis shown in t lie diagram,
and lines the walls of the thonix. Thus each pleura is
a closed sac, and there is no communication from the
one to the other.

The space between the pleura on the lungs and that
on the walls of the thorax is called the pleural cavity. In
fact, however, there is no space between, but the two
linings press against each other. Since they are very
smooth and are kej^t moist by secretions, they glide uj^on
each other without friction when the lungs move as in
breathing.

Inhalation. ^ — It is a principle of physics that a body,
free to move, will always move In the direction of the
greater force. Air is no exception to this law. If we can
produce a condition in the lungs such that the pressure
of the air out through the windpipe is less than the pres-
sure inward, air will be forced into the lungs. This con-
dition is brought about chiefly ])y movements of the ribs
and diaphragm.

Action of the ribs. — The ribs form a true joint
with the dorsal vertebrae and pass around the chest to
the front, where they (all but the two pairs of floating
ones) are joined by their cartilaginous ends to the
sternum. Eibs do not pass straight around the chest,
but droop considerably in front. The contraction of
muscles will raise the sternum and elevate the front end
of the ribs. This will increase the capacity of the chest,

172

THIRD BOOK OF PHYSrOLOGY

and air will rusli into the elastic lungs and expand them

till they fill the chest as before.

The ribs also droop at each side
of the chest, and between them are
intercostal muscles, which by con-
traction elevate the ribs, and in this
way also the chest is enlarged. (See
experiment at end of the chapter.)
This may be illustrated by the de-
vice shown in Fig. 81. The board,
B, represents the backbone 5 the
rings, E, the ribs : and the cylinder,
the lungs.

In the first position the rings just
permit the cylinder to pass through
them. In the second position, where
the rings are elevated, there is room
for a larger cylinder or for this one
to expand, as the lungs would do.

Action of the diaphragm. —

The diaphragm has already been
described as the dome-shaped par-
tition between the thorax and the
abdomen. The top of the dome is
formed of tough connective tissue,

the enlargement of tli-. ^^^^ which layers of musclc radi-
chest bv elevation of the

j.-^g ^ ate to the sides of the thorax.

When these muscles contract, the
diaphragm is flattened. Thus the contents of the abdo-

^Mm

Fig. 81. — Illuatratini

RESPMJATION

173

men are jmslied down and the chest is enlarged, in the
diagram. Fig. 82, if A. and B represent tlif chest and
abdomen respectively, it is plain
that, if the <liaphragni between
them be flattened, the cavity A will
be enlarged and B will be decreased.
The air is not drawn in. The en-
largement of the chest i)roduces a
partial vacuum there, and air is
pushed in by atmospheric pressure.
As soon as the density of the air
within is equal to that without, the

flow of air will cease. ^ ^ ^.

Fig. 82. — Diagram

illustrating action of
Exhalation. — Any increase of the diaphragm.
pressure within the lungs will tend

to cau.se an outward flow of air called exhalation. Ordi-
nary exhalation is accomplished without any muscular
effort. The elastic tissue of the lungs alone tends to expel
the air, and when the ribs, diaphragm, and abdominal
organs settle back to their natural position, the capacity
of the chest is diminished.

For forced exhalations, as in loud speaking and singing,
coughing, and sneezing, other muscles are called into play.
Strong abdominal muscles force the liver and stomach up
against the diaphragm, thus decreasing the chest and
driving the air out of the lungs. Also a set of intercostal
muscles upon contraction lower the ribs, as explained in
the experiment at the end of this chapter, and in that
way also the chest is made smaller.

174 THIRD BOOK OF PHYSIOLOGY

Capacity of lungs. — Lungs of average size will hold
about 330 cubic inches of air. In ordinary quiet breath-
ing only about 30 cubic inches are inhaled at each in-
spiration. Thus only about one- tenth of the available air-
space of the lungs is ordinarily used. By an effort one
may breathe in 130 cubic inches of air, and then breathe
out 230 cubic inches. About 100 cubic inches of air
always remains in the lungs.

Quantity of air breathed. — The quantity of air
breathed varies greatly at different i^eriods of life, and in
various states of the body as to health and exercise. The
adult will, on an average, breathe about eighteen times
every minute. Thus he would inhale 32,400 cubic inches
of air every hour.

^Vben at vigorous work or exercise he will inhale more
than twice that amount, for his food must be rapidly oxi-
dized to produce the necessary amount of energy. The
weight of the air which a man breathes is seven or eight
times that of the food eaten.

Composition of air. — AVater is composed of hydro-
gen and oxygen in the proportion of two to one i^arts by
volume.

This is always so, because water is a chemical com-
pound.

Air, however, is only a mixture of several gases, each
gas being free.

The composition, therefore, may vary, but the quantity
of the essential gases is quite constant.

Outdoor air contains nitrogen, oxygen, water vapor,

RESPIRATION 175

argon, carbon dioxide, ozone, traces of otlMT g;us<'s, i)arti-
cles of dust, and living germs.

Air i)roper is composed of five gas(^s in ahoul tli<; ])i()-
portion named below.

PER CENT.

Oxygen 20.1H)

Nitrogen 78.()()

Argon \.m

Carbon dioxide 0.'j

Ozone 01

Oxygen and ozone. — Oxygen is the i^art of the air
upon which we are most dependent. It is exceedingly

Fig. 83. — Photograph of the combustion of an iron wire in a spoon.
The spoon can he dimly seen. Below it U the flame of a Bunsen
burner. The white lines show the paths of particles of burning iron.

active in entering into chemical combinations with other
substances. Its activity may be shown in the manner

176 THIRD BOOK OF PHYSIOLOGY

represented in Fig. 83 (see experiment iit end of chap-
ter), where it is rapidly forming a chemical combination
with the material in an iron wire.

Ozone is a concentrated kind of oxygen, and, though it
forms but a small per cent, of the air, it plays an imj^or-
tant part in keeping the air pure.

Nitrogen and argon. — Xitrogen and argon are very
inert gases. Until recently they were considered as one
gas. Both are important substances and are necessary
to life, but they are only passive agents in respiration.
Oxygen cannot be breathed in a pure state, but must be
diluted with about four times its weight of nitrogen and
argon.

Carbon dioxide. — Carbon dioxide exists in the air
in only small quantities, and yet it is essential to the life
of plants and, indirectly, to the life of all animals. It is
one of the essential foods of the vegetable world.

Every green leaf, while the sun is shining upon it, is
busy making starch by a chemical union of water and
carbon dioxide. The leaf gets the water from the sap,
and the carbon dioxide from the air. For every mole-
cule of starch thus made, twelve atoms of oxygen are set
free into the air.

The chief sources of carbon dioxide are the breathing
of animals and the burning of fuel.

An adult at work will breathe out one cubic foot of
carbon dioxide e^'er3' hour.

The burning of a ton of coal will give off about 67,200
cubic feet of carbon dioxide.

RESPIKATION

177

For tivery 100 cubic feet of fuel gas consumed, 200
cubic feet of caibon dioxide are given to the air.

This gas is constantly being used up by the growing
vegetation, and a large (quantity of oxygen is set free.

Thus vegetables and animals arc dependent on each
other.

Changes iu inspired air. — The blood which is sent
by the right ^'('nt^icle of the heart to the lungs is purple
because the oxygen has been given up to the tissues. It

Fig. 84. — Showing changes in a green leaf, c, carbon dioxide ;
o, oxygen; A, water when in excess.

is also loaded with carbon dioxide in solution iu the
blood-plasma.

The two chief objects, then, in bringing the blood and
air close together in the lungs is that the blood may get
oxygen from the air and give out carbon dioxide to the air.

This exchange is made by osmosis through the thin
walls of the air-sacs and capillaries.

The raj^idity with which gases will diffuse may be
shown by holding a jar containing hydrogen over a
porous cup containing air.

12

178

THIED BOOK OF PHYSIOLOGY

k\^

i eap/7/

Fig. 85. — Diagram illustrating the exchange of oxygen and carbon
dioxide between the blood and air in lungs. 0, oxygen ; CO2, carbon
dioxide.

Fig. 86. — Ditfusinn through porous cup. (See description of experi-
ment at end of chapter. )

RESPIKATION 179

Till* hyilioo^en will piiss tli rough the walls of the cup
much faster than the air passes in the opposite direction,
as will be shown by the escape of bubbles from the lower
end of the tube. (See experiments at the end of this
chapter.)

The expired air is composed of about 15 per cent, of
oxygen, about 4 per cent, of carbon dioxide, 78 per cent,
of nitrogen, and 1 per cent, of argon. Thus a large
quantity of oxygen is* taken from the air and carbon
dioxide added to it, but other gases of the inspired air
are not sensiblj' changed.

Hygiene of respiration.— Breathing and eating
are the two most important things we do, as far as con-
cerns health and vigor of both body and mind.

Just as neither coal nor oxygen would be of any use as
a source of energy unless they could combine with each
other, so also our food and the oxygen must unite in slow
combustion within the body.

Just as it requires good fuel and a good draft of air to
maintain a hot fire, so it takes good food and good air to
furnish the heat and energy needed in a vigorous body.

How air becomes impure. — Pure air and proper
breathing are quite as essential as good food. Air in the
open country is pure because any impurities there will
be mingled bj' winds and air-currents with a great mass
of air.

Air in the streets of a crowded city is not so pure
as in the country.

180 THIRD BOOK OF PHYSIOLOGY

The most impure air is usually found in rooms, shops,
railway-carriages, and other enclosures where people
live.

The air in a close room may soon become unfit to
breathe. Every respiration takes oxygen from it and
adds carbon dioxide to it. A burning lamp is doing the
same. An oil-stove, however ^'odorless," is vitiating
the air in the same way.

In addition to the carbon dioxide, certain poisonous
organic substances are exhaled with each breath.

When such air is breathed over again, the amount of
carbon dioxide excreted by the lungs grows less and less.
This shows that the activity of the cells has diminished
because the proi)er supply of oxygen is not furnished.

Such a condition soon results in weakness, and makes
the body an easy prey to disease.

Ventilation. — Ventilation is a process by which the
air in an enclosure is removed and fresh air brought in
to take its place.

When the air contains over .06 per cent, of carbon
dioxide (from breath) it is unfit for breathing. The
carbon dioxide alone is not so objectionable, for one may
safely breathe air containing a much larger per cent, of
it. But along with carbon dioxide from the lungs always
comes a quantity of organic poisons, which are the chief
cause of impurity in the air of living-rooms and in halls
where people meet.

It is easy to determine approximately the quantity of
carbon dioxide in the air, and this can be taken as an in-

RESlMUATlOxN 181

dication of the quantity of other impurities if all came
from the lungs.

A lamp may give off more carbon dioxide to the air
than a man does in tlie same time, and yet not vitiate the
air as much.

The purpose of ventilation is to supply air in such a
condition that every inhalation will supply the proi)er
quantity of pure oxygen to the blood, and every exhala-
tion will remove a pro'portionate amount of waste.

Fresh air must be admitted into the room where i^eople
stay for any length of time ; otherwise the fire of life is
sure to burn low. Man does not have appetite for fresh
air as he has for food, but notice of bad air is given by
drowsiness, headache, inability to study, and pallor of
the skin.

The sense of smell will also serve as a guide to one
coming in from the fresh air.

To keep the air fit for respiration, 3000 cubic feet of
fresh air should be supplied to each person every hour.

Methods of ventilation.— Ventilation is ordinarily
an easy matter in summer time, when doors and windows
may stand open. But in cold weather, when the air in
the room nnist be kept warm, there is great danger that
the same air may be breathed over and over.

Many private houses and public buildings are venti-
lated with a constant stream of fresh warm air, which is
brought in from pure sources on the outside and passed
over a furnace or hot coils before it enters the room.

This plan may be more expensive than some other

182

THIED BOOK OF PHYSIOLOGY

methods, but if it is properly constructed and oj^erated,
it will save doctor bills, and will increase the earning
capacity of those who are thus supi:>lied.

Steam and hot-water radiators placed in a room will
heat the air and cause it to move about by convection
icithin the room, but will not provide ventilation.

..£^1.

m

. o o o o o o <

lOOoOOOOO o

OOOOOOOOOO oooooooocooo
DOOOOOOOOOOO.OOOOOOOOOOC

oooooooooooooooooooooo

Fig. 87. — Window arranged for ventilation.

A stove or fireplace connected to a chimney that
^'draws'' well will remove a considerable quantity of air
from a room^ and fresh air will come in through the
cracks at doors and windows. This, however, will not be
sufficient except for one or two persons.

A good plan, where special means of ventilation have

RESPIRATION 183

not been provided, is (o rais«i the lower siush of ;i window
a distance of three or four inches and place beneath it a
board or. better, a perforated zinc box. The zinc l)ox
shonld be about one inch thick, three inches wid(^, and
jnst long enough to fit in beneath the sash. The perfo-
ration in the two sides should not be opposite. In this
way fresh air will be admitted between the sash, and
other air will go out through the holes in the zinc with-
out causing a draft in any part of the room.

Sleeping-rooms need special care. It is better to sleep
in a cold room in winter time, for then the necessary
covers for the night will be needed at once on retiring,
and windows may be freely opened. Sound sleep is not
possible in bad air.

Good breathing. — Though one may be supplied
with fresh air, he may not get the full benefit from it
unless he breathes it to the blood in plentiful quantity.

Tight clothing about the waist displaces the liver,
stomach, lungs, and other organs. This not only gives to
the body a deformed appearance, but makes free respira-
tion impossible.

After all proper conditions are complied with, it is still
necessary for each person to make a business of breathing
for a short time each day.

This may be done in the country or park, on the i>orch,
or in a room before an open window.

A good exercise of this kind is one where the person
stands erect, expands the chest to its fullest capacity,
then, holding the breath, pushes with all the might with

184 THIRD BOOK OF PHYSIOLOGY

ODe hand against the wall for a few moments, stands erect
again, exhales, then fills the lungs once more and pushes
with the other hand.

This may be repeated till one is slightly dizzj'. In a
few days the exercise can be prolonged. Such breathing
will not only furnish warmth and vigor for a winter day,
but will greatly diminish liability to colds.

Dust in air. — The appearance of air gives but slight
indication of its fitness for breathing. Air always con-
tains a large number of
particles which are not vis-
ible to the naked eye ex-
^■■■:'\i->''Sj''^r^:/^:^- cept under special condi-

tions, as when a beam of
light is admitted into a
darkened room.

Fig. 88 shows some dust
particles as seen through
Fig. 88.— Particles of dust from a high-power microscope.

a living-room, magnified. rj.^^^^ ^^^ ^^^.^ ^ ^^^ ^^^^^

in the air of dwelling-rooms,
and consist of a variety of particles of dead matter as
well as living germs.

The particles are very minute, but exceedingly' nu-
merous. A careful count has shown that in country air
there are about 100,000 particles in everj^ cubic inch,
and in towns there are from 1,000,000 to 50,000,000 in
a cubic inch.

It is not possible to avoid all dust particles, and so

KESIMUATION 185

provision is iniide in the iiir-pussages to prevent their
accuniuhition in tlie hmgs, ;is lias already been ex-
plained.

Dusty air, liowever, should be avoided as far as pos-
sible, not only because the dust itself is objectionable,
but also because of the j^ernis of disease which are liable
to be i^resent in larger numbers when dust is plentiful.

Living germs in the air. — About one out of every
seven deaths in civilized countries is caused by consump-
tion of the lungs. This disease is aptly called the '^ great
white plague.'' In all cases it is caused by breathing
into the lungs the living germs which cause that disease.
There they multiply and destroy the lung tissue.

There is no danger of contracting ' ' consumi)tion, ' ' or
tuberculosis of the lungs, if the air is free from tubercu-
lar germs.

The careless spitting of a consumptive may result in
a spread of his disease to others. The sputum may dry
in the room or on the street, and then be blown about
with the dust. The germs, though dry, will live for a
long time in a dormant state. As soon as they fall upon
a spot where they can get moisture and food, they become
active and increase in number.

Old wall paper and carpets maj^ have, clinging to them,
many germs of this and other kinds. To sweep such
carpets, or dust such walls, only sets afloat the dust and
germs. The occupants of the room are then compelled
to breathe them, or the dust is allowed to settle upon
the books, chairs, tables, and clothes in the room, and

18G THIRD BOOK OF PHYSIOLOGY

will be afterwards stirred uj^ by every movement in the
room. Careful dusting with a moist cloth is good, but
is not sufficient.

Ordinary house-cleaning may remove the dirt which
can be seen, but such dirt is often the least objectionable
from a sanitary point of view. A room which has long
been in use as a living apartment cannot be cleaned
unless, in addition to the ordinary means, it be thoroughly
fumigated. This should be done at least once each year,
whether germs of contagion are known to be present or
not.

A formaldehyde generator used according to direc-
tions will effectively cleanse a room of disease germs,
without injury to the furnishings in the room and with
little expense or inconvenience.

Effect of alcohol. — Every one is liable to disease at
all times. Good health depends largely upon ones ability
to resist disease. Good health may be defined as that
condition in which the oxv2:en and the food unite in
proper quantity to produce the available energy needed
by the body, without any interference from poisons.

As already explained under '^Circulation," alcohol
does interfere by extracting oxygen from the red cor-
puscles, and the heat given off by its oxidation is more
than offset by the derangements of the organs of the
body.

The effect of alcohol is not always apparent, but it
always interferes, to some extent, with the normal proc-
esses within the body.

in^:spiij.\Tic)N 187

A wojikeiied condition of any part of the body makes
tlio wliole body liable to disejuse.

A larpfe proportion of those who go to hospitals because
of diseases of the throat and lungs, are those wlio have
been addicted to the use of alcohol.

Continued use of large quantities of alcohol cause the
lungs to become congested with blood, so that less air is
breathed into them. This results in inllammation and
loss of vitality, with th6 consequent inability to resist
disease.

Tobacco smoke. — The smoke of tobacco irritates
and infiames the mucous membrane of the respiratory
tract. Those who smoke, especially those who inhale
tobacco smoke, are particularly liable to catarrhal in-
flammation and colds in the head.

The most injurious effect of tobacco results from the
use of the cigarette. This is not because the cigarette
contains more injurious substances than other tobacco,
but because of the way it is used. All cigarette smokers,
except the merest novice, inhale the smoke deep into the
air-sacs of the lungs. It was shown on page 178 how
easily a gas can transfuse from the air-sac into the blood.
After a few whiffs and inhalations from a cigarette, the
effect of the poison can be felt even to the tips of the
fingers and toes.

The use of the cigarette has an evil effect upon men of
any age.

A boy cannot select a more effective way of stunting
his growth and weakening both body and mind.

188 THIRD BOOK OF PirVSloLOGY

QUESTIONS FOR REVIEW.

1. Describe the atmosphere.

2. In what sense does man live beneath the surface of the earth ?

3. How is man dependent on the air ?

4. Define respiration.

5. What two kinds of respiration ? Define each.

6. Wliy does man need special organs of respiration?

7. Of what use is oxygen to the body ?

8. "UTiere in the body does oxygen combine with food?

9. Name all organs concerned in breathing.

10. Why should air be breathed through the nostrils?

11. Describe the larynx and the vocal cords.

12. How is the trachea constructed?

13. Why are animals choked by swallowing a large morsel of
food?

14. Describe the ciliated cells in the trachea. Of what use are
they ?

15. What are the bronchi ?

16. What are bronchial tubes ? Infundibula?

17. Describe the lungs as to location, weight, density, and com-
position.

18. What is the pleura? Of what use is it?

19. What causes air to move into the lungs?

20. Does the air expand the chest, or does the air go in because
the chest gets larger ?

21. Explain the action of the ribs in inhalation.

22. How does the diaphragm cause inhalation ?

23. Construct an apparatus to illustrate how the elevation of the
ribs will increase the capacitv of the chest.

24. What forces the air out of the lungs ?

25. How is air forced out in case of coughing and loud speaking?

26. What is the capacity of the lung.-?

27. How much air can one breathe out in <jne breath?-

KKSPllJArioN 189

2S. Why can one not breathe out all the air in tin- liingH?

I**.!. How much air i.s breathed?

;;0. What is the C()nii)osition of air?

."51. What i.s the most important gas in tiie air, and how can its
great activity be demonstrated?

.'>2. What is meant ))y saying tliat air is a mixture?

."»:;. What is the use of nitrogen and argon ?

o4. Of what use is carhon dioxide in tiie air? W'ii.ii are lis chief
sources ?

35. How are vegetables and animals dependent on each other?

?A\. AVhat are the two chief objects in breathing?

37. Explain the osmosis of gases.

38. AVhat is the composition of expired air?

30. Compare food and breathing of man to coal and draft of an
engine.

40. Where is impure air found? What causes it to be impure?

41. Why does breath make it impure?

42. What is ventilation?

4?>. What is the purpose of ventilation ?

44. How can impure air be detected?

4-3. Describe various methods of ventilation.

4<). Why is a steam-radiator in a room not a good ventilator?

47. Describe a method oi window ventilation.

48. Describe a breathing exercise.

49. How much dust is in the air?

50. AVhat becomes of the dust we breathe ?

51. How is lung consumption contracted?

52. AVhen is a room dean ?

53. How does alcohol interfere with respiration?

54. AA'hy do drinkers more easily contract disease?

55. How does smoking affect the respiratory tract?

EXPERIMENTS.

Burning an iron wire in oxygen.— Fi{<. 8o of the text is a i>hoto-
graph of the burning of an iron wire in oxygen. For this experimeirt procure

190

THIED BOOK OF PHYSIOLOGY

a large granite-ware spoon, and fill it full of pulverized potassium chlorate
(KClOv). Hold the spoon over a Bunsen flame or large alcohol lamp till the po-
tassium chlorate is all in a liquid form. Have ready a piece of picture-cord
about twelve inches long Avith one end slightly frayed out. Heat this end of the
wire in the flame, and dip it at once into some sulphur. "While the sulphur ad-
hering to the wire is burning, hold it close to the surface of the liquid in the
spoon. Keep the spoon over the flame. The iron wire will burn with the brill-
iant scintillation observed in the photograph.

Osmosis of gases.— Fig. S6 shows the apparatus needed for this experi-
ment. The porous cup is the kind ordinarily used in battery jars. The oi)en
end can be closed, by means of a little plaster of Paris, through which passes
a glass tube. The hydrogen can readily be prepared by pouring some dilute

hydrochloric acid upon some zinc in a bottle.
Place the large glass jar over the bottle and
collect some hydrogen. After one or two min-
utes, or less, lift the jar to a piosition over the
I)orous jar, and watch for bubbles in the water at
the lower end of the glass tube.

Action of the intercostal muscles.—
Between the ribs are two sets of intercostal mus-
cles. In one set the fibres run obliquely down-
ward and forward. In the other, upward and
forward. When the first contracts, the ribs are
raised. The contraction of the second set de-
presses them.

This may be illustrated by the device shown

in Fig. 89. Four pieces of wood are jointed

together in the manner shown. Tacks are driven

into the horizontal pieces at intervals of an inch

or more. These two strips represent two ribs.

Stretch elastic bands between the tacks, as shown

in the upper part of the figure, and their elastic

force will elevate the strips. This is the effect of

the first set of intercostal muscles, and they are

employed in inhalation. Now arrange the bands as shown in the lower part

of the figure, and the strips will be lowered. This is the action of the second

set of intercostals, and they are used in exhalation.

Test for carbon dioxide in the breath.— Procure a piece of un-
slaked lime and place it in a quart jar, nearly full of water. Shake the jar occa-

FiG. 89. — Apparattis il-
lustrating the action of the
intercostal muscles.

RESPIEATrON 191

gionally, and sot asuit' till the linu'settU'.s and tlio liijuid l)ccoMies rHjrffCtly ck-ar.
Decant a little of tlu- clear linuid into a small Ixittle or a test-tuhe. iJlow air
from the hintrs through a tnK' into the lime water. The water will lieeome
milky white. The carhon dioxide has unitt'd with the lime, and formed cal-
cium carbonate, which hangs in small particles in the water.

To test the ventilation of a room.— Prepare some touch-pa[»er by
soaking any kind of soft j'aper in a solntion of .saltpetre. After the paix-r is dry
it can be lighted, and will continue to smoke, but will not burn with a flame.

By use of the smoke from a taper made of such paper, test the doors, win-
dows, and other points where air may enter or leave the room where you live.

Raise the lower sash just a little, and determine whether air is coming in or
going out, above and below the sash. Each one should do this at his own
home.

CHAPTEE XII

BACTERIA

What bacteria are. — Bacteria are a class of very
minute i^lants. During the last t^renty years they have
been studied very closely, and are found to be very use-
ful agents in every-day life.

They are able to bring about
changes in nature without which
neither plants nor animals could
long continue.

They are of use in the manufac-
turing industries and in the pro-
duction of articles of food.

They also cause many of the dis-
eases from which man and the other
animals suffer.

A scientific study of these minute
organisms is called bacteriology.

Fig. 90. — Bacteria. --, , . j? -l x •

A, spheres ; B, rods ; c, Shape and size of bacteria.

spiral.^. — There ai e many different kinds of

bacteria, but. as far as their shape
and size are concerned, there are only three clas.ses, —
the spheres, the rods, and the spirals. The characteristic
shapes are shown in Fig. 90. The spheres may vary in
size, but all are very minute. If lUO.OUO of the largest
192

HACTKRIA

193

of them were placed in a line side by sid<', the line wonld
be only six inches lon«^.

The rods are very narrow, bnt some kinds have con-
siderable length.

The spirahs are similar to the rods in size.

Bacteria are the smallest living things that have ever
been seen in a microscoi)e.

How they multiply. — The great number of bac-
teria and the rapidity with which they can multiply
make them very important agents in the world for good
or evil.

They increase in number by a division of one into
two. two into four, four into eight, and so on.

Fig. 91. — Multiplication liv divi.-ion.

A sphere, as seen in Fig. 01, will become elongated,
and finally divide in the middle and become two.

All bacteria multiply in this way. In this respect
they differ from yeast germs, which multiply l)y a method

Fig. 92. — Yeast-plants.

called huddhuj. Yeast germs are shown in Fig. 92.
This is the chief mark of distinction between yeast and

bacteria.-

13

194 THIED BOOK OF PHYSIOLOGY

Tlie rapidity of multiplication of bacteria depends on
many conditions, such as temperature, moisture, and
the amount of food which the bacteria can get. Some
can double their number every thirty minutes. At this
rate it is easy to calculate that a single bacterium would
in twelve hours have increased in number to more than
8,398,000.

The food of bacteria. — Bacteria are defined as
plants, and yet in some respects they are like animals.
Plants live on food of a very simple kind, which they
can make into complex forms suitable for the food of
animals. Bacteria in this respect are like animals, for
they live only on complex foods, and can live and
thrive only when they can get it. For this reason it is
dangerous to allow certain bacteria to get a lodgement in
the tissues of the body, for there they find the kind of
food they want, and so will multiply and produce poi-
sons which are the cause of many diseases.

Where bacteria are found. — Bacteria are found
in every place where animals and plants live. The soil
is full of them to a depth of two or three feet or more.
They are in all bodies of water. All decaying matter is
crowded with them. Animals, including man, contain
them throughout the whole alimentary tract. They
cling to the skin and the clothes. Any disturbance that
will raise a dust in a room or on the street will cause
great numbers of them to float in the air.

They are not found in the tissues of any healthy
orsran.

BACTKIMA 195

Use of bacteria in the industries.— Mauy tliou-
sands of dollars are invested in industries wliicli ai'e de-
pendent on the help of bacteria. Bacteria are able to
bring abont many useful chemical changes. For ex-
ample, when cidei" is allowed to stand in air it soon be-
comes sour and is changed to vinegar. If the cider had
been boiled and then sealed from the air, it would liave
remained fresh.

The change to vinegar is caused by bacteria, which
find in cider a desirable food. The x^roduct of their life
there is the vinegar. The ''mother of vinegar" is a
mass of millions of bacteria.

Other kind of bacteria find milk a suitable food. One
product of their life is an acid which makes the milk
sour and causes it to curdle. Milk would remain sweet
indefinite!}^ if bacteria could be kept out of it.

The flavor of butter is due to the work of bacteria, and
the ripening of cheese is also a result of changes which
they bring about.

The •'retting" of flax, by which the tough fibres of
linen are separated from the woody part, is effected by
bacteria.

Thus it is possible to name many arts in which bac-
teria play an important part. Enough has been said to
show that these minute organisms are not always an
enemy of man. In fact, most of them are not only harm-
less, but a great aid.

It is man's duty to find out their character and habits
of life and turn them to good use.

196 TRIED BOOK OF PHYSIOLOGY

Bacteria as food producers. — The material of our
food is used over and over. Plants change simple com-
pounds into complex ones, such as proteids, fats, and
carbohydrates. Plants cannot live on these. The car-
bon dioxide which the animals breathe out is a suitable
food for plants. Plants cannot live on the tissues of ani-
mals or i^lants until they are broken up into simple
comi)Ounds.

This is the work of bacteria. When an animal dies in
the field or a tree falls in the woods, their bodies soon
soften and decay. This is the result of the work of mill-
ions of bacteria, whicli find there the complex foods
upon which they thrive. The tissues are thus reduced
to simi^le compounds suitable again for i^lant life.

If no bacteria are present, meat will not spoil and
plants will not decay.

Thus the same material may go round and round,
from air and soil to plants, from plants to animals, from
animals through bacteria back to plants again.

The energy comes from the sunlight, and as long as
the sun shines upon green leaves this circuit of food
material may continue.

Yeast. — Y'east germs are classified as different from
bacteria, for reasons given on page 193. But thej^ are
microscopic plants, and can produce great chemical
changes in the substances in which the}- can live and
multiply.

The chief products of their life are alcohol and carbon
dioxide. The process by which this is done is called

BACTKIMA 197

fermentation, and tliis lias already been explained in
Chapter IX.

The fermentation caused by the yeast-plant is the fii-st
step in the disinti'gration of many substances. Aft^r
the work of the yeast-i^lant is done, certain bacteria may
enter the substance and make other changes until the
simple forms of plant food are produced.

Bacteria which produce disease. — Probably all
bacteria are of some great use in the world. M<jst of
them are harmless to man. A few species, however, can
live and multiply in the tissues and in the alimentary
tract of the bodj. There they j)roduce violent poisons,
which are the cause of serious sickness, which often
results in death. Bacteria themselves are not so danger-
ous, but the violent poisons thej^ produce are taken up
by the blood and distributed through the body.

Cholera infantum. — KSome germs, already de-
scribed as i)leutiful in milk, continue to live after the
milk is taken into the stomach. The effect on infants is
a disease called cholera infantum. The effect is not so
noticeable on those who are older and less delicate.

These bacteria do not enter the tissues of the body,
but onh" continue to live in the milk after it is swal-
lowed.

The projjer precautions, particularly in warm weather,
is to use only milk which has l)een sterilized.

Diphtheria. — The bacteria which cause diphtheria
act only on the mucous membrane of the throat. There

198 THIRD BOOK OF PKYSIOLOGY

they cause a whitish membrane to form, which may
close the air-passages.

Here they produce a violent poison wliich is absorbed
into the body. The germs which produce this dread

disease may easih^ be con-
«5-p.^%:^ veyed from one person to

^r?^*^^'^/^ another. The only safety

*^- "^•^»^- is in the complete isolation

m-<r i ^-m^aa ^jf the patient and all who

S V^ i*^ live in the same house until

Fig. 03.-Germs of diphtheria, the germs are all killed by
Klebs-Loeffler bacilli, from speci- the application of a germi-
mens prepared hv Dr. Coplin and • •,
Dr. Bevan. Fresh culture upon

blood serum. Eye-piece IV.. Physicians are now treat-

Beck; Objective J^oLim. (Lei tz. j ii^g the disease with suc-
This is also the appearance when . . . _ , • , .

obtained directly from the throat ^^^'^^ "^^ mjectmg mto the
and subjected to the same power. blood of the patient a J^rep-

aration called dijyhtheria an-
titoxin. It is obtained from the l;)lood serum of horses
which have been purposely caused to have the disease.

In this way not only have diphtheria i:)atients been
cured, but those who were exposed to the disease have
been made immune from its attack.

Lock-jaw. — The dreaded disease called tetanus, or lock-
jaw, is caused bj' germs which have the appearance shown
in Fig. 94. These germs are plentiful in the soil, and
may be introduced into the flesh through a wound in the
foot or in many other ways.

The bacteria themselves are confined to the locality of

UACTKIMA ]1>9

the wound. Tlicro they j»i<«liu'(' a \ iolent ijoisoiu wliicli
is taken np by tlic Mood. Moir tliaii the usual nund)er
of cases ol" lock-jaw ocenr alter each Fourth of .Tnlj', as
a result of the admission of these bacteria into wounds
eans<Ml ]>y lir(^-era('k<'is an<l toy pistols.

Fig. 94. — Germs of lock-jaw.

Tuberculosis. — Tuberculosis is caused by bacteria
of the rod shaped kind. This disease may be located in
various i^laces in the body, but is commonly found in the
lungs. There the bacteria thrive on the lung tissue.

It was once supposed that tuberculosis could neither be
prevented nor cured. Xow it is known that, with j^roper
care, both prevention and cure are possible.

It is not possible, in most localities, to avoid breathing
the germs ; but it is possible to have such healthy lungs
and such a robust body that they cannot gain entrance to
any part of the lung tissue.

The contraction of colds that •'■settle" in the throat or

200 THIED BOOK OF PHYSIOLOGY

on the lungs, furnishes favorable conditions for the germs
of pneumonia and consumption. If, in addition to this,
the body be poisoned by the inhalation of cigarette smoke
and the drinkiug of alcohol, the body's power of resist-
ance is also greatly weakened.

It is plainly shown that one who has a weak constitu-
tion, or one who is already suffering from some affection
of the lungs, may readily contract tuberculosis from
others who have the disease.

/'^ . k/^\. \J

(

>^ V^ ^

y^

Fig. 95. — Germs of tuLerculosis.

The two fundamental precautions in reference to this
disease are, a vigorous state of health, and avoidance of con-
tamination from others.

Laws of public health require that association with con-
sumptives be avoided. This is particularly so in public
places and close rooms.

Because this disease is not violent, but slow and insidi-
ous, people become careless in regard to it, though it is
known to kill about 15 per cent, of the human race.

BA(TKIMA 201

Typhoid fever. — In Fig. 9G are shown the bacteria
which are the cause of tjfphoid fever. These grow in the
intestines, but also often spread to the liver and other
ghmds. They can move about by motion of the minute
projections called Jlagella. Poisons which they produce
are the cause of the violent fever which is characteristic
of this disease.

These germs are conveyed chiefly by food and water.
The water of a single Well has often been the cause of an

■^

1^-

^^- - ^^"j^

"r^

t r -<-

ir ^'

Fio. 06. — Typhoid fever germs.

epidemic of typhoid fever. A shallow well is always to
be suspected on this account.

Provisions in the body for resisting bacteria.

— We have mentioned only a few of the diseases which
are caiLsed by bacteria. There is a constant contest for
supremacy between the living cells within the body and
the living cells (bacteria) without.

The cells within are an organized body, and are, as it

202 THIRD BOOK OF PHYSIOLOGY

were, fortified in their place ; but the bacteria possess
means of attack which are often successful if the fortifica-
tions are weak.

The body's chief means of protection are the skin, cer-
tain coiuiter-poisom which destroy or check the growth of
bacteria, and the white corpuscles.

The skin as a protection. — Tlie skin may be
likened to a strong wall about the organized body of cells
within. Bacteria may hang in great numbers on the out-
side of the skin, but they cannot go through it. The
linings of the respiratory and alimentary tracts act as a
similar protection against most germs.

When, however, a bruise, cut, or mixture of any kind
occurs in these protective coverings, the bacteria at once
invade the tissues. Even a slight scratch of the skin
may, for this reason, become a bothersome wound.

Surgeons now know how to dress a wound so that bac-
teria are kept away. The wound then heals rapidly and
without the formation of pus.

Alexines. — It is not possible to prevent, at all times,
the access of bacteria into the living tissue. Fortunately,
however, certain substances in the blood and tissue
make most bacterial life impossible there. They are
called alexines. Although their nature is not well known,
it is clear that they serve as protective agents against
bacteria.

Certain disease-producing bacteria are able to neu-
tralize the action of the alexines, and so proceed to
establish themselves in the living tissue.

IU(Ti:iilA 208

The white corpuscle. — AftiM- llu- ordinary moans
h;i\o failed to repel the invading baeteria, the body still
has in reseiNc another means <►!' defence. One of the
chief dnties of the white corpuscle is to go abont throngh
the body, apparently in search of foreign bodies, which
they at once attempt to remove or render harmless.
They are not confined to the blood-vessels, bnt can glide
out into the tissues. They can take into their bodies
minute particles which they dissolve or carry away even
if they must sacrifice themselves in doing so. For this
reason they are often called the scavengers of the body.

When bacteria gain admission to the tissue at any
point, as through a wound, the white corpuscles gather
there in great numbers. The wound becomes swollen
and inflamed because of their presence. They appear to
pour out from their bodies a secretion which checks the
growth of bacteria. Many white corpuscles are killed in
the conflict, and the accumulation of their dead bodies
forms the substance called j^its.

Some bacteria are able to produce such violent poisons
that the white corpuscles are not able to check them.
In such cases the disease will ''run its course," and the
bacteria would continue to multiply until death would
result, except that the body itself then produces sub-
stances which are an antidote to the bacterial poisons.
If the body is able to survive, the disease will reach a
climax and recovery will begin. This changed condi-
tion oft^n renders the body immune from an attack of
the same diseiuse for a certain length of time. Some-
times for a lifetime.

204 THIED BOOK OF PHYSIOLOGY

Argument for a robust body. — Many things in
regard to bacterial diseases are not definitely known.
It is well known, however, that most diseases are caused
by these minute organisms, and that one whose body
is robust and whose habits of life are good can most
effectively resist their attack.

Drugs are effective in killing bacteria outside the
body, but no drug now known will destroy them after
they are lodged in tlie living tissue, without destroying
the body as well.

The effective means of combating them comes in a
natural way from within the body itself. The state of
the body determines its ability to resist disease. This is
a good reason for the maintenance of a body in which
every cell is assimilating its due proportion of food and
oxygen, and performing its part in relation to the welfare
of the body as a whole.

Modern discoveries show that the physician may assist
the body in its effort to neutralize the bacterial poisons.
This he does not attempt to do by the use of drugs
intended to kill the germs, but by injection of certain
substances which will make the poisons harmless. For
examx)le, one who is bitten by a mad dog is almost sure
to suffer from hydrophohia. The disease does not develop
for some time, so that the body may be prepared for it
before it sets in. The physician is prepared with mate-
rial taken from the spinal cord of a rabbit which has
died from the disease. This is injected into the body
of the patient, first in a mild form and then in stronger
and stronger doses. When the disease does develop,

BACTKiUA 20.')

the body is used to the poisons producod, and no serious
results follow.

QUESTIONS FOR REVIEW.

1. What are bacloriii, uiul what do they do?

2. Describe the shape and size of bacteria.

3. How do bacteria muhiply?

4. How do they differ from the yeast germ?

5. On what kind of food do bacteria subsist?

6. Why do some kinds of bacteria invade the tissues of the body ?

7. Where can bacteria be found?

8. Explain the formation of vinegar.

9. Name several arts and industries in which bacteria have a
part.

10. In what condition must the food of plants be? Tlie food of
animals?

11. How do bacteria prepare plant food?

12. What causes meats and fruits to spoil?

13. What is the source of the energy in food?

14. What is the cause and effect of fermentation f

15. How do bacteria produce disease?

16. What is the cause of diolera infantum f

17. What is diphtheria, and how may it be treated?

18. What is tetanus ?

19. How are tubercular germs conveyed from one person to
another?

20. How can consumption be avoided?

21. What is typhoid fever? How is it carried about from one
to another ?

22. What three provisions are made in the body for resisting
bacteria ?

23. How does the skin resist bacteria?

24. What are alexines, and what is their use?

25. How do white corpuscles resist bacteria?

26. Give a good reason for maintaining a robust body.

CHAPTEE XIII

THE SKIN

General character of the skin. — The skin is a
tough, pliable, and elastic covering over the entire out-
side surface of the bod3\ The mucous membrane, which
lines all cavities of the body that communicate with the
outside^ may be considered a continuation of the outer
skin, though much modified in character. The hairs and
nails are only modified forms of the skin. The claws,
hoofs, and horns of animals are modified forms of the
skin which covers their bodies.

Use of skin. — The chief function of the skin is to
serve as a protective covering. AVe have already de-
scribed its use as a protection against the invasion of
bacteria. In every- day life the body must constantly
come in contact with outside objects, and a strong cover-
ing like the skin is needed to protect the delicate parts
beneath.

To make the skin a more effective guardian of the body,
it is filled with terminals of nerves. Thus the mind is
instantly notified when any part of the body comes in
contact with outside objects.

In addition to its use as a protection, it also serves as
an excretory organ. A great deal of water and some
waste are taken from the blood by the glands in the skin.
206

TIIK SKIX

207

The evaiX)ration of the water from the surface of the
skill hits an important nso in ro<rnhitin<^ tlio temperature
of tlie body.

The two layers of the skin. — The skin is com-
posed of two hiyers. The tuiter one is called the ejri-
dennis, cuticle, or scarf-skin. Just beloNV it is the true
skin, also called the demiis, or cutis.

\n

Fig. 07. — Cross-section of skin from the finger of a monkey.
Photographed through a microscope.

Fig. 97 is a microphotograph of a cross-section of
the skin from a monkey's finger. The two layers can be
plainly seen.

The epidermis. — The epidermis is very thin on
most of the surface of the body. It is thicker on the

208 THIRD BOOK OP^ PHYSIOLOGY

palms of the liauds and the soles of the feet. It may
become thick at any point where there is continuous
friction or rubbing. In this way ^'corns'' are formed on
the feet by ill-fitting shoes.

The palms of a workman's hands become hard from
constant pressure on the handles of tools.

Epidermis is formed of several layers of jjavement epi-
thelium. (See page 2-4.) The cells composing it are con-
tinually supplied from beneath, and the old ones are as
constantly being worn away or drop off.

Y^^heu a blister is formed, as from a burn, the epidermis
is separated from the dermis.

Xo blood-vessels or nerves are supplied to the epider-
mis. The cells of its deepest layer are alive, and are
nourished by the lymph which they absorb. These pro-
duce the cells of the outer layers, which gradually dry up
and become cemented together, forming the horny, trans-
parent layer which covers the whole surface of the body
and protects the delicate tissue beneath.

Color of the skin. — The deeper layers of the epider-
mis are supplied with granules of coloring matter. The
amount and kind of granules differ greatly in different
persons and different races. The skin of albinos is entirely
devoid of coloring matter. Xegroes are abundantly sup-
plied with it. A brunette has more of it than a blonde.

Sunlight makes the granules darker. An uneven dis-
tribution of the granules is the cause of frecMes.

The dermis or true skin. — As shown in Fig. 98,
the surface of the true skin is composed of numerous

TUK SKIN

209

rid«j:cs. These are conical projections over wliicli the
epidermis is closelj^ moiihled. They are called jxipillce.
Some of them are filled with blood-vessels. Othei-s are
terminations of nerves of touch. The dermis is plenti-
fully supplied with blood and nerves.

The nerve papilhe are numerous all over the surface of
the body, but are especially numerous in those places

^— p

9

S ■

Fig. 98. — A magnified cross-section of the skin, e, epidermis ; p^
papillae ; 5, sebaceous gland ; r, root of hair ; /, fat ; 7, sweat-glands ;
a, pores.

where they can be of greatest service to the body, as on
the tongue, lips, and tips of the fingers. On the palms
of the hands thej' are arranged in rows, thus causing
ridges which may be plainly seen with the naked eye.
As may be seen in Fig. 98, the larger part of the dermis

14

210 THIRD BOOK OF PHYSIOLOGY

is composed of interlaciug bands of connective and elastic
tissue. These make the skin tough and at the same time
permit it to be stretched. Beneath the skin is the loose
areolar tissue in which fat is dex)Osited, giving the skin an
even surface. When the fat is used up by the body, the
skin becomes wrinkled because it is then too large for the
part which it covers. In the regions just below the dermis

Fig. 99. — From the surface of the paha of the hand. The ridges
are rows of papilhe. The dots are pores.

are numerous sweat-glands which communicate with tlie
surface through their spiral ducts.

The roots of hairs reach down to different depths, most
of them beino^ in the fattv laver. At the sides of the
hairs are oil-glands.

Sweat-glands. — With an ordinary magnifying glass,
a great number of minute spots can be seen on the ridges
of epidermis on the palms of the hands. These are the
pores of the sweat-glands. They are found in all parts

TIIF. SKIN 211

of (lie surface of llu* l>o<ly, hut arc most muiierous on the
palms and soles. It lias been estimated that there are in
all about 2,r)()(),()0() s\\eat-«,^lands.

The gland is a long tube, closed
at one end and coiled up as shown ^f^

in Fiji:. 100. Kound about this coil ^ ./' ': r^M

are numerous blood capillaries, from ''/

, /

which the gland secretes a great Jf'y -,

deal of water and some waste mat- ^rM^^I^

ter, and i^ours them out on the sur- ^

face of the body. ^

Perspiration.— The escape of

the excretions of the sweat-glands ''^?^'^4'

at the surface of the skin is called ^ ^r.c^ c- ^ i ,

Fig. 100. —Sweat-glands,

jyersjnration. It may take j^lace

rapidly, making the skin wet with sweat. It is then
called sensible perspiration because it can be perceived by
the senses.

At all other times the water evai^orates as fast as it
reaches the surface, and it is then called insensible per-
spiration.

The average amount of water persjjired in a day is
about one quart.

Insensible perspiration may be readily shown by in-
serting a finger into a cold, dry bottle or test-tube. The
inner surface of the glass will ''fog," as a result of the
condensation of the vapor from the finger.

Effect of vaporization on the temperature
of the body. — The normal temperature of the human

212 THIED BOOK OF PHYSIOLOGY

body is "between 9S and 99 degrees Fahrenheit. Only
at this temj^erature can the body be said to be in a
health}' condition.

The air is ordinarily cooler than the blood, and so heat
is constantly being radiated from the body. Frequently,
however, this is not sufficient to keep the temperature
down to normal.

In addition to radiation, evaporation acts as a tempera-
ture regulator. A liquid cannot evaporate unless it can
get heat. \Yhen sweat evaporates it can get the needed
heat most conveniently from the body. Thus the body
is cooled.

The body automatically regulates its own temperature.
During a hot da}', or at times of vigorous exercise, a
large amount of sweat is poured out on the surface of
the skin. Its evaporation cools the bod}'. A warm wind
feels cool if the skin is wet, because evaporation is
hastened. Fanning heats the air slightly, but it in-
creases evaporation from the skin, and so the air seems
cooler. Fanning a dry thermometer will not cause the
mercury to fall.

Heavy clothes keep the body warm, because they
check both the radiation and the evaporation. Alcohol
rubbed on the skin will cool the body more rapidly than
water will, because it will evaporate faster.

Hair. — Hairs, in more or less abundance, are dis-
tributed over nearly the whole surface of the body.
There are none on the palms or soles. The root of a hair
is the part beneath the surface of the skin. It is enclosed

TIIK SKIN

213

ill ;i follicle or jmcket tbrined by the involution of the
epidermis, as shown in Fig. 101. At the bottom of the
follicle, the root lits over ii papilhi, which is supplied
with blood-vessels. Thus the cells
in the root of the hair jire nourished
and continue to produce new cells,
which push the old ones ahead of
them, thus increiising the length of
the hair.

When a liair is pulled out, a new
one will grow in its place if the
papilla is not injured.

The outside of a hair is covered
with a single layer of flat cells
which overlap like scales. The free
edge of the scales lie tow^ards the fig. 1 01.— Hair-follicle.
l^oint of the hair. B3' rubbing a

hair lengthwise between the thumb and the finger, it will
be moved along root first.

The color of the hair is determined by a pigment in
the cells. In old age the coloring matter is wanting,
and the hair is white.

Fibres of muscle are attached to the hair-follicles.
When they contract, the follicle is changed from an
oblique i)Osition to one more nearly perpendicular to the
surface. Thus the hair is made to ''stand on end." In
some animals, such as the cat, frequent use is made of
these muscles.

Hair on the head is useful for adornment and for pro-
tection from heat and cold. The eyelashes andej^ebrows

214 THIRD BOOK OF PHYSIOLOGY

protect the delicate organs of sight. Hairs in the nos-
trils and ears guard the entrance to important organs.

Nails. — Xails. like hair, are a modified form of epi-
dermis. Thej' consist of a root, hody, and edffc. The
root is the back i^art where the nail is attached to the
dermis, and where there is a constant addition of new
cells which push the nail forward.

The body is the visible part of the nail, which is
attached to a portion of the true skin called its bed. The
nail increases in thickness by the addition of new cells
from the bed.

The nail itself is quite transjiarent. The color ob-
served is that of the true skiu beneath. The pink color
is due to the suj^ply of blood beneath.

The liuuda, or little moon, near the root is of whiter
color because less blood flows beneath it, and it is less
transparent.

Hygiene of the skin. — The skin is an exceedingly
imi)ortant organ as far as concerns bodily health and
comfort. Its chief functions are protection and excretion.
A temporary suspension of either one of these results in
sickness or even death.

The skin, like any other organ, can effectively do its
part only within certain limits. For example, it can,
under ordinary conditions, regulate the temperature of
the body, keeping it quite close to 98.5 degrees. In ex-
tremes of heat and cold, however, the unaided skin is
helx:>less as a temperature regulator.

TllH SKIN 215

Clothing. — As ill ready explained, heat is constantly
leaving (lie body by radiation and perspiration. When
exposed 1o cold weather, perspiration is checked by
closinjif the i)ores, but radiation becomes more rapid than
before. For this reason the IkkIv must bo piotected with
proper clothing-.

Ch)thing does not warm the body. It only prevents
the escape of heat. In cold weather, then, a garment
should be a poor conductor of heat. A loose woollen
garment is good because much air is enclosed between
its loose fibres, and air is a very i^oor conductor of heat.

Many workmen who are exposed to the hot sun wear
woollen shirts to keep the excessive heat out.

A woollen sweater is an excellent protection during
winter and at all times when there is liability of cooling
off too suddenly.

The effect of the color of clothes is a matter of some
importance. Black is a good absorber of heat and also a
good radiator. White is poor in both.

When a black cloth is exposed to sunlight or some
other source of heat, it will become warmer than the
white cloth ; l)ut when the source of heat is withdrawn
the black will cool more rapidly.

A black garment will, on a cold day, allow more heat
to escape from the body than a white one made of the
same material.

As people ordinarily live, white is the best color the
year round, as far as the absorption and radiation of
heat are concerned.

Cotton and linen goods are good for summer wear

216 THIRD BOOK OF PHYSIOLOGY

under ordinary conditions. They are fairly good con-
ductors of lieat, and for that reason the body will cool
by radiation if the surrounding atmosphere be cool.
The greatest advantage of such goods in hot weather lies
in the fact that they will readily absorb moisture from
the skin and conduct it to the outside, where it can
rapidly evaporate.

The kind and amount of clothing depend upon the
climate, habits of life, and constitution of the body.
Many of the ills of the body result from an improper
kind or quantity of clothing. As a rule, a loose woollen
garment next to the skin is best in winter time, and for
some it is best the year round. Each one must suit his
clothing to his individual needs.

Bathing. — Every i)ore of a healthy body is con-
stantly perspiring. Sometimes, as on exposure to cold,
the amount of matter perspired is very small. At other
times, when there is danger of the body being over-
heated, a large amount of sweat is poured out on the
surface of the body. Along with the perspired water is
a considerable quantity of urea, salts, and other matter.
When the water evaporates, these substances become
dried on the skin and clothing.

The oil which is furnished by the sebaceous glands
also causes dust and dirt to adhere more readily to the
skin and hair.

In addition to this, one who is engaged in any active
occupation must come in contact with more or less dirt
which clings to the body.

THE SKIN 217

Bathing is necessary to assist the skin in its work of
excretion, and also for the mere purpose of being clean.

Beside the mere matter of removing dirt, however, a
cold bath in the morning will, to some people, be a stim
ulus to the whole body during the day ; and a warm bath
just before retiring will often induce sound and restful
sleep.

Times and methods of bathing.— The advice of
various authorities vary in regard to the times and
methods of bathing. One may bathe too often, and thus
do the body more harm than good. A change of the
clothing worn next to the skin is often more essential to
good health than the application of water and soap.
The vocation and manner of life will help to determine
how frequently one should bathe. The skin may be
moistened with water every day and then well rubbed
with a coarse towel; but a thorough bath everj^ week, or
even every two weeks, may be sufficient under ordinary
circumstances.

In hot weather or after severe exercise baths may be
more frequent.

The kind of a bath is a matter to be decided by each
individual in accordance with his state of health and his
circumstances. Baths may be cold^ warm, or hot.

The cold bath may consist in a plunge into cold water,
a cold shower, the application of cold water by means of
a sponge, or even dipping the hands into the water and
rubbing it rapidly over the skin.

The first . effect of the cold water is to close the pores

218 THIPvD BOOK OF PHYSIOLOGY

and contract tbe blood capillaries ; but this should be
quickly followed by a reaction, and a warm, healthful
glow should fee felt all over the surface of the body. The
body should be exposed to the cold water for only a very
short time and then vigorously rubbed with a coarse
towel. Unless a warm glow follows, the cold bath will be
injurious. Persons of weak constitution should be cau-
tious in the use of the cold bath and, if attempted at all,
it should be taken in mild form at first until the body
becomes used to the shock.

The warm bath is the one commonly used with soap to
wash away grease and dirt. Many people will never use
the hot and cold baths, but every one needs the warm bath
and soap, and a frequent change of underclothing, to
keep the skin in a healthy condition. Any one who can
get a sponge or wash-cloth, some mild soap, and a basin
of water, has no excuse for not keeping his body clean.

A clean skin and clean clothes improve not only the
physical, but also the moral condition of the individual.
Hot baths may be recommended by physicians in treat-
ment of certain diseases.

Care of the hair. — A beautiful head of hair is an
ornament to its possessor, but only good care will keep it
so. The hair may occasionally be washed with soft water
and a mild soap, but only often enough to keep it and
the scalp clean. Massage of the scalp and use of the hair-
brush will stimulate the roots of the hairs to healthy
activity.

The natural secretions of the sebaceous glands will

Tin-: sKiK 210

ordinarily keep tlic hiiir soft and <;lossy. If it I>ecoiiies
dry iiiid loses its gloss, a little viiseliin' may be applied
to it.

A large mmiber of loose cells of the epidermis, along
with oil which has dried on the scali), constitutes what
is called dandruff. Tt indicates a diseased condition of
the scalp and is associated with a loss of hair.

Care of nails. — (Mc^an and neatly-trimmed nails are
a recommendation to any one. Dirty nails with jagged
edges indicate careless habits, not only in this but in
other matters. They should be cleaned every day with a
nail-brush and water, and the edges should be occasion-
ally trimmed to a smooth curve.

The epidermis which overlaps the nails at the roots and
sides should be pushed back, for otherwise it adheres
so firmly to the uail that the skin will l>e torn, forming
the ^'hang-nail."

QUESTIONS FOR REVIEW.

1. What is the nature of the skin?

2. How does skin protect the body ?

3. Why is the skin provided with nerves of touch?

4. Describe the two layers of skin.

5. How thick is the epidermis?

6. What kind of cells form the epidermis? How are they
supplied?

7. Are the cells of the epidermis alive?

8. Explain the color of the skin. What causes freckles?

9. Describe the true skin.

10. What are pores ? Can you see them ?

11. Describe a sweat-gland.

220 THIRD BOOK OF PHYSIOLOGY

12. What is perspiration? Describe two kinds.

18. Try an experiment to show insensible perspiration.

14. Explain fully the effect of evaporation from the surface of
the body.

15. Describe the root of a hair.

16. What causes hair to grow?

17. What causes hair to stand on end ?

18. Describe the nail.

19. How does a nail grow ?

20. Explain the lunula.

21. What is the use of clothing?

22. Why will a woollen garment keep the body warmer than a
linen one?

23. What is the effect of the color of clothing?

24. Why do cotton and linen make good summer garments ?

25. Why is bathing necessary?

26. How often should one bathe?

27. What is the advantage of a cold bath ? When and how
should it be taken ?

28. Why should clothing worn next to the skin be frequently
changed ?

29. What is proper care of the hair?

30. Why should nails be kept clean ?

CHAPTEK XIV

EXCRETION

Secretion and excretion compared.— We have
seeu that numerous glands are distributed througliont
the body. All the gl5.nds are enclosures surrounded
with cells, and opening, as a rule, by ducts out onto a
free surface.

Blood constantly flows through the numerous capil-
laries about the cells of the gland, and from it is selected
the various substances, in accordance with the i:)urpose
of the gland.

The cells of a gland may gather out liquids which are
already in the blood, or they may elaborate the materials
which they collect, and produce new compounds.

The hydrochloric acid in the stomach, for example, is
not taken from the blood, but is made by the gastric
glands.

When the material collected by a gland is for further
use in the body, the process is called secretion. For ex-
amples, the saliva and gastric juice are secretions.

When material is collected by a gland only to be cast
out of the body, the process is called excretion. For ex-
ample, urea is excreted by the kidneys and carbon di-
oxide is excreted by the lungs.

Some substances are both secretions and excretions.
For example, the bile is an important agent in digestion,

221

222 THIRD BOOK OF PHYSIOLOGY

aud so may be considered a secretion of the liver ; but
bile would soon make the blood impure unless it be con-
stantly eliminated : and tbus it is also an excretion.

The chief excretory organs.— The chief organs
concerned in excretion are the Jungs. sJcin, liver, and
Jtidneys.

These have all been described except the kidneys. In
this chapter we briefly refer to the work of each, aud
describe the work of the kidnej's in full.

The lungs. — The lungs are excretory organs of
very great importance. We have already compared
breathing to a draft of air through the burning fuel of a
steam-engine. In the engine the air enters below the
grate^ and the waste products of combustion pass out
through a chimney above.

In the body the air is supplied to the blood in the
lungs and the i)roducts of combustion are returned by
the same channel. Thus the air-passage serves both for
damper and chimney.

The chief substance excreted by the lungs is carbon
dioxide (CO,). This is the chief product of combustion
of coal, wood, coal-oil, or any kind of carbonaceous sub-
stance.

Some organic substances are also excreted with every
exhalation. The character of these substances is not
well understood ; but there is no doubt of their presence
in the breath and their vitiating effect on the air in a
close room.

Water is also excreted in large quantity by the lungs.

EXCRETION 223

The skin. — While the skin is chiefly an organ for
tlie protection of the l)0(ly, it also has an additional
donble function of secretion of waste substances and the
regulation of bodily temperature. Thus the skin may
be regarded iis both secretory and excretory. Its chief
excretions are water, urea, and salts.

There is a close relation between the skin and the kid-
neys. When the excretions of the skin are large, the
kidneys are relieved of much of their work ; when the
glands of the skin arc inactive, more work is thrown
upon the kidneys.

The liver. — The excretions of the liver depend upon
the kind of substances in the blood. As already ex-
plained, the liver is a most efficient guardian of the
health of the body. Nothing gets from the stomach or
intestines into the general circulation until it has first
been tested by the liver, and many substances that
would be injurious are either changed in their character
or excreted.

Bile is an excretion of the liver. If the bile should
remain in the blood, serious disorders are sure to follow.
It is made to serve a useful purpose in intestinal diges-
tion, and much of it may again enter the portal veins
and be again excreted, or secreted, by the liver.

Kidneys. — The kidneys are among the most impor-
tant of the excretory organs. A man could not live
more than one day if the action of his kidneys would
cease.

224

THIED BOOK OF PHYSIOLOGY

They are two in number and are located in the abdo-
men, one on each side of the spinal column, in the region
of the loins.

Each is about four inches long, two inches broad, and
one inch thick. They are shaped somewhat like a beau,

Fig. 102. — Cross-section of kidney. C, C. cortex: M, pyramids
of Miilpighi ; L. L, medulla; P, pelvis; .4, artery; T, vein; U,
ureter.

and on the side towards the backbone is a depression
called the hihnn. Three tubes enter the kidney at the
hilum. One is the renal artery, which carries blood to
the kidney ; another is the renal vein, which carries the

EX(MM^TI()X 225

blood away ; and between them is the ureter, wliich ear-
ries the excretions of the kidney to the bhidder.

Internal structure of the kidney. -A longitu-
dinal section of a kidney would lia\e ab(jut th(* appear-
ance shown in Fig. 102. The ureter on entering the

Fig. 108. — Section of cortex of a kidney, showing Malpighian bodies

slightly magnified.

kidney spreads out, forming a cavity called the pelvis of
the kidney. Projecting into the pelvis are a number of
pyramids, from eight to eighteen in number, and known
2iS>i\\Q pyramids of Malpiglu. The pyramids project from
the medullary layer of the kidney. Surrounding the med-
io

226

THIRD BOOK OF PHYSIOLOGY

ullary layer is the cortex. The kidneys are enclosed and
held in place by a capsule of fatty areolar tissue.

Microscopic examination of the kidneys. —
Minute examination of the cortex shows that it contains
numerous spherical bodies about y^^ of an inch in diam-
eter. These are known as the ^lalpighian bodies. It is in
these that the excretion of the kidney is chiefly done.

Each little sphere is composed
of two parts, as shown in Fig,
104. ^\"ithin is a roll, or tuft,
of capillary blood-vessels, to
which blood is supplied by
an artery called the afferent
vpssel. Leading out of the
tuft is an artery called the
efferent vessel. This again
breaks into capillaries around
the convoluted tubule, and
these are gathered into ceins.
The tuft of capillaries is en-
closed in a capsule from which
a tube, called the uriniferoiui
tubule^ carries the excretions to
the pelvis of the kidney.

The uriniferous tubules be-
gin at the Malpighian bodies
in the cortex and pursue a
circuitous route through the cortex and the medullary
layer to straight collecting tubes which open at the apex

Fig. 10-1. — Showing struc-
ture of Malpighian body and
uriniferous tubule. J, artery;
4/". afferent vessel; 3/, Mal-
pighian body ; T, tuft of blood
capillaries ; V, uriniferous tu-
bule ; Ef. efferent vessel; ]'.
vein. The blood first passes
through the capillaries of the
^lalpighian body and then
through the capillaries about
the uriniferous tubule.

EXCEETTOX

227

of the pyramids into the pelvis of the kidney. Fv^. 105
is a liijj^hly inajj^nificd section of kidney, showing some
branchfs of a collecting tube. All the secretions are
thus brought to the pelvis and drained off by the ureter.

^' ?

Fig. 105. — Section of cortex of kidney, hiijhly magnified, show-
ing Malpighiaii bodies and the tubes leading to the pelvis of the
kidney.

The excretions of the kidney.— The substances
excreted by the kidneys are urea, salts, other waste, and
a large quantity of water. The amount of liquid excreted
in one day is about three pints, about one ounce of
which is urea.

The chief function of the kidneys is to excrete urea.
The water is necessary that the other substances may be
in solution and thus be carried along.

The chief excretion of the Malpighian bodies is water.

228 THIED BOOK OF PHYSIOLOGY

The urea is excreted by the cells which line the urinifer-
ous tubules.

Urea is the product resulting from the use of proteid
food. In the chapter on food it was shown that proteid
is the only food which contains nitrogen. Urea also con-
tains nitrogen. The chemical symbol for urea is COX,H^.
Urea is gathered from the blood current by the liver, and
then the kidneys, with a little help from the skin, excrete
this waste product of the proteids. When the amount
of nitrogen excreted is equal to the amount of nitrogen
in the i)roteid food, there is said to be nitrogenous equilib-
rium. In this case the muscles neither gain nor lose in
weight. In case of starvation the urea continues to be
excreted, but it results from the fact that the muscles
themselves are being used as proteid food. Thus the
muscles waste away and the body loses in weight.

Diseases of the kidneys.— When the kidneys are
removed from an animal, death speedily ensues. The
urea accumulates in the blood and produces blood-poison-
ing.

Even a partial and temporary suspension of the work
of the kidneys always results seriously to the welfare of
the whole body.

Colds often cause an affection of the kidneys by causing
the skin to suspend its work as an excretory organ.
Extra work is thus thrown upon the kidneys, and, if it is
overworked, a diseased condition is produced.

Alcoholic drinks injure the kidneys more, probably,
than any other known cause.

EXrHF/nON 229

The cells of the tubules and Malpighian bodies become
changed, so that thoy no lonjjer perform well their
natural functions. Albumen of the blood is then often
allowed to pass out of the cai)illaries with the other
secretions. This condition is known as Bright' s disease.
Eminent physicians say that alcoholic drinks are one
cause of this fatal disease.

Fatty degeneration of the kidneys is another result of
using alcoholic drinks. ' Parts of the tissue of the kidney
are replaced by fat. Thus the secreting organ is in fact
decreased in size, for the fat can have no part in the
work of excretion. Extra work is thus thrown upon the
remaining parts of the kidneys, or the blood is allowed
to pass on through without proj^er purification, and the
whole body suffei's the consequence.

Alcohol also, as already explained, interferes with di-
gestion and the excretions of the liver. Thus injurious
substances are introduced into the circuit of the blood.
The kidney attempts to eliminate these in addition to its
natural work. As a result the kidney is overtaxed and
becomes inflamed and diseased.

Over-eating, also, or the eating of rich and highly-sea-
soned food, is the cause of much kidney trouble.

All parts of the body sutfer from any affection of the
kidneys because the purity of the blood is at once im-
paired.

QUESTIONS FOR REVIEW.

1. What is the source of the hydrochloric acid in the stomach?

2. What is secretion? Give examples.

3. What is excretion? Give examples.

230 THIRD BOOK OF PHYSIOLOGT

4. Is bile a secretion or an excretion?

5. Xame the chief excretory organs.

6. Describe the excretions of the lungs.

7. Do the air-passages correspond to the damper or the chimney
of a stove ?

8. How can you show that there is water in tlie breath?

9. What does the skin excrete?

10. Is the water in sweat an excretion or a secretion ?
. 11. For what two purposes is bile produced by the liver?

12. Locate and describe the kidneys.

13. !Make a drawing of a section of a kidney, showing cortex,
medullary layer, pyramids, pelvis, ureter, and blood-vessels.

14. Describe a Malpighian body.

15. Describe a uriniferous tubule.

16. What is excreted by the kidneys?

17. What is the cause of urea in the blood?

18. Explain "nitrogenous equilibrium."

19. Why does one lose flesh during sickness?

20. How important is the work of the kidneys?

21. How does a cold affect the kidneys?

22. What is Bright' s disease? What may cause it ?

23. Explain "fatty degeneration" of the kidneys.

24. In what other ways does alcohol have a bad effect on the
kidneys ?

25. Why does the whole body suffer when the kidneys do not
act?

CHAPTER XV

THE NERVOUS SYSTEM

The need of a controlling organ. — A number of
dift'erent systems and organs have already l>een explained.
Some are concerned in the movements of the body. Some
take in and digest the food. Some distribute food and
oxvgren to the cells. Others rid the bodv of waste and
impurities, and numerous others still are at work in one
way or another for the welfare of the whole body.

Each organ must work in liarmony with all the others,
or it itself must soon sutler. For example, the tissues of
the hands and arms need food : but. although the hands
be loaded with the best kind of food, the tissues cannot
get it until it is properly prepared by several other
organs. The hand carries the food t<» the mouth : there
it is masticated and mixed with saliva : then it is swal-
lowed, and digested in the stomach and intestines : thence
it passes over into the current of blood, and is distrib-
uted to the cells of the body. Thus the hands, by which
the first act of this process was accomplished, are de-
pendent on the organs of digestion, and the organs of
digestion depend on the hands to bring food within their
reach.

In a similar way each organ must rely upon the co-
operation of the othei^, and the failure of any one im-
portant organ will result in the destruction of all.

231

232 THIPvD BOOK OF PHYSIOLOGY

Froui this it is plain that there must be one organ, or a
collection of them, which shall have a controlling and di-
recting influence uj^on the others, and which shall not
only cause all i^arts to work in harmony, but also iji pro-
portion to the demands of the body at different times.

This important function is performed by the nervous
system.

An organized body of men. — The human body
may be considered as a number of units, each with a dif-
ferent function and all working together as an organized
body. The relation of these various units may be made
clearer by a comparison with a number of men who bind
themselves together in an organized body for the accom-
plishment of a definite purpose. In such an organization
a variety of different kinds of work must be done, and
each man selects the kind which he can do best and does
that only. Each member knows that his success depends
on the success of the whole organization, but however
o'ood his individual work mav be. his efforts mav not be
effective unless there is some way to direct his work in
accordance with what is being done by the other mem-
bers. So, in such an organization, a president is always
selected, and it is his business to so direct the work of
each that the general results may be most effective.

Heads of departments may also be appointed, and they
may look after many matters of detail without reporting
them to the iDresident. Each man may after a time be-
come so expert in his work that he can be trusted to
continue it without constant direction.

THE XKHVorS SYSTI':>r 233

Wlienever one menihei- of the organization fails to do
liis j)art or fails to work in harmony with the others,
then the president must be notified and the matter
adjusted, or the organization will break down.

All the relations just pointed out between the presi-
dent and the other members of the organization are
similar to those between the nervous system and the
other organs of the body.

The nervous system. — Tlie nervom system is com-
posed of nerve-centres, nerves, and special organs at the
ends of nerves. The nerve-centres are the brain, the spinal
card, and ganglia. The nerves all originate in the nerve-
centres and extend out to the parts to which impulses
are to be sent or from which impulses are to be received.

There is but one great nervous system, with centres
here and there, and nerve-trunks and nerve-fibres rami-
fying to every part of the body, the whole system being
more or less intimately joined together. But, because
of certain differences in character and function, the
system is divided into two parts. The first is called the
cerebrospinal or central nervous system, and includes the
brain, the spinal cord, and the nerves leading out from
them.

The second is called the Sympathetic, or Ganglionic,
nervous system, and includes numerous small nerve-centres
called ganglia, and the nerves which issue from them.
The sympathetic system is chiefly concerned with the
involuntary movements of the body, such as those in-
volved in digestion, circulation, and respiration.

23;

THIRD BOOK OF PHYSIOLOGY

The nerve-cell.— Nerve-cells, like other cells, are
composed of minute masses of protoplasm containing a
nucleus and a nucleolus. A very noticeable character-
istic of a nerve-cell is its tending to send off many pro-
cesses from the cell-body. Part of the processes are
short, and soon divide into numerous fine branches

Fig. 106. — Xeurons from the gray matter of the cerebrum. Cell-
body, dendrites, and short portion of the axis-cylinder are shown. A
micro photocrraph.

within the gray matter of the nerve-centres. These
branches are called dendrites because thej^ resemble, in
form, the branches of a tree.

One process of the cell, usually much longer than the
others, is called the axis-cylinder. It may extend out as
far as two or three feet from the bo(h' of the cell. The
axis-cylinder is a fine thread of protoplasm continuous

TllK NERVOUS SYSTEM 235

with the cell material. The cell-body, the dendrites,
and the axis-cylinder with its sheath and special endings
all constitute one cell. This cell is as much alive as any
of the one-celled animals described in the fii-st chapter
of this book. The processes of nerve cells do not have
movement as in the case of the amoeba ; but if the axis-
cylinder of a nerve-cell be severed, that part of it which
is thus deprived of connection with the cell-body and
the nucleus will deteriorate and pass away.

The unusual extension of a fine thread of the cell
material is the one thing about a nerve-cell which makes
it so different from the other cells, and also makes it
possible for nervous matter to exercise a controlling and
directing influence over other cells.

The unit of the nervous system, the neuron. —
Such a cell as we have just described is called a neuron.
The neuron is the unit of the nervous system. The
whole nervous system is a collection of a vast numl)er of
these units.

Since the axis-cylinder is a very delicate thread of
protoplasm, it is protected by one or more membranes
which surround it. Xearly all the axis-cylinders of the
cells in the central nervous system have two coverings,
as shown in Figs. 107 and 108. The first, called the medul-
lary sheath, lies next to the axis-cylinder and consists of
a white, oily substance. It is this sheath which gives to
many nerves their pure white apjjearance. Outside of
this is a thin ehistic sheath called the neurilemma.

The medullary sheath is broken at intervals of about

236

THIRD BOOK OF PHYSIOLOGY

Fig. 107.— Diagram of a neuron, c, body
of cell ; ?i, nucleus ; t^ dendrites ; a, axis-
cylinder ; w, medullary sheath (the white
matter) ; «, neurilemma; L nucleus of the
neurilemma ; f/, nodes ; e, endings.

Fig. 108. — A medullated
nerve-fibre, treated with osmic
acid, and highly magnified. 1,
its nucleus; 2, node; 3, the
axis-cj-linder ; 4, membranous
sheath of the internode ; 5,
medullary sheath (the thick
black line).

TITE NKRVOrS SYSTIOM

237

J^ of :iii iiicli 1)\' mxlrs. Tlu; iiciirilciiniKi is c.ontiniKHis
throuj^huut the whole hMi«;lh of Ihr nerve-libic, and in
it ;ue (Miibedded nnclei, one in cucli intcrnode.

Fibres which are covered )>y bolii tliese sheaths sire
called mnhdlated nerve -fibres, and sncli an- always white.

Other fibres, chielly those of th<' sympathetic nervous
system, have no medullary sheath, and so are gray in
color. These are called non-medullaled nerve fibres.

Nervous tissue. — Nerve tissue is composed of gray
and white matter. The gray is the essential part of the

Fig. 109. — Neuroglia cells.

system and is composed of the protoplasm of the cell
bodies and the axis-cylinder. Wherever a number of
cells are clustered together, the matter is gray, as in the
brain, the spinal cord, and the ganglia.

238 THIRD BOOK OF PHYSIOLOGY

The white matter is composed of nerve-fibres, the
whiteness being due to the medullary sheath around the
axis- cylinder.

Both the gray and the white matter are supported and
held together by the ordinary connective tissue, and also
by another tissue called neurogJia. Xeuroglia is peculiar
to the nervous system. A few of its cells are represented
in Fig. 109.

The brain. — The brain is the large nerve-centre of
the body. It is enclosed within the bony walls of the
cranium and is surrounded by three membranes. The
outer membrane is called the dura mater. It lies next
to the inner surface of the skull. The inner mem-
brane, called the pia mater, adheres closely to the sur-
face of the brain, passing in and out through all of its
folds.

Between the two is the arachnoid (like a spiders web),
so called because it is transparent and very thin. It is
transparent, however, only in the sense that lace or a
spiders web is transparent. It invests the whole sur-
face of the brain, but does not follow the pia mater into
the folds. Spaces between the arachnoid and the pia
mater are filled with cerebrospinal fluid. This fluid is
nearly pure water, and its purpose seems to be to protect
the brain in case of sudden jars or concussions.

The pia mater is a very vascular membrane. — that is,
it contains numerous blood-vessels for the supply of
nourishment to the brain.

The three membranes are together called the meninges,

TUK XKIJVors SYSTEM

239

and wlu'u tliey Ixicoine iiiMamo<l the disease is known as
cen'brospimd mrningitis.

The human brain is lai<;er, in i)roi)ortion to the size
of the body, than tliat of any other animal. Its ayeraj'e
weigcht is a little more than three pounds. The wei^rht
of the brain of Cuyier, the French naturalist, was (JG
ounces; that of Webster, the American orator, G.'!!-
ounces ; of Byron, the English poet, 64 ounces ; of Gauss,
the mathematician, 53 -ounces. The brains of some in-
telligent men are less than the ayerage in weigiit, and
those of some idiots much heavier.

Divisions of the brain.— The brain is divided into
several parts which diifer in function and composition.

Fig. 110. — The brain as seen from the right side.

The most important parts are the cerebrum, the cerebellum^
the pons, and the medulla oblongata. The cerebrum is the
most essential part of the human brain, and is so called

240

THIRD BOOK OF PHYSIOLOGY

from the Latin word cerebrum, wbicli means brain. Cere-
bellum is the diminutive of cerebrum and means little
brain. Pons is a Latin word meaning bridr/e. Medulla
means marroiv.

The cerebrum. — The cerebrum occupies the whole
upper portion of the cavity of the cranium. It is the

Fig. 111. — Top of cerebrum showing median fissure and convolution.s.

brain j)i"oper, the other parts being more or less only
aids. By weight the cerebrum constitutes about two-
thirds of the whole brain.

A median fissure, extending from front to back, di-
vides the cerebrum into the 7'igJit and left hemispheres.
(Fig. 111.) The two hemispheres are connected by a
broad band of nerve- fibres called the corpus callosum,,
shown in Fig. 112.

Other fissures, irregular in outline and not so deep as

TTIR NERVOUS SYSTEM

241

the median, divide the liemisplieies into lobes, which are
given names in accordance with the names of the l>ones
of the skull beneatli wliicli thej' lie.

Thus there are the frontal, the panetaJ, the temporal,
and the oecipital h)l)es.

The whole surface of the cerebrum is covered witli

Fig. 112. — Cross-secdon of brain. Left half.

gray matter to a depth of from one-sixth to one-twelfth
of an inch. It is called the cortex of the cerebrum.

This matter is composed of the cell-bodies, their sup-
porting tissue, and the blood-vessels concerned in their
nutrition. Beneath the gray is the white matter, which
is composed of the medullated nerve-fibres leading from
or to the cells.

On the surface of the cerebrum are numerous deep
convolutions or folds, which afford a large surface for
the gray matter. The number and depth of the convo-

16

242

TIIIED BOOK OF PHYSIOLOGY

lutions are the chief distinguishing marks between the
brain of man and tliat of the lower animals, and also be-
tween that of the liigher and lower races of men.

Fig. 113. — A portion of a horizontal section of a cerebral hemisphere,
showing convolutions.

The cerebellum.— The cerebellum— the lesser brain
— constitutes about one-eighth of the whole brain, and so
is called the lesser brain. It lies beneath the posterior
part of the cerebrum, as shown in Fig. 110. It is com-
posed of gray and white matter, the gray being arranged
in parallel ridges.

A cross-section of the cerebellum shows that the white
matter enters each of its hemispheres as a trunk, and by
numerous branches is distributed to all parts of the sur-
face. (Fig. 112.) From this api^earance the cerebellum
has been called the tree of life.

The pons. — The pons is situated below the cere-
brum and in front of the cerebellum. It is composed

TIIK NKIiVOUS SVSTKM 243

of both gray and white matter', and is ;il)()ut one inch
long and a littk^ more in thickness. Nerves from the
spinal cord pass up througli it lo tlic cerebrum and
cerebellum, and transverse libres i)avSs through it from
one side of the cerebellum to the other. Thus the pons
serves as a bridge by moans of which communication
can be made from one part of the nervous system to
another.

The medulia oblongata. — The medulla oblongata
is that i)art of the upper end of the spinal cord enclosed
within the skull. It is about one and a quarter inches
in length and about one inch through its thickest part.
A fissure on both its anterior and posterior sides divides
it into two equal parts. Both the gray and the white
matter are found in the medulla, the gray being col-
lected into groups which are more or less independent
of each other, and which are the origin of some of the
most important nerves.

Nearly all the fibres of the spinal cord cross over, in
the medulla, to the other side, and, continuing on their
way, make connection with the cerebrum and cerebel-
lum. Thus the nerves from the right hemispheres of the
brain are distributed to the left side of the body, and
those from the left hemispheres to the right side.

Nerves. — The neuron has already been described.
The axis-cylinder with its i>rotecting sheaths is a nerve-
fibre. A nerve is simply a number of nerve-fibres run-
ning side by side and bound together by connective

244

THIRD BOOK OF PHYSIOLOGY

tissue, in wliicli are blood-vessels that coiivej^ uourish-
ment to the nerve tissue.

Around the whole bundle of fibres is another sheath
called the perineurium.

The nerve-fibres lie close together in a nerve, but each
is independent of the others throughout its whole course.

Fig. 114. — Portion of a cross-section of a nerve showing the ends of
nerve-fibres. A niicrophotograph.

Whatever communication there is from one fibre to an-
other, it does not appear to be along any kind of connect-
ing fibre.

I^erves are smooth, white, shining cords which vary
in size from those scarcely visible by the naked eye to
the great sciatic nerve, which is about one-half inch
wide and one-sixth inch thick, and extends from the
lower end of the spinal cord down to the toes, sending
off some fibres along its whole course, and growing less
and less in size as it descends.

A nerve may be compared to a cable such as is used in
a telephone system, where several hundred copper wire3

TUK XI^RVOrS SYSTK.U 245

are encased in a lead tube. Each wire corresponds to
the axis-cylinder of a nerve-fibre. Around each wire is
a loose wrapping of paper, corresponding to the sheaths
about the axis-cylinder. Around the whole bundle of
wires is the lead tube, which corresponds to the peri-
neurium of the nerve.

The copper wires serve only as conductoi'S along
which electricity may flow from a battery or other
source of electricitj^ to a machine or device which it
operates at the other end.

Xerve-fibres, also, are only paths along which impulses
travel from a nerve-centre to the part of the body which
they stimulate. There is this difference, however, be-
tween an electric current passing over a wire and an
impulse passing over a nerve, — the whole of the energy
which operates a telegraph, telephone, or motor passes
over the wire, while in a nerve only enough energy
passes to stimulate to activity the i^otential energy
already stored in the parts to which the nerves are
distributed.

The illustration is more nearly true in the case where,
by pressure of an electric button, a slight current of
electricity is made to operate a device which opens a
valve and admits steam to the engines, which in turn
operate the machinery of a factory or exposition.

Efferent and afferent nerves. — All nerve fibres
appear to be alike in structure, but experiment shows
that there are two kinds, at least as far as their functions
are concerned. One kind conducts impulses out from

246 THIRD BOOK OF PHYSIOLOGY

nerve- centres, and so are called efferent or motor fibres.
Another kind conducts impulses towards the nerve-
centres and are called afferent or sensory nerve-fibres.

Efferent or motor impulses stimulate the muscles,
glands, or other parts of the body to activity.

Afferent or sensory impulses keep the nerve-centres
informed in regard to the condition of the body and its
relation to other objects.

The cranial nerves. — Twelve pairs of nerves
arise in the brain and pass out through openings in the
cranium to the eyes, the ears, the mouth, the nose, and
other important organs of the body. They are called
cranial nerves.

The first are the nerves of the sense of smell. They
are called olfactory nerves, and run from the nostrils to
the base of the cerebrum.

The second are the optic nerves, or nerves of sight.
They extend from the eyeballs to the base of the cere-
brum. Both the first and the second pairs are purely
sensory.

The third, fourth, and sixth i)airs are motor nerves
whieli run to the muscles that move the eyeballs.

The fifth pair are both motor and sensory, and are
distributed to various portions of the face.

The seventh pair are distributed to the muscles of the
face and scali). They arise from the medulla oblongata,
as do all the nerves of the last six pairs.

The eighth are the auditory nerves, or nerves of hear-
ing. They are purely sensory.

TJIE NERVOUS SYSTEM 247

The ninth are the gustatonj nerves, or nerves of taste,
and also the motor nerves of the i^harynx.

The tenth i)air extends farther from the brain than
any other of the twelve pairs. They are called the
pneumogastric nerves because of their important functions
in relation to the lungs and stomach. They are also
called the vagi, or wandering nerves, because they are
distributed to so many organs. Branches of these im-
portant nerves are distributed directly to the pharynx,
the oesophagus, and stomach, the larynx, trachea, and
lungs, and indirectly, through the sympathetic nerves,
to the heart, liver, pancreas, spleen, kidneys, small intes-
tines, and large blood-vessels.

The eleventh pair are distributed to the muscles of the
neck, and the twelfth pair to the muscles of the tongue.
Nerve-fibres from the cells of the brain are distributed
not ouh' to the other parts of the body, but connection
is made from one hemisphere of the cerebrum to the
other by numerous fibres through the corpus callosum,
and numerous other fibres connect the lobes and con-
volutions of the cerebrum with each other.

The spinal cord. — The spinal cord is a bundle of
nerve-fibres enclosing an axis of gray matter composed
of nerve-cells. It is about eighteen inches long in the
adult, and extends from the large opening, the foramen
magnum in the occipital bone, down to the lower part of
the body of the firet lumbar vertebra.

The spinal foramina of the vertebrae form the spinal
canal within which the spinal cord lies.

248

THIRD BOOK OF PHYSIOLOGY

The cord is surrounded by three membranes, the dura
mater, the arachnoid, and the pia mater, all of which are
continuations of membranes of the same names, already
described as coverings of the brain.

y'f^^

: -Wi^

Fig. 115. — Ding-ram of cross-section of spinal cord. A, anterior
fissure ; P, posterior fissure ; G, gray matter ; W, white matter. The
small circle at the centre is a cross-section of a minute canal which
runs the whole length of the cord.

The spinal cord is about one-half inch in diameter,
being a little thicker from side to side than from front to
back.

Two fissures run the whole length of the cord, dividing
it into two equal jiarts. The one in front is called the
anterior or ventral fissure, and the one behind is called the
Xjosterior or dorsal fissure. The anterior fissure is wider
and not quite so deep as the posterior.

A cross-section shows that the cord is composed of
white and gray matter, the white being on the outside
and the gray in the centre. This arrangement, as we
have seen, is just the opposite of that in the brain.

TIIK NF.IJVorS S VST KM 249

Tlie wliitc iii:itt(M- is (•oin])()S('(l cliielly ol" iiuMlullated
nerve-librrs runnin^^ \i\) and down tlie conl, wliilc tlie
gray matter is comi^osed (•hietty of nerve-cells. The two
sides of the cord are connected, as shown in Fig. 115,
by an istlinins of white and gray matter, giving to the
gray a resemblance to the letter H. The anterior horns
of the gray matter are blunt, and do not come very close
to the surface of the cord, while the posterior ones are
pointed, and reach almost to the surface.

In the centre of the isthmus, in the Fig., is seen a
small circle. This is a cross-section of a small tube which
runs the whole length of the cord, and opens above into
cavities called ventricles in the white matter of the brain.

Spinal nerves. — Thirty-one pairs of spinal nerves
issue from the cord and pass out between the vertebrae

A ^'^^^'^ ^1
Fig. lie. — A piece of spinal cord. A^ A, anterior, motor, or efferent
nerve-roots ; P, P, posterior, sensory, or afferent nerve-roots ; Gr, (?,
ganglia on posterior roots ; .S", S, beginning of spinal nerves.

to nearly all parts of the body. On each side of the an-
terior fissure are two shallow grooves, and on each side
of the i^osterior fissure are two similar grooves. From
these grooves the rootlets of the nerves spring in a close
longitudinal row, as may be seen in Figs. 116 and 117. A
number of these rootlets collected together constitute a
spinal nerve. Those that spring from the anterior part

250

THIED BOOK OF PHYSIOLOGY

of the cord, on each side of the fissure, are motor nerves o
Those which appear to originate on the posterior i^art on
each side, are sensory nerves. The motor and sensory
nerves from the same half of the cord
soon unite into one nerve, the two
kinds of nerve-fibres being bound to-
gether in the same bundle, and yet
remaining independent of each other
throughout their whole course.

On the posterior roots, just before
the}^ unite with the anterior ones, is
an enlaro:ement, or knot, called a

spinal ganglion. One of these is found
on each of the posterior nerve-roots.
These are small collections of nerve-
cells with special and important func-
tions.

The roots of the anterior, or motor,
fibres arise from the cells in the ante-
rior horn of the gray matter, and an
impulse from that source moves out on
the different fibres.

The sensory fibres arise from the

cells of the spinal ganglia, as shown

in Fig. 118. These fibres divide into

two, a short distance from the cell, —

one branch running out to the sensory

region, as the skin, and the other branch joining the

spinal cord and passing up through the white matter to

the brain. Here and there along its ascent fine branches

Fig. 117. — Poste-
rior view of the upper
section of spinal cord,
showing the eight
cervical nerves.

TITK XKKVors SYSTExM

251

are given oil" w iiiili aiborize about the cells in tlie ante-
rior horn of tlie gray matter. Tliat is, the libre at its
end divides into line branches, which mingle with the

Fig. 118. — Diairrani showinsr the ori2;in and relation of afferent and
efferent nerves. .?, skin ; G, ganglion ; P, posterior horns ; M, mus-
cle ; af, afferent nerve ; e/, efferent nerve ; A, anterior horns.

dendrites of the motor cell, much as the branches of one
tree may mingle with those of another when the trees
stand close together.

Nerve endings. — As already exi^lained, the neuron
is a cell which is peculiar in that it may send out a very
long process of its own material. The cell-body and its
nucleus are the central parts of the neuron 5 the axis-
cylinder process is the line of communication between
-the cell-bod}^ and the organ to which the neuron is at-
tached ; and the nerve ending is a special arrangement by
which a nervous impulse may be readily communicated
to the cells of other tissues, or by which an outside stim-
ulus, such as light, sound, and touch, uidy be received
with distinctness and inteusit}'.

Xot every neuron, however, is supplied with a special
ending. A single nervous impulse may be transmitted
over several neurons to its destination. As shown in

252

THIRD BOOK OF PHYSIOLOGY

diagram (Fig. 119), the impulse may start from A and
travel to B, thence on the next neuron to C. and finally

reach the ending in the muscle

at M.

M

Fig. 119. — Diagram
showing method by
which one neui'on may
communicate with an-
other.

Motor end plates. — At the
termination of nerves which are
distributed to muscles, the proto-
plasm of the axis-cylinder ai^pears
to be poured out on the muscle-
fibre for a distance in all directions,
as shown in Fig. 120. This is called
the end plate of the nerve.

An end plate is attached to each
muscle-fibre, near its middle.

The nerve-fibre pierces the wall
of the muscle-fibre, the neurilemma
being joined to the sarcolemma,

Fig. 120. — End plate of a motor nerve-
fibre.

and the axis-cylinder of the nerre being joined to the
protoplasmic contents of the muscle-cell. Thus, a uer-

TIIK NKRVOUS SYSTEM 253

vous impulse miiy start in a iiorve-ceiitre, as in the brain
or spinal cord, and Ix' conducted alon<;- a nerve to the
end plate, and thence to the fibres of muscle, causing
them to contract.

Endings of sensory nerves. — I n case of a sensory
nerve, the stimulus is applied at the end and the resulting
impulse travels in to the nerve-centre.

Fig. 121. — Diagnini .sliowing eH)iinection of a nervo-fibre to a cell of
muscle. A^ axis-cylinder of nerve ; ??, neurilemma ; ?/<, cell of muscle.

The office of this set of nerves is to keep the nerve-
centres informed in regard to the condition of the body
and the body's relation to outside objects. Thus, when
any wound is received or any organ is diseased, the mind
is informed by impulses conveyed on the sensory nerves.
The same set of nerves also convey sensations of heat
and cold and pres.suie.

One pair of this kind of nerves has such delicate
endings — the eyes — that even waves of ether can start
in them an imj)ulse which produces the sensation of
light. Another pair has the ears for nerve endings, and
waves of air can start in them an impulse which results
in the sensation of sound.

There are five special sensory nerve endings producing
five special senses^ — aeeing, hearing, feeling^ tasting, and

254 TRIED BOOK OF PHYSIOLOGY

smelling. These are more fully described in a separate
chapter.

Other nerves. — Xerves have been classified as motor
and fiensory because these are their chief functions. But
nerves perform other functions also.

Secretion and excretion are vital operations and are
performed by li\ing cells, which are grouj^ed together in
a form which we have called a gland. Xerve-fibres are

distributed to each cell of a gland,
and the stimulus which comes to
them over the nerves regulates the
activity of the gland. If such a nerve
be severed, the gland will become
inactive.

A nerve plexus. — A nerve
plexus is a point where many nerves
come close together and where fibres
branch off from one nerve and con-
tinue their way in another nerve.

Fig. 122. —Mode Xerve-fibres do not form a net-
of branching of nerve-

fi^j-eg work, like blood capillaries, but, as

shown in Fig. 122. fibres leave one
bundle and join another. Xumerous branches of this
kind occur in the plexuses.

The nerve which comes from a plexus may thus be
put in communication with many nerve-centres. In this
way the parts of the body to which such nerves are dis-
tributed, for example, the legs, are capable of a great
variety of movements.

THE NERVOUS SYSTEM 255

Nnnierous plexuses, some large and some small, are
fouml tlirougiiout llie nervous sj'stem. The chief ones
are found in tlie neck, the regions of the pelvis, and
associated with the sympathetic system in the cavities
of the thorax and abdomen.

The sympathetic nervous system. — The sym-
pathetic nervous system is chielly concerned in the stimu-
lation and control of tfie involuntary processes.

It is called sympathetic because of the close relation
or sympathy which these nerves establish between many
vital organs of the body. For example, increased mus-
cular effort calls for more blood, the arteries relax, and
the heart lesponds by beating faster. This calls for more
oxygen, and breathing is hastened. The product of this
increavsed combustion must be cared for by an increased
activity of the excretory glands.

Thus, by means of the connecting nerves, one organ is
made to work in harmony with another.

The sympathetic system consists of ganglia, nerves, and
plexuses. The chief ganglia are forty-nine in number
and are arranged in two rows, one on each side of the
spinal column and a little to the front of it. Each gang-
lion is connected by a nerve to the one above it and to
the one below it, giving to the whole the appearance of
two chains hung from the base of the cranium, with their
lower ends connected at the coccyx. Thus, there are
twenty-four ganglia on each side and one at the bottom
midway between, and to which the lower ends of the two
chains are attached.

256 THIED BOOK OF PHYSIOLOGY

The nerves of the sympathetic system are, for the most
part, non-medullated, and so are finer and of a grayish
color.

Along with these nerves are mingled many branches
of the spinal and cranial nerves, so that the whole ner-
vous system is intimately connected.

The sympathetic nerves are distributed to the viscera
of the thorax and abdomen, to the blood-vessels, and to
the lymphatics.

In front of the chains of ganglia are three great
plexuses of nerves containing numerous smaller ganglia.
The one in the thorax is called the cardiac plexus. The
one in the abdomen is called the solar plexus. It is just
back of the stomach and has smaller plexuses radiating
from it, the whole resembling somewhat the sun and its
rays, and hence its name. The one in the pelvis is
called the hypogastric plexus.

QUESTIONS FOR REVIEW.

1. Why does the. body need a controlUng organ? Ihustrate.

2. Compare the body as an organism with an organized body
of men.

3. Of what parts is the nervous system composed?

4. What three kinds of nerve-centres?

5. What are the two great nervous systems? Of what is each
composed ?

6. Describe a nerve-ceh.

7. AVhat is the unit of the nervous system?

8. Describe the axis-cylinder and its sheaths.

9. What makes a nerve-fibre white?

10. How does the gray differ from the white matter of tlie ner-
vous system ?

TITF M:iJ\'()rS SYSTK.M 257

11. W\\&t \i^ iietirogl id f

12. What is the ^rain/ Describe ita coverings.

].'>. What is meant by "the pin inatrr \< a vtu^cnlar iiM-rnbrane" ?

14. What is cerebrospinal 7neningiti.<t f

15. What is the weight of the human brain?

1«). What are the principal divisions of the brain?
17. Describe the cerebrum as to its fissures, hemispheres, lobes,
convolutions, and cortex.

IS. Describe the structure of the cerebellum.

19. Describe the poiis.

20. What is the medulla oblongata, and of what is it composed?

21. Describe the structure of a nerve.

22. How lai^e are nerves ?

23. Compare a nerve to a telephone cable.

24. What are the two kinds of nerves, and how do they differ?

25. How many pairs of cranial nerves f To what parts of the
body are they chiefly distributed?

2f>. Describe the pneumogasiric nerves.

27. How is the spinal cord protected ?

28. Make a drawing and explain the appearance of a cross-section
of the spinal cord.

29. How many spinal nerves ?

30. What are the roots of spinal nerves, and what two kinds ?

31. Which roots have ganglia?

32. Explain how the two kinds of nerves connect with the
spinal cord.

33. What are yiene endings f

34. Describe a motor end plate.

35. What kind of endings on the sensory nerves?

36. Explain a nerve plexus.

37. In what way does one nerve branch to another?

38. Why is the sympatJietic system so called?

39. Of what is the sympathetic system composed?

40. Describe the solar plexus.

17

CHAPTEE XVI

PHYSIOLOGY OF THE NERVOUS SYSTEM.

Some functions of the nervous system have already
been alluded to in the preceding chapter to make plainer
the anatomy of the part described. This chapter will be
devoted entirely to a brief description of some of the
fundamental functions of the system as far as known.

Little by little many important facts about nerve-
centres and nerves have been discovered, but as yet
much is unknown both about their anatomy and their
physiology. It is known, for example, that the mind is
in some way intimately associated with the brain : but we
have not even a plausible theory as to the nature of the
association. It is known that some kind of an impulse
passes from cells over nerves ; but nothing is known as to
the nature of the impulse. It is known that an impulse
may be transmitted from one neuron to another ; but it
is not known how this is accomplished.

All such facts will doubtless be satisfactorily explained
when the related sciences have advanced far enough to
make such things intelligible.

Four functions of nerve-centres. — Collections
of nerve-cells, forming nerve-centres, are the essential
parts of the nervous system, the nerves being simply the
carriers of nervous impulses.

258

TIIK NRRVOUS SVSTKM 259

Tlie functions of these centres may be classified ;is four
kinds. (1) They ore rrcfirer.s of imjmJsr.s hvow/ht fo them
over afferent nerves. The elfeet of the impulses is a sensa-
tion of which tlic niin<l uvax or may not become con-
scious. (2) Thei/ (ire the origin of iinputses which cause a
contraction <f )nn.seles. Thus, all movement of the body
is under the control of the nerve-centres. (3) They direct
and control nutrition^ secretion, excretion, and distribution.

0

(4) The highest function of any nerve-centre is that of think-
ing, hnoicing, feeling, ivilling, and remembering, all of which
are in some way connected with the cerebrum. These mental
operations are functions of the cerebrum only in the sense
that mind operates through the matter of that centre.

Function of the cerebrum. — It has been esti-
mated that the gray matter — the cortex of the cerebrum
— contains over 9,000,000,000 nerve-cells. The functions
of this great nerve-centre are the most important per-
formed by a human being, and are the distinguishing
marks between man and all other animals.

The cerebrum is the centre for all mental operations. It
is there that we are conscious of our existence and of what
w^e are doing. It is there that we study, think, imagine f
and remember.

All such mental operations are probably accomj^lished
by all the gray matter of the cerebrum working together.
In the anatomy of the cerebrum it was explained that
numerous fibres connected the hemispheres, lobes, and
convolutions of the cerebrum. By means of these the
cerebrum may act as a unit.

260

THIED BOOK OF PHYSIOLOGY

Localization of functions. — Two other great func-
tions of the cerebrum are volition and sensation. These
are more or less limited to certain areas of the cortex.
For example, one area may be a centre for the movements

W 0

0 R

Fig. 123. — Diagram showing the location of the motor and sensory
areas. It will he noticed that the motor areas are in the central region
of the cortex, and the sensory areas are in the posterior parts.

of the arm, and another for movements of the leg. One
area may receive sensory impulses from the eye and
another from the ear. Thus there is a division of labor
among the cells, each area performing a definite function
peculiar to itself.

By numerous experiments, many of these areas liave

THE XFRVOUS SYSTEM 261

been mapped out. If tliroii^h accident the skull is loade
to press upon certain portions of the cortex, it Ls ob-
served that some portion of the body loses sensation or
the j)Ower of motion — that is, l>ecomes paralyzed. Some-
times a blood-clot becomes lodged over certain parts of
the brain, and similar results follow. In such cases, if
the cause of the pressure be removed, the part of the
body that was affected will regain its normal condition.

Experiments have al9<5 l)eeu made upon the monkey's
brain, which most resembles the human, and when an
electric stimulus is applied to various points on the cor-
tex, it is observed that different parts of the body are
caused to move. Thus, when one point is touched, the
fingers will close. At other points the arms, legs, or toes
will be aflfecteil.

In this way the cortex has been mapped out into motor
areas, as represented in Fig. 123.

The sensory regions are not so definitely determined.
The sensation of vision is located in the occipitiil lobe of
the cerebrum, the region of hearing is iust in front of it.
and taste and smell are located in the temporal lobes.

Tne cerebrum as the controlling organ. —
The muscles uf the body may receive a stimulus from
several different nerve-centres, but all voluntary acts
have their origin in the cerebrum. Tlie cerebrum is the
centre of all voluntary motion.

Sensory impulses, also, may never reach the cerebrum,
or may be unheeded there, but all cautious sensation is in
the cerebrum.

262 THIRD BOOK OF PHYSIOLOGY

While the cerebrum acts as a unit in the higher func-
tions of thinking and knowing, each lieinisphere exer-
cises complete control over the opposite side of the
body, and through the sympathetic system may even
greatly modify the involuntary movements.

Impulses carried over a seusory nerve may produce a
conscious sensation, and the motor nerves may then at
once carry a stimulus to the muscles, and thus execute a
volition. The sensation may, however, be stored in the
meraorj^ and not acted upon for weeks or years. Man,
in this respect, differs from animals, which are in most
instances creatures of sudden impulse.

Intelligence and the size of the brain.— Other

things being equal, intellectual power is i)roportional to
the size of the brain. Size alone, however, is no proof
of a superior intellect. Men whose braius were of aver-
age size have often shown themselves superior in
thought to others who had a large head. The texture
and area of the cortex of the cerebrum seem to have
most to do with the character of a man's mental endow-
ment.

Function of the cerebellum. — The function of
the cerebellum, as far as known, is chiefly to harmonize
and coordinate the various movements of the body.
The act of balancing the body and retaining the proper
position in standing or walking or performing any act in
which many muscles are engaged is j^erformed by the
cerebellum. When this part of the brain is injured the

THK NKRVOUS SYSTPLM 263

sense of o<iiiilibrium is lost, and one will stagger like a
drunken man when he attempts to walk. The cerebrnm
can still order any movement as before, but the muscles
will not act in harmony, and so the execution of the
"movement will be extremely awkward.

Function of the pons.— As might be inferred
from the anatomy of the pons, it is chiefly a passage-way
for nerves from various -parts of the nervous system. It
contains, however, a considerable quantity of gray mat-
ter, and no doubt is the origin of some important func-
tions besides being simply a medium of communication.

General functions of the medulla oblongata
and the spinal cord. — Since the medulla is properly
a continuation of the spinal cord, they have functions
which are common to both. The first is tlie transmission
of impulses over the fibres of white matter to and from the
brain. These fibres cross in the medulla to opposite
sides, so that if they be severed on the right side above
the point of crossing, the left side of the body will be
paralyzed. If they be severed on the right side below
the point of crossing, the right side of the body will be
paralyzed. 3Iost of the motor impulses from the brain
pass through the white matter of the medulla, spinal
cord, and spinal nerves to the muscles, glands, and cells
of the body. Along this same route, though on different
fibres, many of the sensory impulses come to the brain.

The second important function, common to both, is
reflex action.

264 THIRD BOOK OF PHYSIOLOGY

The action is called reflex when a sensory impulse is
sent in to a centre in the medulla or cord, and from that
centre a motor impulse is sent out to a muscle or gland
without the knowledge or action of the cerebrum. By
reference to Fig. 118 the circuit of a reflex action can be
seen. A sensation starting at the skin is conveyed by
an afferent nerve to the cord, where a branch from the
nerve communicates with cells in the anterior horn of
the gray matter, and these cells send back a motor im-
pulse on an efferent nerve to the muscle. Thus a reflex
action is a short-cut from a sensory region to nerve-
centre and back to muscle.

By reference to the illustration in the second para-
graph of Chapter XV it can now be seen that these
centres of reflex action correspond closely to the heads
of departments in the organized body of men. In most
of the ordinary matters no report is made to the presi-
dent of the organization, but only to the head of the de-
partment, and he at once sends out the proper orders.
If anything unusual happens, then a report is made to
the head of the whole organization, — the president. In
the same way all ordinary routine matters of the body
are attended to by the reflex centres ; but when any-
thing arises which requires thought, deliberation, or
choice, the whole matter is referred to the cere-
brum.

The afferent nerve continues its way up the cord to
the brain, so that the same impulse may produce con-
scious sensation, and additional motor impulses may be
sent out by the overruling cerebrum.

THE .\HIiVOUS SYSTKM 205

Examples of reflex action. - A man whose spinal
cord is broken or diseased in the dorsal region will still
move his legs violently if the bottoms of his feet are
tickled. The tickling could not produce any conscious
sensation, for all connection with the cerebrum is sev-
ered. A centre in the lower part of the cord receives
the sensory impulse from the foot and at once sends
back on a motor fibre an impulse which causes the con-
traction of the muscles. ' It is evident from these facts
that certain nerve-centres may receive and send out ner-
vous impulses without the knowledge or interference of
the brain.

Such action is of constant occurrence in the normal
body. If the hand touch a hotobject, it will almost in-
stantly be pulled away. One will, even while uncon-
scious in sleep, brush a fly from his face ; and although
such action is not a result of a conscious effort of the will,
yet it is directed in accordance with a definite i)urpose.

The presence of food in the mouth, or even the sight
of food, may cause an impulse to be sent out to the
glands which secrete saliva or other digestive juices.
Such action is purely reflex and requires no efl'ort of the
mind.

Special functions of the medulla.— The medulla
contains some of the most important reflex centres. The
whole brain above the medulla may be removed, and the
animal so treated will continue to live, but without sen-
sation or volition. Sucli an animal will continue his
breathing in the ordinary manner, his heart will continue

266 THIKD BOOK OF PHYSIOLOGY

to beat, and other vital functions will be performed as
before, but he will remain in one spot until he starves to
death. If, however, he be touched, he will move. If
food be placed on the back of his tongue, he will swallow.
These are purely reflex actions.

If, now, the medulla be destroyed, death will follow
Immediately, for in the medulla is the "vital knot," or
nerve-centre, which operates breathing. This centre is
even stronger than the will itself, for, although we may
voluntarily stop breathing for a time, yet it will soon
begin in spite of any effort of the will.

In the medulla is another centre which regulates the
beating of the heart, causing it to beat faster or more
slowly as the need may be. Another important centre
there is the vasomotor centre, which causes the walls of
the arteries to contract or relax, thus regulating the
supply of blood to various parts of the body. Still
others are the sneezing, coughing, and vomiting centres.

The medulla is the great centre of those reflex actions upon
which the maintenance of life depends.

The economy of life in reflex action.— If every
sensory impulse had to go to the cerebrum, and every
motor impulse had to come from it, the mind could do
little else than attend to the ordinary routine matters of
life, and would do that very poorly. It is much better,
as nature has fixed it, to have certain centres which
become expert in doing those things which are repeated
again and again. In this way the mind is free to devote
itself to a consideration of higher and more important

TIIK NF^:RV0TTS system 267

matters. Thus a student can concentrate his whole mind
upon the solution of a problem, and other nerve-centres
will look after the breathing, digestion, excretion, and
the flow of blood.

Not only is there economy of life in having lellex
centres to perform the vital functions, but also many of
the acts, which at first re(iuired a conscious effort, may
and should become reflex. Those actions, which are
repeated again and again through life, should be made
automatic as completely as possible. Such actions as
walking, writing, playing a musical instrument, proper
forms of speech, dressing, and all actions which are con-
stantly repeated in any occupation in which one is
engaged, should be automatic.

Education of reflex centres.— Some of the reflex
centres, especially those in the medulla, were born with
us in full power of operation. These are indispensable
to the maintenance of life. Many other centres in the
cord and brain are capable of education.

The first efforts at walking require a close attention of
the mind, but by repeated efforts the action becomes
reflex and automatic. Then, when the motion of the legs
is once started, the walking will be continued, though
the mind be directed to other matters.

Writing at first is a laborious process, taking the full
attention of the child, but later the hand makes the
letters while the mind is attending to the thought.

The first attempt to play a violin is awkward, and the
mind must attend every movement of the fingers, but by

268 THIRD BOOK OF PHYSIOLOGY

constant repetition the action becomes reflex, and thought
can then be given to harmony and expression.

Even sach matters as tying shoe-strings or a neck-tie
become, by frequent repetition, purelj' automatic.

Habit. — Habit is an acquired disposition to act or
think in a certain way. It may easily be inferred from
what is said in the x>receding paragraph that habit is
formed by frequent repetition of the same act or thought.

A habit may be of the greatest advantage or disadvan-
tage to its possessor.

The character and mode of action of the nervous system
furnishes the basis for an explanation of the formation of
habit.

Several rei)etitions of the same act, in response to any
stimulus, will make it easier for that same stimulus to
result in a similar act. For illustration, when a boy is
being taught that he should lift his hat when he meets a
lady, he may have to be reminded of the fact a njmbei
of times at first, but after many repetitions of the act he
will perform it without any thought whenever the occa
sion arises.

One who has often wet his fingers or thumb in his
mouth when he wished to turn the leaves of a book is
quite sure to employ that method when he reads a paper
or book before an audience.

The motor impulses come to act in certain grooves, as
it were, and, unless the dominant cerebrum is able to over-
power and direct these impulses in new channels, the habit
becomes fixed.

TIIK NKIJVorS SVSTFM 2f)9

Functions of nerves.— Nerves are tlie conductors
of nervous impulses. While the niiturc of the impulse is
not known, its various effects an^ doubtless due to the
character of the orpin which receives it, just as a cur-
rent of electricity will produce sound in a telephone,
light in an electric lamp, motion in a motor, or elec-
trolysis in certain chemical compounds.

The various sensory organs receive stimuli from the
outside, and the afferent nerves carry them to the nerve-
centres.

The efferent nerves carry orders from the nerve-centres,
and their effect may be a contraction of muscles, secre-
tion of the glands, nutrition of the cells, or a regulation
of the rapidity and frequency of muscular contraction,
as in the heart.

Each fibre of a nerve has its own special work to do,
and if it is disabled the other fibres near by cannot
assume its work. If a small part of the liver or lungs
should be injured, the remaining part can completely
perform the functions of those organs ; but if a single
fibre of the optic nerve, for example, should be severed,
a blind spot will be produced in the eye.

QUESTIONS FOR REVIEW.

1. Give four functions of nerve-centres.

2. What makes the cerebrum such an important centre?

3. In what part of the cerebrum do we think?

4. Name several mental operations that are performed in the
cerebrum.

5. Explain what is meant by the localization of functions. How
was this determined?

270 THIRD BOOK OF PHYSIOLOGY

6. Give the locality of several motor areas in the cortex of the
cerebrum. Also locate several sensory areas.

7. What is voluntary motion, and where is its centre?
S. Where do we become conscious of a sensation?

9. "Why does an injury to the right side of the brain paralyze
the left side of the body ?

10. "What is meant by saying that wild animals are creatures of
sudden impulse?

11. AVhat relation is there between the size of the brain and
mental capacity?

12. What is the chief functioii of the cerebellum?

13. Of what use is the pons?

14. What two important functions are common to the medulla
and the spinal cord ?

15. Explain fully a reflex action.

16. Give several examples of reflex action.

17. Explain how centres of reflex action are like heads of de-
partments in a large store.

18. Describe the important functions of the medulla.

19. What class of reflex actions are centred in the medulla?

20. State fully the advantage of reflex action.

21. How can reflex centres be educated?

22. What is a habit?

23. Explain how habits are formed.

CHAPTEK XVII

HYGIENE OF THE NERVOUS SYSTEM

Nutrition of nervous tissue. — The brain, as well
as other nervous tissue, is directh' de})endent on the food
which we eat for its well-being and its ability to perform
its functions.

It is not known just how nerve tissue appropriates its
food, but it is clear that when the supply of food is in-
adequate, or the blood is for any reason impoverished
or poisoned, the nerve tissue will suffer in common with
the rest of the body.

This is a fundamental fact in considering the relation
between a health}- bodj' and a vigorous mind. All food
must be properly prepared by the organs of digestion,
secretion, and excretion, and then properly distributed
by the organs of circulation before it is ready for assimi-
lation by the nervous tissue or any other tissue. A
healthy nervous tissue is then possible only when other
organs of the body can supply to it good and sufficient
nourishment. It is not necessary to a strong mind that
the muscles be strong and that a man be able to perform
heavy manual labor, but it is necessary that the other
organs be able to perform their functions.

Expenditure of energy in nervous opera-
tions.— Every impulse sent out by a nerve-centre iu-

271

272 TRIED BOOK OF PHYSIOLOGY

volves an expenditure of energy. Every tliought which
passes through the mind, and every mental effort in the
solution of a problem or in pursuance of a line of thought,
uses up some of the store of energy in the brain. The
only source of this energy is the food which we eat and
the air which we breathe. Just as a muscle becomes
fatigued when its store of energy runs low, so a nerve-
centre can work only when it has a stock of energy to
expend.

The brain a favored organ. — All the other
organs are helpless without the direction of the brain.
Such actions as breathing and the beating of the heart
will continue for a time without any directions from the
cerebrum, but all voluntary action will cease, and the
whole body, if left to itself, will soon be without food, and
so without any store of energy to expend. The natural
result is death, which in this case would simply mean
that the store of energy had run out, and consequently
no further activity could be possible.

For this reason every effort is made by the body t6
protect and keep strong the master organ, — the brain.

By referring again to the organized company of men
which we have used for illustration, it is plain that the
life and health of the president, if he is a good one,
should be preserved for the sake of every other member
of the organization. Mnch more so is this true of the
brain, for no other organ can by any means be elected
to its place.

So we find the brain well protected from any chance

1IY(JIENE OF THE NERVOUS SYSTEM 273

injury, uiid it also appears that the other organs will,
when necessary, sacrifice some of their store of energy
for the sustenance of the brain, acting, as it were, on the
principle tliat if the brain should fail, all would fail
with it.

Proper kind of food for the brain. — Much
stress has sometimes been laid on the necessity of certain
kinds of food for the support of particular tissues. One
kind for the brain, another for the muscle or the bone,
and so on. While this is true to some extent, yet it is
fortunate that we do not at each meal have to determine
the needs of the various tissues, and then make out a
bill of fare to supply those needs.

Any good, mixed diet contains the elements necessary
for the sustenance of the brain. Besides, we cannot
conclude that because certain chemical compounds are
found in a tissue, that therefore we should eat foods
which contain those compounds ; for the cells of the
various organs are able to form many new chemical com-
pounds from the food material.

The important matters to be considered are that the
food be healthful for the whole body ; that it be well
masticated and digested ; that it be distributed in the
blood to points where it is needed ; that it be completely
oxidized ; and. last, that the products of the oxidation be
completely removed by excretion.

When all these are performed in a natural way, the
brain will receive its proper nourishment without further
attention on our part.

18

27-t

THIRD BOOK OF PHYSIOLOGY

The supply of blood to the brain.— ^Ve have

tried to emphasize the fact that every nervous impulse
and every process of thinking involve an expenditure
of energy which is obtained from food. The average
brain constitutes only about one-fiftieth of the weight

imfpj

Fig. 124. — The carotid artery conducting: I'lood to the head. C, right
carotid ; I. internal carotid : E. external carotid.

of the body, but about one-eighth of the blood is sent to
it for its nourishment. The internal carotid artery, as
seen in the figure, one on each side, passes in through
the base of the cranium, and is distributed through the
vascular pia mater to the brain -cells. If the blood

IIVCIKNK OF THE XKRVOUS SYSTEM 275

should be witlidrawu. unconsciousness would result at
once, and in a short time death.

This close dependence of mental action upon the blood
supply makes it clear that the blood should be rich in
those materials which are loaded with energy, and also
free from alcohol, nicotine, opium, and all other .sub-
stances that have an injurious effect upon the nervous
tissue.

Brain fatigue. — A machine cannot give out any
energy until it first receives it. That is, it cannot do

Fig. 125. — .4. a cell stored with energy-yielding material: B. same
cell fatigued after a period of work.

any work until work is done upon it. A clock will not
run until it is wound up. If you will transfer enough
of your energy to a clock -spring to keep it running for
eight days, the clock will come to rest at the end of that
time only l^ecause the store of energy which it received
from you has then been expended.

The cells of our bodies are little machines in this
respect. They can convert energy which was in food
into other forms, such as motion and heat, but they can-

276 THIRD BOOK OF PHYSIOLOGY

not expend any more than they receive. This is just as
true of nerve-cells as of any cells of the body.

It is j)lain, then, that after cells have been at work for
a time their store of energy will be expended, and the
cells will become fatigued.

The condition of a fatigued cell can actually be ob-
served by means of a microscope. As seen in Fig. 125,
the cell at first is round and plump, but after a season of
work it became jagged and shrivelled. The cell can now
be stored again, and will then be able to do more work.
Thus the cell is like the clock-spring, and if they are
regularly re-stored with energy they will continue to run
until worn out.

Need of sleep. — Cells may be receiving and expend-
ing energy at the same time, or they may rest and store
up an excess of energy, which may be rapidly expended
later.

Man and all animals are so constituted that periods of
complete rest in sleep are absolutely necessary. Some
organs of the body, as the muscles, may get partial rest
by simply ceasing from work, but there is no complete
rest, particularly for the brain, except in sound sleep.

The nature and cause of sleep are not known ; but it
is known that during that time the fatigued and shrivelled
cells gradually become round and full, and thus are
ready for vigorous effort when the period of sleep has
passed.

During sleep every organ of the bodj' partially or
completely suspends operation. All consciousness and

TTYCIKXK OF TIIK NKRVOFS SYSTRM 277

all voluntary action cease completely in sound sleep.
Even reflex action is slower in response to any stimulus.
Breathing, beating of the heart, and excretion continue,
but at a slower rate.

Sleep, then, is a period of complete rest, during which
the cells constantly gain in energy-yielding material, and
at the same time there is a minimum of expenditure of
energy.

Amount of sleep necessary. — The amount of
time that should be spent in sleep varies with age, occu-
pation, temperament, and state of health. Eight hours
is probably a fair average. Children need more than
eight houi-s, and old people less. Most j^eople take too
little rather than too much sleep. This is especially
true of active young men and women. Xeeded sleep
that is lost can never be completely made up at a later
date. The over-expenditure of energy is not a matter
of much consequence, for energy is plentiful in the world ;
but it is a matter for most serious consideration that the
machine — the cell or organ, — may therebj^ be injured so
that its capacity for receiving and transmitting energy is
thereafter lessened.

Vigorous mental exercise is conducive to strength of
intellect. The more the mind is properly used the
stronger it becomes, just as a proper exercise of muscle
will result in its development. But there are limits
beyond which either brain or muscle will be injured by
further exercise. The limit is reached when the store of
energy runs low and demands are made upon them be-

278 THIED BOOK OF PHYSIOLOGY

yond their ability to perform. At such a time a period
of complete rest in sleep must be taken, and should be
continued until the cells are again stored and ready for
a period of activitj'.

When a youth is healthy and his sleep is natural, he
will not, as a rule, sleep too long. A good rule is, ^' Early
to ])ed and late to rise (if necessary), but wide awake
and intense all day." Things are accomplished in this
world not by long time and weak effort, but by intense
application in a short time. Only those who take plenty
of sound sleep can have a stock of energy sufficient for
sustained effort during even a short time.

A student who si:>ends enough time in sound sleep is
never injured by the amount of work expected of him in
the schools : but one who spends a night amid the excite-
ments and distractions of a social gathering and takes
only a few hours of the morning for a light and fitful
sleep, and ends up a series of injuries with a forced and
hurried breakfast, can hardh' be equipped for a stren-
uous day's work. The efforts of such an one are attempts
to draw from a store which is already exhausted.

How to induce sleep. — Under normal conditions,
sleep is perfectly natural and easy, and nature will herself
determine the time and the amount that are necessary.
But the modern way of living is producing an increasing
number of those who suffer from insomnia. The intense
activity of the day, accompanied by worry and excite-
ment, the overtaxed mind and body, the stimulation of
drugs, the unhygienic forms of dress, the lack of periods

HYGTENR OF TIFF. NKRVOUS SYSTKM 279

of rt'post' :iiul ix'cieatioii, and indulgence in the use of
alcoliolic diinks. and the excessive use of tobacco, all
tend to ])r()duce a condition of the body which is apt to
result in insomnia, or at least in very light and restless
sleeping. Even without any apparent fault of the suf-
ferer, sleep often comes tardily or not at all.

Narcotics, such as morphine, are often taken to pro-
duce artificial sleep, but such a i^ractice is very danger-
ous, and should be resoited to only on the advice of a
competent physician.

Those who have a difficulty in going to sleep may often
profit by a few simple rules, as follows :

(1) After being dressed for the night, take some light
gymnastic exercises with dumb-bells, and also by rising
slowly a number of times upon the toes and then upon
the heels.

(2) Take a warm bath and rub the body, thus re-
moving any cutaneous irritation ; or simply bathe the
feet and legs in cold water.

(3) See that there is sufficient ventilation to keep the
air fresh during the night. Sleep on a fairly hard mat-
tress,— never on feathers. Use only light covers.

(4) Do not attempt to think out a i^roblem or make
any kind of mental effort after retiring. Get the mind
as nearly as possible in a state of inactivity.

(5) Make a serious effort to dismiss all worry and ex-
citement. Keep the mind on some pleasant experience
or anticipation. Do not dwell on an imaginary train of
possible evils.

(6) Relax every muscle in the body. This is impor-

280 THIRD BOOK OF PHYSIOLOGY

taiit. Even when the body appears to be in repose, it will
often be found that several muscles of the legs, arms, or
neck are tense. Practise the art of relaxation several
times each day, until it can be easily and completely
done. Efficiency in the art of complete relaxation is
valuable not only for the purpose of inviting sleep, but
also for periods of repose which should be taken during
the day.

(7) Retire with the intention of at once going to sleep,
and thus a habit may be formed in which sleep is asso-
ciated with that environment.

Good and bad habits. — Habit, as already ex-
plained, is a tendency to do again in the same way the
things which have often been done before. Habits may
be good or bad. Either kind may become fixed. Xo
one cares to get rid of a good habit, and fortunately it
would be difficult to do even if one did wish to change
it. Bad habits become equally fixed and difficult to
change.

It is necessary to any man's success that he should be,
in most things, a creature of habit, and, of course, these
habits must be good ones. In all things which a man
does by force of habit, he will, if his habits are good, do
the right thing in the right way without thinking about
it. Herein is the great advantage and economy of being
a creature of correct habits, and nothing so handicaps a
young man or woman as habits which are incorrect.

Bad habits include more than immoral tendencies. A
very moral man often has some bad habits. An awkward

llV(ilEXE UV THE NEliVOlIS SYSTEM 281

walk, carelessness in dross, impolite address, improper
table manners, wrong forms of speech in common con-
versation, scrawly and illegible writing, lack of intensity
in effort, tendency to slight work, and so on, are all
habits which will remain and grow more and more
marked, unless they can be forcibly corrected. No edu-
cation is more valuable to a man or woman than the
numerous good habits which may be formed in the earlier
years of life, for, in its* broadest sense, habit is only
another name for character.

In earl}^ life the nervous system is in its plastic stage.
Habits are then easily formed or changed. But every
act, every thouglit, and every way of doing things make
a lasting impression even on the youthful mind. At the
age of twenty-five or thirty years the nervous tissue may
be said to have become set. Only by a strong effort of
the will and by continued practice can a habit hitherto
formed be now changed, and it is doubtful that a radical
change can ever be made.

The nervous system, however, never entirely loses its
plastic nature. By persistent effort old habits may be
practically changed, though the tendency to return to the
old habit is always imminent.

These considerations make the education of the youth
of to-day a matter of supreme importance for the sake
of the coming generation.

Effect of alcohol on the nervous system.—
The nervous system, more than any other part of the
body, is injured by the use of alcohol. The same amount

282 THlIiD BOOK OF PHYSIOLOGY

of. injury to the braiu will have a greater evil effect,
because the brain is the controlling organ.

An injury to the head of any organization is more
serious, as far as the welfare of the organization is con-
cerned, than a similar injury to an inferior member.

We have shown that a centre in the medulla controls
the rate of the heart-beat. Any injury to this centre
will, of course, affect the action of the heart, though the
heart itself may be perfectly sound. In a similar manner
whatever affects the vasomotor nerve-centres will modify
the circulation of the blood, and any injury to a motor
area of the cerebral cortex will affect its control of the
muscles which it stimulates to action. The cause of
dyspepsia may lie in the nerve-centre which normally
stimulates the secretion of the gastric glands.

Thus alcohol works a double evil in that it injures the
various organs in ways already explained, and, worst of
all, it weakens or finally destroys the nervous centres
upon which the other organs must rely for stimulation,
nutrition, and recovery from iujurj-.

Mankind has had a long experience with alcohol, and
many scientific investigations have been made as to its
effects on the human system. Almost without exception
its continued use as a drink has been found to have an
evil effect. Whether the matter is considered from a
physiological, a financial, or a moral stand-point, the use
of alcoholic drinks as a beverage is condemned by scien-
tific facts as well as by the experience of mankind. The
so-called arguments in its favor are chiefly apologies for
its continuance, and tjie main motive back of the traffic

IIVCIKNE or TIIK NKIiA^OUS SYSTEM 28;{

ill intoxiciitin<; li({iiors is the; soiirci; of gain to its pro-
moters.

Alcohol holds iiii important place in the arts, and it
may be useful jls a fuel, but it is every day becoming
more evident that alcoholic beverages, even in moderate
quantities, are evil, and only an evil.

Alcohol in small doses.— There has been, and is
now, a prevalent notion 'that if alcoholic liquors are used
in moderate quantity, much good may be derived from
them, or at least no injury would be done.

This mistaken notion is the chief cause of both the
moderate and the immoderate drinking of alcohol.

The masses of people do not have the facilities or the
inclination to investigate the subject ; and because they
know that a moderate use of malted liquors produces no
apparent evil, while it does often bring about a feeling of
bodily comfort and of mental cheer, they are easily de-
ceived.

The body has within itself wonderful agencies of re-
cuperation. It differs from any other machine in that it
can build uj) and repair itself. Whenever any injurious
substance, as alcohol, is taken into the body, an effort is
at once made to excrete it ; but before this can be done
much of it is carried in the current of blood to the various
tissues, where it exerts its poisonous effect upon the pro-
toplasm of the cells — particularly the nerv^e-cells. If the
amount of alcohol is small and is much diluted, the in-
jury to the cells may be slight and easil}^ repaired. It
should be carefully noted, however, that alcohol, in what-

284 THIRD BOOK OF PHYSIOLOGY

ever doses, presents itself to the cells as an enemy, whose
evil effects are to be either prevented or repaired.

Because the cells are able to survive the effects of a
small dose is no proof that it is not a poison, any more
than small doses of arsenic or strychnine might be con-
sidered harmless because they do not at once destroy the
tissues or arrest the functions of the organs. Food, on
the other hand, comes to the cells without any antago-
nism, and is assimilated in a natural manner.

These facts are of the greatest importance in the con-
sideration of this subject, for the apparent immunity from
the evil effects of the small dose is the gateway through
which all immoderate drinking steadily creeps in.

This immunity, however, is only apparent. Each
recovery from the poisonous effects leaves the nervous
system with less ability to resist the next. Its evil effects
are thus cumulative, and sooner or later become apparent
in a weakened condition of some organ or a suspension
of some function.

Most people do not look far into the future or are
willing to take chances. Unless serious pain or sickness
follows at once upon a certain line of conduct, they are apt
to continue in a course which gives present gratification.
As a consequence, the evils from moderate drinking are
most insidious in character, for irreparable harm may be
done before the drinker is aware of his condition.

Alcohol as a mental stimulus. — The first effect
of a drink of alcoholic liquor is an apparent stimulation
of the nerve-centres to greater activity. This has led

TTYGTKNE OF THE XERVOUS SYSTP:M 285

manj' to believe that alcohol has the effect of rousing
mental activity, and that one can write and think more
brilliantly under such a stimulus. But careful examina-
tion will show that alcohol produces in the brain a con-
dition of excitement i-ather than that of healtlifnl stimula-
tion. It may properly be compared to the introduction
of a poisonous serpent into the midst of a company of
people in an enclasure from which they cannot escape.
There would no doubt be intense activity in the com-
pany, and great excitement, but the motive in all their
efforts would be that of self-preservation.

It would not be probable that this increased activity
would result in any worthy accomplishment, and after
the serpent is removed it is quite x»robable that each
member of the company would find himself in a state
of fatigue, which would prevent any, even natural, effort
until after a period of rest.

WTien one's brain is thrown into a state of excitement
by alcohol, he gets an exaggerated idea of his capacity to
think and work. He imagines he is doing more than he
is in fact. One who writes a production in this state of
excitement may at the time be highly j)leased with his
effort, but a calm review later will show that he greatly
overestimated his work.

A hearty meal of good food, abundance of fi-esh air,
and plenty of sleep are the natural and proper provisions
for intense and sustained effort.

Immoderate use of alcohol. — Every one abhors
the coiidition uf a confirmed drunkard, but nearly every

286 THIED BOOK OF PHYSIOLOGY

one who drinks immoderately was at one time only a mod-
erate drinker. Immoderate drinking is a natural result
of moderate drinking. Under the continuous poisonous
effects of alcohol, even in moderate doses, the nervous tis-
sue deteriorates and loses its former delicacy of response to
stimuli. More alcohol must now be taken to produce the
desired effect. Besides, an appetie for alcohol is gradu-
ally contracted, and becomes so strong that all the efforts
of the better side of a man's nature cannot resist it.
The antidote for alcoholic poison is more alcohol. Con-
siderations of home, family, morals, and respect of others
gradually come to count for naught. Such an one is
suffering from a self-inflicted disease which is known as
dipsomania, — madness for drink.

The disease may yield to j^roper treatment and the
patient may again get control of himself, but he never
fully recovers, and a very slight temj^tation will in most
cases lead him again into inebriety.

Complete recovery from the effects of immoderate and
long- continued use of alcohol is imi)ossible because of
the changes made in the character of the nervous tissue.
It is found that the brain becomes shrunken in size and
the space about it becomes filled with water. Many of
the cells degenerate into fat or connective tissue. Thus
the essential and vital part of the tissue is sacrificed, and
of course the power to think and control the body is
^proportionately reduced.

The last stage of dipsomania is often delirium tremens.
This is the most horrible condition to which a human
being can be reduced, and may come on at any time

]TV(;iKNK OF 'niK XKI{Vr)rs SVSTKM 287

iluriiig a period of drinkinjjj, — even early in the career of
the drnnkard. Il in ('IVect transforms a man into a wild
lM*ast. Tlu' iimscles are all in a tremoi-. becanse the
poisoned motor centres can no longer control tliem.
Tli«' mind is delirious and imagines all sorts of horrible
iH'asts, serpents, and insects, which are ever in pursuit
and cannot be driven away. Death may come to the
sutierers relief at any instant, or the tx)rture may hust for
several days, and then be followed by a return of the
rational state.

Hereditary effect. — Nothing in physiology is more
clearly established than the fact that children inherit
traits, dispositions, bodily and mental strength or weak-
ness from their parents.

Children of drunken parents are often at a great disad-
vantage because of some inherited weakness. Defects
of some kind are usually handed down from a father or
grandfather who has been given to the use of alcoholic
drinks. Maybe the child will have weak lungs and be
predisposed to consumption. Maybe there will be some
physical defect in the brain, with a consequent dulness
or tendencj^ to insanity. The general tone of both mind
and body may be inferior, and the child be thus handi-
capped for life.

An appetite for strong drink frequently appears in the
children of drinking parents. Such an appetite may be
aroused by a few drinks of alcohol. Thus, one who per-
sists in drinking alcohol injures not only himself but
also all those dependent upon him while he lives, and

288 THIRD BOOK OF PHYSIOLOGY

may transmit the evil effects of liis course to generations
that follow.

The only safe course. — There is only one safe
course in regard to the use of alcoholic liquors, and that
is totally to abstain from their use. An occasional indul-
gence in some mild alcoholic drink may do no perma-
nent injury that is apparent ; for, as we have explained,
the body is able, within certain limits, to repair any
organ that is injured. But whatever may be said about
the harmlessness of the small dose of alcohol, it is still in
accordance with the testimony of the best experts and of
the best elements of the human race that the only safe
course is total abstinence.

The experience of men in the future will be just as it
has been in the, past ; and the testimony of individuals,
communities, and nations in the past is all against the
use of alcohol as a beverage.

Tobacco and the nervous system. — Many of
the fundamental objections to the use of alcohol can also
be urged against the use of tobacco. Tobacco contains a
violent i^oison called nicotine. A very small quantity
of this poison in a concentrated form would soon cause
death. When by any use of tobacco it is introduced
into the current of blood, it of course is carried to the
brain as well as to other parts of the body.

Its general effect upon the nerve-cells is much the same
as that of alcohol. That is, it tends to do injury, and
must be either warded off or the injury nuist be repaired.

HYGIENE OF TIIF. XERVOUS RVSTFM 289

^\ hen Olio hjus attained liii^ full growth, is healthy, and
is engaged actively in some outdoor work, the noticeable
l)hysical injury from tlio moderate use of tobacco may
not be easily recognized. To students, clerks, or any
whose constitutions are delicate, and whose work is in
close rooms, the use of tobacco is very harmful. This is
particularly true of the cigarette. Many investigations
have been made in regard to the smoking habit among
students in college, and every report of such investiga-
tion shows that the smoker is inferior in his standing.

The worst effect of tobacco is found in its use by the
young. Those who are growing are likely to stunt their
growth by the use of tobacco. Nicotine will seriously
affect certain nervous centres, thereby causing organic
troubles, such as the irregular action and palpitation of
the heart so common with those who use tobacco freely
or with the youth who uses tobacco at all. Other nerve-
centres wdiich regulate secretion and excretion are also
injured, so that blood improperly purified is distributed
to the various cells. The easily fatigued muscle of the
smoker is an evidence of this fact.

Worst of all, the mental powers are weakened. This
results both from the poisoning of the brain-cell itself, and
also from the fact that the other organs do not furnish
pure blood for its nourishment. It will be observ^ed in the
public schools that the youth who smokes (if he smokes
at all he will usually smoke a great deal) will be restless
and inattentive, will lack ability to appl}^ himself and
hold his mind to his studies, and of course will fall be-
hind and want to quit school. It is also observed that

19

290 THIED BOOK OF PHYSIOLOGY

students who are in college and wlio are habitual smokers
cannot with credit meet the requirement in those studies
which can be mastered only by concentrated effort and
attention. This statement can be ^'e^ified by college
statistics on this point.

Cigarette smoking is the most injurious use of tobacco
for the reasons already given under the subject of respi-
ration.

Opium. — Opium is a powerful narcotic poison. Its
use is not so common in the United States as is that of
alcohol and tobacco, but it is all too common. The vic-
tims of the opium habit yield to an appetite which they
are helpless to resist, and sink to extreme degradation of
both mind and body. The druggists of almost every
town can point out a number of both men and women
who will resort to any deception to secure opium. They
will lie or steal, if necessary, to secure the money to l)uy
the drug. The victims are stealthy in their practice, and
will usually deny that they use it, so that the prevalence
of the habit is not commonly known.

The opium habit is easily contracted. Morphine is a
tincture of opium and is frequently used to allay pain.
Its continued use may engender in the system a craving
for it which is difficult to resist.

Some patent medicines, which are advertised as '^pain-
killers" and "stomach bitters," contain as much as 40
per cent, or more of alcohol and often a considerable quan-
tity of morphine. Both drugs are narcotics, and of
course will stop pain by x^aralyzing the sensory nerves.

IIV(rIENR OF TIH^: NRIiVOlTS SYSTIvM 2:il

In such ways the unsuspecting victim may after a time
find liimself a slave to the opium liabil, from wliicli it is
very jn'obable he Mill nevei- l)e ri<M'.

QUESTIONS FOR REVIEW.

1. Why is blood distributed to tiie nervous system ?

2. What connection is there between food and nervous opera-
tions ?

3. Show how tlie brain is the favored organ of the })ody. Why
is this po ?

4. How can we supply the brain with healthful food ?

5. How i.s blood conducted to the brain ?

6. Explain wliy brain-cells become fatigued.

7. How does a fatigued cell differ from a rested one?

8. AVhat is the condition of the body and mind during sleep ?

9. What is the purpose of sleep?

10. How much sleep is necessary?

11. Will study injure the mind ? AVhat will ?

12. What is insomnia? What causes it ?

13. Ciive some good ways of inducing sleep.

14. What is meant by repose and relaxation ?

15. In a broad sense, what is meant by good and bad habits ?

16. What is the best time of life for the formation of habits?
Why ?

17. Why is an injury to the brain more serious than an injury to
other organs ?

18. How does injury to the brain work a double evil ?

19. Tell all you can about the use of alcohol in small doses.

20. Is alcohol beneficial as a stimulus to mental activity? Ex-
plain.

21. What is the best condition of the brain for clear and strong
thinking?

22. Describe dipsomania.

23. What is the hereditary effect of excessive drinking?

292 THIRD BOOK OF PHYSIOLOGY

24. What is the only safe course in reference to the use of
alcohol ?

25. Describe the effects of tobacco on the nervous system.

26. Tell all you can about the opium habit.

27. What is opium, and where is it produced? (See dictionary
and cyclopaedia. )

oil A 1' TKK X \ I I I

Tin: SIMlCI.Vr. SENSES

What the special senses are.— The special senses
art- tiH>S(' whirli arc prodiUMMl by special organs at the
oiiliT ends of sensory nerves. They are seeing, hearing,
toiiehing, tasting, and smelling. Tlie special organs which
piodncc these sensiitions are the eyes, the ears, the touch
corpnseles, and tlio special endings of the gustatorg and
olfactorij nerves.

General sensations.— There are many other sensa-
ti(tus ill the body which may. more properly, be classed
as general sensations. These are such as

(1) 'Vhid sense of temperature, which is located principally
in Ihe skin. By this sense we are promptly informed as
to whether the temperature is too high or too low for the
most successful operation of the cells and organs which
are affected. This sense is also acute in the mouth and
at the entrance of the nose. These are the points of
entrance of food and air, and. as we might expect, we
find here several outposts, or guards, such as touch, taste,
smell, and this additional one. — the sense of temperature.

(2) The sense of pain. Wiien any sensory nerve is in-
jured or is excited beyond what is natural, a sense of
pain results. When the epidermis is removed from any
part, as in case of a blister on the finger, contact with

293

294 THIED BOOK OF PHYSIOLOGY

the exposed true skin will produce pain rather than a
sense of touch. ^Vhile pain is sometimes considered a
great evil, yet it is in fact a very great blessing, for
otherwise we would become verj- careless in regard to
the liealth of our bodies. Even if we always tried to do
what was best, we would often be ignorant of the effects
of our course except as we were checked by pain. The
cause of pain, and not the pain itself, is the thing to be
avoided.

(3) Sense of hunger, thirst, fatigue, or illness are all gen-
eral senses which are very vague in their character.
They cannot be definitely located, and aie probably the
combined result of sensory impulses from all or many
cells of the body. Their purpose is to inform the cere-
brum as to the state of the cells in reference to their
ability to perform their natural functions.

(4) The sense of weight. By this sense it is possible to
determine the weight or resistance of an object by the
amount of muscular exertion. This sense ms-v be so
trained that it becomes fairly reliable.

(5) The sense of pressure. This sense is most delicate
on the forehead, where a slight increase or decrease of
pressure may be detected.

Advantage of the special senses.— By means of
the special senses we are able to gain elearhj defined
knowledge of objects outside the body. If the fine
branches of the optic nerve were distributed in the skin
of the face, we could probably tell darkness from day-
light, but could never have distinct images of objects

THK SPECIAL SKXSp:S 295

such as we ^a't when light tirst passes tliruugh the eye
and then falls upon the nerve-ends. Simihirly, wo might
get an idea of some intense sounds without ears. l>ut the
sensation would lack all distinctness and delicacy.

The five special senses are the five great avenues
through which all, or nearly all. our knowledge is gained.
It is through them that connection is made between the
outside world and the central nervous system. If all
sensiitions were suddenly 4x) cease, a man would continue
to live, but it would be impossible for him to determine
whether he existed or nut. He would for a time con-
tinue to think as a result of his store of previous sensa-
tions, but soon these would fade away, and his mind
would become a complete blank. Thus we are in constant
dependence upon the streams of sensation from our
special sense organs.

The two great media. — Every minute of our lives
we must V)e surrounded l)y two great media, — the air and
the ether. We might expect, then, to find, as we do find,
that two of the most valuable and delicate sense organs
are the ones which record any disturbance in these media,
— the ear being a receiver for waves of air, and the eyes
for waves of ether.

The ether fills all space and permeates all matter.
When it is agitated at any point, waves pass out in every
direction, like the waves which go out from the point
where a stone is thrown into a still pond, only the ether
waves will go out in all directions as radiations from the
centre of a sphere. The sun is constantly sending out

296 THIRD BOOK OF PHYSIOLOGY

waves of this kind, and they travel the whole distance —
about 93,000,000 miles — from the sun to the earth in
eight minutes. Thus the earth is flooded with waves
which cause nearly all the light and heat we have on
earth. In the same manner light comes to us from the
stars, which are vastly farther away than the sun. Thus
the eye, more than any other sense, gives us knowledge
of objects at a great distance from the body. The re-
gion from which we could gain knowledge would be
very limited without this sense.

The air also constantly presses about us, and any
vibrating body will start in it a series of waves that will
travel out in all directions. These waves, however, con-
sist of alternate condensations and rarefactions of air,
while the ether waves are simple undulations. The air
waves travel only about 1100 feet in one second and can-
not go very far, but probably fully as much information
is brought to us on air waves as on the ether waves.

Thus the eye and the ear are our two great sense
organs, because they are made to receive the vibrations
which are constantly brought to us on these two great
and ever-present media.

THE EYE

General anatomy of the eye.— The eye is nearly
spherical in shape, is nearly one inch in diameter, and is
set in a bony socket upon a bed of fat. Its principal
parts may be seen in the cross-section shown in Fig. 126.
On the outside is the sclerotic coat, which on the front
of the eye is transparent and bulges forward, forming

Tin: SPKCIAL SENSES

297

the coiiwn. Just back of the cornea is a cavity filled
with a watery lluid called the aqueous humor. Across
the rear part of this chamber is stretched a curtaiu called
the iris, through the centre of which is a round opening
called the jrupil. Just back of the iris is the crysUdlinr
Jem, resting in a concave depression of tlie vitreous humor,
which fills the large central chamber of the eyeball.
Next within the sclerotic coat is the dark-brown choroid

Fig. 120. — Cross-section of the eye. C, the cornea; A^ aqueous
humor; /, iris; Z/, cr3"stalline lens; F, vitreous humor; .S", sclerotic
coat; CV(, choroid coat: R. retina; O, optic nerve; Y^ yellow spot.

coat, which is continuous in front with the iris. The
inner coat is the retirm. The optic nerve enters the eye a
little below and to the inner side of the ball, and its
numerous branches are distributed to the retina. On
the retina, in the centre of the back part of the ball, is a
spot about one twenty- fourth of an inch in diameter. It
is yellow in color, and so is called the yellow spot. This
spot is in line with the axis through the cornea and the
crystalline lens.

298 THIRD BOOK OF PHYSIOLOGY

The purpose and operation of the anterior

parts. — The function of the cornea, iris, and crystalline
lens, all ^rorking together, is to produce a small but
distinct image and locate it exactly on the jellow spot
of the retina. The cornea is fixed in position. l)ut the
iris will change the size of the pupil in accordance with
the brightness of the light, and the lens will change its
shape in accordance with the distance of the object. The
cornea produces the image, the iris regulates the amount
of light, and the lens locates the image upon the yellow
spot.

The cornea. — The cornea is the transparent part of
the sclerotic coat. It is much more convex than the
remainintr surface of the eyeball, and is set into the re-
maiuing j^ortion of the sclerotic coat much as a crystal
is set into the case of a watch. The distance across the
cornea is about one-sixth the circumference of the ball.
In the normal eye the cornea has the shape of a segment
of a sphere, its curvature being the same in all directions.
The curvature is greatest in youth and becomes less and
less iis age advances.

The function of the cornea is to receive the rays of
light which come to it from a point outside the eye, and
bend them so that they will meet again at a point within
the eye. This is done in accordance with a principle in
light called refraction.

Refraction of light. — Whenever a ray of light
passes obliquely from one medium to another of different
density it will be bent out of its course. This is called

tup: siM^ciAL sf.nses

209

rt'fraction of light. In Fij^. Vl~, A, :i ray of liglitfroin O
enters ohliciuely into a piece of glass. That is, it goes
from a light incdiinn. Ilicair. into a dense modiiim. tlie
glitss. In that Ciuse the ray is always bent towards the

G

^'^

7?"^

^^

.1

\ ^'

A

Fio. yi~. — In A^ a ray starts from 0, in air, and enters plate «>f
glass, G. RU the direction of refracted ray.

In i?, the rays from 0 are refracted by lens L and brought to point
F.

perpendicular, 7* P. In case the light would start in the
glass, as at T, then the ray, T A^ on going out into a
lighter medium, the air, would be bent away from the
perpendicular, P P, and would go to 0.

Xow. if we take a lens in the shape of the cornea, as
in 127, -B, and applj' these laws of refraction, it will be

300

THIED BOOK OF PHYSIOLOGY

plain tliat the rays of light from 0 will be V)ent so that
they will come together at F.

Thus, as shown in Fig. 128. if an arrow, O. l)e the ob-
ject, then rays of light from any point of the arrow will,

Fig. 128. — Eays <>f light from each end of the arrow, 0, are brought

to a focus at I.

after passing through the cornea, be bent so that they
will come together again, and form an image of that
point. In the figure only two rays are drawn from each
end of the arrow, as that is all that is needed to find the
two ends of the image. The image of other points of
the arrow will lie between the two ends. It is observed
that the image is inverted, and that is the i^osition of all
images in the eye. The cornea alone will produce a
distinct image, but it cannot produce satisfactory vision
without the aid of the iris and crystalline lens, as will
now be explained.

The iris. — Iris in mythology was the goddess of the
rainbow, and hence the name of this curtain with its
variety of color. The iris is the chief source of the
beauty of the eye, but nature intended it for a useful
purpose in vision. In the iris are two sets of muscle-
fibres. One kind radiates from the pupil to the outer

TIIK SPECIAL SKNSES

301

edge of the iris. When these contract they pnll the iris
away from tlie centre in all directions, thus making the
pupil larger. In the other set the fibres are concentric
about the pupil, and when they contract the iris is drawn
towards the centre, and thus the pupil is made smaller.
The action is automatic, a bright light causing a contrac-
tion of the concentric fibres and so a smaller pupil, and
a dull light permitting the iris to be drawn back and so
a larger pupil.

The purpose of this arrangement is twofold : (1) To
produce on the retina an image of the Siime brilliancy,

Fig. 129. — Diagram illustraring the aberration of focus caused by a
spherical lens. 0, origin of light ; F, focus where the five rays
through the central part of the lens meet ; a, a, the rays which pass
through outer edge of lens and are focused at .S"; T, T, is a screen cor-
responding to the iris in the eye. It shuts off all rays except those
which pass most nearly through the centre of the lens.

whatever be the intensity of the source of light. Vision
would be dimmed by too much as well as by too little
light, and too bright an image would injure the retina,
(2) To shut out the rays which would otitierwise pass in
through the edges of the cornea and crystalline lens and

302 THIRD BOOK OF PHYSIOLOGY

would not come to a focus at the same point as the other
rays, which entered near the centre of the cornea. This
is illustrated in Fig. 129. The value of the iris in this
respect is experienced by those who have belladonna
placed in the eye to cause the pupil to expand so that
the interior of the eye can be examined. Clear vision is
impossible until the effect of the belladonna has passed
away.

In many optical instruments a screen with a round
hole through the centre is placed in front of the lens to
secure a distinct image according to the principles just
explained.

The crystalline lens. — The crystalline lens is a
transparent colorless body in the shape of a double con-
vex lens. It is about one-third of an inch broad and
one-sixth of an inch through its thickest part. On its
anterior side it is bathed with the aqueous humor and is
in contact with the iris. On its posterior side it rests in
a concave depression of the vitreous humor.

The convexity of the lens is greater on the posterior
side. In old age the lens becomes flatter and less trans-
parent. In structure the lens is made up of a number
of concentric layers, or lamina, much like the structure
of a lily-bulb or onion.

The lens is held in place by a ligament, which is
attached all around its edge. This ligament is attached
also to a ring of muscle-fibres at the front edge of the
choroid coat. This muscle, known as the ciliary muscle^
is composed of both circular and radial fibres. An idea

TUK SPECIAL SENSES 803

of the relation of these ])ails may he ohtaiii<'<l IVoni the
diaiirani in Fig. 130.

The lens is ehustic, and wlien left to itself its sides will
bulire out and beeonie quite convex, but tin* susjiensory

Fig. 130. — Section showing attachments of the lens, cm, ciliarN-
muscle ; cc, front edge of choroid arranged in folds called the ciliary
processes; S, suspensory ligament; P, pupil; /, iris; 0, origin of
ciliary muscle.

ligament is constantly under tension, thus flattening the
sides of the lens. When, however, it becomes necessary
for the lens to be more convex, the ciliary muscle con-
tracts and thus relieves the tension of the ligament.

The chief function of the lens is to regulate the
amount of refraction so that the rays of light will meet
and form an image on the yellow spot of the retina.

How we can see distinctly at various dis-
tances.— iVs long as the distance between any object
and a fixed lens remains the same, the distance of the
image on the other side of the lens will remain the same.
If the distance of the object is changed, the i)osition of
the image will be shifted. This is illustrated in Fig. 131.
When 0 is moved towards the lens, 7*' moNcs farther

304

THIRD BOOK OF PHYSIOLOGY

away, and when 0 is moved away, F approaches the lens.
Thus, if the crystalline lens of the eye were fixed in
position and shape, we would be able to see distinctly only
at a definite distance. If the distance for any eye hap-

FiG. lol. — Diagram showing how the focal distance, F^ depends on
the distance of the object. 0, in the same lens.

pened to be ten feet, say, then only the objects at that
distance could be seen distinctly. This would evidently

Fig. 132. — Diagram .showing the effect of lenses of different curva-
ture. 0 and O are objects at the same distance from lens. The lens
which is more convex brings the rays together at a shorter distance
from the lens.

be very inconvenient, and so nature has provided a
method of adjustment which is very simple and is oper-
ated without any attention on our part.

TIIK SPEC^IAL SENSES 305

The more convex any lens is, the nioie it will refract a
ray of li<j;lit. This is illnstrated in Fi<^. 132. This is
the ])rinciple ntilized in the eye, and the convexity of the
crystalline lens is changed in the manner already ex-
plained, for different distances. Thns, if the upper lens,
Fig. 132, is just the right convexity to throw i^ apon the
retina, then the convexity of the lower lens is too great,
and F there falls short of the retina. In that case the
cilijiry nuiscles relax and* the tension of the suspensory
ligament is restored. This makes the lens flatter, and
thus the image is moved to the proper distance.

The emmetropic eye.— In a normal eye parallel
rays of light will be focused on the retina without any
action of the ciliary muscle. For near objects the

Fig. 133. — Emmetropic eye.

rays that enter the eye will be divergent, and then the
lens will become more convex and will bring the rays
together at the same point. Such an eye is emmetropic,
and is capable of adjustment for any distance to within
about eight inches from the eye.

The myopic eye. — When parallel rays come to a
focus before the retina is reached, the eye is said to be
myopic (Fig. 134). This condition may result from too

20

306 THIED BOOK OF PHYSIOLOGY

great a curvature of the cornea or the lens, or it may
be due to an elongation of the ball of the eye. By refer-
ence to Fig. 131 it is plain that if an object be held
near the eve, a certain distance mav be found where the
image will fall exactly on the retina. F(jr distinct vision
an object must always be held close to such g^n eye. The

Fig. 134. —Myopic eve.

defect is called short-sightedness. It can be corrected by
the use of concave glasses. A concave lens always tends
to scatter the waves of light, while convex lenses always
tend to bring the rays to a focus. Hence concave glasses
may be ground so that they will just correct the defect
in the convex lenses of the eye, and the image will be
thrown upon the retina as in the normal eye.

The hypermetropic eye. — It often occurs that
even when the lens is as convex as the eye can make it,
still the image falls beyond the retina (Fig. 135, c).
This may result from the fact that the cornea is not suf-
ficiently convex, or the distance from the lens to the
retina may be less than in the normal ej'e. This defect
may be so slight that only very near objects are indis-
tinctly seen, or it may be so great that even the parallel
rays from objects at an infinite distance may be focused
beyond the retina. Since greater refraction of the rays

THE SPECIAL SENSES 307

is needed, it is plain that convex glasses will correct the
defect.

Such an eye is said to he far-si ffhted. Nearly every one
who has passed the age of about forty-five years is, to
some degree, far-sighted. The cause is that the cornea

Fig. 135. — Hypermetropic eye.

becomes less convex and the lens less capable of adjust-
ment as age advances. This is why middle-aged and old
people wear glasses when they read or look at minute
objects near by.

Movements of the eyes. — For distinct vision it is
necessary that the image fall upon the most sensitive
part of the retina, which is the yellow spot. This spot
is in line with a ray of light that would pass through the
centre of the cornea, the pupil, and the lens.

One can see indistinctly all four walls of a room by
taking a position near one corner, because the retina lines
the interior of the eyeball almost to the iris. But when
we wish to see anything distinctly, we must look straight
at it. To do this we turn the head or move the eyes in
their sockets.

Six muscles are attached to the sclerotic coat of each,
eye. Four of these are called the recti, or straight^

308

THIED BOOK OF PHYSIOLOGY

muscles. One is attached above, one below, and one on
each side.

When the upper one contracts, the front of the eye
will be turned upward, and each of the other three will
in the same vray turn the front of the eye to the side to
which the muscle is attached. The superior oblique

Fig. 136. — Muscles of the eye. 1, 2, 3. 4. recti muscles ; 4 is oppo-
site 2 and cannot be seen in cut ; 5, superior oblique muscle ; 6, pulley
through which the tendon plays ; 7, inferior oblique muscle ; 8, optic
nerve.

muscle is peculiar in that its tendon passes through a
cartilaginous ring (Fig. 136, 6), and, passing on, is
attached to the side of the eyeball. The ring thus acts
as a fixed pulley, and a contraction of this muscle would
tend to roll the ball in its socket. The inferior ohliqae
muscle also tends to rotate the ball, but in a direction
opposite to that produced by the super ioi' oblique.

THE SPRCIAL SENSES 309

These two inuscles, then, are antagonistic to each other
and hold the ball steadily in place.

Effect of defective eye-muscles. — It is evident
that if any one of the muscles attached to the eyeball
should be paralyzed, or should be too short or too long,
the ball would not have a correct position in its socket.
If the outside recti muscles are too short or the inside
ones should be paralyzed', the eyes would turn outward.
If, as often hai^pens, the inside rectus pulls harder on
the ball than the outside one does, the eye will be turned
inward, and cause squinting or cross-eyes.

Any lack of balance between the eye-muscles will result
in defective vision, and will also be objectionable from the
stand-point of personal appearance. Fortunately, a skil-
ful surgical operation will usually correct such defects.

The posterior parts of the eye. — Thus fiir we
have been chietiy concerned with the descriptions and
functions of those parts of the eye which had to do with
the formation and location of the image. These, we have
seen, are, for the most iDart, in the anterior regions of the
eye. It remains to be seen how the image is received by
the terminations of the optic nerve, and how the stim-
ulus is conducted to the seat of perception in the brain.
This is elBfected through agencies in the posterior part of
the eye.

The retina. — The sclerotic coat is on the outside of
the eyeball. It is composed of tough, white fibrous ma-
terial, and is usually called the ''white of the eye.''

310

THIRD BOOK OF PHYSIOLOGY

^L

The next coat is the choroid,
which is of a dark color, and is
very vascular, being filled with
a net- work of blood-vessels.

The innermost coat is the
retina, which will now l)e more
fully described.

The retina lines the whole
posterior cavity of the eyeball
and extends forward nearly to
the iris. It is only about one-
fiftieth of an inch thick at the
point directly opposite the iris,
where it is thickest. It is
composed chiefly of terminals
of the nerve-fibres of the optic
nerves, with certain sustaining
tissue that holds the nerve ele-
ments in place.

The anatomist distinguishes
ten ditlerent layers of the ret-
ina, the most important of
which are pointed out in Fig.
137. The Avhole distance from

Fig. 137.— Diagram show- F F to L L in the figure repre-

ing the nerve elements of ret- ^^^^ ^^^ thickneSS of the ret-
ina ; aa, rods ; h, cone ; c, nu-

cleus of cone; cZ, nucleus of i^^, SO that the parts here

rod ; ji, nerve-cell ; oo, fibres shown on a large scale cau be

of optic nerve; LL, internal ^^^^ ^^^^, ^^. ^.^ ^^ ^ ^^^^^^
limiting membrane ; PP, pig-
ment-cell laver. microscope. The line L L rep-

THE SPECIAL SENSES

311

resents the limiting membrane which lies next to the
vitreous humor, while (Ijc line P P r(iprevSents the i)ig-
ment-cell layer which lies adja-
cent to the choroid coat. These
are respectively the tirst and
tenth layers of the retina. The
other eight layers are between,
and have a variety of structure,
being composed mainly of nerve-
cells, nuclei, nerve-fibres, and
special nerve terminals.

The ninth layer is composed
of nerve- cells of special forms
called 7'ods and cones. In Fig.
138 is shown one of each of these
two kinds of cells, very highly
magnified. Their name — ''rod"
and ' ' cone"— is plainly suggested ^^^^ i38.-llod and cone

by their shape. Three or four from the retina. R, rod ;

rods are, as a rule, found between ^' ^^^"' ^' P'^^'^'J 2,

body ; 3, nucleus.
every two cones. The light

passes nearly through the retina before it reaches these

cells.

The yellow spot and the blind spot.— Two

spots appear on the posterior wall of the retina. One
is a white circular spot, which is slightly elevated, form-
ing the optic papilla. This is the point of entrance of
the optic nerve, and is called the blind spot^ because it
contains no nerve terminals, and hence an image falling

312

THIRD BOOK OF PHYSIOLOGY

upon it produces no sensation. Near by is another spot
which is circular or oval in shape and yellow in color.
It is called the yellow spot. Its diameter is only about

one-twenty-fourth of an
inch. Here the layer of
nerve- cells is thicker than
elsewhere, and in the ninth
layer only cones are found.
In the centre of the yel-
low spot is a conical de-
X^ression. where all the
layers of the retina are
removed down to the
cones, and the dark pig-
ment layer shows through,
making the depression look
like a hole through the retina. This spot is called the
central fovea. It is a condition for the most distinct
vision that the image fall upon the central fovea.

The blind spot is about one-tenth of an inch from the
yellow spot, towards the inner side of the eye.

4 68

Fig. 139. — Retina seen on its
posterior inner surface. 1. scle-
rotica ; 2. choroidea ; 3, retina ;
4, the optic papilla ; 5, central
retinal artery ; 6, a slight fold of
the retina ; 7, the yellow spot ;
8, its central fovea.

The size of the image. — The image on the retina
may cover a large portion of the posterior part of the
retina, but only a very small portion of it can be dis-
tinctly seen. The whole page of this book is imaged on
the retina while you read, but not more than a single let-
ter can be seen distinctly at one time. Reading is accom-
plished by moving the eyes so that the image of each
letter is rapidly swept across the yellow spot.

THE SI»K(MAL SENSES 313

The smallest object which can be seen as having any
dimension must form an image at least large enough to
reach from one cone to the next adjacent one in the
central fovea of the yellow spot.

Experiment shows that when two points are so close
together that lines drawn from each to the eye make
with each other an angle of fifty seconds, then the image
of these two points on the retina would be only W^tt inch
apart. The distance between two adjacent cones is also
6 00 0 of an inch. Fifty seconds then is the limiting visual
angle for seeing two points as separate. Any less angle
would cause the two points to appear as one. This is
the case with many double stars which, to the naked
eye, appear as one, but in the telescope are seen to be
double.

What seeing is. — Waves of light from 'an object
are refracted so as to form an image on the rod and cone
cells of the retina. These waves act as a stimulus and
set up nervous impulses which travel along the fibres of
the optic nerve to the base of the brain, and thence by
other neurons to the seat of visual sensation in the occip-
ital lobe of the cerebrum. The seeing is in the brain and
not in the eye. If the optic nerves were severed, the eye
could still form perfect images on the retina, but there
would be no vision.

The optic nerves. — The optic nerves arise from the
base of the brain at what is called the optic chiasma.
The nerve-fibres which compose the optic nerves have

3U THIED BOOK OF PHYSIOLOGY

their termination in tlie seat of sensation in the brain,
but on their way from the eyes they meet in the optic
chiasma, where most of the fibres pass across to the other
side, as shown in Fig. 140.

Part of the fibres, however, pass on to the brain on the
same side. Thus each eye sends impulses to both hemi-

FiG. 140.— The optic nerves.

spheres of the brain ; and even if one side of the brain
should be paralyzed, there would still be vision from both
eyes.

Advantage of two eyes. — When both eyes are
used an image is formed on corresponding parts of the
retina in each eye. Similar impulses are thus sent to
each hemisphere of the cerebrum and, as the sensations
agree, an object is seen singly. By a slight pressure of
the finger against the side of one eyeball, the inage on

Till-: SPKCIAF. SKXSES 315

the retina may l>e shifted so that its position does not
agree witli that in the other eye. An obje*et tlien api)eai-s
distorted or double.

By the use of two eyes all objects can be seen witli
greater distinctness, and solid objects are made to stand
out as solids.

Color sensations. — The eye is so constructed that
different nervous impulses are produced by the different
wave-lengths of light. This gives us the ability to dis-
tinguish coloi-s, for difference in color results only from
difference in the wave-length of light.

These waves have been measured, and it is found that
when 395.000,000.000.000 of them flow into the eye in one
second, the sensation will be what we call red. When
the number is 7G0. 000. 000. 000. 000 per second, the sen-
sation is called violet. The waves are longest for red
and shortest for violet, while various other wave-lengths
produce all the intervening colore.

Some able scientists believe that the nerve-terminals in
the eye are of three distinct kinds. One kind, when
stimulated alone, will give rise to the seiLsation of red ;
another kind, green : and a third kind, violet. AVhen
all three are stimulated equally, the combined sensation
is white. Grav is a low dearree of whiteness. All other
coloi-s are mixtures of certain proportions of these three
primary color sensations.

The eyes of some persons are deficient in ability to dis-
tinguish certain colors. Such pei-sons are said to be
color-bliiid.

316 THIED BOOK OF PHYSIOLOGY

The iuability to distinguish red and green is the com-
mon defect.

About four men out of every hundred and one woman
out of every two hundred are said to be color-blind.

Nature's provision for the protection of the

eyes. — Since the eye is such a delicate and useful organ,
it must be well protected from possible harm, for an
injury to it is, indirectly, an injury to the whole organ-
ized body.

The safeguards placed about the eye are (1) its position
in a bony socket, (2) the eyelids and eyebrows, (3) the
tears and oil secretions, and (4) the sensitive conjunc-
tiva.

Any flat object, as a book or the open hand, pressed
over the region of the eye, will be arrested before it
touches the eyeball. Thus the eye is protected bj' its
deep position in a bony socket.

Tlie eyebrows keep sweat or other liquid from run-
ning down into the eyes.

The eyelids and lashes are a constant protection against
dust and insects, and by frequently closing and opening,
the lids wash the surface of the eye and keep it uniformly
moist.

The tears are very necessary for keeping the exposed
part of the eye clear and transparent. Beneath the skin
near the outer end of the eyebrows is a racemose gland
which secretes a liquid called tears, and pours it through
a dozen or more ducts onto the surface of the eye. The
ducts open beneath the upper eyelid, near the outer

TlIK SPECIAL SENSES

317

corner of the eye. At the inner corner of the eye is a
provision for cunvinj^ any excess of teiirs into the nos-
trils. This can Ix' understood from an examination of
Fi^'. 141.

At the inner anjj^le of the eye, on each eyelid, may be
seen a slij^^ht elevation. These are the lachrymal impilloe.
On the summit of these is a small oi)euing called the

.K.>..-v--.::----.v:ii5^

Fig. 141. — The left eye, with a portion of the eyelids removed, to
exhibit the lachrymal canals and sac. 1, lachrymal canals; 2, com-
mencement of these on the lachrymal papilla; ; 4, edges of the eye-
lids ; 5, lachrymal sac ; 6, internal palpebral ligament.

lachrymal punetum. Tears enter these openings, and are
carried back through the canal to the lachrymal sac, and
escape thence into the nose.

In the eyelids are also a number of small glands which
secrete an oily substance and pour it out on the edges of
the lids.

The tears keep the cornea always clean and moist, and

318 THIED BOOK OF PHYSIOLOGY

the oil keeps the tears from flowing over at the edge of
the lids.

The inuer surface of both lids and the whole visible
front of the eyeball are covered by a delicate and very
sensitive mucous membrane called the conjunctiva. The
sensitiveness of this lining quickly calls attention to the
presence of any foreign substance in the eye.

Care of the eyes. — Although every one places a
high estimate upon the value of his eyes, yet no other
organ is more frequently misused. The eye has wonder-
ful powers of recovery from the effects of mistreatment,
but sooner or later some weakness of the eyes will appear
if they are persistently abused.

The reading of fine print is injurious. Reading by
sunlight or a very strong artificial light will injure the
retina. Eeading by twilight or a weak and flickering
artificial light will strain the eyes. It is injurious to
read on a railroad train, because the jolting requires a
constant readjustment of the lens.

The habit of reading while lying on a lounge or after
going to bed, works a serious injury to the eyes, and has
been the direct cause of blindness. Holding a book too
close to the eyes will strain the adjusting mechanism and
cause short-sightedness. One should not bend over and
look down upon the work in which he is engaged. A
book should be held in front about fourteen inches away
for a normal eye.

The light should be admitted at the rear and left side
of the room where j^upils study and write or do any

TIIK SPECIAL SENSES 319

work requiring a constant use of the eyes. Artificial
light should always fall over the left shoulder upon the
page of a book.

If the eyes smart, pain, or have a full feeling, they
need rest, and should l>e examined by an oculist for any
defect which might be corrected by glasses. Permit only
a perfectly reliable and competent physician or oculist
to prescribe for the eyes.

Maintain a healthy tone of the whole system and the
eye.s will be stronger to meet the demands which are con-
stantly made upon them.

Alcohol seriously affects the eyes by its injurious
effects upon the whole body, thus decreasing or poison-
ing the source of nourishment to the eyes, and also di-
rectly by its paralyzing effect upon the optic nerve and
by the intiammation which results from the congested
blood-vessels. Blood-shot eyes are marks of the alcohol
drinker.

The use of tobacco also, particularly the smoking of
cigarettes, frequently works serious injury to the organs
of vision. This is particularly' true of those who are
pupils in school and those whose work is indoors. Doc-
tors often refuse to treat the eyes unless the patient will
cease from smoking, at least during the time of treat-
ment.

THE EAR

The second great medium in which we always must
live is the air. It is natural that we should have an
organ which is capable of receiving any disturbance in the
air and applying it as a stimulus to the ends of a nerve

820 THIED BOOK OF PHYSIOLOGY

so as to produce a sensation in the brain. Such an organ
is the ear, and the sensation produced is called sound.

The nature of air- waves. — Light- waves have been
explained as a series of undulations which might be
compared to the undulating waves which are seen on
water. But waves of air that produce sound are very-
different from light-waves.

If air could be seen while it is carrying sound-waves it
would be noticed that at one point the particles would

^^e crowded together : a

^..5^i^?2^xii^^- ; -^-^^^^^^v little farther on they

ji-??.'-^'

'^'^ "' \:. ^^r.-^^ would be more widely

■yr-M'':

■''*?^

■i^^^^^^^^^:.>^^% separated, and still far-
""^l^i^^^^^^^^^^^^vl^- ther they would be

"^'^-..i^.''%' crowded again, and so

*%:^% on. The crowded con-

dition of the air is called

Fig. 142. — Condensations and rare- .

f .. . . a condensation, and be-

factions m air-waves.

tween the condensations
are the rarefactions. This condition is represented in
Fig. 142, where a vibrating body at O is sending out
condensations and rarefactions in all directions. Only a
small section of the waves is shown in the figure.

When the air is very much condensed and rarefied the
sound is intense or loud. This is the condition of the
air close to a vibrating body, but the amount of conden-
sation grows less and less as the distance increases, and
thus sounds are faint when the vibrating body is far away.

Each wave of sound is composed of one condensation

THE SPECIAL SENSES 321

and one rarefaction. When the waves are very close to-
gether, so that a great niinilx^r of them reach the ear in
one second, a note having a high pitch is prodnced.
These waves travel through the air at the rate of about
1100 feet in one second. They move fiuster when the air
is warm and slower when it is cold. When the number
of waves per second is about sixteen, they begin to pro-
duce a sensiition of a very low sound. As the numl^er
of waves increases, the pitch rises, until, when the num-
ber becomes about 40,000 in a second, the ear is no
lonf]rer affected bv them.

The ear. — It is difficult to decide between thi? eye
and the ear as to which is of greater service to man. It
appeal's that those who are blind are capable of a better
sort of mental culture through their eai'S than those who
are deaf and are compelleil to gain their knowledge
chiefly through their eyes.

The ear is a very delicate and complex organ, and
some of its parts are exceedingly difficult to explain.
The subject may be discussed under three heads, — the ex-
ternal ear J the middle ear. and the internal ear. The first
two are concerned only in receiving and ti^nsforming
the sound-waves so that they may properly excite the
terminals of the auditory nerve. These, then, are simi-
lar in function to the parts in the front of the eye which
formed and located the image on the terminals of the
optic nerve.

The external ear. — The e.vternal ear is composed of
the pinna and meatus. The pinna is the part of the ear

21

322

THIED BOOK OF PHYSIOLOGY

that projects from the side of the head. It is composed
of elastic cartilage covered with skiu. As may be seen

in Fig. 143, the outer rim is
called the helix. The soft,
pendent i)art at the lower
end is tlie lobe. The deep
depression near the centre is
the concha, which is partly
divided by the commence-
ment of the helix. At tlie
bottom of the concha i^ the
entrance to the meatus. The
pinna collects the waves from
a larger area of air and di-
rects them to the month of
the meatus. Thus the sound
is made more intense, just as
a high tide may be caused at
the narrow head of a bay by
the feeble waves collected from a large area at the mouth
of the bay.

In many animals the pinna can be freely moved by the
action of muscles which are attached to it. 3Iuscles are
also provided for this purpose in man, but so seklom
have they l)een used that in most people they have lost
their power.

The second part of the external ear is the auditory
meatus, or caiial. which is about one inch long, and ex-
tends from the concha to the drum-head of the middle
ear. The first part of the canal, about one-half incli in

Fig. 143.— Pinna of ear.
H, helix ; C, concha ; L,
lobe ; E, entrance to audi to ry
meatus.

THE SPECIAL SENSES

323

leiifrtli, is formed of cartilage, and tlie remain in*; part is
througli bone. The wliole is lined with a very thin skin,
which also covei*s the outer side of the drum-heiwl. Be-
neath the skin in the cartila<;inou.s portion are numer-
ous j^lands which secrete the ear wax. This wax is bitter
and sticky, and. with the aid of hairs at the entrance of
the canal, keeps insects and dust from reaching the
drum head.

The middle ear.— The middle ear is a cavity in the
temporal bone between the external and internal ears.
It is called the ti/mpanum, or ear-drum, because it contains

Fig. 144. — The tympanic membrdne and the ossicles of the middle
ear. /n, meatus ; f. tympanum : h. malleus, or hammer ; o, incus, or
anvil ; s, stapes, or stirrup.

air. and a membrane is stretched between it and the
meatus. Upon this membrane the air-waves beat as
upon the head of a drum. The drum communicates with

324 THIRD. BOOK OF PHYSIOLOGY

the outside air through the Eustachian tube, which con-
nects it with the pharynx.

Within the drum is a chaiu of bones which are articu-
lated to each other, one end of the chain being fastened
to the drum-head and the other to the oval window of
the inner ear. The bones are called the ossicles of the
middle ear. Their relation to each other and to the
tympanum may be seen in Fig. 144.

The shape of the bones has suggested the names ham-
me7', anvil, and stirnq). The corresponding Latin names
commonly used are malleus, incus, and stapes.

The purpose of the middle ear is to receive the feeble
waves which beat upon the drum- head and convert them
into vibrations of greater force, so that they may prop-
erly affect the liquid which fills the spaces of the inner
ear. This is done by the tympanic membrane, or drum-
head, and the chain of bones.

The tympanic membrane, or drum-head.—

The chief agency for intensif^'ing the vibrations is the
drum-head. In shape and structure it is admirably
adapted to this end. It is composed of three layers, the
outer one being a continuation of the skin w^hich lines
the meatus, and the inner one being the mucous mem-
brane which lines the whole interior of the drum. The
middle layer is the essential one. It is composed of
radial and circular fibres of connective tissue which are
alwaj^s stretched and kept tense by a muscle which pulls
on the handle of the hammer. Thus the membrane is
made to take the shape of a funnel with its apex at the

TIIK SPFClAf. SF.XSES

325

point of attachment to the hammer. Tlie sides of this
funnel are stretched, but do not piuss straij^ht from the
rim to the apex. They apparently sag towards the centre
of the funnel, thus l)eing convex towards the meatus.
This is important, for it is chietly by this arrangement
that the force of a sound-wave is intensified. Tlie me-
chanical principle involved may be easily understood
by reference to the dia-
gram, Fig. 145, which rep-
resents the outlines of the
drum-head. The radial
fibres are stretched from
the apex to the base of
the cone, and the circular

Fig. 14o. — Diagram showing
mechanical action of tympanum.

fibres keep the sides convex towards the centre. Xow,
any pressure against the inner sides of a and h in
the direction of the arrows would relieve their tension
and permit the apex to move towards c, in which direc-
tion it is constantly pulled by the handle of the ham-
mer. When the pressure ceases, the apex will at once
be brought back to its former position by the tension of a
and b. The sides may move back and forth through a
considerable distance, while the apex will, as a result, be
moved back and forth only a very short distance, but with
proportionately greater force. Thus sound-waves may
exert a considerable force on the handle of the hammer.

The ossicles of the ear-drum.. — The function
of the three bones in the drum is to transfer the vibra-
tions from the drum head to the inner ear, and to still

326 THIRD BOOK OF PTTYSTOLOGY

further intensify the vibration at a sacrifice of distance
moved.

The bones are held in place by ligaments, and are
closely jointed to each other. They act together as a
lever, having its fulcrum at F (Fig. 146). Thus the
power arm of the lever is the distance from the vertex
of the drum-head to 7^, while the resistance arm is only
from F to the end of the long process of the anvil. The
power arm of this lever is found to be one and one-half
times as long as the resistance arm, and so the force is
increased one and one-half times and the distance moved
is made proportionately less. The back and forth move-
ment of the stirrup does not exceed about 2 io of an inch.

The Eustachian tube. — The pressure of the air
within the drum should be the same as that of the air
outside. Air-pressure is constantly changing at any
point on the earth, as is shown by the changes in the
barometer, and also the pressure is different at different
altitudes.

In order that man might retain his power of hearing
while he is subject to these frequent changes, it is neces-
sary that a tube connect the outside air with the drum.
This is the purpose of the Eustachkin tube, which is shaped
like a trumi^et, and is connected by its small end to the
drum and by its large end to the pharynx. It is made
of thin cartilage, so that it usually stands open.

Air may be forced from the mouth into the drum, or
may by suction be drawn from it. In either case a dif-
ference of air tension is caused within and without the

THE SPECIAL SENSES 327

drum. :ni(l lieariiif:; becomes indistinct and confused.
Tliis will colli iiuic, tlioui^li nose :ni(l mouth ])c now open,
loi- the hir<;e opening of the tube is loosely closed by
certain muscles in the ])hai yiix which are concerned in
the act of swallowing. When we swallow, then, the
l)assage through the tube is free, and the equjil tension
of the air is restored.

When the i)harynx is inilamed, as from colds, the
Eustachian tube often becomes partly or wholly closed,
thus causing a roaring and feeling of fulness in the
drum. I'

Oipenings into the drum. — The Eustachian tube is
the only opening through which substances, such as gases
and liquids, can pass into and from the middle ear, or
drum. There are three other openings, however, through
which waves or other disturbances may easily pass in or
out. These are all covered with thin membranes. One
is the tympanic membrane, which has already been de-
scribed, and the other two are the oval and circular win-
dows which open into the internal ear. There are, also,
openings, near the top of the drum, into air-chambers
in the temporal bone. These chambers are called the
tiiaslokl cells.

Size of parts of the drum.— The student is apt
to get the idea that the parts just described are much
larger than they are in fact. A statement of the size of a
few parts may assist in getting a correct idea of the size
of all.

328

THIED BOOK OF PHYSIOLOGY

The tympanic membrane is not quite one-half inch in
diameter. The length of the malleus, or hammer, is
nearly seven-tenths of an inch. The total lensrth of the

Fig. 146. — Diagram showing the relative position of the three parts
of the ear. //i, meatus ; ^?n, tympanic memhrane ; i. tympanum ; A,
malleus ; a. incus ; .s, stapes ; o. oval window ; en^ Eustachian tube ;
sc, semicircular canals ; r, vestibule ; ^, cochlea ; F. fulcrum of the
lever formed by the ossicles.

stapes, or stirrup, is not quite two-tenths of an inch.
The weight of all the bones together is only a few grains.

The internal ear.— The relation of the three parts
of the ear may be learned by an observation of the dia-
gram in Fig. 146. The sound-waves pass in through the
meatus, in, and cause a vibration of the tympanic mem-

TriK SPECIAL SENSES 329

brane, tni. The chain of hones acts as a lever witli the
fulcruiu at J'] and transmits the vibrations to tlic oval
window, (>, the entrance into the third division of the
ear.

The internal ear is called the lahyrinth because of its
many winding passage-ways. Tlie labyrmth is an irregu-
lar chamber in the hard part of the temporal bone. It
may be described as composed of three parts, — the vesti-

FiG. 147. — The right labyrinth, viewed outwardly in front, magni-
fied two and a half times. 1, vestibule ; 2, oval window ; 3, round
window ; 4, superior semicircular canal ; 5, posterior semicircular
canal; G, inferior semicircular canal ; 7, ampullae; 8, cochlea.

hule^ the semicircular canals, and the cochlea. These are
simply cavities in the hard bone. If some plaster of
Paris were poured into these cavities and allowed to
remain there till it would harden and form a cast, it
would, when cut out, have the form shown in Fig. 147.
These cavities are called the osseous labyrinth, as distin-
guished from another which is contained within it and
known as the membranous lahyrinth.

The osseous labyrinth. — The osseous, or bony,
vestibule lies between the cochlea and the semicircular

830 TIUVJ) BOOK OF PHYSTOLOOY

canals. On its front side, that is the side towards the
tympanum, is the oval loindow, which is covered with a
membrane to which the stirrup is attached. Below is
the round icindoic. covered with a thin membrane which
separates the liquid within the vestibule from the air in
the middle ear.

In the back part of the vestibule are five holes, wdiich
are the openings into the semicircular canals. These
canals are not complete circles, but arch over somewhat
in the shape of a horseshoe, both ends opening into the
vestibule. Two of the ends unite and pass together into
the vestibule, and hence there are but five openings as
seen from within the vestibule.

The plane of each of the semicircular canals is at right
angles to the planes of the other two. just a,s the three
faces of a cube that meet at one corner are each at right
angles to the other two. This is important, as will be
explained later on.

The osseous cochlea is a spiral canal resembling in
shape the interior of a snail shell, and hence its name.

The axis of the cochlea is a conical pillar of bone called
the modiolus. The canal passes sj^irally around the modi-
olus, making two and one-half turns.

A thin spiral shelf of bone, called the spiral lamina,
projects from the modiolus much as the blades of steel
project from the central axis of an augur. The spiral
lamina extends about half-way across the canals, as shown
in Fig. 148. The remaining distance across the canal is
filled in by tlie membranous cochlea, which will later be
described. Thus, the osseous canal is divided into two

TIIK SIM^^>(UAL SF.NSKS

381

nearly equal channels thronghont its w liolo. l(»ngtli. The
MpjK'r one connnunieatcs at its hiusc witli the vestibule,
and so is callcMl tln^ Ncstibnlsu"
passjig(\

The base of the lower one is
over the round window, through
the membrane of which it may
communicate with the tympanum,
and so it is called the* lympanic
passage. The two are connected
only b}^ a small orifice at the top
of the canal.

The whole labyrinth is lined
with x^eriosteum, which secretes
a fluid called perilymph, with
which the labyrinth is filled.

Fig. 148.— The cochlea
luid open, its summit
turned upward, mtigni-
liod three diameters. 1,
2, 3, the tympanic pas-
sage ; 4, 5, G, tlie vestibu-
lar passage ; 7, 8, osseous
spiral lamina; 9, mem-
branous spiral lamina ;
10, orifice of communica-
tion of the two passages
at the summit of the
cochlea; 11, 12, termina-
tion of the osseous and
membranous spiral lami-
n:e.

The membranous laby-
rinth. -The membranous lahy-
rlnth, shown in Fig. 149, is nearly
the form and shape of the bony
labyrinth in which it is enclosed.
It occupies about two-thirds of
the space in the bony cavity and
partly floats in the i^erilymph. It is comi^osed of three
parts, having names of the corresponding parts of the
bony labyrinth, and is filled with a liquid called endo-
lymph.

In the membranous vestibule are two pouches, the
smaller called the saccukj and the larger, the utricle.

332

THIRD BOOK OF PHYSIOLOGY

These are fastened together, but do not communicate
except through the Y"-shaped tube called the vestibular

aqueduct, sliown in Fig.

Connected to the utri-
cle are the three mem-
branous semicircular
canals which are lightly
attached along one side
to the bony canal.

A division of the au-
ditory nerve enters the
saccule, utricle, and

^C^ — ^6

Fig. 149. — The membranous laby-
rinth, magnified two and a half times.
1, utricle ; 2, saccule ; 3, semicircu-
lar canals ; 4. ampullae of semicircu-
lar canals ; o, vestibular aqueduct ;
6, membranous cochlea ; 7. canal
connecting saccule and membranous
cochlea.

semicircular canals, and
at these points the membrane closely adheres to the
bone. At the entrance to the semicircular canals and
on spots in the membranous labyrinth are epithelial
cells of a peculiar formation, known as hair-cells. These
are directly surrounded by a liquid somewhat thicker
than the endolymph, and in it are embedded numerous
small crvstals of calcium carbonate, known as the otoliths.
In these hair-cells the nerve-fibres of the vestibular
branch of the auditory nerve end. These, however,
probably have no part in producing the sensations of
sound.

The membranous cochlea is a three-sided tube with
one side attached to the bony wall of the canal and the
opposite corner to the edge of the spiral lamina. Thus,
it completes the division of the bony canal into two
parts. In fact, the canal of the cochlea ma}' be con-

TllK SPECIAL SENSES

333

sidered as divi(l<Kl into tliroe spiral tiil>es, — the vestibular

tnlH'. tlif fi/iHjKUii'c tuhc. and the monhnfuniis tnbf Ik?-

twcon ihv othiT two and on the

outer side of the eanal. In Fig.

151 is shown a eross-section of

one of the bony eanals of the

cochlea.

The membranous canal, ur pas-
sage, is filled with endoly-mph and
winds about with the other pas-
sages to the top of the cochlea,
where it is closed. Its only open
ing is at its base through a small
canal into the saccule. See Fig.
140. 7.

Fig. 150.— Diagram of
acoustic epithelium. 1,
acoustic hair-cell ; 2, sup-
porting cell ; 3, immature
cell.

The organ of Corti.— The
membranous canal of the cochlea
is the most essential part of the
organ of hearing. On its floor
is the organ of Corti. where the

nerve-fibres receive the impulses that arise from the
vibrations of sound-waves.

By reference to Fig. 152 it is seen that a membrane is
stretched from the edge of the spiral lamina at O to the
wall of the cochlea at W. This is the basilar membrane.
Upon it stand the rods of Corti and the hair-cells.

The rods are comparatively stiff and are arranged in
an inner and an outer row. The tops of the two rows
are bent towards each other and connected, thus forming

334

TIIIED BOOK OF PHYSIOLOGY

the tunnel, A. The base of the rods are attached by
broad feet to the basilar membrane. About 4500 i)airs
of these rods are placed along the course of the canal.

On the inner side of the tunnel formed by the rods is
a row of hair-cells, and on the outer side there are three
or four rows of the same kind of cells. (Fig. 152.)

•- ;-';!i=-ii~fir A

Fig. 151. — Cross-section of one of the canals of the cochlea, show-
ing the three passages. 1, bon}- wall of cochlea ; 2, position of modio-
lus ; 3, bone of spiral lamina ; 4, periosteum ; 5, basilar membrane ;
G, under the arch of Cord's fibres ; 7, cochlear nerve ; 8, ganglion.

A fibre of the auditory nerve is attached to each of
the hair-cells. There are, in the cochlea, about 16,000
of these cells.

The basilar membrane is stretched from side to side,

THE SPECIAL SENSES

335

but lies loose ill ;i direction Jiloiij;' the canal. The layer
of this ineini»iaii(' to which the rods and hair-cells are
attached is stri[)cd by fibres IVoni side to side. These
fibres difler in length, the shortest being at the base of

Fig. 152. — Diagram of a section of the membranous cochlea, j«how~
ing position and arrangement of Corti's organ, i and e, interior and
exterior rods of Corti ; .1, tunnel formed by the arching rods ; //, in-
terior row of hair-cells; //, A, A, exterior row of hair-celKs.

the cochlea, and the longest at the top. The length
varies from about .00162 inch for the shortest to about
.01949 inch for the longest. Thus, the latter is a little
more than twelve times the former.

Function of the cochlea. — The cochlea alone is
the organ of hearing. All sense of sound and music
arises in the cochlea.

When the stapes sets up a vibratory motion, or quiver,
in the perilymph, the motion is easily communicated to
the delicate membranes about the membianous cochlea,

336 THIRD BOOK OF PHYSIOLOGY

aiul tlie eiidolyinph partakes uf tlie same vi]>rations.
The fibres of tlie basilar membrane, which have the
proper length to vibrate in sympathy, will be most agi-
tated. The rods and haii-cells which are attached to
these fibres will convej^ the motion to the terminals of
the nerve-fibres.

A nervous impulse thus started will travel along the
auditory nerve to the medulla oblongata and thence by
other neurons to the seat of perception in the cerebrum.

The difference in the length of the fibres of the basilar
membrane is sufficient to explain the ear's ability to dis-
tinguish all differences of pitch in music, even when the
difference is very slight.

The ear is most sensitive in the first octave above
middle C. Here the ear of some trained musicians have
been able to distinguish a difference of one-half a wave
per second, thus making about 1000 distinguishable notes
in the octave.

Function of the round window. — Since the
whole labyrinth is enclosed in a hard, bony cavity and is
filled with a liquid which is almost incompressible, it is
necessary to have some spot which will yield. The pur-
pose of the round icbidow is to yield to j)ressare upon the
liquid in the labyrinth. ^Vhen the stapes presses in-
ward, the pressure is communicated along the vestibular
pa*ssage of the cochlea and then across to the tympanic
passage and down to the oval window, which is thus
made to bulge out into the tympanum A decrease of
pressure in the labyrinth would cause the round window

TIIK SPECIAL SENSRS 337

to bnljxe in. The oval window thus permits greater
tVeedoiii of vibration in the liquid.

Function of the semicircular canals— The

seniicircuhir canals and vestibule pr()bal)ly liave no part
in produeiufj the seusation of hearing.

The position and structure of the canals as well as
many experiments which have been made all go to show
tliat their function is to give a sense of equilibnum. 'By
this sensation it is possible for us to maintain any desired
])osture of the body. The least tendency to fall to one
side or the other is at once made known and checked by
the use of the proper muscles.

The planes of the three canals are each at right angles
to the other two, and hence any motion of the head will
cause a motion of the liquid in one or more of the canals.
This motion affects the auditory hair-cells to which the
nerve-fibres are attached, and thus a nervous impulse is
sent on the vestibular branch of the auditory nerve to
the medulla and on to the cerebellum.

Experiments made with birds and other animals show
that when the semicircular canals are injured, the animal
will fall from side to side when it attempts to move. All
sense of balance and ability to co-ordinate muscular
movement appear to be gone. The nerve terminals
in the vestibule are probably associated in function with
those of the semicircular canals.

Care of the ear. — The inner ear is so well protected
that it needs no care except in so far as it shares in the

22

338 THIED BOOK OF PHYSIOLOGY

general health or weakness of the whole system. It is,
however, capable of a very high degree of culture and
refinement.

A great deal of the pleasure and enjoyment of this
world is derived from music, but only those whose ears
and minds have been educated to that which is best in
music can get the full enjoyment from it.

The external and middle ear open to the outside, and
so can receive direct care at our hands.

Sometimes ear-wax in excess will gather in the meatus
or collect on the tympanic membrane. In such cases it
is always better to consult a i:)hysiciau, for the attempt
to get it out with a pinhead or other hard instrument
may cause a still more serious injury.

Insects sometimes get into the meatus, but seldom do
any injury. A little warm water or sweet oil poured in
will usually cause them to come out, or a physician can
remove them with proper instruments.

The middle ear is probably the greatest source of
trouble and needs our greatest care.

When the throat is inflamed and sore, thei-e is
always danger that the inflammation may be com-
municated to the Eustachian tube and thence into the
middle ear.

An inflammation of the linings of the middle ear may
cause serious illness or even death. Xot only the middle
ear proper may be affected, but also the mastoid cells in
the temporal bone. Here, back of the ear, pus may col-
lect where there is only a very thin partition of bone
between it and the brain. In that case it may be neces-

THE ^^PECIAL SENSES 330

sary t<> l)ore throiiirh the outer layer of the skull Id the
pus au(l thus drain it otY.

CoUls often ''settle'' in the middle ear and caust' a
great deal of pain and annoyance.

sp:nse of touch

Location and purpose of the touch organs.—

The whole surface of the skin, and the mucous membrane
at points of entrance to the body, are covered with
minute conical elevations called the papilla?. These are
on the outer surface of the true skin and are covered by
the epidermis. In some regions of the skin the papillie
are very numerous, and on the palmar surface of the
hands and fingei*s they are arranged in rows which can
be plainly seen.

Some of the papillie contain only loops of capillary
blood-vessels and lymphatics, but othei*s contain a special
organ called the tactile corpuscle.

The purpose of the tactile corpuscle is to give us
knowledge by contact with outside bodies.

The eye and the ear are the two great organs, of about
equal importance, through which we gain knowledge bj^
means of waves coming from the objects that are seen or
heard.

The sense of touch is third in importance.

The tactile corpuscle. — Many of the papilke con-
tain an oval-shaped body called the tactile coipuscle.
These are found on the palms and soles, i>articularly on

340

THIED BOOK OF PHYSIOLOGY

the fiugers and toes, where about one out of every five
of the i^apillae contains this organ. One, two, or three
nerve- fibres may enter directly into the corpuscle or
after winding three or four times around it.

Other tactile end organs which are distributed gener-
ally in the skin of the bod}' are the end bidbs. These

u ^

Pig. 153. — Two tactile papillae from skin of finger. Touch corpuscle
within and nerve-fibres below.

are small collections of epithelial cells to which nerve-
fibres are connected. They are quite as sensitive as the
corpuscles described above.

The Pacinian corpuscle. — The Pacinian cor-
puscles are small, oval-shaped, white bodies found in
many parts of the alveolar tissue beneath the skin. They
are formed of thirty or more tunics of connective tissue
and contain at the centre a terminal of a nerve-fibre.
Their function is not clearlv understood.

TIIK SI»KCIAI> Sl'^.NSES 341

Sensitiveness of different parts of the body. —
Ry layin^!: the t\\<> i)()iiits of ;i compjiss upon the skin at
various i)laees, a test can easily be made of one's ability
to distin<rnish two points of contact. By bringing the
points of the compass closer and closer together, a dis-
tance will be reached where the two points are judged
}is one. This, then, is a test of the closeness and delicacy
of the tactile organs.

Fig. lo-i. — Two Pacinian corpuscles. (Microphotograph.)

The place where the two points may be most nearly
together, and yet be felt as two, is on the tip of the
tongue. The place of least sensitiveness is in the middle
of the back. Some of these tests show that this dis-
tance on the tip of the tongue is about 2V of an inch ;
on the end of the finger about tV inch ; on the lip, I inch :
on the forehead, nearlj^ one inch ; and on the upper arm
and back, about two inches.

342 THIED BOOK OF PHYSIOLOGY

Path of the nervous impulse.— The nervous
impulses resulting from touch are carried chiefly by the
sensory fibres of the spinal nerves to the spinal cord.
There a reflex action may occur and a motor impulse be
at once sent out. This happens when the touch is such
as to indicate an injury of the part touched.

At the same time the sensory impulse is carried by
other neurons to the proper centre in the cortex of the
cerebrum. There not only do we perceive that the body
has been touched, but the point is exactly located, and
other motor impulses may be sent out from that centre.

Training of the sense organs. — The organs of
touch, particularly those in the ends of the fingers,
are capable of training, so that they will be a valuable
means of gaining information in regard to outside objects.
The sense of touch may be more reliable than any of the
other senses, as in judging the shape and surface of ob-
jects, or the texture of fabrics. One who is blind soon
learns to read by moving the fingers along a row of raised
letters, and can quicklj^ recognize a friend by passing the
hand over the face.

Miss Helen Keller has not been able to see or hear
since she was two years old, and yet she has been able,
through the sense of touch, to become highly educated.

SENSE OF SMELE

The nose. — The sense of smell is located in the nose.
The large cavity in the skull, between the two orbits of
the eyes, is occupied by the nasal passages. The cavity

THE SPECIAL SENSES

343

is divided into two coinpartiiients by ii i)iirtitioii whidiis
bone ill the posterior i>iut, but is continued us cartilage
towards the end of the nose.

Iloth passages open freely to the air in front and to the
l)harynx in the rear. Both passages are covered with
mucous membrane, a large surface being presented not

T

Fig. loo. — o, olfactory })ulb ; ?i, nerves descondirif; to the mucous

membrane.

onlj^ by the i)lain walls, but also by the three turbinated
bones which x)roject from the exterior sides of the nostrils
The lower j)art of the nose cavity is called the I'esjnra-
tory region^ for it is properly fitted for receiving air into
the body, as has been exi)lained under the subject of
respiration. Here the lining membrane is composed of
ciliated ei^ithelium. The upper part of the cavity is
called the olfactory region.

344 THIRD B(30K OF PHYSIOLOGY

The olfactory region. — In the upper part of the
Dostrils the organ of smell is located. Here the surface
is also covered with epithelial cells, but they are not
ciliated and their construction is peculiar. Part of them
contain an oval nucleus from which long projections ex-
tend on each end, one coming to the surface of the mem-
brane and the other extending back to a nerve-fibre.
Numerous cells of this kind reach the free surface of the
mucous membrane at one end, and connect with a nerve-
fibre at the other.

Xumerous glands in this region keep the surface con-
stantly moist.

The act of smeHing. — Odors which arise from
substances are carried in the air. In ordinary breathing,
a small area of the olfactory region is always exposed to
the air passing through the nostrils, but by '^sniffing,"
the air is admitted to a much larger area and many more
of the nerves of smell are affected.

The fine x>articles suspended in the air must fall ux^on
the moist mucous membrane and be dissolved, or, if a gas,
must enter into solution before they produce any effect.

An impulse started by this stimulus will travel to the
olfactory bulbs, as shown in Fig. 155, and will there be
taken up by other neurons and carried to the seat of per-
ception in the temporal lobes of the cerebrum.

The use of the smelling sense. — In many of the
lower animals, as in certain breeds of dogs, the sense of
smell is the most important of the five senses.

TIM-: SIM-^CIAL SENSKS 345

In man tliis sense is nflen uiuleresti mated. Tlie pri-
mary purpose is to j^ive us knowledge of any liarmful
substance in the air wliich we ))reathe. As a secondary
use, it enables us to distinguish objects by their odor, and
to give pleasui-e in the presence of pleasjint odors. Tlie
impressions made by the sense of smell appear to l)e
very distinct and lasting.

When the same odor is breathed through the nostrils
for a time, it ceases to aifect the organ of smell. When
one comes from fresh air into a close room, the bad con-
dition of the air is very noticeable at first, but after a
few breaths the ability to distinguish the foul from the
pure air is lost, until a change of air is again made.
The air in Mammoth Cave is quite free from the float-
ing particles which are plentiful in the air we ordi-
narily breathe. After a few hours in the cave, one will,
on coming out into the air again, feel a keen pain in the
nostrils until he becomes accustomed to the outside air.

Since the mucous membrane of the nostrils is the first
to be exposed to the air which we inhale, it will intercept
most of the i^articles which are floating in the air, and
thus it is often irritated and inflamed, and a catarrhal
condition is brought about, which is very destructive to
the organ of smell.

THE SENSE OF TASTE

Location and structure of the organs of
taste. — Just as the organ of smell is a guard at the gate-
way to the lungs, so the organ of taste is a guard at the
gateway to the stomach.

34G

THIRD BOOK OF PHYSIOLOGY

A ^^^

si

•13

Fig. 156. — View of the dorsum of the tongue. 1, 2, Y-like row
of the circumvallate papilhie ; 3, fungiform papiUae ; 4, 5, conical
papilUe ; 6, 6, floor of the fauces, with numerous lymphoid follicular
glands ; 7, tonsils ; 8, summit of the epiglottis.

TIIK SPK(^IAIi SKNSKS

347

The organs of taste are found in various parts of the
mouth, but chiefly on the palate and tonjj^ue. On the
ton<;^ue numerous little eminences may be plainly seen
with the naked eye. These are papilke, wliich contain
the organs of tiiste. On the frout part of the tongue
there are small conical projections called filiform papilhv.
On the middle region they are larger and appear like a
fungus growth, and so are called fungiform papillw. On

Fig. 157. — Cross-section of a circumvallate papilla, f^ taste-buds; i/>,
wall ; g^ nerve-fibres connected to taste-buds.

the back of the tongue are eight or ten large elevations
arranged in a V form with the vertex of the V towards the
throat. Each of these appears to be surrounded wath a
ditch and a w^all, and so are called cireumvaUate papillce.

Within the latter two kinds of papillae are clusters of
cells called taste-huds. Within the buds are several cells
which i:)roject from the end of the bud, and to which
fibres of nerves are attached. These are the taste-cells.

These buds are arranged in the sides of the depressions

348 THIRD BOOK OF PHYSIOLOGY

around the circumvallate papillae as shown in Fig. 157.
Thej^ are also found in the fungiform papillae.

Conditions and kinds of taste. — A substance
must be in solution before it can affect the taste-cells.
If the tip of the tongue he wiped dry and some dry
sugar be touched to it, no taste will follow until the tongue
again becomes moist. By the sense of taste it is possible
to distinguish sweet, sour, bitter, and salt.

The tip of the tongue is best adapted for receiving a
stimulus from sweet substances, and the sides and back
of the tongue for sour or bitter substances.

Cultivation of taste. — By proper attention the
sense of taste may be made very acute. Some persons
are i^aid good salaries for doing nothing but determine
the quality of liquors by their cultivated sense of taste.
The constant use of tobacco and alcoholic liquors will,
however, so blunt this sense that most substances will
have no taste or will all taste alike.

Smell and taste are closely associated and often con-
fused. The odor from substances in the mouth may
easily pass up. from the throat into the nostrils, and
thus we attribute to the sense of taste what belongs to
the sense of smell. If while eating an onion the nostrils
be held shut, the so-called onion taste will not be per-
ceived.

TlIK SPECIAL SKXSKS 349

QT^ESTIONS FOR KEVIKW.

1. "Wliat are the special senses?

2. Name and describe five general senses.

3. "What is the great advantage of the five special senses?

4. What are the two great media through which stimuli reach
the special senses, — the eye and the ear?

5. Make a sketch and locate the parts of the eye.

6. "What is the use of the front parts of the eye?

7. Describe the cornea.

8. When is light refracted?

9. ^lake a drawing to show how rays of light are affected by
the cornea.

10. Describe the iris.

11. What is the use of the iris?

12. Describe the crystalline lens.

13. What is the chief use of the lens?

14. Explain how the convexity of the lens is changed for dif-
ferent distances .

15. AVhen is the eye emmetropic?

10. Explain the condition of the myopic eye.

17. When is the eye said to be hypermetropic?

18. What kind of glasses must be used for near-sighted or far-
sighted eyes ? Why ?

19. How is the eye moved?

20. Explain the cause of cross-eyes.

21. What is the function of the posterior parts of the eye?

22. What are the three coats of the eye? Which is most essen-
tial? Why?

23. Describe the retina.

24. AVhat are the rods and cones, and where are they placed ?

25. Locate and describe the yellow spot.

26. Where is the blind spot ?

27. AVhat is the size of the image on the retina?

350 THIRD BOOK OF PHYSIOLOGY

28. How close can two points be together and still be seen as two ?

29. Describe the optic nerve.

30. How are two eyes better than one ?

31. Explain the perception of color.

32. Explain all the ways by which the eyes are protected.

33. What care should be taken of the eyes ?

34. How do alcohol and tobacco injure the eyes ?

35. Explain the nature of air-waves.

36. How fast does sound travel ? Light ?

37. AVhat are the three parts of the ear ?

38. Describe the pinna and give its use.

39. Describe the meatus.

40. Why is the middle ear called a drum ?

41. Xame the parts of the drum.

42. Describe the structure and use of the tympanum.

43. Make a drawing of the three bones and describe them.

44. How do the bones increase the force of the vibrations ?

45. What is tlie use of the Eustachian tube?

46. What are the openings into the drum ?

47. How large is the drum ?

48. Where is the labyrinth located, and what are its three parts?

49. Describe the osseous labyrinth.

50. Describe the membranous labyrinth.

51. How do the nerves end in the utricle, saccule, and semi-
circular canals ?

52. Describe the membranous cochlea.

53. Give a full description of the oi^an of Corti.

54. What is the function of the cochlea ?

55. Of what use is the round window?

56. What is the function of the semicircular canals?

57. How can the ear be properly cared for ?

58. Wliere are the organs of touch located ?

59. Describe a tactile corpuscle.

60. What is a Pacinian corpuscle ?

THE SPF.CIAL SENSES 351

61. What part <>f i\w body \n most sensitive to touch? Wliat
least? HoNv can this be determined?

62. How do we know wlien we are touched?

63. Describe the structure of the nostrils.

64. Explain the use of "sniffing."

66. Of what advantage is a keen sense of smell?

66. Where are the organs of taste located?

67. Describe the taste-buds.

68. What are the four taste sensations?

69. How are smell and taste confused?

70. Which of the special senses do you prize most highly?
Why?

EXPERIMENTS.

1. Secure at the butcher-shop two or three eyes of the ox or sheep. Closely
examine one of them, noting the tough, white sclerotic coat on the outside; the
point of entrance of the optic nerve ; the bulging, transparent cornea on the
front ; the iris and pupil beneath. Cut through the cornea, noting its thickness
and the limpid aqueous humor within. Find the crystalline lens and notice
the curvature of its two sides. Open the back part, noting the three coats and
the thick vitreous humor within.

2. Hold a mirror close before the face and notice the size of the pupil.
Shade the eyes from the light, and the iris can be seen to draw back on all
sides, thus making the pupil larger. Suddenly admit more light to the eyes
and the pupil will grow smaller.

3. Make on a piece of white paper two black spots about three inches
apart. Hold the left eye shut and look with the right eye steadily at the spot on
the left. By varying the distance a position of the paper can ea,sily be found
■where the image of the spot on the right side will fall upon the place where the
optic nerve enters the right eye. This is the blind spot, and so the image makes
no impression, that is, cannot be seen.

A. Try to see a whole line of this jjage distinctly without moving the eyes.
Try a single small word. Try a single letter. Only the images of very small
objects can be wholly contained in the yellow spot. Hence the need of many
muscles to freely move the eyes from point to point.

5. Use a pocket microscope as a len.s. Hold it near the wall of a room and

352 THIRD BOOK OF PHYSIOLOGY

note the image of a window or burning lamp. This is the action of the eomea
of the eye.

(). Look through a window and adjust the crystalline lens so that some
object, as a tree or a house, can be seen distinctly. At the same time the
window can be seen, but only indistinctly. Now readjust the lens so that the
window can be distinctly seen, and then the objects beyond can be seen only
indistinctly.

7. The image on the retina of an eye may be seen by cutting away the two
outside coats from the back of the eye of an ox. The thin retina must be care-
fully left in place. If the eye thus prepared be now pointed towards a candle
or lamp, and the light be screened from the eyes of the observer, an inverted
image can be seen on the retina.

8. Rapidly rotate a wheel and notice that the spokes will all apparently be
blended. The space between the spokes and the spokes themselves unite to
form a transparent disc. This is because a retinal impression lasts for about
one-seventh of a second. If the rotating wheel is seen by the light from a

stroke of lightning, it will appear to be standing still.

9. Prepare two discs of card-board, about six inches in diameter, one blue
and the other yellow. Hold the blue one against a white background and
look steadily at it for a minute, then suddenly jerk it away. A yellow disc will
be seen in its place. Try the same with the yellow one, and a blue outline of
the disc will appear on the white background.

These are two complementary colors and will when mixed produce white.
When the eye was fatigued by looking at the yellow it was still sensitive to its
complement, — the blue. When it was fatigued by the blue it could more dis-
tinctly see the yellow.

10. Close the nose and mouth and blow air through the Eustachian tube into
the ear-drum. Notice that hearing is then less distinct.

11. Utter quick, explosive notes into a piano and notice how it returns the
same note whatever the pitch may be. By this illustrate the sympathetic action
of the fibres in the basilar membrane of the cochlea.

12. Use a compass with blunt points and try on various parts of the body
how close together the points may be and yet be felt as two points.

18. It is an interesting test of one's ability to locate the spot where he has
been touched, if one will close his eyes while another touches him with the

THE SPECIAL SENSES 353

point of 11 pencil. Then sec how nearly the one who is touched can locate the
exact spot.

U. Cn)s.s two finpers and roll a hullet or small naind body between them.
One will appear as two.

1;'). I'hu-e the .same numljer of shot in each of two bottles. Balance one
lK)ttk' in each hand to determine, by the mn.scnlar .sen.se, the weij^ht. Then
have some one change a few siiot from one bottle to the other and then try to
determine which bottle is the heavier. By continued practice the rau.scular
sense becomes very acute.

1(). Prepare three vessels of water. One hot, one cold, and a third luke-
warm. Place one hand in the hot water and the other in the cold. After a
short time transfer both to the lukewarm water, and it will feel cold to the hand
that was in the not water, and warm to the hand that was in the cold water.

£3

GLOSSARY

A LIST of physiological ternjs likely to be mispronounced.

It is a good plan to have the class pronounce this list of words
occasionally until the pupils become accustomed to the sounds and
accents.

Ab do'men

Ad'i pose (ad'i pos)

Af'fer ent

Al bu'meu

Al ex'ines (al eks'ins)

Al i men'ta ry

A mci/ba (a me ba)

Am phib'i a (am fib'e ah)

A nat'o my

An ti tox'in (an te lok'sin)

A or'ia

Ap pen di ci'tis

A 'que ous (a'kwe us)

Ar ach'noid (ar ak'noid)

Ar e'o lar

Ar'ter y

Ar tic'u lar

Au'di to ry

Au'ri cle (aw'rik 1)

Au ric'u lo ven tric'u lar

Bac te'ri a
Bac te ri ol'o gy
Bas'i lar
Bi'ceps (bi'seps)
Bi cus'pids
Bron'chi (bron'ki)

Cae'cum (se'kum)

Cal'o rie (kal'o re)

Can al ic'u li

Can'cel lous

Ca' nines

Cap'il la ries

Car bo hy'drates

Car'di ac

Car ti lag'in ous (g = j)

Ca tarrh'al

Cen'tral fo'vea (fo've ah)

Cer e bel'lum

Cer'e bro spi'nal

Cer'e bro spi'nal men in gi'tis

(Ser'e bro spi'nal men in ji'tis)

Cer'e brum (ser'e brum)

Cer'vi cal (ser'vi kal)

Cho'roid (ko'roid)

Chro'ma tin (kro'mat in)

Chyle (kii;

Chyme (kim)

Cil'i a ted

Cir'cum val'late

Co ag u la'tion

Coc'cyx (kok'six)

Coch'lea (kok'leah)

Con'cha (kong^kah)

355

356

GLOSSAEY

Cor'ne a (kor'neah)
Cor'pus cal lo'sum
Cor'pus cle
Cra'ni um
Crys'tal line
Cy clo slo'ma la

Deg lu ti'tion

De lir'i um tre'mens

Den'drites

Den'tiue (den'tin)

Di'a phragni (di'af ram )

Diph the'ri a (dif the're ah)

Dip soma'ni a

Dis sec'tion

Du 0 de'num

Du'ra ma'ter

Ef'fer ent

E lee trol'y sis

Em me trop'ic

E mul'si fied

En am'el

En do car'di um

En'do lymph (en'do limi)

En dos'te um

En vi'ron ment

Ep i glot'tis

Ep i the'li um

E qui lib'ri um

Er'go graph

Eu sta'chi an ( u sta'ke an)

E vap o ra'tion

Ex' ere to ry

Ex ha la'tion

Fah'ren heit (Fah'ren hit)
Fas cise (fash'e e)
Fas cic'u li ( fas ik'u li)
Fau'ces ( law'sez)
Fer men ta'tion

Fi brin'o gen

Fib'u la

Fil'i form

Fis'sure (fish'ur)

Flagei'la(fla jel'la)

Fo ra'men

Fun'gi form (.fun'ji form)

Gan'gli a (gang'gle a)
Gly'co gen (gli'ko jen)
Gus'ta to ry
Gym na'si a

Ha ver'si an ( Ha ver'zhan )

Hem o glo'bin

Hi'lum

Hy dro chlo'ric

Hy dro pho'bia

Hy'gi ene

Hy per me trop'ic

Hy po gas'tric

II e o col'ic

Il'e um

In ci'sors

In'cus (ing'kus)

In fun dib'u la

In ha la'tiou

In nom i ua'tum

In sal 1 va'tion

In som'ni a

In ter cos'tal

In tes'tine (in tes'tin)

In Torun ta ry

Je ju'num

Ki net'ic

Lab'y rinth

Lach'ry mal ( lak'rim al )

GLOSSARY

357

Lac'te al

Lar'ynx ( 'ar'ingx)

Lie'ber kuhn (le'ber k6n)

Lo'cal i /a'tion

Ln'mi la

Lym phat'ics (lim fat'ics)

Mag ne'si urn

Mal'le us

Mai pig'hi an (nial pig'e an)

Mas li ca'tion

Mas'toid

Max'il la ry

Mo a'tus

Me (lul'la

Me dul'la ob Ion ga'ta

Med'ul la ry

Mem'bra nous

Men in'ges (men in'jez)

Mes'en te ry

Met a ear' pal

Met a tar'sal

Mi cro pho'to graph

Mi cro scop'ic

Mo di'olus

Mor'phine ( mor'fin )

Mu'cous (mu'kus)

Mu riat'ic

My op'ic

My'o sin

Neu'ron

Nic'o tine (nic'o tin)

Nu'cle us

Oc cip'i tal

0 don'toid

Oe soph'a gus (e sof a gus)

01 fac'to ry
Os mo'sis

Os'se ous(os'e us)

Os'si cle (os'e kl)
5'to lith
Ox i (la'tion

Pa cin'i an

Pan'cre as

Pa i)il'la) (03 = e)

Par'a lyzed

Pa ri'e tal

I'a roL'id

I'a tel'la

Per i ear'di um

Per'i lyiuph

Per i os'te um

Per i star tic

Per i to ne'um

Per spi ra'tion

Pha lan'ges (fa lan'jez)

Phar'ynx (far'inx)

Phos'pho rus ( fos'fo rus)

Phys i ol'o gy

Pi'a ma'ter

Pleu'ra (plu'rah)

Pneu mo gas' trie (nu mo gas'tric)

Pneu mo'ni a (nu mo'ne ah)

Po tas'si um

Po teu'tial ( po ten'shal )

Pro'te id

Pro'to plasm

Pro to zo'a

Pty'a iin ( ti'a lin )

Pul'mo na ry

Py lo'rus

Rac'e mose (ras'e mos)
Re frac'tion
Res'pi ra'tion
Res' pi ra to ry
Ret'i na

Sac'cule

Sar CO lem'ma

358

GLOSSAEY

Scle rot'ic (skle rot'ic)

Se cre'tion

Sem i cir'cu lar

Sem i lu'nar

Se'rous (se'rus)

Skel'e tal

Sta'pes ( sta'pez )

Sto'ma ta

Stri'a ted

Sub cla'vi an (sub kla've an)

Sub lin'gual (sub ling'gwal)

Sub max'il la ry

Sul phu'ric

Su'ture

Sym pa tbet'ic

Syn o'vi al

Tet'a nus

Tho rac'ic (tho ras'ic)

Tib'ia

Tis'sue (tish'u)

Tra'che a ( tra'ke ah)

Trans pi ra'tion
Tri chi'n£E (triki'ne)
Tu ber cu lo'sis
Tym'pan um
Ty'phoid

Un du la'tions
U re'a (u re'ah)
U rin if'er ous
U'vu la

Vac'u um

Val'vu Ise con ni ven'tes

Vas o mo' tor

Ven'tri cle

Ver'te bra (plural se = e)

Ves'ti bule

Vil'li

Vil'lus

Vit're ous

Vol'un ta ry

INDEX

Abdomen, 30

Adam's apple, 166

Adipose tissue, 26

Afferent nerves, 245

Air, 162, 163, 295

composition of, 174
germs in, 1S5
quantity breathed, 174
waves of, 320

Alcohol

and oxygen, 158
as a food, 91, 92
as a mental stimulus, 284
effect on muscle, 74
effect on digestion, 114
effect on circulation, 157, 158
effect on respiration, 186
effect on kidneys, 229
effect on the nervous sys-
tem, 281
effect on eye. 319
excessive use of. 2S5
hereditary effect, 287
quantity in drinks. 123
small doses of, 283

Alexines, 202

Alimentary canal, 96

Amneba. 21

Anatomy, 9

Animals and vegetables, 6

Antitoxin, 198

Aorta. 134

Appendicitis, 112

Arachnoid, 238

Argon, 176
Arteries, 136
Atlas, 39
Auricles, 132
Auriculo-ventricular valves,

133
■Axis, 40
Axis-cylinder, 234

B

Bacteria, 192

food of, 194

use of, 195
Ball-and-socket joint, 56
Basilar membrane, 333
Bathing, 216
Beating of heart, 153
Biceps, 61
Bicuspids, 98
Bile, 110

action of. Ill
Bleeding, 156
Blind spot. 311
Blood

composition of, 142

experiments on, 161

function of, 142

quantity of, 142
Blood-clots. 145
Blood-plasma, 142
Blushing, 150
Bone, 33

classes of, 36

composition of, 47

experiments on, 52

359

560

i:NrDEX

Bone, fracture of. oO

health of, 48

microscopic appearance, 46

names of, 35

nourishment of, 47

number of, 33

of ear, 325

strength of, 45

use of, 33
Brain, 238

a favored organ, 272

convolutions of, 242

lobes of, 241

parts of, 239

supply of blood to, 274

weiglit of, 239, 262
Bright's disease, 229
Bronchi, 167
Bronchial tubes, 169

Caecum, 112
Canaliculi, 46
Cancellous bone tissue, 45
Canines, 98
Capillaries, 137
Carbohydrates, 84, 86
Carbon dioxide, 176
Cardiac orifice, 102
Carotid artery, 274
Cartilage, 27
Cells, 13

division of, 19

how formed, 19

origin of, 16

parts of, 17
Centrosome, 19
Cerebellum, 242

function of, 262
Cerebrospinal meningitis, 239
Cerebrum, 240

Cerebrum, function of, 259

Cholera infantum, 197

Chromatin, 18

Chyle, 111

Chyme, 105

Cilia, 25

Circulation, 128

effect of exercise on, 155

hygiene of, 155

organs of, 130

scheme of, 148

systems of, 149
Circumvallate papillse, 347
Coagulation, 146
Coccyx, 40
Cochlea, 330, 335
Colds, 156

Color sensations, 315
Composition of body, 33, 34
Cones, 311
Conjunctiva, 318
Connective tissue, 25
Convolutions of brain, 242
Corn, 87

Cornea, 297, 298
Corpus eallosum, 240
Cortex of cerebrum, 241
Cortex of kidney, 226
Corti's arches, 335.
Cranial nerves, 246
Cranium, 38
Cross-eyes, 309
Crystalline lens, 302

D

Deglutition, 102
Delirium tremens, 286
Dendrites, 234
Dentine, 99
Dermis, 208
Diaphragm, 30

IN1)P]X

36^

] )i:;-c'stioii, 9.")

experiments on, 117
in intestines, 110
in stomach, 104
organs of, 07
why necessary, 95

Diphtheria, 107

Drum of ear, 323

Duodenum, lOG

Dura mater, 238

Dust in air, 184

E
Ear, 321

anatomy of, 322

care of, 337
p]fFerent nerves, 245
Emmetropic eye, 305
Enamel, 00
Endolymph, 331
Endosteum, 47
End plates, 252
Energy, 80, 81
]]pidermis, 207
Epiglottis, 101, 166
Epithelium, 24
Ether, 295

Eustachian tube, 326
Excretions, 221

organs of, 222
Exercise, 71
Exhalation, 173
External ear, 322
Eye, 296

anatomy of, 296

care of, 318

protection of, 316

Fascia, 67
Fasciculi, 67

Fat, 84
Fatigue, 275
Fauces, 101

Fermentation, 197
I'ihres of musch', 67
Fihrin, 145
Fibrinogen, 14o
Flat bones, 37
Food, 79

a complex compound, 85

amount of, 89

compared to coal in engine,
81

cooking of, 90

definition of, 85

for brain, 273

mixed, 88

produced by bacteria, 196

Gall-bladder, 110
Ganglia, 233
Gastric gland, 104

juice, 104
General sensations, 293
Germs in air, 185
Glands, 29
Gliding joint, 57
Glycogen, 129
Gout, 57

H

Habit, 268, 280
Hair, 212

care of, 218
Haversian canals, 46
Health, 204
Heart, 130

divisions of, 132

valves of, 132

work of, 154

362

IXDEX

Hemispheres of brain, 240
Hemoglobin, 144
Hilum, 224
Hinge- joint, 56
Hip-joint, 55
Hydrochloric acid, 105
Hvdrophobia, 204
Hygiene, 10
Hypermetropic eye, 306

Heocolic valve, 112

Ilium, 106

Image on retina, 312

Incisors, 98

Inferior vena cava, 139

Inhalation. 171

Inspired air, 177

Internal ear, 328

Involuntary muscles, 66

Iris, 300

Irregular bones, 38

Jejunum, 106

Joints, 53

health of, 57
kinds of, 55
structure of. 53

K

Kidnevs. 223

Lachrymal gland, 317
Lacteal, 108
Lacuna^, 46
Large intestine, 112

action of, 112
Larynx, 165
Levers. 02

Life, 5

Ligaments, 54
Light, 296
Liver, 108

action of, 129
Lobes of brain, 241
Lock-jaw, 198
Long bones, 36
Lungs, 169

as excretory organ, 222

capacity of, 174
Lymph, 138
Lymphatic nodes, 141
Lymphatics, 140

M

Malpighian bodies, 226
^lammal, 7
Z\larrow, 48
Mastication, 97, 113
Matter and life, 5
Medulla oblongata, 243

function of, 263
Medullary layer, 225
Medullary sheath, 235
Medullated nerve-fibre, 237
Membranous labyrinth, 331
Meninges, 238
Mesentery, 106
Middle ear, 323
Modiolus, 330
Molars, 98

Movements of the eyes, 307
Mucous membrane, 30
Muscles, 60

attachment of, 61

development of, 69, 70

food of, 70

kinds of, 65

of the eyes, 308

skill of, 73

INDKX

363

Muscles, stnicturo of, 07
Muscular tissue, 27
Mj'opic eye, 305

N
Nails, 214

care of, 21!)
Nerve-cell, 234
Nerve-centres, 258
Nerve endiiifjs, 2.")!
Nerves, 243

functions of, 209
Nervous system, 233

divisions of, 233
Nervous tissue, 27, 237

nutrition of, 271
Neuroglia, 238
Neurilemma, 235
Neuron, 235
Nitrogen, 176

Nitrogenous equilibrium, 228
Nodes, 237
Nose, 342
Nostrils, 165
Nucleus, 18

O

Odontoid process, 40
Q^]sophagus, 102
Olfactory region, 344
Opium, 290
Optic nerves, 313
Organ of C'orti, 335
Organs, 28

Origin of muscles, 61
Osmosis, 95
Osseous tissue, 27
Osseous labyrinth, 329
Otoliths, 332
Oval window, 330
Oxidation, 82

Oxygen, 175
Ozone, 175

Piicininn corpuscles, 341
Pancreas, 110
Pancreatic juice. 111
Patent medicines, 290
Pelvis, 41

Pelvis of kidney, 224
Pepsin, 105
Peptone, 105
Pericardium, 131
Perilymph, 331
Perineurium, 244
Periosteum, 47
Peristaltic motion, 105
Peritoneum, 103
Perspiration, 211
Pharjnix, 101
Physical culture, 72
Physiology, 9
Pia mater, 238
Pinna of ear, 322
Pivot- joint, 50
Pleura, 170
Pleural cavity, 171
Plexus of nerves, 254
Pneumogastric nerves, 247
Pons, 242

function of, 203
Pores, 210

Portal circulation, 151
Proteid, 83, 80
Protozoa, 0

Pulmonary artery, 137
Pulmonary circulation, 152
Pulse, 147
Pus, 203

Pyloric orifice, 102
Pyramids of Malpighi, 225

3G4

IXDEX

R

Eacemose gland. 100

Red corpuscles, 142

Keflex action, 2G3

advantage of, 260
education of, 267

Refraction of light, 298

Renal circulation, 152

Rennin, 105

Respiration, 162

experiments on, 189
hygiene of, 179
organs of, 165
use of, 164

Retina, 309

Ribs, 42

Rickets. 49

Rods, 311

Round window. 330. 336

Sacculus. 331

Sacrum, 40

Salivary glands, 100

Sarcolemma, 67

Secretion. 221

Semicircular canals, 330, 337

Semilunar valves, 134

Serous membrane, 29

Short bones, 37

Size of brain, 239, 262

Skeletal muscles, 60

Skeleton, 34

Skin

as an excretory organ, 223

as a protection, 202

color of, 208

hygiene of, 214

layers of, 207

use of, 206
Sleep, 276

^mall intestine, 105

digestion in, 110
Smell, 342
Soft palate, 101
Solar plexus, 256
Sound, 296
Sound of heart, 154
Sound-waves, 320
Special senses, 293
Spinal cord, 247
Spinal nerves, 249
Spleen. 141
Sprains, 58
Stomach, 102

health of, 114
Striated muscle, 68
Superior vena cava, 139
Suture, 38
Sweat-glands. 210
Sympathetic nervous system,

255
SynoA'ia, 54

Systemic circulation, 151
Systems, 28

Tactile corpuscles, 339

Tartar, 113

Taste, 345

Taste-buds, 347

Tears, 317

Teeth, 97

care of, 113

Temperature of body, 211

Tetanus, 198

Thoracic duct, 129

Thorax, 30

Tissue, 23

Tobacco

effect on circulation, 158
effect on respiration, 187

INDEX

365

Tobacco

effect oil tlie nerves, 288
Tonsils, 101
Touch, 339
Trachea, 167
Trichinie, 1»0
Tuberculosis, 185, 109
Tympanum, 323
Typhoid fever, 201

U
Urea, 228
Ureter, 227

Uriniferous tubules, 226
Utricle, 331
U\-ula, 101

Vagi, 247

Vahnilae conniventes, 106

Veins, 139
Ventilation, 180
Ventricles, 132
Vertebral column, 39
Vertebrates, 7

classes of, 7
Villi, 106
\'oeal cords, lOi
Voluntar}' muscles, 65

w

Water, 123

Wheat, 86

White corpuscles, 144, 203

Work of heart, 154

Yeast, 193. 196
Yellow spot, 311

THE END

«r-

SEP 11

1928

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wr

llUit!