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* * * * *
[Illustration: THE VISCERA IN POSITION.]
* * * * *
A
TREATISE
ON
PHYSIOLOGY AND HYGIENE
FOR
EDUCATIONAL INSTITUTIONS AND GENERAL READERS.
_FULLY ILLUSTRATED._
BY
JOSEPH C. HUTCHISON, M. D.,
_President of the New York Pathological Society, Vice-President of the New
York
Academy of Medicine, Surgeon to the Brooklyn City Hospital, late
President
of the Medical Society of the State of New York, etc._
* * * * *
NEW YORK:
CLARK & MAYNARD, PUBLISHERS,
5 BARCLAY STREET.
1872.
* * * * *
Entered according to Act of Congress, in the year 1870,
By CLARK & MAYNARD.
In the Office of the Librarian of Congress, at Washington.
Stereotyped by LITTLE, RENNIE & CO.
645 and 647 Broadway.
* * * * *
TO MY WIFE,
WHOSE SYMPATHY HAS, FOR MORE THAN TWENTY YEARS, LIGHTENED THE
CARES INCIDENT TO
_AN ACTIVE PROFESSIONAL LIFE_,
THIS HUMBLE VOLUME
IS AFFECTIONATELY INSCRIBED.
* * * * *
{3}
PREFACE.
------o------
This work is designed to present the leading facts and principles of human
Physiology and Hygiene in clear and concise language, so that pupils in
schools and colleges, and readers not familiar with the subjects, may
readily comprehend them. Anatomy, or a description of the structure of an
organ, is of course necessary to the understanding of its Physiology, or
its uses. Enough of the former study has, therefore, been introduced, to
enable the pupil to enter intelligently upon the latter.
Familiar language, as far as practicable, has been employed, rather than
that of a technical character. With a view, however, to supply what might
seem to some a deficiency in this regard, a Pronouncing Glossary has been
added, which will enable the inquirer to understand the meaning of many
scientific terms not in common use.
In the preparation of the work the writer has carefully examined all the
best material at his command, and freely used it; the special object being
to have it abreast of the present knowledge on the subjects treated, as far
as such is possible in a work so elementary as this. The discussion of
disputed points has been avoided, it being manifestly inappropriate in a
work of this kind.
Instruction in the rudiments of Physiology in schools does not necessitate
the general practice of dissections, or of experiments upon animals. The
most important subjects may be illustrated by {4} drawings, such as are
contained in this work. Models, especially those constructed by AUZOUX of
Paris, dried preparations of the human body, and the organs of the lower
animals, may also be used with advantage.
The writer desires to acknowledge his indebtedness to R. M. WYCKOFF, M.D.,
for valuable aid in the preparation of the manuscript for the press; and to
R. CRESSON STILES, M.D., a skilful microscopist and physician, for the
chapter "On the Use of the Microscope in the Study of Physiology." Mr. AVON
C. BURNHAM, the well-known teacher of gymnastics, furnished the drawing of
the parlor gymnasium and the directions for its use.
_Brooklyn, N. Y., 1870._
* * * * *
{5}
CONTENTS.
CHAPTER I.
PAGE
THE FRAMEWORK OF THE BODY 15
_The Bones--Their form and composition--The Properties of Bone--The
Skeleton--The Joints--The Spinal Column--The Growth of Bone--The
Repair of Bone._
CHAPTER II.
THE MUSCLES 25
_The Muscles--Flexion and Extension--The Tendons--Contraction--Physical
Strength--Necessity for Exercise--Its Effects--Forms of
Exercise--Walking--Riding--Gymnastics--Open-air Exercise--Sleep--
Recreation._
CHAPTER III.
THE INTEGUMENT, OR SKIN 41
_The Integument--Its Structure--The Nails and Hair--The Complexion--The
Sebaceous Glands--The Perspiratory Glands--Perspiration
and its uses--Importance of Bathing--Different kinds of Baths--Manner
of Bathing--The Benefits of the Sun--Importance of
Warm Clothing--Poisonous Cosmetics._
CHAPTER IV.
THE CHEMISTRY OF FOOD 53
_The Source of Food--Inorganic Substances--Water--Salt--Lime--Iron--
Organic Substances--Albumen, Fibrin, and Casein--The Fats or
Oils--The Sugars, Starch, and Gum--Stimulating Substances--Necessity
of a Regulated Diet._
{6}
CHAPTER V.
FOOD AND DRINK 64
_Necessity for Food--Waste and Repair--Hunger and Thirst--Amount
of Food--Renovation of the Body--Mixed Diet--Milk--Eggs--Meat--Cooking
--Vegetable Food--Bread--The Potato--Fruits--Purity
of Water--Action of Water upon Lead--Coffee, Tea, and Chocolate--Effects
of Alcohol._
CHAPTER VI.
DIGESTION 80
_The Principal Processes of Nutrition--The General Plan of Digestion--
Mastication--The Teeth--Preservation of the Teeth--Insalivation--The
Stomach and the Gastric Juice--The Movements of the
Stomach--Gastric Digestion--The Intestines--The Bile and Pancreatic
Juice--Intestinal Digestion--Absorption by means of Blood-vessels
and Lacteals--The Lymphatic or Absorbent System--The
Lymph--Conditions which affect Digestion--The Quality, Quantity,
and Temperature of the Food--The Influence of Exercise and
Sleep._
CHAPTER VII.
THE CIRCULATION 101
_The Blood--Its Plasma and Corpuscles--Coagulation of the Blood--The
Uses of the Blood--Transfusion--Change of Color--The Organs of
the Circulation--The Heart, Arteries, and Veins--The Cavities
and Valves of the Heart--Its Vital Energy--Passage of the Blood
through the Heart--The Frequency and Activity of its Movements--The
Pulse--The Sphygmograph--The Capillary Blood-vessels--The
Rate of the Circulation--Assimilation--Injuries to the Blood-vessels._
CHAPTER VIII.
RESPIRATION 123
_The Objects of Respiration--The Lungs--The Air-Passages--The Movements
of Respiration--Expiration and Inspiration--The Frequency
of Respiration--Capacity of the Lungs--The Air we Breathe--Changes
in the Air from Respiration--Changes in the Blood--Interchange
of Gases in the Lungs--Comparison between Arterial and
{7}
Venous Blood--Respiratory Labor--Impurities of the Air--Dust--Carbonic
Acid--Effects of Impure Air--Nature's Provision for
Purifying the Air--Ventilation--Animal Heat_.
CHAPTER IX.
THE NERVOUS SYSTEM 148
_Animal and Vegetative Functions--Sensation, Motion, and Volition--The
Structure of the Nervous System--The White and Gray Substances--The
Brain--Its Convolutions--Cerebellum--The Spinal
Cord and its System of Nerves--The Anterior and Posterior
Roots--The Sympathetic System of Nerves--The Properties of Nervous
Tissue--Excitability of Nervous Tissues--The Functions of the
Spinal Nerves and Cord--The Direction of the Fibres of the Cord--Reflex
Activity and its Uses--The Functions of the Medulla Oblongata
and the Cranial Ganglia--The Reflex Action of the Brain._
CHAPTER X.
THE SPECIAL SENSES 177
_The Production of Sensations--Variety of Sensations--General
Sensibility--Pain
and its Function--Special Sensation, Touch, Taste,
Smell, Sight, and Hearing--The Hand, the Organ of Touch--The
Sense of Touch--Delicacy of Touch--Sensation of Temperature and
Weight--The Tongue the Organ of Taste--The Nerves of Taste--The
Sense of Taste, and its Relations with the other Senses--The
Influence of Education on the Taste--The Nasal Cavities, or the
Organs of Smell--The Olfactory Nerve--The Uses of the Sense of
Smell--The Sense of Sight--Light--The Optic Nerve--The
Eyeball and its Coverings--The Function of the Iris--The
Sclerotic, Choroid, and Retina--The Tears and their Function--The
Movements of the Eyeball--The Function of Accommodation--The
Sense of Hearing and Sound--The Ear, or
the organ of Hearing--The External, Middle, and Internal Ear._
CHAPTER XI.
THE VOICE 227
_Voice and Speech--The Larynx, or the Organ of the Voice--The Vocal
Cords--The Laryngoscope--The Production of the Voice--The Use
of the Tongue--The different Varieties of Voice--The Change of
Voice--Its Compass--Purity of Tone--Ventriloquy._
{8}
CHAPTER XII.
THE USE OF THE MICROSCOPE IN THE STUDY OF
PHYSIOLOGY 236
_The Law of Tissues--Necessity of the Microscope--Different kinds of
Microscopes--Additional Apparatus--Preliminary Studies--The
Study of Human Tissues--Tissues of the Inferior Animals--Incentives
to Study._
APPENDIX.
POISONS AND THEIR ANTIDOTES 247
GLOSSARY 252
{9}
LIST OF ILLUSTRATIONS
FIG. PAGE
FRONTISPIECE, }
VISCERA IN POSITION,}
1. Section of bone, 17
2. Structure of bone, magnified, 17
3. The skeleton, 18
4. Cells of cartilage, 20
5. Elbow-joint, 21
6. Spinal column, 22
7. The muscles, 24
8. Muscular tissue, magnified, 25
9. Biceps muscle of the arm, 26
10. View of knee-joint, 27
11. Appliance for strengthening the muscles, 35
12. Appliance for strengthening the muscles, 35
13. Parlor gymnasium, 36
14. Root and transverse section of hair, magnified, 43
15. Granules of potato starch, 61
16. Section of the trunk, 81
17. Section of a tooth, 82
18. Section of the jaws, 82
19. Section of the jaws--right side, 84
20. Structure of a salivary gland, 87
21. Head of a horse, showing salivary gland, etc. 87
22. Section of chest and abdomen, 90
23. Organs of digestion, 91
24. The lacteals, 97
25. Blood corpuscles, 102
26. Blood corpuscles of man and lower animals, 103
27. Circulation of the blood, 108
{10}
28. Heart and large vessels, 109
29. Section of the heart, 110
30. Form of the pulse, 116
31. Valves of the veins, 117
32. Web of frog's foot, magnified, 119
33. Circulation in a frog's foot, 119
34. Organs of the chest, 124
35. Larynx, trachea, and bronchial tubes, 125
36. Diagram of the structure of the air-cells, 125
37. Section of the lungs, 126
38. Section of mouth and throat, 127
39. Ciliated cells, 128
40. Cerebro-spinal system, 151
41. Upper surface of the cerebrum, 153
42. Vertical section of the brain, 154
43. Base of the brain, 155
44. Brain and spinal cord, 156
45. Sense of touch, 185
46. Section of nasal cavity, 193
47. Front view of the eye, 200
48. Vertical section of eye, 202
49. Diagram for blind point of eye, 207
50. Retinal image, 210
51. Different shapes of the globe of the eye, 212
52. Function of accommodation, 214
53. Diagram of the ear, 218
54. Section of the ear, 221
55. Section of larynx and trachea, 229
56. View of vocal cords by the laryngoscope, 232
57. Different positions of vocal cords, 232
58. Simple microscope, 238
59. Compound microscope, 239
60. Household microscope, 240
61. Popular microscope, 241
{11}
INTRODUCTION.
------o------
The Human Body is the abode of an immortal spirit, and is the most complete
and perfect specimen of the Creator's handiwork. To examine its structure,
to ascertain the uses and modes of action of its various parts, how to
protect it from injury, and maintain it in a healthy condition, is the
design of this work.
The departments of knowledge which are concerned in these investigations,
are the science of Human Physiology and the art of Hygiene.
PHYSIOLOGY treats of the vital actions and uses of the various parts of
living bodies, whether vegetable or animal. Every living thing, therefore,
has a Physiology. We have a _Vegetable_ Physiology, which relates to
plants; and an _Animal_ Physiology, relating to the animal kingdom. The
latter is also divided into _Comparative_ Physiology, which treats of the
inferior races of animals, and _Human_ Physiology, which teaches the uses
of the various parts of the human body.
HYGIENE, or the art of preserving health, is the practical use of
Physiology. It teaches us how to cultivate our bodily and mental powers, so
as to increase our strength and to fit us for a higher enjoyment of life.
It also shows us how to prevent some of the accidents which may befall the
body, and to avoid disease. It is proper that we should {12} understand the
construction and powers of our bodies; but it is our duty, as rational
beings, to know the laws by which health and strength may be maintained and
disease warded off.
There are various means by which we gain important information respecting
the Physiology of man. Plants aid us in understanding the minute structure
of the human body, its circulation, and absorption. From inferior animals
we learn much in respect to the workings of the different _organs_, as we
call those parts of the system which have a particular duty to perform. In
one of them, as in the foot of the frog, we can study the circulation of
the blood; in another, we can study the action of the brain.
By _vivisection_, or the laying bare of some organ of a living animal, we
are able to investigate certain vital processes which are too deeply hidden
in the human body to be studied directly. This is not necessarily a cruel
procedure, as we can, by the use of anæsthetics, so blunt the sensibility
of the animal under operation, that he need not suffer while the experiment
is being performed. There are other means by which we gather our
information. There are occasionally men, who, from some accident, present
certain parts, naturally out of view, in exposed positions. In these cases,
our knowledge is of much greater value than when obtained from creatures
lower in the scale of being than man.
We are greatly aided, also, by the use of various instruments of modern
invention. Chief among these is the microscope, which is, as we shall learn
hereafter, an arrangement and combination of lenses in such a way as
greatly to magnify the objects we wish to examine. {13}
We have much to say of Life, or vital activity, in the course of our study
of Physiology; but the most that we know of it is seen in its results. What
Life is, or where its precise position is, we are not able to determine. We
discover one thing, however, that all the parts of the body are united
together with wonderful sympathy, so that one part cannot be injured and
other parts not suffer damage. It is further evident that all organs are
not equally important in carrying on the work of Life; for some may
temporarily suspend their action, without serious results to the system,
while others must never cease from acting. Yet there is nothing superfluous
or without aim in our frames, and no part or organ can suffer harm without
actual loss to the general bodily health. On this point Science and Holy
Writ strictly agree.
* * * * *
{14}
{15}
PHYSIOLOGY,
AND
HYGIENE.
CHAPTER I.
THE FRAMEWORK OF THE BODY.
_The Bones--Their Form and Composition--The Properties of Bone--The
Skeleton--The Joints--The Spinal Column--The Growth of Bone--The Repair of
Bone._
[Sidenote: 1. The framework of the body? The superstructure? Softness and
delicacy of the organs? How protected?]
1. THE BONES.--The framework which sustains the human body is composed of
the _Bones_. The superstructure consists of the various organs on which the
processes of life depend. These organs are soft and delicately formed, and,
if unprotected, would, in most cases, rapidly be destroyed when subjected
to violence, however slight. The bones, having great strength and power of
resistance, afford the protection required.
[Sidenote: 2. The more delicate the organ? Example in relation to the
brain? The eye? The lungs? The services performed by the bones?]
2. The more delicate the organ, the more completely does Nature shield it.
For example: the brain, which is soft in structure, is enclosed on all
sides by a complete box of bone; the eye, though it must be near the
surface of the body to command an extensive view, is sheltered from injury
within a deep recess of bone; the lungs, requiring freedom of motion as
well as protection, are surrounded by a large case of bone and muscle. The
bones serve other useful purposes. They give permanence of form to the
body, by {16} holding the softer parts in their proper places. They assist
in movement, by affording points of attachment to those organs which have
power of motion--the muscles.
[Sidenote: 3. Their shape and size? Of what composed? Possibility of being
separated? Effect of fire? Of dilute acid?]
3. THE FORM AND COMPOSITION OF THE BONES.--Their shape and size vary
greatly in different parts of the body, but generally they are arranged in
pairs, one bone for each side of the body. They are composed of both
mineral and animal substances, united in the proportion of two parts of the
former to one of the latter; and we may separate each of these substances
from the other for examination. First, if we expose a bone to the action of
fire, the animal substance is driven off, or "burned out." We now find
that, though the shape of the bone is perfectly retained, what is left is
no longer tough, and does not sustain weight as before. Again, we may
remove the mineral portion, which is a form of lime, by placing a bone into
a dilute acid. The lime will be dissolved out, and the shape of the bone
remain as before; but now its firmness has disappeared, and it may be bent
without breaking.
[Sidenote: 4. Effect of deficiency of ingredient? Usefulness of the lime?
Of the animal substance? Effect of their union? Condition, in youth? Old
age?]
4. If, for any reason, either of these ingredients is disproportionate in
the bone during life, the body is in danger. The lime is useful in giving
rigidity of form, while the animal substance insures toughness and
elasticity. By their union, we are able to withstand greater shocks and
heavier falls than would be possible with either alone. In youth, the
period of greatest activity, the animal constituent is in excess: a bone
then does not break so readily, but, when broken, unites with great
rapidity and strength. On the other hand, the bones of old persons are more
easily broken, and in some cases fail to unite. The mineral matter being
then in excess, indicates that the period of active exertion is drawing to
a close.
{17}
[Illustration: FIG. 1.--SECTION OF BONE.]
[Illustration: FIG. 2.
Structure of bone enlarged.]
[Sidenote: 5. In what respect admirably fashioned? Its formation?
Microscopic examination? The inference? "Line of beauty?"]
5. THE STRUCTURE OF THE BONES.--If we examine one of the long bones, which
has been sawn through lengthwise, we observe that it is admirably fashioned
for affording lightness as well as strength (Fig. 1). Its exterior is hard
and resisting, but it is porous at the broad extremities, while through the
central portion there is a cavity or canal which contains an oily
substance, called _marrow_. Let us now take a thin section of bone, and
examine it under the microscope; we discover that it is pierced by numerous
fine tubes (Fig. 2), about which layers of bone-substance are arranged.
Accordingly, though a bone be as hard as stone externally, it is by no
means as heavy as stone, by reason of its light interior texture. Another
element of power is found in the curved outline of the bones. The curved
line is said to be "the line of beauty," as it certainly is the line of
strength, and is uniformly employed in the bones whose position exposes
them to accident.
{18}
[Illustration: FIG. 3.--THE SKELETON]
{19}
[Sidenote: 6. Number of bones? Skeleton? The skull? Chest? The trunk? The
trunk and skull, how maintained? What of the arms? Legs?]
6. THE SKELETON.--The number of bones in the human body exceeds two
hundred. When these are joined together in the proper places, they form
what is termed the _Skeleton_ (Fig. 3). It embraces three important
cavities. The first, surmounting the frame, is a box of bone, called the
_skull;_ below this, is a bony case, or "chest;" and lower down is a bony
basin, called the _pelvis_. The two latter compose the trunk. The trunk and
skull are maintained in their proper relations by the "spinal column."
Branching from the trunk are two sets of limbs: the arms, which are
attached to the chest by means of the "collar-bone" and "shoulder-blade;"
and the legs, directly joined to the lower part of the trunk.
[Sidenote: 7. Design of the cavities? Give the examples.]
7. The cavities of which we have spoken, are designed for the lodgment and
protection of the more delicate and perishable parts of the system. Thus,
the skull, together with the bones of the face, shelters the brain and the
organs of four senses--sight, hearing, smell, and taste. The chest contains
the heart, lungs, and great blood-vessels, while the lower part of the
trunk sustains the liver, stomach, and other organs.
[Sidenote: 8. Joint or articulation? Movable joints, how compacted? The
ligaments of the movable joints? What is a sprain? Consequence of a serious
sprain?]
8. THE JOINTS.--The point of union of two or more bones forms a joint or
_articulation_, the connection being made in various ways according to the
kind and amount of motion desired. The movable joints are compacted
together by certain strong fibrous bands, called ligaments. These ligaments
are of a shining, silvery whiteness, and very unyielding; so much so, that
when sudden violence is brought to bear in the vicinity of a joint, the
bone to which a ligament is attached may be broken, while the ligament
itself remains uninjured. When this connecting material of the joints is
strained or lacerated by an {20} accident, a "sprain" is the consequence.
An injury of this sort may be, and frequently is, quite as serious as the
breaking of a bone.
[Illustration: FIG. 4.--CELLS OF CARTILAGE.]
[Sidenote: 9. Office of the ligament? What must it have? How accomplished?
Describe it. Synovia?]
9. The ligament, then, secures firmness to the joint; it must also have
flexibility and smoothness of motion. This is accomplished by a beautiful
mechanism the perfection of which is only feebly imitated by the most
ingenious contrivance of man. The ends of the bones are covered by a thin
layer of _cartilage_, which being smooth and elastic, renders all the
movements of the joint very easy. In addition to this, there is an
arrangement introduced for "lubricating" the joint, by means of a delicate
sac containing fluid. This fluid is constantly supplied in small
quantities, but only so fast as it is used up in exercise. In appearance,
it is not unlike the white of an egg, and hence its name _synovia_, or
egg-like.
[Sidenote: 10. What do we observe as regards the composition of a joint?
The ligament and cartilage? What varies? Example of the skull? Other
examples? The ball-and-socket joint?]
10. Thus, we observe, that two very different substances enter into the
composition of a joint. The ligament, very unyielding, affords strength,
while the cartilage, elastic and moist, gives ease and smoothness of
motion. The amount of motion provided for varies greatly in different
joints. In some there is none at all, as in the skull, where one bone is
dove-tailed into another by what are termed _sutures_. Others have a
hinge-like motion, such as those of the elbow, wrist, ankle, and knee; the
most complete of these being the elbow-joint (Fig. 5). Belonging to another
class, the {21} ball-and-socket joint, is that at the shoulder, possessing
a freedom of motion greater than any other in the body.
[Illustration: FIG. 5.--ELBOW JOINT. A, Bone of the arm; B, C, Bones of the
fore-arm.]
[Sidenote: 11. What is the spinal column? What does it connect and form?
Joints of the vertebræ? Amount of motion? Result?]
11. THE SPINAL COLUMN.--The spinal column is often spoken of as the
"back-bone," as if it were a single bone, while, in reality, it is composed
of a chain of twenty-six small bones, called _vertebræ_. The spinal column
is a wonderful piece of mechanism. It not only connects the important
cavities of the body, as has already been shown, but, also, itself forms a
canal, which contains the spinal cord. The joints of the vertebræ are
remarkable for the thick layers of cartilage which separate the adjacent
surfaces of bone. The amount of motion between any two of these bones is
not great; but these little movements, taken together, admit of very
considerable flexibility, in several directions, without endangering the
supporting power of the column.
{22}
[Sidenote: 12. Elasticity of the frame? Protection of the brain from
shocks? Tallness of persons? Effects of reclining?]
[Illustration: FIG. 6--THE SPINAL COLUMN.]
12. The abundant supply of intervertebral cartilage has another important
use, namely, it adds greatly to the elasticity of the frame. It is due, in
part, to this elastic material, and in part to the frequent curves of the
spine, that the brain and other delicate organs are protected from the
shock of sudden falls or jars. During the day, the constant pressure upon
these joints, while the body is erect, diminishes the thickness of the
cartilages; so that a person is not so tall in the evening as in the
morning. The effects of this compression pass away when the body reclines
in a horizontal position.
[Sidenote: 13. Change in bone? Example--animal and madder. Rapidity of
change in color? Waste and repair?]
13. THE GROWTH OF BONE.--Bone, like all the other tissues of the body, is
constantly undergoing change, old material being withdrawn, and new
particles taking their place. This has been shown conclusively by
experiments. If an animal be fed with madder--a red coloring matter--for a
day or two, the bones soon become tinged; then, if the madder be
discontinued for a few days, the original color returns. If, however, this
material be alternately given and withheld, at short intervals, the bone
will be marked by a succession of red and white rings. In very young
animals, all the bones become colored in a single day; in older ones, a
longer time is required. The process of waste and repair, therefore, is
constantly taking place in this hard substance, and with astonishing
rapidity. {23}
14. THE REPAIR OF BONE.--Nature's provision for uniting broken bones is
very complete. At first, blood is poured out around the ends of the bone,
as a result of the injury. This is gradually absorbed, and gives place to a
watery fluid, which, thickening from day to day, acquires, at the end of
two weeks, the consistency of jelly. This begins to harden, by a deposit of
new bone-substance, until, at the expiration of five or six weeks, the
broken bone may be said to be united. It is, however, still fragile, and
must be used carefully a few weeks longer. The process of hardening
continues, and months must pass before the union can be said to be
complete.
QUESTIONS FOR TOPICAL REVIEW.
PAGE
1. What useful purposes do the bones serve? 15, 16
2. State what you can of the composition of the bones. 16
3. Of the usefulness of lime in the bones. 16
4. Of the usefulness of animal substance in the bones. 16
5. State what you can of the structure of the bones. 17
6. Of the strength belonging to the bones. 15, 16, 17
7. What is meant by the human skeleton? 19
8. Give a description of its construction. 19
9. What is meant by a joint in the human frame? 19
10. State what you can of the movable joints. 19, 20
11. What office is performed by the ligaments of the joints? 19, 20
12. What by the cartilage at the joints? 20
13. What movable joints are there? 20, 21
14. Describe the construction of the spinal column. 21
15. What properties and powers does the spinal column possess? 21, 22
16. When is a person taller than at other times? 22
17. Give the reason for this. 22
18. What can you state of the growth of bone? 22
19. Describe the process by which a broken bone is repaired. 23
* * * * * {24}
[Illustration: FIG. 7.--THE MUSCLES.]
{25}