A Treatise on Physiology and Hygiene
by Joseph C. Hutchison · English · Gutenberg #34211 · 543,628 chars · public domain (US)
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Title: A Treatise on Physiology and Hygiene
Author: Joseph C. Hutchison
Release date: November 5, 2010 [eBook #34211]
Most recently updated: June 23, 2018
Language: English
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*** START OF THE PROJECT GUTENBERG EBOOK A TREATISE ON PHYSIOLOGY AND HYGIENE ***
Produced by Bryan Ness, Keith Edkins and the Online
Distributed Proofreading Team at http://www.pgdp.net (This
file was produced from images generously made available
by The Internet Archive/American Libraries.)
Transcriber's note: A few typographical errors have been corrected: they
are listed at the end of the text.
* * * * *
[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}
CHAPTER II.
THE MUSCLES.
_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._
[Sidenote: 1. What are the muscles? Their number? The design of most of
them? Of a few?]
1. THE MUSCLES.-- The great mass of the body external to the skeleton, is
composed of the flesh, or _Muscles_, which largely determines its outline
and weight. The muscles are the organs of motion. Their number is about
four hundred, and to each of them is assigned a separate and distinct
office. They have all been studied, one by one, and a name given to each,
by the anatomist. Each is attached to bones which it is designed to move. A
few are circular in form, and enclose cavities, the size of which they
diminish by contraction.
[Illustration: FIG. 8.--MUSCULAR TISSUE.
_a_, _b_, Striped muscular fibres: _c_, The same more highly magnified.]
[Sidenote: 2. The structure of flesh? Its color, etc.? The composition of
the fibres? How marked?]
2. If we examine a piece of flesh, we observe that it is soft, and of a
deep red color. Its structure appears to be composed of layers and bundles
of small fibres. Let us further examine these fibres under the microscope.
We now discover that they are, in turn, made up of still finer fibres, of
_fibrillæ_: these are seen in Fig. 8. The fibres are beautifully {26}
marked by parallel wavy lines, about ten thousand to an inch, which give
the fibre its name of the _striped_ muscular fibre. All of the voluntary
muscles present this appearance.
[Sidenote: 3. Arrangement of the muscles? Their action? Flexion and
extension? Action of the muscles when we stand erect?]
3. FLEXION AND EXTENSION.--The muscles are, for the most part, so arranged
in pairs, or corresponding sets, that when motion is produced in one
direction by one set, there is, opposite to it, another muscle, or group of
muscles, which brings the limb back to its place. When they act
alternately, a to-and-fro movement results. When a joint is bent, the
motion is called _flexion_; and when it is made straight again, it is
called _extension_. When both sets act equally, and at the same moment, no
motion is produced, but the body or limb is maintained in a fixed position:
this occurs when we stand erect. The muscles which produce extension are
more powerful than those opposite to them.
[Illustration: FIG. 9.--A, Biceps muscle of the arm: B, C, Its tendons.]
[Sidenote: 4. Kinds of muscles? The voluntary? Involuntary? The heart? Give
the example. The hand? Arm?]
4. The muscles are also distinguished, on the other hand, as the voluntary
and involuntary muscles, according as they are, or are not, under the
control of the will. The heart is an example of the involuntary variety. We
cannot change its action in the least by an effort of the will. When we
sleep, and the will ceases to act, the heart continues to beat without
cessation. The voluntary muscles, on the other hand, are such as are used
only when we wish or _will_ to use them--as the muscles of the hand or arm
(Fig. 9).
{27}
[Sidenote: 5. What are the tendons or sinews? Their strength? Color?
Location? Tendon of Achilles? The fable? Muscles of the leg?]
5. THE TENDONS.--Tendons, or sinews, are the extremities of muscles, and
are compactly fastened upon bone. They are very strong, and of a silvery
whiteness. They may be felt just beneath the skin, in certain parts of the
body, when the muscles are being used, as at the bend of the elbow or knee.
The largest tendon of the body is that which is inserted into the heel,
called the tendon of Achilles, after the hero of the Grecian poet, the
fable relating that it was at this point that he received his death-wound,
no other part of his body being vulnerable. The muscles which extend into
the leg unite to form a single and very powerful tendon, and enclose a
small bone called the knee-pan, which, acting like a pulley, greatly
increases their power, and at the same time protects the front of the
knee-joint (Fig. 10).
[Illustration: FIG. 10.--VIEW OF KNEE-JOINT. A, Thigh bone: B, Knee-pan: C,
D, Leg bones.]
[Sidenote: 6. Contraction of the muscles? Bending of the arm or finger?
Other agencies? Automatic movements? In cold-blooded animals?]
6. MUSCULAR CONTRACTION.--The muscles, when acted upon by the appropriate
stimulus, contract, or so change {28} their shape, that their extremities
are brought nearer together. The bending of the arm, or of a finger, is
effected in this manner, by the will; but the will is not the only means of
producing this effect. Electricity, a sharp blow over a muscle, and other
stimuli, also cause it. Contraction does not always cease with life. In
man, after death from cholera, automatic movements of hands and feet have
been observed, lasting not less than an hour. In certain cold-blooded
animals, as the turtle, contraction has been known to take place for
several days after the head has been cut off.
[Sidenote: 7. Contractility? Give the illustration. What was supposed? What
is the case?]
7. The property which, in muscle, enables these movements to take place is
called _contractility_. If we grasp a muscle while in exercise (for
example, the large muscle in the front of the arm), we notice the alternate
swelling and decrease of the muscle, as we move the forearm to and fro. It
was at one time supposed that the muscle actually increased in volume
during contraction. This, however, is not the case; for the muscle, while
gaining in thickness, loses in length in the same proportion; and thus, the
volume remains the same in action and at rest.
[Sidenote: 8. What further in relation to contraction? Weariness of a
muscle? Beating of the heart? Standing and walking?]
8. Contraction is not the permanent, or normal, state of a muscle. It
cannot long remain contracted, but after a shorter or longer time, it
wearies and is obliged to relax. After a short rest, it can then again
contract. It is for this reason that the heart can beat all through life,
night and day, by having, as we shall hereafter see, a brief interval of
rest between successive pulsations. For the same reason, it is more
fatiguing to stand for any great length of time in one position, than to be
walking the same period.
[Sidenote: 9. Muscular power of animals? How tested? Man's power? Horse's?
The comparison?]
9. RELATIVE STRENGTH OF ANIMALS.--The amount of muscular power which
different animals can exert, has {29} been tested by experiment. By
determining the number of pounds which an animal can drag upon a level
surface, and afterward comparing that with its own weight, we can judge of
its muscular force. It is found that man is able to drag a little less than
his own weight. A draught-horse can exert a force equal to about two-thirds
of his weight. The horse, therefore, though vastly heavier than man, is
relatively not so powerful.
[Sidenote: 10. Power of insects? Beetles? Give the conclusion.]
10. Insects are remarkable for their power of carrying objects larger and
heavier than themselves. Many of them can drag ten, and even twenty times
their weight. Some of the beetles have been known to move bodies more than
forty times their own weight. So far, therefore, from it being a fact that
animals have strength in proportion to their weight and bulk, the reverse
of that statement seems to be the law.
[Sidenote: 11. Difference in strength of individuals? How caused?]
11. PHYSICAL STRENGTH.--The difference in strength, as seen in different
individuals, is not due to any original difference in their muscles. Nature
gives essentially the same kind and amount of muscles to each person, and
the power of one, or the weakness of another, arises, in great part, from
the manner in which these organs are used or disused.
[Sidenote: 12. Complaint in relation to degeneracy? How true? How
determined by armor? The fair supposition?]
12. Many authors complain of the physical degeneracy of men at the present
day, as compared with past generations. There is room for doubt as to the
correctness of this statement. Certain experiments have recently been made
with the metallic armor worn seven hundred years ago, by which it is found
that any man, of ordinary height and muscular development, can carry the
armor and wield the weapons of an age supposed to be greatly our superior
in strength. When we consider that in those days, only very strong men
could endure the hardships of soldier-life, {30} it is fair to suppose that
our age has not so greatly degenerated in respect to physical strength.
[Sidenote: 13 Action? Use of organs? Training of the mind? The child's
brain? Education of the body?]
13. IMPORTANCE OF EXERCISE.--Action is the law of the living body. Every
organ demands use to preserve it in full vigor, and to obtain from it its
best services. The value of that training of the mind, which we call
education, is everywhere recognized. The child is early put to school, and
for many years continues to study, in order that his brain, which is the
great centre of mental power, may act healthfully and with force. It is
important that the body, also, should receive its education by exercise.
This is especially true of persons belonging to certain classes of society,
whose occupation confines them within doors, and requires chiefly
brain-work.
[Sidenote: 14 Work in the open air? A perfect business? The consequence of
universal perfect business? Occupation of children?]
14. Persons who are engaged in manual labor in the open air obtain all the
exercise necessary for bodily health in their regular business: their need
is more likely to be a discipline or exercise of the mind. A perfect
business of life, therefore, would be one which would combine both physical
and mental labor in their proper proportions. If such a business were
possible for all the human race, life would thereby be vastly prolonged.
Such is, in fact, to a large extent, the occupation pertaining to one
period of life--childhood. A part of the time is spent by the child in
improving his mind by study, and another part of the time he has physical
exercise in his games and sports.
[Sidenote: 15 In what does exercise consist? Effects of it?]
15. THE EFFECTS OF EXERCISE.--Exercise consists in a well-regulated use of
the voluntary muscular system. The effects, however, are not limited to the
parts used. Other organs, which are not under the control of the will, are
indirectly influenced by it. For instance, the heart beats more rapidly,
the skin acts more freely, and {31} becomes hotter, as well as the parts
beneath it, and the appetite and power of digestion are increased. An
increased exhalation from the lungs and skin purifies the current of the
circulation, and the body as a whole thrives under its influence.
[Sidenote: 16. General effect upon the muscles? Special effect? Effects of
inaction? Of excessive exercise?]
16. The immediate effect of exercise, however, is upon the muscles
themselves; for by use they become firm and large, and increase in power.
If we examine a muscle thus improved by exercise, we find that its fibres
have become larger and more closely blended together, that its color is of
a darker red, and that the supply of blood-vessels has increased. Without
exercise the muscle appears thin, flabby, and pale. On the other hand,
excessive exercise, without sufficient relaxation, produces in the muscle a
condition not very different from that which follows disuse. The muscle is
worn out faster than nature builds it up, and it becomes flabby, pale, and
weak.
[Sidenote: 17. Of violent and spasmodic efforts? Strength, how attained?
Give the particulars.]
17. Violent exercise is not beneficial; and spasmodic efforts to increase
the muscular strength are not calculated to secure such a result. Strength
is the result of a gradual growth, and is most surely acquired if the
exercise be carried to a point short of fatigue, and after an adequate
interval of rest. To gain the most beneficial results, the exercise should
be at regular hours, and during a regular period. The activity of the
exercise, and the time devoted to it must vary, of course, with the
strength of the individual, and should be carefully measured by it.
[Sidenote: 18. What may walking be called? What further is said of
walking?]
18. DIFFERENT MODES OF EXERCISE.--There are very few who have not the power
to walk. There is required for it no expensive apparatus, nor does it
demand a period of preliminary training. _Walking may be called the
universal exercise._ With certain foreign nations, the English {32}
especially, it is a very popular exercise, and is practised habitually by
almost every class of society; by the wealthy as well as by those who have
no carriages; by women as well as by men.
[Sidenote: 19. What is said of running, and other like movements? What, as
related to childhood? What instances are alluded to? Example?]
19. Running, leaping, and certain other more rapid and violent movements,
are the forms of exercise that are most enjoyed in childhood. For the
child, they are not too severe, but they may be so prolonged as to become
injurious. Instances have been recorded where sudden death has resulted
after violent playing, from overtaxing the heart: for example, we have the
case of a young girl who, while skipping the rope, and endeavoring to excel
her playmates by jumping the greatest number of times, fell dead from
rupture of the heart.
[Sidenote: 20. Carriage-riding? Horseback-riding?]
20. Carriage-riding, as a means of passive exercise, is particularly well
suited to invalids, and persons advanced in life. Horseback exercise brings
into use a greater number of muscles than any other one exercise, and with
it there is an exhilaration of feeling which refreshes the mind at the same
time. It is one of the manliest of exercises, but not less suitable for
women than for men. To be skilful in riding, it is best to begin its
practice in youth; but there are very few kinds of exercise of which the
same is not equally true.
[Sidenote: 21. Boating, swimming, and skating?]
21. For those who live near streams or bodies of water, there are the
delightful recreations of boating, swimming, and skating. Certain of these
exercises have a practical importance aside from and above their use in
increasing the physical vigor. This is especially true of boating and
swimming, since they are often the means of saving life. Practice in these
exercises also teaches self-reliance, courage, and presence of mind.
Persons who have become proficient in these vigorous exercises are
generally the ones, {33} who, in times of danger, are the quickest to act
and the most certain to do so with judgment.
[Sidenote: 22. What kind of exercise yields the best results? What advice
is given?]
22. PHYSICAL CULTURE.--That form of exercise which interests and excites
the mind, will yield the best results; but to some persons no kind of
exertion whatever is, at first, agreeable. They should, nevertheless, make
a trial of some exercise, in the expectation that, as they become
proficient in it, it will become more pleasant. In exercise, as many sets
of muscles should be employed as possible, open-air exercise being the
best. Parlor gymnastics, and the discipline of the gymnasium are desirable,
but they should not be the sole reliance for physical culture. No in-door
exercise, however excellent in itself, can fill the place of hearty and
vigorous activity in the open air.
[Sidenote: 23. Physical culture among the ancients? In Greece? In schools
and colleges at the present time? Result to the body and mind?]
23. GYMNASTIC EXERCISES FOR SCHOOLS AND COLLEGES.--In the system of
education among the ancients, physical culture predominated. In ancient
Greece, physical exercises in schools were prescribed and regulated by law,
and hence these schools were called _gymnasia_. At the present time, on the
contrary, this culture is almost wholly unknown, as a part of the course of
education, in our schools and colleges. In a few of our institutions of
learning, however, physical exercises have been introduced, with manifest
advantage to the students, and they form a part of the regular curriculum
of exercises,--as much so as the recitations in geography, grammar, or
Greek. The good effect of the experiments, as shown in improved scholarship
as well as increased bodily vigor, in the institutions where the plan has
been tried, will, it is hoped, lead to its universal adoption. We should
then hear less frequently of parents being obliged to withdraw their
children from school, because they become exhausted {34} or, perchance,
have lost their health from intense and protracted mental application.
[Sidenote: 24. The result of gymnastics in our colleges and other
institutions of learning?]
24. Were gymnastics more common in our educational institutions we should
not so often witness the sad spectacle of young men and women leaving our
colleges and seminaries, with finished educations it may be, but with
constitutions so impaired, that the life which should be devoted to the
accomplishment of noble purposes must be spent in search of health. Spinal
curvatures, which, according to the experience of physicians, are now
extremely frequent, especially among ladies, would give place to the steady
gait and erect carriage which God designed his human creatures should
maintain.
25. All the exercises necessary for the proper development of the body may
be obtained from the use of a few simple contrivances that every one can
have at home, at little cost--less by far than is spent for useless toys.
Many of these may be made available in the parlor or chamber, though all
exercises are far more useful in the open air. A small portion of the day
thus spent will afford agreeable recreation as well as useful exercise. The
Indian club, the wand, the ring, and the dumb-bells answer ordinary
purposes very well. Illustrations are here introduced of a few simple
contrivances that may be useful for general exercises, and are specially
suitable for persons with _weak spines_, or with spines that are the
subject of lateral curvature.
26. One of the simplest appliances for strengthening the muscles of the
spine, designed chiefly to exercise the muscles on either side of the
spine, consists of two wooden handles attached to india-rubber cords, one
of which is attached to a hook made fast in the ceiling, or in the top of
the door-case; and the other to another hook fastened in the wall,
door-post, or window-casing, about the height {35} of the shoulder. When
traction is made with the left hand, it exercises the muscles on the left
side of the spine, while those on the opposite side are left almost at
rest, owing to the oblique direction given to the shoulders when the right
hand grasps the horizontal cord. (This appliance will be understood by
referring to Fig. 13.)
[Illustration: FIG. 11.]
[Illustration: FIG. 12.]
{36}
27. Fig. 11 shows an appliance consisting of two strong elastic cords, with
handles, secured to a hook in the floor, so arranged that the patient has
to stoop forward to reach them. On raising the body the spinal muscles are
powerfully exercised. Fig. 12 shows other modes of using the elastic cords
for strengthening the spine and chest.
[Illustration: FIG. 13.]
28. These various appliances have been combined so as to form a system of
gymnastics suitable for parlor use; other appliances have been added by
which the muscles of {37} the legs may be called into action as well as
those of the spine and upper part of the body (Fig. 13). Combinations of
cords suitable for particular cases may also be made, and by using one or
several cords on the same hook, their power may be adapted to the strength
of the most robust as well as to that of the invalid, or of the most
delicate child. The entire apparatus is quite simple in its construction
and inexpensive, requiring but little space, and at the same time affording
a great variety of exercises.
EXERCISES THAT MAY BE PRACTISED ON THIS APPARATUS.
EXERCISE I. (Fig. 13).--Stand erect under the cords and place the heels
together. Grasp the handles firmly, keeping the knees and elbows stiff,
and pull downward and forward until the fingers nearly touch the toes.
Return slowly to the erect position. Repeat.
EXERCISE II. (Fig. 13).--Stand erect, and having grasped the handles
overhead firmly, separate them and bring them down slowly until they
touch the sides: then return them slowly to the original position.
Repeat.
EXERCISE III. (Fig. 13).--Stand erect, heels together, grasp the
handles overhead, and charge forward with the right foot. Return to
first position, and then charge with the left. Repeat, using the right
and left foot alternately.
EXERCISE IV. (Fig. 13).--Stand erect, heels together. Grasp the handle
overhead, and charge forward with the right foot, knee bent. Remain in
this position and bring the arms down to the sides so that the arm and
fore-arm may form a right angle. Still holding the handles, thrust
forward, first the right hand and then the left, until the arm is
straight. Repeat. Return to first position, then charge forward with
the left foot, performing the same movements as before.
EXERCISE V. (Fig. 13).--In this exercise we change to the pulleys
leading from the side posts, which can be used in several different
ways. 1st. Stand erect, heels together, facing one of the posts, grasp
the handle with the right hand, the arm being extended, then flex the
fore-arm on the arm. Repeat. Perform the same movements with the left
hand. 2d. Stand with back to the post; grasp the pulley behind with the
right hand, then gradually bring the hand forward until it is extended
in a straight line in front. Repeat. Perform the same exercise with the
left hand.
{38} EXERCISE VI. (Fig. 13).--This exercise is especially adapted to
the legs. Stirrups are so arranged that they can be attached to the
pulleys overhead, and can hang down to within three or four feet of the
floor. Place the foot in the stirrup, and then press down until it
touches the floor. Repeat. Exercise the left foot in the same way.
EXERCISE VII. (Fig. 13.)--This exercise requires a little attention in
the adjustment of the apparatus. Under the pulleys in the floor are
passed ropes which can be attached to the snap-hooks that hold the
handles overhead. Stoop forward with the knees stiff, and take hold of
the handles, and then raise the body to the erect position. Repeat.
EXERCISE VIII. (Fig. 13).--Sit on the floor or on a seat three or four
inches high; bend forward, take hold of the handles, and perform the
same movements that you would in rowing a boat.
EXERCISE IX. (Fig. 13).--The trapeze can now be let down; take hold of
it with both hands, sustaining the weight of the body with the arms,
then rotate the body first from right to left, then from left to right
alternately. This exercise is especially suitable for females.
EXERCISE X. (Fig. 13).--Grasp the trapeze as before, bearing all the
weight with the arms: then draw the body up slowly until you can place
the chin over the bars. This requires strength of muscle, and might
strain if done too violently; if slowly performed there is no danger.
These are but a few of the exercises that can be practised with this
apparatus. As these become familiar they can easily be modified, and
new ones can be arranged to meet the requirements of particular cases.
Most of the exercises described can be practised with one hand so as to
strengthen the muscles on one side.
[Sidenote: 29. Need of repose? How do we obtain rest? Alfred the Great? The
eight-hour division of time?]
29. REST.--We cannot always be active: repose must succeed labor. We obtain
this rest partly by suspending all exertion, as in sleep, and partly by a
change of employment. It is said that Alfred the Great recommended that
each day should be divided in the following manner: "Eight hours for work,
eight hours for recreation, and eight hours for sleep." This division of
time is as good as any that could now be made, if it be borne in mind that,
when the work is physical, the time of recreation should {39} be devoted to
the improvement of the mind; and when mental, we should then recreate by
means of physical exercise.
[Sidenote: 30. Cessation of voluntary activity? Temperature of the body?
Consequence? Body and mind during sleep? Nutrition? Describe it.
Consequences of insufficient sleep?]
30. During sleep, all voluntary activity ceases, the rapidity of the
circulation and breathing diminishes, and the temperature of the body falls
one or two degrees. In consequence, the body needs warmer coverings than
during the hours of wakefulness. During sleep, the body seems wholly at
rest, and the mind is also inactive, if we except those involuntary mental
wanderings which we call dreams. Nevertheless a very active and important
physical process is going on. Nutrition, or the nourishing of the tissues,
now takes place. While the body is in action, the process of pulling down
predominates, but in sleep, that of building up takes place more actively.
In this way we are refreshed each night, and prepared for the work and
pleasures of another day. If sleep is insufficient, the effects are seen in
the lassitude and weakness which follow. Wakefulness is very frequently the
forerunner of insanity, especially among those who perform excessive mental
labor.
[Sidenote: 31. Amount of sleep in different persons? Cases? Frederick the
Great? Bonaparte? Instances of long deprivation of sleep?]
31. All persons do not require the same amount of sleep, but the average of
men need from seven to nine hours. There are well-authenticated cases where
individuals have remained without sleep for many days without apparent
injury. Frederick the Great required only five hours of sleep daily.
Bonaparte could pass days with only a few hours of rest. But this long
continued absence of sleep is attended with danger. After loss of sleep for
a long period, in some instances, stupor has come on so profoundly, that
there has been no awaking.
[Sidenote: 32. Instances of sailors? French soldiers? During torture?]
32. There are instances related of sailors falling asleep {40} on the
gun-decks of their ships while in action. On the retreat from Moscow, the
French soldiers would fall asleep on the march, and could only be aroused
by the cry, "The Cossacks are coming!" Tortured persons are said to have
slept upon the rack in the intervals of their torture. In early life, while
engaged in a laborious country practice, the writer not unfrequently slept
soundly on horseback. These instances, and others, show the imperative
demand which nature makes for rest in sleep.
QUESTIONS FOR TOPICAL REVIEW.
PAGE
1. What can you state of the number and division of the muscles? 25, 26
2. Describe the structure of the muscles. 25, 26
3. Their arrangement in pairs and consequent action. 26
4. What is the difference between the motion called flexion and that
called extension? 26
5. Describe their action, and state which are the more powerful. 26
6. What is the difference between voluntary and involuntary muscles? 26
7. Illustrate the difference between the two. 26
8. State all you can of the tendons or sinews. 27
9. What is meant by contraction of the muscles? 27, 28
10. In how many and what ways may contraction be effected? 28
11. What is stated of after-death contraction? 28
12. Why cannot a muscle in life continue contracted a long time? 28
13. How then can the constant beating of the heart be explained? 28
14. How does the strength of a man compare with that of a horse? 29
15. What can you state in relation to the relative strength
of animals? 28, 29
16. What, in relation to physical strength? 29
17. What, in relation to physical degeneracy? 29, 30
18. What, in relation to the importance of exercise? 30
19. What is the effect of exercise upon the heart, skin,
and appetite? 30, 31
20. How does exercise affect the current of the body's circulation? 31
21. How does judicious exercise affect the muscles? 31
22. What is stated of violent and spasmodic exercise? 31
23. Of the exercise of walking? 31, 32, 33
24. Of running, leaping, and other modes of exercise? 32
25. Of physical culture, in connection with out-door exercises? 33
26. Of the importance of gymnastics in our schools and colleges? 33, 34
27. Of the importance of rest from labor or exercise? 38, 39
28. What processes take place during sleep? 39
29. What effects follow insufficient sleep? 39
* * * * *
{41}
CHAPTER III.
THE INTEGUMENT, OR SKIN.
_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._
[Sidenote: 1. What is the skin? Parts directly beneath? What is shown?]
1. THE INTEGUMENT.--The skin is the outer covering of the body. The parts
directly beneath it are very sensitive, and require protection. This is
shown whenever by accident the skin is broken, pierced, or torn off, the
bared surface being very tender, and painful to the touch. Nature has
provided the body with a garment that is soft, pliable, close-fitting, and
very thin, and yet sufficiently strong to enable us to come in contact with
the objects that surround us, without inconvenience or suffering.
[Sidenote: 2. Microscopic examination? What is the cutis? The cuticle?
Their union? How separated? What further is said of the cuticle?]
2. THE STRUCTURE OF THE SKIN.--When examined with the aid of the
microscope, the skin is found to be made up of two layers--the outer and
the inner. The inner one is called the _cutis_, or true skin; the outer one
is the _epidermis_, or scarf-skin. The latter is also known as the
_cuticle_. These two layers are closely united, but they may be separated
from each other. This separation takes place whenever, from a burn, or
other cause, a blister is formed; a watery fluid is poured out between the
two layers, and lifts the epidermis from the true skin.
Of the two layers, the cuticle is the thinner in most parts of the body,
and has the appearance of a whitish membrane. It is tough and elastic, is
without feeling, and does {42} not bleed, when cut. Examine it more
closely, and we observe that it is composed of minute flat cells, closely
compacted, and arranged layer upon layer.
[Sidenote: 3. Wearing out of the cuticle? What then? Variety in thickness
of cuticle? How accounted for?]
3. The outer layer is constantly being worn out, and falls from the body in
the form of very fine scales. It is, also, continually forming anew on the
surface of the inner layer. Its thickness varies in different parts of the
body. Where exposed to use, it is thick, hard, and horn-like, as may be
seen on the soles of the feet, or on the palms of the hands, especially of
those who are accustomed to perform much manual labor. This is an admirable
provision for the increased protection of the sensitive parts below the
skin against all extraordinary exposure. Even the _liabilities_ of these
parts to injury, are thus kindly provided for by "the Hand that made us."
[Sidenote: 4. Location and office of the cutis? What further is said of it?
Papillæ? Touch?]
4. The cutis, or true skin, lies beneath the epidermis, and is its origin
and support. It is firm, dense, elastic, very sensitive, and is freely
supplied with blood-vessels. It is closely connected with the tissues below
it, but may be separated by means of a sharp instrument. The surface of the
cutis is not smooth, but is covered here and there with minute elevations,
called _papillæ_. These are arranged in rows, along fine lines, or ridges,
such as those which mark the palm and fingers; their number is about 80 to
the square line (a line being one-twelfth of an inch). These _papillæ_
contain the blood-vessels which carry the supply of blood needed by the
ever-wasting skin. They contain nerves also, and are largely concerned in
the sense of touch; hence they are particularly abundant where the touch is
most delicate, as at the ends of the fingers.
[Sidenote: 5. What are the nails and hair? The growth of the nail? The
rapidity of its growth? Accident to the nail?]
{43} [Illustration: Fig. 14.
_a, b._ THE ROOT OF A HAIR.
1, 2, 3. The skin forming the hair sac. 4. Sebaceous glands. 5. The hair
sac.
_c._ TRANSVERSE SECTION OF A HAIR.]
5. THE NAILS AND HAIR.--These are appendages of the skin, and although very
unlike the cuticle as it appears on the surface of the body, they are, in
reality, modified forms of that layer of the skin. The nail grows from a
fold of the cuticle at the root, and from the under surface. As fast as it
is formed, it is constantly being pushed outward. The rapidity of its
growth can be ascertained by filing a slight groove on its surface, and
noticing how the space between it and the root of the nail increases, in
the course of a few weeks. When the nail is removed by any accident, it
will be replaced by a new one, if the root be not injured.
[Sidenote: 6. How are the hairs produced? Difference in their length?]
6. The hairs are produced in a similar manner; the skin forming
depressions, or hair sacs, from the bottom of which they grow and are
nourished (Fig. 14). They are found, of greater or less length, on almost
all parts of the surface, except the palms of the hands and soles of the
feet. On certain parts of the body, they grow to great length; on other
parts they are so short, that they do not rise beyond the hair sac in which
they originate.
[Sidenote: 7. Root of the hair? Shaft? Firmness and softness of the hair?]
7. The bulb, or root, from which the hair arises, is lodged in a small
pouch, or depression in the skin. The shaft is the part which grows out
beyond the level of the skin. Its growth is altogether in one direction, in
length alone. The outer part of the hair is quite firm, while its {44}
interior is softer, and probably conveys the fluids by which it is
nourished. The hair is more glossy in health than at other times.
[Sidenote: 8. Office of the nail? Of the hair? Give the illustrations.]
8. The nail serves as a protection to the end of the finger, and also
enables us to grasp more firmly, and to pick up small objects. The hair,
too, is a protection to the parts it covers. On the head, it shields the
brain from extremes of heat and cold, and moderates the force of blows upon
the scalp. On the body, it is useful in affording a more extensive surface
for carrying off the perspiration.
[Sidenote: 9. On what does the complexion depend? Light and dark races?
Freckles?]
9. COMPLEXION.--In the deeper cells of the cuticle lies a pigment, or
coloring matter, consisting of minute colored grains. On this pigment
_complexion_ depends; and, according as it is present in less or greater
amount, occasions the difference of hue, that exists between the light and
dark races of men, and between the blonde and brunette of the white races.
Freckles are due to an irregular increase of coloring matter.
[Sidenote: 10. Influence of the sun? How illustrated? Jews?]
10. The sun has a powerful influence over the development of this pigment,
as is shown by the swarthy hue of those of the white race who have
colonized in tropical climates. It is also well illustrated by the fact,
that among the Jews who have settled in northern Europe, there are many who
are fair complexioned, while those residing in India, are as dark as the
Hindoos around them.
[Sidenote: 11. What is an Albino? Where are Albinos found?]
11. An Albino is a person who may be said to have no complexion; that is,
there is an entire absence of coloring matter from the skin, hair, and
_iris_ of the eye. This condition more frequently occurs among the dark
races, and in hot climates, although it has been observed in almost every
race and clime.
[Sidenote: 12. What are sebaceous glands? How do they act? Sebaceous glands
of the face? How do they act?]
12. SEBACEOUS GLANDS.--There are in the skin certain {45} small glands,
which produce an oily substance, called _sebaceous_ matter. These glands
are little rounded sacs, usually connected with the hair-bulbs; and upon
these bulbs, they empty their product of oil, which acts as a natural and
adequate dressing for the hair (4, Fig. 14). A portion of the sebaceous
matter passes out upon the surface, and prevents the cuticle from becoming
dry and hard. The glands situated upon the face and forehead, open directly
upon the skin. In these, the sebaceous matter is liable to collect, and
become too hard to flow off naturally.
[Sidenote: 13. Black points, called worms? Animalcules? Service performed
by sebaceous matter?]
13. These glands on the face and forehead frequently appear, on the faces
of the young, as small black points, which are incorrectly called "worms."
It is true, that occasionally living animalcules are found in this
thickened sebaceous matter, but they can only be detected by the aid of the
microscope. This sebaceous matter acts not only to keep the skin flexible,
and furnish for the hair an oily dressing, but it especially serves to
protect the skin and hair, from the acridity arising from the perspiration.
[Sidenote: 14. Perspiration? Sweat glands? Of what do they consist?
Dimension of the tubes?]
14. THE PERSPIRATORY GLANDS.--The chief product of the skin's action is the
perspiration. For the formation of this, there are furnished countless
numbers of little sweat-glands in the true skin. They consist of fine
tubes, with globe-like coils at their deeper extremity. Their mouths or
openings may be seen with an ordinary magnifying glass, upon the fine
ridges which mark the fingers. These tubes, if uncoiled, measure about
one-tenth of an inch in length. In diameter, they are about one
three-hundredth of an inch, and upon certain parts of the body there are
not far from three thousand of these glands to the square inch. Their whole
number in the body is, therefore, very great; and, in fact, it is computed
if they were all united, end to end, their combined measurement would
exceed three miles. {46}
[Sidenote: 15. What is sensible perspiration? Insensible perspiration?]
15. THE SENSIBLE AND INSENSIBLE PERSPIRATION.--The pores of the skin are
constantly exhaling a watery fluid; but, under ordinary circumstances,
there is no moisture apparent upon the surface, for it evaporates as
rapidly as it is formed. This is called insensible perspiration. Under the
influence of heat or exercise, however, this fluid is excreted more
abundantly, and appears on the surface in the form of minute, colorless
drops. It is then termed sensible perspiration.
[Sidenote: 16. Components of perspiration? Upon what does perspiration
depend? Amount of perspiration daily?]
16. Water is the chief component of this fluid, there being about
ninety-eight parts of water to two parts of solid matter. The quantity
escaping from the body varies greatly, according to the temperature of the
air, the occupation of the individual, and other circumstances. The average
daily amount of this excretion, in the adult, is not far from thirty
ounces, nearly two pints, or more than nine grains each minute.
[Sidenote: 17. What does perspiration set free from the blood? What other
service does perspiration perform? Explain the process.]
17. THE USES OF THE PERSPIRATION.--Besides liberating from the blood this
large amount of water, with the effete matter it contains, the perspiration
serves to regulate the temperature of the body. That is to say, as
evaporation always diminishes temperature, so the perspiration, as it
passes off in the form of fine vapor, cools the surface. Accordingly, in
hot weather this function is much more active, and the cooling influence
increases in proportion. When the air is already charged with moisture, and
does not readily receive this vapor of the body, the heat of the atmosphere
apparently increases, and the discomfort therefrom is relatively greater.
[Sidenote: 18. Effect of interruption of excretion? What experiments are
mentioned?]
18. The importance of this excretion is shown by the effects that often
follow its temporary interruption, namely, headache, fever, and the other
symptoms that accompany {47} "taking cold." When the perspiration is
completely checked, the consequences are very serious. Experiments have
been performed upon certain smaller animals, as rabbits, to ascertain the
results of closing the perspiratory tubes. When they are covered by a
coating of varnish impervious to water and gases, death ensues in from six
to twelve hours; the attendant symptoms resembling those of suffocation.
[Sidenote: 19. Give the story in relation to the boy covered with gold
foil.]
19. It is related that, at the coronation of one of the Popes about three
hundred years ago, a little boy was chosen to act the part of an angel; and
in order that his appearance might be as gorgeous as possible, he was
covered from head to foot with a coating of gold foil. He was soon taken
sick, and although every known means were employed for his recovery, except
the removal of his fatal golden covering, he died in a few hours.
[Sidenote: 20. Give the quotation. Perspiration?]
20. THE IMPORTANCE OF BATHING.--From these considerations, it is evident
that health must greatly depend upon the free action of the skin. "He who
keeps the skin ruddy and soft, shuts many gates against disease." When the
watery portion of the perspiration evaporates, the solid matter is left
behind on the surface. There, also, remain the scales of the worn-out
cuticle, and the excess of sebaceous matter. In order to secure the natural
action of the skin, these impurities require to be removed by the frequent
application of water.
[Sidenote: 21. Ablution in warm climates? What advice is given?]
21. In warm climates, and during hot weather, ablution should be more
frequently practised. For a person in good health, a daily cold bath is
advisable. To this should be added occasionally a tepid bath, with soap,
water alone not being sufficient to remove impurities of a greasy nature.
Soap facilitates this, by forming with such substances a chemical mixture,
which is readily soluble in water, and is by it removed from the body. {48}
[Sidenote: 22. Liebig's maxim? What further is added?]
22. There is a maxim by the chemist Liebig, to the effect, that the
civilization of a nation is high, in proportion to the amount of soap that
it consumes; and that it is low, in proportion to its use of perfumes. In
some degree, we may apply the same test to the refinement of an individual.
The soap removes impurity; the perfume covers, while retaining it.
[Sidenote: 23. What is said about cold bathing?]
23. THE DIFFERENT KINDS OF BATHS.--All persons are not alike able to use
the cold bath. When the health is vigorous, and the system does not feel a
shock after such a bath, a prompt reaction and glow upon the surface will
show that it is beneficial. Where this pleasurable feeling is not
experienced, but rather a chill and sense of depression ensues, we are
warned that the system will not, with impunity, endure cold bathing.
[Sidenote: 24. What is said about warm bathing?]
24. It should also be borne in mind, that the warm or hot bath cannot be
continued so long, or repeated so frequently as the cold, on account of the
enervating effect of unusual heat so applied to the body. For persons who
are not in robust health, one warm bath each week is sufficient; this class
should be careful to avoid every extreme in reference to bathing, clothing,
and whatever greatly affects the action of the skin.
[Sidenote: 25. What is said about sea-bathing?]
25. Sea-bathing is even more invigorating than fresh-water bathing. Those
who cannot endure the fresh water, are often benefited by the salt-water
baths. This may be accounted for, in part, by the stimulant action upon the
surface, of the saline particles of the sea-water; but the exciting scenes
and circumstances of sea-bathing also exert an important influence. The
open-air exercise, the rolling surf, the genial weather, and usually the
cheerful company, add to its intrinsic benefits. {49}
[Sidenote: 26. What is said as to the time and manner of bathing?]
26. TIME AND MANNER OF BATHING.--A person in sound health may take a bath
at almost any time, except directly after a full meal. The most appropriate
time is about three hours after a meal, the noon-hour being probably the
best. For the cold bath, taken rapidly, no time is better than immediately
after rising. Those beginning the use of cold baths should first try them
at 70° Fahr., and gradually use those of a lower temperature. From five to
twenty minutes may be considered the proper limit of time to remain in a
bath; but a sensation of chilliness is a signal to withdraw instantly,
whether at home, or at the sea-side. Two sea-baths may be taken daily; one
of any other kind is sufficient.
[Sidenote: 27. Condition of the body when bathing? Direction, after
bathing?]
27. The body should be warm, rather than cold, when stepping into the bath;
and after it, the skin should be thoroughly dried with a coarse towel. It
is best to continue friction until there is a sensation of warmth or "glow"
throughout the entire surface. This reaction is the test of the good
effects of the bath. If reaction is still incomplete, a short walk may be
taken, especially in the sunshine. It is very congenial, however, both to
health and comfort, to rest for a short time directly after bathing, or to
take some light refreshment. This is better than severe exercise or a full
meal.
[Sidenote: 28. Bathing among the ancients? Baths of Rome?]
28. BATHING AMONG THE ANCIENTS.--The Romans and other nations of antiquity
made great use of the vapor-bath as a means of preserving the health, but
more particularly as a luxury. Their method was not unlike that employed in
northern Europe at the present day. The public baths of Rome and other
cities are among the grandest and most interesting monuments of ancient
luxury and splendor; and from their ruins have been recovered some of the
most beautiful works of art. {50}
[Sidenote: 29. After the bath? Swimming among the ancients?]
29. The Thermæ, as the baths of Rome were called, were of great extent,
built very substantially, and ornamented at vast expense. They were
practically free to all, the cost of a bath having been less than a cent.
It is related that some persons bathed seven times a day. After the bath
their bodies were anointed with perfumed oil. If the weather was fine, they
passed directly from the Thermæ into the gymnasium, and engaged in some
gentle exercise previous to taking the midday meal. Between two and three
in the afternoon was the favorite hour for this ancient luxury. Swimming
was a favorite exercise, and a knowledge of it was regarded as necessary to
every educated man. Their common expression, when speaking of an ignorant
person, was, "He can neither read nor swim."
[Sidenote: 30. The Sun-bath? The story of Pliny?]
30. THE SUN-BATH.--Some also were accustomed daily to anoint themselves,
and lie or walk in apartments arranged for the purpose, with naked bodies
exposed to the direct rays of the sun. There is an interesting allusion to
this practice, in a letter of the younger Pliny to the historian Tacitus,
describing the destruction of Pompeii by an eruption of Vesuvius. "My
uncle," (Pliny the elder,) "was at that time in command of the fleet at
Misenum. On the 24th of August, about one in the afternoon, my mother
desired him to notice a cloud which seemed of unusual shape and dimensions.
He had just returned from _taking the benefit of the sun_, and after a cold
bath, and a slight repast, had retired to his study." Then follows a
description of the destruction of Pompeii, and the death of the elder
Pliny.
[Sidenote: 31. Benefit of the sun? Effect upon plants? Skin?]
31. We may judge somewhat of "the benefits of the sun," by observing the
unnatural and undeveloped condition of plants and animals which are
deprived of light. Plants become blanched and tender; the fish of {51}
subterranean lakes, where no light enters, are undersized, and have no
eyes; tadpoles kept in the dark do not develop into frogs; men growing up
in mines are sallow, pale, and deformed. Besides the well-known effect of
solar light in tanning the skin, it also makes it thicker and better able
to resist exposure; though the complexion may be thereby injured, the
health gains more than compensate for the loss of beauty. "To make good
the loss of the lily, where the sun has cast his ray, he seldom fails to
plant the rose."
[Sidenote: 32. Direction about clothing? Exposing limbs of children?
Clothing, night and day?]
32. CLOTHING.--In reference to clothing, we are far more apt, in our
changeful climate, to use too little than too much. An aphorism of
Boerhaave, worth remembering, if not of adopting, is, "We should put off
our winter clothing on midsummer's day, and put it on again the day after."
He also says, "Only fools and beggars suffer from the cold; the latter not
being able to get sufficient clothes, the others not having the sense to
wear them." The practice of exposing the limbs and necks of young children,
for the alleged purpose of "hardening" them, is quite hazardous. It is not
to be denied that some seem to be made tough by the process; but it is so
only with the rugged children, the delicate ones will invariably suffer
under this fanciful treatment. As has been stated before, the skin is
constantly acting, by night as well as by day. It is therefore conducive
both to cleanliness and comfort to change entirely the clothing on retiring
for the night. The day-clothing should be aired during the night, and the
bedding should be aired in the morning, for the same reason.
[Sidenote: 33. Cosmetics? Painters' colic?]
33. POISONOUS COSMETICS.--The extensive use of _cosmetics_ for the
complexion is a fertile source of disease. The majority of these
preparations contain certain poisonous mineral substances, chiefly lead.
Now, the skin rapidly absorbs the fine particles of lead, and the system
{52} experiences the same evil effects that are observed among the
operatives in lead works and painters, namely, "painters' colic," and
paralysis of the hands, called "wrist-drop."
34. Certain hair-dyes also contain lead, together with other noxious and
filthy ingredients. These do not work as great harm as the cosmetics, since
they are purposely kept away from the skin, but they rob the hair of its
vitality. Eye-washes, too, are made from solutions of lead, and many an eye
has been ruined by their use. They deposit a white metallic scale on the
surface of the eye, which becomes a permanent obstruction to the vision.
QUESTIONS FOR TOPICAL REVIEW.
PAGE
1. What are the characteristics of the skin, and what office
does it perform? 41
2. What can you state of the structure of the skin? 41
3. Describe the cuticle and tell its use. 41, 42
4. Describe the cutis or true skin and tell its use. 42
5. What can you state of the nature and growth of the nail? 42, 43
6. Of the nature and growth of the hair? 42, 43, 44
7. Of the offices performed by the nails and hair? 44
8. How is the difference in complexion in different persons
accounted for? 44
9. How is the presence of freckles accounted for? 44
10. How does Nature provide a dressing for the hair? 44, 45
11. What other service do the sebaceous glands perform? 45
12. State what you can of the perspiratory glands. 45
13. What is the difference between sensible and insensible
perspiration? 46
14. State the uses and importance of perspiration. 46, 47
15. What impurities gather naturally on the skin? 47
16. Repeat what is said of the importance of bathing. 47, 48
17. When should we indulge in cold, warm, and sea bathing? 48, 49
18. What is the effect in each case? 48
19. What directions are given as to the time and manner for
bathing? 49
20. What is related of bathing among the ancients? 49, 50
21. What is related to show the antiquity of sun-bathing? 50
22. What are the effects of sun-bathing? 50, 51
23. What directions are given in relation to clothing the body? 51
24. What can you state of poisonous cosmetics? 51, 52
25. Of hair-dyes and eye-washes? 52
* * * * *
{53}
CHAPTER IV.
THE CHEMISTRY OF FOOD.
_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._
[Sidenote: 1. The term food? Source of food? Need of preparing food?]
1. THE SOURCE OF FOOD.--The term _food_ includes all those substances,
whether liquid or solid, which are necessary for the nourishment of the
body. The original source of all food is the earth, which the poet has
fitly styled the "Mother of all living." In her bosom, and in the
atmosphere about her, are contained all the elements on which life depends.
But man is unable to obtain nourishment directly from such crude chemical
forms as he finds in the inorganic world. They must, with a few exceptions,
be prepared for his use, by being transformed into new and higher
combinations, more closely resembling the tissues of his own body.
[Sidenote: 2. Usefulness and hurtfulness of plants? What then must man do?
Parts of the same plant or tree?]
2. This transformation is effected, first, by the vegetable world. But all
plants are not alike useful to man; while some are absolutely hurtful.
Accordingly, he must learn to discriminate between that which is poisonous
and that which is life-supporting. Again, all parts of the same plant or
tree are not alike beneficial: in some, the fruit, in others, the leaves,
and in others, the seeds only are sufficiently refined for his use. These
he must learn to select; he must also learn the proper modes of preparing
each kind for his table, whether by cooking or other processes. {54}
[Sidenote: 3. Certain forms of vegetable creation? Example of the bee?
Cattle? The inference?]
3. Again, certain forms of the vegetable creation which are unfit, in their
crude state, for man's food, and which he rejects, are chosen as food by
some of the lower animals, and are, by them, made ready for his use. Thus
the bee takes the clover, that man cannot eat, and from it collects honey.
The cattle eat the husks of corn and the dried grass, that are by far too
coarse for man, and in their own flesh convert them into tissues closely
resembling his muscular tissue. In this way, by the aid of the transforming
processes of the vegetable and animal creations, the simple chemical
elements of the mineral kingdom are elaborated into our choice articles of
food.
[Sidenote: 4. What classification? Define organic substances. Inorganic.
Organic, how spoken of? The inorganic? Water and salt?]
4. INORGANIC SUBSTANCES.--The substances we use as food are classified as
_organic_ and _inorganic_. By organic substances are meant those derived
from living forms, such as vegetables and animals. Inorganic substances are
those simpler inanimate forms which belong to the mineral kingdom. The
former alone are commonly spoken of as food, but the latter enter very
largely into the constitution of the body, and must therefore be present in
our food. With the exception of two articles, water and common salt, these
substances only enter the system when blended with organic substances.
[Sidenote: 5. Water in physiology? Where found? Computation? Water in the
teeth? Muscle, tendons, and ligaments? How ascertained? Water in the fluids
of the body? What is the advantage?]
5. WATER.--Water, from a physiological point of view, is the most important
of all the articles of food. It is everywhere found in the body, even in
the bones and the teeth. It has been computed that as large a proportion as
two-thirds of the body is water. The teeth, the densest of the solids in
the human system, contain ten per cent. of water. The muscles, tendons, and
ligaments are more than half water; for it is found that they lose more
than half their {55} weight when dried with moderate heat. But it is in the
_fluids_ of the body that water is found most abundantly. It gives to them
the power of holding a great variety of substances in solution, and is the
great highway by which new supplies are conveyed to the point where they
are required, and by which old particles of matter, that have served their
uses, are brought to the outlets of the body to be thus removed from the
system.
[Sidenote: 6. Length of time man can do without food or water? Give the
comparison? Bulk of drinks? Constituent of meats, etc.? Fruits?]
6. Man can remain a longer time without solid food than without water. He
may be deprived of the former for ten to twelve hours without great
suffering, but deprivation of water for the same length of time will
produce both severe pain and great weakness. The food should contain not
less than two parts of water to one of solid nutriment. Water constitutes
the great bulk of all our drinks, and is also a large constituent of the
meats, vegetables, and fruits which come upon the table. Fruits,
especially, contain it in great abundance, and, in their proper season,
furnish most agreeable and refreshing supplies of the needed fluid.
[Sidenote: 7. Salt, how obtained? Where found? In the human body?
Importance of salt? What else can you state of the value of salt?]
7. COMMON SALT.--Salt, or sodium chloride, as an article of food, is
obtained chiefly from the mineral kingdom; although plants contain it in
small quantities, and it is also found in the tissues of nearly all animals
used as food. In the human body, it is an ingredient of all the solids and
fluids. The importance of salt to animal life in general, is shown by the
great appetite for it manifested by domestic animals, and also by the
habitual resort of herds of wild beasts to the "salt-licks" or springs. In
those parts of the world where salt is obtained with difficulty, man places
a very high price upon it.
[Sidenote: 8. Experiments upon animals?]
8. Experiments upon domestic animals show that the withdrawal of salt from
their food, not only makes their {56} hides rough and causes the hair to
fall out, but also interferes with the proper digestion of food. If it be
withheld persistently, they become entirely unable to appropriate
nourishment, and die of starvation.
[Sidenote: 9. Salt, how taken into the system? Its use in cooking?
Consumption?]
9. Salt is usually taken into the system in sufficient quantities in our
food. Even the water we drink often has traces of it. The habitual use of
much salt in cooking, or as a seasoning at the table, is not wise; and
while it may not lead to consumption, as some writers declare, it is a bad
habit in itself, and leads to the desire for other and more injurious
condiments.
[Sidenote: 10. Lime in the bones? What does it impart? Chief ingredient of
the bones and teeth? Where else found?]
10. LIME.--This is the mineral substance which we have spoken of before as
entering very largely into the composition of the bones. It is the
important element which gives solidity and permanence to the framework upon
which the body is built. Calcium tri-phosphate, or "bone-earth," is the
chief ingredient of the bones and teeth, but is found in the cartilages and
other parts of the body in smaller quantities.
[Sidenote: 11. How does lime find its way into the body? Early life? Effect
of its derivation?]
11. How does this substance find its way into the body? Meat, milk, and
other articles obtained from the animal kingdom contain it, and it is
abundantly stored away also in the grains from which our bread is made, in
wheat, rye, and Indian corn. In early life, while the body is growing, the
supplies of this substance should be carefully provided. The evil effects
of the deprivation of it are too often and painfully evident in the
softening of the bones, and in the predisposition to curvature of the
spine--deformities which are most deplorable and which continue through
life.
[Sidenote: 12. Iron, its abundance and diffusion? Where found? What part of
the blood is it? How supplied to the system? In case of loss of blood or
wasting disease?]
12. IRON.--This substance is probably the most abundant and widely diffused
of the metals. It is found in {57} most of the vegetables, and is a very
important component of animal tissues. It enters into the composition of
human blood in about one part per thousand. Ordinarily, the food conveys to
the system enough iron for its use, but it must sometimes be introduced
separately as a remedy, especially after great loss of blood, or after some
wasting disease. Under its influence the blood seems to be rapidly
restored, and a natural color of the lips and skin replaces the pallor
caused by disease.
[Sidenote: 13. Soda, potash, and magnesia? How do they occur?]
13. OTHER INORGANIC SUBSTANCES.--In addition to the substances mentioned,
the mineral kingdom supplies compounds of soda, potash, and magnesia, which
are essential for the use of the body. They occur in small quantities in
the body, and enter it in combination with the various articles of diet.
[Sidenote: 14. Organic substances, whence derived? What do they comprise?
Groups?]
14. ORGANIC SUBSTANCES.--These substances are derived from the vegetable
and animal creations. They comprise all those articles which are commonly
spoken of as "food," and which are essential to sustain the body in life
and strength. They are divided into three groups, namely: the Albuminoid
substances, the Fats, and Sugars.
[Sidenote: 15. The Albuminoid class, includes what? These compounds
constitute what? The food? Their importance? Their properties?]
15. THE ALBUMINOIDS.--This class includes three important nutritive
substances--(1) _Albumen_, which gives it its name; (2) _Fibrin_, including
_gluten_; and (3) _Casein_. These compounds constitute a large part of the
human body, and the food contains them in proportionally large quantities.
Their importance is so great, and the system so promptly suffers from their
absence, that they have been styled the "_nutritious_ substances." The
properties which they hold in common are, that they do not crystallize, and
have a jelly-like form, except when heat is applied to them, when they
harden, or _coagulate_. {58}
[Sidenote: 16. Decomposition? Effect of cold? Illustrations? Elephants?]
16. They likewise decompose, or _putrefy_, under the influence of warmth
and moisture. Hence the decay of all dead animal tissues. Cold arrests this
process. It is well known that milk, eggs, and the like, "keep" much longer
in winter than at other seasons. The bodies of elephants, caught in the ice
many hundred years ago, are occasionally borne by the icebergs to the coast
of Siberia, completely frozen, but preserved almost perfectly in form and
limb.
[Sidenote: 17. In what substances does albumen exist? What further is said
of the egg?]
17. ALBUMEN exists in milk, meat, the grains, and the juices of many
plants; but the purest form is obtained from the white of egg. When we
consider that an egg is composed chiefly of albumen and water--namely, six
parts in seven; and when we also consider the numerous, diverse, and
complex tissues--the muscles, bones, internal organs, bill, claws, and
feathers--with which the chick is equipped on leaving his shell, we are
impressed with the importance of these apparently simple constituents of
the food and body.
[Sidenote: 18. Fibrin, gluten, clotting of the blood?]
18. FIBRIN is derived from meats, and exists in the blood both of man and
the lower animals. _Gluten_, or vegetable fibrin, resembles closely true
fibrin, and is abundantly furnished in wheat and other grains from which
flour is commonly made. Animal fibrin coagulates spontaneously when it is
removed from the body, and thus causes the "clotting" of the blood.
[Sidenote: 19. Casein? Its coagulation? Effect of rennet? Making of
cheese?]
19. CASEIN is the curdy ingredient of milk, and a highly important
food-substance. Its coagulation in milk takes place not from heat, but by
the addition of an acid, and also when milk becomes sour from exposure to
the air. It is commonly effected, however, by introducing a piece of
_rennet_, a preparation made from a calf's stomach. The _curds_, or casein,
may then be separated from the _whey_, {59} and made into cheese, by
pressing it sufficiently to drive off the water.
[Sidenote: 20. What are the fats? The oils? How supplied? How alike?
Emulsifying? Example? How do we know it?]
20. THE FATS OR OILS.--This is the second group of organic foods. Those
which are more solid are called _fats_: the more fluid ones are the _oils_.
Oleaginous substances are supplied in both animal and vegetable food; but,
from whatever source derived, they are chemically much alike. They are
insoluble in water, and yet they unite readily with the watery fluids of
the body, and are by them conveyed to its various parts for their
nourishment. This is due to their property of "emulsifying;" that is, they
are held in suspension, in a finely divided state, in water. Ordinary milk
is an example of an _emulsion_. We know that it contains fat; for butter is
obtained from it, and, under the microscope, the minute oil-globules may be
distinctly seen.
[Sidenote: 21. Whence are fatty articles of food derived?]
21. In our country and climate, and also in colder climates, fatty articles
of food are principally derived from the animal creation, such as meat or
flesh, milk and butter. But most of the bread-stuffs contain more or less
fat or oil; Indian meal as much as nine parts in a hundred.
[Sidenote: 22. Appetite of persons in cold climates? What do they require?
Upon what must they rely? Why? The Esquimaux? Laplander? Olive and palm?]
22. Among persons living in cold climates, the appetite for oleaginous food
is especially eager; and they require large quantities of it to enable them
to resist the depressing influences of cold. Since vegetation is scanty and
innutritious, and the waters of the frozen regions abound in animal life,
they must rely wholly upon a diet derived from the latter source. The
Esquimaux consumes daily from ten to fifteen pounds of meat or blubber, a
large proportion of which is fat. The Laplander will drink train-oil, and
regards tallow-candles as a great delicacy. In hot climates, on the
contrary, where flourish the olive {60} and the palm, this kind of food may
be obtained from vegetable sources in abundant quantities.
[Sidenote: 23. Which are the third of the organic groups? What do they
embrace? Points of resemblance?]
23. THE SUGARS, OR THE SACCHARINE SUBSTANCES.--These constitute the third,
and last, group of the organic substances, which are employed as food. This
group embraces, in addition to the different kinds of _Sugar_, the
varieties of starch and gum, from whatever source derived. The two
substances last named do not, at first sight, present many points of
similarity to sugar; but they closely resemble it in respect to their
ultimate chemical composition, being made up of the same elements, in
nearly the same proportions. And their office in the system is the same,
since they are all changed into sugar by the processes of digestion.
[Sidenote: 24. Origin of the sugars? Ordinary sugar? Beetroot? Maple-sugar?
Grape-sugar? Cane-sugar?]
24. SUGAR is chiefly of vegetable origin; the animal varieties being
obtained from honey and milk. The most noticeable characteristic of this
substance is its agreeable, sweet taste, which makes it everywhere a
favorite article of food. But this quality of sweetness is not possessed by
all the varieties of sugar in the same degree; that obtained from milk, for
instance, has a comparatively feeble taste, but rather imparts a gritty
feeling to the tongue. The other important properties of sugar are, its
power to crystallize when evaporated from watery solutions, such as the
juices of many plants; a tendency to ferment, by which process alcohol is
produced; and a ready solubility in water. This latter quality renders it
very easy of digestion, and more so than any other of the saccharine group.
It is computed that the annual production of sugar, in all parts of the
world, is more than one million of tons. The kind of sugar that is in
ordinary use, in this country, is prepared from the juice of the
sugar-cane, which contains eighteen per cent. of sugar. In France it is
manufactured from the {61} beet root, which holds about nine per cent.; the
maple-tree of our climate yields a similar sugar. The sweet taste of fruits
is due to the presence of grape-sugar: the white grains seen on raisins
belong to this variety. Cane-sugar is more soluble than the latter, and has
twice the sweetening power.
[Illustration: FIG. 15.--GRANULES OF POTATO STARCH.]
[Sidenote: 25. Starch, how widely distributed? Its qualities? Its
constituents? Its solubility?]
25. STARCH.--This is the most widely distributed of the vegetable
principles. It is tasteless, inodorous, and does not crystallize. It
consists of minute rounded granules, which, under the microscope, reveal a
somewhat uniform structure (Fig. 15). Starch will not dissolve in cold
water, but in boiling water the small grains burst open, and may then be
dissolved and digested.
[Sidenote: 26. How much starch in bread-stuffs? In rice? Unripe fruits?
Ripe fruits?]
26. The bread stuffs, wheat, corn, and rye flours, are more than one-half
starch. Rice, which is the "staff of life" to one-third of the human
family, contains eighty per cent. Unripe fruits have much starch in them,
which renders them indigestible when eaten uncooked; for the grains of raw
starch are but slightly acted upon within the body. But, under the potent
chemistry of the sun's ray, this crude material is converted into sugar.
Thus are the fruits prepared by the careful hand of Nature, so that when
ripe they may be freely used without further preparation.
[Sidenote: 27. Gum, where found? Its composition? Gum Arabic?]
27. GUM is commonly found in those articles which {62} also contain starch;
and has the same chemical composition as the latter, but is much less
nutritious. In the East, gum-arabic and similar substances are largely
employed as food. Persons who travel by caravan across vast, sandy deserts,
find such substances well adapted to their wants, since they are not
perishable, and are easily packed and carried.
[Sidenote: 28. The three classes of food principles? What besides? What is
said of them? Name the articles not nutritious.]
28. STIMULATING SUBSTANCES.--The three classes of food-principles already
considered--the Albuminoids, the Fats, and the Sugars--comprise all the
more important organic ingredients of our food. There are, besides, a great
variety of coloring and flavoring matters that stimulate or increase the
appetite for food by appealing to the eye and taste; but they are not
nutritious, and are quickly separated from the truly useful substances, and
do not long remain in the body. Among these may be classed spices, flavors
of fruits, tea, coffee, and vegetable acids.
[Sidenote: 29. What is said of experiments that have been tried?]
29. NECESSITY OF A REGULATED DIET.--A great variety of experiments have
been tried in order to test the relative value of the different nutritive
principles. They have been practised to some extent upon man, but chiefly
upon those inferior animals which require a similar diet to man.
[Sidenote: 30. What has been demonstrated in the first place? Example?
Second demonstration? Example? Give the illustration in relation to
convertibility.]
30. By this means it has been demonstrated that--first, when any one of
these substances is eaten exclusively, the body is imperfectly nourished,
and life is shortened. Dogs fed exclusively upon either albumen, fat, or
sugar, soon die of starvation. Second, a diet long deprived of either of
these principles, is a fertile cause of disease; for example, on
ship-board, where fresh vegetables are not dealt out for a long period,
_scurvy_ becomes prevalent among the sailors. They are, however, to a
certain extent mutually convertible, and thus the missing article is
indirectly supplied. For {63} instance, sugar changes to fat in the body;
and hence, as is well known, the "hands" on a sugar plantation grow fat
during the sugar season, by partaking freely of the ripened juices of the
cane.
31. That is the best diet therefore which contains some of each of these
principles, in due proportion; and that is the worst which excludes the
most of them. The cravings and experience of man had unerringly guided him
to a correct regulation of his diet, long before the chemistry of food was
understood; so that his ordinary meals long ago combined these various
principles, the necessity and value of which are now explained.
QUESTIONS FOR TOPICAL REVIEW.
PAGE
1. What is understood by the term food? 53
2. What can you state in relation to the source of food? 53
3. What discriminations and selections are necessary? 53, 54
4. How can you tell the organic from the inorganic substances? 54
5. What relative position does water hold as an article of food? 54
6. In what parts of the body is water found? 54, 55
7. In what articles that we eat is it found? 55
8. If you were required to go without water or solid food for a
number of days, which would you prefer to have, and why? 55
9. What can you state of the importance of salt as an article
of food? 55, 56
10. How abundant is salt, and how does it find its way into the
human system? 55, 56
11. What can you state of the importance of lime in the body? 56
12. What, of the importance of iron? 56, 57
13. What further is stated of other inorganic substances? 57
14. What in relation to organic substances? 57
15. What can you state in relation to the albuminoids? 57, 58
16. What, in relation to albumen? 58
17. What, in relation to casein? 58, 59
18. In relation to the fats or oils, and how generally consumed? 59, 60
19. What do we understand by the sugars or saccharine substances? 60
20. State what you can of sugar--its origin and various qualities. 60, 61
21. Of starch--its varieties and qualities. 61
22. Of the abundance of starch, and its importance as a food
principle. 61
23. What is stated in relation to stimulating substances? 62
24. Of the necessity for regulation in diet? 62, 63
* * * * *
{64}
CHAPTER V.
FOOD AND DRINK.
_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._
[Sidenote: 1. What follow activity? Examples? Necessity for food?]
1. NECESSITY FOR FOOD.--Activity is everywhere followed by waste. The
engine uses up coal and water to produce motion, the stream wears away its
bank, the growing corn-blade draws tribute from the soil. When the human
body acts, and it is always in action during life, some of its particles
are worn out and thrown off. This waste must constantly be repaired, or the
body suffers. In this fact is seen the necessity for food. The particles,
thus worn out, being henceforth useless, are removed from the body. Our
_food_ and _drink_ are rapidly transformed into a new supply of living,
useful material, to be in turn used up and replaced by a fresher supply.
[Sidenote: 2. Give the theory in relation to waste and repair.]
2. WASTE AND REPAIR.--In this way the healthful body, though always
wasting, is always building up, and does not greatly change in size, form,
or weight. At two periods of life the processes of waste and repair are not
exactly balanced. In early life the process of building up is more active,
and in consequence the form is plump, and the stature increases. Repair now
exceeds waste. On the other hand, when old age comes on, the wasting
process is more active, the flesh and weight diminish, the skin falls in
wrinkles, and the senses become dull. Only during the prime of life--from
about twenty to sixty years of age--is the balance exact between loss and
gain. {65}
[Sidenote: 3. System deprived of food? Warning? What is the pain? How
proved?]
3. HUNGER AND THIRST.--When the system is deprived of its supply of solid
food during a longer time than usual, nature gives warning by the sensation
of hunger, to repair the losses that have taken place. This sensation or
pain appears to be located in the stomach, but it is really a distress of
the system at large. Let a sufficient quantity of nourishment be introduced
into the system in any other way than by the mouth, and it will appease
hunger just as certainly as when taken in the usual manner.
[Sidenote: 4. Feeling of thirst? Seat of the pain? How proved? Time a
person can exist without food?]
4. The feeling of thirst, in like manner, is evidence that the system is
suffering from the want of water. The apparent seat of the distress of
thirst is in the throat; but the injection of water into the blood-vessels
is found to quench thirst, and by the immersion of the body in water, the
skin will absorb sufficient to satisfy the demands of the system. The
length of time that man can exist without food or drink is estimated to be
about seven days. If water alone be supplied, life will last much longer;
there being cases recorded where men have lived twenty days and over,
without taking any solid food.
[Sidenote: 5. Amount of food required? The young and others? Those living
in hot and cold climates? Habits?]
5. QUANTITY OF FOOD.--The quantity of food required varies greatly,
according to the individual and his mode of life. The young, and others who
lead active lives, or who live in the open air, require more food than the
old, the inactive, or the sedentary. Those who live in cold regions require
more than the inhabitants of hot climates. Habit, also, has much to do with
the quantity of food required. Some habitually eat and drink more than they
actually need, while a few eat less than they should.
[Sidenote: 6. Quantity of food daily? How divided? Compare with the weight
of the body?]
6. The average daily quantity of food and drink for a healthy man of active
habits is estimated at six pounds. This amount may be divided in about the
following {66} proportions: the mineral kingdom furnishes three and
one-half pounds, including water and salt; the vegetable kingdom, one and
one-half pounds, including bread, vegetables, and fruits; the animal
kingdom, one pound, comprising meat, eggs, butter, and the like. This
quantity is about one twenty-fourth the weight of the body, as it is
generally computed; the average weight of an adult man being placed at 140
pounds. A man, therefore, consumes an amount of solid and liquid nutriment
every twenty-four days equal in weight to that of his body, a corresponding
amount being _excreted_, or removed from the system in the same time.
[Sidenote: 7. How often then might the body be renewed? Why is it not?
Opinion? How correct? What further is stated?]
7. RENOVATION OF THE BODY.--By this process, so far as weight is concerned,
the body might be renewed every twenty-four days; but these pounds of food
are not all real nutriment. A considerable portion of that which we eat is
innutritious, and though useful in various ways, is not destined to repair
the losses of the system. An opinion has prevailed that the body is renewed
throughout once in seven years; how correct this may be it is not easy to
decide, but probably the renovation of the body takes place in a much
shorter period. Some parts are very frequently renewed, the nutritive
fluids changing more or less completely, several times during the day. The
muscles, and other parts in frequent exercise, change often during a year;
the bones not so often, and the enamel of the teeth probably never changes
after being once fully formed.
[Sidenote: 8. Habits of nations? Give the different cases.]
8. MIXED DIET.--The habits of different nations in respect to diet exhibit
the widest and strangest diversity. The civilized, cook their food, while
savages often eat it in a raw state. Some prefer it when fresh, others
allow it to remain until it has become tainted with decay. Those dwelling
in the far north subsist almost wholly on {67} animal food, while those
living in hot climates have bountiful supplies of delicious fruits with
which to satisfy all their bodily wants. One race subsists upon the banana,
another upon the blubber of seals. In temperate climates, a diet composed
partly of vegetable and partly of animal food is preferred.
[Sidenote: 9. The point to consider? Vegetable diet? Louis Cornaro? John
the Baptist?]
9. The important point to consider is, however, not one of origin, but
whether the chemical principles (mentioned in the last chapter) enter into
the composition of the diet. A purely vegetable diet may be selected which
would contain all the principles necessary to sustain life. It is recorded
of Louis Cornaro, a Venetian noble, that he supported himself comfortably
for fifty-eight years on a daily allowance of twelve ounces of vegetable
food, and about a pint of light wine. On the other hand, the food of John
the Baptist, consisting of "locusts and wild honey," is an example of the
sustaining power of a diet chiefly animal in its origin.
[Sidenote: 10. What has been found in our climate? Exclusive vegetable
diet?]
10. In our climate, those who lead active lives crave an allowance of
animal food; and it has been found by experience that with it they can
accomplish more work and are less subject to fatigue, than without it.
Among nations where an exclusively vegetable diet is employed, indigestion
is a disorder especially prevalent.
[Sidenote: 11. Necessity for change in diet? Continuous use of the same
diet? Exception? Why? Too rich diet? Horses?]
11. The necessity for occasionally changing or varying the diet, is seen in
the fact that no single article comprises all the necessary principles of
food, and that the continuous use of any one diet, whether salt or fresh,
is followed by defective nutrition and disease. There is one exception to
this rule: in infancy, milk alone is best calculated to support life; for
then the digestive powers are incompletely developed, and the food must be
presented in the simplest form possible. It should also be remembered {68}
that too rich diet is injurious, just as truly as one that is inadequate.
When the food of horses is too nutritious, instinct leads them to gnaw the
wood-work of their mangers.
[Sidenote: 12. Milk as a model food? Cow's milk? The constituents when
separated?]
12. DIFFERENT ARTICLES OF DIET--MILK.--Milk is the earliest nutriment of
the human race, and in the selection and arrangement of its constituents,
may be regarded as a model food, no other single article being capable of
sustaining life so long. Cow's milk holds casein, one of the albuminoids,
about five parts in one hundred; a fatty principle, when separated, known
as butter, about four parts; sugar of milk four parts; water and salts
eighty-seven parts. The casein and fatty substance are far more digestible
in milk, than after they have been separated from it in the form of cheese
and butter.
[Sidenote: 13. Milk as a beverage? Milk sold in cities? How to detect the
cheat?]
13. Since milk, in itself, is so rich an article of food, the use of it as
a beverage is unwise, unless the quantity of the other articles consumed be
reduced at the same time. The milk sold in cities is apt to be diluted with
water. The way to detect the cheat is by testing the specific gravity of
the article. Good milk is about 1030; skimmed milk 1035; but milk diluted
one-fifth is 1024. An instrument called the lactometer is also used, by
which the amount of cream present is ascertained.
[Sidenote: 14. Composition of eggs? Yolk? How should eggs be eaten? Why?
How boiled? Why?]
14. EGGS.--The egg is about two-thirds water, the balance is pure albumen
and fat in nearly equal proportions. The fat is in the yolk, and gives it
its yellow color. Eggs contain none of the sugar-principles, and should be
eaten with bread or vegetables that contain them. Soft-boiled eggs are more
wholesome than those which are hard-boiled or fried, as the latter require
longer time to digest.
[Sidenote: 15. Meats, whence derived? Why important? Flesh of young
animals?]
15. MEATS.--The meats, so called, are derived from the muscular parts of
various animals. They are most {69} important articles of food for adults,
inasmuch as they are richly stored with albuminoid substances, and contain
more or less fat. Such food is very nourishing and easily digested if eaten
when fresh,--veal and pork being exceptions. The flesh of young animals is
more tender and, in general, more digestible than that of older ones. All
meat is more tough immediately after the killing of the animal, but
improves by being kept a certain length of time.
[Sidenote: 16. Preference of persons? Venison? Mutton? Cheese? Uncooked
flesh?]
16. Some persons prefer flesh that has begun to show signs of
decomposition, or is unmistakably putrid. By some, venison is not
considered to have its proper flavor until it is tainted. In England,
people prefer mutton that is in a similar condition, just as on the
continent of Europe many delight in cheese that is in a state of
decomposition. In certain less civilized countries flesh is not only eaten
uncooked, but in a mouldy, rotten condition. The use of such food is not
always immediately injurious, but it predisposes to certain diseases, as
indigestion and fevers.
[Sidenote: 17. Cold as a preserver? Meat in Russia? Beef and pork, how
preserved? Salted meat as food? Scurvy?]
17. Cold is one means of preserving meat from decay. In the markets of
northern Russia, the frozen carcases of animals stand exposed for sale in
the winter air for a considerable time, and are sawn in pieces, like sticks
of wood, as the purchases are made; such meat, when thawed, being entirely
fit for food. Beef and pork are preserved by salting down in brine, and in
this condition may be carried on long voyages or kept for future use.
Salted meat is not as nutritious as fresh, since the brine absorbs its rich
juices and hardens its fibres. Long continued use of salt meats, without
fresh vegetables, gives rise to the disease called scurvy, formerly very
prevalent on shipboard and in prisons; but now scarcely known.
[Sidenote: 18. The antiquity of the custom of cooking food? Object of
cooking? The oyster? Raw meat as an occasional food?]
18. COOKING.--The preparation of food by the agency {70} of fire is of
almost universal practice, even among the rudest nations. The object of
cooking is to render food more easy of digestion by softening it, to
develop its flavor, and to raise its temperature more nearly to that of the
body. A few articles of flesh-food are eaten uncooked in civilized lands,
the oyster being an instance. Raw meat is occasionally eaten by invalids
with weak digestive powers, and by men training for athletic contests.
[Sidenote: 19. Effect of boiling meat? How may the cooking be done? The
proper method? Effect? Making of soup?]
19. In boiling meat, the water in which it is placed tends to dissolve its
nutrient juices. In fact, the cooking may be so conducted as to rob the
meat of its nourishment, its tenderness, and even of its flavor. The proper
method, in order to preserve or promote these qualities, is to place the
meat in boiling water, which, after a few minutes, should be reduced in
temperature. In this way the intense heat, at first, coagulates the
exterior layers of albumen, and imprisons the delicate juices; after that,
moderate heat best softens it throughout. When soup is to be made, an
opposite course should be pursued; for then the object is to extract the
juices and reject the fibre. Meat, for such purpose, should be cut in small
pieces and put into cold water, which should then be gradually raised to
boiling heat.
[Sidenote: 20. Roasting? How should it be done? Give the philosophy of the
process. Frying?]
20. Roasting is probably the best method of cooking meat, especially
"joints" or large pieces, as by this process the meat is cooked in its own
juices. Roasting should begin with intense heat, and be continued at a
moderate temperature, in order to prevent the drying out of the nutritious
juices, as by this process an outer coating or crust of coagulated albumen
is formed. During this process the meat loses one-fourth of its weight, but
the loss is almost wholly water, evaporated by the heat. Too {71} intense
or prolonged heat will dry the meat, or burn it. Frying is the worst
possible method, as the heated fat, by penetrating the meat, or other
article placed in it, dries and hardens it, and thus renders it
indigestible.
[Sidenote: 21. What is "Trichina?" How guarded against?]
21. TRICHINA.--It should be remembered that ham, sausages, and other forms
of pork, should never be eaten in a raw or imperfectly cooked condition.
The muscle of the pig is often infested by a minute animal parasite, or
worm, called _trichina spiralis_. This worm may be introduced alive into
the human body in pork food, where it multiplies with great rapidity, and
gives rise to a painful and serious disease. This disease has been
prevalent in Germany, and cases of it occur from time to time in this
country.
[Sidenote: 22. What part of fish is eaten? What does it resemble? Fish as
food for digestion? Fish as a diet?]
22. FISH.--The part of fish that is eaten is the muscle, just as in the
case of the meats and poultry. It closely resembles flesh in its
composition, but is more watery. Some varieties are very easy of digestion,
such as salmon, trout, and cod; others are quite indigestible, especially
lobsters, clams, and shell-fish generally. A diet in which fish enters as
the chief article, is ill adapted to strengthen mind or body, while its
continued use is said to be the fertile source of nearly every form of
disease of the skin. Some persons are so constituted that they can eat no
kind of fish without experiencing unpleasant results.
[Sidenote: 23. List of vegetable articles? Usefulness of the different
vegetables? Strychnia? What further is said in relation to the nourishing
and other qualities of vegetables?]
23. VEGETABLE FOOD.--The list of vegetable articles of diet is a very long
one, including the grains from which our bread-stuffs are made, the
vegetables from the garden, and the fruits. All the products of the
vegetable kingdom are not alike useful. Some are positively hurtful;
indeed, the most virulent poisons, as strychnia and prussic acid, are
obtained from certain vegetables. Again, of such {72} articles as have been
found good for food, some are more nourishing than others: some require
very little preparation for use, while others are hard and indigestible,
and can only be used after undergoing many preparatory processes. Great
care must therefore be exercised, and many experiments made, before we can
arrive at a complete knowledge in reference to these articles of diet. Tea,
coffee, and other substances from which drinks are made, are of vegetable
origin.
[Sidenote: 24. Wheat? "Staff of life?" White flour? Hard-grain wheats?
Bolting? Graham bread?]
24. BREAD.--Wheat is the principal and most valuable kind of grain for the
service of man. Bread made from wheat-flour has been in use for many
hundreds of years, and on this account, as well as because of its highly
nourishing properties, has been aptly called "the staff of life." We never
become tired of good bread as an article of daily food.
The white kinds of flour contain more starch and less gluten than the
darker, and are therefore less nutritious. The hard-grain wheat yields the
best flour. In grinding wheat, the chaff or bran is separated by a process
called "bolting." Unbolted flour is used for making brown or Graham bread.
[Sidenote: 25. Leavened bread? Unleavened? Hot bread?]
25. The form of bread most easily digested is that which has been
"leavened," or rendered porous by the use of yeast, or by some similar
method. Unleavened bread requires much more mastication. Hot bread is
unwholesome, because it is not firm enough to be thoroughly masticated, but
is converted into a pasty, heavy mass that is not easily digested.
[Sidenote: 26. Wheaten bread? Bread and butter? Experiment on the dog?]
26. Wheaten bread contains nearly every principle requisite for sustaining
life, except fat. This is commonly added in other articles of diet,
especially in butter,--"bread and butter," consequently, forming an almost
perfect article of {73} food. The following experiment is recorded: "A dog
eating _ad libitum_ of white bread, made of pure wheat, and freely supplied
with water, did not live beyond fifty days. He died at the end of that time
with all the signs of gradual exhaustion." Death took place, not because
there was anything hurtful in the bread, but because of the absence of one
or more of the food-principles.
[Sidenote: 27. State what is said of the Irish potato?]
27. THE POTATO.--The common or Irish potato is the vegetable most
extensively used in this country and Great Britain. Among the poorer
classes in Ireland it is the main article of food. While it is not so rich
in nutritious substances as many others, it has some very useful qualities.
It keeps well from season to season, and men do not weary of its continuous
use. It is more than two-thirds water, the balance being chiefly starch,
with a little albumen.
[Sidenote: 28. Sweet potato? Nightshades? Potatoes when germinating?]
28. The sweet potato differs from the white or common, in containing more
water and a small proportion of sugar. The common potato and the tomato
belong to the same botanical order as the "nightshades," but do not possess
their poisonous qualities, unless we except potatoes that are in the
process of germination or sprouting, when they are found injurious as food.
[Sidenote: 29. Fruits? Use of ripe fruit? Nutriment they contain? Starch in
unripe fruits? Cooking of unripe fruits?]
29. FRUITS.--These are produced, in this country, in great abundance, and
are remarkable alike for their variety and delicious flavor; consequently
they are consumed in large quantities, especially during the warmer months.
The moderate use of ripe fruits, in their season, is beneficial, because
they offer a pleasant substitute for the more concentrated diet that is
used in cold weather. The amount of solid nutriment they contain is,
however, small. The percentage of water in cherries is seventy-five, in
grapes eighty-one, in apples eighty-two. Unripe fruits contain starch,
which, during the process of ripening, {74} is converted into sugar. Such
fruits are indigestible and should be avoided: cooking, however, in part
removes the objections to them.
[Sidenote: 30. How should drinking-water be as regards color and smell?
Chemically pure water? How obtained? Agreeableness of perfectly pure
water?]
30. PURE WATER.--It is important that the water we drink and use in the
preparation of food should be pure. It should be clear and colorless, with
little or no taste or smell, and free from any great amount of foreign
ingredients. Chemically pure water does not occur in nature: it is only
obtained by the condensation of steam, carefully conducted, and is not as
agreeable for drinking purposes as the water furnished by springs and
streams. Rain-water is the purest occurring in nature; but even this
contains certain impurities, especially the portion which falls in the
early part of a shower; for in its descent from the clouds, the particles
floating in the air are caught by the falling drops.
[Sidenote: 31. Spring and well water? Whence the sparkle, or life? The
water supply of cities? Croton water? Ridgewood?]
31. Water from springs and wells always contains more or less foreign
matter of mineral origin. This imparts to the drink its pleasant taste--the
sparkle, or "life," coming from the gases absorbed by the water during its
passage under ground. The ordinary supply of cities is from some pure
stream or pond conveyed from a distance through pipes, the limpid fluid
containing generally only a small amount of impurity. Croton water, the
supply of New York City, is very pure, and contains only four and a half
grains to a gallon: the Ridgewood water of Brooklyn holds even less foreign
matter.
[Sidenote: 32. Impurities in drinking-water? Mineral springs?]
32. Drinking-water may contain as large a proportion as sixty to seventy
grains per gallon of impurity, but a much larger quantity renders it
unwholesome. The mineral spring waters, used popularly as medicines, are
highly charged with mineral substances. Some of them, such as {75} the
waters at Saratoga, contain three hundred grains and more to the gallon.
[Sidenote: 33. What is stated of the action of water upon lead?]
33. ACTION OF WATER UPON LEAD.--The danger of using water that has been in
contact with certain metals is well known. Lead is one of the most readily
soluble, and probably the most poisonous of these substances in common use.
When pure water and an untarnished surface of lead come in contact, the
water gradually corrodes the metal, and soon holds an appreciable quantity
of it in solution. When this takes place the water becomes highly
injurious: the purer the water, and the more recent the use of the metal,
the greater will be the danger.
[Sidenote: 34. Lead in pipes and other things? Advice? What takes place
after the articles of lead have been used much? What is wise?]
34. In cities, lead pipes are commonly used to convey water through the
houses; lead being also used in the construction of roofs, cisterns, and
vessels for keeping water and other liquids. After the articles of lead
have been in use several months, the danger of lead-poisoning diminishes.
An insoluble coating of the sulphate of lead forms upon the exposed
surface, thus protecting it from further corrosion. It is, however, a wise
precaution, at all times to reject the water or other fluid that has been
in contact with leaden vessels over night, or for a number of hours. Allow
the water in pipes to run freely before using.
[Sidenote: 35. Coffee as an article of diet? Of what does it consist? How
does the water affect the coffee? The peculiar stimulant? How does it
affect most persons?]
35. COFFEE.--This is an important addition to diet, and if moderately used
is beneficial to persons of adult age. As commonly employed, it consists of
an infusion in boiling water of the roasted and ground berry. The water
extracts certain flavoring and coloring matters, but that which gives it
its peculiar stimulant qualities is the alkaloid _caffein_. With most
persons its action is that of a gentle stimulant, without any injurious
reaction. It produces a restful feeling after exhausting efforts of mind or
{76} body; it tranquilizes, but does not disqualify for labor; and hence it
is highly esteemed by persons of literary pursuits.
[Sidenote: 36. Another property of coffee? Miners of Belgium? The Caravans?
Among armies? Taken with meals?]
36. Another property of coffee is, that it diminishes the waste of the
tissues, and consequently permits the performance of excessive labor upon
an economical and inadequate diet. This has been tested among the miners of
Belgium. Their allowance of solid food was below that found necessary in
prisons and elsewhere; but, with the addition of about four pints of coffee
daily, they were enabled to undergo severe labor without reducing their
muscular strength. The caravans which traverse the deserts are supported by
coffee during long journeys and lengthened privation of food. Among armies
it is indispensable in supplementing their imperfect rations, and in
relieving the sense of fatigue after great exposure and long marches. When
taken with meals, coffee is also thought to promote digestion.
[Sidenote: 37. Effects of tea-drinking? Peculiar principle? The tea
beverage, how made? Black and green tea? Excessive use of tea or coffee?]
37. TEA.--The effects of tea-drinking are very similar to those of coffee,
and are due to a peculiar principle called _thein_. This principle is
probably the same as that found in coffee, _caffein_, since the chemical
composition of both is precisely alike. Tea, as a beverage, is made from
the dried leaves of the plant by the addition of hot water; if the tea is
boiled, the oil which gives it its agreeable flavor is driven off with the
steam. There are two kinds of tea--the black and the green: the latter is
sometimes injurious, producing wakefulness and other nervous symptoms. The
excessive use of either coffee or tea will cause wakefulness.
[Sidenote: 38. Experiments made during Kane's expedition?]
38. During Dr. Kane's expedition in the Arctic regions, the effects of
these articles were compared. "After {77} repeated trials, the men took
most kindly to coffee in the morning and tea in the evening. The coffee
seemed to continue its influence throughout the day, and they seemed to
grow hungry less rapidly than after drinking tea, while tea soothed them
after a day's hard labor, and the better enabled them to sleep. They both
operated upon fatigued men like a charm, and their superiority over
alcoholic stimulants was very decided."
[Sidenote: 39. State what is said of chocolate.]
39. Chocolate is made from the seeds of the cocoa-tree, a native of
tropical America. Its effects resemble somewhat those of tea and coffee,
but it is very rich in nutriment. Linnæus, the botanist, was so fond of
this beverage, that he gave to the cocoa-tree the name, _Theobroma_--"the
Food of the Gods." Its active principle is _theobromin_.
[Sidenote: 40. Use of alcoholic drinks, how general? The rule given?]
40. ALCOHOL.--The list of beverages that are consumed for the sake of the
alcohol they contain is a very long one. Their use is almost universally
prevalent, every civilized nation, and nearly every barbarous one, having
its favorite alcoholic drink; and, as a general rule, the nations which
stand the highest in civilization have the greatest varieties of these
beverages,--at the same time using them the most intelligently and wisely.
[Sidenote: 41. The beverages produced by fermentation? The ardent spirits?
Grains and fruits employed? Long use of wine? Of distilled liquors?]
41. The wines and malt liquors that contain a small amount of alcohol are
produced by fermentation. The beverages that hold a large proportion of
alcohol, the "ardent spirits," are made by distillation. Enormous
quantities of grains and fruits are thus yearly diverted from their proper
uses as food; some of these being corn, wheat, rye, barley, potatoes, and
rice; also the grape, apple, pear, peach, sugar-cane, cherry, fig, and
orange. Wine, the fermented juice of the grape, has been in use from time
immemorial, while the introduction of distilled liquors dates from a
comparatively recent period. {78}
[Sidenote: 42. Describe the action of alcohol upon the human system?
Experience of Dr. Hayes and others?]
42. What is the physiological action of alcohol? Its first and most evident
action is stimulation: this effect is transient, and is followed by a
variable degree of depression. At first it sharpens the appetite and
quickens digestion, but its habitual use impairs both. This stimulation is
efficient in giving the system an artificial strength during some temporary
derangement, and in enabling the endurance of unusual fatigue or exposure.
The experience of Dr. Hayes, and other explorers of the polar regions, is
that alcohol does not enable the body to resist the influence of cold, but,
on the contrary, is always injurious.
[Sidenote: 43. Another property of alcohol? How do we explain the
restorative influence of wines and liquors?]
43. Another property it has in common with tea and coffee. It supports the
powers of life, economizes food, and retards the waste of tissues; in other
words, it "banks the fires," and prevents their burning wastefully. On this
principle we explain the restorative influence of wines or liquors during
exhausting diseases, in convalescence, and after excessive labors of mind
or body.
[Sidenote: 44. Alcohol, a poison? Moderate stimulants? Prevailing opinion?
Hence?]
44. Pure alcohol, or an excessive quantity of ardent spirits, is an
undoubted poison, and has been frequently known to produce fatal results.
Stimulants in moderate quantities have been thought to increase strength,
and in this view they have been called "alcoholic foods." This is not now
conceded by scientific men. The prevailing opinion is, that they serve no
useful purpose as an article of diet, and that their beneficial influence
is limited to cases where the system is enfeebled, where some unnatural
demand is made upon the vital powers, or where the supply of food is
insufficient. Hence, while alcohol has not the power to build up, it may
obstruct the process of pulling down. {79}
QUESTIONS FOR TOPICAL REVIEW.
PAGE
1. How is the necessity for food shown? 64
2. To what process of waste and repair is the body constantly
subjected? 64
3. How do you account for the sensations of hunger and thirst? 65
4. What further can you state having relation to the subject? 65
5. What can you state in regard to the quantity of food required
for the support of life? 65, 66
6. What circumstances change the needs of persons, old and young,
as regards food and drink? 65, 67
7. What becomes of all the food and drink we consume? 66
8. What further can you state in relation to the process of
renovation through which the body passes? 66
9. What can you state of the habits of nations in respect to
diet? 66, 67, 69
10. What in relation to the selection of articles for food? 67
11. What as respects the necessity for changing or varying the diet? 67
12. What has been proved as regards animal food? 67
13. Of what importance is milk as an article of food? 67, 68
14. What are the constituents of milk? 68
15. What can you state of eggs as an article of food? 68
16. Of the meats, so called, as an article of food? 68, 69
17. What effect does cold have upon meats? 69
18. In what other way may beef and pork be preserved? 69
19. What can you state of salted meat as food, and of its
continued use? 69
20. What change does meat undergo in the cooking? 70, 71
21. What directions are given for boiling meat? 70
22. What for roasting, and with what results? 70, 71
23. What is said about the frying of meats? 71
24. Give the statement in relation to trichina. 71
25. State what is said in relation to fish. 71
26. What is stated of the usefulness and other properties of the
products of the vegetable kingdom? 71, 72
27. What further is said of vegetable food? 71, 72
28. Why is bread made of wheat flour so important as an article
of food? 72
29. State whatever else you can in relation to bread. 72, 73
30. Give the statement respecting the potato. 73
31. What is stated of fruits, the use of them, their nutritious
qualities, etc.? 73, 74
32. How general is the existence of perfectly pure water? 74
33. What is stated in relation to drinking water? 74, 75
34. How does the action of water upon lead affect lead? 75
35. What further can you state on the subject? 75
36. What properties has coffee as an article of diet? 75, 76
37. In what circumstances has coffee been found peculiarly
beneficial? 76
38. What comparison is made between coffee, tea, and chocolate? 76
39. How are the wines, and malt and other alcoholic beverages
produced? 77
40. What articles are employed in their production? 77
41. Describe the physiological action of alcohol. 78
42. What comparison is made between tea, coffee, and alcohol? 78
43. What can you state of alcohol, as a poison, a stimulant, and
article of diet? 78
44. What, then, can be said of alcohol as a recommendation? 78
* * * * *
{80}
CHAPTER VI.
DIGESTION.
_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._
[Sidenote: 1. Design of food? How accomplished?]
1. NUTRITION.--The great design of food is to give _nutriment_ or
nourishment to the body. But this is not accomplished directly, as the food
must first pass through certain preparatory changes, as follows: (1),
_Digestion_, by which the food is reduced to a soluble condition; (2),
_Absorption_, by which, when digested, it is imbibed into the blood; (3),
_Circulation_, which carries the enriched blood to the various parts of the
system; and (4), _Assimilation_, by which each tissue derives from the
blood the materials necessary for its support.
[Sidenote: 2. Sustaining power of food? Simile of the engine? Operation in
the human body?]
2. By these means the sustaining power of food is gradually developed and
employed, and the vital machinery kept in working order, somewhat after the
manner of the steam-engine. To operate the latter, the force imprisoned
within the coal and water is set free and converted into motion by the
combustion of the fuel and the vaporization of the water. It will be seen,
however, when we come to study these operations in the human body, that
they are conducted silently and harmoniously, with marvellous delicacy and
completeness, and without that friction, and {81} consequent loss of power,
which attend the working of the most perfect machinery of man's invention.
[Sidenote: 3. Change of food in digestion? Process of digestion? Describe
the alimentary canal.]
3. GENERAL PLAN OF DIGESTION.--The great change which food undergoes in
digestion is essentially a reforming process, reducing articles of diet,
which are at first more or less solid, crude, and coarse, to a liquid and
finely comminuted condition, suitable for absorption into the blood. The
entire process of digestion takes place in what is called the alimentary
canal, a narrow, tortuous tube, about thirty feet in its entire length.
This canal begins in the mouth, extends thence downward through the gullet
to the stomach (a receptacle in which the principal work of digestion is
performed), and thence onward through the small and large intestines.
[Illustration: FIG. 16.--SECTION OF THE TRUNK SHOWING THE CAVITIES OF THE
CHEST AND ABDOMEN.
A, Cavity of Chest; B, Diaphragm; C, Abdomen; D, E, Spinal Column.]
[Sidenote: 4. Situation of the stomach and intestines? Action of the food?
Mechanical action? Chemical?]
4. The stomach and intestines are situated in the cavity of the abdomen
(Fig. 16, C, and Fig. 22), and occupy about two-thirds of its space. The
action to which the food is subjected in these organs is of two
kinds--mechanical and chemical. By the former it is crushed, agitated, and
carried onward from one point to another; by the latter it is changed in
form through the solvent power of the various digestive juices. {82}
[Sidenote: 5. Describe the process of mastication? How many and what
movements?]
5. MASTICATION.--As soon as solid food is taken into the mouth, it
undergoes mastication, or chewing. It is caught between the opposite
surfaces of the teeth, and by them is cut and crushed into very small
fragments. In the movements of chewing, the lower jaw plays the chief part;
the upper jaw, having almost no motion, acts simply as a point of
resistance, to meet the action of the former. These movements of the lower
jaw are of three sorts: a vertical or cutting, a lateral or grinding, and a
_to-and-fro_ or gnawing motion.
[Illustration: FIG. 17.--SECTION OF A TOOTH.
_a_, Enamel; _b_, Cavity; _c c_, Roots; _d_, Body of the Tooth.]
[Sidenote: 6. Composition of the teeth? Enamel of the teeth? Interior of
teeth?]
6. The teeth are composed of a bone-like material, and are held in place by
roots running deeply into the jaw. The exposed portion, or "crown," is
protected by a thin layer of enamel (Fig. 17, _a_), the hardest substance
in the body, and, like flint, is capable of striking fire with steel. In
the interior of each tooth is a cavity, containing blood-vessels and a
nerve, which enter it through a minute opening at the point of the root
(Fig. 19).
[Sidenote: 7. The milk teeth? The permanent teeth?]
7. There are two sets of teeth; first, those belonging to the earlier years
of childhood, called the milk teeth, which are twenty in number and small.
At six or eight years of age, when the jaw expands, and when the growing
body requires a more powerful and numerous set, the roots of {83} the milk
teeth are absorbed, and the latter are "shed," or fall out, one after
another (Fig. 18), to make room for the permanent set.
[Illustration: FIG. 18.--SECTION OF THE JAWS.
1' 2' 3' 4' 5', The Milk Teeth; 1" to 8", The Germs of the Permanent Set.]
[Sidenote: 8, 9. Number of teeth? How distributed?]
8. There are thirty-two teeth in the permanent set, as many being in one
jaw as the other. Each half-jaw has eight teeth, similarly shaped and
arranged in the same order: thus, two incisors, one canine, two bicuspids,
and three molars. The front teeth are small, sharp, and chisel-edged, and
are well adapted for cutting purposes; hence their name incisors. The
canines stand next, one on each side of the jaw; these receive their name
from their resemblance to the long, pointed tusks of the dog (Fig. 19).
{84}
[Illustration: FIG. 19.--SECTION OF THE JAWS--RIGHT SIDE.
V, A, N, Veins, Arteries, and Nerves of the Teeth. The root of one tooth in
each jaw is cut vertically to show the cavity and the blood-vessels, etc.,
within it. 1 to 8, Permanent Teeth.]
9. The bicuspids, next in order, are larger and have a broader crown than
the former; while behind them are the molars, the largest and most powerful
of the entire set. These large back teeth, or "grinders," present a broad,
rough surface, suitable for holding and crushing the food. The third molar,
or "wisdom tooth," is the last to be cut, and does not appear until about
the twenty-first year. {85} The order of arrangement of the teeth is
indicated by the following dental formula:--
[Illustration]
[Sidenote: 10. Different forms of teeth? Human teeth? The inference?]
10. It is interesting, at this point, to notice the different forms of
teeth in different animals, and observe how admirably their teeth are
suited to the respective kinds of food upon which they subsist. In the
_carnivora_, or flesh-feeders, the teeth are sharp and pointed, enabling
them both to seize their prey, and tear it in pieces; while the
_herbivora_, or vegetable-feeders, have broad, blunt teeth, with rough
crowns, suitable for grinding the tough grasses and grains upon which they
feed. Human teeth partake of both forms; some of them are sharp, and others
are blunt; they are therefore well adapted for the mastication of both
flesh and vegetables. Hence we argue that, although man may live
exclusively upon either vegetable or animal food, he should, when possible,
choose a diet made up of both varieties.
[Sidenote: 11. Cleaning of teeth? Effects of not cleaning?]
11. PRESERVATION OF THE TEETH.--In order that the teeth shall remain in a
sound and serviceable condition, some care is of course requisite. In the
first place, they require frequent cleansing; for every time we take food,
some particles of it remain in the mouth; and these, on account of the heat
and moisture present, soon begin to putrefy. This not only renders the
breath very offensive, but promotes decay of the teeth. {86}
[Sidenote: 12. Effects upon the saliva? Formation of tartar? How prevented?
How destroyed?]
12. The saliva, or moisture of the mouth, undergoes a putrefactive change,
and becomes the fertile soil in which a certain minute fungus has its
growth. This fluid, too, if allowed to dry in the mouth, collects upon the
teeth in the form of an unsightly, yellow concretion, called tartar. To
prevent this formation, and to remove other offensive substances, the teeth
should be frequently cleaned with water, applied by means of a soft
tooth-brush. The destruction of the tartar fungus is best effected by the
use of a weak solution of carbolic acid.
[Sidenote: 13. Destruction of the enamel? How guarded against?]
13. Again, it should be borne in mind that the enamel, Nature's protection
for the teeth, when once destroyed, is not formed anew; and the body of the
tooth thus exposed, is liable to rapid decay. On this account, certain
articles are to be guarded against; such as sharply acid substances that
corrode the enamel, and hard substances that break or scratch it--as gritty
tooth powders, metal tooth picks, and the shells of hard nuts. Sudden
alternations from heat to cold, when eating or drinking, also tend to crack
the enamel.
[Sidenote: 14. Mixing of food with the saliva? What is the saliva? How
secreted? The salivary glands?]
14. INSALIVATION.--When the morsel of food is cut and ground by the teeth,
it is at the same time also intimately mixed with the saliva, or fluids of
the mouth. This constitutes the second step of digestion, and is called
insalivation. The saliva, the first of the digestive solvents, is a
colorless, watery, and frothy fluid. It is secreted (_i. e._ separated from
the blood) partly by the mucous membrane which lines the mouth; but chiefly
by the salivary glands, of which there are three pairs situated near the
mouth.
[Sidenote: 15. The flow of saliva? The thought of food? Anxiety and grief?
Animals fed upon dry and coarse food?]
{87} 15. These glands consist of clusters of very small pouches, around
which a delicate network of blood-vessels is arranged: they empty into the
mouth by means of little tubes, or ducts. The flow from these glands is at
all times sufficient to maintain a soft and moist condition of the tongue
and mouth; but when they are excited by the presence and taste of food,
they pour forth the saliva more freely. Even the mere thought of food will
at times cause the saliva to flow, as when the appetite is stimulated by
the sight or smell of some savory article; so that the common expression is
correct that "the mouth waters" for the favorite articles of food. Anxiety
and grief prevent its flow, and cause "the tongue to cleave to the roof of
the mouth." In the horse and other animals, that feed upon dry and coarse
fodder, and require an abundant supply of saliva, we find large salivary
glands, as well as powerful muscles of mastication.
[Illustration: FIG. 20.--STRUCTURE OF A SALIVARY GLAND.]
[Illustration: FIG. 21.--THE HEAD OF A HORSE, showing the large salivary
gland (_a_), its duct (_b_), the muscles of mastication (_c_, _d_, _e_,
_f_, and _g_).]
[Sidenote: 16. Importance of the process? The first place? The second? The
third?]
16. The mingling of the saliva with the food seems a simple process, but it
is one that plays an important part {88} in digestion. In the first place,
it facilitates the motions of mastication, by moistening the food and
lubricating the various organs of the mouth. Secondly, it prepares the way
for other digestive acts: by the action of the teeth, the saliva is forced
into the solid food, softens the harder substances, and assists in
converting the whole morsel into a semi-solid, pulpy mass, that can be
easily swallowed, and readily permeated by other digestive fluids. The
saliva also, by dissolving certain substances, as sugar and salt, develops
the peculiar taste of each; whereas, if the tongue be dry and coated, they
are tasteless. Hence, if substances are insoluble, they are devoid of
taste.
[Sidenote: 17. Its final importance? Starch? How effected? Ptyalin?]
17. Finally, the saliva has the property of acting chemically upon the
food. As we have before stated (Chap. IV.), starch, as starch, cannot enter
the tissues of the body; but, in order to become nutriment, must first be
changed to grape sugar. This change is, in part, effected by the saliva,
and takes place almost instantly, whenever it comes in contact with cooked
starch. This important function is due to an organic ingredient of the
saliva called _ptyalin_. This substance has been extracted from the saliva
by the chemist, and has been found, by experiment, to convert into sugar
two thousand times its own weight of starch.
[Sidenote: 18. Each of the processes? Why is a knowledge of the digestive
functions important? How shown?]
18. IMPORTANCE OF MASTICATION AND INSALIVATION.--Each of these processes
complements the other, and makes the entire work available; for, by their
joint action, they prepare the food in the best possible manner for further
digestive changes. The knowledge of these preliminary functions will appear
the more important, when we reflect that they are the only ones which we
can regulate by the will. For, as soon as the act of swallowing begins, the
food not only passes out of sight, but beyond {89} control; and the
subsequent acts of digestion are consequently involuntary and unconsciously
performed.
[Sidenote: 19. Rapid eating? Describe the process and effects.]
19. It is generally known that rapid eating interferes with digestion. How
does this occur? In the first place, in rapid eating, the flow of the
saliva is insufficient to moisten the solid parts of the food, so that they
remain too hard and dry to be easily swallowed. This leads to the free and
frequent use of water, or some other beverage, at meals, to "wash down" the
food,--a most pernicious practice. For these fluids, not only cannot take
the place of the natural digestive juices, but, on the contrary, dilute and
weaken them.
[Sidenote: 20. Loss of taste? Another effect of rapid eating? Mistakes?]
20. Secondly, the saliva being largely the medium of the sense of taste,
the natural flavors of the food are not developed, and consequently it
appears comparatively insipid. Hence the desire for high-seasoned food, and
pungent sauces, that both deprave the taste and over excite the digestive
organs. Rapid eating also permits the entrance of injurious substances
which may escape detection by the taste, and be unconsciously received into
the system. In some instances, the most acrid and poisonous substances have
frequently been swallowed "by mistake," before the sense of taste could
act, and demand their rejection.
[Sidenote: 21. Effect of imperfectly broken food in the stomach? Dyspepsia?
Overeating?]
21. Thirdly, the food, being imperfectly broken up by the teeth, is hurried
onward to the stomach, to be by it more thoroughly divided. But the task
thus imposed upon the stomach, it is not at all adapted to perform; so that
the crude masses of food remain a heavy burden within the stomach, and a
source of distress to that organ, retarding the performance of its
legitimate duty. Hence persons who habitually eat too rapidly, frequently
fall victims to dyspepsia. Rapid eating also conduces to overeating. The
food is introduced so rapidly, that the system has not {90} time to
recognize that its real wants are met, and that its losses have been made
good; and hence the appetite continues, although more nutriment has been
swallowed than the system requires, or can healthfully appropriate.
[Illustration: FIG. 22.--SECTION OF CHEST AND ABDOMEN.
A, Heart. B, The Lungs. C, Stomach. D, The Liver. E, Large Intestine.
G, Small Intestine.]
[Sidenote: 22. Gullet? Describe the stomach and its location. Effects of
gormandizing?]
22. THE STOMACH.--As soon as each separate portion of food is masticated
and insalivated, it is swallowed; that is, it is propelled downward to the
stomach, through a narrow muscular tube about nine inches in length, called
the _oesophagus_, or gullet (Fig. 23). The stomach is the only large
expansion of the digestive canal, and is the most important organ of
digestion. It is a hollow, pear-shaped pouch, having a capacity of three
pints, in the adult. Its walls are thin and yielding, and may become
unnaturally distended, as in the case of those who subsist on a bulky,
innutritious diet, and of those who habitually gormandize.
[Sidenote: 23. Heart-orifice? Gatekeeper? Coins, etc.? Indication of the
soft and yielding texture of the stomach?]
23. The stomach has also two openings; that by which food enters, being
situated near the heart, is called the _cardiac_, or heart orifice; the
other is the _pylorus_, or "gatekeeper," which guards the entrance to the
intestines, {91} and, under ordinary circumstances, permits only such
matters to pass it as have first been properly acted upon in the stomach.
Coins, buttons, and the like are, however, readily allowed to pass, because
they can be of no use if retained. The soft and yielding texture of this
organ--the stomach--indicates that it is not designed to crush and
comminute solid articles of food.
[Illustration: FIG. 23.--THE ORGANS OF DIGESTION.
O, Oesophagus. S, Stomach. L, Liver. M, Pylorus. C, Large Intestines.
P, Pancreas. I, Small Intestines. N, Spleen. G, Gall-bladder. ]
[Sidenote: 24. What is meant by the gastric juice?]
24. THE GASTRIC JUICE.--We have seen how the presence of food in the mouth
excites the salivary glands, causing the saliva quickly to flow. In the
same manner, when food reaches the stomach, its inner lining, the mucous
membrane, is at once excited to activity. (At first its surface, which
while the stomach is empty presents a pale pink hue, turns to a bright red
color, for the minute blood-vessels which course through it, are filled
with blood. Presently a clear, colorless, and acid fluid exudes, drop by
drop, from its numerous minute glands or "tubules," until finally the
surface is moistened in every part, and the fluid begins to mingle with the
food. This fluid is termed the gastric juice. {92}
[Sidenote: 25. What is the office of the gastric juice? Acidity of the
gastric juice? Quantity of gastric juice used? What becomes of it?]
25. The gastric juice is the proper solvent of certain articles of food,
especially those belonging to the albuminoid class. This solvent power is
due to its peculiar ingredient, _pepsin_; in digestion, this substance acts
like a ferment; that is, it induces changes in the food simply by its
presence, but does not itself undergo change. The acidity of the gastric
juice, which is due to _lactic acid_, is not accidental; for we find that
the pepsin cannot act in an alkaline solution--that is, one which is not
acid or neutral. The quantity of gastric juice secreted daily is very
large, probably not less than three or four pints at each meal. Though this
fluid is at once used in the reduction of the food, it is not lost; since
it is soon re-absorbed by the stomach, together with those parts of the
food which it has digested and holds in solution.
[Sidenote: 26. Muscular coat of the stomach? Expansion and contraction of
its fibres? Action of the fibres?]
26. MOVEMENTS OF THE STOMACH.--The inner coating of the stomach is the
mucous membrane, which, as we have seen, furnishes the gastric juice. Next
to this coating lies another, called the muscular coat, composed of
involuntary muscular fibres, some of which run circularly, and others in a
longitudinal direction. These expand to accommodate the food as it is
introduced, and contract as it passes out. In addition, these fibres are in
continual motion while food remains in the stomach, and they act in such
manner that the contents are gently turned round from side to side, or from
one end of it to the other.
[Sidenote: 27. Peristaltic movements? What is said of our consciousness of
and power over these movements? Describe the movements of the pylorus.]
27. By these incessant movements of the stomach, called the _peristaltic_
movements, the gastric juice comes in contact with all parts of the food.
We are, however, not conscious that these movements take place, nor have we
the power to control them. When such portions of the food as are
sufficiently digested approach the pylorus, it {93} expands to allow them
to pass out, and it closes again to confine the residue for further
preparation.
[Sidenote: 28. How has the knowledge and the workings of the stomach been
ascertained? St. Martin? How else?]
28. The knowledge of these and other interesting and instructive facts has
been obtained by actual observation; the workings of the stomach of a
living human being have been laid open to view and examined--the result of
a remarkable accident. Alexis St. Martin, a Canadian _voyageur_, received a
gun-shot wound which laid open his stomach, and which, in healing, left a
permanent orifice nearly an inch in diameter. Through this opening the
observer could watch the progress of digestion, and experiment with
different articles of food. Since that occurrence, artificial openings into
the stomach of the inferior animals have been repeatedly made, so that the
facts of stomach-digestion are very well ascertained and verified.
[Sidenote: 29. What was formerly thought? What do we now know? What else do
we now know? Water, salt, and sugar? Absorption?]
29. GASTRIC DIGESTION.--What portions of the food are digested in the
stomach? It was formerly thought that all the great changes of digestion
were wrought here, but later investigation has taught us better. We now
know that the first change in digestion takes place in the mouth, in the
partial conversion of starch into sugar. We also know that, of the three
organic food principles (considered in Chapter IV.) two--the fats and the
sugars--are but slightly affected by the stomach; but that its action is
confined to that third and very important class, from which the tissues are
renewed, the albuminoids. A few articles need no preparation before
entering the system, as water, salt, and grape-sugar. These are rapidly
taken up by the blood-vessels of the stomach, which everywhere underlie its
mucous membrane in an intricate and most delicate network. In this way the
function of absorption begins.
[Sidenote: 30. Albuminose? The process? Chyme?]
30. The albuminoid substances are speedily attacked and {94} digested by
the gastric juice. From whatever source they are derived, vegetable or
animal, they are all transformed into the same digestive product, called
_albuminose_. This is very soluble in water, and is readily absorbed by the
blood-vessels of the stomach. After a longer or shorter time, varying from
one to five hours, according to the individual and the quantity and quality
of his food, the stomach will be found empty. Not only has the digested
food passed out, but also those substances which the stomach could not
digest or absorb have passed little by little through the pylorus, to
undergo further action in the intestines. At the time of its exit, the
digested food is of a pulpy consistence, and dark color, and is then known
as the _chyme_.
[Sidenote: 31. What are the intestines? The small intestines? The large
intestines? Their structure?]
31. THE INTESTINES.--The intestines, or "bowels," are continuous with the
stomach, and consist of a fleshy tube, or canal, twenty-five feet in
length. The small intestine, whose diameter is about one inch and a half,
is twenty feet long and very tortuous. The large intestine is much wider
than the former, and five feet long (Fig. 23). The general structure of
these organs resembles that of the stomach. Like it, they are provided with
a mucous membrane, or inner lining, whence flow their digestive juices;
and, just outside of this, a muscular coat, which propels the food onward
from one point to another.
[Sidenote: 32. Peritoneum? The work of digestion?]
32. Moreover, both the intestines and stomach are enveloped in the folds of
the same outer tunic or membrane, called the _peritoneum_. This is so
smooth and so well lubricated, that the intestines have the utmost freedom
of motion. In the small intestines, the work of digestion is completed, the
large intestine receiving from them the indigestible residue of the food,
and in time expelling it from the body.
[Sidenote: 33. The presence of food in the intestines? Bile?]
33. INTESTINAL DIGESTION.--As soon as the food passes the pylorus and
begins to accumulate in the upper {95} part of the intestines, it excites
the flow of a new digestive fluid, which enters through a small tube, or
_duct_, about three inches below the stomach. It is formed by the union of
two distinct fluids--the _bile_ and the _pancreatic_ juice. The bile is
secreted by the liver, which is the largest gland of the body, and is
situated on the right side and upper part of the abdomen (Fig. 22). The
bile is constantly formed, but it flows most rapidly during digestion.
During the intervals of digestion it is stored in the _gall-bladder_, a
small membranous bag attached to the under side of the liver. This fluid is
of a greenish-yellow color, having a peculiar smell, and a very bitter
taste.
[Sidenote: 34. The pancreatic juice? The joint action of these fluids?]
34. The pancreatic juice is the product of a gland called the _pancreas_,
situated behind the stomach. This fluid is colorless, viscid, and without
odor. Like the digestive juices previously described, it owes its solvent
power to its peculiar ferment principle, called _pancreatin_. By the joint
action of these fluids, the fatty parts of the food are prepared for
absorption. By previous steps of digestion the fats are merely separated
from the other components of the food; but here, within the intestines,
they are reduced to a state of minute division, or _emulsion_, resembling
the condition of butter in milk, before it has been churned. There results
from this action a white and milky fluid, termed the _chyle_, which holds
in solution the digestible portions of the food, and is spread over the
extensive absorbent surface of the small intestines.
[Sidenote: 35. The mucous membrane? Experiments on inferior animals?]
35. The mucous membrane of the intestines, also, secretes or produces, a
digestive fluid by means of numerous "follicles," or minute glands; this is
called the intestinal juice. From experiments on the inferior animals, it
has been ascertained that this fluid exerts a solvent influence over each
of the three organic food principles, and in this way may supplement and
complete the action of the {96} fluids previously mentioned, viz.:--of the
saliva in converting starch into sugar, of the gastric juice in digesting
the albuminoids, and of the pancreatic juice and bile in emulsifying the
fats.
[Sidenote: 36, 37. How much thus far has been done with the food? The next
process? Give the first way.]
36. ABSORPTION.--With the elaboration of the chyle, the work of digestion
is completed; but, in a certain sense, the food is yet outside of the body;
that is, the blood is not yet enriched by it, and it is not in a position
to nourish the tissues. The process by which the liquefied food passes out
of the alimentary canal into the blood is called absorption. This is
accomplished in two ways; first, by the _blood-vessels_. We have seen how
the inner membrane of the stomach is underlaid by a tracery of minute and
numerous vessels, and how some portions of the food are by them absorbed.
The supply of blood-vessels to the intestines is even greater; particularly
to the small intestines, where the work of absorption is more actively
carried on.
37. The absorbing surface of the small intestines, if considered as a plane
surface, amounts to not less than half a square yard. Besides, the mucous
membrane is formed in folds with an immense number of thread-like
prolongations, called _villi_, which indefinitely multiply its absorbing
capacity. These minute processes, the villi, give the surface the
appearance and smoothness of velvet; and during digestion, they dip into
the canal, and, by means of their blood-vessels, absorb its fluid contents,
just as the _spongioles_ which terminate the rootlets of plants, imbibe
moisture from the surrounding soil.
[Sidenote: 38. How is absorption effected in another way? Describe it. Name
of the lacteals? Thoracic duct?]
38. Secondly, absorption is also effected by the _lacteals_, a set of
vessels peculiar to the small intestines. These have their beginnings in
the little villi just mentioned, side by side with the blood-vessels. These
two sets of absorbents run in different courses, but their destination is
the same, {97} which is the right side of the heart. The lacteals receive
their name from their milky-white appearance. After a meal containing a
portion of fat, they are then distended with chyle, which they are
specially adapted to receive: at other times they are hardly discernible.
The lacteals all unite to form one tube, the _thoracic duct_, which passes
upward through the _thorax_, or chest, and empties into a large vein,
situated just beneath the left collar-bone.
[Illustration: FIG. 24.--THE LACTEALS.
A, Small Intestine. B, Lacteals. C, Thoracic Duct. D, Absorbents.
E, Blood-vessel. ]
[Sidenote: 39. The absorbents? Lymph? What further of the lymph?]
39. THE ABSORBENTS.--The lacteals belong to a class of vessels known as
absorbents, or lymphatics, which ramify in nearly all parts of the body,
except the brain and spinal cord. The fluid which circulates through the
lymphatics of the limbs, and all the organs not concerned in digestion, is
called _lymph_. This fluid is clear and colorless, like water, and thus
differs from the milky chyle which the lacteals carry after digestion: it
consists chiefly of the watery part of the blood, which was not required by
the tissues, and is returned to the blood by the absorbents or lymphatics.
[Sidenote: 40. What can you state as to the time required for digestion?]
40. CIRCUMSTANCES AFFECTING DIGESTION.--What length of time is required for
the digestion of food? From observations made, in the case of St. Martin,
the Canadian {98} already referred to, it has been ascertained that, at the
end of two hours after a meal, the stomach is ordinarily empty. How much
time is needed to complete the digestion of food, within the small
intestines, is not certain; but, from what we have learned respecting their
functions, it must be evident that it largely depends upon the amount of
starch and fat which the food contains.
[Sidenote: 41. Circumstances affecting duration of digestion? Fresh food?]
41. In addition to the preparations which the food undergoes in cooking,
which we have already considered, many circumstances affect the duration of
digestion; such as the quality, quantity, and temperature of the food; the
condition of the mind and body; sleep, exercise, and habit. Fresh food,
except new bread and the flesh of animals recently slain, is more rapidly
digested than that which is stale; and animal food more rapidly than that
from the vegetable kingdom.
[Sidenote: 42. Food in concentrated form? A large quantity of food?
Experiment on the dog? Ice-water? Variety of articles?]
42. Food should not be taken in too concentrated a form, the action of the
stomach being favored when it is somewhat bulky; but a large quantity in
the stomach often retards digestion. If the white of one egg be given to a
dog, it will be digested in an hour, but if the white of eight eggs be
given it will not disappear in four hours. A wineglassful of ice-water
causes the temperature of the stomach to fall thirty degrees; and it
requires a half-hour before it will recover its natural warmth--about a
hundred degrees--at which the operations of digestion are best conducted. A
variety of articles, if not too large in amount, is more easily disposed of
than a meal made of a single article; although a single indigestible
article may interfere with the reduction of articles that are easily
digested.
[Sidenote: 43. Strong emotion? The tongue of the patient?]
43. Strong emotion, whether of excitement or depression, checks digestion,
as do also a bad temper, anxiety, long fasting, and bodily fatigue. The
majority of these {99} conditions make the mouth dry, that is, they
restrain the flow of the saliva; and without doubt they render the stomach
dry also, by preventing the flow of the gastric juice. And, as a general
rule, we may decide, from a parched and coated tongue, that the condition
of the stomach is not very dissimilar, and that it is unfit for the
performance of digestive labor. This is one of the points which the
physician bears in mind when he examines the tongue of his patient.
[Sidenote: 44. Eating between meals? Severe exercise? Sleep after meals?]
44. The practice of eating at short intervals, or "between meals," as it is
called, has its disadvantage, as well as rapid eating and over-eating,
since it robs the stomach of its needed period of entire rest, and thus
overtasks its power. With the exception of infants and the sick, no persons
require food more frequently than once in four hours. Severe exercise
either directly before or directly after eating retards digestion; a period
of repose is most favorable to the proper action of the stomach. The
natural inclination to rest after a hearty meal may be indulged, but should
not be carried to the extent of sleeping; since in that state the stomach,
as well as the brain and the muscles, seeks release from labor.
{100}
QUESTIONS FOR TOPICAL REVIEW.
PAGE
1. What do you understand by nutrition? 80
2. How is the process of nutrition carried on? 80
3. What further can you state on the subject? 80, 81
4. Describe the general plan of digestion. 81
5. How is the process of mastication carried on? 80, 82
6. State what you can in relation to the formation of the
teeth. 82, 86
7. What, in relation to their arrangement? 83, 84
8. What, in relation to the process of "shedding?" 82, 83, 84
9. In relation to the different forms of teeth in different
animals? 85
10. What causes operate to injure or destroy the teeth? 85, 86
11. What suggestions and directions are given for the
preservation of the teeth? 85, 86
12. What do you understand by insalivation? 80, 86
13. How is the process of insalivation carried on? 86, 87, 88
14. Of what importance is the saliva to the process? 87, 88
15. Of what importance are mastication and insalivation? 88, 89
16. Describe the consequences of rapid eating. 89, 90
17. What becomes of the food directly after it has undergone
mastication and insalivation? 90
18. Describe the location and formation of the stomach. 90, 91, 92
19. Describe the process by which the gastric juice is formed. 91
20. What are the properties and uses of the gastric juice? 92
21. What are the movements of the stomach, and what their
uses? 92, 93
22. What further can you state on the subject? 93
23. What portions of the food are digested in the stomach? 93, 94
24. What are the first changes of digestion? 93
25. Describe the location and formation of the stomach. 94
26. What further can you state in relation to the stomach? 94
27. Describe the process of intestinal digestion. 94, 95, 96
28. What do you understand by absorption? 80, 96
29. How is the process of absorption effected? 96, 97
30. What are the lacteals and of what use are they? 96, 97
31. What length of time is required for the digestion of
food? 97, 98
32. What circumstances, of food, affect digestion? 98
33. What circumstances, of emotion, affect digestion? 98, 99
34. What suggestions and directions are given upon the subject of
eating and drinking? 98, 99
* * * * *
[Illustration: CIRCULATION OF THE BLOOD.
[Heart, Lungs, Arteries & Veins.]
{101}
CHAPTER VII.
THE CIRCULATION.
_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._
[Sidenote: 1. What is required by every living organism? In plants?
Insects? Reptiles? Man?]
1. THE BLOOD.--Every living organism of the higher sort, whether animal or
vegetable, requires for the maintenance of life and activity, a circulatory
fluid, by which nutriment is distributed to all its parts. In plants, this
fluid is the sap; in insects, it is a watery and colorless blood; in
reptiles and fishes, it is red but cold blood; while in the nobler animals
and man, it is the red and warm blood.
[Sidenote: 2. Importance and abundance of blood? Dependence of life? Abel?
Mosaic law? In what part of the body is blood not found? Quantity of blood
in the body?]
2. The blood is the most important, as it is the most abundant, fluid of
the body; and upon its presence, under certain definite conditions, life
depends. On this account it is frequently, and very properly, termed "the
vital fluid." The importance of the blood, as essential to life, was
recognized in the earliest writings. In the narration of the death of the
murdered Abel, it is written, "the voice of his _blood_ crieth from the
ground." In the Mosaic law, proclaimed over thirty centuries ago, the
Israelites were forbidden to eat food that contained blood, for the reason
that "the life of the flesh is in the blood." With the exception of a few
tissues, such as the hair, the nails, and the _cornea_ of the eye, blood
everywhere pervades the body, as may be proven by puncturing any part with
a {102} needle. The total quantity of blood in the body is estimated at
about one-eighth of its weight, or eighteen pounds.
[Sidenote: 3. Color of blood? Its consistence? Odor?]
3. The color of the blood, in man and the higher animals, as is well known,
is red; but it varies from a bright scarlet to a dark purple, according to
the part whence it is taken. "Blood is thicker than water," as the adage
truly states, and has a glutinous quality. It has a faint odor, resembling
that peculiar to the animal from which it is taken.
[Sidenote: 4. What is stated of the blood as viewed under the microscope?]
4. When examined under the microscope, the blood no longer appears a simple
fluid, and its color is no longer red. It is then seen to be made up of two
distinct parts: first, a clear, colorless fluid, called the _plasma_; and
secondly, of a multitude of minute solid bodies, or corpuscles, that float
in the watery plasma. The plasma, or nutritive liquid, is composed of water
richly charged with materials derived from the food, viz., albumen, which
gives it smoothness and swift motion; fibrin; certain fats; traces of
sugar; and various salts.
[Illustration: FIG 25.--THE BLOOD CORPUSCLES.]
[Sidenote: 5. State what you can of the little bodies called corpuscles.]
5. THE BLOOD CORPUSCLES.--In man, these remarkable "little bodies," as the
word _corpuscles_ signifies, are of a yellow color, but by their vast
numbers impart a red hue to the blood. They are very small, having a
diameter of about 1/3500 of an inch, and being one-fourth of that fraction
in thickness; so that if 3,500 of them were placed in line, side by side,
they would only extend one inch; or, if {103} piled one above another, it
would take at least 14,000 of them to stand an inch high. Although so small
in size, they are very regular in form. As seen under the microscope, they
are not globular or spherical, but flat, circular, and disc-like, with
central depressions on each side, somewhat like a pearl button that has not
been perforated. In freshly-drawn blood they show a disposition to arrange
themselves in little rolls like coins (Fig. 25).
[Illustration: FIG. 26.
_a_, Oval Corpuscles of a fowl. _b_, Corpuscles of a frog. _c_, Those of a
shark.
The five small ones at the upper part of the figure, represent the human
corpuscles magnified 400 times.]
[Sidenote: 6. The size and shape of corpuscles? Why is the fact important?]
6. The size and shape of the blood corpuscles vary in different animals, so
that it is possible to discriminate between those of man and the lower
animals (Fig. 26). This is a point of considerable practical importance.
For example, it is sometimes desirable to decide in a court of justice the
source, whether from man or an inferior animal, of blood stains upon the
clothing of an accused person, or upon some deadly weapon. This may be done
by a microscopical examination of a minute portion of the dried stain,
previously refreshed by means of gum-water. Certain celebrated cases are
recorded in which the guilt of criminals has been established, and they
have been condemned and punished upon the evidence which science rendered
on this single point, the detecting of the human from other blood.
[Sidenote: 7. The character of the blood of dead animals? Means of
detecting such blood?]
7. The character of the blood of dead, extinct, and even fossil animals,
such as the mastodon, has been ascertained by obtaining and examining
traces of it which had been shut up, perhaps for ages, in the circulatory
canals of bone. A means of detecting blood in minute quantities is found
{104} in the spectroscope, the same instrument by which the constitution of
the heavenly bodies has been studied. If a solution containing not more
than one-thousandth part of a grain of the coloring matter of the
corpuscle, be examined, this instrument will detect it.
[Sidenote: 8. White corpuscles? Total number of corpuscles in the body?]
8. The corpuscles, just described, are known as the red blood corpuscles.
Besides these, and floating along in the same plasma, are the white
corpuscles. These are fewer in number, but larger and globular in form.
They are colorless, and their motion is less rapid than that of the other
variety. The total number of both varieties of these little bodies in the
blood is enormous. It is calculated that in a cubic inch of that fluid
there are eighty-three millions, and at least five hundred times that
number in the whole body.
[Sidenote: 9. The blood in its natural condition in the body? Describe the
process by which the coagulation of blood takes place?]
9. COAGULATION.--The blood, in its natural condition in the body, remains
perfectly fluid; but, within a few minutes after its removal from its
proper vessels, whether by accident or design, a change takes place. It
begins to coagulate, or assume a semi-solid consistence. If allowed to
stand, after several hours it separates into two distinct parts, one of
them being a dark red jelly, the coagulum, or clot, which is heavy and
sinks; and the other, a clear, straw-colored liquid, called serum, which
covers the clot. This change is dependent upon the presence in the blood of
fibrin, which possesses the property of solidifying under certain
circumstances; one of these circumstances being when the blood is separated
from living tissues. The color of the clot is due to the entanglement of
the corpuscles with the fibrin.
[Sidenote: 10. If coagulation were impossible? How is it in fact?]
10. In this law of the coagulation of the blood is our safeguard against
death by hæmorrhage, or against undue loss of blood. If coagulation were
impossible, the {105} slightest injury in drawing blood would prove fatal.
Whereas now, in vastly the larger proportion of cases, bleeding ceases
spontaneously, because the blood, as it coagulates, stops the mouths of the
injured blood-vessels. In another class of cases, where larger vessels are
cut or torn, it is simply necessary to close them by a temporary pressure;
for in a few minutes the clot will form and seal them up. In still more
serious cases, where the blood-vessel is of large size, the surgeon is
obliged to tie a "ligature" about it, and thus prevent the force of the
blood-current from washing away the clots, which, forming within and around
the vessel, would close it effectually.
[Sidenote: 11. What is worthy of remark? Coagulation of the blood of
inferior animals? Of the blood of birds?]
11. It is worthy of remark that this peculiarity is early implanted in the
blood, even before birth, and in advance of any existing necessity for it;
thus anticipating and guarding against danger. But this is not all. Of most
of the inferior animals, which, as compared with man, are quite helpless,
the blood coagulates more rapidly, and in the case of the birds, almost
instantly. The relative composition of fluid and coagulated blood may be
thus represented:
_Fluid Blood._ _Coagulated Blood._
Plasma----------Serum---------Serum
\
\
--------Fibrin--------
\
\
Corpuscles------Corpuscles-------Clot.
[Sidenote: 12. The blood, as a provider and purifier? What uses does the
blood subserve? Experiments? Transfusion?]
12. THE USES OF THE BLOOD.--The blood is the great provider and purifier of
the body. It both carries new materials to all the tissues, and removes the
worn out particles of matter. This is effected by the plasma. It both
conveys oxygen and removes carbonic acid. This is done through the
corpuscles. Some singular experiments have {106} been tried to illustrate
the life-giving power of the blood. An animal that has bled so freely as to
be at the point of dying, is promptly brought back to life by an operation
called transfusion, by which fresh blood from a living animal is injected
into the blood-vessels of his body.
[Sidenote: 13. The case of the deaf and feeble dog? Horse? Dead dog?]
13. It is related that a dog, deaf and feeble from age, had hearing and
activity restored to him by the introduction into his veins of blood taken
from a young dog; and, that a horse, twenty-six years old, having received
the blood of four lambs acquired new vigor. And further, that a dog, just
dead from an acute disease, was so far revived by transfusion, as to be
able to stand and make a few movements.
[Sidenote: 14. Transfusion, as a fashionable remedy? What further of
transfusion?]
14. Transfusion has been practised upon man. At one time, shortly after
Harvey's discovery of the "Circulation of the Blood," it became quite a
fashionable remedy, it being thought possible by it to cure all forms of
disease, and even to make the old young again. But these claims were soon
found extravagant, and many unhappy accidents occurred in its practice; so
that being forbidden by government and interdicted by the Pope, it rapidly
fell into disuse. At the present time, however, it is sometimes resorted to
in extreme cases, when there has been a great and rapid loss of blood; and
there are upon record several instances where, other means having failed,
life has been restored or prolonged by the operation of transfusion.
[Sidenote: 15. The seat of the reviving power of the blood? What further is
related?]
15. This reviving power of the blood seems to reside in the corpuscles; for
transfusion, when attempted to be performed with the serum alone, has, in
every case, proved fruitless. Now, though so much depends upon the blood
and its corpuscles, it is a mistake to suppose that in them alone is the
seat of life, or that they are, in an exclusive manner, alive. All the
organs and parts of the body are mutually dependent one upon the other; and
the complete usefulness {107} of the blood, or of any other part, flows out
of the harmonious action of all the parts.
[Sidenote: 16. Changes in the blood? What further is stated?]
16. CHANGE OF COLOR.--The blood undergoes a variety of changes in its
journey through the system. As it visits the different organs it both gives
out and takes up materials. In one place it is enriched, in another it is
impoverished. By reason of these alterations in its composition, the blood
also changes its color. In one part of the body it is bright red, or
arterial; in another it is dark blue, or venous. In the former case it is
pure and fit for the support of the tissues; in the latter, it is impure
and charged with effete materials. (The details of the change from dark to
bright will be given in the chapter on Respiration.)
[Sidenote: 17. Motion of the blood? What is meant by the circulation of the
blood? How confined? Discovery made by Harvey?]
17. CIRCULATION.--The blood is in constant motion during life. From the
heart, as a centre, a current is always setting toward the different
organs; and from these organs a current is constantly returning to the
heart. In this way a ceaseless circular movement is kept up, which is
called the Circulation of the Blood. This stream of the vital fluid is
confined to certain fixed channels, the blood-vessels. Those branching from
the heart are the arteries; those converging to it are the veins. The true
course of the blood was unknown before the beginning of the seventeenth
century. In 1619 it was discovered by the illustrious William Harvey. Like
many other great discoverers, he suffered persecution and loss, but unlike
some of them, he was fortunate enough to conquer and survive opposition. He
lived long enough to see his discovery universally accepted, and himself
honored as a benefactor of mankind.
{108}
[Illustration: FIG. 27.--THE ORGANS OF CIRCULATION.]
{109} [Illustration: FIG. 28.--THE HEART AND LARGE VESSELS.
A, Right Ventricle. B, Left Ventricle. C, Right Auricle. D, Left Auricle.
E, Aorta. F, Pulmonary Artery.]
[Sidenote: 18. Office of the heart? Location of the heart? Its beat? Its
shape? Protection to the heart? What else is said in relation to the
heart?]
18. THE HEART.--The heart is the central engine of the circulation. In this
wonderful little organ, hardly larger than a man's fist, resides that
sleepless force by which, during the whole of life, the current of the
blood is kept in motion. It is placed in the middle and front part of the
chest, inclining to the left side. The heartbeat may be felt and heard
between the fifth and sixth ribs, near the breast-bone. The shape of the
heart is conical, with the apex or point downward and in front. The base,
which is upward, is attached so as to hold it securely in its place, while
the apex is freely moveable. In order that loss of power from friction may
be obviated, the heart is enclosed between two layers of serous membrane,
which forms a kind of sac. This membrane is as smooth as satin, and itself
secretes a fluid in sufficient quantities to keep it at all times well
lubricated. The lining membrane of the heart, likewise, is extremely
delicate and smooth.
{110} [Illustration: FIG. 29.--SECTION OF THE HEART.
A, Right Ventricle. B, Left Ventricle. C, Right Auricle. D, Left Auricle.
E, F, Inlets to the Ventricles. G, Pulmonary Artery. H, Aorta.]
[Sidenote: 19. Formation of the heart? Right and left heart?]
19. THE CAVITIES OF THE HEART.--The heart is hollow, and so partitioned as
to contain four chambers or cavities; two at the base, known as the
_auricles_, from a fancied resemblance to the ear of a dog, and two at the
apex or point, called _ventricles_. An auricle and a ventricle on the same
side, communicate with each other, but there is no opening from side to
side. It is customary to regard the heart as a double organ, and to speak
of its division into the right and left heart. For while both halves act
together in point of time, each half sustains an entirely distinct portion
of the labor of the circulation. Thus, the right heart always carries the
dark or venous blood, and the left always circulates the bright or arterial
blood.
[Sidenote: 20. Capacity of the chambers of the heart? What wise provision
is mentioned? The auricles?]
20. If we examine the heart, we at once notice that though its various
chambers have about the same capacity, the walls of the ventricles are
thicker and stronger than those of the auricles. This is a wise provision,
for it is by the powerful action of the former that the blood is forced to
the most remote regions of the body. The auricles, on the contrary, need
much less power, for they simply discharge their contents into the cavities
of the heart near at hand and below them--into the ventricles. {111}
[Sidenote: 21. Substance of the heart? Its fibres? Its movements? The
advantage of such movements? Action of the heart? Its period of repose?]
21. ACTION OF THE HEART.--The substance of the heart is of a deep red
color, and its fibres resemble those of the voluntary muscles by which we
move our bodies. But the heart's movements are entirely involuntary. The
advantage of this is evident; for if it depended upon us to will each
movement, our entire attention would be thus engaged, and we would find no
time for study, pleasure, or even sleep. The action of the heart consists
in alternate contractions and dilatations. During contraction the walls
come forcibly together, and thus drive out the blood. In dilatation, they
expand and receive a renewed supply. These movements are called _systole_
and _diastole_. The latter may be called the heart's period of repose; and
although it lasts only during two-fifths of a heart-beat, or about a third
of a second, yet during the day it amounts to more than nine hours of total
rest.
[Sidenote: 22. Remarkable property of the tissue of the heart? How shown?
How interesting? In cold-blooded animals? Heart of a turtle? Of a frog?
Alligator?]
22. A remarkable property of the tissue of the heart is its intense
vitality. For while it is more constantly active than any other organ of
the body, it is the last to part with its vital energy. This is especially
interesting in view of the fact that after life is apparently extinguished,
as from drowning, or poisoning by chloroform, there yet lingers a spark of
vitality in the heart, which, by continued effort, may be fanned into a
flame so as to revivify the whole body. In cold-blooded animals this
irritability of the heart is especially remarkable. The heart of a turtle
will pulsate, and the blood circulate for a week after its head has been
cut off; and the heart will throb regularly many hours after being cut out
from the creature's chest. The heart of a frog or serpent, separated
entirely from the body, will contract at the end of ten or twelve hours:
that of an alligator has been known to beat twenty-eight hours after the
death of the animal. {112}
[Sidenote: 23. Course of the blood through the heart? Course of
heart-currents?]
23. PASSAGE OF THE BLOOD THROUGH THE HEART.--Let us now trace the course of
the blood through the several cavities of the heart. In the first place,
the venous blood, rendered dark and impure by contact with the changing
tissues of the body, returns to the right heart by the veins. It enters and
fills the right auricle during its dilatation: the auricle then contra
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