Hygienic Physiology
by
Joel Dorman Steele
Part 1 out of 7
Richard Prairie, Charles Franks and the Online Distributed Proofreading Team
[Illustration]
PATHFINDER PHYSIOLOGY No. 3
HYGIENIC PHYSIOLOGY
WITH SPECIAL REFERENCE TO THE USE OF
ALCOHOLIC DRINKS AND NARCOTICS
BEING A REVISED EDITION OF THE
FOURTEEN WEEKS IN HUMAN PHYSIOLOGY
BY JOEL DORMAN STEELE, PH.D.
ENLARGED EDITION WITH SELECTED READINGS
_Edited for the use of Schools, in accordance with the recent
Legislation upon Temperance Instruction_
INDORSEMENT.
BOSTON, _June_ 20, 1889.
The Pathfinder Series of Text-books on Anatomy, Physiology, and Hygiene
consists of the following volumes:
I. Child's Health Primer (for Primary Grades).
II. Hygiene for Young People or, Young People's Physiology. (for
Intermediate Classes)
III. Hygienic Physiology (for Advanced Pupils).
The above are the series originally prepared (as their general title
indicates) to supply the demand created by the laws for temperance
instruction in public schools in the United States. They were written by
experts under the supervision of the Scientific Department of the National
Woman's Christian Temperance Union, published by the instigation of the
same, and have been carefully revised from time to time, under the same
supervision, to keep them abreast with the latest teachings of science.
Being both teachable and well adapted to grade, their educational value,
as proven by schoolroom tests, is of the highest order. We therefore
cordially indorse and highly recommend the Pathfinder Series for use in
schools.
MARY H. HUNT,
_National and International Superintendent of the Scientific Dep't of
the Woman's Christian Temperance Union; Life Director of the National
Educational Association._
ADVISORY BOARD:
JOSEPH COOK, WILLIAM E. SHELDON, ALBERT H. PLUMB, D.D., DANIEL DORCHESTER,
D.D.
PREFACE
The term Physiology, or the science of the functions of the body, has come
to include Anatomy, or the science of its structure, and Hygiene, or the
laws of health; the one being essential to the proper understanding of
physiology, and the other being its practical application to life. The
three are intimately blended, and in treating of the different subjects
the author has drawn no line of distinction where nature has made none.
This work is not prepared for the use of medical students, but for the
instruction of youth in the principles which underlie the preservation of
health and the formation of correct physical habits. All else is made
subservient to this practical knowledge. A simple scientific dress is used
which, while conducing to clearness, also gratifies that general desire of
children to know something of the nomenclature of any study they pursue.
To the description of each organ is appended an account of its most common
diseases, accidents, etc., and, when practicable, their mode of treatment.
A pupil may thus learn, for example, the cause and cure of "a cold," the
management of a wound, or the nature of an inflammation.
The Practical Questions, which have been a prominent feature in other
books of the series, will be found, it is hoped, equally useful in this
work. Directions for preparing simple microscopic objects, and
illustrations of the different organs, are given under each subject.
The Readings, which represent the ideas but not always the exact
phraseology of the author quoted, have, in general, been selected with
direct reference to Practical Hygiene, a subject which now largely
occupies the public mind. The dangers that lurk in foul air and
contaminated water, in bad drainage, leaky gas pipes, and defective
plumbing, in reckless appetites, and in careless dissemination of
contagious diseases, are here portrayed in such a manner as, it is
trusted, will assist the pupil to avoid these treacherous quicksands, and
to provide for himself a solid path of health.
Under the heading of Health and Disease will be found Hints about the sick
room, Directions for the use of Disinfectants, Suggestions as to what to
do "Till the Doctor comes," and a list of antidotes for Poisons. Questions
for Class Use, a full Glossary, and an ample Index complete the book.
Believing in a Divine Architect of the human form, the author can not
refrain from occasionally pointing out His inimitable workmanship, and
impressing the lesson of a Great Final Cause.
The author has gleaned from every field, at home and abroad, to secure
that which would interest and profit his pupils. In general, Flint's great
work on the "Physiology of Man," an undisputed authority on both sides of
the Atlantic, has been adopted as the standard in digestion, respiration,
circulation, and the nervous system. Leidy's "Human Anatomy," and Sappey's
"Traité d'Anatomie" have been followed on all anatomical questions, and
have furnished many beautiful drawings. Huxley's "Physiology" has afforded
exceedingly valuable aid. Foster's "Text-Book of Physiology," Hinton's
"Health and its Conditions," Black's "Ten Laws of Health," Williams's
practical essay on "Our Eyes and How to Use them," Le Pileur's charming
treatise on "The Wonders of the Human Body," and that quaint volume, "Odd
Hours of a Physician," have aided the author with facts and fancies. The
writings of Draper, Dalton, Carpenter, Yalentin, Mapother, Watson,
Lankester, Letheby, Hall, Hamilton, Bell, Wilson, Bower, Cutter,
Hutchison, Wood, Bigelow, Stille, Holmes, Beigel, and others have been
freely consulted.
PUBLISHERS' NOTE.
An ABRIDGED EDITION of this work is published, to afford a cheaper manual
--adapted to Junior Classes and Common Schools. The abridgment contains
the essence of this text, nearly all its illustrations, and the whole of
the Temperance matter as here presented.
ORDER "HYGIENIC PHYSIOLOGY, ABRIDGED."
READING REFERENCES.
Foster's "Text-Book of Physiology"; Leidy's "Human Anatomy"; Draper's
"Human Physiology"; Dalton's "Physiology and Hygiene"; Cutter's
"Physiology"; Johnston and Church's "Chemistry of Common Life"; Letheby's
"Food"; Tyndall "On Light," and "On Sound"; Mint's "Physiology of Man ";
Rosenthal's "Physiology of the Muscles and Nerves"; Bernstein's "Five
Senses of Man"; Huxley and Youmans's "Physiology and Hygiene"; Sappey's
"Traité d'Anatomie "; Luys's "Brain and its Functions"; Smith's "Foods";
Bain's "Mind and Body"; Pettigrew's "Animal Locomotion"; Carpenter's
"Human Physiology," and "Mental Physiology"; Wilder and Gage's "Anatomy";
Jarvis's "Physiology and Laws of Health."
Hargreaves's "Alcohol and Science"; Richardson's "Ten Lectures on
Alcohol," and "Diseases of Modern Life"; Brown's "Alcohol"; Davis's
"Intemperance and Crime"; Pitman's "Alcohol and the State"; "Anti-
Tobacco"; Howie's "Stimulants and Narcotics"; Hunt's "Alcohol as Food or
Medicine"; Schützenberger's "Fermentation"; Hubbard's "Opium Habit and
Alcoholism"; Trouessart's "Microbes, Ferments, and Molds."
CONTENTS
INTRODUCTION
I.--THE SKELETON
THE HEAD
THE TRUNK
THE LIMBS
II.--THE MUSCLES
III.--THE SKIN
THE HAIR AND THE NAILS
THE TEETH
IV.--RESPIRATION AND THE VOICE
V.--THE CIRCULATION
THE BLOOD
THE HEART
THE ARTERIES
THE VEINS
VI.--DIGESTION AND FOOD
VII.--THE NERVOUS SYSTEM
THE BRAIN
THE SPINAL CORD AND THE NERVES
THE SYMPATHETIC SYSTEM
VIII.--THE SPECIAL SENSES
TOUCH
TASTE
SMELL
HEARING
SIGHT
IX.--HEALTH AND DISEASE.--DEATH AND DECAY
1. HINTS ABOUT THE SICK ROOM
2. DISINFECTANTS
3. WHAT TO DO "TILL THE DOCTOR COMES"
4. ANTIDOTES TO POISONS
X.--SELECTED READINGS
XI.--APPENDIX
QUESTIONS FOR CLASS USE
GLOSSARY
INDEX
SUGGESTIONS To Teachers
Seeing is believing--more than that, it is often knowing and remembering.
The mere reading of a statement is of little value compared with the
observation of a fact. Every opportunity should therefore be taken of
exhibiting to the pupil the phenomena described, and thus making them
real. A microscope is so essential to the understanding of many subjects,
that it is indispensable to the proper teaching of Physiology. A suitable
instrument and carefully prepared specimens, showing the structure of the
bones, the skin, and the blood of various animals, the pigment cells of
the eye, etc., may be obtained at a small cost from any good optician.
On naming the subject of a paragraph, the pupil should be prepared to tell
all he knows about it. No failure should discourage the teacher in
establishing this mode of study and recitation. A little practice will
produce the most satisfactory results. The unexpected question and the apt
reply develop a certain sharpness and readiness which are worthy of
cultivation. The questions for review, or any others that the wit of the
teacher may suggest, can be effectively used to break the monotony of a
topical recitation, thereby securing the benefits of both systems.
The pupil should expect to be questioned each day upon any subject passed
over during the term, and thus the entire knowledge gained will be within
his grasp for instant use. While some are reciting to the teacher, let
others write on slates or on the blackboard. At the close of the
recitation, let all criticise the ideas, the spelling, the use of
capitals, the pronunciation, the grammar, and the mode of expression.
Greater accuracy and much collateral drill may thus be secured at little
expense of valuable school time.
The Introduction is designed merely to furnish suggestive material for the
first lesson, preparatory to beginning the study. Other subjects for
consideration may be found in the section on Health and Disease, in the
Selected Readings, and among the questions given in the Appendix. Where
time will allow, the Selected Readings may profitably be used in
connection with the topics to which they relate. Questions upon them are
so incorporated with those upon the text proper that they may be employed
or not, according to the judgment of the teacher.
NOTE.--Interest in the study of Physiology will be much increased by the
use of the microscope and prepared slides. These may be obtained from any
good optician.
INTRODUCTION.
Physiological study in youth is of inestimable value. Precious lives are
frequently lost through ignorance. Thousands squander in early years the
strength which should have been kept for the work of real life. Habits are
often formed in youth which entail weakness and poverty upon manhood, and
are a cause of lifelong regret. The use of a strained limb may permanently
damage it. Some silly feat of strength may produce an irreparable injury.
A thoughtless hour of reading by twilight may impair the sight for life. A
terrible accident may happen, and a dear friend perish before our eyes,
while we stand by powerless to render the assistance we could so easily
give did we "only know what to do." The thousand little hints which may
save or lengthen life, may repel or abate disease, and the simple laws
which regulate our bodily vigor, should be so familiar that we may be
quick to apply them in an emergency. The preservation of health is easier
than the cure of disease. Childhood can not afford to wait for the lesson
of experience which is learned only when the penalty of violated law has
been already incurred, and health irrevocably lost.
NATURE'S LAWS INVIOLABLE.--In infancy, we learn how terribly Nature
punishes a violation of certain laws, and how promptly she applies the
penalty. We soon find out the peril of fire, falls, edged tools, and the
like. We fail, however, to notice the equally sharp and certain
punishments which bad habits entail. We are quick to feel the need of
food, but not so ready to perceive the danger of an excess. A lack of air
drives us at once to secure a supply; foul air is as fatal, but it gives
us no warning.
Nature provides a little training for us at the outset of life, but leaves
the most for us to learn by bitter experience. So in youth we throw away
our strength as if it were a burden of which we desire to be rid. We eat
anything, and at any time; do anything we please, and sit up any number of
nights with little or no sleep. Because we feel only a momentary
discomfort from these physical sins, we fondly imagine when that is gone
we are all right again. Our drafts upon our constitution are promptly
paid, and we expect this will always be the case; but some day they will
come back to us, protested; Nature will refuse to meet our demands, and we
shall find ourselves physical bankrupts.
We are furnished in the beginning with a certain vital force upon which we
may draw. We can be spendthrifts and waste it in youth, or be wise and so
husband it till manhood. Our shortcomings are all charged against this
stock. Nature's memory never fails; she keeps her account with perfect
exactness. Every physical sin subtracts from the sum and strength of our
years. We may cure a disease, but it never leaves us as it found us. We
may heal a wound, but the scar still shows. We reap as we sow, and we may
either gather in the thorns, one by one, to torment and destroy, or we may
rejoice in the happy harvest of a hale old age.
I.
THE SKELETON.
"Not in the World of Light alone,
Where God has built His blazing throne,
Nor yet alone on earth below,
With belted seas that come and go,
And endless isles of sunlit green
Is all thy Maker's glory seen--
Look in upon thy wondrous frame,
Eternal wisdom still the same!"
HOLMES.
ANALYSIS OF THE SKELETON.
NOTE.--The following Table of 206 bones is exclusive of the 8 sesamoid
bones which occur in pairs at the roots of the thumb and great toe, making
214 as given by Leidy and Draper. Gray omits the bones of the ear, and
names 200 as the total number.
THE SKELETON.
_
| I. THE HEAD (_28 bones._)
| _
| | Frontal Bone (forehead).
| _ | Two Parietal Bones.
| | 1. CRANIUM..............| Two Temporal (temple) Bones.
| | (_8 bones._) | Sphenoid Bone.
| | | Ethmoid (sieve-like bone at root of nose).
| | |_Occipital Bone (back and base of skull).
| | _
| | | Two Superior Maxillary (upper jaw) Bones.
| | | Inferior Maxillary (lower jaw) Bone.
| | | Two Malar (cheek) Bones.
| | 2. FACE.................| Two Lachrymal Bones.
| | (_14 bones._) | Two Turbinated (scroll like) Bones, each
| | | side of nose.
| | | Two Nasal Bones (Bridge of nose).
| | | Vomer (the bone between the nostrils).
| | |_Two Palate Bones.
| | _
| | | Hammer.
| | 3. EARS.................| Anvil.
| |_ (_6 bones._) |_Stirrup.
|
| II. THE TRUNK (_54 bones._)
| _
| | Cervical Vertebræ (seven vertebræ of the
| _ | neck).
| | 1. SPINAL COLUMN........| Dorsal Vertebræ (twelve vertebræ of the
| | | back).
| | | Lumbar Vertebræ (five vertebræ of the
| | |_ loins).
| | _
| | | True Ribs.
| | 2. RIBS.................|_False Ribs.
| |
| | 3. STERNUM (breastbone).
| |
| | 4. OS HYOIDES (bone at the root of tongue).
| | _
| | | Two Innominata.
| |_5. PELVIS...............| Sacrum.
| |_Coccyx.
|
| III. THE LIMBS (_124 bones._)
| _
| _ | _Clavicle._
| | Shoulder...|__Scapula._
| _ | _
| | 1. UPPER LIMBS..........| | _Humerus._
| | (_64 bones._) | Arm........|__Ulna and Radius._
| | | _
| | | | _Eight Wrist or Carpal
| | | | Bones._
| | |_Hand.......| _Five Metacarpal Bones._
| | |__Phalanges (14 bones)._
| | _
| | _ | _Femur._
| | | Leg........| _Patella._
| | | |__Tibia and Fibula._
| | 2. LOWER LIMBS..........| _
| |_ (_60 bones._) | | _Seven Tarsal Bones._
|_ | Foot.......| _Five Metatarsal Bones._
|_ |__Phalanges (14 bones)._
_
| 1. Uses.
_ | 2. Composition.
| 1. FORM, STRUCTURE, | 3. Structure.
| ETC., OF THE BONES | 4. Growth.
| | 5. Repair.
THE SKELETON | |_6. The Joints.
| _
| 2. CLASSIFICATION OF | 1. The Head.
|_ THE BONES. | 2. The Trunk.
|_3. The Limbs.
THE SKELETON.
I. FORM, STRUCTURE, ETC., OF THE BONES.
(_See page 269_.)
THE SKELETON, or framework of the "House we live in," is composed of about
200 bones. [Footnote: The precise number varies in different periods of
life. Several which are separated in youth become united in old age. Thus
five of the "false vertebræ" at the base of the spine early join in one
great bone--the sacrum; while four tiny ones below it often run into a
bony mass--the coccyx (Fig. 6); in the child, the sternum is composed of
eight pieces, while in the adult it consists of only three. While,
however, the number of the bones is uncertain, their relative length is so
exact that the length of the entire skeleton, and thence the height of the
man, can be obtained by measuring a single one of the principal bones.
Fossil bones and those found at Pompeii have the same proportion as our
own.]
USES AND FORMS OF THE BONES.--They have three principal uses: 1. To
protect the delicate organs; [Footnote: An organ is a portion of the body
designed for a particular use, called its _function_. Thus the heart
circulates the blood; the liver produces the bile.] 2. To serve as levers
on which the muscles may act to produce motion; and 3. To preserve the
shape of the body.
Bones differ in form according to the uses they subserve. For convenience
in walking, some are long; for strength and compactness, some are short
and thick; for covering a cavity, some are flat; and for special purposes,
some are irregular. The general form is such as to combine strength and
lightness. For example, all the long bones of the limbs are round and
hollow, thus giving with the same weight a greater strength, [Footnote:
Cut a sheet of foolscap in two pieces. Roll one half into a compact
cylinder, and fold the other into a close, flat strip; support the ends of
each and hang weights in the middle until they bend. The superior strength
of the roll will astonish one unfamiliar with this mechanical principle.
In a rod, the particles break in succession, first those on the outside,
and later those in the center. In a tube, the particles are all arranged
where they resist the first strain. Iron pillars are therefore cast
hollow. Stalks of grass and grain are so light as to bend before a breath
of wind, yet are stiff enough to sustain their load of seed. Bone has been
found by experiment to possess twice the resisting property of solid oak.]
and also a larger surface for the attachment of the muscles.
The Composition of the Bones at maturity is about one part animal to two
parts mineral matter. The proportion varies with the age. In youth it is
nearly half and half, while in old age the mineral is greatly in excess.
By soaking a bone in weak muriatic acid, and thus dissolving the mineral
matter, its shape will not change, but its stiffness will disappear,
leaving a tough, gristly substance [Footnote: Mix a wineglass of muriatic
acid with a pint of water, and place in it a sheep's rib. In a day or two,
the bone will become so soft that it can be tied into a knot. In the same
way, an egg may be made so pliable that it can be crowded into a narrow-
necked bottle, within which it will expand, and become an object of great
curiosity to the uninitiated. By boiling bones at a high temperature, the
animal matter separates in the form of gelatine. Dogs and cats extract the
animal matter from the bones they eat. Fossil bones deposited in the
ground during the Geologic period, were found by Cuvier to contain
considerable animal matter. Gelatine was actually extracted from the
Cambridge mastodon, and made into glue. A tolerably nutritious food might
thus be manufactured from bones older than man himself.] (cartilage) which
can be bent like rubber.
If the bone be burned in the fire, thus consuming the animal matter, the
shape will still be the same, but it will have lost its tenacity, and the
beautiful, pure-white residue [Footnote: From bones thus calcined, the
phosphorus of the chemist is made. See Steele's "Popular Chemistry," page
114. If the animal matter be not consumed, but only charred, the bone will
be black and brittle. In this way, the "boneblack" of commerce is
manufactured.] may be crumbled into powder with the fingers.
FIG. 2.
[Illustration: _The Thigh Bone, or Femur, sawed lengthwise._]
We thus see that a bone receives hardness and rigidity from its mineral,
and tenacity and elasticity from its animal matter.
The entire bone is at first composed of cartilage, which gradually
_ossifies_ or turns to bone. [Footnote: The ossification of the bones
on the sides and upper part of the skull, for example, begins by a rounded
spot in the middle of each one. From this spot the ossification extends
outward in every direction, thus gradually approaching the edges of the
bone. When two adjacent bones meet, there will be a line where their edges
are in contact with each other, but have not yet united; but when more
than two bones meet in this way, there will be an empty space between them
at their point of junction. Thus, if you lay down three coins upon the
table with their edges touching one another, there will be a three-sided
space in the middle between them; if you lay down four coins in the same
manner, the space between them will be four-sided. Now at the back part of
the head there is a spot where three bones come together in this way,
leaving a small, three-sided opening between them: this is called the
"posterior fontanelle." On the top of the head, four bones come together,
leaving between them a large, four-sided opening: this is called the
"anterior fontanelle." These openings are termed the _fontanelles_,
because we can feel the pulsations of the brain through them, like the
bubbling of water in a fountain. They gradually diminish in size, owing to
the growth of the bony parts around them, and are completely closed at the
age of four years after birth.--DALTON.] Certain portions near the joints
are long delayed in this process, and by their elasticity assist in
breaking the shock of a fall. [Footnote: Frogs and toads, which move by
jumping, and consequently receive so many jars, retain these unossified
portions (epiphyses) nearly through, life, while alligators and turtles
whose position is sprawling, and whose motions are measured do not have
them at all--LEIDY] Hence the bones of children are tough, are not readily
fractured, and when broken easily heal again; [Footnote: This is only one
of the many illustrations of the Infinite care that watches over helpless
infancy, until knowledge and ability are acquired to meet the perils of
life.] while those of elderly people are liable to fracture, and do not
quickly unite.
FIG. 3.
[Illustration: _A thin slice of Bone, highly magnified showing the
lacunæ, the tiny tubes (canaliculi) radiating from them, and four
Haversian canals, three seen crosswise and one lengthwise._]
THE STRUCTURE OF THE BONES--When a bone is sawed lengthwise, it is found
to be a compact shell filled with a spongy substance This filling
increases in quantity, and becomes more porous at the ends of the bone,
thus giving greater size to form a strong joint, while the solid portion
increases near the middle, where strength alone is needed. Each fiber of
this bulky material diminishes the shock of a sudden blow, and also acts
as a beam to brace the exterior wall. The recumbent position of the
alligator protects him from falls, and therefore his bones contain very
little spongy substance.
In the body, bones are not the dry, dead, blanched things they commonly
seem to be, but are moist, living, pinkish structures, covered with a
tough membrane, called the per-i-os'-te-um [Footnote: The relations of the
periosteum to the bone are very interesting. Instances are on record where
the bone has been removed, leaving the periosteum, from which the entire
bone was afterward renewed.] (_peri_, around, and _osteon_, a
bone), while the hollow is filled with marrow, rich in fat, and full of
blood vessels. If we examine a thin slice with the microscope, we shall
see black spots with lines running in all directions, and looking very
like minute insects. These are really little cavities, called la-cu'-næ
[Footnote: When the bone is dry, the lacunæ are filled with air, which
refracts the light, so that none of it reaches the eye, and hence the
cavities appear black.] from which radiate tiny tubes. The lacunæ are
arranged in circles around larger tubes, termed from their discoverer,
_Haversian canals_, which serve as passages for the blood vessels
that nourish the bone.
GROWTH OF THE BONES.--By means of this system of canals, the blood
circulates as freely through the bones as through any part of the body,
The whole structure is constantly but slowly changing, [Footnote: Bone is
sometimes produced with surprising rapidity. The great Irish Elk is
calculated by Prof. Owen to have cast off and renewed, annually in its
antlers eighty pounds of bone.] old material being taken out and new put
in. A curious illustration is seen in the fact that if madder be mixed
with the food of pigs, it will tinge their bones red.
REPAIR OF THE BONES.--When a bone is broken, the blood at once oozes out
of the fractured ends. This soon gives place to a watery fluid, which in a
fortnight thickens to a gristly substance, strong enough to hold them in
place. Bone matter is then slowly deposited, which in five or six weeks
will unite the broken parts. Nature, at first, apparently endeavors to
remedy the weakness of the material by excess in the quantity, and so the
new portion is larger than the old. But the extra matter will be gradually
absorbed, sometimes so perfectly as to leave no trace of the injury. (See
p. 271.)
A broken limb should be held in place by splints, or a plaster cast, to
enable this process to go on uninterruptedly, and also lest a sudden jar
might rupture the partially mended break. For a long time, the new portion
consists largely of animal matter, and so is tender and pliable. The
utmost care is therefore necessary to prevent a malformation.
THE JOINTS are packed with a soft, smooth cartilage, or gristle, which
fits so perfectly as to be airtight. Upon convex surfaces, it is thickest
at the middle, and upon concave surfaces, it is thickest at the edge, or
where the wear is greatest. In addition, the ends of the bones are covered
with a thin membrane, the _synovial_ (_sun_, with; _ovum_,
an egg), which secretes a viscid fluid, not unlike the white of an egg.
This lubricates the joints, and prevents the noise and wear of friction.
The body is the only machine that oils itself.
The bones which form the joint are tied with stout ligaments (_ligo_,
I bind), or bands, of a smooth, silvery white tissue, [Footnote: The
general term _tissue_ is applied to the various textures of which the
organs are composed. For example, the osseous tissue forms the bones; the
fibrous tissue, the skin, tendons, and ligaments.] so strong that the
bones are sometimes broken without injuring the fastenings.
II. CLASSIFICATION OF THE BONES.
For convenience, the bones of the skeleton are considered in three
divisions: the _head_, the _trunk_, and the _limbs_.
1. THE HEAD.
THE BONES OF THE SKULL AND THE FACE form a cavity for the protection of
the brain and the four organs of sense, viz.: sight, smell, taste, and
hearing. All these bones are immovable except the lower jaw, which is
hinged [Footnote: A ring of cartilage is inserted in its joints, something
after the manner of a washer in machinery. This follows the movements of
the jaw, and admits of freer motion, while it guards against dislocation.]
at the back so as to allow for the opening and shutting of the mouth.
THE SKULL is composed, in general, of two compact plates, with a spongy
layer between. These are in several pieces, the outer ones being joined by
notched edges, sutures (su'tyurs,), in the way carpenters term
dovetailing. (See Fig. 4.)
FIG. 4.
[Illustration: _The Skull._--1. _frontal bone;_ 2, _parietal bone;_
3, _temporal bone;_ 4, _the sphenoid bone;_ 5, _ethmoid bone;_ 6,
_superior maxillary (upper jaw) bone;_ 7, _malar bone;_ 8, _lachrymal
bone;_ 9, _nasal bone;_ 10, _inferior maxillary (lower jaw) bone._]
The peculiar structure and form of the skull afford a perfect shelter for
the brain--an organ so delicate that, if unprotected, an ordinary blow
would destroy it. Its oval or egg shape adapts it to resist pressure. The
smaller and stronger end is in front, where the danger is greatest.
Projections before and behind shield the less protected parts. The hard
plates are not easy to penetrate. [Footnote: Instances have been known
where bullets, striking against the skull, have glanced off, been
flattened, or even split into halves. In the Peninsular Campaign, the
author saw a man who had been struck in the forehead by a bullet which,
instead of penetrating the brain, had followed the skull around to the
back of the head, and there passed out.] The spongy packing deadens every
blow. [Footnote: An experiment resembling the familiar one of the balls in
Natural Philosophy ("Steele's Popular Physics," Fig. 6, p. 26),
beautifully illustrates this point. Several balls of ivory are suspended
by cords, as in Fig. 5. If A be raised and then let fall, it will transmit
the force to B, and that to C, and so on until F is reached, which will
fly off with the impulse. If now a ball of spongy bone be substituted for
an ivory one anywhere in the line, the force will be checked, and the last
ball will not stir.] The separate pieces with their curious joinings
disperse any jar which one may receive, and also prevent fractures from
spreading.
FIG. 5.
[Illustration]
The frequent openings in this strong bone box afford safe avenues for the
passage of numerous nerves and vessels which communicate between the brain
and the rest of the body.
FIG. 6.
[Illustration: _The Spine; the seven vertebræ of the neck, cervical; the
twelve of the back, dorsal; the five of the loins, lumbar;_ a, _the
sacrum, and_ b, _the coccyx, coming the nine "false vertebræ."_
(p. 3).]
2 THE TRUNK.
THE TRUNK has two important cavities. The upper part, or _chest_,
contains the heart and the lungs, and the lower part, or _abdomen_,
holds the stomach, liver, kidneys, and other organs (Fig. 31). The
principal bones are those of the _spine_, the _ribs_, and the
_hips_.
THE SPINE consists of twenty-four bones, between which are placed pads of
cartilage. [Footnote: These pads vary in thickness from one fourth to one
half an inch. They become condensed by the weight they bear during the
day, so that we are somewhat shorter at evening than in the morning.
Their elasticity causes them to resume their usual size during the night,
or when we lie down for a time.] A canal is hollowed out of the column
for the safe passage of the spinal cord. (See Fig. 50.) Projections
(processes) at the back and on either side are abundant for the attachment
of the muscles. The packing acts as a cushion to prevent any jar from
reaching the brain when we jump or run, while the double curve of the
spine also tends to disperse the force of a fall. Thus on every side the
utmost caution is taken to guard that precious gem in its casket.
THE PERFECTION OF THE SPINE surpasses all human contrivances. Its various
uses seem a bundle of contradictions. A chain of twenty-four bones is made
so stiff that it will bear a heavy burden, and so flexible that it will
bend like rubber; yet, all the while, it transmits no shock, and even
hides a delicate nerve within that would thrill with the slightest touch.
Resting upon it, the brain is borne without a tremor; and, clinging to it,
the vital organs are carried without fear of harm.
FIG. 7.
[Illustration: B, _the first cervical vertebra, the atlas;_ A, _the
atlas, and the second cervical vertebra, the axis;_ e, _the odontoid
process;_ c, _the foramen._]
THE SKULL ARTICULATES with (is jointed to) the spine in a peculiar manner.
On the top of the upper vertebra (atlas [Footnote: Thus called because,
as, in ancient fable, the god Atlas supported the world on his shoulders,
so in the body this bone bears the head.]) are two little hollows
(_a_, _b_, Fig. 7), nicely packed and lined with the synovial
membrane, into which fit the corresponding projections on the lower part
of the skull, and thus the head can rock to and fro. The second vertebra
(axis) has a peg, _e_, which projects through a hole, _c_, in
the first.
FIG. 8.
[Illustration: _The Thorax or Chest._ a, _the sternum;_ b _to_ c, _the
true ribs;_ d _to_ h, _the false ribs;_ g, h, _the floating ribs;_ i, k,
_the dorsal vertebræ._]
The surfaces of both vertebræ are so smooth that they easily glide on each
other, and thus, when we move the head side wise, the atlas turns around
the peg, _e_, of the axis.
THE RIBS, also twenty-four in number, are arranged in pairs on each side
of the chest. At the back, they are all attached to the spine. In front,
the upper seven pairs are tied by cartilages to the breastbone (sternum);
three are fastened to each other and to the cartilage above, and two, the
floating ribs, are loose.
The natural form of the chest is that of a cone diminishing upward. But,
owing to the tightness of the clothing commonly worn, the reverse is often
the case. The long, slender ribs give lightness, [Footnote: If the chest
wall were in one bone thick enough to resist a blow, it would be unwieldy
and heavy As it is, the separate bones bound by cartilages yield
gradually, and diffuse the force among them all, and so are rarely
broken.] the arched form confers strength, and the cartilages impart
elasticity,--properties essential to the protection of the delicate organs
within, and to freedom of motion in respiration. (See note, p. 80.)
FIG. 9.
[Illustration: _The Pelvis._ a, _the sacrum;_ b, b, _the right
and the left innominatum._]
THE HIP BONES, called by anatomists the innominata, or nameless bones,
form an irregular basin styled the _pelvis_ (_pelvis_, a basin).
In the upper part, is the foot of the spinal column--a wedge-shaped bone
termed the _sacrum_ [Footnote: So called because it was anciently
offered in sacrifice.] (sacred), firmly planted here between the
widespreading and solid bones of the pelvis, like the keystone to an arch,
and giving a steady support to the heavy burden above.
3. THE LIMBS.
TWO SETS OF LIMBS branch from the trunk, viz.: the upper, and the lower.
They closely resemble each other. The arm corresponds to the thigh; the
forearm, to the leg; the wrist, to the ankle; the fingers, to the toes.
The fingers and the toes are so much alike that they receive the same
name, _digits_, while the several bones of both have also the common
appellation, _phalanges_. The differences which exist grow out of
their varying uses. The foot is characterized by strength; the hand, by
mobility.
FIG. 10.
[Illustration: _The Shoulder Joint._ a, _the clavicle;_ b,
_the scapula._]
1. THE UPPER LIMBS.--THE SHOULDER.--The bones of the shoulder are the
collar bone (clavicle), and the shoulder blade (scapula). The
_clavicle_ (_clavis_, a key) is a long, slender bone, shaped
like the Italic _f_. It is fastened at one end to the breastbone and
the first rib, and, at the other, to the shoulder blade. (See Fig. 1.) It
thus holds the shoulder joint out from the chest, and gives the arm
greater play. If it be removed or broken, the head of the arm bone will
fall, and the motions of the arm be greatly restricted. [Footnote: Animals
which use the forelegs only for support (as the horse, ox, etc.), do not
possess this bone. "It is found in those that dig, fly, climb and seize."]
THE SHOULDER BLADE is a thin, flat, triangular bone, fitted to the top and
back of the chest, and designed to give a foundation for the muscles of
the shoulder.
THE SHOULDER JOINT.--The arm bone, or _humerus_, articulates with the
shoulder blade by a ball-and-socket joint. This consists of a cup-like
cavity in the latter bone, and a rounded head in the former, to fit it,--
thus affording a free rotary motion. The shallowness of the socket
accounts for the frequent dislocation of this joint, but a deeper one
would diminish the easy swing of the arm.
FIG. 11.
[Illustration: _Bones of the right Forearm._ H, _the humerus;_
R, _the radius; and_ U, _the ulna._]
THE ELBOW.--At the elbow, the humerus articulates with the _ulna_--a
slender bone on the inner side of the forearm--by a hinge joint which
admits of motion in only two directions, _i. e._, backward and
forward. The ulna is small at its lower end; the _radius_, or large
bone of the forearm, on the contrary, is small at its upper end, while it
is large at its lower end, where it forms the wrist joint. At the elbow,
the head of the radius is convex and fits into a shallow cavity in the
ulna, while at the wrist the ulna plays in a similar socket in the radius.
Thus the radius may roll over and even cross the ulna.
THE WRIST, or _carpus_, consists of two rows of very irregular bones,
one of which articulates with the forearm; the other, with the hand. They
are placed side to side, and so firmly fastened as to admit of only a
gliding motion. This gives little play, but great strength, elasticity,
and power of resisting shocks.
THE HAND.--The _metacarpal_ (_meta_, beyond; _karpos_,
wrist), or bones of the palm, support each a thumb or a finger. Each
finger has three bones, while the thumb has only two. The first bone of
the thumb, standing apart from the rest, enjoys a special freedom of
motion, and adds greatly to the usefulness of the hand.
FIG. 12.
[Illustration: _Bones of the Hand and the Wrist._]
The first bone (Figs. 11, 12) of each finger is so attached to the
corresponding metacarpal bone as to move in several directions upon it,
but the other phalanges form hinge joints.
The fingers are named in order: the thumb, the index, the middle, the
ring, and the little finger. Their different lengths cause them to fit the
hollow of the hand when it is closed, and probably enable us more easily
to grasp objects of varying size. If the hand clasps a ball, the tips of
the fingers will be in a straight line.
The hand in its perfection belongs only to man. Its elegance of outline,
delicacy of mold, and beauty of color have made it the study of artists;
while its exquisite mobility and adaptation as a perfect instrument have
led many philosophers to attribute man's superiority even more to the hand
than to the mind. [Footnote: How constantly the hand aids us in explaining
or enforcing a thought! We affirm a fact by placing the hand as if we
would rest it firmly on a body; we deny by a gesture putting the false or
erroneous proposition away from us; we express doubt by holding the hand
suspended, as if hesitating whether to take or reject. When we part from
dear friends, or greet them again after long absence, the hand extends
toward them as if to retain, or to bring them sooner to us. If a recital
or a proposition is revolting, we reject it energetically in gesture as in
thought. In a friendly adieu we wave our good wishes to him who is their
object; but when it expresses enmity, by a brusque movement we sever every
tie. The open hand is carried backward to express fear or horror, as well
as to avoid contact; it goes forward to meet the hand of friendship; it is
raised suppliantly in prayer toward Him from whom we hope for help; it
caresses lovingly the downy cheek of the infant, and rests on its head
invoking the blessing of Heaven,--_Wonders of the Human Body_.]
FIG. 13.
[Illustration: _The Mechanism of the Hip Joint._]
2. THE LOWER LIMBS.--THE HIP--The thigh bone, or _femur_, is the
largest and necessarily the strongest in the skeleton, since at every step
it has to bear the weight of the whole body. It articulates with the hip
bone by a ball-and-socket joint. Unlike the shoulder joint, the cup here
is deep, thus affording less play, but greater strength. It fits so
tightly that the pressure of the air largely aids in keeping the bones in
place. [Footnote: In order to test this, a hole was bored through a hip
bone, so as to admit air into the socket, the thigh bone at once fell out
as far as the ligaments would permit. An experiment was also devised
whereby a suitably prepared hip joint was placed under the receiver of an
air pump. On exhausting the air, the weight of the femur caused it to drop
out of the socket, while the readmission of the air raised it to its
place. Without this arrangement, the adjacent muscles would have been
compelled to bear the additional weight of the thighbone every time it was
raised. Now the pressure of the air rids them of this unnecessary burden,
and hence they are less easily fatigued--WEBER] Indeed, when the muscles
are cut away, great force is required to detach the limbs.
THE KNEE is strengthened by the patella_, or kneepan (_patella_,
little dish), a chestnut-shaped bone firmly fastened over the joint.
The shin bone, or _tibia_, the large, triangular bone on the inner
side of the leg, articulates both with the femur and the foot by hinge
joints. The kneejoint is so made, however, as to admit of a slight rotary
motion when the limb is not extended.
The _fibula_ (_fibula_, a clasp), the small, outside bone of the
leg, is firmly bound at each end to the tibia. (See Fig. 1.) It is
immovable, and, as the tibia bears the principal weight of the body, the
chief use of this second bone seems to be to give more surface to which
the muscles may be attached. [Footnote: A young man in the hospital at
Limoges had lost the middle part of his tibia. The lost bone was not
reproduced, but the fibula, the naturally weak and slender part of the
leg, became thick and strong enough to support the whole body.--STANLEY'S
_Lectures_.]
THE FOOT.--The general arrangement of the foot is strikingly like that of
the hand (Fig. 1). The several parts are the _tarsus_, the
_metatarsus_, and the _phalanges_. The graceful arch of the
foot, and the numerous bones joined by cartilages, give an elasticity to
the step that could never be attained by a single, flat bone. [Footnote:
The foot consists of an arch, the base of which is more extended in front
than behind, and the whole weight of the body is made to fall on this arch
by means of a variety of joints. These joints further enable the foot to
be applied, without inconvenience, to rough and uneven surfaces.--HINTON.]
The toes naturally lie straight forward in the line of the foot. Few
persons in civilized nations, however, have naturally formed feet. The big
toe is crowded upon the others, while crossed toes, nails grown-in,
enormous joints, corns, and bunions abound.
THE CAUSE OF THESE DEFORMITIES is found in the shape and size of
fashionable boots and shoes. The sole ought to be large enough for full
play of motion, the uppers should not crowd the toes, and the heels should
be low, flat, and broad. As it is, there is a constant warfare between
Nature and our shoemakers, [Footnote: When we are measured for boots or
shoes, we should stand on a sheet of paper, and have the shoemaker mark
with a pencil the exact outline of our feet as they bear our whole weight.
When the shoe is made, the sole should exactly cover this outline.] and we
are the victims. The narrow point in front pinches our toes, and compels
them to override one another; the narrow sole compresses the arch; while
the high heel, by throwing all the weight forward on the toes, strains the
ankle, and, by sending the pressure where Nature did not design it to
fall, causes that joint to become enlarged. The body bends forward to meet
the demand of this new motion, and thus loses its uprightness and beauty,
making our gait stiff and ungraceful. (See p. 271.)
DISEASES, ETC.--l. _Rickets_, a disease of early life, is caused by a
lack of mineral matter in the bones, rendering them soft and pliable, so
that they bend under the weight of the body. They thus become permanently
distorted, and of course are weaker than if they were straight, [Footnote:
Just here appears an exceedingly beautiful provision. As soon as the
disproportion of animal matter ceases, a larger supply of mineral is sent
to the weak points, and the bones actually become thicker, denser, harder,
and consequently stronger at the very concave part where the stress of
pressure is greatest.--WATSON'S _Lectures_. We shall often have
occasion to refer to similar wise and providential arrangements whereby
the body is enabled to remedy defects, and to prepare for accidents.]
Rickets is most common among children who have inherited a feeble
constitution and who are ill fed, or who live in damp, ill-ventilated
houses. "Rickety" children should have plenty of fresh air and sunlight,
nourishing food, comfortable clothing, and, in short, the best of hygienic
care.
2. _A Felon_ is a swelling of the finger or thumb, usually of the
last joint. It is marked by an accumulation beneath the periosteum and
next the bone. The physician will merely cut through the periosteum, and
let out the effete matter.
3. _Bowlegs_ are caused by children standing on their feet before the
bones of the lower limbs are strong enough to bear their weight. The
custom of encouraging young children to stand by means of a chair or the
support of the hand, while the bones are yet soft and pliable, is a cruel
one, and liable to produce permanent deformity. Nature will set the child
on its feet when the proper time comes.
4. _Curvature of the Spine_.--When the spine is bent, the packing
between the vertebræ becomes compressed on one side into a wedge-like
shape. After a time, it will lose its elasticity, and the spine will
become distorted. This often occurs in the case of students who bend
forward to bring their eyes nearer their books, instead of lifting their
books nearer their eyes, or who raise their right shoulder above their
left when writing at a desk which is too high. Round shoulders, small,
weak lungs, and, frequently, diseases of the spine are the consequences.
An erect posture in reading or writing conduces not alone to beauty of
form, but also to health of body. We shall learn hereafter that the action
of the muscles bears an important part in preserving the symmetry of the
spine. Muscular strength comes from bodily activity; hence, one of the
best preventives of spinal curvature is daily exercise in the open air.
5. _Sprains_ are produced when the ligaments which bind the bones of
a joint are strained, twisted, or torn from their attachments. They are
quite as serious as a broken bone, and require careful attention lest they
lead to a crippling for life. By premature use a sprained limb may be
permanently impaired. Hence, the joint should be kept quiet, even after
the immediate pain is gone.
6. _A Dislocation_ is the forcible displacement of a bone from its
socket. It is, generally, the result of a fall or a violent blow. The
tissues of the joint are often ruptured, while the contraction of the
muscles prevents the easy return of the bone to its place. A dislocation
should be reduced as soon as possible after the injury, before
inflammation supervenes.
PRACTICAL QUESTIONS.
1. Why does not a fall hurt a child as much as it does a grown person?
2. Should a young child ever be urged to stand or walk?
3. What is meant by "breaking one's neck"?
4. Should chairs or benches have straight backs?
5. Should a child's feet be allowed to dangle from a high seat?
6. Why can we tell whether a fowl is young by pressing on the point of the
breastbone?
7. What is the use of the marrow in the bones?
8. Why is the shoulder so often put out of joint?
9. How can you tie a knot in a bone?
10. Why are high pillows injurious?
11. Is a stooping posture a healthful position?
12. Should a boot have a heel piece?
13. Why should one always sit and walk erect?
14. Why does a young child creep rather than walk?
15. What is the natural direction of the big toe?
16. What is the difference between a sprain and a fracture? A dislocation?
17. Does the general health of the system affect the strength of the
bones?
18. Is living bone sensitive? _Ans_.--Scrape a bone, and its vessels
bleed; cut or bore a bone, and its granulations sprout up; break a bone,
and it will heal; cut a piece away, and more bone will readily be
produced; hurt it in any way, and it inflames; burn it, and it dies. Take
any proof of sensibility but the mere feeling of pain, and it will answer
to the proof.--BELL'S _Anatomy_. Animal sensibility would be
inconvenient; it is therefore not to be found except in diseased bone,
where it sometimes exhibits itself too acutely.--TODD'S _Cyclopedia of
Anatomy_.
19. Is the constitution of bone the same in animals as in man?
_Ans_.--The bones of quadrupeds do not differ much from those of man.
In general they are of a coarser texture, and in some, as in those of the
elephant's head, we find extensive air cells.--TODD'S _Anatomy_.
II.
THE MUSCLES.
"Behold the outward moving frame,
Its living marbles jointed strong
With glistening band and silvery thong,
And link'd to reason's guiding reins
By myriad rings in trembling chains,
Each graven with the threaded zone
Which claims it as the Master's own."
HOLMES.
ANALYSIS OF THE MUSCLES.
_
| 1. The Use of the Muscles.
| 2. Contractility of the Muscles.
_ | 3. Arrangement of the Muscles.
| 1. THE USE, STRUCTURE | 4. The two Kinds of Muscles.
| AND ACTION OF THE | 5. The Structure of the Muscles.
| MUSCLES. | 6. The Tendons for Fastening Muscles.
| | 7. The Muscles and Bones as Levers.
| | 8. The Effect of Big Joints.
| | 9. Action of the Muscles in Walking.
| |_10. Action of the Muscles in Walking.
|
| 2. THE MUSCULAR SENSE.
| _
| 3. HYGIENE OF THE | 1. Necessity of Exercise.
| MUSCLES. | 2. Time for Exercise.
| |_ 3. Kinds of Exercise.
|
| 4. WONDERS OF THE MUSCLES.
| _
| | 1. St. Vitus's Dance.
| | 2. Convulstions.
| | 3. Locked-jaw.
|_5. DISEASES. | 4. Gout.
| 5. Rheumatism.
| 6. Lumbago.
|_ 7. A Ganglion.
FIG. 14.
[Illustration]
THE MUSCLES.
THE USE OF THE MUSCLES.--The skeleton is the image of death. Its unsightly
appearance instinctively repels us. We have seen, however, what uses it
subserves in the body, and how the ugly-looking bones abound in nice
contrivances and ingenious workmanship. In life, the framework is hidden
by the flesh. This covering is a mass of muscles, which by their
arrangement and their properties not only give form and symmetry to the
body, but also produce its varied movements.
In Fig. 14, we see the large exterior muscles. Beneath these are many
others; while deeply hidden within are tiny, delicate ones, too small to
be seen with the naked eye. There are, in all, about five hundred, each
having its special use, and all working in exquisite harmony and
perfection.
CONTRACTILITY.--The peculiar property of the muscles is their power of
contraction, whereby they decrease in length and increase in thickness.
[Footnote: The maximum force of this contraction has been estimated as
high as from eighty-five to one hundred and fourteen pounds per square
inch.] This may be caused by an effort of the will, by cold, by a sharp
blow, etc. It does not cease at death, but, in certain cold-blooded
animals, a contraction of the muscles is often noticed long after the head
has been cut off.
ARRANGEMENT OF THE MUSCLES. [Footnote: "Could we behold properly the
muscular fibers in operation, nothing, as a mere mechanical exhibition,
can be conceived more superb than the intricate and combined actions that
must take place during our most common movements. Look at a person running
or leaping, or watch the motions of the eye. How rapid, how delicate, how
complicated, and yet how accurate, are the motions required! Think of the
endurance of such a muscle as the heart, that can contract, with a force
equal to sixty pounds, seventy-five times every minute, for eighty years
together, without being weary."]--The muscles are nearly all arranged in
pairs, each with its antagonist, so that, as they contract and expand
alternately, the bone to which they are attached is moved to and fro. (See
p. 275.)
If you grasp the arm tightly with your hand just above the elbow joint,
and bend the forearm, you will feel the muscle on the inside (biceps,
_a_, Fig. 14) swell, and become hard and prominent, while the outside
muscle (triceps, _f_) will be relaxed. Now straighten the arm, and
the swelling and hardness of the inside muscle will vanish, while the
outside one will, in turn, become rigid. So, also, if you clasp the arm
just below the elbow, and then open and shut the fingers, you can feel the
alternate expanding and relaxing of the muscles on opposite sides of the
arms.
If the muscles on one side of the face become palsied, those on the other
side will draw the mouth that way. Squinting is caused by one of the
straight muscles of the eye (Fig. 17) contracting more strongly than its
antagonist.
KINDS OF MUSCLES.--There are two kinds of muscles, the _voluntary_,
which are under the control of our will, and the _involuntary_,
which are not. Thus our limbs stiffen or relax as we please, but the
heart beats on by day and by night. The eyelid, however, is both
voluntary and involuntary, so that while we wink constantly without
effort, we can, to a certain extent, restrain or control the motion.
STRUCTURE OF THE MUSCLES.--If we take a piece of lean beef and wash out
the red color, we can easily detect the fine fibers of which the meat is
composed. In boiling corned beef for the table, the fibers often separate,
owing to the dissolving of the delicate tissue which bound them together.
By means of the microscope, we find that these fibers are made up of
minute filaments (_fibrils_), and that each fibril is composed of a
row of small cells arranged like a string of beads. This gives the muscles
a peculiar striped (striated) appearance. [Footnote: The involuntary
muscles consist generally of smooth, fibrous tissue, and form sheets or
membranes in the walls of hollow organs. By their contraction they change
the size of cavities which they inclose. Some functions, however, like the
action of the heart, or the movements of deglutition (swallowing), require
the rapid, vigorous contraction, characteristic of the voluntary muscular
tissue--FLINT.] (See p. 276.) The cells are filled with a fluid or
semifluid mass of living (protoplasmic) matter.
FIG. 15.
[Illustration: _Microscopic view of a Muscle, showing, at one end, the
fibrillæ; and, at the other, the disks, or cells, of the fiber._]
The binding of so many threads into one bundle [Footnote: We shall learn
hereafter how these fibers are firmly tied together by a mesh of fine
connective tissue which dissolves in boiling, as just described] confers
great strength, according to a mechanical principle that we see
exemplified in suspension bridges, where the weight is sustained, not by
bars of iron, but by small wires twisted into massive ropes.
FIG. 16.
[Illustration: _Tendons of the Hand._]
THE TENDONS.--The ends of the muscles are generally attached to the bone
by strong, flexible, but inelastic tendons. [Footnote: The tendons may be
easily seen in the leg of a turkey as it comes on our table; so we may
study Physiology while we pick the bones.] The muscular fibers spring from
the sides of the tendon, so that more of them can act upon the bone than
if they went directly to it. Besides, the small, insensible tendon can
better bear the exposure of passing over a joint, and be more easily
lodged in some protecting groove, than the broad, sensitive muscle. This
mode of attachment gives to the limbs strength, and elegance of form.
Thus, for example, if the large muscles of the arm extended to the hand,
they would make it bulky and clumsy. The tendons, however, reach only to
the wrist, whence fine cords pass to the fingers (Fig. 16).
Here we notice two other admirable arrangements. 1. If the long tendons at
the wrist on contracting should rise, projections would be made and thus
the beauty of the slender joint be marred. To prevent this, a stout band
or bracelet of ligament holds them down to their place. 2. In order to
allow the tendon which moves the last joint of the finger to pass through,
the tendon which moves the second joint divides at its attachment to the
bone (Fig. 16). This is the most economical mode of packing the muscles,
as any other practicable arrangement would increase the bulk of the
slender finger.
FIG. 17.
[Illustration: _Muscles of the Right Eye:_ A, _superior
straight,_ B, _superior oblique passing through a pulley,_ D; G,
_inferior oblique,_ H, _external straight, and, back of it, the
internal straight muscle._]
Since the tendon can not always pull in the direction of the desired
motion, some contrivance is necessary to meet the want. The tendon (B)
belonging to one of the muscles of the eye, for example, passes through a
ring of cartilage, and thus a rotary motion is secured.
FIG. 18.
[Illustration: _The three classes of Levers, and also the foot as a
Lever._]
THE LEVERS OF THE BODY. [Footnote: A _lever_ is a stiff bar resting
on a point of support, called the _fulcrum_ (_F_), and having connected
with it a _weight_ (_W_) to be lifted, and a _power_ (_P_) to move it.
There are three classes of levers according to the arrangement of the
power, weight, and fulcrum. In the first class, the _F_ is between the
_P_ and _W_; in the second, the _W_ is between the _P_ and _F_; and in
the third, the _P_ is between the _W_ and _F_ (Fig. 18). A pump handle
is an example of the first; a lemon squeezer, of the second; and a
pair of fire tongs, of the third. See "Popular Physics," pp. 81-83, for a
full description of this subject, and for many illustrations.]--In
producing the motions of the body, the muscles use the bones as levers. We
see an illustration of the _first class_ of levers in the movements
of the head. The back or front of the head is the weight to be lifted, the
backbone is the fulcrum on which the lever turns, and the muscles at the
back or front of the neck exert the power by which we toss or bow the
head.
FIG. 19.
[Illustration: _The hand as a Lever of the third class._]
When we raise the body on tiptoe, we have an instance of the _second
class_. Here, our toes resting on the ground form the fulcrum the
muscles of the calf (gas-troc-ne'-mi-us, _j_ and so-le'-us, Fig. 14),
acting through the tendon of the heel, [Footnote: This is called the
Tendon of Achilles (_k_, Fig. 14) and is so named because, as the
fable runs, when Achilles was an infant his mother held him by the heel
while she dipped him in the River Styx, whose water had the power of
rendering one invulnerable to any weapon. His heel, not being wet, was his
weak point, to which Paris directed the fatal arrow--"This tendon," says
Mapother, "will bear one thousand pounds weight before it will break." The
horse is said to be "hamstrung," and is rendered useless, when the Tendon
of Achilles is cut. (see p. 284.)] are the power and the weight is borne
by the ankle joint.
An illustration of the _third class_ is found in lifting the hand
from the elbow. The hand is the weight, the elbow the fulcrum, and the
power is applied by the biceps muscle at its attachment to the radius (A,
Fig. 19.) In this form of the lever there is great loss of force, because
it is applied at such a distance from the weight, but there is a gain of
velocity, since the hand moves so far by such a slight contraction of the
muscle. The hand is required to perform quick motions, and therefore this
mode of attachment is desirable.
The nearer the power is applied to the resistance, the more easily the
work is done. In the lower jaw, for example, the jaw is the weight, the
fulcrum is the hinge joint at the back, and the muscles (temporal,
_d_, and the mas'-se'ter, _e_, Fig. 14) on each side are the
power. [Footnote: We may feel the contraction of the masseter by placing
our hand on the face when we work the jaw, while the temporal can be
readily detected by putting the fingers on the temple while we are
chewing. The tendon of the muscle (digastric)--one of those which open the
jaw--passes through a pulley (_c_, Fig. 14) somewhat like the one in
the eye.] They act much closer to the resistance than those in the hand,
since here we desire force, and there, speed.
FIG. 20.
[Illustration: _The Kneejoint;_ k, _the patella;_ f, _the
tendon._]
THE ENLARGEMENT OF THE BONES AT THE JOINTS not only affords greater
surface for the attachment of the muscles, as we have seen, but also
enables them to work to better advantage. Thus, in Fig. 20 it is evident
that a muscle acting in the line _f b_ would not bend the lower limb
so easily as if it were acting in the line _f k_, since in the former
case its force would be about all spent in drawing the bones more closely
together, while in the latter it would pull more nearly at a right angle.
Thus the tendon _f_, by passing over the patella, which is itself
pushed out by the protuberance _b_ of the thigh bone, pulls at a
larger angle, [Footnote: The chief use of the processes of the spine (Fig.
6) and other bones is, in the same way, to throw out the point on which
the power acts as far from the fulcrum as possible. The projections of the
ulna ("funny bone") behind the elbow, and that of the heel bone to which
the Tendon of Achilles is attached, are excellent illustrations (Fig. 1).]
and so the leg is thrown forward with ease in walking and with great force
in kicking.
HOW WE STAND ERECT.--The joints play so easily, and the center of gravity
in the body is so far above the foot, that the skeleton can not of itself
hold our bodies upright. Thus it requires the action of many muscles to
maintain this position. The head so rests upon the spine as to tend to
fall in front, but the muscles of the neck steady it in its place.
[Footnote: In animals the jaws are so heavy, and the place where the head
and spine join is so far back, that there can be no balance as there is in
man. There are therefore large muscles in their necks. We readily find
that we have none if we get on "all fours" and try to hold up the head. On
the other hand, gorillas and apes can not stand erect like man, for the
reason that their head, trunk, legs, etc., are not balanced by muscles, so
as to be in line with one another.] The hips incline forward, but are held
erect by the strong muscles of the back. The trunk is nicely balanced on
the head of the thigh bones. The great muscles of the thigh acting over
the kneepan tend to bend the body forward, but the muscles of the calf
neutralize this action. The ankle, the knee, and the hip lie in nearly the
same line, and thus the weight of the body rests directly on the keystone
of the arch of the foot. So perfectly do these muscles act that we never
think of them until science calls our attention to the subject, and yet to
acquire the necessary skill to use them in our infancy needed patient
lessons, much time, and many hard knocks.
FIG. 21.
[Illustration: _Action of the Muscles which keep the body erect._]
HOW WE WALK.--Walking is as complex an act as standing. It is really a
perilous performance, which has become safe only because of constant
practice. We see how violent it is when we run against a post in the dark,
and find with what headlong force we were hurling ourselves forward.
Holmes has well defined walking as a perpetual falling with a constant
self-recovery. Standing on one foot, we let the body fall forward, while
we swing the other leg ahead like a pendulum. Planting that foot on the
ground, to save the body from falling farther, we then swing the first
foot forward again to repeat the same operation. [Footnote: It is a
curious fact that one side of the body tends to outwalk the other; and so,
when a man is lost in the woods, he often goes in a circle, and at last
comes round to the spot whence he started.]
The shorter the pendulum, the more rapidly it vibrates; and so short-
legged people take quicker and shorter steps than long-legged ones.
[Footnote: In this respect, Tom Thumb was to Magrath, whose skeleton,
eight and one half feet high, is now in the Dublin Museum, what a little
fast-ticking, French mantel clock is to a big, old-fashioned, upright,
corner timepiece.] We are shorter when walking than when standing still,
because of this falling forward to take a step in advance. [Footnote:
Women find that a gown that will swing clear of the ground when they are
standing still, will drag the street when they are walking. The length of
the step may be increased by muscular effort, as when a line of soldiers
keep step in spite of their having legs of different lengths. Such a mode
of walking is necessarily fatiguing. (See p. 280.)]
In running, we incline the body more, and so, as it were, fall faster.
When we walk, one foot is on the ground all the time, and there is an
instant when both feet are planted upon it; but in running there is an
interval of time in each step when both feet are off the ground, and the
body is wholly unsupported. As we step alternately with the feet, we are
inclined to turn the body first to one side and then to the other. This
movement is sometimes counterbalanced by swinging the hand on the opposite
side. [Footnote: In ordinary walking the speed is nearly four miles an
hour, and can be kept up for a long period. But exercise and a special
aptitude for it enable some men to walk great distances in a relatively
short space of time. Trained walkers have gone seventy-five miles in
twenty hours, and walked the distance of thirty-seven miles at the rate of
five miles an hour. The mountaineers of the Alps are generally good
walkers, and some of them are not less remarkable for endurance than for
speed. Jacques Balmat, who was the first to reach the summit of Mont
Blanc, at sixteen years of age could walk from the hamlet of the Pélerins
to the mountain of La Côte in two hours,--a distance which the best-
trained travelers required from five to six hours to get over. At the time
of his last attempt to reach the top of Mont Blanc, this same guide, then
twenty years old, passed six days and four nights without sleeping or
reposing a single moment. One of his sons, Édouard Balmat, left Paris to
join his regiment at Genoa; he reached Chamouni the fifth day at evening,
having walked three hundred and forty miles. After resting two days, he
set off again for Genoa, where he arrived in two days. Several years
afterward, this same man left the baths at Louèche at two o'clock in the
morning, and reached Chamouni at nine in the evening, having walked a
distance equal to about seventy-five miles in nineteen hours. In 1844, an
old guide of De Saussure, eighty years old, left the hamlet of Prats, in
the valley of Chamouni, in the afternoon, and reached the Grand-Mulets at
ten in the evening; then, after resting some hours, he climbed the glacier
to the vicinity of the Grand Plateau, which has an altitude of about
thirteen thousand feet, and then returned to his village without
stopping.--_Wonders of the Body_.]
THE MUSCULAR SENSE.--When we lift an object, we feel a sensation of
weight, which we can compare with that experienced in lifting another
body. [Footnote: If a small ivory ball be allowed to roll down the cheek
toward the lips, it will appear to increase in weight. In general, the
more sensitive parts of the body recognize smaller differences in weight,
and the right hand is more accurate than the left. We are very apt,
however, to judge of the weight of a body from previous conceptions. Thus,
shortly after Sir Humphrey Davy discovered the metal potassium, he placed
a piece of it in the hand of Dr. Pierson, who exclaimed: "Bless me! How
heavy it is!" Really, however, potassium is so light that it will float on
water like cork.] By balancing it in the hand. The muscular sense is
useful to us in many ways. It guides us in standing or moving. We gratify
it when we walk erect and with an elastic step, and by dancing, jumping,
skating, and gymnastic exercises.
NECESSITY OF EXERCISE.--The effect of exercise upon a muscle is very
marked. [Footnote: The greater size of the breast (pectoral muscle) of a
pigeon, as compared with that of a duck, shows how muscle increases with
use. The breast of a chicken is white because it is not used for flight,
and therefore gets little blood.] By use it grows larger, and becomes
hard, compact, and darker-colored; by disuse it decreases in size, and
becomes soft, flabby, and pale.
Violent exercise, however, is injurious, since we then tear down faster
than nature can build up. Feats of strength are not only hurtful, but
dangerous. Often the muscles are strained or ruptured, and blood vessels
burst in the effort to outdo one's companions. [Footnote: Instances have
been known of children falling dead from having carried to excess so
pleasant and healthful an amusement as jumping the rope, and of persons
rupturing the Tendon of Achilles in dancing. The competitive lifting of
heavy weights is unwise, sometimes fatal.] (See p. 278.)
Two thousand years ago, Isocrates, the Greek rhetorician, said: "Exercise
for health, not for strength." The cultivation of muscle for its own sake
is a return to barbarism, while it enfeebles the mind, and ultimately the
body. The ancient gymnasts are said to have become prematurely old, and
the trained performers of our own day soon suffer from the strain they put
upon their muscular system. Few men have sufficient vigor to become both
athletes and scholars. Exercise should, therefore, merely supplement the
deficiency of our usual employment. _A sedentary life needs daily,
moderate exercise, which always stops short of fatigue_. This is a law
of health. (See p. 280.)
No education is complete which fails to provide for the development of the
muscles. Recesses should be as strictly devoted to play as study hours are
to work. Were gymnastics or calisthenics as regular an exercise as grammar
or arithmetic, fewer pupils would be compelled to leave school on account
of ill health; while spinal curvatures, weak backs, and ungraceful gaits
would no longer characterize so many of our best institutions.
TIME FOR EXERCISE.--We should not exercise after long abstinence from
food, nor immediately after a meal, unless the meal or the exercise be
very light. There is an old-fashioned prejudice in favor of exercise
before breakfast--an hour suited to the strong and healthy, but entirely
unfitted to the weak and delicate. On first rising in the morning, the
pulse is low, the skin relaxed, and the system susceptible to cold. Feeble
persons, therefore, need to be braced with food before they brave the
outdoor air.
WHAT KIND OF EXCERCISE TO TAKE.--For children, games are unequaled.
Walking, the universal exercise, [Footnote: The custom of walking, so
prevalent in England, has doubtless much to do with the superior physique
of its people. It is considered nothing for a woman to take a walk of
eight or ten miles, and long pedestrian excursions are made to all parts
of the country. The benefits which accrue from such an open-air life are
sadly needed by the women of our own land. A walk of half a dozen miles
should be a pleasant recreation for any healthy person.] is beneficial, as
it takes one into the open air and sunlight. Running is better, since it
employs more muscles, but it must not be pushed to excess, as it taxes the
heart, and may lead to disease of that organ. Rowing is more effectual in
its general development of the system. Swimming employs the muscles of the
whole body, and is a valuable acquirement, as it may be the means of
saving life. Horseback riding is a fine accomplishment, and refreshes both
mind and body. Gymnastic or calisthenic exercises bring into play all the
muscles of the body, and when carefully selected, and not immoderately
employed, are preferable to any other mode of indoor exercise. [Footnote:
The employment of the muscles in exercise not only benefits their especial
structure, but it acts on the whole system. When the muscles are put in
action, the capillary blood vessels with which they are supplied become
more rapidly charged with blood, and active changes take place, not only
in the muscles, but in all the surrounding tissues. The heart is required
to supply more blood, and accordingly beats more rapidly in order to meet
the demand. A larger quantity of blood is sent through the lungs, and
larger supplies of oxygen are taken in and carried to the various tissues.
The oxygen, by combining with the carbon of the blood and the tissues,
engenders a larger quantity of heat, which produces an action on the skin,
in order that the superfluous warmth may be disposed of. The skin is thus
exercised, as it were, and the sudoriparous and sebaceous glands are set
at work. The lungs and skin are brought into operation, and the lungs
throw off large quantities of carbonic acid, and the skin large quantities
of water, containing in solution matters which, if retained, would produce
disease in the body. Wherever the blood is sent, changes of a healthful
character occur. The brain and the rest of the nervous system are
invigorated, the stomach has its powers of digestion improved, and the
liver, pancreas, and other organs perform their functions with more vigor.
By want of exercise, the constituents of the food which pass into the
blood are not oxidized, and products which produce disease are engendered.
The introduction of fresh supplies of oxygen induced by exercise oxidizes
these products, and renders them harmless. As a rule, those who exercise
most in the open air will live the longest.--LANKESTER.] (See p. 280.)
THE WONDERS OF THE MUSCLES.--The grace, ease, and rapidity with which the
muscles contract are astonishing. By practice, they acquire a facility
which we call mechanical. The voice may utter one thousand five hundred
letters in a minute, yet each requires a distinct position of the vocal
organs. We train the muscles of the fingers till they glide over the keys
of the piano, executing the most exquisite and difficult harmony. In
writing, each letter is formed by its peculiar motions, yet we make them
so unconsciously that a skillful penman will describe beautiful curves
while thinking only of the idea that the sentence is to express. The mind
of the violinist is upon the music which his right hand is executing,
while his left determines the length of the string and the character of
each note so carefully that not a false sound is heard, although the
variation of a hair's breadth would cause a discord. In the arm of a
blacksmith, the biceps muscle may grow into the solidity almost of a club;
the hand of a prize fighter will strike a blow like a sledge hammer; while
the engraver traces lines invisible to the naked eye, and the fingers of
the blind acquire a delicacy that almost supplies the place of the missing
sense.
DISEASES, ETC.--l. _St. Vitus's Dance_ is a disease of the voluntary
muscles, whereby they are in frequent, irregular, and spasmodic motion
beyond the control of the will. All causes of excitement, and especially
of fear, should be avoided, and the general health of the patient
invigorated, as this disease is closely connected with a derangement of
the nervous system.
2. _Convulsions_ are an involuntary contraction of the muscles.
Consciousness is wanting, while the limbs may be stiff or in spasmodic
action. (See p. 261.)
3. _Locked-jaw_ is a disease in which there are spasms and a
contraction of the muscles, usually beginning in the lower jaw. It is
serious, often fatal, yet it sometimes follows as trivial an injury as the
stroke of a whip lash, the lodgment of a bone in the throat, a fishhook in
the finger, or a tack in the sole of the foot.
4. _Gout_ is characterized by an acute pain located chiefly in the
small joints of the foot, especially those of the great toe, which become
swollen and extremely sensitive. It is generally accompanied by an excess
of uric acid in the blood, and a deposit of urate of soda about the
affected joint. Gout is often the result of high living, and of too much
animal food. It is frequently inherited.
5. _Rheumatism_ affects mainly the connective, white, fibrous tissue
of the larger joints. While gout is the punishment of the rich who live
luxuriously, rheumatism afflicts alike the poor and the rich. There are
two common forms of rheumatism--the inflammatory or acute, and the
chronic. The latter is of long continuance; the former terminates more
speedily. The acute form is probably a disease of the blood, which carries
with it some poisonous matter that is deposited where the fibrous tissue
is most abundant. The disease flies capriciously from one joint to
another, and the pain caused by even the slightest motion deprives the
sufferer of the use of the disabled part and its muscles. Its chief danger
lies in the possibility of its affecting the vital organs. Chronic
rheumatism--the result of repeated attacks of the acute--leads to great
suffering, and oftentimes to disorganization of the joints and an
interference with the movements of the heart.
6. _Lumbago_ is an inflammation of the lumbar muscles and fascia.
[Footnote: Lumbago is really a form of myalgia, a disease which, has its
seat in the muscles, and may thus affect any part of the body. Doubtless
much of what is commonly called "liver" or "kidney complaint" is only, in
one case, myalgia of the chest or abdominal walls near the liver, or, in
the other, of the back and loins near the kidneys. Chronic liver disease
is comparatively rare in the Northern States, and pain in the side is not
a prominent symptom; while certain diseases of the kidneys, which are as
surely fatal as pulmonary consumption, are not attended by pain in the
back opposite these organs.--WEY.] It may be so moderate as to produce
only a "lame back," or so severe as to disable, as in the case of what is
popularly termed a "crick in the back." Strong swimmers who sometimes
drown without apparent cause are supposed to be seized in this way.
7. _A Ganglion_, or what is vulgarly called a "weak" or "weeping"
sinew, is the swelling of a bursa. [Footnote: A bursa is a small sack
containing a lubricating fluid to prevent friction where tendons play over
hard surfaces. There is one shaped like an hourglass on the wrist, just at
the edge of the palm. By pressing back the liquid it contains, this bursa
may be clearly seen.] It sometimes becomes so distended by fluid as to be
mistaken for bone. If on binding something hard upon it for a few days it
does not disappear, a physician will remove the liquid by means of a
hypodermic syringe, or perhaps cause it to be absorbed by an external
application of iodine.
PRACTICAL QUESTIONS.
1. What class of lever is the foot when we lift a weight on the toes?
2. Explain the movement of the body backward and forward, when resting
upon the thigh bone as a fulcrum.
3. What class of lever do we use when we lift the foot while sitting down?
4. Explain the swing of the arm from the shoulder.
5. What class of lever is used in bending our fingers?
6. What class of lever is our foot when we tap the ground with our toes?
7. What class of lever do we use when we raise ourselves from a stooping
position?
8. What class of lever is the foot when we walk?
9. Why can we raise a heavier weight with our hand when lifting from the
elbow than from the shoulder?
10. What class of lever do we employ when we are hopping, the thigh bone
being bent up toward the body and not used?
11. Describe the motions of the bones when we are using a gimlet.
12. Why do we tire when we stand erect?
13. Why does it rest us to change our work?
14. Why and when is dancing a beneficial exercise?
15. Why can we exert greater force with the back teeth than with the front
ones?
16. Why do we lean forward when we wish to rise from a chair?
17. Why does the projection of the heel bone make walking easier?
18. Does a horse travel with less fatigue over a flat than a hilly
country?
19. Can you move your upper jaw?
20. Are people naturally right or left-handed?
21. Why can so few persons move their ears by the muscles?
22. Is the blacksmith's right arm healthier than the left?
23. Boys often, though foolishly, thrust a pin into the flesh just above
the knee. Why is it not painful?
24. Will ten minutes' practice in a gymnasium answer for a day's exercise?
25. Why would an elastic tendon be unfitted to transmit the motion of a
muscle?
26. When one is struck violently on the head, why does he instantly fall?
27. What is the cause of the difference between light and dark meat in a
fowl?
III.
THE SKIN.
A protection from the outer world, it is our only means of communicating
with it. Insensible itself, it is the organ of touch. It feels the
pressure of a hair, yet bears the weight of the body. It yields to every
motion of that which it wraps and holds in place. It hides from view the
delicate organs within, yet the faintest tint of a thought shines through,
while the soul paints upon it, as on a canvas, the richest and rarest of
colors.
ANALYSIS OF THE SKIN.
_
_ | 1. The Cutis; its Composition and Character.
| 1. THE STRUCTURE | 2. The Cuticle; its Composition and Character.
| OF THE SKIN. | 3. The Value of the Cuticle.
| |_4. The Complexion.
| _
| | a. _Description._
| _ | b. _Method of Growth._
| | 1. The Hair.....| c. _As an Instrument of
| | | Feeling._
| 2. THE HAIR AND | | d. _Indestructibility of
| THE NAILS. | |_ the Hair._
| | _
| |_2. The Nails....| a. _Uses._
| |_b. _Method of Growth._
| _
| 3. THE MUCOUS | 1. The Structure.
| MEMBRANE | 2. Connective Tissue.
| |_3. Fat.
| _
| | 1. Number and Kinds of Teeth.
| | _
| | 1. The Two Sets.| 1. _The Milk Teeth._
| | |_2. _The Permanent Teeth._
| |
| 4. THE TEETH. | 2. Structure of the Teeth.
| | 3. The Setting of the Tooth in the Jaw.
| | 4. The Decay of the Teeth.
| |_5. The Preservation of the Teeth.
| _ _
| | 1. The Two Kinds.| 1. _Oil Glands._
| | |_2. _Perpiratory Glands._
| |
| 5. THE GLANDS | 2. The Perspiration.
| | 3. The Absorbing Power of the Skin. (See
| |_ Lymphatics.)
| _
| | 1. About Washing and Bathing.
| | 2. The Reaction.
| | 3. Sea Bathing. _
| 6. HYGIENE | | a. _General Principles._
| | | b. _Linen._
| | | c. _Cotton._
| |_4. Clothing.......| d. _Woolen._
| | e. _Flannel._
| | f. _Color of Clothing._
| | g. _Structure of
| | Clothing._
| | h. _Insufficient
| _ |_ Clothing._
| | 1. Erysipelas.
| | 2. Salt Rheum.
|_7. DISEASES. | 3. Corns.
| 4. Ingrowing Nails.
| 5. Warts.
|_6. Chilblains.
THE SKIN.
THE SKIN is a tough, thin, close-fitting garment for the protection of the
tender flesh. Its perfect elasticity beautifully adapts it to every motion
of the body. We shall learn hereafter that it is more than a mere
covering, being an active organ, which does its part in the work of
keeping in order the house in which we live. It oils itself to preserve
its smoothness and delicacy, replaces itself as fast as it wears out, and
is at once the perfection of use and beauty.
1. STRUCTURE OF THE SKIN.
CUTIS AND CUTICLE.--What we commonly call the skin--viz., the part raised
by a blister--is only the cuticle [Footnote: _Cuticula_, little skin.
It is often styled the scarfskin, and also the epidermis (_epi_,
upon; and _derma_, skin).] or covering of the cutis or true skin. The
latter is full of nerves and blood vessels, while the former neither
bleeds [Footnote: We notice this in shaving; for if a razor goes below the
cuticle, it is followed by pain and blood. So insensible is this outer
layer that we can run a pin through the thick mass at the roots of the
nails without discomfort.] nor gives rise to pain, neither suffers from
heat nor feels the cold.
The cuticle is composed of small, flat cells or scales. These are
constantly shed from the surface in the form of scurf, dandruff, etc., but
are as constantly renewed from the cutis [Footnote: We see how rapidly
this change goes on by noticing how soon a stain of any kind disappears
from the skin. A snake throws off its cuticle entire, and at regular
intervals.] below.
Under the microscope, we can see the round cells of the cuticle, and how
they are flattened and hardened as they are forced to the surface. The
immense number of these cells surpasses comprehension. In one square inch
of the cuticle, counting only those in a single layer, there are over a
billion horny scales, each complete in itself.--HARTING.
FIG. 22.
[Illustration: A _represents a vertical section of the Cuticle._ B,
_lateral view of the cells._ C, _flat side of scales like_ d,
_magnified 250 diameters, showing the nucleated cells transformed into
broad scales._]
VALUE OF THE CUTICLE.--In the palm of the hand, the sole of the foot, and
other parts especially liable to injury, the cuticle is very thick. This
is a most admirable provision for their protection. [Footnote: We can hold
the hand in strong brine with impunity, but the smart will quickly tell us
when there is even a scratch in the skin. Vaccine matter must be inserted
beneath the cuticle to take effect. This membrane doubtless prevents many
poisonous substances from entering the system.] By use, it becomes callous
and horny. The boy who goes out barefoot for the first time, "treading as
if on eggs," can soon run where he pleases among thistles and over stones.
The blacksmith handles hot iron without pain, while the mason lays stones
and works in lime, without scratching or corroding his flesh.
THE COMPLEXION.--In the freshly made cells on the lower side of the
cuticle, is a pigment composed of tiny grains. [Footnote: These grains are
about 1/2000 of an inch in diameter, and, curiously enough, do not appear
opaque, but transparent and nearly colorless.--MARSHALL.] In the varying
tint of this coloring matter, lies the difference of hue between the
blonde and the brunette, the European and the African. In the purest
complexion, there is some of this pigment, which, however, disappears as
the fresh, round, soft cells next the cutis change into the old, flat,
horny scales at the surface.
Scars are white, because this part of the cuticle is not restored. The sun
has a powerful effect upon the coloring matter, and so we readily "tan" on
exposure to its rays. If the color gathers in spots, it forms freckles.
[Footnote: This action of the sun on the pigment of the skin is very
marked. Even among the Africans, the skin is observed to lose its intense
black color in those who live for many months in the shades of the forest.
It is said that Asiatic and African women confined within the walls of the
harem, and thus secluded from the sun, are as fair as Europeans. Among the
Jews who have settled in Northern Europe, are many of light complexion,
while those who live in India are as dark as the Hindoos. Intense heat
also increases this coloring matter, and thus a furnace-man's skin, even
where protected by clothing, becomes completely bronzed. The black pigment
has been known to disappear during severe illness, and a lighter color to
be developed in its place. Among the negroes, are sometimes found people
who have no complexion, _i. e._, there is no coloring matter in their
skin, hair, or the iris of their eyes. These persons are called Albinos.]
II. HAIR AND NAILS.
The Hair and the Nails are modified forms of the cuticle.
FIG. 23.
[Illustration: A _Hair, magnified 600 diameters._ S, _the sac
(follicle);_ P, _the papilla, showing the cells and the blood
vessels:_ V.]
THE HAIR is a protection from heat and cold, and shields the head from
blows. It is found on nearly all parts of the body, except the palms of
the hands and the soles of the feet. The outside of a hair is hard and
compact, and consists of a layer of colorless scales, which overlie one
another like the shingles of a house; the interior is porous, [Footnote:
In order to examine a hair, it should be put on the slide of the
microscope, and covered with a thin glass, while a few drops of alcohol
are allowed to flow between the cover and the slide. This causes the air,
which fills the hair and prevents our seeing its structure, to escape.]
and probably conveys the liquids by which it is nourished.
Each hair grows from a tiny bulb (papilla), which is an elevation of the
cutis at the bottom of a little hollow in the skin. From the surface of
this bulb, the hair is produced, like the cuticle, by the constant
formation of new cells at the bottom. When the hair is pulled out, this
bulb, if uninjured, will produce a new one; but, when once destroyed, it
will never grow again. [Footnote: Hair grows at the rate of about five to
seven inches in a year. It is said to grow after death. This appearance is
due to the fact that by the shrinking of the skin the part below the
surface is caused to project, which is especially noticeable in the
beard.] The hair has been known to whiten in a single night by fear,
fright, or nervous excitement. When the color has once changed, it can not
be restored. [Footnote: Hair dyes, or so-called "hair restorers," are
almost invariably deleterious substances, depending for their coloring
properties upon the action of lead or lunar caustic. Frequent instances of
hair poisoning have occurred, owing to the common use of such dangerous
articles. If the growth of the hair be impaired, the general constitution
or the skin needs treatment. This is the work of a skillful physician, and
not of a patent remedy. Dame Fashion has her repentant freaks as well as
her ruinous follies, and it is a healthful sign that the era of universal
hair dyeing has been blotted out from her present calendar, and the gray
hairs of age are now honored with the highest place in "style" as well as
in good sense and cleanliness.] (See p. 285.)
Wherever hair exists, tiny muscles are found, interlaced among the fibers
of the skin. These, when contracting under the influence of cold or
electricity, pucker up the skin, and cause the hair to stand on end.
[Footnote: In horses and other animals which are able to shake the whole
skin, this muscular tissue is much more fully developed than in man.] The
hairs themselves are destitute of feeling. Nerves, however, are found in
the hollows in which the hair is rooted, and so one feels pain when it is
pulled. [Footnote: These nerves are especially abundant in the whiskers of
the cat, which are used as feelers.] Thus the insensible hairs become
wonderfully delicate instruments to convey an impression of even the
slightest touch.
FIG. 24.
[Illustration: A, _a perspiratory tube with its gland;_ B, _a hair
with a muscle and two oil glands;_ C, _cuticle;_ D, _the
papillæ;_ and E, _fat cells._]
Next to the teeth and bones, the hair is the least destructible part of
the body, and its color is often preserved for many years after the other
portions have gone to decay. [Footnote: Fine downy hairs, such as are
general upon the body, have been detected in the little fragments of skin
found beneath the heads of the nails by which, centuries ago, certain
robbers were fastened to the church doors, as a punishment for their
sacrilege.]
THE NAILS protect the ends of the tender finger, and toe, and give us
power more firmly to grasp and easily to pick up any object we may desire.
They enable us to perform a hundred little, mechanical acts which else
were impossible. At the same time, their delicate color and beautiful
outline give a finish of ornament to that exquisite instrument, the hand.
The nail is firmly set in a groove (matrix) in the cuticle, from which it
grows at the root in length [Footnote: By making a little mark on the nail
near the root we can see, week by week, how rapidly this process goes on,
and so form some idea of what a multitude of cells must be transformed
into the horny matter of the nail.] and from beneath in thickness. So long
as the matrix at the root is uninjured, the nail will be replaced after
any accident. (See p. 288.)
III. THE MUCOUS MEMBRANE.
STRUCTURE.--At the edges of the openings into the body, the skin seems to
stop and give place to a tissue which is redder, more sensitive, more
liable to bleed, and is moistened by a fluid, or mucus, as it is called.
Really, however, the skin does not cease, but passes into a more delicate
covering of the same general structure, viz., an outer, hard, bloodless,
insensible layer, and an inner, soft, sanguine, nervous one. [Footnote:
With a dull knife, we can scrape from the mucous membrane which lines the
mouth some of the cuticle for examination under the microscope. In a
similar way, we can obtain cuticle from the surface of the body for study
and comparison.] Thus every part of the body is wrapped in a kind of
double bag, made of tough skin on the outside, and tender mucous membrane
on the inside.
CONNECTIVE TISSUE.--The cutis and the corresponding layer of the mucous
membrane consist chiefly of a fibrous substance interlaced, like felt. It
is called connective tissue, because it connects all the different parts
of the body. It spreads from the cutis, invests muscles, bones, and
cartilages, and thence passes into the mucous membrane. So thoroughly does
it permeate the body, that, if the other tissues were destroyed, it would
give a perfect model of every organ. [Footnote: It is curious to notice
how our body is wrapped in membrane. On the outside, is the skin
protecting from exterior injury, and, on the inside, is the mucous
membrane reaching from the lips to the innermost air cell of the lungs.
Every organ is enveloped in its membrane. Every bone has its sheath. Every
socket is lined. Even the separate fibers of muscles have their covering
tissue. The brain and the spinal cord are triply wrapped, while the eye is
only a membranous globe filled with fluid. These membranes protect and
support the organs they enfold, but, with that wise economy so
characteristic of nature everywhere, they have also an important function
to perform. They are the _filters_ of the body. Through their pores
pass alike the elements of growth, and the returning products of waste. On
one side, bathed by the blood, they choose from it suitable food for the
organ they envelop, and many of them in their tiny cells, by some
mysterious process, form new products,--put the finishing touches, as it
were, upon the material ere it is deposited in the body.] It can be seen
in a piece of meat as a delicate substance lying between the layers of
muscle, where it serves to bind together the numerous fibers of which they
are composed.
Connective tissue yields gelatine on boiling, and is the part which tans
when hides are manufactured into leather. It is very elastic, so that when
you remove your finger after pressing upon the skin, no indentation is
left. [Footnote: In dropsy, this elasticity is lost by distension, and
there is a kind of "pitting," as it is called, produced by pressure.] It
varies greatly in character,--from the mucous membrane, where it is soft
and tender, to the ligaments and tendons which it largely composes, where
it is strong and dense. [Footnote: The leather made from this tissue
varies as greatly, from the tough, thick oxhide, to the soft, pliable kid
and chamois skin.]
FAT is deposited as an oil in the cells [Footnote: So tiny are these
cells, that there are over sixty-five million in a cubic inch of fat. As
they are kept moist, the liquid does not ooze out, but, on drying, it
comes to the surface, and thus a piece of fat feels oily when exposed to
the air. The quantity of fat varies with the state of nutrition. In
corpulent persons, the masses of fat beneath the skin, in the mesentery,
on the surface of the heart and great vessels, between the muscles, and in
the neighborhood of the nerves, are considerably increased. Conversely, in
the emaciated we sometimes find beneath the skin nucleated cells, which
contain only one oil drop. Many masses of fat which have an important
relation to muscular actions--such as the fat of the orbit or the cheek--
do not disappear in the most emaciated object. Even in starvation, the
fatty substances of the brain and spinal cord are retained.--VALENTIN.] of
this tissue, just beneath the skin (Fig. 24), giving roundness and
plumpness to the body, and acting as an excellent nonconductor for the
retention of heat. It collects as pads in the hollows of the bones, around
the joints, and between the muscles, causing them to glide more easily
upon each other. As marrow, it nourishes the skeleton, and also
distributes the shock of any jar the limb may sustain.
It is noticeable, however, that fat does not gather within the cranium,
the lungs, or the eyelids, where its accumulation would clog the organs.
IV. THE TEETH.
THE TEETH [Footnote: Although the teeth are always found in connection
with the skeleton, and are, therefore, figured as a part of it (Fig. 1),
yet they do not properly belong to the bones of the body, and are merely
set in the solid jaw to insure solidity. They are hard, and resemble bony
matter, yet they are neither true bone nor are they formed in the same
manner. "They are properly appendages of the mucous membrane, and are
developed from it."--LEIDY. "They belong to the Tegumentary System, which,
speaking generally of animals, includes teeth, nails, horns, scales, and
hairs."--MARSHALL. They are therefore classed with the mucous membrane, as
are the nails and hair with the skin.] are thirty-two in all,--there being
eight in each half jaw, similarly shaped and arranged. In each set of
eight, the two nearest the middle of the jaw have wide, sharp, chisel-like
edges, fit for cutting, and hence are called _incisors_. The next one
corresponds to the great tearing or holding tooth of the dog, and is
styled the _canine_, or eye-tooth. The next two have broader crowns,
with two points, or cusps, and are hence termed the _bicuspids_. The
remaining three are much broader, and, as they are used to crush the food,
are called the _grinders_, or _molars_. The incisors and
eyeteeth have one fang, or root; the others have two or three fangs.
THE MILK TEETH.--We are provided with two sets of teeth. The first, or
milk teeth, are small and only twenty in number. In each half jaw there
are two incisors, one canine, and two molars. The middle incisors are
usually cut about the age of seven months, the others at nine months, the
first molars at twelve months, the canines at eighteen months, and the
remaining molars at two or three years of age. The lower teeth precede the
corresponding upper ones. The time often varies, but the order seldom.
THE PERMANENT TEETH.--At six years, when the first set is usually still
perfect, the jaws contain the crowns of all the second, except the wisdom
teeth. About this age, to meet the wants of the growing body, the crowns
of the permanent set begin to press against the roots of the milk teeth,
which, becoming absorbed, leave the loosened teeth to drop out, while the
new ones rise and occupy their places. [Footnote: If the milk teeth, do
not promptly loosen on the appearance of the second set, the former should
be at once removed to permit the permanent teeth to assume their natural
places. If any fail to come in regularly, or if they crowd the others, a
competent dentist should be consulted.]
FIG. 25.
[Illustration: _The teeth at the age of six and one half years._ I,
_the incisors;_ O, _the canine;_ M, _the molars; the last
molar is the first of the permanent teeth;_ F, _sacs of the permanent
incisors;_ C, _of the canine;_ B, _of the bicuspids;_ N,
_of the second molar; the sac of the third molar is empty._--
MARSHALL.]
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