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Hygienic Physiology

J >> Joel Dorman Steele >> Hygienic Physiology




3. _The Internal Ear_, or labyrinth, as it is sometimes called from
its complex character, is hollowed out of the solid bone. In front, is the
vestibule or antechamber, _A_, about as large as a grain of wheat;
from it open three _semicircular canals_, _D_, and the winding
stair of the _cochlea_, or snail shell, _E_. Here expand the
delicate fibrils of the auditory nerve. Floating in the liquid which fills
the labyrinth is a little bag containing hair-like bristles, fine sand,
and two ear stones (_otoliths_). All these knocking against the ends
of the nerves, serve to increase any impulse given to the liquid in which
they lie. Finally, to complete this delicate apparatus, in the cochlea are
minute tendrils, named the fibers of Corti, from their discoverer. These
are regularly arranged,--the longest at the bottom, and the shortest at
the top. Could this spiral plate, which coils two and a half times around,
be unrolled and made to stand upright, it would form a beautiful
microscopic harp of three thousand strings. If it were possible to strike
these cords as one can the keyboard of a piano, he could produce in the
mind of the person experimented upon every variety of tone which the ear
can distinguish.

HOW WE HEAR.--Whenever one body strikes another in the air, waves are
produced, just as when we throw a stone into the water a series of
concentric circles surrounds the spot where it sinks. These waves of air
strike upon the membrane. This vibrates, and sends the motion along the
chain of bones in the middle ear to the fluids of the labyrinth. Here
bristles, sand, and stones pound away, and the wondrous harp of the
cochlea, catching up the pulsations, [Footnote: The original motion is
constantly modified by the medium through which it passes. The bristles,
otoliths, and Cortian fibers of the ear, and the rods and cones of the eye
(p. 239) serve to convert the vibrations into pulsations which act as
stimuli of the appropriate nerve. The molecular change thus produced in
the nerve fibers is propagated to the brain.--See _Popluar
Physics_, p. 182.] carries them to the fibers of the auditory nerve,
which conveys them to the brain, and gives to the mind the idea of sound.

CARE OF THE EAR.--The delicacy of the ear is such that it needs the
greatest care. Cold water should not be allowed to enter the auditory
canal. If the wax accumulate, never remove it with a hard instrument, lest
the delicate membrane be injured, but with a little warm water, after
which turn the head to let the water run out, and wipe the ear dry. The
hair around the ears should never be left wet, as it may chill this
sensitive organ. If an insect get in the external ear, pour in a little
oil to kill it, and then remove with tepid water. The object of the
Eustachian tube is to admit air into the ear, and thus equalize the
pressure on the membrane. If it become closed by a cold, or if, from any
cause, the pressure be made unequal, so as to produce an unpleasant
feeling in the ear, relief may often be obtained by grasping the nose and
forcibly swallowing. (See p. 350.)

5. SIGHT.

FIG. 61.

[Illustration: _The Eye._]

DESCRIPTION.--The eye is lodged in a bony cavity, protected by the
overhanging brow. It is a globe, about an inch in diameter. The ball is
covered by three coats--(l) the _sclerotic_, _d_, a tough, horny
casing, which gives shape to the eye, the convex, transparent part in
front forming a window, the _cornea_, _d_; (2) the _choroid_, _e_, a
black lining, to absorb the superfluous light [Footnote: Neither white
rabbits nor albinos have this black lining, and hence their sight is
confused.] and (3) the _retina_, _b_, a membrane in which expand fibers
of the _optic nerve_, _o_. The _crystalline lens_, _a_, brings the rays
of light to a focus on the retina. The lens is kept in place by the
ciliary processes, _g_, arranged like the rays in the disk of a passion
flower. Between the cornea and the crystalline lens is a limpid fluid
termed the _aqueous humor_; while the _vitreous humor_--a transparent,
jelly-like liquid fills the space (_h_) back of the crystalline lens.
The pupil, _k_, is a hole in the colored, muscular curtain, _i_, the
_iris_ (rainbow). (See p. 352.)

FIG. 62.

[Illustration: _The Eyelashes and the Tear Glands._]

EYELIDS AND TEARS.--The eyelids are close-fitting shutters to screen the
eye. The inner side is lined with a mucous membrane that is exceedingly
sensitive, and thus aids in protecting the eye from any irritating
substance. The looseness of the skin favors swelling from inflammation or
the effusion of blood, as in a "black eye." The eyelashes serve as a kind
of sieve to exclude the dust, and, with the lids, to shield against a
blinding light. Just within the lashes are oil glands, which lubricate the
edges of the lids, and prevent them from adhering to each other. The tear
or _lachrymal_ gland, _G_, is an oblong body lodged in the bony
wall of the orbit. It empties by several ducts upon the inner surface, at
the outer edge of the upper eyelid. Thence the tears, washing the eye, run
into the _lachrymal lake_, _D_, a little basin with a rounded
border fitted for their reception. On each side of this lake two canals,
_C_, _C_, drain off the overplus through the duct, _B_,
into the nose. In old age and in disease, these canals fail to conduct the
tears away, and hence the lachrymal lake overflows upon the face.

FIG. 63.

[Illustration: _Structure of the Retina._]

STRUCTURE OF THE RETINA.--In Fig. 63 is shown a section of the retina,
greatly magnified, since this membrane never exceeds 1/80 an inch in
thickness. On the inner surface next to the vitreous humor, is a lining
membrane not shown in the cut. Next to the choroid and comprising about
1/4 the entire thickness of the retina, is a multitude of transparent,
colorless, microscopic rods, _a_, evenly arranged and packed side by
side, like the seeds on the disk of a sunflower. Among them, at regular
intervals, are interspersed the cones, _b_. Delicate nerve fibers
pass from the ends of the rods and cones, each expanding into a granular
body, _c_, thence weaving a mesh, _d_, and again expanding into
the granules, _f_. Last is a layer of fine nerve fibers, _g_,
and gray, ganglionic cells, _h_, like the gray matter of the brain,
whence filaments extend into _i_, the fibers of the optic nerve. (See
p. 354.)

The layer of rods and cones is to the eye what the bristles, otoliths, and
Cortian fibers are to the ear. Indeed, the nerve itself is insensible to
light. At the point where it enters the eye, there are no rods and cones,
and this is called the _blind spot_. A simple experiment will
illustrate the fact. Hold this book directly before the face, and, closing
the left eye, look steadily with the right at the left-hand circle in Fig.
64. Move the book back and forth, and a point will be found where the
right-hand circle vanishes from sight. At that moment its light falls upon
the spot where the rods and cones are lacking.

FIG. 64.

[Illustration:]

HOW WE SEE.--There is believed to be a kind of universal atmosphere,
termed _ether_, filling all space. This substance is infinitely more
subtle than the air, and occupies its pores, as well as those of all other
substances. As sound is caused by waves in the atmosphere, so light is
produced by waves in the ether. A lamplight, for example, sets in motion
waves of ether, which pass in through the pupil of the eye, to the retina,
where the rods and cones transmit the vibration through the optic nerve to
the brain, and then the mind perceives the light. (Note, p. 236.)

THE USE OF THE CRYSTALLINE LENS. [Footnote: The uses of the eye and ear
are dependent upon the principles of Optics and Acoustics. They are
therefore best treated in Physics.]--A convex lens, as a common burning
glass, bends the rays of light which pass through it, so that they meet at
a point called the _focus_. The crystalline lens converges the rays
of light which enter the eye, and brings them to a focus on the retina.
[Footnote: The cornea and the humors of the eye act in the same manner as
the crystalline lens, but not so powerfully.] The healthy lens has a power
of changing its convexity so as to adapt [Footnote: The simplest way of
experimenting on the "adjustment of the eye" is to stick two stout needles
upright into a straight piece of wood,--not exactly, but nearly in the
same straight line, so that, on applying the eye to one end of the piece
of wood, one needle (A) shall be seen about six inches off, and the other
(B) just on one side of it, at twelve inches distance. If the observer
looks at the needle B he will find that he sees it very distinctly, and
without the least sense of effort; but the image of A is blurred, and more
or less double. Now, let him try to make this blurred image of the needle
A distinct. He will find he can do so readily enough, but that the act is
accompanied by a sense of fatigue. And in proportion as A becomes
distinct, B will become blurred. Nor will any effort enable him to see A
and B distinctly at the same time.--HUXLEY.] itself to near and to distant
objects. (See Fig. 66.)

FIG. 65.

[Illustration: _Diagram showing how an image of an object is formed upon
the Retina by the Crystalline Lens._]

NEAR AND FAR SIGHT.--If the lens be too convex, it will bring the rays to
a focus before they reach the retina; if too flat, they will reach the
retina before coming to a focus. In either case, the sight will be
indistinct. A more common defect, however, is in the shape of the globe of
the eye, which is either flattened or elongated. In the former case (see
_G_, Fig. 67), objects at a distance can be seen most distinctly--
hence that is called farsightedness. [Footnote: This should not be
confounded with the long sight of old people, which is caused by the
stiffness of the ciliary muscles, whereby the lens can not adapt itself to
the varying distances of objects.] In the latter, objects near by are
clearer, and hence this is termed nearsightedness. Farsightedness is
remedied by convex glasses; nearsightedness, by concave. When glasses will
improve the sight they should be worn; [Footnote: Dr. Henry W. Williams,
the celebrated ophthalmologist, says that, in some cases, glasses are more
necessary at six or eight years of age than to the majority of healthy
eyes at sixty. Sometimes children find accidentally that they can see
better through grandmother's spectacles. They should then be supplied with
their own.] any delay will be liable to injure the eyes, by straining
their already impaired power. Cataract is a disease in which there is an
opacity of the crystalline lens or its capsules, which obscures the
vision. The lens may be caused to be absorbed, or may be removed by a
skillful surgeon and the defect remedied by wearing convex glasses.

FIG. 66.

[Illustration: _Adjustment of the Crystalline Lens._--A, _for far
objects, and_ B, _for near._]

FIG. 67.

[Illustration: _Diagram illustrating the position of the Retina._--B,
_in natural sight;_ G, _in far sight; and_ C, _in near sight._]

COLOR-BLIND PERSONS receive only two of the three elementary color
sensations (green, red, violet). The spectrum appears to them to consist
of two decidedly different colors, with a band of neutral tint between.
The extreme red end is invisible, and a bright scarlet and a deep green
appear alike. They are unable to distinguish between the leaves of a
cherry tree and its fruit by the color of the two, and see no difference
between blue and yellow cloth. Whittier, the poet, it is said, could not
tell red from green unless in direct sunlight. Once he patched some
damaged wall paper in his library by matching a green vine in the pattern
with one of a bright autumnal crimson. This defect in the eye is often
unnoticed, and many railway accidents have doubtless happened through an
inability to detect the color of signal lights.

CARE OF THE EYES.--The shape of the eye can not be changed by rubbing and
pressing it, as many suppose, but the sight may thus be fatally injured.
Children troubled by nearsightedness should not lean forward at their
work, as thereby the vessels of the eye become overcharged with blood.
They should avoid fine print, and try, in every possible way, to spare
their eyes. If middle age be reached without especial difficulty of sight,
the person is comparatively safe. Most cases of squinting are caused by
longsightedness, the muscles being strained in the effort to obtain
distinct vision. In childhood, it may be cured by a competent surgeon, who
will generally cut the muscle that draws the eye out of place.

After any severe illness, especially after measles, scarlatina, or typhoid
fever, the eyes should be used with extreme caution, since they share in
the general debility of the body, and recover their strength slowly.
Healthy eyes even should never be used to read fine print or by a dim
light. Serious injury may be caused by an imprudence of this kind. Reading
upon the cars is also a fruitful source of harm. The lens, striving to
adapt itself to the incessantly varying distance of the page, soon becomes
wearied. Whenever the eyes begin to ache, it is a warning that they are
being overtaxed and need rest.

Objects that get into the eye should be removed before they cause
inflammation; rubbing in the meantime only irritates and increases the
sensitiveness. If the eye be shut for a few moments, so as to let the
tears accumulate, and the upper lid be then lifted by taking hold of it at
the center, the cinder or dust is often washed away at once. Trifling
objects can be removed by simply drawing the upper lid as far as possible
over the lower one; when the lid flies back to its place, the friction
will detach any light substance. If it becomes necessary, turn the upper
lid over a pencil, and the intruder may then be wiped off with a
handkerchief. "Eye-stones" are a popular delusion. When they seem to take
out a cinder, it is only because they raise the eyelid, and allow the
tears to wash it out. No one should ever use an eyewash, except by medical
advice. The eye is too delicate an organ to be trifled with, and when any
disease is suspected, a reliable physician should be consulted. This is
especially necessary, since, when one eye is injured, the other, by
sympathy, is liable to become inflamed, and perhaps be destroyed.

When reading or working, the _light should be at the left side, or at
the rear; never in front_.

The constant increase of defective eyesight among the pupils in our
schools is an alarming fact. Dr. Agnew considers that our schoolrooms are
fast making us a spectacle-using people. Nearsightedness seems to increase
from class to class, until in the upper departments, there are sometimes
as high as fifty per cent of the pupils thus afflicted. The causes are
(1), desks so placed as to make the light from the windows shine directly
into the eyes of the scholars; (2), cross lights from opposite windows;
(3), insufficient light; (4), small type that strains the eyes; and (5),
the position of the pupil as he bends over his desk or slate, causing the
blood to settle in his eyes. All these causes can be remedied; the
position of the desks can be changed; windows can be shaded, or new ones
inserted; books and newspapers that try the eyes can be rejected; and
every pupil can be taught how to sit at study.

PRACTICAL QUESTIONS.

1. Why does a laundress test the temperature of her flatiron by holding it
near her cheek?

2. When we are cold, why do we spread the palms of our hands before the
fire?

3. What is meant by a "furred tongue"?

4. Why has sand or sulphur no taste?

5. What was the origin of the word palatable?

6. Why does a cold in the head injure the flavor of our coffee?

7. Name some so-called flavors that are really sensations of touch.

8. What is the object of the hairs in the nostrils?

9. What use does the nose subserve in the process of respiration?

10. Why do we sometimes hold the nose when we take unpleasant medicine?

11. Why was the nose placed over the mouth?

12. Describe how the hand is adapted to be the instrument of touch.

13. Besides being the organ of taste, what use does the tongue subserve?

14. Why is not the act of tasting complete until we swallow?

15. Why do all things have the same flavor when one's tongue is "furred"
by fever?

16. Which sense is the more useful--hearing or sight?

17. Which coat is the white of the eye?

18. What makes the difference in the color of eyes?

19. Why do we snuff the air when we wish to obtain a distinct smell?

20. Why do red-hot iron and frozen mercury (-40°) produce the same
sensation?

21. Why can an elderly person drink tea which to a child would be
unbearably hot?

22. Why does an old man hold his paper so far from his eyes?

23. Would you rather be punished on the tips of your fingers than on the
palm of your hand?

24. What is the object of the eyelashes? Are the hairs straight?

25. What is the use of winking?

26. When you wink, do the eyelids touch at once along their whole length?
Why?

27. How many rows of hairs are there in the eyelashes?

28. Do all nations have eyes of the same shape?

29. Why does snuff taking cause a flow of tears?

30. Why does a fall cause one to "see stars"?

31. Why can we not see with the nose, or smell with the eyes?

32. What causes the roughness of a cat's tongue?

33. Is the cuticle essential to touch?

34. Can one tickle himself?

35. Why does a bitter taste often produce vomiting?

36. Is there any danger in looking "crosseyed" for fun?

37. Should schoolroom desks face a window?

38. Why do we look at a person to whom we are listening attentively?

39. Do we really feel with our fingers?

40. Is the eye a perfect sphere? (See Fig. 61.)

41. How often do we wink?

42. Why is the interior of a telescope or microscope often painted black?

43. What is "the apple of the eye"?

44. What form of glasses do old people require?

45. Should we ever wash our ears with cold water?

46. What is the object of the winding passages in the nose?

47. Can a smoker tell in the dark, whether or not his cigar is lighted?

48. Will a nerve reunite after it has been cut?

49. Will the sight give us an idea of solidity? [Footnote: A case occurred
a few years ago, in London, where a friend of my own performed an
operation upon a young woman who had been born blind, and, though an
attempt had been made in early years to cure her, it had failed. She was
able just to distinguish large objects, the general shadow, as it were,
without any distinct perception of form, and to distinguish light from
darkness. She could work well with her needle by the touch, and could use
her scissors and bodkin and other implements by the training of her hand,
so to speak, alone Well, my friend happened to see her, and he examined
her eyes, and told her that he thought he could get her sight restored; at
any rate, it was worth a trial. The operation succeeded; and, being a man
of intelligence and quite aware of the interest of such a case, he
carefully studied and observed it; and he completely confirmed all that
had been previously laid down by the experience of similar cases. There
was one little incident which will give you an idea of the education which
is required for what you would suppose is a thing perfectly simple and
obvious. She could not distinguish by sight the things that she was
perfectly familiar with by the touch, at least when they were first
presented to her eyes. She could not recognize even a pair of scissors.
Now, you would have supposed that a pair of scissors, of all things in the
world, having been continually used by her, and their form having become
perfectly familiar to her hands, would have been most readily recognized
by her sight; and yet she did not know what they were; she had not an idea
until she was told, and then she laughed, as she said, at her own
stupidity. No stupidity at all; she had never learned it, and it was one
of those things which she could not know without learning. One of the
earliest cases of this kind was related by the celebrated Cheselden, a
surgeon of the early part of last century. Cheselden relates how a youth
just in this condition had been accustomed to play with a cat and a dog;
but for some time after he attained his sight he never could tell which
was which, and used to be continually making mistakes. One day, being
rather ashamed of himself for having called the cat the dog, he took up
the cat in his arms and looked at her very attentively for some time
stroking her all the while; and in this way he associated the impression
derived from the touch, and made himself master (so to speak) of the whole
idea of the animal. He then put the cat down, saying: "Now, puss, I shall
know you another time."--CARPENTER.]

50. Why can a skillful surgeon determinate the condition of the brain and
other internal organs by examining the interior of the eye? [Footnote:
This is done by means of an instrument called the ophthalmoscope. Light is
thrown into the eye with a concave mirror, and the interior of the organ
examined with a lens.]

51. Is there any truth in the idea that the image of the murderer can be
seen in the eye of the dead victim?

52. What is the length of the optic nerve? _Ans_. About three fourths
of an inch.

53. Why does an injury to one eye generally affect the other eye?
_Ans_. The optic nerves give off no branches in passing from their
origin in two ganglia situated between the cerebrum and the cerebellum,
and their termination in the eyeballs; but, in the middle of their course,
they _decussate_, or unite in one mass. The fibers of the two nerves
here pass from side to side, and intermingle. The two ganglia are also
united directly by fibers. Thus the eyes are not really separate organs of
sight, but a kind of double organ to perform, a single function.




IX.


HEALTH AND DISEASE.--DEATH AND DECAY.

"Health is the vital principle of bliss."

THOMSON.

"There are three wicks to the lamp of a man's life: brain, blood, and
breath. Press the brain a little, its light goes out, followed by both the
others. Stop the heart a minute, and out go all three of the wicks. Choke
the air out of the lungs, and presently the fluid ceases to supply the
other centers of flame, and all is soon stagnation, cold, and darkness."

O. W. HOLMES.

"Calmly he looked on either Life, and here
Saw nothing to regret, or there to fear;
From Nature's temp'rate feast rose satisfy'd,
Thank'd Heaven that he had lived, and that he died."

POPE.

HEALTH AND DISEASE.--DEATH AND DECAY.

VALUE OF HEALTH.--The body is the instrument which the mind uses. If it be
dulled or nicked, the effect of the best labor will be impaired. The
grandest gifts of mind or fortune are comparatively valueless unless there
be a healthy body to use and enjoy them. The beggar, sturdy and brave with
his outdoor life, is really happier than the rich man in his palace with
the gout to twinge him amid his pleasures. The day has gone by when
delicacy is considered an element of beauty. Weakness is timid and
irresolute; strength is full of force and energy. Weakness walks or
creeps; strength speeds the race, wins the goal, and rejoices in the
victory.

FALSE IDEAS OF DISEASE.--It was formerly supposed that diseases were
caused by evil spirits, who entered the body, and deranged its action.
Incantations, spells, etc., were resorted to in order to drive them out.
By others, disease was thought to come arbitrarily, or as a special
visitation of an overruling power. Hence, it was to be removed by fasting
and prayer. Modern science teaches us that disease is not a thing, but a
state. When our food is properly assimilated, the waste matter promptly
excreted, and all the organs work in harmony, we are well; when any
derangement of these functions occurs, we are sick. Sickness is discord,
as health is concord. If we abuse or misuse any instrument, we impair its
ability to produce a perfect harmony. A suffering body is simply the
penalty of violated law.

PREVENTION OF DISEASE.--Doubtless a large proportion of the ills which now
afflict and rob us of so much time and pleasure might easily be avoided. A
proper knowledge and observance of hygienic laws would greatly lessen the
number of such diseases as consumption, catarrh, gout, rheumatism,
dyspepsia, etc. There are parts of England where one half the children die
before they are five years old. Every physiologist knows that at least
nine tenths of these lives could be saved by an observance of the simple
laws of health. Professor Bennet, in a lecture at Edinburgh, estimated
that one hundred thousand persons die annually in Great Britain from
causes easily preventable.

With the advance of science, the causes of many diseases have been
determined. Vaccination has been found to prevent or mitigate the ravages
of smallpox. Scurvy, formerly so fatal among sailors that it was deemed "a
mysterious infliction of Divine Justice against which man strives in
vain," is now entirely avoided by the use of vegetables or lime juice.
Cholera, whose approach still strikes dread, and for which there is no
known specific, is but the penalty for filthy streets, bad drainage, and
overcrowded tenements, and may be controlled, if not prevented, by
suitable sanitary measures. It was, no doubt, the intention that we should
wear out by the general decay of all the organs, [Footnote: So long as the
phenomena of waste and repair are in harmony--so long, in other words, as
the builder follows the scavenger--so long man exists in integrity and
repair--just, indeed, as houses exist. Derange nutrition, and at once
degeneration, or rather let us say, alteration begins. Alas! that we are
so ignorant that there are many things about our house, which, seeing
them, weaken, we know not how to strengthen. About the brick and the
mortar, the frame and the rafters, we are not unlearned; but within are
many complexities, many chinks and crannies, full in themselves of
secondary chinks and crannies, and these so small, so deep, so recessed,
that it happens every day that the destroyer settles himself in some place
so obscure, that, while he kills, he laughs at defiance. You or I meet
with an accident in our watch. We consult the watchmaker, and he repairs
the injury. If we were all that watchmakers, like ourselves, should be, a
man could be made to keep time until he died from old age or annihilating
accident. This I firmly and fully believe.--_Odd Hours of a
Physician_.] rather than by the giving out of any single part, and that
all should work together harmoniously until the vital force is exhausted.

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