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.]
The central incisors appear at about seven years of age; the others at
eight; the first bicuspids at nine, the second at ten; the canines at
eleven or twelve; the second [Footnote: The first molar appears much
earlier. (See Fig. 25.)] molars at twelve or thirteen, and the last, or
wisdom teeth, are sometimes delayed until the twenty-second year, or even
later.
STRUCTURE OF THE TEETH.--The interior of the tooth consists principally of
_dentine_, a dense substance resembling bone. [Footnote: In the tusk
of the elephant this is known as ivory.] The crown of the tooth, which is
exposed to wear, is protected by a sheath of _enamel_. This is a
hard, glistening, white substance, containing only two and a half per cent
of animal matter. The fang is covered by a thin layer of true bone
(cement).
FIG. 26.
[Illustration: _Vertical section of a Molar Tooth, moderately
magnified._ a, _enamel of the crown, the lines of which indicate the
arrangement of its columns;_ b, _dentine;_ c, _cement;_ d,
_pulp cavity._]
At the center of the tooth is a cavity filled with a soft, reddish-white,
pulpy substance full of blood vessels and nerves. This pulp is very
sensitive, and toothache is caused by its irritation.
THE FITTING OF THE TOOTH INTO THE JAW is a most admirable contrivance. It
is not set like a nail in wood, having the fang in contact with the bone;
but the socket is lined with a membrane which forms a soft cushion. While
this is in a healthy state, it deadens the force of any shock, but, when
inflamed, it becomes the seat of excruciating pain.
THE DECAY OF THE TEETH [Footnote: Unlike the other portions of the body,
there is no provision made for any change in the permanent teeth. That
part, however, which is thus during life most liable to change, after
death resists it the longest. In deep-sea dredgings teeth are found when
all traces of the frame to which they belonged have disappeared. Yet hard
and incorruptible as they seem, their permanence is only relative. Exposed
to injury and disease, they break or decay. Even if they escape accident,
they yet wear at the crown, are absorbed at the fang, and, in time, drop
out, thus affording another of the many signs of the limitations
Providence has fixed to the endurance of our bodies and the length of our
lives.] is commonly caused (1) by portions of the food which become
entangled between them, and, on account of the heat and moisture, quickly
decompose; and (2) by the saliva, as it evaporates, leaving on the teeth a
sediment, which we call tartar. This collects organic matter that rapidly
changes, and also affords a soil in which a sort of fungus speedily
springs up. From both these causes, the breath becomes offensive, and the
teeth are injured.
PRESERVATION OF THE TEETH.--Children should early be taught to brush their
teeth at least every morning with tepid water, and twice a week with white
castile soap and powdered orris root, or with some dentifrice recommended
by a responsible dentist. They should also be instructed to remove the
particles of food from between the teeth, after each meal, by means of a
quill or wooden toothpick.
The enamel once injured is never restored, and the whole interior of the
tooth is exposed to decay. We should not, therefore, crack hard nuts, bite
thread, or use metal toothpicks, gritty tooth powders, or any acid which
"sets the teeth on edge," _i. e._. that acts upon the enamel. It is
well also to have the teeth examined yearly by a dentist, that any small
orifice may be filled, and further decay prevented.
V. THE GLANDS OF THE SKIN.
1. THE OIL GLANDS are clusters of tiny sacs which secrete an oil that
flows along the duct to the root of the hair, and thence oozes out on the
cuticle (Fig. 24). [Footnote: This secretion is said to vary in different
persons, and on that account the dog is enabled to trace his master by the
scent.] This is nature's efficient hair-dressing, and also keeps the skin
soft and flexible. These glands are not usually found where there is no
hair, as on the palm of the hand, and hence at those points only can water
readily soak through the skin into the body. They are of considerable size
on the face, especially about the nose. When obstructed, their contents
become hard and dark-colored, and are vulgarly called "worms." [Footnote:
Though they are not alive, yet, under the microscope, they are sometimes
found to contain a curious parasite, called the pimple mite, which is
supposed to consume the superabundant secretion.]
II. THE PERSPIRATORY GLANDS are fine tubes about 1/300 of an inch in
diameter, and a quarter of an inch in length, which run through the cutis,
and then coil up in little balls (Fig. 24). They are found in all parts of
the body, and in almost incredible numbers. In the palm of the hand, there
are about two thousand eight hundred in a single square inch. On the back
of the neck and trunk, where they are fewest, there are yet four hundred
to the square inch. The total number on the body of an adult is estimated
at about two and a half million. If they were laid end to end, they would
extend nearly ten miles. [Footnote: The current statement, that they would
extend twenty-eight miles, is undoubtedly an exaggeration. Krause
estimates the total number at 2,381,248, and the length of each coil, when
unraveled, at 1/10 of an inch, which would make the total length much less
than even the statement in the text. Seguin states that the proportion of
impurities thrown off by the skin and the lungs, is eleven to seven.] The
mouths of these glands--"pores," as we commonly call them--may be seen
with a pocket lens along the fine ridges which cover the palm of the hand.
THE PERSPIRATION.--From these openings, there constantly passes a vapor,
forming what we call the insensible perspiration. Exercise or heat causes
it to flow more freely, when it condenses on the surface in drops. The
perspiration consists of about ninety-nine parts water, and one part solid
matter. The amount varies greatly, but on the average is, for an adult,
not far from two pounds per day. Any suppression of this constant drainage
will lead to disagreeable and even dangerous results. If it be entirely
and permanently checked, death will inevitably ensue. [Footnote: Once, on
an occasion of great solemnity at Rome, a child was, it is said,
completely covered with gold leaf, closely applied to the skin, so as to
represent, according to the idea of that age, the golden glory of an angel
or seraph. In a few hours, after contributing to this pageant, the child
died; the cause being suffocation, from stopping the exhalation of the
skin; although, in the ignorance of the common people of those days, the
death was attributed to the anger of the Deity, and looked upon as a
circumstance of evil omen.]
THE ABSORBING POWER OF THE SKIN.--We have already described two uses of
the skin: (1) Its _protective_, (2) its _exhaling_, and now we
come to (3) its _absorbing_ power. This is not so noticeable as the
others, and yet it can be illustrated. Persons frequently poison their
hands with the common wood ivy. Contagious diseases are taken by touching
a patient, or even his clothing, especially if there be a crack in the
cuticle. [Footnote: If one is called upon to handle a dead body, it is
well, especially if the person has died of a contagious disease, to rub
the hand with lard or olive oil. Poisonous matter has been fatally
absorbed through the breaking of the cuticle by a hangnail, or a simple
scratch. There is a story that Bonaparte, when a lieutenant of artillery,
in the heat of battle, seized the rammer and worked the gun of an
artilleryman who had fallen. From the wood which the soldier had used,
Bonaparte absorbed a poison that gave him a skin disease, by which he was
annoyed the remainder of his life.] Painters absorb so much lead through
the pores of their hands that they are attacked with colic. [Footnote:
Cosmetics, hair dyes, etc., are exceedingly injurious, not only because
they tend to fill the pores of the skin, but because they often contain
poisonous matters that may be absorbed into the system, especially if they
are in a solution.] Snuff and lard are frequently rubbed on the chest of a
child suffering with the croup, to produce vomiting. It is said that
seamen in want of water drench their clothing in salt spray, when the skin
will absorb enough moisture to quench thirst (see Lymphatic System).
By carefully conducted experiments, it has been found that the skin acts
in the same way as the lungs (see Respiration) in absorbing oxygen from
the air, and giving off carbonic acid to a small but appreciable amount.
Indeed, the skin has not inaptly been styled the third lung. Hence, the
importance of absolute cleanliness and a frequent ablution of the entire
body.
VI. HYGIENE.
HINTS ABOUT WASHING AND BATHING.--The moment of rising from bed is the
proper time for the full wash or bath with which one should commence the
day. The body is then warm, and can endure moderately cold water better
than at any other time; it is relaxed, and needs bracing; and the nerves,
deadened by the night's repose, require a gentle stimulus. If the system
be strong enough to resist the shock, cold water is the most invigorating;
if not, a tepid bath will answer. [Footnote: Many persons have not the
conveniences for a bath. To them, the following plan, which the author has
daily employed for years, is commended. The necessities are: a basin full
of soft water, a mild soap, a large sponge or a piece of flannel, and two
towels--one soft, the other rough. The temperature of the water should
vary with the season of the year--cold in summer and tepid in winter. Rub
quickly the entire body with the wet sponge or flannel. (If more
agreeable, wash and wipe only a part at a time, protecting the rest in
cold weather with portions of clothing.) Dry the skin gently with a soft
towel, and when quite dry, with the rough towel or flesh brush rub the
body briskly four or five minutes till the skin is all aglow. The chest
and abdomen need the principal rubbing. The roughness of the towel should
be accommodated to the condition of the skin. Enough friction, however,
must be given to produce at least a gentle warmth, indicative of the
reaction necessary to prevent subsequent chill or languor. An invalid will
find it exceedingly beneficial if a stout, vigorous person produce the
reaction by rubbing with the hands.]
Before dressing, the whole body should be thoroughly rubbed with a coarse
towel or flesh brush. At first, the friction may be unpleasant, but this
sensitiveness will soon be overcome, and the keenest pleasure be felt in
the lively glow which follows. A bath should not be taken just before nor
immediately after a meal, as it will interfere with the digestion of the
food. Soap should be employed occasionally, but its frequent use tends to
make the skin dry and hard.
REACTION.--After taking a cold bath, there should be a prompt reaction.
When the surface is chilled by cold water, the blood sets to the heart and
other vital organs, exciting them to more vigorous action, and then, being
thrown back to the surface, it reddens, warms, and stimulates the skin to
an unwonted degree. This is called the reaction, and in it lies the
invigorating influence of the cold bath. When, on the contrary, the skin
is heated by a hot bath, the blood is drawn to the surface, less blood
goes to the heart, the circulation decreases, and languor ensues. A dash
of cold water is both necessary and refreshing at the close of a hot bath.
[Footnote: The Russians are very fond of vapor baths, taken in the
following manner. A large room is heated by stoves. Red-hot stones being
brought in, water is thrown upon them, filling the room with steam. The
bathers sit on benches until they perspire profusely, when they are rubbed
with soapsuds and dashed with cold water. Sometimes, while in this state
of excessive perspiration, they run out of doors and leap into snow
banks.]
If, after a cold bath, there be felt no glow of warmth, but only a
chilliness and depression, we are thereby warned that either proper means
were not taken to bring on this reaction, or that the circulation is not
vigorous enough to make such a bath beneficial. The general effect of a
cool bath is exhilarating, and that of a warm one depressing. [Footnote:
The sudden plunge into a cold bath is good for the strong and healthy, but
too severe for the delicate. One should always wet first the face, neck,
and chest. It is extremely injurious to stand in a bath with only the feet
and the lower limbs covered by the water, for the blood is thus sent from
the extremities to the heart and internal organs, and they become so
burdened that reaction may be out of their power. A brisk walk, or a
thorough rubbing of the skin, before a cold bath or swim, adds greatly to
its value and pleasure.] Hence the latter should not ordinarily be taken
oftener than once a week, while the former may be enjoyed daily. (See p.
289.)
SEA BATHING is exceedingly stimulating, on account of the action of the
salt and the exciting surroundings. Twenty minutes is the utmost limit for
bathing or swimming in salt or fresh water. A chilly sensation should be
the signal for instant removal. It is better to leave while the glow and
buoyancy which follow the first plunge are still felt. Gentle exercise
after a bath is beneficial.
CLOTHING in winter, to keep us warm, should repel the external cold and
retain the heat of the body. In summer, to keep us cool, it should not
absorb the rays of the sun, and should permit the passage of the heat of
the body. At all seasons, it should be porous, to give ready escape to the
perspiration, and a free admission of air to the skin. We can readily
apply these essential conditions to the different kinds of clothing.
_Linen_ is soft to the touch, and is a good conductor of heat. Hence
it is pleasant for summer wear, but, being apt to chill the surface too
rapidly, it should not be worn next the skin.
_Cotton_ is a poorer conductor of heat and absorber of moisture, and
is therefore warmer than linen. It is sufficiently cool for summer wear,
and affords better protection against sudden changes.
_Woolen_ absorbs moisture slowly, and contains much air in its pores.
It is therefore a poor conductor of heat, and guards the wearer against
the vicissitudes of our climate.
The outer clothing may be adapted largely to ornament, and may be varied
to suit our fancy and the requirements of society. The underclothing
should always be sufficient to keep us warm. Woolen should be worn next
the skin at all times; light gossamer garments in the heat of summer, and
warm, porous flannels in midwinter.
Light-colored clothing is not only cooler in summer, but warmer in winter.
As the warmth of clothing depends greatly on the amount of air contained
in its fibers, fine, loose, porous cloth with a plenty of nap is best for
winter wear. Firm and heavy goods are not necessarily the warmest. Furs
are the perfection of winter clothing, since they combine warmth with
lightness. Two light woolen garments are warmer than one heavy one, as
there is between them a layer of nonconducting air.
All the body except the head should be equally protected by clothing.
Whatever fashion may dictate, no part covered to-day can be uncovered
tonight or to-morrow, except at the peril of health. It is a most
barbarous and cruel custom to leave the limbs of little children
unprotected, when adults would shiver at the very thought of exposure.
Equally so is it for children to be thinly clad for the purpose of
hardening them. To go shivering with cold is not the way to increase one's
power of endurance. The system is made more vigorous by exercise and food;
not by exposure. In winter, we should wear warm shoes with thick soles,
and rubbers when it is damp. At night, and after exercise, we require
extra clothing. (See p. 295.)
DISEASES, ETC.--l. _Erysipelas_ is an inflammation (see Inflammation)
of the skin, and often begins in a spot not larger than a pin head, which
spreads with great rapidity. It is very commonly checked by the
application of a solution of iodine. The burning and contracting sensation
may be relieved by cloths wrung out of hot water.
2. _Eczema_ (Salt Rheum, etc.) is of constitutional origin. It is
characterized by an itching, burning, reddened eruption, in which a serous
discharge exudes and dries into crusts or scales. The skin thickens in
patches, and painful fissures are formed, which are irritated by exposure
to air or water. Eczema denotes debility. It occurs in various forms, and,
like erysipelas, should be treated by a physician.
3. _Corns_ are thickened cuticle, caused by pressure or friction.
They most frequently occur on the feet; but are produced on the
shoemaker's knee by constant hammering, and on the soldier's shoulder by
the rubbing of his musket. This hard portion irritates the sensitive cutis
beneath, and so causes pain. A corn will soften in hot water, when it may
be pared with a sharp knife. If the cause be removed, the corn will not
return.
4. _Ingrowing Nails_ are caused by pressure, which forces the edge of
the toe nail into the flesh. They may be cured by carefully cutting away
the part which has mal-grown, and then scraping the back of the nail till
it is thin, making a small incision in the center, at the top. The two
portions, uniting, will draw away the nail from the flesh at the edge.
Ingrowing nails may be prevented by wearing broad-toed shoes.
5. _Warts_ are overgrown papillæ (Fig. 24). They may generally be
removed by the application of glacial acetic acid, or a drop of nitric
acid, repeated until the entire structure is softened. Care must be taken
to keep the acid from touching the neighboring skin. The capricious
character of warts has given rise to the popular delusion concerning the
influence of charms upon them.
6. _Chilblain_ is a local inflammation affecting generally the feet,
the hands, or the lobes of the ear. Liability to it usually passes away
with manhood. It is not caused by "freezing the feet," as many suppose,
though attacks are brought on, or aggravated, by exposure to cold,
followed by sudden warming. Chilblain is subject to daily congestion (see
Congestion), manifested by itching, soreness, etc., commonly occurring at
night. The best preventive is a uniform temperature, and careful
protection against the cold by warm clothing, especially for the feet.
PRACTICAL QUESTIONS.
1. If a hair be plucked out, will another grow in its place?
2. What causes the hair to "stand on end" when we are frightened?
3. Why is the skin roughened by riding in the cold?
4. Why is the back of a washerwoman's hand less water-soaked than the
palm?
5. What would be the length of the perspiratory tubes in a single square
inch of the palm, if placed end to end?
6. What colored clothing is best adapted to all seasons?
7. What is the effect of paint and powder on the skin?
8. Is waterproof clothing healthful for constant wear?
9. Why are rubbers cold to the feet?
10. Why does the heat seem oppressive when the air is moist?
11. Why is friction of the skin invigorating after a cold bath?
12. Why does the hair of domestic animals become roughened in winter?
13. Why do fowls spread their feathers before they perch for the night?
14. How can an extensive burn produce congestion of the lungs?
15. Why do we perspire so profusely after drinking cold water?
16. How can we best prevent skin diseases, colds, and rheumatism?
17. What causes the difference between the hard hand of a blacksmith and
the soft hand of a woman?
18. Why should a painter avoid getting paint on the palm of his hand?
19. Why should we not use the soap or the soiled towel at a hotel?
20. Which teeth cut like a pair of scissors?
21. Which teeth cut like a chisel?
22. Which should be clothed the warmer, a merchant or a farmer? 23. Why
should we not crack nuts with our teeth?
24. Do the edges of the upper and the lower teeth meet?
25. When fatigued, would you take a cold bath?
26. Why is the outer surface of a kid glove finer than the inner?
27. Why will a brunette endure the sun's rays better than a blonde?
28. Does patent leather form a healthful covering for the feet?
29. Why are men more frequently bald than women?
30. On what part of the head does baldness commonly occur? Why?
31. What does the combination in our teeth of canines and grinders suggest
as to the character of our food?
32. Is a staid, formal promenade suitable exercise?
33. Is there any danger in changing the warm clothing of our daily wear
for the thin one of a party?
34. Should we retain our overcoat, shawl, or furs when we come into a warm
room?
35. Which should bathe the oftener, students or outdoor laborers?
36. Is abundant perspiration injurious?
37. How often should the ablution of the entire body be performed?
38. Why is cold water better than warm, for our daily ablution?
39. Why should our clothing always fit loosely?
40. Why should we take special pains to avoid clothing that is colored by
poisonous dyestuffs? (See p. 296.)
41. What general principles should guide us as to the length and frequency
of baths In salt or fresh water?
42. What is the beneficial effect of exercise upon the functions of the
skin?
43. How can we best show our admiration and respect for the human body?
44. Why is the scar of a severe wound upon a negro sometimes white?
IV.
RESPIRATION AND THE VOICE.
"The smooth soft air with pulse-like waves
Flows murmuring through its hidden caves,
Whose streams of brightening purple rush,
Fired with a new and livelier blush;
While all their burden of decay
The ebbing current steals away."
ANALYSIS OF RESPIRATION AND THE VOICE.