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Hygienic Physiology by Joel Dorman Steele

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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

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

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.


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


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

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.

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

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.


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

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

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

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?



"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."


| 1. The Larnyx.
_ | 2. The Vocal Cords.
| 1. ORGANS OF VOICE.....| 3. Different Tones of Voice.
| | 4. Speech.
| |_5. Formation of Vocal Sounds.
| _
| | 1. The Trachea.
| | 2. The Bronchial Tubes.
| 2. ORGANS OF RESPIRA- | 3. The Cells.
| TION.........| 4. The Lung Wrapping.
| |_5. The Cilia.
| _
| | 1. Inspiration.
| 3. HOW WE BREATHE......|_2. Expiration.
| _
| | 1. Sighing.
| | 2. Coughing.
| | 3. Sneezing.
| 4. MODIFICATIONS OF | 4. Snoring.
| THE BREATH.......| 5. Laughing, and Crying.
| | 6. Hiccough.
| |_7. Yawning.
| _
| | 1. The Need of Air.
| | 2. Action of Air in the Lungs.
| | 3. Tests of the Breath.
| | 4. Analysis of Expired Air.
| | 5. Effect of Rebreathed Air.
| | _
| 6. HYGIENE.............| | a. _The Sources of
| | | Impurity._
| | | b. _The Sick Room._
| | 6. Concerning | c. _The Sitting Room._
| | the Need of | d. _The Bedroom._
| |_ Ventilation.| e. _The Church._
| | f. _The Schoolroom._
| | g. _How we should
| |_ Ventilate._
| _
| | 1. Constriction of the Lungs.
| | 2. Bronchitis.
| | 3. Pleurisy.
| | 4. Pneumonia.
|_8. DISEASES............| 5. Consumption
| 6. Asphyxia.
| 7. Diptheria.
| 8. Croup.
|_9. Stammering.


The Organs of Respiration and the Voice are the _larynx_, the
_trachea_, and the _lungs_.

neck, is a prominence sometimes called Adam's apple. It is the front of
the _larynx_. This is a small triangular, cartilaginous box, placed
just below the root of the tongue, and at the top of the windpipe. The
opening into it from the throat is called the _glottis_; and the
cover, the _epiglottis_ (_epi_, upon; _glotta_, the tongue). The
latter is a spoon-shaped lid, which opens when we breathe, but, by
a nice arrangement, shuts when we try to swallow, and so lets our
food slip over it into the _œsophagus_ (e-sof'-a-gus), the tube leading
from the pharynx to the stomach (Fig. 27).

If we laugh or talk when we swallow, our food is apt to "go the wrong
way," _i. e._, little particles pass into the larynx, and the
tickling sensation which they produce forces us to cough in order to expel
the intruders.

2. _The Vocal Cords_.--On each side of the _glottis_ are the so-
called _vocal cords_. They are not really cords, but merely elastic
membranes projecting from the sides of the box across the opening.
[Footnote: The cartilages and vocal cords may be readily seen in the
larynx of an ox or sheep. If the flesh be cut off, the cartilages will
dry, and will keep for years.] When not in use, they spread apart and
leave a V-shaped orifice (Fig. 28), through which the air passes to and
from the lungs. If the cords are tightened, the edges approach sometimes
within 1/100 of an inch of each other, and, being thrown into vibration,
cause corresponding vibrations in the current of air. Thus sound is
produced in the same manner as by the vibrations of the tongues of an
accordion, or the strings of a violin, only in this case the strings are
scarcely an inch long.

FIG. 27.

[Illustration: _Passage to the Œsophagus and Windpipe._ c, _the
tongue;_ d, _the soft palate, ending in_ g, _the uvula;_ h,
_the epiglottis;_ i, _the glottis;_ I, _the œsophagus;_ f,
_the pharynx._]

DIFFERENT TONES OF THE VOICE.--The higher tones of the voice are produced
when the cords are short, tight, and closely in contact; the lower, by the
opposite conditions. Loudness is regulated by the quantity of air and
force of expulsion. A falsetto voice is thought to be the result of a
peculiarity in the pharynx (Fig. 27) at the back part of the nose; it is
more probably produced by some muscular maneuver not yet fully understood.
When boys are about fourteen years of age, the larynx enlarges, and the
cords grow proportionately longer and coarser; hence, the voice becomes
deeper, or, as we say, "changes." The peculiar harshness of the voice at
this time seems to be due to a congestion of the mucous membrane of the
cords. The change may occur very suddenly, the voice breaking in a single

FIG. 28.

[Illustration: e, e, _the vocal cords;_ d, _the epiglottis._]

Speech is voice modulated by the lips, tongue, [Footnote: The tongue is
styled the "unruly member," and held responsible for all the tattling of
the world; but when the tongue is removed, the adjacent organs in some way
largely supply the deficiency, so that speech is still possible. Huxley
describes the conversation of a man who had two and one half inches of his
tongue preserved in spirits, and yet could converse intelligibly. Only the
two letters _t_ and _d_ were beyond his power; the articulation
of these involves the employment of the tip of the tongue; hence, "tin" he
converted into "fin," and "dog" into "thog."] palate, and teeth.
[Footnote: An artificial larynx may be made by using elastic bands to
represent the vocal cords, and by placing above them chambers which by
their resonance will produce the same effect as the cavities lying above
the larynx. An artificial speaking machine was constructed by Kempelen,
which could pronounce such sentences as, "I love you with all my heart,"
in different languages, by simply touching the proper keys.] Speech and
voice are commonly associated, but speech may exist without the voice, for
when we whisper we articulate the words, although there is no
vocalization, _i. e._, no action of the larynx. [Footnote: We can
observe this by placing the hand on the throat, and noticing the absence
of vibrations when we whisper, and their presence when we talk. The
difference between vocalization and non-vocalization is seen in a sigh and
a groan, the latter being the former vocalized. Whistling is a pure mouth
sound, and does not depend on the voice. Laughter is vocal, being the
aspirated vowels, a, e, or o, convulsively repeated.] (See p. 297.)

FIG. 29.

[Illustration: _The Lungs, showing the Larynx._ A, _the
windpipe;_ B, _the bronchial tubes._]

FORMATION OF VOCAL SOUNDS.--The method of modulating voice into speech may
be seen by producing the pure vowel sounds _a, e_, etc., from one
expiration, the mouth being kept open while the form of the aperture is
changed for each vowel by the tongue and the lips. _H_ is only an
explosion, or forcible throwing of a vowel sound from the mouth.
[Footnote: When, in sounding a vowel, the sound coincides with a sudden
change in the position of the vocal cords from one of divergence to one of
approximation, the vowel is pronounced with the _spiritus asper_.
When the vocal cords are brought together before the blast of air begins,
the vowel is pronounced with the _spiritus lenis._--FOSTER.]

The consonants, or short sounds, may also be made without interrupting the
current of air, by various modifications of the vocal organs. In sounding
singly any one of the letters, we can detect its peculiar requirements.
Thus _m_ and _n_ can be made only by blocking the air in the
mouth and sending it through the nose; _l_ lets the air escape at the
sides of the tongue; _r_ needs a vibratory movement of the tongue;
_b_ and _p_ stop the breath at the lips; _k_ and _g_ (hard), at the
back of the palate. Consonants like _b_ and _d_ are abrupt, or, like
_l_ and _s_, continuous. Those made by the lips are termed _labials_;
those by pressing the tongue against the teeth, _dentals_; those by the
tongue, _linguals_.

The child gains speech slowly, first learning to pronounce the vowel
_a_, the consonants _b, m_, and _p_, and then their unions --_ba, ma, pa_.

windpipe, or _trachea_ (see Fig. 29), so called because of its
roughness. It is strengthened by C-shaped cartilages with the openings
behind, where they are attached to the œsophagus. At the lower end, the
trachea divides into two branches, called the right and left
_bronchi_. These subdivide in the small bronchial tubes, which ramify
through the lungs like the branches of a tree, the tiny twigs of which at
last end in clusters of cells so small that there are six hundred million
in all. This cellular structure renders the lungs exceedingly soft,
elastic, and sponge-like. [Footnote: The lungs of slaughtered animals are
vulgarly called "lights," probably on account of their lightness. They are
similar in structure to those of man. They will float on water, and if a
small piece be forcibly squeezed between the fingers (notice the creaking
sound it gives), it will retain sufficient air to make it buoyant.]

FIG. 30.

[Illustration: _Bronchial Tubes, with clusters of cells._]

The stiff, cartilaginous rings, so noticeable in the rough surface of the
trachea and the bronchi, disappear as we reach the smaller bronchial
tubes, so that while the former are kept constantly open for the free
admission of air, the latter are provided with elastic fibers by which
they may be almost closed.

WRAPPING OF THE LUNGS.--The lungs are invested with a double covering--the
_pleura_--one layer being attached to the lungs and the other to the
walls of the chest. It secretes a fluid which lubricates it, so that the
layers glide upon each other with perfect ease. [Footnote: These pleural
sacs are distinct and closed; hence, when the ribs are raised, a partial
vacuum being formed in the sacs, air rushes in, and distends the pulmonary
lobules.] The lungs are lined with mucous membrane, exceedingly delicate
and sensitive to the presence of anything except pure air. We have all
noticed this when we have breathed any thing offensive.

FIG. 31.

[Illustration: A, _the heart;_ B, _the lungs drawn aside to show
the internal organs;_ C, _the diaphragm;_ D, _the liver;_ E,
_the gall cyst;_ F, _the stomach;_ G,_ the small intestines;_ H,
_the transverse colon._]

THE CILIA.--Along the air passages are minute filaments (_cilia_,
Fig. 32), which are in constant motion, like a field of grain stirred by a
gentle breeze. They serve to fan the air in the lungs, and produce an
outward current, which is useful in catching dust and fine particles swept
inward with the breath.

HOW WE BREATHE.--Respiration consists of two acts--taking in the air, or
_inspiration_, and expelling the air, or _expiration_.

FIG. 32.

[Illustration: B, _a section of the mucous membrane, showing the cilia
rising from the peculiar epithelial cells on the outside of the mucous
membrane lining the tubes;_ A, _a single cell more highly

1. _Inspiration_.--When we draw in a full breath, we straighten the
spine and throw the head and shoulders back, so as to give the greatest
advantage to the muscles. [Footnote: If we examine the bony cage of the
thorax or chest in Fig. 8, we shall see that the position of the ribs may
alter its capacity in two ways.

1. As they run obliquely downward from the spine, if the sternum or
breastbone be lifted in front, the diameter of the chest will be

2. The ribs are fastened by elastic cartilages, which stretch as the
muscles that lift the ribs contract, and so increase the breadth of the

At the same time, the diaphragm [Footnote: The diaphragm is the muscular
partition between the chest and the abdomen. It is always convex toward
the former, and concave toward the latter (Fig. 31). Long muscular fibers
extend from its center toward the ribs in front and the spine at the back.
When these contract, they depress and flatten the diaphragm; when they
relax, it becomes convex again. In the former case, the bowels are pressed
downward and the abdomen pushed outward; in the latter, the bowels spring
upward, and the abdomen is drawn inward.] descends and presses the walls
of the abdomen outward. Both these processes increase the size of the
chest. Thereupon, the elastic lungs expand to occupy the extra space,
while the air, rushing in through the windpipe, pours along the bronchial
tubes and crowds into every cell. [Footnote: It is said that in drawing a
full breath, the muscles exert a force equal to raising a weight of seven
hundred and fifty pounds. When we are about to make a great effort, as in
striking a heavy blow, we naturally take a deep inspiration, and shut the
glottis. The confined air makes the chest tense and firm, and enables us
to exert a greater force. As we let slip the blow, the glottis opens and
the air escapes, often with a curious aspirated sound as is noticeable in
workmen. To make a good shot with a rifle, we should take aim with a full
chest and tight breath, since then the arms will have a steadier support.]

2. _Expiration_.--When we forcibly expel the air from our lungs, the
operation is reversed. We bend forward, draw in the walls of the abdomen,
and press the diaphragm upward, while the ribs are pulled downward,--all
together diminishing the size of the chest, and forcing the air outward.

Ordinary, quiet breathing is performed mainly by the diaphragm,--one
breath to every four beats of the heart, or eighteen per minute. (See p.

MODIFICATIONS OF THE BREATH.--_Sighing_ is merely a prolonged
inspiration followed by an audible expiration. _Coughing_ is a
violent expiration in which the air is driven through the mouth.
_Sneezing_ differs from coughing, the air being forced through the
nose. _Snoring_ is produced by the passage of the breath through the
pharynx when the tongue and soft palate are in certain positions.
[Footnote: The soft palate must have fallen back in such a manner as
nearly or quite to close the entrance to the nasal cavity from the throat,
and the tongue must also be thrown back so far as to leave only a narrow
opening between it and the soft palate. The noise is produced by the air
being forced either inward or outward through this opening. A snore
results also when, with a closed mouth, the air is forced between the soft
palate and the back wall of the pharynx into the nasal cavity. With deep
breathing, perhaps accompanied by a variation in the position of the soft
palate, a rattling noise may be heard in addition to the snoring, which is
due to a vibration of the soft palate.--F. A. FERNALD, in "How we Sneeze,
Laugh, Stammer, and Sigh."--_Popular Science Monthly_, Feb., 1884.]
_Laughing_ and _crying_ are very much alike. The expression of
the face is necessary to distinguish between them. The sounds are produced
by short, rapid contractions of the diaphragm. _Hiccough_ is confined
to inspiration. It is caused by a contraction of the diaphragm and a
constriction of the glottis; the current of air just entering, as it
strikes the closed glottis, gives rise to the well-known sound.
_Yawning_, or _gaping_, is like sighing. [Footnote: The
usefulness of a yawn lies in bringing up the arrears, as it were, of
respiration, when it has fallen behindhand, either through fatigue or
close attention to other occupation. The stretching of the jaws and limbs
may also serve to equalize the nervous influence, certain muscles having
become uneasy on account of being stretched or contracted for a long
time.] It is distinguished by a wide opening of the mouth and a deep,
profound inspiration. Both processes furnish additional air, and therefore
probably meet a demand of the system for more oxygen. Frequently, however,
they are like laughing, sobbing, etc., merely a sort of contagion, which
runs through an audience, and seems almost irresistible.

THE CAPACITY OF THE LUNGS.--If we take a deep inspiration, and then
forcibly exhale all the air we can expel from the lungs, this amount,
which is termed the _breathing capacity_, will bear a very close
correspondence to our stature. For a man of medium height (five feet eight
inches) it will be about two hundred and thirty cubic inches, [Footnote:
Of this amount, one hundred cubic inches can be forced in only by an extra
effort, and is available for emergencies, or for purposes of training, as
in singing, climbing, etc. It is of great importance, since, if the
capacity of the lungs only equaled our daily wants, the least obstruction
would prove fatal.] or a gallon, and for each inch of height between five
and six feet there will be an increase of eight cubic inches. In addition,
it is found that the lungs contain about one hundred cubic inches which
can not be expelled, thus making their entire contents about three hundred
and thirty cubic inches, or eleven pints. The extra amount always on hand
in the lungs is of great value, since thereby the action of the air goes
on continuously, even during a violent expiration. In ordinary breathing,
only about twenty or thirty cubic inches (less than a pint) of air pass in
and out.

THE NEED OF AIR.--The body needs food, clothing, sunshine, bathing, and.
drink; but none of these wants is so pressing as that for air. The other
demands may be met by occasional supplies, but air must be furnished every
moment or we die. Now the vital element of the atmosphere is oxygen gas.
[Footnote: See "Steele's Popular Chemistry," p. 30. The atmosphere
consists of one fifth oxygen and four fifths nitrogen. The former is the
active element; and the latter, the passive. Oxygen alone would be too
stimulating, and must be restrained by the neutral nitrogen. Separately,
either element of the air would kill us.] This is a stimulating, life-
giving principle. No tonic will so invigorate as a few full, deep breaths
of cold, pure air. Every organ will glow with the energy of the fiery

ACTION OF THE AIR IN THE LUNGS.--In the delicate cells of the lungs, the
air gives up its oxygen to the blood, and receives in turn carbonic-acid
[Footnote: More properly _Carbon dioxide_.] gas and water, foul with
waste matter which the blood has picked up in its circulation through the
body. The blood, thus purified and laden with the inspiring oxygen, goes
bounding through the system, while the air we exhale carries off the
impurities. In this process, the blood changes from purple to red. If we
examine our breath, we can readily see what it has removed from the blood.

TESTS OF THE BREATH.--1. Breathe into a jar, and on lowering into it a
lighted candle, the flame will be instantly extinguished; thus indicating
the presence of carbonic-acid gas. 2. Breathe upon a mirror, and a film of
moisture will show the vapor. [Footnote: There is a close relation between
the functions of the skin, the lungs, and the kidneys--the scavengers of
the body. They all carry off water from the blood, and when the function
of one of the three is, in this respect, interfered with, the others are
called upon to perform its functions. When the function of perspiration is
deranged, the lungs and kidneys are required to perform heavier duty, and
this may lead to disease (see p. 62).] 3. If breath be confined in a
bottle, the animal matter will decompose and give off an offensive odor.

ANALYSIS OF THE EXPIRED AIR shows that it has lost about twenty-five per
cent of its oxygen, and gained an equal amount of carbonic-acid gas,
besides moisture, and organic impurities. Our breath, then, is air robbed
of its vitality, and containing in its place a gas as fatal to life
[Footnote: Carbonic-acid gas can not be breathed when undiluted, as the
glottis closes and forbids its passage into the lungs. Air containing only
three or four per cent acts as a narcotic poison (MILLER), and a much
smaller proportion will have an injurious effect. The great danger,
however, lies in the organic particles constantly exhaled from the lungs
and the skin, which, it is believed, are often direct and active poisons.]
as it is to a flame, and effete matter which is disagreeable to the smell,
injurious to the health, and which may contain the germs of serious

THE EVIL EFFECT OF REBREATHING the air can not be overestimated. We take
back into our bodies that which has just been rejected. The blood
thereupon leaves the lungs, bearing, not the invigorating oxygen, but
refuse matter to obstruct the whole system. We soon feel the effect. The
muscles become inactive. The blood stagnates. The heart acts slowly. The
food is undigested. The brain is clogged. The head aches. Instances of
fatal results are only too frequent. [Footnote: During the English war in
India, in the eighteenth century, one hundred and forty-six prisoners were
shut up in a room scarcely large enough to hold them. The air could enter
only by two narrow windows. At the end of eight hours, but twenty-three
persons remained alive, and these were in a most deplorable condition.
This prison is well called "The Black Hole of Calcutta."--Percy relates
that after the battle of Austerlitz, three hundred Russian prisoners were
confined in a cavern, where two hundred and sixty of them perished in a
few hours.--The stupid captain of the ship _Londonderry_, during a
storm at sea, shut the hatches. There were only seven cubic feet of space
left for each person, and in six hours ninety of the passengers were
dead.] The constant breathing of even the slightly impure air of our
houses can not but tend to undermine the health. The blood is not
purified, and is thus in a condition to receive the seeds of disease at
any time. The system uninspired by the energizing oxygen is sensitive to
cold. The pale cheek, the lusterless eye, the languid step, speak but too
plainly of oxygen starvation. In such a soil, catarrh, scrofula, and
kindred diseases run riot. [Footnote: One not very strong, or unable
powerfully to resist conditions unfavorable to health, and with a
predisposition to lung disease, will be sure, sooner or later, by partial
lung starvation and blood poisoning, to develop pulmonary consumption.
_The lack of what is so abundant and so cheap--good, pure air--is
unquestionably the one great cause of this terrible disease_.--BLACK'S
_Ten Laws of Health_.]

CONCERNING THE NEED FOR VENTILATION.--The foul air which passes off from
the lungs and through the pores of the skin does not fall to the floor,
but diffuses itself through the surrounding atmosphere. A single breath
will to a trifling but certain extent taint the air of a whole room.
[Footnote: This grows out of a well-known philosophical principle called
the Diffusion of Gases, whereby two gases tend to mix in exact
proportions, no matter what may be the quantity of each.--STEELE'S
_Popular Chemistry,_ p. 86, and _Popular Physics,_ p. 52.] A
light will vitiate as much air as a dozen persons. Many breaths and lights
therefore rapidly unfit the air for our use.

The perfection of ventilation is reached when the air of a room is as pure
as that out of doors. To accomplish this result, it is necessary to allow
for each person six hundred cubic feet of space, while ventilation is
still going on in the best manner known.

In spite of these well-known facts, scarcely any pains are taken to supply
fresh air, while the doors and windows where the life-giving oxygen might
creep in are hermetically stopped.

How often is this true of the sick room. Yet here the danger of bad air is
intensified. The expired breath of the patient is peculiarly threatening
to himself as well as to others. Nature is seeking to throw off the poison
of the disease. The scavengers of the body are all at work. The breath and
the insensible perspiration are loaded with impurities. [Footnote: The
floating dust in the air, revealed to us by the sunbeam shining through a
crack in the blinds, shows the abundance of these impurities, and also the
presence of germs which, lodging in the lungs, may implant disease, unless
thrown off by a vigorous constitution. "On uncovering a scarlet fever
patient, a cloud of fine dust is seen to rise from the body--contagious
dust, that for days will retain its poisonous properties."--YOUMANS. (See
p. 300.)] The odor is oftentimes exceedingly offensive. Sick and well
alike need an abundance of fresh air. But, too often, it is the only want
not supplied.

Our sitting rooms, heated by furnaces or red-hot stoves, generally have no
means of ventilation, or, if provided, they are seldom used. A window is
occasionally dropped to give a little relief, as if pure air were a
rarity, and must be doled out to the suffering lungs in morsels, instead
of full and constant draughts. The inmates are starved by scanty lung
food, and stupefied by foul air. The process goes on year by year. The
weakened and poisoned body at last succumbs to disease, while we, in our
blindness and ignorance, talk of the mysterious Providence which thus
untimely cuts down the brightest intellects. The truth is, death is often
simply the penalty for violating nature's laws. Bad air begets disease;
disease begets death.

In our churches, the foul air left by the congregation on Sunday is shut
up during the week, and heated for the next Lord's day, when the people
assemble to rebreathe the polluted atmosphere. They are thus forced, with
every breath they take, to violate the physical laws of Him whom they meet
to worship,--laws written not three thousand years ago upon Mount Sinai on
tables of stone, but to-day engraved in the constitution of their own
living, breathing bodies. On brains benumbed and starving for oxygen, the
purest truth and the highest eloquence fall with little force.

We sleep in a small bedroom from which every breath of fresh air is
excluded, because we believe night air to be unhealthy, [Footnote: There
is a singular prejudice against the night air. Yet, as Florence
Nightingale aptly says, what other air can we breathe at night? We then
have the choice between foul air within and pure air without. For, in
large cities especially, the night air is far more wholesome than that of
the daytime. To secure fresh air at night, we must open the windows of our
bedroom.] and so we breathe its dozen hogsheads of air over and over
again, and then wonder why we awaken in the morning so dull and
unrefreshed! Return to our room after inhaling the fresh, morning air, and
the fetid odor we meet on opening the door, is convincing proof how we
have poisoned our lungs during the night.

Each room should be supplied with two thousand feet of fresh air per hour
for every person it contains. Our ingenuity ought to find some way of
doing this advantageously and pleasantly. A moiety of the care we devote
to delicate articles of food, drink, and dress would abundantly meet this
prime necessity of our bodies.

Open the windows a little at the top and the bottom. Put on plenty of
clothing to keep warm by day and by night, and then let the inspiring
oxygen come in as freely as God has given it. Pure air is the cheapest
necessity and luxury of life. Let it not be the rarest!

SCHOOLROOM VENTILATION.--Who, on going from the open air of a clear,
bracing winter's day, into a crowded schoolroom, late in the session, has
not noticed the disagreeable odor, and been for a moment nauseated and
half stifled by the oppressive atmosphere! It is not strange. See how many
causes here combine to pollute the air. If the room is heated by a stove,
quantities of carbonic-oxide and carbonic-acid gases, as well as other
products of combustion, driven by downward drafts in the flue, escape
through seams and cracks and the occasionally opened door of the stove. In
the case of a furnace, the same effect is too often experienced, and the
odor of coal gas is a common one, especially when the fire is replenished.
The insensible perspiration is more active in children than in adults;
they, moreover, rush in with their clothing saturated with the
perspiration induced by their sports; so that, on the average, each pupil,
during school hours, loads the air with about half a pint of aqueous
vapor. The children come, oftentimes, from homes that are close, ill-
ventilated, and uncleanly; and frequently from sick rooms, bringing in
their clothing the germs of disease. (See p. 304.) Some of the pupils may
even bear traces of illness, or have unsound organs, and so their breath
and exhalations be poisonous.

In addition to all this, the air is filled with dust brought in and kept
astir by many busy feet; with ashes floating from the stove or furnace;
and especially with chalk dust. The modern method of teaching requires a
large amount of blackboard work, and the air of the schoolroom is thus
loaded with chalk particles. These collect in the nasal passages, and the
upper part of the larynx, and irritate the membrane, perhaps laying the
foundation of catarrh.

The usual schoolroom atmosphere bears in the pupils the natural fruit of
frequent headaches, inattention, weariness, and stupor; but in the teacher
its frightful influence is most apparent. His labor is severe, his worry
of mind is constant, and, when he finishes his day's work, he is generally
too tired to take proper physical exercise. He consequently labors on with
impaired health, or is forced to abandon his profession.

Instead of six hundred feet of space being allowed for each pupil, as
perfect ventilation demands--the lowest estimate being two hundred and
fifty feet--often not over one hundred feet are afforded. Instead of two
thousand cubic feet of fresh air being supplied every hour for each
person, and as much foul air removed, which, all physiologists assert, is
needed for perfect health, perhaps no means of ventilation at all are
provided, and none is secured except what an occasionally opened door, or
the benevolent cracks and chinks in the building furnish the suffering
lungs. [Footnote: Imagine fifty pupils put into a class room thirty feet
long, twenty-five feet wide, and ten feet high. This would generally be
considered a very liberal provision. Such a room contains seven thousand
five hundred cubic feet of air. But it furnishes only one hundred and
fifty feet of space for each pupil. Allowing ten cubic feet of air per
pupil each minute, in fifteen minutes after assembling, the entire
atmosphere of the room is tainted, and unfit to be rebreathed. The demand
of health is that at least one thousand five hundred cubic feet of pure
air should be admitted into this room every minute, and as much be

HOW SHALL WE VENTILATE?--The usual method of ventilation depends upon the
fact that hot air is lighter than cold air, and so the cold air tends, by
the force of gravity, to fall and compel the warm air to rise. Thus, if we
open the door of a heated room, and hold a lighted candle first at the
top, and then at the bottom, we can see, by the deflection of the flame,
that there is a current of air setting outward at the top, and another
setting inward at the bottom of the opening. A handkerchief held loosely,
or the smoke of a smoldering match, in front of a fireplace will show a
current of air passing up the chimney; this is caused by the difference of
temperature between the air in the room and the outside atmosphere.
_Upon this difference of temperature, all ordinary ventilation is
based_. [Footnote: Public buildings are sometimes ventilated by
mechanical means, _i. e._, immense fans which are turned by
machinery, and thus set the air in motion. Such methods are, however,
expensive, and rarely adopted, except where power is also used for other
purposes.] A proper treatment of this subject and its practical
applications, would require a book by itself. There is room here for only
a few general statements and suggestions.

1. Two openings are always necessary to produce a thorough change of air.
(See "Popular Chemistry," p. 70.) Put a lighted candle in a bottle. The
flame will soon be extinguished. The oxygen of the little air in the
bottle is burned out, and carbonic acid has taken its place. Now place
over the mouth of the bottle a lamp chimney, and insert in the chimney a
strip of cardboard, thus dividing the passage. On relighting the candle,
it will burn freely. The smoke of a bit of smoldering paper will show that
two opposite currents of air are established, one setting into the bottle,
the other outward.

2. In the winter, when our schoolrooms, churches, public halls, etc., are
heated artificially, ventilation is comparatively easy if properly
arranged. [Footnote: For the escape of bad air, Dr. Bell suggests that an
efficient foul-air shaft may be fitted to the commonest of stoves by
simply inclosing the stovepipe in a jacket--that is, in a pipe two or
three inches greater in diameter. This should be braced round the
stovepipe and left open at the end next the stove. At its entrance into
the chimney, a perforated collar should separate it from the stovepipe.]
The required difference of temperature is kept up with little difficulty.
The fresh air admitted to the room should then be heated [Footnote:
Ventilation is change of air, and, unless scientifically arranged, and
especially unless the incoming volume of air be warmed in cold weather,
such change of atmosphere means cold currents, with their attendant train
of catarrhs, bronchitis, neuralgia, rheumatism, and all the evils that
spring from these diseases. The raw, damp, frosty air of our ever-changing
winter temperature ought not to have uncontrolled and constant ingress to
our dwellings. Air out of doors is suited to out of door habits. It is
healthy and bracing when the body is coated and wrapped, and prepared to
meet it, and when exercise can be taken to keep up the circulation; but to
live under cover is to live artificially, and such essential conditions
must be observed as suit an abnormal state. All the evils attaching to
ventilation, as it is generally effected, spring from the neglect of this
consistency.--_Westminster Review_.] either by a furnace, or by
passing over a stove, or through a coil of steam pipes. This cold air
should always be taken directly from out of doors, and not from a cellar,
or from under a piazza, where contamination is possible.

3. In order to remove the impure air, there should be ventilators provided
at or near the floor, opening into air shafts, or pipes leading upward
through the roof, with proper orifices at the top. These ventilating pipes
should be heated artificially so as to produce a draught. They may form
one of the flues of a chimney in which there is a constant fire; or be
carried upward in a large flue through the center of which runs the smoke
pipe of the furnace or stove; [Footnote: This plan has been adopted in the
newer school buildings of Elmira, N. Y. The older buildings were provided
with ventilating pipes, not heated artificially, and hence of no service.
These pipes are rendered effective, however, by conducting them into a
small room in the garret, heated by a coal stove. From this room, a large
exit pipe leads to the roof, where it terminates in an Emerson's
ventilator. So strong a draught is thus established that throughout the
building air is taken from the floors, and consequently the cooler portion
of the rooms, at a velocity of three to five feet per second or one
hundred and eighty to three hundred cubic feet per minute for each square
foot of flue opening. In perpendicular flues, heated throughout with a
smoke flue from the furnace, ten feet per second is attained.] or the
ventilating pipe be itself conveyed through the center of the larger
chimney flue. If the register for hot air be on the floor at one side of
the room, two or more ventilators may be placed near the floor on the
opposite side. The warm air will thus make the complete circuit of the
room, and thoroughly warm it before passing out.

If the ventilating shaft be not heated artificially; the ventilator must
be placed at the top of the room in order that the hot air may escape
through it, thus producing an upward draught. But the objection to this
method is that it allows the warmer air to escape, while economy requires
that the cooler air at the bottom of the room should be removed and the
warm air be made to descend, thus securing uniformity of temperature.

4. In the summer, ventilation may be commonly provided for by opening
windows _at the top and the bottom_, on the sheltered side of the
building, so as to avoid draughts of air injurious to the occupants. On a
dull, still, hot day, when there is little difference of temperature
between the inner and the outer air, ventilation can be secured only by
having a fire provided in the ventilating shaft; this, by exhausting the
air from the room, will cause a fresh current to pour in through the open
windows. At recess, all the children should, if the weather permit, be
sent out of doors, to allow their clothing to be exposed to the purifying
influence of the open air; meantime, the windows should be thrown wide
open, that the room may be thoroughly ventilated during their absence. In
bad weather, rapid marching or calisthenic exercises will furnish
exercise, and also permit the airing of the room.

5. The school and the church are the centers for spreading contagious
diseases. The former offers especially dangerous facilities for scattering
disease germs. Great pains, therefore, should be taken to exclude pupils
attacked by or recovering from diphtheria, scarlet fever, whooping cough,
etc., and even those who live in houses where such sickness exists.

6. In our houses [Footnote: The air of our homes is often contaminated by
decaying vegetables and other filth in the cellar; by bad air drawn up
from the soil into the cellar, by the powerful draughts that our fires
create; by defective gas and waste pipes that let the foul air from
cesspool or sewer spread through the house; and by piles of refuse, or
puddles of slops emptied at the back door. Too often, also, the water in
our wells, or in the streams that supply our towns and cities, receives
the drainage from outhouses and barnyards, and so introduces into our
systems, in the liquid--and thus easily assimilated--form, the most
dangerous poisons. The question of sanitary precautions is one that
presses upon every observant mind, and demands constant and thoughtful
attention. (See p. 305.)] open fireplaces are efficient ventilators, and
they should never be closed for any cause. Fresh air admitted by a hot-air
register and impure air passed out by a chimney, form a simple and
thorough system. Our sleeping apartments demand especial care. As soon as
the occupants leave the room, the bedclothes should be removed, and laid
on the backs of chairs to air; the bed be shaken up; and the windows
thrown open. In the summer, the windows may be closed before the sun is
high; the house is then left filled with the cool morning air. In damp and
cold weather, a fire should be lighted in sleeping apartments,
particularly if used by children [Footnote: In winter, children should
always be given a moderately warm, well-ventilated bedroom, with light,
fleecy bed coverings. Says a recent English writer: "The loving care which
prescribes for children a cold bedroom and a hot, sweltering bed is of the
nature that kills. Buried in blankets, their delicate skins become
overheated and relaxed, while they are irritated by perspiration; at the
same time, the most delicate tissues of all, in the lungs, are dealing
with air abnormally frigid. The poor little victims of combined ignorance
and kindness thus toss and dream, feverish and troubled, under a mass of
bedclothes, while the well-meaning mother, soothed by a bedroom fire,
slumbers peacefully through this working out of the sad process of the
'survival of the fittest.'"] or delicate persons, to dry the bedclothing,
and also to prevent a chill on the part of the occupants. It is not
necessary to go shivering to bed in order to harden one's constitution.

WONDERS OF RESPIRATION.--The perfection of the organs of respiration
challenges our admiration. So delicate are they that the least pressure
would cause exquisite pain, yet tons of air surge to and fro through their
intricate passages, and bathe their innermost cells. We yearly perform at
least seven million acts of breathing, inhaling one hundred thousand cubic
feet of air, and purifying over three thousand five hundred tons of blood.
This gigantic process goes on constantly, never wearies or worries us, and
we wonder at it only when science reveals to us its magnitude. In
addition, by a wise economy, the process of respiration is made to
subserve a second use no less important, and the air we exhale, passing
through the organs of voice, is transformed into prayers of faith, songs
of hope, and words of social cheer.

FIG. 33.

[Illustration: A, _the natural position of the internal organs._ B
_when deformed by tight lacing Marshall says that the liver and the
stomach have, in this way, been forced downward almost as low as the

DISEASES, ETC.--1. _Constriction of the Lungs_ is produced by tight
clothing. The ribs are thus forced inward, the size of the chest is
diminished, and the amount of inhaled air decreased. Stiff clothing, and
especially a garment that will not admit of a full breath without
inconvenience, will prevent that free movement of the ribs so essential to
health. Any infraction of the laws of respiration, even though it be
fashionable, will result in diminished vitality and vigor, and will be
fearfully punished by sickness and weakness through the whole life.

2. _Bronchitis_ (bron-ki'-tis) is an inflammation (see Inflammation)
of the mucous membrane of the bronchial tubes. It is accompanied by an
increased secretion of mucus, and consequent coughing.

3. _Pleurisy_ is an inflammation of the pleura. It is sometimes
caused by an injury to the ribs, and results in a secretion of water
within the membrane.

4. _Pneumonia_ (_pneuma_, breath) is an inflammation of the
lungs, affecting chiefly the air cells.

5. _Consumption_ is a disease which destroys the substance of the
lungs. Like other lung difficulties, it is caused largely by a want of
pure air, a liberal supply of which is the best treatment that can be
prescribed for it. [Footnote: If I were seriously ill of consumption, I
would live outdoors day and night, except in rainy weather or midwinter;
then I would sleep in an unplastered log house. Physic has no nutriment,
gaspings for air can not cure you, monkey capers in a gymnasium can not
cure you, stimulants can not cure you. What consumptives want is pure air,
not physic, plenty of meat and plenty of bread.--DR. MARSHALL HALL.]

6. _Asphyxia_ (as-fix'-i-a).--When a person is drowned, strangled, or
choked in any way, what is called asphyxia occurs. The face turns black;
the veins become turgid; insensibility and often convulsions ensue. If
relief is not secured within a few minutes, death will be inevitable.
[Footnote: The lack of oxygen, and the presence of carbonic-acid gas, are
the combined causes. Oxygen starvation and carbonic-acid poisoning, each
fatal in itself, work together to destroy life.] (See p. 264.)

7. _Diphtheria_ (_diphthera_, a membrane) is characterized by
fever, debility, and a peculiar sore throat, in which exuding fibrinous
matter forms a grayish white membrane, which afterward decomposes with a
fetid odor. Its sudden and insidious approach, contagious character, and
frequent fatality, render it an exceedingly dreaded disease. A
diphtheritic patient should be quarantined, and everything connected with
the sick room thoroughly disinfected.

8. _Croup_, which often attacks young children, is an inflammation of
the mucous membrane of the larynx and trachea. It is commonly preceded by
a cold. The child sneezes, coughs, and is hoarse, but the attack
frequently comes on suddenly, and usually in the night. It is accompanied
by a peculiar "brassy," ringing cough, which, once heard, can never be
mistaken. It may prove fatal within a few hours. (See p. 260.)

9. _Stammering_ depends, not on defects of the muscles, but on a want
of due control of the mind. When a stammerer is not too conscious of his
lack, and tries to form his words slowly, he speaks plainly, and may sing
well, for then his words must follow one another in rhythmic time. Many
persons who stammer in common conversation can talk with fluency when
making a speech. The stammerer should seek to discover the cause of his
difficulty, and to overcome it by vocal and respiratory exercise,
especially by speaking only after a full inspiration, and during a long,
slow expiration.


1. What is the philosophy of "the change of voice" in a boy?

2. Why can we see our breath on a frosty morning?

3. When a law of health and a law of fashion conflict, which should we

4. If we use a "bunk" bed, should we pack away the clothes when we first
rise in the morning?

5. Why should a clothespress be well ventilated?

6. Should the weight of our clothing hang from the waist, or the shoulder?

7. Describe the effects of living in an overheated room.

8. What habits impair the power of the lungs?

9. For full, easy breathing in singing, should we use the diaphragm and
lower ribs, or the upper ribs alone?

10. Why is it better to breathe through the nose than the mouth?

11. Why should not a speaker talk while returning home on a cold night
after a lecture?

12. What part of the body needs the loosest clothing?

13. What part needs the warmest?

14. Why is a "spare bed" generally unhealthful?

15. Is there any good in sighing?

16. Should a hat be thoroughly ventilated? How?

17. Why do the lungs of people who live in cities become of a gray color?

18. How would you convince a person that a bedroom should be aired?
[Footnote: "If the condensed breath collected on the cool windowpanes of a
room where a number of persons have been assembled, be burned, a smell as
of singed hair will show the presence of organic matter; and if the
condensed breath be allowed to remain on the windows for a few days, it
will be found, on examination by the microscope, that it is alive with

19. What persons are most liable to catarrhs, consumption, etc.?

20. If a person is plunged under water, will it enter his lungs?

21. Are bed curtains healthful?

22. Why do some people take "short breaths" after a meal?

23 What is the special value of public parks?

24. Can a person become used to bad air, so that it will not injure him?

25. Why do we gape when we are sleepy?

26. Is a fashionable waist a model of art in sculpture or painting?

27. Should a fireplace be closed? [Footnote: Thousands of lives would be
saved if all fireplaces were kept open. If you are so fortunate as to have
a fireplace in your room, paint it when not in use, put a bouquet of fresh
flowers in it every morning, if you please, or do anything to make it
attractive, but never _close it_; better use the fireboards for
kindling wood. It would be scarcely more absurd to take a piece of
elegantly-tinted court-plaster and stop up the nose, trusting to the
accidental opening and shutting of the mouth for fresh air, because you
thought it spoiled the looks of your face to have two such great, ugly
holes in it, than to stop your fireplace with elegantly-tinted paper, or a
Japanese fan, because it looks better.--Leeds.]

28. Why does embarrassment or fright cause a stammerer to stutter still
more painfully?

29. In the organs of voice, what parts have somewhat the same effect as
the case of a violin and the sounding-board of a piano?

30. Why should we be careful not to "take the breath of a sick person"?

31. What special care should be taken with regard to keeping a cellar

32. How is the air strained as it passes into the lungs?

33. Can one really "draw the air into his lungs"?

34. How often do we breathe?

35. Describe some approved method of ventilation.

36. What is at once the floor of the chest and the roof of the abdomen?

37. What would you do in a case of apparent death by drowning, or by coal
gas? (See p. 264.)

38. What would you do in a case of croup, while the doctor was coming?
(See p. 260.)

39. How would you treat a severe burn? (See p. 257.)

40. Describe the various ways in which the water in a well is liable to
become unwholesome.

FIG. 34.




"No rest this throbbing slave may ask,
Forever quivering o'er his task,
While far and wide a crimson jet
Leaps forth to fill the woven net,
Which in unnumber'd crossing tides
The flood of burning life divides,
Then, kindling each decaying part,
Creeps back to find the throbbing heart."



_ | 1. Its Composition.
| 1. THE BLOOD | 2. Its Uses.
| | 3. Transfusion.
| |_4. Coagulation
| _
| | 1. _Description._
| | 2. _Movements._
| | 3. _Auricles and Ventricles._
| _ | _
| | 1. The | | a. Need of.
| | Heart.| | b. Tricuspid and
| | | | Bicuspid.
| | | 4. _The | c. The Strengthen-
| | | Valves._ | ing of the
| | | | Valves.
| | | | d. Semilunar
| | |_ |_ Valves.
| | _
| 2. ORGANS OF THE | 2. The | 1. _Description._
| CIRCULATION | Arteries | 2. _The Arterial System._
| | |_3. _The Pulse._
| | _
| | 3. The | 1. _General Description._
| | Veins |_2. _Valves._
| | _
| | 4. The | 1. _Description._
| | Capilla-| 2. _Use._
| |_ ries |_3. _Under the Microscope._
| _
| | 1. The Lesser.
| 3. THE CIRCULATION.| 2. The Greater.
| |_3. The Velocity of the Blood.
| _
| 4. THE HEAT OF THE | 1. Distribution.
| BODY. |_2. Regulation.
| _
| | 1. Description
| 9. THE LYMPHATIC | 2. The Glands.
| CIRCULATION. | 3. The Lymph.
| |_4. The Office of the Lymphatics.
| _
| | 1. Congestion.
| | 2. Inflammation.
| | 3. Bleeding.
| 10. DISEASES. | 4. Scrofula.
| | 5. A Cold.
| |_6. Catarrh.
| _
| | 1. Effect of Alcohol upon the Circulation.
| 11. ALCOHOLIC | 2. Effect of Alcohol upon the Heart.
| DRINKS AND | 3. Effect of Alcohol upon the Membrane.
|_ NARCOTICS. | 4. Effect of Alcohol upon the Blood.
|_5. Effect of Alcohol upon the Lungs.


THE ORGANS OF THE CIRCULATION are the _heart_, the _arteries_,
the _veins_, and the _capillaries_.

FIG. 35.

[Illustration: A, _corpuscles of human blood, highly magnified;_ B,
_corpuscles in the blood of an animal (a non mammal)._]

THE BLOOD is the liquid by means of which the circulation is effected. It
permeates every part of the body, except the cuticle, nails, hair, etc.
The average quantity in each person is about eighteen pounds. [Footnote:
It is difficult to estimate the exact amount, and therefore authorities
disagree. Foster places it at about one thirteenth of the body weight.] It
is composed of a thin, colorless liquid, the _plasma_, filled with
red disks or cells, [Footnote: There is also one white globular cell to
every three or four hundred red ones. The blood is no more red than the
water of a stream would be if you were to fill it with little red fishes.
Suppose the fishes to be very, very small--as small as a grain of sand--
and closely crowded together through the whole depth of the stream; the
water would look quite red, would it not? And this is the way in which,
blood looks red--only observe one thing; a grain of sand is a mountain in
comparison with the little red fishes in the blood. If I were to tell you
they measured about 1/3500 of an inch in diameter, you would not be much
wiser; so I prefer saying (by way of giving you a more perfect idea of
their minuteness) that there would be about a million in such a drop of
blood as would hang on the point of a needle. I say so on the authority of
a scientific microscopist--M. Bouillet. Not that he has ever counted
them, as you may suppose, any more than I have done; but this is as near
an approach as can be made by calculation to the size of 1/3500 part of an
inch in diameter.--JEAN MACE.] so small that about three thousand five
hundred placed side by side would measure only an inch, and it would take
sixteen thousand laid flatwise upon one another to make a column of that
height. Under the microscope, they are found to be rounded at the edge and
concave on both sides. [Footnote: By pricking the end of the finger with a
needle, we can obtain a drop for examination. Place it on the slide, cover
with a glass, and put it at once under the microscope. The red disks will
be seen to group themselves in rows, while the white disks will seem to
draw apart, and to be constantly changing their form. After a gradual
evaporation, the crystals (Fig. 36) may be seen. In animals, they have
various, though distinctive forms.] They have a tendency to collect in
piles like rolls of coin. The size and shape vary in the blood of
different animals. [Footnote: Authorities differ greatly in their estimate
of the size of the disks (corpuscles) in human blood. The fact is that the
size varies in different persons, probably also in the same individual.
Many of the best microscopists therefore hesitate to state whether a
particular specimen of blood belonged to a human being or to an animal.
Others claim that they can distinguish with accuracy. Evidently, the
question is one of great uncertainty. The following statement of the size
of the cells in different animals is taken from Gulliver's tables: Cat,
1/4404 of an inch in diameter; whale, 1/3100; mouse, 1/3614; hog, 1/4230;
camel, 1/3123; sheep, 1/3352; horse, 1/4800; Virginia deer, 1/5038; dog-
faced baboon, 1/4861; brown baboon, 1/3493; red monkey, 1/3396; black
monkey, 1/3530.] Disks are continually forming in the blood, and are
constantly dying--twenty million at every breath.--DRAPER.

The plasma also contains fibrin, [Footnote: it is usual to say that fibrin
is contained in the blood. It probably does not exist as such, but there
are present in the blood certain substances known as _paraglobulin_
and _fibrinogen_, which by the action of a third substance, _fibrin
ferment_ under certain circumstances, form fibrin and so cause
coagulation. The exact nature of the process by which fibrin is produced
by these three factors is not understood--See Foster's _Text Book of
Physiology_, p 22.] albumin--which is found nearly pure in the white of
an egg--and various mineral substances, as iron, [Footnote: Enough iron
has been found in the ashes of a burned body to form a mourning ring.]
lime, magnesia, phosphorus, potash, etc.

FIG. 36.

[Illustration: _Blood Crystals_]

USES OF THE BLOOD.--The blood has been called "liquid flesh"; but it is
more than that, since it contains the materials for making every organ.
The plasma is rich in mineral matter for the bones, and in albumen for the
muscles. The red disks are the air cells of the blood. They contain the
oxygen so essential to every operation of life. Wherever there is work to
be done or repairs to be made, there the oxygen is needed. It stimulates
to action, and tears down all that is worn out. In this process, it
combines with and actually burns out parts of the muscles and other
tissues, as wood is burned in the stove. [Footnote: For the sake of
simplicity, perhaps to conceal our own ignorance, we call this process
"burning." The simile of a fire is good so far as it goes. But as to the
real nature of the change which the physiologist briefly terms
"oxidation," we know nothing. This much only can be asserted positively. A
stream of oxygen is carried by the blood to the muscles (in fact to every
tissue in the body), while, from the muscles the blood carries away a
stream of carbonic acid and water. But what takes place in the muscles,
when and what chemical change occurs, no one can tell. We see the first
and the last stage. We know that contraction of the muscles somehow comes
about, oxygen disappears, carbonic acid appears, energy is released, and
force is exhibited as motion, heat, and electricity. But the intermediate
step is hidden.

There are certain theories advanced, however, that are worth considering.
Some physiologists hold that the muscle has the power of taking up the
oxygen from the _hemoglobin_ (a body that comprises ninety per cent
of the red corpuscles when dried, and is the oxygen carrier of the blood),
and fixing it, as well as the raw material (food) furnished by the blood,
thus forming a true contractile substance. The breaking down or
decomposition of this contractile substance in the muscle, sets free its
potential energy. The process is gentle so long as the muscle is at rest,
but becomes excessive and violent when contraction occurs. (See "Foster's
Physiology," p. 118.) It is also believed by some that the chemical change
in the muscle partakes of a fermentive character; that, under the
influence of the proper ferments, the substances break up into other and
simpler products, thus setting free heat and force; and that this chemical
change is followed by a secondary oxidation by the oxygen in the arterial
blood, thereby forming carbonic acid and water, as in all putrefactive
processes. But these and other views are not as yet fully understood;
while they utterly fail to tell us how a collection of simple cells,
filled merely with a semifluid mass of matter, can contract and set free
muscular power. The commonness of this act hides from us its wonderful
nature. But here, hidden in the cell--Nature's tiny laboratory--lies the
mystery of life. Before its closed door we ponder in vain, confessing the
unskillfulness of our labor, and fearing all the while lest the _Secret
of the Cell_ will always elude our search.] The blood, now foul with
the burned matter, the refuse of this fire, is caught up by the
circulation, and whirled back to the lungs, where it is purified, and
again sent bounding on its way.

There are then two different kinds of the blood in the body: the red or
arterial, and the dark or venous.

TRANSFUSION.--As the blood is really the "vital fluid" it would seem that
feeble persons might be restored to vigor by infusing healthy blood into
their veins. This hypothesis, so valuable in its possible results in
prolonging human life, has been carefully tested. Animals which have
ceased to breathe have thus had their vitality recalled. In the
seventeenth century the theory became a subject of special investigation.
A maniac was restored to reason by the blood of a calf, and the most
extravagant hopes were entertained. But many fatal accidents occurring,
experiments upon human beings were forbidden by law, and transfusion soon
fell into disuse. It has, however, been successfully practiced in several
cases within the last few years, and is a method still in repute for
saving lives.

COAGULATION.--When blood is exposed to the air, it coagulates. This is
caused by the solidifying of the fibrin, which entangling the disks, forms
the "clot." The remaining clear, yellow liquid is the _serum_. The
value of this peculiar property of the blood can hardly be overestimated.
The coagulation soon checks all ordinary cases of bleeding. [Footnote: In
the case of the lower animals, which have no means of stopping hemorrhages
as we have, the coagulation is generally still more rapid. In some species
of birds it takes place almost instantaneously.] When a wound is made, and
bleeding commences, the fibrin forms a temporary plug, as it were, which
is absorbed when the healing process is finished. Thus we see how a Divine
foresight has provided not only for the ordinary wants of the body, but
also for the accidents to which it is liable. [Footnote: The fibrin is not
an essential ingredient of the blood. All the functions of life are
regularly performed in people whose blood lacks fibrin; and, in cases of
transfusion, where blood deprived of its fibrin was used, the vivifying
influence seemed to be the same. Its office, therefore, must mainly be to
stanch any hemorrhage which may occur.--FLINT.]

FIG. 37.

[Illustration: _The Heart._ A, _the right ventricle;_ B, _the
left ventricle;_ C, _the right auricle;_ D, _the left auricle._]

THE HEART is the engine which propels the blood. It is a hollow, pear-
shaped muscle, about the size of the fist. It hangs, point downward, just
to the left of the center of the chest. (See Fig. 31.) It is inclosed in a
loose sac of serous membrane, [Footnote: The mucous membrane lines the
open cavities of the body; the serous, the closed. The pericardium is a
sac composed of two layers--a fibrous membrane on the outside, and a
serous one on the inside. The latter covers the external surface of the
heart, and is reflected back upon itself in order to form, like all the
membranes of this nature, a sac without an opening. The heart is thus
covered by the pericardial sac, but not contained inside its cavity. A
correct idea may be formed of the disposition of the pericardium around
the heart by recalling a very common and very convenient, though now
discarded headdress, the cotton nightcap. The pericardium incloses the
heart exactly as this cap covered the heads of our forefathers.--
_Wonders of the Human Body_.] called the pericardium (_peri_,
about; and _kardia_, the heart). This secretes a lubricating fluid,
and is smooth as satin.

THE MOVEMENTS OF THE HEART consist of an alternate contraction and
expansion. The former is called the _sys'-to-le_, and the latter the
_di-as'-to-le_. During the diastole, the blood flows into the heart,
to be expelled by the systole. The alternation of these movements
constitutes the beating of the heart which we hear so distinctly between
the fifth and sixth ribs. [Footnote: Two sounds are heard if we put our
ear over the heart,--the first and longer as the blood is leading the
organ, the second as it falls into the pockets of the two arteries, and
the valves then striking together cause it. The first sound is mainly the
noise made by the muscular tissue. During the first, the two ventricles
contract; during the second the two auricles do so. The hand may feel the
heart striking the ribs as it contracts,--a feeling called the impulse,
or, if quicker and stronger than usual, palpitation. This is not always a
sign of disease, but in hypochondriacs is often an effect of the mind on
the nerves of the heart.--MAPOTHER]

FIG. 38.

[Illustration: _Chambers of the Heart_ A, _right ventricle;_ B,
_left ventricle,_ C, _right auricle,_ D, _left auricle,_ E,
_tricuspid valve,_ F, _bicuspid valve;_ G, _semilunar valves,_ H,
_valve of the aorta;_ I, _inferior vena cava,_ K, _superior vena
cava,_ L, L, _pulmonary veins._]

THE AURICLES AND VENTRICLES--The heart is divided into four chambers. In
an adult, each holds about a wineglassful. The upper ones, from appendages
on the outside resembling the ears of a dog, are called _auricles
(aures_, ears). are termed _ventricles_. The auricle and ventricle
on each side communicate with each other, but the right and left halves of
the heart are entirely distinct, and perform different offices. The left
side propels the red blood; and the right, the dark. The auricles are
merely reservoirs to receive the blood (the left auricle, as it filters in
bright and pure from the lungs; the right, as it returns dark and foul
from the tour of the body), and to furnish it to the ventricles as they
need. Their work being so light, their walls are comparatively thin and
weak. On the other hand, the ventricles force the blood (the left, to all
parts of the body; the right, to the lungs), and are, therefore, made very
strong. As the left ventricle drives the blood so much farther than the
right, it is correspondingly thicker and stronger.

NEED OF VALVES IN THE HEART.--As the auricles do not need to contract with
much force simply to empty their contents into the ventricles below them,
there is no demand for any special contrivance to prevent the blood from
setting back the wrong way. Indeed, it would naturally run down into the
ventricle, which is at that moment open to receive it. But, when the
strong ventricles contract, especially the left one, which must drive the
blood to the extremities, some arrangement is necessary to prevent it from
returning into the auricle. Besides, when they expand, the "suction power"
would tend to draw back again from the arteries all the blood just forced
out. This difficulty is obviated by means of little doors, or valves,
which will not let it go the wrong way. [Footnote: The heart of an ox or a
sheep may be used to show the chambers and valves. The aorta should be cut
as far as possible from the heart, and then by pumping in water the
perfection of these valves will be finely exhibited. Cutting the heart
across near the middle will show the greater thickness of the left

THE TRICUSPID AND BICUSPID VALVES.--At the opening into the right
ventricle, is a valve consisting of three folds or flaps of membrane,
whence it is called the _tricuspid_ valve (_tri_, three; and
_cuspides_, points), and in the left ventricle, one containing two
flaps, and named the _bicuspid_ valve. These hang so loosely as to
oppose no resistance to the passage of the blood into the ventricles; but,
if any attempts to go the other way, it gets between the flaps and the
walls of the heart, and, driving them outward, closes the orifice.

FIG. 39.

[Illustration: _Diagram showing the peculiar Fibrous Structure of the
Heart and the Shape of the Valves._ A, _tricuspid valve,_ B,
_bicuspid valve;_ C, _semilunar valves of the aorta;_ D,
_semilunar valves of the pulmonary artery._]

THESE FLAPS ARE STRENGTHENED like sails by slender cords, which prevent
their being pressed back through the opening. If the cords were attached
directly to the walls of the heart, they would be loosened in the systole,
and so become useless when most needed. They are, therefore, fastened to
little muscular pillars projecting from the sides of the ventricle; when
that contracts, the pillars contract also, and thus the cords are held

THE SEMILUNAR VALVES.--In the passages outward from the ventricles, are
valves, called from their peculiar half-moon shape _semilunar_ valves
(_semi_, half; _Luna_, Moon). Each consists of three little
pocket-shaped folds of membrane, with their openings in the direction
which the blood is to take. When it sets back, they fill, and, swelling
out, close the passage (Fig. 40).

THE ARTERIES [Footnote: _Aer,_ air; and _tereo,_ I contain--so
named because after death they contain air only, and hence the ancients
supposed them to be air tubes leading through the body.] are the tube-like
canals which convey the blood _from_ the heart. They carry the red
blood (see note, p. 119). They are composed of an elastic tissue, which
yields at every throb of the heart, and then slowly contracting again,
keeps up the motion of the blood until the next systole. The elasticity of
the arteries acts like the air chamber of a fire engine, which converts
the intermittent jerks of the brakes or pump into the steady stream of the
hose nozzle.

The arteries sometimes communicate by means of branches or by meshes of
loops, so that if the blood be blocked in one, it can pass round through
another, and so get by the obstacle. [Footnote: This occurs especially
about the joints, where it serves to maintain the circulation during the
bending of a limb, or when the main artery is obstructed by disease or
injury, or has been tied by the surgeon. In the last case, the small
adjacent arteries gradually enlarge, and form what is called a collateral
circulation.] When an artery penetrates a muscle, it is often protected by
a sheath or by fibrous rings, which prevent its being pulled out of place
or compressed by the play of the muscles.

The arteries are generally located as far as possible beneath the surface,
out of harm's way, and hence are found closely hugging the bones or
creeping through safe passages provided for them. They are generally
nearly straight, and take the shortest routes to the parts which they are
to supply with blood.

THE ARTERIAL SYSTEM starts from the left ventricle by a single trunk--the
_aorta_--which, after giving off branches to the head, sweeps back of
the chest with a bold curve--the _arch of the aorta_ (_c_, Fig.
34)--and thence runs downward (_f_), dividing and subdividing, like a
tree, into numberless branches, which, at last, penetrate every nook and
corner of the body.

THE PULSE.--At the wrist (_k_, radial artery) and on the temple
(temporal artery) we can feel the expansion of the artery by each little
wave of blood set in motion by the contraction of the heart. In health,
there are about seventy-two [Footnote: This number varies much with age,
sex, and individuals. Napoleon's pulse is said to have been only forty,
while it is not infrequent to find a healthy pulse at one hundred or over.
In general, the pulse is quicker in children and in old people than in the
middle-aged; in short persons than in tall; in women than in men. Shame
makes the heart send more blood to the blushing cheek, and fear almost
stops it. The will can not check the heart. There is said, however, to
have been a notable exception to this in the case of one Colonel Townsend,
of Dublin, who, after having succeeded several times in stopping the
pulsation, at last lost his life in the act.] pulsations per minute. They
increase with excitement or inflammation, weaken with loss of vigor, and
are modified by nearly every disease. The physician, therefore, finds the
pulse a good index of the state of the system and the character of the
disorder. (See p. 314.)

THE VEINS are the tube-like canals which convey the blood _to_ the
heart. [Footnote: There is one exception to the general course of the
veins. The _portal_ vein carries the blood from the digestive organs
to the liver, where it is acted upon, thence poured into the ascending
vena cava, and goes back to the heart.] They carry the dark or venous
blood (note, p. 119). As they do not receive the direct impulse of the
heart, their walls are made much thinner and less elastic than those of
the arteries. At first small, they increase in size and diminish in number
as they gradually pour into one another, like tiny rills collecting to
form two rivers, the vena cava ascending and the vena cava descending
(_l, m_, Fig. 34), which empty into the right auricle.

Some of the veins creep along under the skin, where they can be seen, as
in the back of the hand; while others accompany the arteries, some of
which have two or more of these companions.

VALVES similar in construction to those already described (the semilunar
valves of the heart, page 114) are placed at convenient intervals, in
order to guide the blood in its course, and prevent its setting backward.
[Footnote: Too much standing, or tight elastics, often cause the veins in
the leg to swell, so that the valves can not work; the veins then become
_varicose_, or permanently enlarged, and, if they burst, the bleeding
may be profuse and even dangerous. Raising the leg and pressing the finger
on the bleeding spot will stay it. Walking does not encourage this
disease, for the active muscles force on the venous blood. Clerks who are
subject to varicose veins should have seats behind the counters where they
may rest when not actually employed. A deep breath helps the flow in the
veins, and a wound may suck in air with fatal effect. A maimed horse is
most mercifully killed by blowing a bubble of air into the veins of his
neck. As the deep-sea pressure would burst valves, the whale has none;
hence a small wound by the harpoon causes him to bleed to death.--
MAPOTHER.] We can easily examine the working of these valves. On baring
the arm, blue veins may be seen running along the arm toward the hand.
Their diameter is tolerably even, and they gradually decrease in size. If
now the finger be pressed on the upper part of one of these veins, and
then passed downward so as to drive its blood backward, swellings like
little knots will make their appearance. Each of these marks the location
of a valve, which is closed by the blood we push before our finger. Remove
the pressure, and the valve will swing open, the blood set forward, and
the vein collapse to its former size.

FIG. 40.

[Illustration: _Valves of the Veins._]

THE CAPILLARIES (_capillus,_ a hair) form a fine network of tubes,
connecting the ends of the arteries with the veins. They blend, however,
with the extremities of these two systems, so that it is not easy to tell
just where an artery ends and a vein begins. So closely are they placed,
that we can not prick the flesh with a needle without injuring, perhaps,
hundreds of them. The air cells of the blood deposit there their oxygen,
and receive carbonic acid, while in the delicate capillaries of the lungs
[Footnote: The capillary tubes are there so fine that the disks of the
blood have to go one by one, and are sadly squeezed at that. However,
their elasticity enables them to resume their old shape as soon as they
have escaped from this labyrinth.] they give up their load of carbonic
acid in exchange for oxygen.

FIG. 41.

[Illustration: _Circulation of the Blood in the Web of a Frog's Foot,
highly magnified._ A, _an artery;_ B, _capillaries crowded with
disks, owing to a rupture just above, where the disks are jammed into an
adjacent mesh;_ C, _a deeper vein; the black spots are pigment

If, by means of a microscope, we examine the transparent web of a frog's
foot, we can trace the route of the blood. [Footnote: With small splints
and twine, a frog's foot can be easily stretched and tied so that the
transparent web can be placed on the table of the microscope.] It is an
experiment of wonderful interest. The crimson stream, propelled by the
heart, rushes through the arteries, until it reaches the intricate meshes
of the capillaries. Here it breaks into a thousand tiny rills. We can see
the disks winding in single file through the devious passages, darting
hither and thither, now pausing, swaying to and fro with an uncertain
motion, and anon dashing ahead, until, at last, gathered in the veins, the
blood sets steadily back on its return to the heart.

THE CIRCULATION [Footnote: The circulation of the blood was discovered by
Harvey in 1619. For several years, he did not dare to publish his belief.
When it became known, he was bitterly persecuted, and his practice as a
physician greatly decreased in consequence. He lived, however, to see his
theory universally adopted, and his name honored. Harvey is said to have
declared that no man over forty years of age accepted his views.] consists
of two parts--the _lesser_, and the _greater_.

FIG. 42.

[Illustration: _Diagram illustrating the Circulation of the Blood._--
MARSHALL. A, _vena cava descending (superior);_ Z, _vena cava
ascending (inferior);_ C, _right auricle;_ D, _right ventricle;_ E,
_pulmonary artery;_ F P, _lungs and pulmonary veins;_ G, _left auricle;_
H, _left ventricle;_ I, K, _aorta._]

1. _The Lesser Circulation_.--The dark blood from the veins collects
in the right auricle, and, going through the tricuspid valve, empties into
the right ventricle. Thence it is driven past the semilunar valves,
through the pulmonary artery, to the lungs. After circulating through the
fine capillaries of the air cells contained in the lungs, it is returned,
bright and red, through the four pulmonary veins, [Footnote: It is
noticeable that the pulmonary set of veins circulates red blood, and the
pulmonary set of arteries circulates dark blood. Both are connected with
the lungs.] to the left auricle.

2. _The Greater Circulation_.--From the left auricle, the blood is
forced past the bicuspid valve to the left ventricle; thence it is driven
through the semilunar valves into the great aorta, the main trunk of the
arterial system. Passing through the arteries, capillaries, and veins, it
returns through the venæ cavæ, ascending and descending, gathers again in
the right auricle, and so completes the "grand round" of the body. Both
these circulations are going on constantly, as the two auricles contract,
and the two ventricles expand simultaneously, and _vice versa_.

THE VELOCITY OF THE BLOOD varies so much in different parts of the body,
and is influenced by so many circumstances, that it can not be calculated
with any degree of accuracy. It has been estimated that a portion of the
blood will make the tour of the body in about twenty-three seconds
(FLINT), and that the entire mass passes through the heart in from one to
two minutes. [Footnote: The total amount of blood in an adult of average
weight is about eighteen pounds. Dividing this by five ounces, the
quantity discharged by the left ventricle at each systole, gives fifty-
eight pulsations as the number necessary to transmit all the blood in the
body. This, however, is an extremely unreliable basis of calculation, as
the rapidity of the blood is itself so variable. Chauvreau has shown by
experiments with his instrument that, corresponding to the first dilation
of the vessels, the blood moves with immense rapidity; following this, the
current suddenly becomes nearly arrested; this is succeeded by a second
acceleration in the current, not quite so rapid as the first; and after
this there is a gradual decline in the rapidity to the time of the next
pulsation.] (See p. 314.)

_Distribution_.--The natural temperature is not far from 98°.
[Footnote: The average temperature is, however, easily departed from.
Through some trivial cause the cooling agencies may be interfered with,
and then, the heating processes getting the superiority, a high
temperature or fever comes on. Or the reverse may ensue. In Asiatic
cholera, the constitution of the blood is so changed that its disks can no
longer carry oxygen into the system, the heat-making processes are put a
stop to, and, the temperature declining, the body becomes of a marble
coldness, characteristic of that terrible disease.--DRAPER.] This is
maintained, as we have already seen, by the action of the oxygen within
us. Each capillary tube is a tiny stove, where oxygen is combining with
the tissues of the body (see note, p. 107). Every contraction of a muscle
develops heat, the latent heat being set free by the breaking up of the
tissue. The warmth so produced is distributed by the circulation of the
blood. Thus the arteries, veins, and capillaries form a series of hot-
water pipes, through which the heated liquid is forced by a pump--the
heart--while the heat is kept up, not by a central furnace and boiler, but
by a multitude of little fires placed here and there along its course.

2. _Regulation_.--The temperature of the body is regulated by means
of the pores of the skin and the mucous membrane in the air passages. When
the system becomes too warm, the blood vessels on the surface expand, the
blood fills them, the fluid exudes into the perspiratory glands, pours out
upon the exterior, and by evaporation cools the body. [Footnote: Just as
water sprinkled on the floor cools a room.--_Popular Physics_, p.
255.] When the temperature of the body is too low, the vessels contract,
less blood goes to the surface, the perspiration decreases, and the loss
of heat by evaporation diminishes. [Footnote: Thus one is enabled to go
into an oven where bread is baking, or into the arctic regions where the
mountains are snow and the rivers ice. Even by these extremes the
temperature of the blood will be but slightly affected. In the one case,
the flood gates of perspiration will be opened and the superfluous heat
expended in turning the water to vapor; and, in the other, they will be
tightly closed and all the heat retained.]

LIFE BY DEATH.--The body is being incessantly corroded, and portions borne
away by the tireless oxygen. The scales of the epidermis are constantly
falling off and being replaced by secretion from the cutis. The disks of
the blood die, and new ones spring into being. On the continuance of this
interchange depend our health and vigor. Every act is a destructive one.
Not a bend of the finger, not a wink of the eye, not a thought of the
brain but is at some expense of the machine itself. Every process of life
is thus a process of death. The more rapidly this change goes on, and
fresh, vigorous tissue takes the place of the old, the more elasticity and
strength we possess.

CHANGE OF OUR BODIES.--There is a belief that our bodies change once in
seven years. From the nature of the case, the rate must vary with the
labor we perform; the organs most used altering oftenest. Probably the
parts of the body in incessant employment are entirely reorganized many
times within a single year. [Footnote: To use a homely simile, our bodies
are like the Irishman's knife, which, after having had several new blades,
and at least one new handle, was yet the same old knife.]

THE THREE VITAL ORGANS.--Death is produced by the stoppage of the action
of any one of the three organs--the heart, the lungs, or the brain. They
have, therefore, been termed the "Tripod of Life." Really, however, as
Huxley has remarked, "Life has but two legs to stand upon." If respiration
and circulation be kept up artificially, the removal of the brain will not
produce death. [Footnote: When death really does take place, _i. e._,
when the vital organs are stopped, it is noticeable that the tissues do
not die for some time thereafter. If suitable stimulants be applied, as
the galvanic battery, transfusion of blood, etc., the muscles may be made
to contract, and many of the phenomena of life be exhibited. Dr. Brown-
Sequard thus produced muscular action in the hand of a criminal, fourteen
hours after his execution.]

WONDERS OF THE HEART.--The ancients thought the heart to be the seat of
love. There were located the purity and goodness as well as the evil
passions of the soul. [Footnote: Our common words, hearty, large-hearted,
courage (_cor_, the heart), are remains of this fanciful theory.]
Modern science has found the seat of the mental powers to be in the brain.
But while it has thus robbed the heart of its romance, it has revealed
wonders which eclipse all the mysteries of the past. This marvelous little
engine throbs on continually at the rate of one hundred thousand beats per
day, forty millions per year, often three billions without a single stop.
It is the most powerful of machines. "Its daily work is equal to one third
that of all the muscles. If it should expend its entire force in lifting
its own weight vertically, it would rise twenty thousand feet in an hour."
[Footnote: "The greatest exploit ever accomplished by a locomotive, was to
lift itself through less than one eighth of that distance." Vast and
constant as is this process, so perfect is the machinery, that there are
persons who do not even know where the heart lies until disease or
accident reveals its location.] Its vitality is amazing. The most tireless
of organs while life exists, it is one of the last to yield when life
expires. So long as a flutter lingers at the heart, we know the spark of
being is not quite extinguished, and there is hope of restoration. During
a life such as we sometimes see, it has propelled half a million tons of
blood, yet repaired itself as it has wasted, during its patient,
unfaltering labor. The play of its valves and the rhythm of its throb have
never failed until, at the command of the great Master Workman, the
"wheels of life have stood still." [Footnote: Our brains are seventy-five-
year clocks. The Angel of Life winds them up once for all, then closes the
case, and gives the key into the hand of the Angel of the Resurrection.
Ticktack! Ticktack! go the wheels of thought; our will can not stop them,
they can not stop themselves; sleep can not stop them; madness only makes
them go faster; death alone can break into the case, and, seizing the
ever-swinging pendulum which we call the heart, silence at last the
clicking of the terrible escapement we have carried so long beneath our
wrinkled foreheads.--HOLMES.]

FIG. 43.

[Illustration: _Lymphatics of the Head and Neck, showing the Glands,
and,_ B, _the thoracic duct as it empties into the left innominate
vein at the junction of the left jugular and subclavian veins._]

THE LYMPHATIC CIRCULATION is intimately connected with that of the blood.
It is, however, more delicate in its organization, and less thoroughly
understood. Nearly every part of the body is permeated by a second series
of capillaries, closely interlaced with the blood capillaries already
described, and termed the Lymphatic system. The larger number converge
into the thoracic duct--a small tube, about the size of a goose quill,
which empties into the great veins of the neck (Fig. 43). Along their
course the lymphatics frequently pass through _glands_,--hard,
pinkish bodies of all sizes, from that of a hemp seed to an almond. These
glands are often enlarged by disease, and then are easily felt.

_The Lymph_, which circulates through the lymphatics like blood
through the veins, is a thin, colorless liquid, very like the serum. This
fluid, probably in great measure an overflow from the blood vessels, is
gathered up by the lymphatics, undergoes in the glands some process of
preparation not well understood, and is then returned to the circulation.

FIG. 44.

[Illustration: _Lymphatics in the Leg, with Glands at the Hip_.]

OFFICE OF THE LYMPHATICS.--It is thought that portions of the waste matter
of the body capable of further use are thus, by a wise economy, retained
and elaborated in the system.

The _lacteals_, a class of lymphatics which will be described under
Digestion (p. 166), aid in taking up the food; after a meal they become
milk white. In the lungs, the lymphatics are abundant; sometimes absorbing
the poison of disease, and diffusing it through the system. [Footnote:
Persons have thus been poisoned by tiny particles of arsenic which
evaporate from green wall paper, and float in the air.]

The lymphatics of the skin we have already spoken of as producing the
phenomena of absorption, [Footnote: Pain is often relieved by injecting
under the cuticle a solution of morphine, which is taken up by the
absorbents, and so carried through the system.] Nature in her effort to
heal a cut deposits an excess of matter to fill up the breach. Soon, the
lymphatics go to work and remove the surplus material to other parts of
the body.

Animals that hibernate are supported during the winter by the fat which
their absorbents carry into the circulation from the extra supply they
have laid up during the summer. In famine or in sickness, a man
unconsciously consumes his own flesh.

DISEASES, ETC.--l. _Congestion_ is an unnatural accumulation of blood
in any part of the body. The excess is indicated by the redness. If we put
our feet in hot water, the capillaries will expand by the heat, and the
blood will set that way to fill them. The red nose and purplish face of
the drunkard show a congestion of the capillaries. Those vessels have lost
their power of contraction, and so are permanently increased in size and
filled with blood. Blushing is a temporary congestion. The capillaries
being expanded only for an instant by the nervous excitement, contract
again and expel the blood. [Footnote: Blushing is a purely local
modification of the circulation of this kind, and it will be instructive
to consider how a blush is brought about. An emotion--sometimes
pleasurable, sometimes painful--takes possession of the mind; thereupon a
hot flush is felt, the skin grows red, and according to the intensity of
the emotion these changes are confined to the cheeks only, or extend to

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