CHAPTER VI

THE RESPIRATION

_Experiment 1._ (Home.) =Study of the Throat.=--Sit with the back to the light. Study the open mouth and throat with a mirror and make out the uvula, tonsils, and other parts shown in Fig. 68.

_Experiment 2._ =Anatomy of Lungs.=--Study fresh lungs of sheep, hog, fowl, or frog. Will they float? Will they contract when expanded by air blown in through a quill or other tube? What is the structure of the windpipe? Can you distinguish the arteries from the veins by the stiffness of their walls? Which contain pure blood? Study branching of air tubes. Make a sketch.

_Experiment 3._ =Tests of Expired Air.=--Breathe upon a mirror, bright knife blade, or cold window pane. Result? State your conclusion. _Experiment 4._--Carbon dioxid added to limewater will cause a white cloud consisting of particles of limestone. Breathe through a tube or straw or the hollow stem of a reed into clear limewater. Result? Conclusion? (Limewater may be had at druggist’s or made by pouring water upon a lump of unslackened lime and draining it off when lime has settled.) _Experiment 5._ Breathe for several minutes upon the bulb of a thermometer. Result? Conclusion? _Experiment 6._ Breathe a few times into a large, carefully cleaned pickle jar, or a bottle. Cork it tightly, and set it in a warm place for several days. Then uncork and smell the air in it. Result? Conclusion? _Experiment 7._ Pierce a small hole in a card, place card over a wide-mouthed bottle, and breathe into bottle through a tube, lemonade straw, or hollow reed. Pull out straw. Place bottle, mouth downward, on table, and slip out card. Slide bottle to edge of table and lift lighted candle into bottle. Result? _Experiment 8._ Place bottle of fresh air over lighted candle. Result? Conclusion? (See Animal Biology, p. 4.)

_Experiment 9._ (School.) =Testing the Air of a Room.=--Fill a fruit jar or large bottle with water, and take it into a room containing many people. Pour out the water. (This insures that all the air now in the jar is air obtained in the room to be tested.) Seal the jar if test is not to be made at once. Test by pouring in two tablespoonfuls of clear limewater and shake. If the limewater turns milky, the ventilation is bad.

_Experiment 10._ (Home and school.) =Homemade Current Detector.=--Dangle a bit of paper by means of a spider web or thread from the end of a walking stick or ruler. (Or test with the flame of a candle.) Hold it near cracks of window, above and below doors, and especially before openings intended for entry and exit of air, and test if air moves as desired.

_Experiment 11._ =Ventilation of the Schoolroom.=--Let the whole class rise, and with the fingers test cracks around doors and windows. Wherever the air feels cold to the hand the air is entering.

_Experiment 12._ =Dust.=--With a mirror cause a sunbeam to play like a search light into a closed room several hours after it has been swept. Result? Do the same in a room where every window and door were open during sweeping and left open afterwards. Result? Conclusion? Note also the amount of dust on the furniture of each room.

_Experiment 13._ =Study of Habitual Quiet Breathing.=--Without any more disturbance of the breathing than can be helped, direct your attention to your breathing while sitting quietly. Record motions of any parts of chest and abdominal walls that may be noticeable. If necessary, lay the hands successively against different parts of the wall to test for motion. Think of another subject, and later repeat observations.

_Experiment 14._ =Study of Deep Breathing.=--Place your hands successively upon the front and sides of your chest, waist, and abdomen, while drawing in and sending out deep breaths. What motions of the several parts are observed at each stage?

_Experiment 15._ =Study of Elasticity as a Factor in Breathing.=--(1) Notice whether in quiet breathing there is an elastic rebound as the breath goes either in or out. If so, it is due to the elasticity of the cartilages or air cells of lungs, or both. (2) Breathe by inflating the lungs strongly at each breath. Is the air then forced out without effort? (3) Breathe by flattening the chest and abdomen as much as possible at each breath. Does the air then rush in without effort?

_Experiment 16._ =Chest Breathing.=--Try to breathe wholly by deep expansions and contractions of chest wall. What motions, if any, are noticed in abdominal wall as breath goes in? As it goes out? (Test motions with hand.)

_Experiment 17._ =Abdominal Breathing.=--Try to hold the chest walls still and breathe by strong contraction and expansion of abdomen. Do the chest walls move at all? Neither “chest breathing” nor “abdominal breathing” is the normal way. See text.

_Experiment 18._ =Full Breathing.=--Try breathing by outward and inward movement of walls of chest, _waist_, and abdomen. Do you succeed? This is normal breathing. Is the motion greater at the front or the sides of the waist? Put a belt around the waist tight enough to stay in place and repeat. Is the waist motion interfered with?

_Experiment 19._ =How the Ribs are Lifted.=--Make a model-like sketch to represent backbone, breastbone, and two ribs, using pins to make joints loose at corners. Use cords for diagonals. What happens when cord _ac_ is pulled? When cord _bd_ is pulled? The cords correspond to the two sets of muscles between the ribs.

[Illustration]

_Experiment 20._ =Study of Laughing.=--Place the hands upon the waist and abdomen when laughing. What motion occurs at each sound of laugh? Draw in the abdominal wall with a jerk. What is the effect upon the breath?

_Experiment 21._ =Modifications of the Breath.=--Write I, E, or IE after each word in this list, according as inspiration, expiration, or both, are involved in the action. (Test with sham acts if possible.) Sighing, sobbing, crying (of a child), coughing, laughing, yawning, sneezing, hiccoughing, snoring.

_Experiment 22._ =Effects of Exercise.=--Count and record the rates of breathing before and after vigorous exercise.

_Experiment 23._ =Comparative Study.=--Observe and record the rate and manner of breathing of cow, horse, dog, cat, etc. Is the air drawn in or sent out more quickly? Is there a pause? If so, after which stage of breathing?

_Experiment 24._ =Emergency Drill.=--Resuscitation from drowning, etc. See Coleman’s “Elements of Physiology,” page 356.

=Necessity for Breathing and for Specialized Organs of Breathing.=--The body is a self-regulating machine which possesses energy. This energy, like that of steam engines, arises from oxidation which takes place continually, but at a varying rate. Food for fuel is taken at intervals, but oxygen must be taken in continually. Man breathes about eighteen times per minute. The blood in the tissues soon becomes dark because of loss of oxygen and absorption of carbon dioxid. It is then pumped through the heart to the organ which has the function of absorbing oxygen and giving off carbon dioxid (Fig. 67). In some animals, as the ameba and the earthworm, the surface of the body suffices for breathing. This cell breathing is the true essential respiration; it is universal among living things, both plants and animals. _To supply the deeper cells large animals require a breathing surface greater than the area of the skin. This is supplied by having the oxygen-absorbing surface folded inward to form folds, tubes, and cavities_ of great complexity. If the lungs of a man were unfolded and all their tubes and cavities spread upon one surface, an area of more than one hundred square feet (or ten feet square) would be covered.

Each =respiration=, or breath, consists of the passing in of the air, or _inspiration_, sending it out, or _expiration_, and a _pause_ after one but not after both of the other stages.

[Illustration: FIG. 67.--CIRCULATION THROUGH LUNGS (schematic): “venous” blood (in pulmonary artery) black; “arterial” blood (in pulmonary veins) white.]

[Illustration: FIG. 68.--OPEN MOUTH, showing palate and tonsils.]

[Illustration: FIG. 69.--LUNGS, _P_; with trachea, _TA_; thyroid gland, _th_; larynx, _L_; and hyoid bone, _H_.]

=The Air Passages.=--The air usually passes in at the nose and returns by the same way, except during talking or singing. Observe your mouth with a mirror (Fig. 68); at the back part, an arch is seen which is the rear boundary line of the mouth (Exp. 1). Just above the arch is likewise the rear boundary line of the nasal passages. The funnel-shaped cavity beyond, into which both the mouth and nasal passages open, is called the _pharynx_ (far′inks), or throat (see Fig. 68, also Fig. 83). Below, two tubes open from the pharynx. One is the _trachea_ (trā′kea) or windpipe, the other is the _esophagus_ or _gullet_. At the top of the trachea is the cartilaginous _larynx_, or voice box. If the finger is placed upon the larynx or Adam’s apple, it is plainly felt to move up and down when swallowing. The opening into the larynx is provided with a lid of cartilage, the epiglottis. Inside the larynx, the vocal cords are stretched from front to back. Just below the larynx comes the _trachea_ proper, which is a tube about three fourths of an inch in diameter and about four inches long (Fig. 69). It consists of hoops of cartilage (Fig. 69) which are not complete circles, but are shaped somewhat like the letter C, being completed at the rear by involuntary muscular tissue, whose function is to draw the ends together at times (for instance, during coughing) and reduce the size of the tube. The function of the hoops of cartilage is to keep the windpipe open at all times. If it should be closed by pressure, life might be lost. These rings of cartilage may be felt in the neck.

[Illustration: FIG. 70.--LOBULE OF LUNG.]

The lower end of the trachea is just behind the upper end of the breastbone; there it divides into two large tubes. These subdivide into a great number of smaller branches called _bronchial tubes_. Cartilage is found in the walls of all but the smallest of the tubes. The subdivision continues, somewhat like the branching of a tree, until the whole lung is penetrated by bronchial tubes. Each tiny tube finally ends in a wider funnel-shaped chamber called a _lobule_ (Fig. 70), into which so many dilated sacs, called _air cells_, open, that the walls of the terminal chamber or lobule may be said to consist of tiny cups, or air cells, placed side by side. The lobules, or clusters of air cells, are chiefly near the surface of the lung. (The word “cell” is here used in its original sense to denote a cavity or chamber, and not in the sense of a protoplasmic cell.)

[Illustration: FIG. 71.--CAPILLARIES AROUND AIR SACS OF LUNGS (enlarged 30 diameters). Air sacs in white spaces. Dark lines are capillaries. (Peabody.)]

The _air cells are elastic_ and enlarge by stretching as the chest expands; hence, the cells must have many of the _yellow_ elastic fibers of connective tissue in their walls. They are lined with an exceedingly thin membrane of epithelial cells through which _oxygen and carbon dioxid are exchanged_. In the walls of the air cells there is _a network of capillaries_ (Fig. 71). The dark red blood comes into these capillaries from the pulmonary arteries, and is changed to a bright red by the time it leaves them to enter the pulmonary veins. The air leaves the lungs warmer, moister, and containing more carbon dioxid than when it entered.

Most of the =mucous membrane lining the air passages= has a surface layer of ciliated cells. _Cilia are tiny thread-like projections_ (Fig. 72) which continually wave to and fro, the quicker stroke always being outward; for their function is to remove particles of dust and germs that may find entrance to the air passages. When the mucus containing the dust is raised nearly to the larynx, it may be thrown out by coughing. _Near the opening of the nostrils are placed many hairs_, hundreds of times larger than cilia, through which the air is strained as it enters the nose. Hairs are multicellular; cilia are parts of cells. See Animal Biology, Fig. 14.

[Illustration: FIG. 72.--CILIATED CELLS, lining the air passages.]

=The Lungs.=--The entire _chest cavity_ is occupied by the lungs except the space occupied by the heart, the larger blood vessels, and the gullet. The right lung has three lobes, or divisions, and the left lung has two lobes. The lungs are light pink in early life, but become grayish and darker as age advances. This change is more marked in those who dwell in cities, or wherever the atmosphere is smoky and dusty. The lungs are covered and inclosed by a smooth membrane called the _pleura_. This membrane turns back and lines the chest wall, so that when the chest expands, the two sleek membranes glide over each other with far less friction than would be the case if the lungs and chest wall were touching (Exp. 2).

[Illustration: FIG. 73.--VERTICAL SECTION OF TRUNK, showing diaphragm, cavities of thorax and abdomen.]

=The Respiratory Muscles.=--(Repeat Exps. 13, 14, 15.) The chief breathing muscles are the _diaphragm_ (see Figs. 73 and 74), the muscles _forming the abdominal walls_ (see Fig. 44), and _two sets of short muscles_ (an internal and an external set), _between the ribs_. They are called _intercostals_. (They are the flesh eaten when eating pork ribs.) The _diaphragm_, which is shaped like a bowl turned upside down, rounds up under the base of the lungs somewhat like a dome and separates the chest from the abdomen. Its hollow side is toward the abdomen and its edges are attached to the lowest ribs and the vertebra of the loins. Inspiration is brought about by the rising of the ribs and the descent of the diaphragm. Expiration takes place when the ribs descend, the abdominal walls draw in, and the transmitted pressure lifts the relaxed diaphragm.

[Illustration: FIG. 74.--DIAPHRAGM (or midriff), seen from below. (Cunningham.)

The central portion (light) is tendinous. As the diaphragm descends, it acts like the piston of a great pump and the blood is forced up through the vena cava, and the lymph through the thoracic duct (Fig. 66).]

=Inspiration.=--To cause inspiration the diaphragm contracts, it flattens and descends, since its edges are attached lower than its middle (Fig. 73); the lungs descend with it, thus lengthening the chest from top to bottom; at the same time the ribs are raised upward and outward (Fig. 76) by the contraction of the outer set of muscles between the ribs. Thus the _chest is made longer, broader, and deeper from front to back_. The lungs expand when the chest expands, and the air rushes in. Why is this? The lungs contain no muscles and cannot expand themselves; the air cannot be pulled in, for its parts do not stick together. The true reason is that the air has weight. The atmosphere has a height of many miles, and the air above is pressing on that below. When the chest walls are raised there would be an empty space or vacuum between these walls and the lungs, did not the pressure of _the outside air push air through the windpipe into the lungs and expand them_ (Exp. 19).

[Illustration: FIG. 75.--FRAMEWORK OF CHEST.]

=Expiration.=--In very active breathing the abdominal walls actively contract so that they press strongly upon the digestive organs, which in turn _press the diaphragm up. The ribs are also drawn down and in_. Thus the chest becomes smaller and forces the air to flow out through the windpipe (Exps. 20 and 21).

[Illustration: FIG. 76.--BLACKBOARD SKETCH, to show how the chest is expanded when the ribs move upward and outward.]

THOUGHT QUESTIONS.--_Why breathing with the waist is easier than breathing with the upper chest. Effects of confining the waist_.

1. There are two pairs of ____ ribs below, while there are none above. 2. There are three pairs of ____ ribs below, while there are none above, but all ribs of the upper chest are ____ ribs. 3. The lower of the joints between the seven pairs of true ribs and the sternum are more flexible than the upper joints because ____. (Observe the joints in Fig. 75.) 4. The walls of the waist swing ____ and ____, while the walls of the upper chest must move ____ and ____. 5. The bones of the ____ rest upon the upper chest. In upper chest breathing their weight, and the weight of both of the ____ must, therefore, be lifted. (Fig. 28.) Test by trying it.

[Illustration: FIG. 77.

FIG. 78.

FIG. 79.

FIG. 77.--FEMALE FIGURE ENCASED IN CORSET. Expansion at the waist is here impossible and the breathing is called “collar-bone breathing.”

FIG. 78.--MALE FIGURE. Here, owing to pressure of clothing and faulty position, expansion of chest is hindered and breath is taken by the “abdominal method.”

FIG. 79.--FIGURE PROPERLY POISED AND FREE. Here the entire thorax can move freely, and natural breathing is the result. (For blackboard.) From Latson.]

=Hygienic Habits of Breathing.=--Chest breathing uses chest chiefly, abdominal breathing uses abdomen chiefly, full breathing uses both. These three forms depend upon whether the breathing is carried on by using the muscles of (1) the chest, (2) the abdomen, or (3) both (see Figs. 77, 78, 79). There has been much debate among physicians, surgeons, and singers as to which of these methods is best. Probably this question would not have been raised but for the confining and deforming effect of clothing upon the waist. _Full breathing is used by children of all races, by both men and women of wild tribes, and by men of civilized countries._ It is undoubtedly the natural way, as well as the easiest and most effective way (Exps. 16, 17, 18).

Breathing with the upper chest is exhausting because of the stiffness of the upper part of the bony cage (see Fig. 75); for it is inclosed by true ribs fixed to the breastbone by short cartilages. The ribs in the waist (Fig. 75) are either floating in front or fixed by long cartilages to the ribs above. In pure abdominal breathing the diaphragm must contract more than in full breathing in order to descend, because its edges have been drawn together and fixed by binding the ribs at the waist. In full breathing the floating and false ribs at the waist (five pairs in all) float in and out as nature provided. As they move out, this broadens and deepens the chest, and aids the flattening of the diaphragm by moving its edges farther apart. Those persons, perhaps one in a thousand, who voluntarily deform the body with tight clothing are beneath contempt. But so uniform is the pressure of tight clothes and shoes that the wearer soon becomes unconscious of them, and so powerful are the effects that not one person in a thousand escapes deformity and injury. Children’s clothing should be supported by the shoulders, and adults’ clothing by both shoulders and hips, but by the waist, never.

=Cellular Respiration.=--The chemical activities within the cells and their need of oxygen, not the amount of oxygen in the lungs or blood, determine how much oxygen the cells absorb from the blood. Oxygen cannot be forced even into the blood beyond the required amount. Deep breathing movements, however, help the flow of the blood and lymph. Carried to excess, they tire the will and exhaust the nerves.

=Changes in Blood while in the Lungs.=--The coloring matter (or hemoglobin) of the corpuscles absorbs oxygen (and becomes oxy-hemoglobin). Carbon dioxid is given off from the plasma. The blood becomes a brighter red.

=Changes in Air in the Lungs.=--The air entering the lungs consists of about one fifth oxygen and four fifths nitrogen. This nitrogen is of no use to the body, and is exhaled unchanged. _A part of the oxygen inspired is taken up by the blood, and carbon dioxid is sent out in its place._ About half a pint of water is given off through the lungs in a day. Minute quantities of injurious animal matter are also given off in the breath from even the soundest person. The air leaves the lungs warmer, damper, and with more carbon dioxid than when it entered (Exps. 3 to 9).

[Illustration: FIG. 80.--VENTILATION OF STOVE-HEATED ROOM.[5]

How are the inlet and outlet situated with reference to the stove?]

[5] From Coleman’s Elements of Physiology (400 pp.). The Macmillan Co., N.Y.

Persons with decayed teeth, catarrh, indigestion, diseased lungs, or other unsoundness give off still more of this material. When many people are assembled in a badly ventilated room, the amount of injurious animal matter in the air is much increased, and is called “_crowd poison_.” Its odor is strong and repulsive to one who just enters the room, but the sense of smell becomes dull to it in a few minutes. It would seem that nature gives a fair warning against harm; but if we disregard the warning it soon ceases.

=People who are really Unclean.=--Nature’s plan seems to be for us to live out of doors. Air once breathed is impure. It is just as unfit to enter our bodies as muddy water or decayed food. Yet many who call themselves cleanly and refined, and _will not allow a speck of dirt to remain on their clothes, nor use a spoon just used by another, do not object to breathing into their lungs, over and over again, the cast-off air from the lungs of others_. If a window is opened for ventilation, they are horror-stricken for fear of drafts. Drafts are injurious only to persons perspiring, or to those who have coddled the skin by continually overheating it. There are thousands of schools, churches, and theaters all over the land which reek daily with the malodorous particles from the lungs of their occupants. Although the air in them is odorless to those who occupy them, it is disgusting to any one who enters from the fresh air. Figure 80 shows the correct ventilation of a stove-heated schoolroom.

=Dust= causes catarrh of the bronchial tubes and chronic inflammation of the lungs; it prepares for consumption, by gradually weakening the lungs of those who breathe it. Intelligence and common sense are necessary to prevent it from accumulating in the house. The chief purpose of the house cleaning should be not only to remove bits of paper from the floor, which do no harm even to the shoes, but _to remove impurities from the air_. _It does no good to stir up the dust and allow it to settle down again_ (Exp. 12). In many houses dust is thus allowed to accumulate for months. Experiments show that dust and germs floating in the air are not diminished to a great extent by a gentle draft through the room. The windows must be open and sweeping done in the direction of the air currents; the windows should be _left open for a long while after the sweeping_. A windy day is best for sweeping.

The habit some housekeepers have of buying furnishings and bric-à-brac for the home until it looks like a retail store or junk shop, makes it almost impossible to clean their houses. A few articles, carefully selected, adorn a home more than many bought at random, and they do not litter the house and serve as traps for dust. With all precautions some dust may settle down. This should not simply be stirred up again with a feather duster, but _the dusting should be done with a damp cloth_. Ashes should be sprinkled before they are moved. Carpet sweepers, but never brooms, should be used upon carpets. Carpets and lace curtains are truly dust traps, in which dust will accumulate without limit. Those who value the health will not use such uncleanly abominations, at least in bedrooms. Though linoleum, bare floors with movable rugs, oiled and painted floors, may not look so comfortable as a fixed carpet, they bring far more comfort in the end. _The weakening effect of ordinary dust is one of the chief causes of lung diseases_, and prepares a fertile soil for the consumptive germ. The sputum coughed up by consumptives falls upon the floor or street, soon dries, and the germs are driven about by the wind. In many cities there is a law against spitting in public places, and the streets are flushed with water before they are swept.

[Illustration: FIG. 81.--The air enters through a special inlet and is warmed as it passes through hood surrounding the stove.]

[Illustration: FIG. 82.--Chimney with a passage behind fireplace, or grate, in which the air is warmed as it enters.]

=Ventilation= presents no difficulties in the summer time or in warm climates. The reason that it is a difficult question in cold weather is because the air furnished must be not only pure, but warm. To keep cold air out often means to keep foul air in. _Heating with hot air_, by which system pure air is passed over a furnace, and fresh air constantly admitted, may be a good method (Figs. 80, 81), but is often a dismal failure because it dries out the air, which in turn dries out the skin. To prevent this, wide vessels of water should be set at the inlets. Dry air is cooling. Why? Dr. Barnes proved that moist air at 65° is as comfortable as dry air at 71°. Air saturated with vapor at 60° will _only be 50 per cent saturated at 80°_. Such air dries out the mucous membrane of eyes, nose, and throat. Heating by _hot water_ circulating in pipes, or _by steam_, gives no means of introducing fresh air, and is likely to cause worse ventilation than any other method. The radiators should stand close to windows or other fresh-air inlet, that the air may be heated as it enters, and the outlet for air should be farthest from the radiators. The same rules apply to heating by _stoves_. An oil stove for heating is an inconceivable iniquity to any but a person densely ignorant of hygiene. Heating by _fireplaces_ (Fig. 82) is the most healthful of all methods, for there is a constant removal of air through the chimney, and this air will be replaced; even if all doors and windows are closed, it will come in through tiny cracks. _Radiant heat_ travels in straight lines from a fireplace and _warms solid objects_, but not the air passed through. Hence an open fire will keep the body warm with the room at a low temperature. Fireplaces, however, do not afford sufficient heat in severe climates.

_Stoves_ are not as healthful as fireplaces, for there is not so much air removed through the pipe as through the chimney. _Carbon monoxid_, unlike carbon dioxid, is an _active_ poison causing the blood corpuscles to shrivel. It passes through red-hot iron or a cracked stove or furnace.

[Illustration: FIG. 83.--BLACKBOARD SKETCH.]

[Illustration: FIG. 84.--Facial expression in mouth breathing, and breathing through the nose.]

=Reasons for Breathing through the Nose= (Fig. 83).--(1) The many blood vessels in the mucous membrane lining the nasal passages so _heat the air_ that it does not irritate the bronchial tubes. (2) _The hairs in the nostrils strain the air_ and catch dust; the cilia of the nasal passages also do this. (3) A mouth-breather often _swallows food before chewing it sufficiently_, because he cannot hold his breath longer. (4) The nasal mucous membrane of an habitual mouth-breather _dries and shrinks_ and obstructs the circulation, bringing on _catarrh of the nose_. (5) Mouth breathing causes an _unpleasant expression of countenance_ (see Fig. 84). (6) The breath does not come through the nose as quickly as through the mouth; the _lungs are kept more expanded_, and one does not get “out of breath” so quickly. (7) _The voice of the mouth breather has a hard twang_, not a full, resonant tone as when the nostrils are open. (8) _Flavors and odors_ are better appreciated. Sometimes the sense of smell is almost lost by mouth breathers. If one cannot breathe through the nose, even for a short time, there is probably an adenoid, or tonsil-like, growth in nose or pharynx, and a physician should be consulted. “Adenoids” are glandular or grapelike in form.

=Diseases of the Respiratory Organs.=--_A cold or catarrh is an inflammation of a mucous membrane._ If the inflammation is in the nasal passages, it is called a _cold_ in the head; if it is in the pharynx, it is called a _sore throat_; if it is in the larynx or voice box, there is _hoarseness_; if it is in the bronchial tubes, it is _bronchitis_; finally, if it is in the air cells, it is _pneumonia_. If the air is cut off from access to the air cells, there is an attack of the painful disease called _asthma_, which is accompanied by a feeling of suffocation. Some believe that asthma is caused by the mucous membrane lining the finest bronchial tubes becoming inflamed and swollen, and closing the tubes; others think that the muscles in the large bronchial tubes contract and close the tubes. _Pleurisy_ is inflammation of the pleura and makes breathing painful. If much fluid forms between the pleuras, the inner pleura may press upon the lungs and interfere with breathing.

=Alcohol= not only weakens the blood vessels near the surface, but the blood vessels in general. Weakened and congested blood vessels in the lungs make them more liable to pneumonia and other congestive diseases. Continual congestion causes an abnormal growth of connective tissue fiber in the walls of the cells. This diminishes the capacity of the lungs and interferes with the exchange of carbon dioxid and oxygen.

=Tobacco.=--It is often asked why cigarettes are so much more injurious to the health than pipes and cigars. The nature of the paper of cigarettes and various other absurd reasons have been assigned. The true reason is that the cigarette smoker usually _inhales_ the tobacco smoke. Cigar smoke, if drawn into the lungs, would usually be coughed up at once. Cigarette smoke is weaker--it is so weak that the smoker is not content simply to absorb the nicotine through the mucous membrane of the mouth; he draws it into the lungs. The very mildness of the smoke leads to inhalation. Hence, as the _surface_ of the lungs is a _hundred times greater_ than the surface of the mouth, and _its lining much thinner_, cigarette smoking is far more injurious than cigar smoking.

The poison accumulates in the bowl of a pipe; hence an old pipe is very injurious. The irritation of tobacco smoke often sets up a chronic dry catarrh of the air passages; rarely it causes cancer of lips or tongue. Sir Henry Thompson says: “The only persons who enjoy smoking and find it tranquillizing at times are those who smoke in great moderation. Men who are rarely seen without a cigar between the lips, have long ceased to enjoy smoking. They are confirmed in a habit, and are merely miserable when the cigar is absent.” They do not smoke for pleasure, but to escape misery which wiser men escape by avoiding tobacco altogether.

[Illustration: FIG. 85.

FIG. 86.

FIG. 85.--FLATTENED CHEST and waist organs sunken from wearing tight clothing since the age of fourteen. Such women often walk with bodies bent forward to hide the prominent abdomen.

FIG. 86.--A NATURAL WOMAN.]

PRACTICAL QUESTIONS.--=1.= State how in the case of a person with round shoulders a gradual remolding of cartilages (which ones?), the strengthening of the muscles (which ones?), and the practice of deep breathing may each contribute toward acquiring an erect and perfect figure. =2.= Should a hat be well ventilated? (A punch for making the holes costs a dime.) Should a hat be stiff or soft? =3.= Name habits that impair the power of the lungs. =4.= How could you convince a person that a bedroom should be open while and after it is swept? That it should be ventilated at night? =5.= Which is the more injurious to others, tobacco chewing which causes the ground to be unclean, or smoking which renders the air impure? =6=. Why do those who stand straight up to hoe not get tired half so quickly as those who bend or “hump” over? (Chap. VI.) =7.= Why do students who sit in rocking chairs, or from other causes lean the head forward when they study, often find that they recover from drowsiness if they sit erect, or sit in a straight chair? =8.= How are high collars a fruitful source of bad colds? =9.= If the draft up the chimney of the fireplace, when the fire is burning, takes up a volume of air sufficient for many people, why is it unnecessary to open a window? =10.= Why does cold impure air make a person colder than cold pure air? (p. 14.) =11.= Do the modern customs of uniformity in dress for all classes and climates, shipping foods from great distances, one section or nation imitating the ways of another section or nation, lead toward health or disease? Do such customs violate or conform to the great biological law that life is a process of adaptation to environment?

[Illustration: FIG. 87.--SUSPENDERS should have a pulley or lever at the back, that the strap on one side may loosen when one shoulder is raised.]

[Illustration: COLORED FIGURE 6.--ORGANS OF THE TRUNK.

_cb_, collar bone; _r_, ribs; _z_, tongue bone (hyoid); _k_, _k_, cartilages of larynx; _l_, windpipe; _s_, thyroid gland; _rv_, right ventricle; _lv_, left ventricle; _ru_, right auricle; _lu_, left auricle; _a_, aorta; _ka_, artery to head (carotid); _sa_, subclavian artery; _la_, pulmonary artery; _oh_, superior vena cava; _hv_, jugular vein; _lu_, lungs; _f_, diaphragm; _lb_, liver; _g_, gall bladder; _s_, stomach; _x_, spleen; _n_, mesentery with vessels; _d_, small intestine; _gd_, large intestine; _b_, cæcum; _w_, vermiform appendix; _h_, bladder.]