[Ill.u.s.tration: Fig. 81.--Showing the Carotid Artery and Jugular Vein on the Right Side, with Some of their Main Branches. (Some branches of the cervical plexus, and the hypoglossal nerve are also shown.)]

[NOTE. "An alcoholic heart loses its contractile and resisting power, both through morbid changes in its nerve ganglia and in its muscle fibers. In typhoid fever, muscle changes are evidently the cause of the heart-enfeeblement; while in diphtheria, disturbances in innervation cause the heart insufficiency. 'If the habitual use of alcohol causes the loss of contractile and resisting power by impairment of both the nerve ganglia and muscle fibers of the heart, how can it act as a heart tonic?'"--Dr. Alfred L. Loomis, Professor of Medicine in the Medical Department of the University of the City of New York.]

200. Other Results from the Use of Intoxicants. Other disastrous consequences follow the use of intoxicants, and these upon the blood. When any alcohol is present in the circulation, its greed for water induces the absorption of moisture from the red globules of the blood, the oxygen-carriers. In consequence they contract and harden, thus becoming unable to absorb, as theretofore, the oxygen in the lungs. Then, in turn, the oxidation of the waste matter in the tissues is prevented; thus the corpuscles cannot convey carbon dioxid from the capillaries, and this fact means that some portion of refuse material, not being thus changed and eliminated, must remain in the blood, rendering it impure and unfit for its proper use in nutrition. Thus, step by step, the use of alcoholics impairs the functions of the blood corpuscles, perverts nutrition, and slowly poisons the blood.

[Ill.u.s.tration: Fig. 82.--The Right Axillary and Brachial Arteries, with Some of their Main Branches.]

[NOTE. "Destroy or paralyze the inhibitory nerve center, and instantly its controlling effect on the heart mechanism is lost, and the accelerating agent, being no longer under its normal restraint, runs riot. The heart's action is increased, the pulse is quickened, an excess of blood is forced into the vessels, and from their becoming engorged and dilated the face gets flushed, all the usual concomitants of a general engorgement of the circulation being the result."--Dr.

George Harley, F.R.S., an eminent English medical author.

"The habitual use of alcohol produces a deleterious influence upon the whole economy. The digestive powers are weakened, the appet.i.te is impaired, and the muscular system is enfeebled. The blood is impoverished, and nutrition is imperfect and disordered, as shown by the flabbiness of the skin and muscles, emaciation, or an abnormal acc.u.mulation of fat."--Dr. Austin Flint, Senior, formerly Professor of the Practice of Medicine in Bellevue Medical College, and author of many standard medical works.

"The immoderate use of the strong kind of tobacco, which soldiers affect, is often very injurious to them, especially to very young soldiers. It renders them nervous and shaky, gives rise to palpitation, and is a factor in the production of the irritable or so-called "trotting-heart" and tends to impair the appet.i.te and digestion."--London _Lancet_.

"I never smoke because I have seen the most efficient proofs of the injurious effects of tobacco on the nervous system."--Dr.

Brown-Sequard, the eminent French physiologist.

"Tobacco, and especially cigarettes, being a depressant upon the heart, should be positively forbidden."--Dr. J. M. Keating, on "Physical Development," in _Cyclopaedia of the Diseases of Children_.]

201. Effect of Tobacco upon the Heart. While tobacco poisons more or less almost every organ of the body, it is upon the heart that it works its most serious wrong. Upon this most important organ its destructive effect is to depress and paralyze. Especially does this apply to the young, whose bodies are not yet knit into the vigor that can brave invasion.

The _nicotine_ of tobacco acts through the nerves that control the heart's action. Under its baneful influence the motions of the heart are irregular, now feeble and fluttering, now thumping with apparently much force: but both these forms of disturbed action indicate an abnormal condition. Frequently there is severe pain in the heart, often dizziness with gasping breath, extreme pallor, and fainting.

The condition of the pulse is a guide to this state of the heart. In this the physician reads plainly the existence of the "tobacco heart," an affection as clearly known among medical men as croup or measles. There are few conditions more distressing than the constant and impending suffering attending a tumultuous and fluttering heart. It is stated that one in every four of tobacco-users is subject, in some degree, to this disturbance. Test examinations of a large number of lads who had used cigarettes showed that only a very small percentage escaped cardiac trouble. Of older tobacco-users there are very few but have some warning of the hazard they invoke. Generally they suffer more or less from the tobacco heart, and if the nervous system or the heart be naturally feeble, they suffer all the more speedily and intensely.

Additional Experiments.

Experiment 93. Touch a few drops of blood fresh from the finger, with a strip of dry, smooth, neutral litmus paper, highly glazed to prevent the red corpuscles from penetrating into the test paper. Allow the blood to remain a short time; then wash it off with a stream of distilled water, when a blue spot upon a red or violet ground will be seen, indicating its _alkaline_ reaction, due chiefly to the sodium phosphate and sodium carbonate.

Experiment 94. Place on a gla.s.s slide a thin layer of defibrinated blood; try to read printed matter through it. This cannot be done.

Experiment 95. _To make blood transparent or laky_. Place in each of three test tubes two or three teaspoonfuls of defibrinated blood, obtained from Experiment 89, labeled _A, B_, and _C. A_ is for comparison. To _B_ add five volumes of water, and warm slightly, noting the change of color by reflected and transmitted light. By reflected light it is much darker,--it looks almost black; but by transmitted light it is transparent. Test this by looking at printed matter as in Experiment 94.

Experiment 96. To fifteen or twenty drops of defibrinated blood in a test tube (labeled _D_) add five volumes of a 10-per-cent solution of common salt. It changes to a very bright, florid, brick-red color.

Compare its color with _A, B_, and _C_. It is opaque.

Experiment 97. Wash away the coloring matter from the twigs (see Experiment 89) with a stream of water until the fibrin becomes quite white. It is white, fibrous, and elastic. Stretch some of the fibers to show their extensibility; on freeing them, they regain their elasticity.

Experiment 98. Take some of the serum saved from Experiment 88 and note that it does not coagulate spontaneously. Boil a little in a test tube over a spirit lamp, and the alb.u.men will coagulate.

Experiment 99. _To ill.u.s.trate in a general way that blood is really a ma.s.s of red bodies which give the red color to the fluid in which they float._ Fill a clean white gla.s.s bottle two-thirds full of little red beads, and then fill the bottle full of water. At a short distance the bottle appears to be rilled with a uniformly red liquid.

Experiment 100. _To show how blood holds a mineral substance in solution_. Put an egg-sh.e.l.l crushed fine, into a gla.s.s of water made acid by a teaspoonful of muriatic acid. After an hour or so the egg-sh.e.l.l will disappear, having been dissolved in the acid water. In like manner the blood holds various minerals in solution.

Experiment 101. _To hear the sounds of the heart_. Locate the heart exactly. Note its beat. Borrow a stethoscope from some physician. Listen to the heart-beat of some friend. Note the sounds of your own heart in the same way.

Experiment 102. _To show how the pulse may be studied_. "The movements of the artery in the human body as the pulse-wave pa.s.ses through it may be shown to consist in a sudden dilatation, followed by a slow contraction, interrupted by one or more secondary dilatations. This demonstration may be made by pressing a small piece of looking-gla.s.s about one centimeter square (? of an inch) upon the wrist over the radial artery, in such a way that with each pulse beat the mirror may be slightly tilted. If the wrist be now held in such a position that sunlight will fall upon the mirror, a spot of light will be reflected on the opposite side of the room, and its motion upon the wall will show that the expansion of the artery is a sudden movement, while the subsequent contraction is slow and interrupted."--Bowditch's _Hints for Teachers of Physiology_.

[Ill.u.s.tration: Fig. 83.--How the Pulse may be studied by Pressing a Mirror over the Radial Artery.]

Experiment 103. _To ill.u.s.trate the effect of muscular exercise in quickening the pulse_. Run up and down stairs several times. Count the pulse both before and after. Note the effect upon the rate.

Experiment 104. _To show the action of the elastic walls of the arteries._ Take a long gla.s.s or metal tube of small caliber. Fasten one end to the faucet of a water-pipe (one in a set bowl preferred) by a very short piece of rubber tube. Turn the water on and off alternately and rapidly, to imitate the intermittent discharge of the ventricles.

The water will flow from the other end of the rubber pipe in jets, each jet ceasing the moment the water is shut off.

The experiment will be more successful if the rubber bulb attached to an ordinary medicine-dropper be removed, and the tapering gla.s.s tube be slipped on to the outer end of the rubber tube attached to the faucet.

Experiment 105. Subst.i.tute a piece of rubber tube for the gla.s.s tube, and repeat the preceding experiment. Now it will be found that a continuous stream flows from the tube. The pressure of water stretches the elastic tube, and when the stream is turned off, the rubber recoils on the water, and the intermittent flow is changed into a continuous stream.

Experiment 106. _To ill.u.s.trate some of the phenomena of circulation._ Take a common rubber bulb syringe, of the Davidson, Household, or any other standard make. Attach a piece of rubber tube about six or eight feet long to the delivery end of the syringe.

To represent the resistance made by the capillaries to the flow of blood, slip the large end of a common gla.s.s medicine-dropper into the outer end of the rubber tube. This dropper has one end tapered to a fine point.

Place the syringe flat, without kinks or bends, on a desk or table.

Press the bulb slowly and regularly. The water is thus pumped into the tube in an intermittent manner, and yet it is forced out of the tapering end of the gla.s.s tube in a steady flow.

Experiment 107. Take off the tapering gla.s.s tube, or, in the place of one long piece of rubber tube, subst.i.tute several pieces of gla.s.s tubing connected together by short pieces of rubber tubes. The obstacle to the flow has thus been greatly lessened, and the water flows out in intermittent jets to correspond to the compression of the bulb.

Chapter VIII.

Respiration.

202. Nature and Object of Respiration. The blood, as we have learned, not only provides material for the growth and activity of all the tissues of the body, but also serves as a means of removing from them the products of their activity. These are waste products, which if allowed to remain, would impair the health of the tissues. Thus the blood becomes impoverished both by the addition of waste material, and from the loss of its nutritive matter.

We have shown, in the preceding chapter, how the blood carries to the tissues the nourishment it has absorbed from the food. We have now to consider a new source of nourishment to the blood, _viz._, that which it receives from the oxygen of the air. We are also to learn one of the methods by which the blood gets rid of poisonous waste matters. In brief, we are to study the set of processes known as respiration, by which oxygen is supplied to the various tissues, and by which the princ.i.p.al waste matters, or chief products of oxidation, are removed.

Now, the tissues are continually feeding on the life-giving oxygen, and at the same time are continually producing carbon dioxid and other waste products. In fact, the life of the tissues is dependent upon a continual succession of oxidations and deoxidations. When the blood leaves the tissues, it is poorer in oxygen, is burdened with carbon dioxid, and has had its color changed from bright scarlet to purple red. This is the change from the arterial to venous conditions which has been described in the preceding chapter.

Now, as we have seen, the change from venous to arterial blood occurs in the capillaries of the lungs, the only means of communication between the pulmonary arteries and the pulmonary veins. The blood in the pulmonary capillaries is separated from the air only by a delicate tissue formed of its own wall and the pulmonary membrane. Hence a gaseous interchange, the essential step in respiration, very readily takes place between the blood and the air, by which the latter gains moisture and carbon dioxid, and loses its oxygen. These changes in the lungs also restore to the dark blood its rosy tint.

The only condition absolutely necessary to the purification of the blood is an organ having a delicate membrane, on one side of which is a thin sheet of blood, while the other side is in such contact with the air that an interchange of gases can readily take place. The demand for oxygen is, however, so incessant, and the acc.u.mulation of carbon dioxid is so rapid in every tissue of the human body, that an All-Wise Creator has provided a most perfect but complicated set of machinery to effect this wonderful purification of the blood.

We are now ready to begin the study of the arrangement and working of the respiratory apparatus. With its consideration, we complete our view of the sources of supply to the blood, and begin our study of its purification.

[Ill.u.s.tration: Fig. 84.--The Epiglottis.]

203. The Trachea, or Windpipe. If we look into the mouth of a friend, or into our own with a mirror, we see at the back part an arch which is the boundary line of the mouth proper. There is just behind this a similar limit for the back part of the nostrils. The funnel-shaped cavity beyond, into which both the mouth and the posterior nasal pa.s.sages open, is called the pharynx. In its lower part are two openings; the trachea, or windpipe, in front, and the sophagus behind.

The trachea is surmounted by a box-like structure of cartilage, about four and one-half inches long, called the larynx. The upper end of the larynx opens into the pharynx or throat, and is provided with a lid,-- the epiglottis,--which closes under certain circ.u.mstances (secs. 137 and 349). The larynx contains the organ of voice, and is more fully described in Chapter XII.

The continuation of the larynx is the trachea, a tube about three-fourths of an inch in diameter, and about four inches long. It extends downwards along the middle line of the neck, where it may readily be felt in front, below the Adam's apple.