Now, when the diaphragm contracts, it descends and thus increases the depth of the chest cavity. A quantity of air is now drawn into the lungs and causes them to expand, thus filling up the increased space. As soon as the diaphragm relaxes, returning to its arched position and reducing the size of the chest cavity, the air is driven from the lungs, which then diminish in size. After a short pause, the diaphragm again contracts, and the same round of operation is constantly repeated.

The walls of the chest being movable, by the contractions of the intercostals and other muscles, the ribs are raised and the breastbone pushed forward. The chest cavity is thus enlarged from side to side and from behind forwards. Thus, by the simultaneous descent of the diaphragm and the elevation of the ribs, the cavity of the chest is increased in three directions,—downwards, side-ways, and from behind forwards.

It is thus evident that inspiration is due to a series of muscular contractions. As soon as the contractions cease, the elastic lung tissue resumes its original position, just as an extended rubber band recovers itself. As a result, the original size of the chest cavity is restored, and the inhaled air is driven from the lungs. Expiration may then be regarded as the result of an elastic recoil, and not of active muscular contractions.

]

211. Varieties of Breathing. This is the mechanism of quiet, normal respiration. When the respiration is difficult, additional forces are brought into play. Thus when the windpipe and bronchial tubes are obstructed, as in croup, asthma, or consumption, many additional muscles are made use of to help the lungs to expand. The position which asthmatics often assume, with arms raised to grasp something for support, is from the need of the sufferer to get a fixed point from which the muscles of the arm and chest may act forcibly in raising the ribs, and thus securing more comfortable breathing.

The visible movements of breathing vary according to circumstances. In infants the action of the diaphragm is marked, and the movements of the abdomen are especially obvious. This is called abdominal breathing. In women the action of the ribs as they rise and fall, is emphasized more than in men, and this we call costal breathing. In young persons and in men, the respiration not usually being impeded by tight clothing, the breathing is normal, being deep and abdominal.

Disease has a marked effect upon the mode of breathing. Thus, when children suffer from some serious chest disease, the increased movements of the abdominal walls seem distressing. So in fracture of the ribs, the surgeon envelops the overlying part of the chest with long strips of firm adhesive plaster to restrain the motions of chest respiration, that they may not disturb the jagged ends of the broken bones. Again, in painful diseases of the abdomen, the sufferer instinctively suspends the abdominal action and relies upon the chest breathing. These deviations from the natural movements of respiration are useful to the physician in ascertaining the seat of disease.

212. The Nervous Control of Respiration. It is a matter of common experience that one's breath may be held for a short time, but the need of fresh air speedily gets the mastery, and a long, deep breath is drawn. Hence the efforts of criminals to commit suicide by persistent restraint of their breathing, are always a failure. At the very worst, unconsciousness ensues, and then respiration is automatically resumed. Thus a wise Providence defeats the purpose of crime. The movements of breathing go on without our attention. In sleep the regularity of respiration is even greater than when awake. There is a particular part of the nervous system that presides over the breathing function. It is situated in that part of the brain called the medulla oblongata, and is fancifully called the "vital knot" (sec. 270). It is injury to this respiratory center which proves fatal in cases of broken neck.

From this nerve center there is sent out to the nerves that supply the diaphragm and other muscles of breathing, a force which stimulates them to regular contraction. This breathing center is affected by the condition of the blood. It is stimulated by an excess of carbon dioxid in the blood, and is quieted by the presence of oxygen.

Experiment 108. To locate the lungs. Mark out the boundaries of the lungs by "sounding" them; that is, by percussion, as it is called. This means to put the forefinger of the left hand across the chest or back, and to give it a quick, sharp rap with two or three fingers. Note where it sounds hollow, resonant. This experiment can be done by the student with only imperfect success, until practice brings some skill.

Experiment 109. Borrow a stethoscope, and listen to the respiration over the chest on the right side. This is known as auscultation. Note the difference of the sounds in inspiration and in expiration. Do not confuse the heart sounds with those of respiration. The respiratory murmurs may be heard fairly well by applying the ear flat to the chest, with only one garment interposed.

Experiment 110. Get a sheep's lungs, with the windpipe attached. Ask for the heart and lungs all in one mass. Take pains to examine the specimen first, and accept only a good one. Parts are apt to be hastily snipped or mangled. Examine the windpipe. Note the horseshoe-shaped rings of cartilage in front, which serve to keep it open.

Experiment 111. Examine one bronchus, carefully dissecting away the lung tissue with curved scissors. Follow along until small branches of the bronchial tubes are reached. Take time for the dissection, and save the specimen in dilute alcohol. Put pieces of the lung tissue in a basin of water, and note that they float.

The labored breathing of suffocation and of lung diseases is due to the excessive stimulation of this center, caused by the excess of carbon dioxid in the blood. Various mental influences from the brain itself, as the emotions of alarm or joy or distress, modify the action of the respiratory center.

Again, nerves of sensation on the surface of the body convey influences to this nerve center and lead to its stimulation, resulting in a vigorous breathing movement. Thus a dash of cold water on the face or neck of a fainting person instantly produces a deep, long-drawn breath. Certain drugs, as opium, act to reduce the activity of this nerve center. Hence, in opium poisoning, special attention should be paid to keeping up the respiration. The condition of the lungs themselves is made known to the breathing center, by messages sent along the branches of the great pneumogastric nerve (page 276), leading from the lungs to the medulla oblongata.

213. Effects of Respiration upon the Blood. The blood contains three gases, partly dissolved in it and partly in chemical union with certain of its constituents. These are oxygen, carbon dioxid, and nitrogen. The latter need not be taken into account. The oxygen is the nourishing material which the tissues require to carry on their work. The carbon dioxid is a waste substance which the tissues produce by their activity, and which the blood carries away from them.

As before shown, the blood as it flows through the tissues loses most of its oxygen, and carbon dioxid takes its place. Now if the blood is to maintain its efficiency in this respect, it must always be receiving new supplies of oxygen, and also have some mode of throwing off its excess of carbon dioxid. This, then, is the double function of the process of respiration. Again, the blood sent out from the left side of the heart is of a bright scarlet color. After its work is done, and the blood returns to the right side of the heart, it is of a dark purple color. This change in color takes place in the capillaries, and is due to the fact that there the blood gives up most of its oxygen to the tissues and receives from them a great deal of carbon dioxid.

In brief, while passing through the capillaries of the lungs the blood has been changed from the venous to the arterial blood. That is to say, the blood in its progress through the lungs has rid itself of its excess of carbon dioxid and obtained a fresh supply of oxygen.[36]

214. Effects of Respiration upon the Air in the Lungs. It is well known that if two different liquids be placed in a vessel in contact with each other and left undisturbed, they do not remain separate, but gradually mix, and in time will be perfectly combined. This is called diffusion of liquids. The same thing occurs with gases, though the process is not visible. This is known as the diffusion of gases. It is also true that two liquids will mingle when separated from each other by a membrane (sec. 129). In a similar manner two gases, especially if of different densities, may mingle even when separated from each other by a membrane.

In a general way this explains the respiratory changes that occur in the blood in the lungs. Blood containing oxygen and carbon dioxid is flowing in countless tiny streams through the walls of the air cells of the lungs. The air cells themselves contain a mixture of the same two gases. A thin, moist membrane, well adapted to allow gaseous diffusion, separates the blood from the air. This membrane is the delicate wall of the capillaries and the epithelium of the air cells. By experiment it has been found that the pressure of oxygen in the blood is less than that in the air cells, and that the pressure of carbon dioxid gas in the blood is greater than that in the air cells. As a result, a diffusion of gases ensues. The blood gains oxygen and loses carbon dioxid, while the air cells lose oxygen and gain the latter gas.



The blood thus becomes purified and reinvigorated, and at the same time is changed in color from purple to scarlet, from venous to arterial. It is now evident that if this interchange is to continue, the air in the cells must be constantly renewed, its oxygen restored, and its excess of carbon dioxid removed. Otherwise the process just described would be reversed, making the blood still more unfit to nourish the tissues, and more poisonous to them than before.

215. Change in the Air in Breathing. The air which we exhale during respiration differs in several important particulars from the air we inhale. Both contain chiefly the three gases, though in different quantities, as the following table shows.

Oxygen. Nitrogen. Carbon Dioxid. Inspired air contains 20.81 79.15 .04 Expired air contains 16.03 79.58 4.38

That is, expired air contains about five per cent less oxygen and five per cent more carbon dioxid than inspired air.

The temperature of expired air is variable, but generally is higher than that of inspired air, it having been in contact with the warm air passages. It is also loaded with aqueous vapor, imparted to it like the heat, not in the depth of the lungs, but in the upper air passages.

Expired air contains, besides carbon dioxid, various impurities, many of an unknown nature, and all in small amounts. When the expired air is condensed in a cold receiver, the aqueous product is found to contain organic matter, which, from the presence of micro-organisms, introduced in the inspired air, is apt to putrefy rapidly. Some of these organic substances are probably poisonous, either so in themselves, as produced in some manner in the breathing apparatus, or poisonous as being the products of decomposition. For it is known that various animal substances give rise, by decomposition, to distinct poisonous products known as ptomaines. It is possible that some of the constituents of the expired air are of an allied nature. See under "Bacteria" (Chapter XIV).

At all events, these substances have an injurious action, for an atmosphere containing simply one per cent of pure carbon dioxid has very little hurtful effect on the animal economy, but an atmosphere in which the carbon dioxid has been raised one per cent by breathing is highly injurious.

The quantity of oxygen removed from the air by the breathing of an adult person at rest amounts daily to about 18 cubic feet. About the same amount of carbon dioxid is expelled, and this could be represented by a piece of pure charcoal weighing 9 ounces. The quantity of carbon dioxid, however, varies with the age, and is increased also by external cold and by exercise, and is affected by the kind of food. The amount of water, exhaled as vapor, varies from 6 to 20 ounces daily. The average daily quantity is about one-half a pint.

216. Modified Respiratory Movements. The respiratory column of air is often used in a mechanical way to expel bodies from the upper air passages. There are also, in order to secure special ends, a number of modified movements not distinctly respiratory. The following peculiar respiratory acts call for a few words of explanation.

A sigh is a rapid and generally audible expiration, due to the elastic recoil of the lungs and chest walls. It is often caused by depressing emotions. Yawning is a deep inspiration with a stretching of the muscles of the face and mouth, and is usually excited by fatigue or drowsiness, but often occurs from a sort of contagion.

Hiccough is a sudden jerking inspiration due to the spasmodic contraction of the diaphragm and of the glottis, causing the air to rush suddenly through the larynx, and produce this peculiar sound. Snoring is caused by vibration of the soft palate during sleep, and is habitual with some, although it occurs with many when the system is unusually exhausted and relaxed.

Laughing consists of a series of short, rapid, spasmodic expirations which cause the peculiar sounds, with characteristic movements of the facial muscles. Crying, caused by emotional states, consists of sudden jerky expirations with long inspirations, with facial movements indicative of distress. In sobbing, which often follows long-continued crying, there is a rapid series of convulsive inspirations, with sudden involuntary contractions of the diaphragm. Laughter, and sometimes sobbing, like yawning, may be the result of involuntary imitation.

Experiment 112. Simple Apparatus to Illustrate the Movements of the Lungs in the Chest.—T is a bottle from which the bottom has been removed; D, a flexible and elastic membrane tied on the bottle, and capable of being pulled out by the string S, so as to increase the capacity of the bottle. L is a thin elastic bag representing the lungs. It communicates with the external air by a glass tube fitted air-tight through a cork in the neck of the bottle. When D is drawn down, the pressure of the external air causes L to expand. When the string is let go, L contracts again, by virtue of its elasticity.



Coughing is produced by irritation in the upper part of the windpipe and larynx. A deep breath is drawn, the opening of the windpipe is closed, and immediately is burst open with a violent effort which sends a blast of air through the upper air passages. The object is to dislodge and expel any mucus or foreign matter that is irritating the air passages.

Sneezing is like coughing; the tongue is raised against the soft palate, so the air is forced through the nasal passages. It is caused by an irritation of the nostrils or eyes. In the beginning of a cold in the head, for instance, the cold air irritates the inflamed mucous membrane of the nose, and causes repeated attacks of sneezing.

217. How the Atmosphere is Made Impure. The air around us is constantly being made impure in a great variety of ways. The combustion of fuel, the respiration of men and animals, the exhalations from their bodies, the noxious gases and effluvia of the various industries, together with the changes of fermentation and decomposition to which all organized matter is liable,—all tend to pollute the atmosphere.

The necessity of external ventilation has been foreseen for us. The forces of nature,—the winds, sunlight, rain, and growing vegetation,—all of great power and universal distribution and application, restore the balance, and purify the air. As to the principal gases, the air of the city does not differ materially from that of rural sections. There is, however, a vastly greater quantity of dust and smoke in the air of towns. The breathing of this dust, to a greater or less extent laden with bacteria, fungi, and the germs of disease, is an ever-present and most potent menace to public and personal health. It is one of the main causes of the excess of mortality in towns and cities over that of country districts.

This is best shown in the overcrowded streets and houses of great cities, which are deprived of the purifying influence of sun and air. The fatal effect of living in vitiated air is especially marked in the mortality among infants and children living in the squalid and overcrowded sections of our great cities. The salutary effect of sunshine is shown by the fact that mortality is usually greater on the shady side of the street.

218. How the Air is Made Impure by Breathing. It is not the carbon dioxid alone that causes injurious results to health, it is more especially the organic matter thrown off in the expired air. The carbon dioxid which accompanies the organic matter is only the index. In testing the purity of air it is not difficult to ascertain the amount of carbon dioxid present, but it is no easy problem to measure the amount of organic matter. Hence it is the former that is looked for in factories, churches, schoolrooms, and when it is found to exceed .07 per cent it is known that there is a hurtful amount of organic matter present.

The air as expelled from the lungs contains, not only a certain amount of organic matter in the form of vapor, but minute solid particles of debris and bacterial micro-organisms (Chap. XIV). The air thus already vitiated, after it leaves the mouth, putrefies very rapidly. It is at once absorbed by clothing, curtains, carpets, porous walls, and by many other objects. It is difficult to dislodge these enemies of health even by free ventilation. The close and disagreeable odor of a filthy or overcrowded room is due to these organic exhalations from the lungs, the skin, and the unclean clothing of the occupants.

The necessity of having a proper supply of fresh air in enclosed places, and the need of removal of impure air are thus evident. If a man were shut up in a tightly sealed room containing 425 cubic feet of air, he would be found dead or nearly so at the end of twenty-four hours. Long before this time he would have suffered from nausea, headache, dizziness, and other proofs of blood-poisoning. These symptoms are often felt by those who are confined for an hour or more in a room where the atmosphere has been polluted by a crowd of people. The unpleasant effects rapidly disappear on breathing fresh air.

219. The Effect on the Health of Breathing Foul Air. People are often compelled to remain indoors for many hours, day after day, in shops, factories, or offices, breathing air perhaps only slightly vitiated, but still recognized as "stuffy." Such persons often suffer from ill health. The exact form of the disturbance of health depends much upon the hereditary proclivity and physical make-up of the individual. Loss of appetite, dull headache, fretfulness, persistent weariness, despondency, followed by a general weakness and an impoverished state of blood, often result.

Persons in this lowered state of health are much more prone to surfer from colds, catarrhs, bronchitis, and pneumonia than if they were living in the open air, or breathing only pure air. Thus, in the Crimean War, the soldiers who lived in tents in the coldest weather were far more free from colds and lung troubles than those who lived in tight and ill-ventilated huts. In the early fall when typhoid fever is prevalent, the grounds of large hospitals are dotted with canvas tents, in which patients suffering from this fever do much better than in the wards.

This tendency to inflammatory diseases of the air passages is aggravated by the overheated and overdried condition of the air in the room occupied. This may result from burning gas, from overheated furnaces and stoves, hot-water pipes, and other causes. Serious lung diseases, such as consumption, are more common among those who live in damp, overcrowded, or poorly ventilated homes.

220. The Danger from Pulmonary Infection. The germ of pulmonary consumption, known as the bacillus tuberculosis, is contained in the breath and the sputa from the lungs of its victims. It is not difficult to understand how these bacilli may be conveyed through the air from the lungs of the sick to those of apparently healthy people. Such persons may, however, be predisposed, either constitutionally or by defective hygienic surroundings, to fall victims to this dreaded disease. Overcrowding, poor ventilation, and dampness all tend to increase the risk of pulmonary infection.

It must not be supposed that the tubercle bacillus is necessarily transmitted directly through the air from the lungs of the sick to be implanted in the lungs of the healthy. The germs may remain for a time in the dust turn and debris of damp, filthy, and overcrowded houses. In this congenial soil they retain their vitality for a long time, and possibly may take on more virulent infective properties than they possessed when expelled from the diseased lungs.[37]



221. Ventilation. The question of a practicable and economical system of ventilation for our homes, schoolrooms, workshops, and public places presents many difficult and perplexing problems. It is perhaps due to the complex nature of the subject, that ventilation, as an ordinary condition of daily health, has been so much neglected. The matter is practically ignored in building ordinary houses. The continuous renewal of air receives little if any consideration, compared with the provision made to furnish our homes with heat, light, and water. When the windows are closed we usually depend for ventilation upon mere chance,—on the chimney, the fireplace, and the crevices of doors and windows. The proper ventilation of a house and its surroundings should form as prominent a consideration in the plans of builders and architects as do the grading of the land, the size of the rooms, and the cost of heating.

The object of ventilation is twofold: First, to provide for the removal of the impure air; second, for a supply of pure air. This must include a plan to provide fresh air in such a manner that there shall be no draughts or exposure of the occupants of the rooms to undue temperature. Hence, what at first might seem an easy thing to do, is, in fact, one of the most difficult of sanitary problems.

222. Conditions of Efficient Ventilation. To secure proper ventilation certain conditions must be observed. The pure air introduced should not be far below the temperature of the room, or if so, the entering current should be introduced towards the ceiling, that it may mix with the warm air.

Draughts must be avoided. If the circuit from entrance to exit is short, draughts are likely to be produced, and impure air has less chance of mixing by diffusion with the pure air. The current of air introduced should be constant, otherwise the balance may occasionally be in favor of vitiated air. If a mode of ventilation prove successful, it should not be interfered with by other means of entrance. Thus, an open door may prevent the incoming air from passing through its proper channels. It is desirable that the inlet be so arranged that it can be diminished in size or closed altogether. For instance, when the outer air is very cold, or the wind blows directly into the inlet, the amount of cold air entering it may lower the temperature of the room to an undesirable degree.

In brief, it is necessary to have a thorough mixing of pure and impure air, so that the combination at different parts of the room may be fairly uniform. To secure these results, the inlets and outlets should be arranged upon principles of ventilation generally accepted by authorities on public health. It seems hardly necessary to say that due attention must be paid to the source from which the introduced air is drawn. If it be taken from foul cellars, or from dirty streets, it may be as impure as that which it is designed to replace.



Animal Heat.

223. Animal or Vital Heat. If a thermometer, made for the purpose, be placed for five minutes in the armpit, or under the tongue, it will indicate a temperature of about 98-1/2 degrees F., whether the surrounding atmosphere be warm or cold. This is the natural heat of a healthy person, and in health it rarely varies more than a degree or two. But as the body is constantly losing heat by radiation and conduction, it is evident that if the standard temperature be maintained, a certain amount of heat must be generated within the body to make up for the loss externally. The heat thus produced is known as animal or vital heat.

This generation of heat is common to all living organisms. When the mass of the body is large, its heat is readily perceptible to the touch and by its effect upon the thermometer. In mammals and birds the heat-production is more active than in fishes and reptiles, and their temperatures differ in degree even in different species of the same class, according to the special organization of the animal and the general activity of its functions. The temperature of the frog may be 85 degrees F. in June and 41 degrees F. in January. The structure of its tissues is unaltered and their vitality unimpaired by such violent fluctuations. But in man it is necessary not only for health, but even for life, that the temperature should vary only within narrow limits around the mean of 98-1/2 degrees F.

We are ignorant of the precise significance of this constancy of temperature in warm-blooded animals, which is as important and peculiar as their average height, Man, undoubtedly, must possess a superior delicacy of organization, hardly revealed by structure, which makes it necessary that he should be shielded from the shocks and jars of varying temperature, that less highly endowed organisms endure with impunity.

224. Sources of Bodily Heat. The heat of the body is generated by the chemical changes, generally spoken of as those of oxidation, which are constantly going on in the tissues. Indeed, whenever protoplasmic materials are being oxidized (the process referred to in sec. 15 as katabolism) heat is being set free. These chemical changes are of various kinds, but the great source of heat is the katabolic process, known as oxidation.

The vital part of the tissues, built up from the complex classes of food, is oxidized by means of the oxygen carried by the arterial blood, and broken down into simpler bodies which at last result in urea, carbon dioxid, and water. Wherever there is life, this process of oxidation is going on, but more energetically in some tissues and organs than in others. In other words, the minutest tissue in the body is a source of heat in proportion to the activity of its chemical changes. The more active the changes, the greater is the heat produced, and the greater the amount of urea, carbon dioxid, and water eliminated. The waste caused by this oxidation must be made good by a due supply of food to be built up into protoplasmic material. For the production of heat, therefore, food is necessary. But the oxidation process is not as simple and direct as the statement of it might seem to indicate. Though complicated in its various stages, the ultimate result is as simple as in ordinary combustion outside of the body, and the products are the same.

The continual chemical changes, then, chiefly by oxidation of combustible materials in the tissues, produce an amount of heat which is efficient to maintain the temperature of the living body at about 98-1/2 degrees F. This process of oxidation provides not only for the heat of the body, but also for the energy required to carry on the muscular work of the animal organism.

225. Regulation of the Bodily Temperature. While bodily heat is being continually produced, it is also as continually being lost by the lungs, by the skin, and to some extent, by certain excretions. The blood, in its swiftly flowing current, carries warmth from the tissues where heat is being rapidly generated, to the tissues or organs in which it is being lost by radiation, conduction, or evaporation. Were there no arrangement by which heat could be distributed and regulated, the temperature of the body would be very unequal in different parts, and would vary at different times.

The normal temperature is maintained with slight variations throughout life. Indeed a change of more than a degree above or below the average, indicates some failure in the organism, or some unusual influence. It is evident, then, that the mechanisms which regulate the temperature of the body must be exceedingly sensitive.

The two chief means of regulating the temperature of the body are the lungs and the skin. As a means of lowering the temperature, the lungs and air passages are very inferior to the skin; although, by giving heat to the air we breathe, they stand next to the skin in importance. As a regulating power they are altogether subordinate to the skin.

Experiment 113. To show the natural temperature of the body. Borrow a physician's clinical thermometer, and take your own temperature, and that of several friends, by placing the instrument under the tongue, closing the mouth, and holding it there for five minutes. It should be thoroughly cleansed after each use.

226. The Skin as a Heat-regulator. The great regulator of the bodily temperature is, undoubtedly, the skin, which performs this function by means of a self-regulating apparatus with a more or less double action. First, the skin regulates the loss of heat by means of the vaso-motor mechanism. The more blood passes through the skin, the greater will be the loss of heat by conduction, radiation, and evaporation. Hence, any action of the vaso-motor mechanism which causes dilatation of the cutaneous capillaries, leads to a larger flow of blood through the skin, and will tend to cool the body. On the other hand, when by the same mechanism the cutaneous vessels are constricted, there will be a smaller flow of blood through the skin, which will serve to check the loss of heat from the body (secs. 195 and 270).

Again, the special nerves of perspiration act directly as regulators of temperature. They increase the loss of heat when they promote the secretion of the skin, and diminish the loss when they cease to promote it.

The practical working of this heat-regulating mechanism is well shown by exercise. The bodily temperature rarely rises so much as a degree during vigorous exercise. The respiration is increased, the cutaneous capillaries become dilated from the quickened circulation, and a larger amount of blood is circulating through the skin. Besides this, the skin perspires freely. A large amount of heat is thus lost to the body, sufficient to offset the addition caused by the muscular contractions.

It is owing to the wonderful elasticity of the sweat-secreting mechanism, and to the increase in respiratory activity, and the consequent increase in the amount of watery vapor given off by the lungs, that men are able to endure for days an atmosphere warmer than the blood, and even for a short time at a temperature above that of boiling water. The temperature of a Turkish bath may be as high as 150 degrees to 175 degrees F. But an atmospheric temperature may be considerably below this, and yet if long continued becomes dangerous to life. In August, 1896, for instance, hundreds of persons died in this country, within a few days, from the effects of the excessive heat.

A much higher temperature may be borne in dry air than in humid air, or that which is saturated with watery vapor. Thus, a shade temperature of 100 degrees F. in the dry air of a high plain may be quite tolerable, while a temperature of 80 degrees F. in the moisture-laden atmosphere of less elevated regions, is oppressive. The reason is that in dry air the sweat evaporates freely, and cools the skin. In saturated air at the bodily temperature there is little loss of heat by perspiration, or by evaporation from the bodily surface.

This topic is again discussed in the description of the skin as a regulator of the bodily temperature (sec. 241).

227. Voluntary Means of Regulating the Temperature. The voluntary factor, as a means of regulating the heat loss in man, is one of great importance. Clothing retards the loss of heat by keeping in contact with it a layer of still air, which is an exceedingly bad conductor. When a man feels too warm and throws off his coat, he removes one of the badly conducting layers of air, and increases the heat loss by radiation and conduction. The vapor next the skin is thus allowed a freer access to the surface, and the loss of heat by evaporation of the sweat becomes greater. This voluntary factor by which the equilibrium is maintained must be regarded as of great importance. This power also exists in the lower animals, but to a much smaller extent. Thus a dog, on a hot day, runs out his tongue and stretches his limbs so as to increase the surface from which heat is radiated and conducted.

The production, like the loss, of heat is to a certain extent under the control of the will. Work increases the production of heat, and rest, especially sleep, lessens it. Thus the inhabitants of very hot countries seek relief during the hottest part of the day by a siesta. The quantity and quality of food also influence the production of heat. A larger quantity of food is taken in winter than in summer. Among the inhabitants of the northern and Arctic regions, the daily consumption of food is far greater than in temperate and tropical climates.

228. Effect of Alcohol upon the Lungs. It is a well recognized fact that alcohol when taken into the stomach is carried from that organ to the liver, where, by the baneful directness of its presence, it produces a speedy and often disastrous effect. But the trail of its malign power does not disappear there. From the liver it passes to the right side of the heart, and thence to the lungs, where its influence is still for harm.

In the lungs, alcohol tends to check and diminish the breathing capacity of these organs. This effect follows from the partial paralyzing influence of the stupefying agent upon the sympathetic nervous system, diminishing its sensibility to the impulse of healthful respiration. This diminished capacity for respiration is clearly shown by the use of the spirometer, a simple instrument which accurately records the cubic measure of the lungs, and proves beyond denial the decrease of the lung space.

"Most familiar and most dangerous is the drinking man's inability to resist lung diseases."—Dr. Adoph Frick, the eminent German physiologist of Zurich.

"Alcohol, instead of preventing consumption, as was once believed, reduces the vitality so much as to render the system unusually susceptible to that fatal disease."—R. S. Tracy, M.D., Sanitary Inspector of the N. Y. City Health Dept.

"In thirty cases in which alcoholic phthisis was present a dense, fibroid, pigmented change was almost invariably present in some portion of the lung far more frequently than in other cases of phthisis."—Annual of Medical Sciences.

"There is no form of consumption so fatal as that from alcohol. Medicines affect the disease but little, the most judicious diet fails, and change of air accomplishes but slight real good.... In plain terms, there is no remedy whatever for alcoholic phthisis. It may be delayed in its course, but it is never stopped; and not infrequently, instead of being delayed, it runs on to a fatal termination more rapidly than is common in any other type of the disorder."—Dr. B. W. Richardson in Diseases of Modern Life.

229. Other Results of Intoxicants upon the Lungs. But a more potent injury to the lungs comes from another cause. The lungs are the arena where is carried on the ceaseless interchange of elements that is necessary to the processes of life. Here the dark venous blood, loaded with effete material, lays down its carbon burden and, with the brightening company of oxygen, begins again its circuit. But the enemy intrudes, and the use of alcohol tends to prevent this benign interchange.

The continued congestion of the lung tissue results in its becoming thickened and hardened, thus obstructing the absorption of oxygen, and the escape of carbon dioxid. Besides this, alcohol destroys the integrity of the red globules, causing them to shrink and harden, and impairing their power to receive oxygen. Thus the blood that leaves the lungs conveys an excess of the poisonous carbon dioxid, and a deficiency of the needful oxygen. This is plainly shown in the purplish countenance of the inebriate, crowded with enlarged veins. This discoloration of the face is in a measure reproduced upon the congested mucous membrane of the lungs. It is also proved beyond question by the decreased amount of carbon dioxid thrown off in the expired breath of any person who has used alcoholics.

The enfeebled respiration explains (though it is only one of the reasons) why inebriates cannot endure vigorous and prolonged exertion as can a healthy person. The hurried circulation produced by intoxicants involves in turn quickened respiration, which means more rapid exhaustion of the life forces. The use of intoxicants involves a repeated dilatation of the capillaries, which steadily diminishes their defensive power, rendering the person more liable to yield to the invasion of pulmonary diseases.[38]

230. Effect of Alcoholics upon Disease. A theory has prevailed, to a limited extent, that the use of intoxicants may act as a preventive of consumption. The records of medical science fail to show any proof whatever to support this impression. No error could be more serious or more misleading, for the truth is in precisely the opposite direction. Instead of preventing, alcohol tends to develop consumption. Many physicians of large experience record the existence of a distinctly recognized alcoholic consumption, attacking those constitutions broken down by dissipation. This form of consumption is steadily progressive, and always fatal.

The constitutional debility produced by the habit of using alcoholic beverages tends to render one a prompt victim to the more severe diseases, as pneumonia, and especially epidemical diseases, which sweep away vast numbers of victims every year.

231. Effect of Tobacco upon the Respiratory Passages. The effects of tobacco upon the throat and lungs are frequently very marked and persistent. The hot smoke must very naturally be an irritant, as the mouth and nostrils were not made as a chimney for heated and narcotic vapors. The smoke is an irritant, both by its temperature and from its destructive ingredients, the carbon soot and the ammonia which it conveys. It irritates and dries the mucous membrane of the mouth and throat, producing an unnatural thirst which becomes an enticement to the use of intoxicating liquors. The inflammation of the mouth and throat is apt to extend up the Eustachian tube, thus impairing the sense of hearing.

But even these are not all the bad effects of tobacco. The inhalation of the poisonous smoke produces unhealthful effects upon the delicate mucous membrane of the bronchial tubes and of the lungs. Upon the former the effect is to produce an irritating cough, with short breath and chronic bronchial catarrh. The pulmonary membrane is congested, taking cold becomes easy, and recovery from it tedious. Frequently the respiration is seriously disturbed, thus the blood is imperfectly aerated, and so in turn the nutrition of the entire system is impaired. The cigarette is the defiling medium through which these direful results frequently invade the system, and the easily moulded condition of youth yields readily to the destructive snare.

"The first effect of a cigar upon any one demonstrates that tobacco can poison by its smoke and through the lungs."—London Lancet.

"The action of the heart and lungs is impaired by the influence of the narcotic on the nervous system, but a morbid state of the larynx, trachea, and lungs results from the direct action of the smoke."—Dr. Laycock, Professor of Medicine in the University of Edinburgh.



Additional Experiments.

Experiment 114. To illustrate the arrangement of the lungs and the two pleurae. Place a large sponge which will represent the lungs in a thin paper bag which just fits it; this will represent the pulmonary layer of the pleura. Place the sponge and paper bag inside a second paper bag, which will represent the parietal layer of the pleura. Join the mouths of the two bags. The two surfaces of the bags which are now in contact will represent the two moistened surfaces of the pleurae, which rub together in breathing.

Experiment 115. To show how the lungs may be filled with air. Take one of the lungs saved from Experiment 110. Tie a glass tube six inches long into the larynx. Attach a piece of rubber to one end of the glass tube. Now inflate the lung several times, and let it collapse. When distended, examine every part of it.

Experiment 116. To take your own bodily temperature or that of a friend. If you cannot obtain the use of a physician's clinical thermometer, unfasten one of the little thermometers found on so many calendars and advertising sheets. Hold it for five minutes under the tongue with the lips closed. Read it while in position or the instant it is removed. The natural temperature of the mouth is about 98-1/2 degrees F.

Experiment 117. To show the vocal cords. Get a pig's windpipe in perfect order, from the butcher, to show the vocal cords. Once secured, it can be kept for an indefinite time in glycerine and water or dilute alcohol.

Experiment 118. To show that the air we expire is warm. Breathe on a thermometer for a few minutes. The mercury will rise rapidly.

Experiment 119. To show that expired air is moist. Breathe on a mirror, or a knife blade, or any polished metallic surface, and note the deposit of moisture.

Experiment 120. To show that the expired air contains carbon dioxid. Put a glass tube into a bottle of lime water and breathe through the tube. The A liquid will soon become cloudy, because the carbon dioxid of the expired air throws down the lime held in solution.

Experiment 121. "A substitute for a clinical thermometer may be readily contrived by taking an ordinary house thermometer from its tin case, and cutting off the lower part of the scale so that the bulb may project freely. With this instrument the pupils may take their own and each other's temperatures, and it will be found that whatever the season of the year or the temperature of the room, the thermometer in the mouth will record about 99 degrees F. Care must, of course, be taken to keep the thermometer in the mouth till it ceases to rise, and to read while it is still in position."—Professor H. P. Bowditch.

Experiment 122. To illustrate the manner in which the movements of inspiration cause the air to enter the lungs. Fit up an apparatus, as represented in Fig. 95, in which a stout glass tube is provided with a sound cork, B, and also an air-tight piston, D, resembling that of an ordinary syringe. A short tube, A, passing through the cork, has a small India-rubber bag, C, tied to it. Fit the cork in the tube while the piston is near the top. Now, by lowering the piston we increase the capacity of the cavity containing the bag. The pressure outside the bag is thus lowered, and air rushes into it through the tube, A, till a balance is restored. The bag is thus stretched. As soon as we let go the piston, the elasticity of the bag, being free to act, Movements of drives out the air just taken in, and the piston returns to its former place.



It will be noticed that in this experiment the elastic bag and its tube represent the lungs and trachea; and the glass vessel enclosing it, the thorax.

For additional experiments on the mechanics of respiration, see Chapter XV.



Chapter IX.

The Skin and the Kidneys.



232. The Elimination of Waste Products. We have traced the food from the alimentary canal into the blood. We have learned that various food materials, prepared by the digestive processes, are taken up by the branches of the portal vein, or by the lymphatics, and carried into the blood current. The nutritive material thus absorbed is conveyed by the blood plasma and the lymph to the various tissues to provide them with nourishment.

We have learned also that oxygen, taken up in the air cells of the lungs, is being continually carried to the tissues, and that the blood is purified by being deprived in the lungs of its excess of carbon dioxid. From this tissue activity, which is mainly oxidation, are formed certain waste products which, as we have seen, are absorbed by the capillaries and lymphatics and carried into the venous circulation.

In their passage through the blood and tissues, the albumens, sugars, starches, and fats are converted into carbon dioxid, water, and urea, or some closely allied body. Certain articles of food also contain small amounts of sulphur and phosphorus, which undergo oxidation into sulphates and phosphates. We speak, then, of carbon dioxid, salts, and water as waste products of the animal economy. These leave the body by one of the three main channels,—the lungs, the skin, or the kidneys.

The elimination of these products is brought about by a special apparatus called organs of excretion. The worn-out substances themselves are called excretions, as opposed to secretions, which are elaborated for use in the body. (See note, p. 121.) As already shown, the lungs are the main channels for the elimination of carbon dioxid, and of a portion of water as vapor. By the skin the body gets rid of a small portion of salts, a little carbon dioxid, and a large amount of water in the form of perspiration. From the kidneys are eliminated nearly all the urea and allied bodies, the main portion of the salts, and a large amount of water. In fact, practically all the nitrogenous waste leaves the body by the kidneys.



233. The Skin. The skin is an important and unique organ of the body. It is a blood-purifying organ as truly as are the lungs and the kidneys, while it also performs other and complex duties. It is not merely a protective covering for the surface of the body. This is indeed the most apparent, but in some respectes, the lest important, of its functions. This protective duty is necessary and efficient, as is proved by the familiar experience of the pain when a portion of the outer skin has been removed.

The skin, being richly supplied with nerves, is an important organ of sensibility and touch. In some parts it is closely attached to the structures beneath, while in others it is less firmly adherent and rests upon a variable amount of fatty tissue. It thus assists in relieving the abrupt projections and depressions of the general surface, and in giving roundness and symmetry to the entire body. The thickness of the skin varies in different parts of the body. Where exposed to pressure and friction, as on the soles of the feet and in the palms of the hands, it is much thickened.

The true skin is 1/12 to 1/8 of an inch in thickness, but in certain parts, as in the lips and ear passages, it is often not more than 1/100 of an inch thick. At the orifices of the body, as at the mouth, ears, and nose, the skin gradually passes into mucous membrane, the structure of the two being practically identical. As the skin is an outside covering, so is the mucous membrane a more delicate inside lining for all cavities into which the apertures open, as the alimentary canal and the lungs.



The skin ranks as an important organ of excretion, its product being sweat, excreted by the sweat glands. The amount of this excretion evaporated from the general surface is very considerable, and is modified as becomes necessary from the varied conditions of the temperature. The skin also plays an important part in regulating the bodily temperature(sec. 241).

234. The Cutis Vera, or True Skin. The skin is remarkably complex in its structure, and is divided into two distinct layers, which may be readily separated: the deeper layer,—the true skin, dermis, or corium; and the superficial layer, or outer skin,—the epidermis, cuticle, or scarf skin.

The true skin consists of elastic and white fibrous tissue, the bundles of which interlace in every direction. Throughout this feltwork structure which gradually passes into areolar tissue are numerous muscular fibers, as about the hair-follicles and the oil glands. When these tiny muscles contract from cold or by mental emotion, the follicles project upon the surface, producing what is called "goose flesh."

The true skin is richly supplied with blood-vessels and nerves, as when cut it bleeds freely, and is very sensitive. The surface of the true skin is thrown into a series of minute elevations called the papillae, upon which the outer skin is moulded. These abound in blood-vessels, lymphatics, and peculiar nerve-endings, which will be described in connection with the organ of touch (sec. 314). The papillae are large and numerous in sensitive places, as the palms of the hands, the soles of the feet, and the fingers. They are arranged in parallel curved lines, and form the elevated ridges seen on the surface of the outer skin (Fig. 103).

235. The Epidermis, or Cuticle. Above the true skin is the epidermis. It is semi-transparent, and under the microscope resembles the scales of a fish. It is this layer that is raised by a blister.

As the epidermis has neither blood-vessels, nerves, nor lymphatics, it may be cut without bleeding or pain. Its outer surface is marked with shallow grooves which correspond to the deep furrows between the papillae of the true skin. The inner surface is applied directly to the papillary layer of the true skin, and follows closely its inequalities. The outer skin is made up of several layers of cells, which next to the true skin are soft and active, but gradually become harder towards the surface, where they are flattened and scale-like. The upper scales are continually being rubbed off, and are replaced by deeper cells from beneath. There are new cells continually being produced in the deeper layer, which push upward the cells already existing, then gradually become dry, and are cast off as fine, white dust. Rubbing with a coarse towel after a hot bath removes countless numbers of these dead cells of the outer skin. During and after an attack of scarlet fever the patient "peels," that is, sheds an unusual amount of the seal; cells of the cuticle.

The deeper and more active layer of the epidermis, the mucosum, is made up of cells some of which contain minute granules of pigment, or coloring matter, that give color to the skin. The differences in the tint, as brunette, fair, and blond, are due mainly to the amount of coloring matter in these pigment cells. In the European this amount is generally small, while in other peoples the color cells may be brown, yellow, or even black. The pinkish tint of healthy skin, and the rosy-red after a bath are due, not to the pigment cells, but to the pressure of capillaries in the true skin, the color of the blood being seen through the semi-transparent outer skin.

]

Experiment 123. Of course the living skin can be examined only in a general way. Stretch and pull it, and notice that it is elastic. Note any liver spots, white scars, moles, warts, etc. Examine the outer skin carefully with a strong magnifying glass. Study the papillae on the palms. Scrape off with a sharp knife a few bits of the scarf skin, and examine them with the microscope.

236. The Hair. Hairs varying in size cover nearly the entire body, except a few portions, as the upper eyelids, the palms of the hands, and the soles of the feet.

The length and diameter of the hairs vary in different persons, especially in the long, soft hairs of the head and beard. The average number of hairs upon a square inch of the scalp is about 1000, and the number upon the entire head is estimated as about 120,000.

Healthy hair is quite elastic, and may be stretched from one-fifth to one-third more than its original length. An ordinary hair from the head will support a weight of six to seven ounces. The hair may become strongly electrified by friction, especially when brushed vigorously in cold, dry weather. Another peculiarity of the hair is that it readily absorbs moisture.

237. Structure of the Hair. The hair and the nails are structures connected with the skin, being modified forms of the epidermis. A hair is formed by a depression, or furrow, the inner walls of which consist of the infolded outer skin. This depression takes the form of a sac and is called the hair-follicle, in which the roots of the hair are embedded. At the bottom of the follicle there is an upward projection of the true skin, a papilla, which contains blood-vessels and nerves. It is covered with epidermic cells which multiply rapidly, thus accounting for the rapid growth of the hair. Around each papilla is a bulbous expansion, the hair bulb, from which the hair begins to grow.



The cells on the papillae are the means by which the hairs grow. As these are pushed upwards by new ones formed beneath, they are compressed, and the shape of the follicle determines their cylindrical growth, the shaft of the hair. So closely are these cells welded to form the cylinder, that even under a microscope the hair presents only a fibrous appearance, except in the center, where the cells are larger, forming the medulla, or pith (Fig. 106).

The medulla of the hair contains the pigment granules or coloring matter, which may be of any shade between a light yellow and an intense black. It is this that gives the great variety in color. Generally with old people the pigment is absent, the cells being occupied by air; hence the hair becomes gray or white. The thin, flat scales on the surface of the hair overlap like shingles. Connected with the hair-follicles are small bundles of muscular fibers, which run obliquely in the skin and which, on shortening, may cause the hairs to become more upright, and thus are made to "stand on end." The bristling back of an angry cat furnishes a familiar illustration of this muscular action.



Opening into each hair-follicle are usually one or more sebaceous, or oil, glands. These consist of groups of minute pouches lined with cells producing an oily material which serves to oil the hair and keep the skin moist and pliant.

238. The Nails. The nails are also formed of epidermis cells which have undergone compression, much like those forming the shaft of a hair. In other words, a nail is simply a thick layer of horny scales built from the outer part of the scarf skin. The nail lies upon very fine and closely set papillae, forming its matrix, or bed. It is covered at its base with a fold of the true skin, called its root, from beneath which it seems to grow.

The growth of the nail, like that of the hair and the outer skin, is effected by the production of new cells at the root and under surface. The growth of each hair is limited; in time it falls out and is replaced by a new one. But the nail is kept of proper size simply by the removal of its free edge.

239. The Sweat Glands. Deep in the substance of the true skin, or in the fatty tissue beneath it, are the sweat glands. Each gland consists of a single tube with a blind end, coiled in a sort of ball about 1/60 of an inch in diameter. From this coil the tube passes upwards through the dermis in a wavy course until it reaches the cuticle, which it penetrates with a number of spiral turns, at last opening on the surface. The tubes consist of delicate walls of membrane lined with cells. The coil of the gland is enveloped by minute blood-vessels. The cells of the glands are separated from the blood only by a fine partition, and draw from it whatever supplies they need for their special work.



With few exceptions every portion of the skin is provided with sweat glands, but they are not equally distributed over the body. They are fewest in the back and neck, where it is estimated they average 400 to the square inch. They are thickest in the palms of the hands, where they amount to nearly 3000 to each square inch. These minute openings occur in the ridges of the skin, and may be easily seen with a hand lens. The length of a tube when straightened is about 1/4 of an inch. The total number in the body is estimated at about 2,500,000, thus making the entire length of the tubes devoted to the secretion of sweat about 10 miles.

240. Nature and Properties of Sweat. The sweat is a turbid, saltish fluid with a feeble but characteristic odor due to certain volatile fatty acids. Urea is always present in small quantities, and its proportion may be largely increased when there is deficiency of elimination by the kidneys. Thus it is often observed that the sweat is more abundant when the kidneys are inactive, and the reverse is true. This explains the increased excretion of the kidneys in cold weather. Of the inorganic constituents of sweat, common salt is the largest and most important. Some carbon dioxid passes out through the skin, but not more than 1/50 as much as escapes by the lungs.

The sweat ordinarily passes off as vapor. If there is no obvious perspiration we must not infer that the skin is inactive, since sweat is continually passing from the surface, though often it may not be apparent. On an average from 1-1/2 to 4 pounds of sweat are eliminated daily from the skin in the form of vapor. This is double the amount excreted by the lungs, and averages about 1/67 of the weight of the body.

The visible sweat, or sensible perspiration, becomes abundant during active exercise, after copious drinking of cold water, on taking certain drugs, and when the body is exposed to excessive warmth. Forming more rapidly than it evaporates it collects in drops on the surface. The disagreeable sensations produced by humid weather result from the fact that the atmosphere is so loaded with vapor that the moisture of the skin is slowly removed by evaporation.

Experiment 124. Study the openings of the sweat glands with the aid of a strong magnifying glass. They are conveniently examined on the palms.

A man's weight may be considerably reduced within a short time by loss through the perspiration alone. This may explain to some extent the weakening effect of profuse perspiration, as from night sweats of consumption, convalescence from typhoid fever, or the artificial sweating from taking certain drugs.

241. The Skin as a Regulator of the Temperature of the Body. We thus learn that the skin covers and protects the more delicate structures beneath it; and that it also serves as an important organ of excretion. By means of the sweat the skin performs a third and a most important function, viz., that of regulating the temperature of the body.

The blood-vessels of the skin, like those of other parts of the body, are under the control of the nervous system, which regulates their diameter. If the nervous control be relaxed, the blood-vessels dilate, more blood flows through them, and more material is brought to the glands of the skin to be acted upon. External warmth relaxes the skin and its blood-vessels. There results an increased flow of blood to the skin, with increased perspiration. External cold, on the other hand, contracts the skin and its blood-vessels, producing a diminished supply of blood and a diminished amount of sweat.

Now, it is a law of physics that the change from liquid to vapor involves a loss of heat. A few drops of ether or of any volatile liquid placed on the skin, produce a marked sense of coldness, because the heat necessary to change the liquid into vapor has been drawn rapidly from the skin. This principle holds good for every particle of sweat that reaches the mouth of a sweat gland. As the sweat evaporates, it absorbs a certain amount of heat, and cools the body to that extent.

242. How the Action of the Skin may be Modified. After profuse sweating we feel chilly from the evaporation of a large amount of moisture, which rapidly cools the surface. When the weather is very warm the evaporation tends to prevent the bodily temperature from rising. On the other hand, if the weather be cold, much less sweat is produced, the loss of heat from the body is greatly lessened, and its temperature prevented from falling. Thus it is plain why medicine is given and other efforts are made to sweat the fever patient. The increased activity of the skin helps to reduce the bodily heat.

The sweat glands are under the control of certain nerve fibers originating in the spinal cord, and are not necessarily excited to action by an increased flow of blood through the skin. In other words, the sweat glands may be stimulated to increased action both by an increased flow of blood, and also by reflex action upon the vaso-dilator nerves of the parts. These two agencies, while working in harmony through the vaso-dilators, produce phenomena which are essentially independent of each other. Thus a strong emotion, like fear, may cause a profuse sweat to break out, with cold, pallid skin. During a fever the skin may be hot, and its vessels full of blood, and yet there may be no perspiration.



The skin may have important uses with which we are not yet acquainted. Death ensues when the heat of the body has been reduced to about 70 degrees F., and suppression of the action of the skin always produces a lowering of the temperature. Warm-blooded animals usually die when more than half of the general surface has been varnished. Superficial burns which involve a large part of the surface of the body, generally have a fatal result due to shock.

If the skin be covered with some air-tight substance like a coating of varnish, its functions are completely arrested. The bodily heat falls very rapidly. Symptoms of blood-poisoning arise, and death soon ensues. The reason is not clearly known, unless it be from the sudden retention of poisonous exhalations.

243. The Skin and the Kidneys. There is a close relationship between the skin and the kidneys, as both excrete organic and saline matter. In hot weather, or in conditions producing great activity of the skin, the amount of water excreted by the kidneys is diminished. This is shown in the case of firemen, stokers, bakers, and others who are exposed to great heat, and drink heavily and sweat profusely, but do not have a relative increase in the functions of the kidneys. In cool weather, when the skin is less active, a large amount of water is excreted by the kidneys, as is shown by the experience of those who drive a long distance in severe weather, or who have caught a sudden cold.



244. Absorbent Powers of the Skin. The skin serves to some extent as an organ for absorption. It is capable of absorbing certain substances to which it is freely exposed. Ointments rubbed in, are absorbed by the lymphatics in those parts where the skin is thin, as in the bend of the elbow or knee, and in the armpits. Physicians use medicated ointments in this way, when they wish to secure prompt and efficient results. Feeble infants often grow more vigorous by having their skin rubbed vigorously daily with olive oil.

A slight amount of water is absorbed in bathing. Sailors deprived of fresh water have been able to allay partially their intense thirst by soaking their clothing in salt water. The extent to which absorption occurs through the healthy skin is, however, quite limited. If the outer skin be removed from parts of the body, the exposed surface absorbs rapidly. Various substances may thus be absorbed, and rapidly passed into the blood. When the physician wishes remedies to act through the skin, he sometimes raises a small blister, and dusts over the surface some drug, a fine powder, like morphine.

The part played by the skin as an organ of touch will be considered in sections 314 and 315.

Experiment 125. To illustrate the sense of temperature. Ask the person to close his eyes. Use two test tubes, one filled with cold and the other with hot water, or two spoons, one hot and one cold. Apply each to different parts of the surface, and ask the person whether the touching body is hot or cold. Test roughly the sensibility of different parts of the body with cold and warm metallic-pointed rods.

Experiment 126. Touch fur, wood, and metal. The metal feels coldest, although all the objects are at the same temperature. Why?

Experiment 127. Plunge the hand into water at about 97 degrees F. One experiences a feeling of heat. Then plunge it into water at about 86 degrees F.; at first it feels cold, because heat is abstracted from the hand. Plunge the other hand direct into water at 86 degrees F. without previously placing it in water at 97 degrees F.,—it will feel pleasantly warm.

Experiment 128. To illustrate warm and cold spots. With a blunt metallic point, touch different parts of the skin. Certain points excite the sensation of warmth, others of cold, although the temperatures of the skin and of the instrument remain constant.

245. Necessity for Personal Cleanliness. It is evident that the skin, with its myriads of blood-vessels, nerves, and sweat and oil glands, is an exceedingly complicated and important structure. The surface is continually casting off perspiration, oily material, and dead scales. By friction and regular bathing we get rid of these waste materials. If this be not thoroughly done, the oily secretion holds the particles of waste substances to the surface of the body, while dust and dirt collect, and form a layer upon the skin. When we remember that this dirt consists of a great variety of dust particles, poisonous matters, and sometimes germs of disease, we may well be impressed with the necessity of personal cleanliness.

This layer of foreign matter on the skin is in several ways injurious to health. It clogs the pores and retards perspiration, thus checking the proper action of the skin as one of the chief means of getting rid of the waste matters of the body. Hence additional work is thrown upon other organs, chiefly the lungs and the kidneys, which already have enough to do. This extra work they can do for only a short time. Sooner or later they become disordered, and illness follows. Moreover, as this unwholesome layer is a fertile soil in which bacteria may develop, many skin diseases may result from this neglect. It is also highly probable that germs of disease thus adherent to the skin may then be absorbed into the system. Parasitic skin diseases are thus greatly favored by the presence of an unclean skin. It is also a fact that uncleanly people are more liable to take cold than those who bathe often.

The importance of cleanliness would thus seem too apparent to need special mention, were it not that the habit is so much neglected. The old and excellent definition that dirt is suitable matter, but in the wrong place, suggests that the place should be changed. This can be done only by regular habits of personal cleanliness, not only of the skin, the hair, the teeth, the nails, and the clothing, but also by the rigid observance of a proper system in daily living.

246. Baths and Bathing. In bathing we have two distinct objects in view,—to keep the skin clean and to impart vigor. These are closely related, for to remove from the body worn-out material, which tends to injure it, is a direct means of giving vigor to all the tissues. Thus a cold bath acts upon the nervous system, and calls out, in response to the temporary abstraction of heat, a freer play of the general vital powers. Bathing is so useful, both locally and constitutionally, that it should be practiced to such an extent as experience proves to be beneficial. For the general surface, the use of hot water once a week fulfills the demands of cleanliness, unless in special occupations. Whether we should bathe in hot or cold water depends upon circumstances. Most persons, especially the young and vigorous, soon become accustomed to cool, and even cold water baths, at all seasons of the year.

The hot bath should be taken at night before going to bed, as in the morning there is usually more risk of taking cold. The body is readily chilled, if exposed to cold when the blood-vessels of the skin have been relaxed by heat. Hot baths, besides their use for the purposes of cleanliness, have a sedative influence upon the nervous system, tending to allay restlessness and weariness. They are excellent after severe physical or mental work, and give a feeling of restful comfort like that of sleep.



Cold baths are less cleansing than hot, but serve as an excellent tonic and stimulant to the bodily functions. The best and most convenient time for a cold bath is in the morning, immediately after rising. To the healthy and vigorous, it is, if taken at this time, with proper precautions, a most agreeable and healthful luxury. The sensation of chilliness first felt is caused by the contraction of the skin and its blood-vessels, so that the blood is forced back, as it were, into the deeper parts of the body. This stimulates the nervous system, the breathing becomes quicker and deeper, the heart beats more vigorously, and, as a consequence, the warm blood is sent back to the skin with increased force. This is known as the stage of reaction, which is best increased by friction with a rough towel. This should produce the pleasant feeling of a warm glow all over the body.

A cold bath which is not followed by reaction is likely to do more harm than good. The lack of this reaction may be due to the water being too cold, the bath too prolonged, or to the bather being in a low condition of health. In brief, the ruddy glow which follows a cold bath is the main secret of its favorable influence.

The temperature of the water should be adapted to the age and strength of the bather. The young and robust can safely endure cold baths, that would be of no benefit but indeed an injury to those of greater age or of less vigorous conditions of health. After taking a bath the skin should be rapidly and vigorously rubbed dry with a rough towel, and the clothing at once put on.

247. Rules and Precautions in Bathing. Bathing in cold water should not be indulged in after severe exercise or great fatigue, whether we are heated or not. Serious results have ensued from cold baths when the body is in a state of exhaustion or of profuse perspiration. A daily cold bath when the body is comfortably warm, is a safe tonic for almost all persons during the summer months, and tends especially to restore the appetite. Cold baths, taken regularly, render persons who are susceptible to colds much less liable to them, and less likely to be disturbed by sudden changes of temperature. Persons suffering from heart disease or from chronic disease of an important organ should not indulge in frequent cold bathing except by medical advice. Owing to the relaxing nature of hot baths, persons with weak hearts or suffering from debility may faint while taking them.

Outdoor bathing should not be taken for at least an hour after a full meal, and except for the robust it is not prudent to bathe with the stomach empty, especially before breakfast. It is a wise rule, in outdoor or sea bathing, to come out of the water as soon as the glow of reaction is felt. It is often advisable not to apply cold water very freely to the head. Tepid or even hot water is preferable, especially by those subject to severe mental strain. But it is often a source of great relief during mental strain to bathe the face, neck, and chest freely at bedtime with cold water. It often proves efficient at night in calming the sleeplessness which results from mental labor.

Hot baths, if taken at bedtime, are often serviceable in preventing a threatened cold or cutting it short, the patient going immediately to bed, with extra clothing and hot drinks. The free perspiration induced helps to break up the cold.

Salt water acts more as a stimulant to the skin than fresh water. Salt-water bathing is refreshing and invigorating for those who are healthy, but the bather should come out of the water the moment there is the slightest feeling of chilliness. The practice of bathing in salt water more than once a day is unhealthful, and even dangerous. Only the strongest can sustain so severe a tax on their power of endurance. Sea bathing is beneficial in many ways for children, as their skin reacts well after it. In all cases, brisk rubbing with a rough towel should be had afterwards.



The golden rule of all bathing is that it must never be followed by a chill. If even a chilliness occur after bathing, it must immediately be broken up by some appropriate methods, as lively exercise, brisk friction, hot drinks, and the application of heat.

Swimming is a most valuable accomplishment, combining bathing and exercise. Bathing of the feet should never be neglected. Cleanliness of the hair is also another matter requiring strict attention, especially in children.

248. Care of the Hair and Nails. The hair brush should not be too stiff, as this increases the tendency towards scurfiness of the head. If, however, the hair is brushed too long or too hard, the scalp is greatly stimulated, and an increased production of scurf may result. If the head be washed too often with soap its natural secretion is checked, and the scalp becomes dry and scaly. The various hair pomades are as a rule undesirable and unnecessary.

The nails should be kept in proper condition, else they are not only unsightly, but may serve as carriers of germs of disease. The nails are often injured by too much interference, and should never be trimmed to the quick. The upper surfaces should on no account be scraped. The nail-brush is sufficient to cleanse them without impairing their smooth and polished surfaces.



249. Use of Clothing. The chief use of clothing, from a hygienic point of view, is to assist in keeping the body at a uniform temperature. It also serves for protection against injury, and for personal adornment. The heat of the body, as we have learned, is normally about 98-1/2 degrees F. This varies but slightly in health. A rise of temperature of more than one degree is a symptom of disturbance. The normal temperature does not vary with the season. In summer it is kept down by the perspiration and its rapid evaporation. In winter it is maintained by more active oxidation, by extra clothing, and by artificial heat.

The whole matter of clothing is modified to a great extent by climatic conditions and local environments,—topics which do not come within the scope of this book.

250. Material Used for Clothing. It is evident that if clothing is to do double duty in preventing the loss of heat by radiation, and in protecting us from the hot rays of the sun, some material must be used that will allow the passage of heat in either direction. The ideal clothing should be both a bad conductor and a radiator of heat. At the same time it must not interfere with the free evaporation of the perspiration, otherwise chills may result from the accumulation of moisture on the surface of the body.

Wool is a bad conductor, and should be worn next the skin, both in summer and winter, especially in variable climates. It prevents, better than any other material, the loss of heat from the body, and allows free ventilation and evaporation. Its fibers are so lightly woven that they make innumerable meshes enclosing air, which is one of the best of non-conductors.

Silk ranks next to wool in warmth and porosity. It is much softer and less irritating than flannel or merino, and is very useful for summer wear. The practical objection to its general use is the expense. Fur ranks with wool as a bad conductor of heat. It does not, however, like wool, allow of free evaporation. Its use in cold countries is universal, but in milder climates it is not much worn.

Cotton and linen are good conductors of heat, but are not absorbents of moisture, and should not be worn next the skin. They are, however, very durable and easily cleansed. As an intermediate clothing they may be worn at all seasons, especially over wool or silk. Waterproof clothing is also useful as a protection, but should not be worn a longer time than necessary, as it shuts in the perspiration, and causes a sense of great heat and discomfort.

The color of clothing is of some importance, especially if exposed directly to the sun's rays. The best reflectors, such as white and light gray clothing, absorb comparatively little heat and are the coolest, while black or dark-colored materials, being poor reflectors and good absorbents, become very warm.

251. Suggestions for the Use of Clothing. Prudence and good sense should guide us in the spring, in changing winter flannels or clothing for fabrics of lighter weight. With the fickle climate in most sections of this country, there are great risks of severe colds, pneumonia, and other pulmonary diseases from carelessness or neglect in this matter. A change from heavy to lighter clothing should be made first in the outer garments, the underclothing being changed very cautiously.

The two essentials of healthful clothing are cleanliness and dryness. To wear garments that are daily being soiled by perspiration and other cutaneous excretions, is a most uncleanly and unhealthful practice. Clothing, especially woolen underclothing, should be frequently changed. One of the objections to the use of this clothing is that it does not show soiling to the same extent as do cotton and linen.

Infectious and contagious diseases may be conveyed by the clothing. Hence, special care must be taken that all clothing in contact with sick people is burned or properly disinfected. Children especially are susceptible to scarlet fever, diphtheria, and measles, and the greatest care must be exercised to prevent their exposure to infection through the clothing.

We should never sleep in a damp bed, or between damp sheets. The vital powers are enfeebled during sleep, and there is always risk of pneumonia or rheumatism. The practice of sitting with wet feet and damp clothing is highly injurious to health. The surface of the body thus chilled may be small, yet there is a grave risk of serious, if not of fatal, disease. No harm may be done, even with clothing wet with water or damp with perspiration, so long as exercise is maintained, but the failure or inability to change into dry garments as soon as the body is at rest is fraught with danger.

Woolen comforters, scarfs, and fur mufflers, so commonly worn around the neck, are more likely to produce throat troubles and local chill than to have any useful effect. Harm ensues from the fact that the extra covering induces local perspiration, which enfeebles the natural defensive power of the parts; and when the warmer covering is removed, the perspiring surface is readily chilled. Those who never bundle their throats are least liable to suffer from throat ailments.

252. Ill Effects of Wearing Tightly Fitting Clothing. The injury to health caused by tight lacing, when carried to an extreme, is due to the compression and displacement of various organs by the pressure exerted on them. Thus the lungs and the heart may be compressed, causing short breath on exertion, palpitation of the heart, and other painful and dangerous symptoms. The stomach, the liver, and other abdominal organs are often displaced, causing dyspepsia and all its attendant evils. The improper use of corsets, especially by young women, is injurious, as they interfere with the proper development of the chest and abdominal organs. The use of tight elastics below the knee is often injurious. They obstruct the local venous circulation and are a fruitful source of cold feet and of enlarged or varicose veins.

Tightly fitting boots and shoes often cause corns, bunions, and ingrowing nails; on the other hand, if too loosely worn, they cause corns from friction. Boots too narrow in front crowd the toes together, make them overlap, and render walking difficult and painful. High-heeled boots throw the weight of the body forwards, so that the body rests too much on the toes instead of on the heels, as it should, thus placing an undue strain upon certain groups of muscles of the leg, in order to maintain the balance, while other groups are not sufficiently exercised. Locomotion is never easy and graceful, and a firm, even tread cannot be expected.

The compression of the scalp by a tight-fitting hat interferes with the local circulation, and may cause headaches, neuralgia, or baldness, the nutrition of the hair-follicles being diminished by the impaired circulation. The compression of the chest and abdomen by a tight belt and various binders interferes with the action of the diaphragm,—the most important muscle of respiration.

253. Miscellaneous Hints on the Use of Clothing. Children and old people are less able to resist the extreme changes of temperature than are adults of an average age. Special care should be taken to provide children with woolen underclothing, and to keep them warm and in well-ventilated rooms. Neither the chest nor limbs of young children should be unduly exposed, as is often done, to the cold blasts of winter or the fickle weather of early spring. Very young children should not be taken out in extremely cold weather, unless quite warmly clad and able to run about. The absurd notion is often entertained that children should be hardened by exposure to the cold. Judicious "hardening" means ample exposure of well-fed and well-clothed children. Exposure of children not thus cared for is simple cruelty. The many sicknesses of children, especially diseases of the throat and lungs, may often be traced directly to gross carelessness, ignorance, or neglect with reference to undue exposure. The delicate feet of children should not be injured by wearing ill-fitting or clumsy boots or shoes. Many deformities of the feet, which cause much vexation and trouble in after years, are acquired in early life.

No one should sleep in any of the clothes worn during the day, not even in the same underclothing. All bed clothing should be properly aired, by free exposure to the light and air every morning. Never wear wet or damp clothing one moment longer than necessary. After it is removed rub the body thoroughly, put on at once dry, warm clothing, and then exercise vigorously for a few minutes, until a genial glow is felt. Neglect of these precautions often results in rheumatism, neuralgia, and diseases of the chest, especially among delicate people and young women.

Pupils should not be allowed to sit in the schoolroom with any outer garments on. A person who has become heated in a warm room should not expose himself to cold without extra clothing. We must not be in a hurry to put on heavy clothes for winter, but having once worn them, they must not be left off until milder weather renders the change safe. The cheaper articles of clothing are often dyed with lead or arsenic. Hence such garments, like stockings and colored underclothing, worn next the skin have been known to produce severe symptoms of poisoning. As a precaution, all such articles should be carefully washed and thoroughly rinsed before they are worn.



The Kidneys.

254. The Kidneys. The kidneys are two important organs in the abdomen, one on each side of the spine. They are of a reddish-brown color, and are enveloped by a transparent capsule made up of a fold of the peritoneum. Embedded in fat, the kidneys lie between the upper lumbar vertebrae, and the crest of the hip bone. The liver is above the right kidney, and the spleen above the left, while both lie close against the rear wall of the abdomen, with the intestines in front of them. The human kidneys, though somewhat larger, are exactly of the same shape, color, and general appearance as those of the sheep, so commonly seen in the markets.

The kidneys are about four inches long, two inches across, one inch thick, and weigh from 41/2 to 51/2 ounces each. The hollow or concave side of the kidneys is turned inwards, and the deep fissure of this side, known as the hilus, widens out to form the pelvis. Through the hilus the renal artery passes into each kidney, and from each hilus passes outwards the renal vein, a branch of the inferior vena cava.

A tube, called the ureter, passes out from the concave border of each kidney, turns downwards, and enters the bladder in the basin of the pelvis. This tube is from 12 to 14 inches long, about as large as a goose quill, and conveys the secretion of the kidneys to the bladder.

255. Structure of the Kidneys. The pelvis is surrounded by reddish cones, about twelve in number, projecting into it, called the pyramids of Malpighi. The apices of these cones, known as the papillae, are crowded with minute openings, the mouths of the uriniferous tubules, which form the substance of the kidney. These lie parallel in the medullary or central structure, but On reaching the cortical or outer layer, they wind about and interlace, ending, at last, in dilated closed sacs called Malpighian capsules.



256. Function of the Kidneys. The Malpighian capsules are really the beginning of the tubules, for here the work of excretion begins. The thin wall of the capillaries within each capsule separates the blood from the cavity of the tubule. The blood-pressure on the delicate capillary walls causes the exudation of the watery portions of the blood through the cell walls into the capsule. The epithelial cell membrane allows the water of the blood with certain salts in solution to pass, but rejects the albumen. From the capsules, the excretion passes through the tubules into the pelvis, and on through the ureters to the bladder. But the delicate epithelial walls of the tubules through which it passes permit the inflow of urea and other waste products from the surrounding capillaries. By this twofold process are separated from the blood the fluid portions of the renal secretion with soluble salts, and the urea with other waste material.

257. How the Action of the Kidneys may be Modified. The action of the kidneys is subject to very marked and sudden modifications, especially those operating through the nervous system. Thus whatever raises the blood-pressure in the capillaries of the capsules, will increase the quantity of fluid filtering through them. That is, the watery portion of the secretion will be increased without necessarily adding to its solids. So anything which lowers the blood-pressure will diminish the watery portion of the secretion, that is, the secretion will be scanty, but concentrated.

The Renal Secretion.—The function of the kidneys is to secrete a fluid commonly known as the urine. The average quantity passed in 24 hours by an adult varies from 40 to 60 fluid ounces. Normal urine consists of about 96 per cent of water and 4 per cent of solids. The latter consist chiefly of certain nitrogenous substances known as urea and uric acid, a considerable quantity of mineral salts, and some coloring matter. Urea, the most important and most abundant constituent of urine, contains the four elements, but nitrogen forms one-half its weight. While, therefore, the lungs expel carbon dioxid chiefly, the kidneys expel nitrogen. Both of these substances express the result of oxidations going on in the body. The urea and uric acids represent the final result of the breaking down in the body of nitrogenous substances, of which albumen is the type.

Unusual constituents of the urine are albumen, sugar, and bile. When albumen is present in urine, it often indicates some disease of the kidneys, to which the term albuminuria or Bright's Disease is applied. The presence of grape sugar or glucose indicates the disease known as diabetes. Bile is another unusual constituent of the urine, appearing in jaundice.

The bladder is situated in the pelvic cavity or in the lowest part of the abdomen. When full, the bladder is pear-shaped; when empty, it is collapsed and lies low in the pelvis. The functions of the bladder are to collect and retain the urine, which has reached it drop by drop from the kidneys through the ureters, until a certain quantity accumulates, and then to expel it from the body.



A, 12th dorsal vertebra; B, diaphragm; C, receptaculum chyli; D, small intestines ]

In the kidneys, as elsewhere, the vaso-motor nerves are distributed to the walls of the blood-vessels, and modify the quantity and the pressure of blood in these organs. Thus, some strong emotion, like fear or undue anxiety, increases the blood-pressure, drives more blood to the kidneys, and causes a larger flow of watery secretion. When the atmosphere is hot, there is a relaxation of the vessels of the skin, with a more than ordinary flow of blood, which is thus withdrawn from the deeper organs. The blood-pressure in the kidneys is not only diminished, but the total quantity passing through them in a given time is much lessened. As a result, the secretion of the kidneys is scanty, but it contains an unusual percentage of solids.

When the atmosphere is cold, the reverse is true. The cutaneous vessels contract, the blood is driven to the deeper organs with increased pressure, and there is a less amount of sweat, but an increased renal secretion, containing a smaller proportion of solids. Certain drugs have the power of increasing or diminishing the renal secretion. As the waste matters eliminated by the kidneys are being constantly produced in the tissues, the action of the renal organs is continuous, in marked contrast with the intermittent flow of most of the secretions proper, as distinguished from the excretions.

258. Effects of Alcoholic Drinks upon the Kidneys. The kidneys differ from some of the other organs in this: those can rest a while without any harm to themselves, or to the body. We can keep the eyes closed for a few days, if necessary, without injury, and in fact often with benefit; or, we can abstain from food for some days, if need be, and let the stomach rest. But the kidneys cannot, with safety, cease their work. Their duty in ridding the blood of waste products, and of any foreign or poisonous material introduced, must be done not only faithfully, but continually, or the whole body at once suffers from the evil effects of the retained waste matters.

This vital fact is the key to the injurious results developed in the kidneys by the use of alcoholic drinks. These two organs have large blood-vessels conveying full amounts of blood to and from their structures, and they feel very quickly the presence of alcohol. Alcoholic liquors excite and irritate the delicate renal membranes, and speedily disturb and eventually destroy their capacity to excrete the proper materials from the blood.