1.Difference between the two sets of capillaries? Change effected by respiration or breathing?1. The Object of Respiration.—In one set of capillaries, or hair-like vessels, the blood is impoverished for the support of the different members and organs of the body. In another capillary system the blood is refreshed and again made fit to sustain life. The former belongs to the greater orsystemiccirculation; the latter to the lesser orpulmonary, so called frompulmo, the lungs, in which organs it is situated. The blood, as sent from the right side of the heart to the lungs, is venous, dark, impure, and of a nature unfit to circulate again through the tissues. But, when the blood returns from the lungs to the left side of the heart, it has become arterial, bright, pure, and no longer hurtful to the tissues. This marvellous purifying change is effected by means of the very familiar act of respiration, or breathing.2.What are the lungs? How many lungs are there? Lung-substance? Its properties? The pleura?2. The Lungs.—The lungs are the special organs of respiration. There are two of them, one on each side of the chest, which cavity they, with the heart, almost wholly occupy. The lung-substance is soft, elastic, and sponge-like. Under pressure of the finger, itcrepitates, or crackles, and floats when thrown into water; these properties beingdue to the presence of air in the minute air-cells of the lungs. To facilitate the movements necessary to these organs, each of them is provided with a double covering of an exceedingly smooth and delicate membrane, called thepleura. One layer of the pleura is attached to the walls of the chest, and the other to the lungs; and they glide, one upon the other, with utmost freedom. Like the membrane which envelops the heart, the pleura secretes its own lubricating fluid, in quantities sufficient to keep it always moist.Fig. 34.--Organs of the Chest.Fig. 34.—Organs of the Chest.A, Lungs. B, Heart. D, Pulmonary Artery. E, Trachea.Fig. 36.--Diagram and Section of the Air-cells.Fig. 36.—Diagram and Section of the Air-cells.Fig. 35.--Larynx, Trachea, and Bronchial Tubes.Fig. 35.—Larynx, Trachea, and Bronchial Tubes.3.Communication of the lungs with the external air? Bronchial tubes?3. The Air-Passages.—The lungs communicate with the external air by means of certain air-tubes, the longest of which, thetrachea, or windpipe, runs along the front of the neck (Fig. 34, E, and 35). Within the chest this tube divides into two branches, one entering each lung; these in turn give rise to numerous branches, or bronchial tubes, as they are called, which gradually diminish in size until they are about one-twenty-fifth of an inch in diameter. Each of these terminates in a cluster of little pouches, or "air-cells," having very thin walls, and covered with a capillary network, the most intricate in the body (Fig. 36).4.Office of the bronchial tubes? What further can you state of them?4.These tubes are somewhat flexible, sufficiently so to bend when the parts move in which they are situated; but they are greatly strengthened by bands or rings of cartilage which keep the passages always open; otherwise there would be a constantly-recurring tendency to collapse after every breath. The lung-substance essentially consists of these bronchial tubes and terminal air-cells, with the blood-vessels ramifying about them (Fig. 37). At the top of the trachea is the larynx, a sort ofbox of cartilage, across which are stretched the vocal cords. Here the voice is produced chiefly by the passage of the respired air over these cords, causing them to vibrate.Fig. 37.--Section of the Lungs.Fig. 37.—Section of the Lungs.5.The epiglottis? When it does not close in time, what is the consequence?5.Over the opening of the larynx is found theepiglottis, which fits like the lid of a box at the entrance to the lungs, and closes during the act of swallowing, so that food and drink shall pass backward to the œsophagus, or gullet (Fig. 38). Occasionally it does not close in time, and some substance intrudes within the larynx, when we at once discover, by a choking sensation, that "something has gone the wrong way," and, by coughing, we attempt to expel the unwelcome intruder. The epiglottis is one of the many safeguards furnished by nature for our security andcomfort, and is planned and put in place long before these organs are brought into actual use in breathing and in taking food.Fig. 38.--Section of Mouth and Throat.Fig. 38.—Section of Mouth and Throat.A, The Tongue. B, The Uvula C, Vocal Cord. E, Epiglottis. L, Larynx. N, Trachea. O, Œsophagus.6.Lining of the air-passages? Ciliated cells? Their uses? The three diseases of the lungs?Fig. 39.--Ciliated Cells.Fig. 39.—Ciliated Cells.6.The air-passages are lined through nearly their whole extent with mucous membrane, which maintains these parts in a constantly moist condition. This membrane has a peculiar kind of cells upon its outer surface. If examined under a powerful microscope, we may see, even for a considerable time after their removal from the body, that these cells have minute hair-like processes in motion, which wave like a field of grain under the influence of a breeze (Fig. 39). This is a truly beautiful sight; and since it is found that these littlecilia, as they are called, always produce currents in one direction, from within outward, it is probable that they serve a useful purpose in catching and carrying away from the lungs dust and other small particles drawn in with the breath (Fig. 39). The three diseases which more commonly affect the lungs, as the result of exposure, are pneumonia, or inflammation of the lungs, implicating principally the air-cells; bronchitis, an inflammation of the large bronchial tubes; and pleurisy, an inflammation of the investing membrane of the lungs, or pleura. Among the young, an affection of the trachea takes place, known as croup.7.The act of breathing? Extension of the chest by breathing?7. The Movements of Respiration.—The act of breathing has two parts—(1),inspiration, or drawing air into the lungs, and (2),expiration, or expelling it from the lungs again. In inspiration, the chest extends in its length, breadth, and height, or width. We can prove that this is the case as regards the two latter, by observing the effect of a deep breath. The ribs are elevated by means of numerous muscles, some of which occupy the entire spaces between those bones. But the increase in length, or vertically, is not so apparent, as it is caused by a muscle within the body called thediaphragm, it being the thin partition which separates the chest from the abdomen, rising like a dome within the chest. (Fig. 16).8.Contraction of the diaphragm? Power of the diaphragm? Effects of extending the walls of the chest? The habit of taking frequent and deep inspirations?8.With every inspiration, the diaphragm contracts, and in so doing, approaches more nearly a plane, or horizontal, surface, and thus enlarges the capacity of the chest. Laughing, sobbing, hiccoughing, and sneezing are caused by the spasmodic or sudden contraction of the diaphragm. The special power of this muscle is important in securing endurance, or "long wind," as it is commonly expressed; which may be obtained mainly by practice. It is possessed in a marked degree by the mountaineer, the oarsman, and the trained singer. As the walls of the chest extend, the lungs expand, and the air rushes in to fill them. This constitutes an inspiration. The habit of taking frequent and deep inspirations, in the erect position, with the shoulders thrown back, tends greatly to increase the capacity and power of the organs of respiration.9.Expiration? The mechanism of expiration?9. Expirationis a less powerful act than inspiration. The diaphragm relaxes its contraction, and ascends in the form of a dome; the ribs descend and contract the chest; while the lungs themselves, being elastic, assist to drive out the air. The latter passes out through the same channels by which it entered. At the end of each expiration there is a pause, or period of repose, lasting about as long as the period of action.10.Frequency of respiration? Effect of hurried action of the heart?10. Frequency of Respiration.—It is usually estimated that we breathe once during every four beats of the heart, or about eighteen times in a minute. There is, of course, a close relation between the heart and lungs, and whatever modifies the pulse, in like manner affects the breathing. When the action of the heart is hurried, a larger amount of blood is sent to the lungs, and, as the consequence, they must act more rapidly. Occasionally, the heart beats so very forcibly that the lungs cannot keep pace with it, and then we experience a peculiar sense ofdistress from the want of air. This takes place when we run until we are "out of breath." At the end of every fifth or sixth breath, the inspiration is generally longer than usual, the effect being to change more completely the air of the lungs.11.Respiration controlled by the will? Advantage of the knowledge to us?11.Although, as a general rule, the work of respiration goes on unconsciously and without exertion on our part, it is nevertheless under the control of the will. We can increase or diminish the frequency of its acts at pleasure, and we can "hold the breath," or arrest it altogether for a short time. From twenty to thirty seconds is ordinarily the longest period in which the breath can be held; but if we first expel all the impure air from the lungs, by taking several very deep inspirations, the time may be extended to one and a half or even two minutes. This should be remembered, and acted upon, before passing through a burning building, or any place where the air is very foul. The arrest of the respiration may be still further prolonged by training and habit; thus it is said, the pearl-fishers of India can remain three or four minutes under water without being compelled to breathe.12.Capacity of the lungs? Time required to renovate the air in the lungs? In tranquil respiration? Importance of the provision?12. Capacity of the Lungs.—The lungs are not filled and emptied by each respiration. For while their full capacity, in the adult, is three hundred and twenty cubic inches, or more than a gallon, the ordinary breathing air is only one-sixteenth part of that volume, or twenty cubic inches, being two-thirds of a pint. Accordingly, a complete renovation, or rotation, of the air of the lungs does not take place more frequently than about once in a minute; and by the gradual introduction of the external air, its temperature is considerably elevated before it reaches the delicate pulmonary capillaries. In tranquil respiration, less than two-thirds of the breathing power iscalled into exercise, leaving a reserve capacity of about one hundred and twenty cubic inches, equivalent to three and one half pints. This provision is indispensable to the continuation of life; otherwise, a slight embarrassment of respiration, by an ordinary cold, for instance, would suffice to cut off the necessary air, and the spark of life would be speedily extinguished.13.The atmosphere? How high or deep? How essential to life? Marine life in perfectly pure water and air?13. The Air we breathe.—The earth is enveloped on all sides by an invisible fluid, called the atmosphere. It forms a vast and shoreless ocean of air, forty-five miles deep, encircling and pervading all objects on the earth's surface, which is absolutely essential for the preservation of all vegetable and animal life,—in the sea, as well as on the land and in the air. At the bottom, or in the lower strata of this aerial ocean, we move and have our being. Perfectly pure water will not support marine life, for a fish may be drowned in water from which the air has been exhausted, just as certainly as a mouse, or any other land animal, will perish if put deeply into the water for a length of time. The cause is the same in both cases: the animal is deprived of the requisite amount of air. It is also stated, that if the water-supply of the plant be deprived of air, its vital processes are at once checked.14.Composition of the air? Properties of the two gases?14.The air is not a simple element, as the ancients supposed, but is formed by the mingling of two gases, known to the chemist as oxygen and nitrogen, in the proportion of one part of the former to four parts of the latter. These gases are very unlike, being almost opposite in their properties: nitrogen is weak, inert, and cannot support life; while oxygen is powerful, and incessantly active; and is the essential element which gives to the atmosphere its power to support life and combustion. The discovery of this fact was made by the French chemist, Lavoisier, in 1778.15.Air once breathed? An animal in it? A candle? Analysis of expired air? Change in volume?15. Changes in the Air from Respiration.—Air that has been once breathed is no longer fit for respiration. An animal confined within it will sooner or later die; so too, a lighted candle placed in it will be at once extinguished. If we collect a quantity of expired air and analyze it, we shall find that its composition is not the same as that of the inspired air. When the air entered the lungs it was rich in oxygen; now it contains twenty-five per cent. less of that gas. Its volume, however, remains nearly the same; its loss being replaced by another and very different gas, which the lungs exhaled, calledcarbonic acid, or, as the chemist terms it,carbon dioxide.16.What else has the expired air gained? When and where noticed?16.The expired air has also gained moisture. This is noticed when we breathe upon a mirror, or the window-pane, the surface being tarnished by the condensation of the watery vapor exhaled by the lungs. In cold weather, this causes the fine cloud which is seen issuing from the nostrils or mouth with each expiration, and contributes in forming the feathery crystals of ice which decorate our window-panes on a winter's morning.17.Nature of the watery vapor? Its effects upon animals?17.This watery vapor contains a variable quantity of animal matter, the exact nature of which is unknown; but when collected it speedily putrefies and becomes highly offensive. From the effects, upon small animals, of confinement in their own exhalations, having at the same time an abundant supply of fresh air, it is believed that the organic matters thrown off by the lungs and skin are direct and active poisons; and that to such emanations from the body, more than to any other cause, are due the depressing and even fatal results which follow the crowding of large numbers of persons into places of limited capacity.18.Give some of the instances furnished by history.18.History furnishes many painful instances of the ill effects of overcrowding. In 1756, of one hundred and forty-six Englishmen imprisoned in the Black Hole of Calcutta, only twenty-three, at the end of eight hours, survived. After the battle of Austerlitz, three hundred prisoners were crowded into a cavern, where, in a few hours, two-thirds of their number died. On board a steam-ship, during a stormy night, one hundred and fifty passengers were confined in a small cabin, but when morning came, only eighty remained alive.19.Change in the blood from blue to red. Upon what does the change depend? How shown?19. Changes in the Blood from Respiration.—The most striking change which the blood undergoes by its passage through the lungs, is the change of color from a dark blue to bright red. That this change is dependent upon respiration has been fully proved by experiment. If the trachea, or windpipe, of a living animal be so compressed as to exclude the air from the lungs, the blood in the arteries will gradually grow darker, until its color is the same as that of the venous blood. When the pressure is removed the blood speedily resumes its bright hue. Again, if the animal be made to breathe an atmosphere containing more oxygen than atmospheric air, the color changes from scarlet to vermilion, and becomes even brighter than arterial blood. This change of color is not of itself a very important matter, but it indicates a most important change of composition.20.What does the air lose and gain by respiration? What, the blood? Air as food?20.The air, as we have seen, by respiration loses oxygen and gains carbonic acid: the blood, on the contrary, gains oxygen and loses carbonic acid. The oxygen is the food of the blood corpuscles; while the articles we eat and drink belong more particularly to the plasma of the blood. The air, then, it is plain, is a sort of food, and we shouldundoubtedly so regard it, if it were not for the fact that we require it constantly, instead of taking it at stated intervals, as is the case with our articles of diet. Again, as the demand of the system for food is expressed by the sensation of hunger, so the demand for air is marked by a painful sensation called suffocation.21.Moist animal membranes? How shown with the bladder?21. Interchange of Gases in the Lungs.—As the air and the blood are not in contact, they being separated from each other by the walls of the air-cells and of the blood-vessels, how can the two gases, oxygen and carbonic acid, exchange places? Moist animal membranes have a property which enables them to transmit gases through their substance, although they are impervious to liquids. This may be beautifully shown by suspending a bladder containing dark blood in a jar of oxygen. At the end of a few hours the oxygen will have disappeared, the blood will be brighter in color, and carbonic acid will be found in the jar.22.Gaseous diffusion? If oxygen be not received? If carbonic acid be retained?22.If this interchange takes place outside of the body, how much more perfectly must it take place within, where it is favored by many additional circumstances! The walls of the vessels and the air-cells offer no obstacle to this process, which is known as gaseous diffusion. Both parts of the process are alike of vital importance. If oxygen be not received, the organs cease to act; and if carbonic acid be retained in the blood, its action is that of a poison; unconsciousness, convulsions, and death following.23.Difference in the appearance and composition of the blood? Temperature of the blood? The blood while passing through the lungs? The consequence?23. Difference between Arterial and Venous Blood.—The following table presents the essential points of difference in the appearance and composition of the blood, before and after its passage through the lungs:—Venous Blood.Arterial Blood.Color,Dark blue,Scarlet.Oxygen,8 per cent.,18 per cent.Carbonic Acid,15 to 20 per cent.,6 per cent., or less.Water,More,Less.The temperature of the blood varies considerably; but the arterial stream is generally warmer than the venous. The blood imparts heat to the air while passing through the lungs, and consequently the contents of the right side of the heart has a higher temperature than the contents on the left side.24.What do we learn by means of the spectroscope? "Carriers of oxygen?" Blue blood in the system?24.By means of the spectroscope, we learn that the change of color in the blood has its seat in the corpuscles; and that, according as they retain oxygen, or release it, they present the spectrum of arterial or venous blood. There evidently exists, on the part of these little bodies, an affinity for this gas, and hence they have been called "carriers of oxygen." It was long ago thought that blue blood was a trait peculiar to persons of princely and royal descent, and boastful allusions to the "sang azure" of kings and nobles are quite often met with. Physiology, however, informs us that blue blood flows in the veins of the low as well as the high, and that so far from its presence indicating a mark of purity, it, in reality, represents the waste and decay of the system.25.The amount of air that passes in and out of the lungs?25. Amount of Respiratory Labor.—During ordinary calm respiration, we breathe eighteen times in a minute; and twenty cubic inches of air pass in and out of the lungs with every breath. This is equivalent to the use of three hundred and sixty cubic inches, or more than ten pints of air each minute. From this we calculate that the quantity of air which hourly traverses the lungs is about thirteen cubic feet, or seventy-eight gallons; and daily, notless than three hundred cubic feet, an amount nearly equal to the contents of sixty barrels.26.Air absorbed in its transit through the lungs? The loss? Carbonic acid exhaled? Effect of excitement or exertion? What estimate?26.Of this large volume of air five per cent. is absorbed in its transit through the lungs. The loss thus sustained is almost wholly of oxygen, and amounts to fifteen cubic feet daily. The quantity of carbonic acid exhaled by the lungs during the day is somewhat less, being twelve cubic feet. Under the influence of excitement or exertion, the breathing becomes more frequent and more profound; and then the internal respiratory work increases proportionately, and may even be double that of the above estimate. It has been estimated that in drawing a full breath, a man exerts a muscular force equal to raising two hundred pounds placed upon the chest.27.Importance of the oxygen in the atmosphere? Injurious character of gases?27. Impurities of the Air.—The oxygen in the atmosphere is of such prime importance, and its proportion is so nicely adjusted to the wants of man, that any gas or volatile substance which supplants it must be regarded as a hurtful impurity. All gases, however, are not alike injurious. Some, if inhaled, are necessarily fatal;arsenuretted hydrogenbeing one of these, a single bubble of which destroyed the life of its discoverer, Gehlen. Others are not directly dangerous, but by taking the place of oxygen, and excluding it from the lungs, they become so. Into this latter class we place carbonic acid.28.Pungency of gases? The inference? Our safeguard?28.Most of the actively poisonous gases have a pungent or offensive odor; and, as may be inferred, most repugnant odors indicate the presence of substances unfit for respiration. Accordingly, as we cannot see or taste these impurities, the sense of smell is our principal safeguard against them; and we recognize the design which has planted this sense, like a sentinel at the proper entrance of theair-passages, the nostrils, to give us warning of approaching harm. Take, as an example, the ordinary illuminating gas of cities, from which so many accidents happen. How many more deaths would it cause if, when a leak occurs, we were not able to discover the escape of the gas by means of its disagreeable odor.29.The air of rooms in which fever-sick persons are confined?29.Organic matters exist in increased measure in the expired breath of sick persons, and impart to it, at times, a putrid odor. This is especially true in diseases which, like typhus and scarlet fever, are referable to a blood poison. In such cases the breath is one of the means by which nature seeks to expel the offending material from the system. Hence, those who visit or administer to fever-sick persons should obey the oft-repeated direction, "not to take the breath of the sick." At such times, if ever, fresh air is demanded, not alone for the sick, but as well for those who are in attendance.30.Animalcula in the water? Dust in the air?30. Dust in the Air.—Attention has lately been directed to the dust, or haze, that marks the ray of sunshine across a shaded room. Just as, many years ago, it was discovered that myriads of animalcula infested much of the water we drank, so now the microscope reveals "the gay motes that dance along a sunbeam" to be, in part, composed of multitudes of animal and vegetable forms of a very low grade, the germs of fermentation and putrefaction, and the probable sources of disease.31.The best air filter? The remarks of Prof. Tyndall?31.It is found that the best filter by which to separate this floating dust from the air is cotton wool, although a handkerchief will imperfectly answer the same purpose. In a lecture on this subject by Prof. Tyndall, he remarks that, "by breathing through a cotton wool respirator, the noxious air of the sick room is restored to practical purity. Thus filtered, attendants may breathe the air unharmed.In all probability, the protection of the lungs will be the protection of the whole system. For it is exceedingly probable that the germs which lodge in the air-passages are those which sow epidemic disease in the body. If this be so, then disease can certainly be warded off by filters of cotton wool. By this means, so far as the germs are concerned, the air of the highest Alps may be brought into the chamber of the invalid."32.Carbonic acid in volcanic regions? In Java? At Lake Avernus? In mines?32. Carbonic Acid in the Air.—We have already spoken of this gas as an exhalation from the lungs, and a source of impurity; but it exists naturally in the atmosphere in the proportion of one half part per thousand. In volcanic regions it is poured forth in enormous quantities from fissures in the earth's surface. Being heavier than air, it sometimes settles into caves and depressions in the surface. It is stated that in the island of Java, there is a place called the "Valley of Poison," where the ground is covered with the bones of birds, tigers, and other wild animals, which were suffocated by carbonic acid while passing. The Lake Avernus, the fabled entrance to the infernal regions, was, as its name implies, bird-less, because the birds, while flying over it, were poisoned by the gas and fell dead into its waters. In mines, carbonic acid forms the dreadedchoke-damp, while carburetted hydrogen is thefire-damp.33.In the open air? Amount of carbonic acid exhaled by a man? A gas-burner? A room fire? From furnaces?33.In the open air, men seldom suffer from carbonic acid, for, as we shall see presently, nature provides for its rapid distribution, and even turns it to profitable use. But its ill effects are painfully evident in the abodes of men, in which it is liable to collect as the waste product of respiration and of that combustion which is necessary for lighting and warming our homes. A man exhales, during repose, not less than one-half cubic foot of carbonic acid per hour. One gas-burner liberates five cubic feet in thesame time, and spoils about as much air as ten men. A fire burning in a grate or stove emits some gaseous impurity, and at the same time abstracts from the air as much oxygen as twelve men would consume in the same period, thus increasing the relative amount of carbonic acid in the air. From furnaces, as ordinarily constructed, this gas, with other products of combustion, is constantly leaking and vitiating the air of tightly-closed apartments.34.Effects of inhaling carbonic acid alone? In small quantities?34. Effects of Impure Air.—Carbonic acid, in its pure form, is irrespirable, causing rapid death by suffocation. Air containing forty parts per thousand of this gas (the composition of the expired breath) extinguishes a lighted candle, and is fatal to birds; when containing one hundred parts, it no longer yields oxygen to man and other warm-blooded animals; and is of course at once fatal to them. In smaller quantities, this gas causes headache, labored respiration, palpitation, unconsciousness, and convulsions.35.Effects of the air in crowded and badly ventilated rooms?35.In crowded and badly ventilated apartments, where the atmosphere relatively contains from six to ten times the natural amount of carbonic acid, the contaminated air causes dulness, drowsiness, and faintness; the dark, impure blood circulating through the brain, oppressing that organ and causing it to act like a blunted tool. This is a condition not uncommon in our schools, churches, court-rooms, and the like, the places of all others where it is desirable that the mind should be alert and free to act; but, unhappily, an unseen physiological cause is at work, dispensing weariness and stupor over juries, audience, and pupils.36.A cause of consumption? How was the fact illustrated?36.Another unmistakable result of living in and breathing foul air is found in certain diseases of the lungs, especially consumption. For many years the barracks ofthe British army were constructed without any regard to ventilation; and during those years the statistics showed that consumption was the cause of a very large proportion of deaths. At last the government began to improve the condition of the buildings, giving larger space and air-supply; and as a consequence, the mortality from consumption has diminished more than one-third.37.How, in the case of the lower animals? Tendency of certain occupations?37.The lower animals confined in the impure atmosphere of menageries, contract the same diseases as man. Those brought from a tropical climate, and requiring artificial warmth, generally die of consumption. In the Zoological gardens of Paris, this disease affected nearly all monkeys, until care was taken to introduce fresh air by ventilation; and then it almost wholly disappeared. The tendency of certain occupations to shorten life is well known; disease being occasioned by the fumes and dust which arise from the material employed, in addition to the unhealthful condition of the workshop or factory where many hours are passed daily.38.Give the fact as set forth in the table.38.The following table shows the comparative amount of carbonic acid in the air under different conditions and the effects sometimes produced:—Proportion of Carbonic Acid.In 1000 parts of Air.Air of country..4" " city..5In hospital, well ventilated..6In school, church, etc., fairly ventilated.1.2 to 2.5In court-house, factory, etc., without ventilation.4. to 40.In bedroom, before being aired.4.5In bedroom, after being aired.1.5Constantly breathed, causing ill health.2.Occasionally breathed, causing discomfort.3.Occasionally breathed, causing distress.10.Expired air.40.Air no longer yielding oxygen100.39.What can you state of the diffusive power of gases? The added influence of the winds?39. Nature's Provision for Purifying the Air.—We have seen that carbonic acid is heavier than air, and is poisonous. Why, then, does it not sink upon and overwhelm mankind with a silent, invisible wave of death? Among the gases there is a more potent force than gravity, which forever precludes such a tragedy. It is known as the diffusive power of gases. It acts according to a definite law, and with a resistless energy compelling these gases, when in contact, to mingle until they are thoroughly diffused. The added influence of the winds is useful, by insuring more rapid changes in the air; air in motion being perfectly wholesome. The rains also wash the air.40.How is the constant purity of the air secured? Explain the process?40.We have seen that the whole animal creation is constantly abstracting oxygen from the atmosphere, and as constantly adding to it vast volumes of a gas injurious alike to all, even in small quantities. How, then, does the air retain, unchanged, its life-giving properties? The constant purity of the air is secured by means of the vegetable creation. Carbonic acid is the food of the plants, and oxygen is its waste product. The leaves are its lungs, and under the stimulus of sunlight a vegetable respiration is set in motion, the effects of which are just the reverse of the function we have been considering. Thus nature purifies the air, and at the same time builds up beautiful and useful forms of life from elements of decay.41.What process occurs in the sea? How is the fact illustrated?41.In the sea, as in the air, the same circle of changes is observed. Marine animals consume oxygen and give off carbonic acid; while marine plants consume carbonic acid and liberate oxygen. Taking advantage of this fact, we may so arrange aquaria with fishes and sea-plants, in their proper combinations, so that each supplies the needs of the other, and the water requires seldom to be renewed. Thisaffords us, on a small scale, an illustration of the mutual dependence of the two great kingdoms of nature; as well as of those compensating changes which are taking place on such a grand scale in the world about us.42.Character of the external air? Of the air in our dwellings? What becomes imperative? Imperfect ventilation of our dwellings?42. Ventilation.—Since the external atmosphere, as provided by nature, is always pure, and since the air in our dwellings and other buildings is almost always impure, it becomes imperative that there should be a free communication from the one to the other. This we aim to accomplish by ventilation. As our houses are ordinarily constructed, the theory of ventilation, "to make the internal as pure as the external air," is seldom carried out. Doors, windows, and flues, the natural means of replenishing the air, are too often closed, almost hermetically, against the precious element. Special means, or special attention, must therefore be used to secure even a fair supply of fresh air. This is still more true of those places of public resort, where many persons are crowded together.43.What hints are given for the ventilation of our dwellings?43.If there are two openings in a room, one as a vent for foul air, and the other an inlet for atmospheric air, and if the openings be large, in proportion to the number of air consumers, the principal object will be attained. Thus, a door and window, each opening into the outer air, will ordinarily ventilate a small apartment; or a window alone will answer, if it be open both above and below, and the open space at each end be not less than one inch for each occupant of the room, when the window is about a yard wide. The direction of the current is generally from below upward, since the foul, heated air tends to rise; but this is not essential. Its rate need not be rapid; a "draught," or perceptible current, is never necessary to good ventilation. The temperature of the air admitted may be warm or cold. It is thought by many that if theair is cold, it is pure; but this is an error, since cold air will receive and retain the same impurities as warm air.44.State what Florence Nightingale says about inhaling night air?44.Shall we open our bedrooms to the night air? Florence Nightingale says, in effect, that night air is the only air that we can then breathe. "The choice is between pure air without and impure air within. Most people prefer the latter,—an unaccountable choice. An open window, most nights in the year, can hurt no one. In great cities, night air is the best and purest to be had in twenty-four hours. I could better understand, in towns, shutting the windows during the day than during the night."45.Warmth of the bird as compared with that of the air? Of the fish and the water? Heat in animals and plants? How illustrated with the thermometer?45. Animal Heat.—Intimately connected with respiration is the production of animal heat, or the power of maintaining the temperature of the body above that of the medium in which the creature moves; thus, the bird is warmer than the air, and the fish than the water. This elevation of temperature is a result of the various chemical changes which are constantly taking place in the system. Although common to all animals, in a greater or less degree, heat is not peculiar to them; since plants also generate it, especially at the time of sprouting and flowering. If a thermometer be placed in a cluster of geranium flowers, it will indicate a temperature several degrees above that of the surrounding air.46.Amount of heat in animals, how apportioned? As regards the birds? Frogs, and other sluggish animals? Arrangement made byzoologists?46.Among animals great differences are noticed in this respect, but the degree of heat produced is always proportional to the activity of respiration and the amount of oxygen consumed. Accordingly, the birds, whose habits are extremely active, and whose breathing capacity is the greatest, have uniformly the highest temperature. Sluggish animals, on the contrary, as frogs, lizards, and snakes, have little need for oxygen, and have incompletelydeveloped lungs; these animals are cold to the touch, that is, they have relatively a lower temperature than man, and their positive temperature is but little above that of the external air. Accordingly, zoologists have so arranged the animal kingdom thatwarm-bloodedanimals, including man, the birds, and the quadrupeds, are classified together; while thecold-bloodedanimals, such as the fish, tortoise, frog, and all that have no vertebral column, are classed by themselves.47.State what is said respecting the temperature of the human body.47.The temperature of the human body is about 100° Fahrenheit, and remains about the same through winter and summer, in the tropics as well as in the frozen regions of the north. It may change temporarily within the range of about twelve degrees; but any considerable, or long-continued elevation or diminution of the bodily heat is certain to result disastrously.48.Ability of man to adapt himself to different climates? In what does the power to resist cold consist? What is said about warm clothing?48.Man is able to adapt himself to all extremes of climate; and, in fact, by means of clothing, shelter, and food, is able to create for himself an artificial climate where-ever he choses to reside. The power to resist cold consists chiefly in preventing the heat which is generated by the vital processes of the body from being lost by radiation. Warm clothing, such as we wear in winter, has, in reality, the same temperature as that which is worn in summer; but, by reason of being thick and porous, it is a bad conductor of heat, and thus prevents the escape of that produced by the body. If woollen fabrics were intrinsically warm, no one would wrap a piece of flannel, or blanket, around a block of ice to prevent its melting in summer.
1.Difference between the two sets of capillaries? Change effected by respiration or breathing?
1. The Object of Respiration.—In one set of capillaries, or hair-like vessels, the blood is impoverished for the support of the different members and organs of the body. In another capillary system the blood is refreshed and again made fit to sustain life. The former belongs to the greater orsystemiccirculation; the latter to the lesser orpulmonary, so called frompulmo, the lungs, in which organs it is situated. The blood, as sent from the right side of the heart to the lungs, is venous, dark, impure, and of a nature unfit to circulate again through the tissues. But, when the blood returns from the lungs to the left side of the heart, it has become arterial, bright, pure, and no longer hurtful to the tissues. This marvellous purifying change is effected by means of the very familiar act of respiration, or breathing.
2.What are the lungs? How many lungs are there? Lung-substance? Its properties? The pleura?
2. The Lungs.—The lungs are the special organs of respiration. There are two of them, one on each side of the chest, which cavity they, with the heart, almost wholly occupy. The lung-substance is soft, elastic, and sponge-like. Under pressure of the finger, itcrepitates, or crackles, and floats when thrown into water; these properties beingdue to the presence of air in the minute air-cells of the lungs. To facilitate the movements necessary to these organs, each of them is provided with a double covering of an exceedingly smooth and delicate membrane, called thepleura. One layer of the pleura is attached to the walls of the chest, and the other to the lungs; and they glide, one upon the other, with utmost freedom. Like the membrane which envelops the heart, the pleura secretes its own lubricating fluid, in quantities sufficient to keep it always moist.
Fig. 34.--Organs of the Chest.Fig. 34.—Organs of the Chest.A, Lungs. B, Heart. D, Pulmonary Artery. E, Trachea.
A, Lungs. B, Heart. D, Pulmonary Artery. E, Trachea.
Fig. 36.--Diagram and Section of the Air-cells.Fig. 36.—Diagram and Section of the Air-cells.
Fig. 35.--Larynx, Trachea, and Bronchial Tubes.Fig. 35.—Larynx, Trachea, and Bronchial Tubes.
3.Communication of the lungs with the external air? Bronchial tubes?
3. The Air-Passages.—The lungs communicate with the external air by means of certain air-tubes, the longest of which, thetrachea, or windpipe, runs along the front of the neck (Fig. 34, E, and 35). Within the chest this tube divides into two branches, one entering each lung; these in turn give rise to numerous branches, or bronchial tubes, as they are called, which gradually diminish in size until they are about one-twenty-fifth of an inch in diameter. Each of these terminates in a cluster of little pouches, or "air-cells," having very thin walls, and covered with a capillary network, the most intricate in the body (Fig. 36).
4.Office of the bronchial tubes? What further can you state of them?
4.These tubes are somewhat flexible, sufficiently so to bend when the parts move in which they are situated; but they are greatly strengthened by bands or rings of cartilage which keep the passages always open; otherwise there would be a constantly-recurring tendency to collapse after every breath. The lung-substance essentially consists of these bronchial tubes and terminal air-cells, with the blood-vessels ramifying about them (Fig. 37). At the top of the trachea is the larynx, a sort ofbox of cartilage, across which are stretched the vocal cords. Here the voice is produced chiefly by the passage of the respired air over these cords, causing them to vibrate.
Fig. 37.--Section of the Lungs.Fig. 37.—Section of the Lungs.
5.The epiglottis? When it does not close in time, what is the consequence?
5.Over the opening of the larynx is found theepiglottis, which fits like the lid of a box at the entrance to the lungs, and closes during the act of swallowing, so that food and drink shall pass backward to the œsophagus, or gullet (Fig. 38). Occasionally it does not close in time, and some substance intrudes within the larynx, when we at once discover, by a choking sensation, that "something has gone the wrong way," and, by coughing, we attempt to expel the unwelcome intruder. The epiglottis is one of the many safeguards furnished by nature for our security andcomfort, and is planned and put in place long before these organs are brought into actual use in breathing and in taking food.
Fig. 38.--Section of Mouth and Throat.Fig. 38.—Section of Mouth and Throat.A, The Tongue. B, The Uvula C, Vocal Cord. E, Epiglottis. L, Larynx. N, Trachea. O, Œsophagus.
A, The Tongue. B, The Uvula C, Vocal Cord. E, Epiglottis. L, Larynx. N, Trachea. O, Œsophagus.
6.Lining of the air-passages? Ciliated cells? Their uses? The three diseases of the lungs?
Fig. 39.--Ciliated Cells.Fig. 39.—Ciliated Cells.
6.The air-passages are lined through nearly their whole extent with mucous membrane, which maintains these parts in a constantly moist condition. This membrane has a peculiar kind of cells upon its outer surface. If examined under a powerful microscope, we may see, even for a considerable time after their removal from the body, that these cells have minute hair-like processes in motion, which wave like a field of grain under the influence of a breeze (Fig. 39). This is a truly beautiful sight; and since it is found that these littlecilia, as they are called, always produce currents in one direction, from within outward, it is probable that they serve a useful purpose in catching and carrying away from the lungs dust and other small particles drawn in with the breath (Fig. 39). The three diseases which more commonly affect the lungs, as the result of exposure, are pneumonia, or inflammation of the lungs, implicating principally the air-cells; bronchitis, an inflammation of the large bronchial tubes; and pleurisy, an inflammation of the investing membrane of the lungs, or pleura. Among the young, an affection of the trachea takes place, known as croup.
7.The act of breathing? Extension of the chest by breathing?
7. The Movements of Respiration.—The act of breathing has two parts—(1),inspiration, or drawing air into the lungs, and (2),expiration, or expelling it from the lungs again. In inspiration, the chest extends in its length, breadth, and height, or width. We can prove that this is the case as regards the two latter, by observing the effect of a deep breath. The ribs are elevated by means of numerous muscles, some of which occupy the entire spaces between those bones. But the increase in length, or vertically, is not so apparent, as it is caused by a muscle within the body called thediaphragm, it being the thin partition which separates the chest from the abdomen, rising like a dome within the chest. (Fig. 16).
8.Contraction of the diaphragm? Power of the diaphragm? Effects of extending the walls of the chest? The habit of taking frequent and deep inspirations?
8.With every inspiration, the diaphragm contracts, and in so doing, approaches more nearly a plane, or horizontal, surface, and thus enlarges the capacity of the chest. Laughing, sobbing, hiccoughing, and sneezing are caused by the spasmodic or sudden contraction of the diaphragm. The special power of this muscle is important in securing endurance, or "long wind," as it is commonly expressed; which may be obtained mainly by practice. It is possessed in a marked degree by the mountaineer, the oarsman, and the trained singer. As the walls of the chest extend, the lungs expand, and the air rushes in to fill them. This constitutes an inspiration. The habit of taking frequent and deep inspirations, in the erect position, with the shoulders thrown back, tends greatly to increase the capacity and power of the organs of respiration.
9.Expiration? The mechanism of expiration?
9. Expirationis a less powerful act than inspiration. The diaphragm relaxes its contraction, and ascends in the form of a dome; the ribs descend and contract the chest; while the lungs themselves, being elastic, assist to drive out the air. The latter passes out through the same channels by which it entered. At the end of each expiration there is a pause, or period of repose, lasting about as long as the period of action.
10.Frequency of respiration? Effect of hurried action of the heart?
10. Frequency of Respiration.—It is usually estimated that we breathe once during every four beats of the heart, or about eighteen times in a minute. There is, of course, a close relation between the heart and lungs, and whatever modifies the pulse, in like manner affects the breathing. When the action of the heart is hurried, a larger amount of blood is sent to the lungs, and, as the consequence, they must act more rapidly. Occasionally, the heart beats so very forcibly that the lungs cannot keep pace with it, and then we experience a peculiar sense ofdistress from the want of air. This takes place when we run until we are "out of breath." At the end of every fifth or sixth breath, the inspiration is generally longer than usual, the effect being to change more completely the air of the lungs.
11.Respiration controlled by the will? Advantage of the knowledge to us?
11.Although, as a general rule, the work of respiration goes on unconsciously and without exertion on our part, it is nevertheless under the control of the will. We can increase or diminish the frequency of its acts at pleasure, and we can "hold the breath," or arrest it altogether for a short time. From twenty to thirty seconds is ordinarily the longest period in which the breath can be held; but if we first expel all the impure air from the lungs, by taking several very deep inspirations, the time may be extended to one and a half or even two minutes. This should be remembered, and acted upon, before passing through a burning building, or any place where the air is very foul. The arrest of the respiration may be still further prolonged by training and habit; thus it is said, the pearl-fishers of India can remain three or four minutes under water without being compelled to breathe.
12.Capacity of the lungs? Time required to renovate the air in the lungs? In tranquil respiration? Importance of the provision?
12. Capacity of the Lungs.—The lungs are not filled and emptied by each respiration. For while their full capacity, in the adult, is three hundred and twenty cubic inches, or more than a gallon, the ordinary breathing air is only one-sixteenth part of that volume, or twenty cubic inches, being two-thirds of a pint. Accordingly, a complete renovation, or rotation, of the air of the lungs does not take place more frequently than about once in a minute; and by the gradual introduction of the external air, its temperature is considerably elevated before it reaches the delicate pulmonary capillaries. In tranquil respiration, less than two-thirds of the breathing power iscalled into exercise, leaving a reserve capacity of about one hundred and twenty cubic inches, equivalent to three and one half pints. This provision is indispensable to the continuation of life; otherwise, a slight embarrassment of respiration, by an ordinary cold, for instance, would suffice to cut off the necessary air, and the spark of life would be speedily extinguished.
13.The atmosphere? How high or deep? How essential to life? Marine life in perfectly pure water and air?
13. The Air we breathe.—The earth is enveloped on all sides by an invisible fluid, called the atmosphere. It forms a vast and shoreless ocean of air, forty-five miles deep, encircling and pervading all objects on the earth's surface, which is absolutely essential for the preservation of all vegetable and animal life,—in the sea, as well as on the land and in the air. At the bottom, or in the lower strata of this aerial ocean, we move and have our being. Perfectly pure water will not support marine life, for a fish may be drowned in water from which the air has been exhausted, just as certainly as a mouse, or any other land animal, will perish if put deeply into the water for a length of time. The cause is the same in both cases: the animal is deprived of the requisite amount of air. It is also stated, that if the water-supply of the plant be deprived of air, its vital processes are at once checked.
14.Composition of the air? Properties of the two gases?
14.The air is not a simple element, as the ancients supposed, but is formed by the mingling of two gases, known to the chemist as oxygen and nitrogen, in the proportion of one part of the former to four parts of the latter. These gases are very unlike, being almost opposite in their properties: nitrogen is weak, inert, and cannot support life; while oxygen is powerful, and incessantly active; and is the essential element which gives to the atmosphere its power to support life and combustion. The discovery of this fact was made by the French chemist, Lavoisier, in 1778.
15.Air once breathed? An animal in it? A candle? Analysis of expired air? Change in volume?
15. Changes in the Air from Respiration.—Air that has been once breathed is no longer fit for respiration. An animal confined within it will sooner or later die; so too, a lighted candle placed in it will be at once extinguished. If we collect a quantity of expired air and analyze it, we shall find that its composition is not the same as that of the inspired air. When the air entered the lungs it was rich in oxygen; now it contains twenty-five per cent. less of that gas. Its volume, however, remains nearly the same; its loss being replaced by another and very different gas, which the lungs exhaled, calledcarbonic acid, or, as the chemist terms it,carbon dioxide.
16.What else has the expired air gained? When and where noticed?
16.The expired air has also gained moisture. This is noticed when we breathe upon a mirror, or the window-pane, the surface being tarnished by the condensation of the watery vapor exhaled by the lungs. In cold weather, this causes the fine cloud which is seen issuing from the nostrils or mouth with each expiration, and contributes in forming the feathery crystals of ice which decorate our window-panes on a winter's morning.
17.Nature of the watery vapor? Its effects upon animals?
17.This watery vapor contains a variable quantity of animal matter, the exact nature of which is unknown; but when collected it speedily putrefies and becomes highly offensive. From the effects, upon small animals, of confinement in their own exhalations, having at the same time an abundant supply of fresh air, it is believed that the organic matters thrown off by the lungs and skin are direct and active poisons; and that to such emanations from the body, more than to any other cause, are due the depressing and even fatal results which follow the crowding of large numbers of persons into places of limited capacity.
18.Give some of the instances furnished by history.
18.History furnishes many painful instances of the ill effects of overcrowding. In 1756, of one hundred and forty-six Englishmen imprisoned in the Black Hole of Calcutta, only twenty-three, at the end of eight hours, survived. After the battle of Austerlitz, three hundred prisoners were crowded into a cavern, where, in a few hours, two-thirds of their number died. On board a steam-ship, during a stormy night, one hundred and fifty passengers were confined in a small cabin, but when morning came, only eighty remained alive.
19.Change in the blood from blue to red. Upon what does the change depend? How shown?
19. Changes in the Blood from Respiration.—The most striking change which the blood undergoes by its passage through the lungs, is the change of color from a dark blue to bright red. That this change is dependent upon respiration has been fully proved by experiment. If the trachea, or windpipe, of a living animal be so compressed as to exclude the air from the lungs, the blood in the arteries will gradually grow darker, until its color is the same as that of the venous blood. When the pressure is removed the blood speedily resumes its bright hue. Again, if the animal be made to breathe an atmosphere containing more oxygen than atmospheric air, the color changes from scarlet to vermilion, and becomes even brighter than arterial blood. This change of color is not of itself a very important matter, but it indicates a most important change of composition.
20.What does the air lose and gain by respiration? What, the blood? Air as food?
20.The air, as we have seen, by respiration loses oxygen and gains carbonic acid: the blood, on the contrary, gains oxygen and loses carbonic acid. The oxygen is the food of the blood corpuscles; while the articles we eat and drink belong more particularly to the plasma of the blood. The air, then, it is plain, is a sort of food, and we shouldundoubtedly so regard it, if it were not for the fact that we require it constantly, instead of taking it at stated intervals, as is the case with our articles of diet. Again, as the demand of the system for food is expressed by the sensation of hunger, so the demand for air is marked by a painful sensation called suffocation.
21.Moist animal membranes? How shown with the bladder?
21. Interchange of Gases in the Lungs.—As the air and the blood are not in contact, they being separated from each other by the walls of the air-cells and of the blood-vessels, how can the two gases, oxygen and carbonic acid, exchange places? Moist animal membranes have a property which enables them to transmit gases through their substance, although they are impervious to liquids. This may be beautifully shown by suspending a bladder containing dark blood in a jar of oxygen. At the end of a few hours the oxygen will have disappeared, the blood will be brighter in color, and carbonic acid will be found in the jar.
22.Gaseous diffusion? If oxygen be not received? If carbonic acid be retained?
22.If this interchange takes place outside of the body, how much more perfectly must it take place within, where it is favored by many additional circumstances! The walls of the vessels and the air-cells offer no obstacle to this process, which is known as gaseous diffusion. Both parts of the process are alike of vital importance. If oxygen be not received, the organs cease to act; and if carbonic acid be retained in the blood, its action is that of a poison; unconsciousness, convulsions, and death following.
23.Difference in the appearance and composition of the blood? Temperature of the blood? The blood while passing through the lungs? The consequence?
23. Difference between Arterial and Venous Blood.—The following table presents the essential points of difference in the appearance and composition of the blood, before and after its passage through the lungs:—
The temperature of the blood varies considerably; but the arterial stream is generally warmer than the venous. The blood imparts heat to the air while passing through the lungs, and consequently the contents of the right side of the heart has a higher temperature than the contents on the left side.
24.What do we learn by means of the spectroscope? "Carriers of oxygen?" Blue blood in the system?
24.By means of the spectroscope, we learn that the change of color in the blood has its seat in the corpuscles; and that, according as they retain oxygen, or release it, they present the spectrum of arterial or venous blood. There evidently exists, on the part of these little bodies, an affinity for this gas, and hence they have been called "carriers of oxygen." It was long ago thought that blue blood was a trait peculiar to persons of princely and royal descent, and boastful allusions to the "sang azure" of kings and nobles are quite often met with. Physiology, however, informs us that blue blood flows in the veins of the low as well as the high, and that so far from its presence indicating a mark of purity, it, in reality, represents the waste and decay of the system.
25.The amount of air that passes in and out of the lungs?
25. Amount of Respiratory Labor.—During ordinary calm respiration, we breathe eighteen times in a minute; and twenty cubic inches of air pass in and out of the lungs with every breath. This is equivalent to the use of three hundred and sixty cubic inches, or more than ten pints of air each minute. From this we calculate that the quantity of air which hourly traverses the lungs is about thirteen cubic feet, or seventy-eight gallons; and daily, notless than three hundred cubic feet, an amount nearly equal to the contents of sixty barrels.
26.Air absorbed in its transit through the lungs? The loss? Carbonic acid exhaled? Effect of excitement or exertion? What estimate?
26.Of this large volume of air five per cent. is absorbed in its transit through the lungs. The loss thus sustained is almost wholly of oxygen, and amounts to fifteen cubic feet daily. The quantity of carbonic acid exhaled by the lungs during the day is somewhat less, being twelve cubic feet. Under the influence of excitement or exertion, the breathing becomes more frequent and more profound; and then the internal respiratory work increases proportionately, and may even be double that of the above estimate. It has been estimated that in drawing a full breath, a man exerts a muscular force equal to raising two hundred pounds placed upon the chest.
27.Importance of the oxygen in the atmosphere? Injurious character of gases?
27. Impurities of the Air.—The oxygen in the atmosphere is of such prime importance, and its proportion is so nicely adjusted to the wants of man, that any gas or volatile substance which supplants it must be regarded as a hurtful impurity. All gases, however, are not alike injurious. Some, if inhaled, are necessarily fatal;arsenuretted hydrogenbeing one of these, a single bubble of which destroyed the life of its discoverer, Gehlen. Others are not directly dangerous, but by taking the place of oxygen, and excluding it from the lungs, they become so. Into this latter class we place carbonic acid.
28.Pungency of gases? The inference? Our safeguard?
28.Most of the actively poisonous gases have a pungent or offensive odor; and, as may be inferred, most repugnant odors indicate the presence of substances unfit for respiration. Accordingly, as we cannot see or taste these impurities, the sense of smell is our principal safeguard against them; and we recognize the design which has planted this sense, like a sentinel at the proper entrance of theair-passages, the nostrils, to give us warning of approaching harm. Take, as an example, the ordinary illuminating gas of cities, from which so many accidents happen. How many more deaths would it cause if, when a leak occurs, we were not able to discover the escape of the gas by means of its disagreeable odor.
29.The air of rooms in which fever-sick persons are confined?
29.Organic matters exist in increased measure in the expired breath of sick persons, and impart to it, at times, a putrid odor. This is especially true in diseases which, like typhus and scarlet fever, are referable to a blood poison. In such cases the breath is one of the means by which nature seeks to expel the offending material from the system. Hence, those who visit or administer to fever-sick persons should obey the oft-repeated direction, "not to take the breath of the sick." At such times, if ever, fresh air is demanded, not alone for the sick, but as well for those who are in attendance.
30.Animalcula in the water? Dust in the air?
30. Dust in the Air.—Attention has lately been directed to the dust, or haze, that marks the ray of sunshine across a shaded room. Just as, many years ago, it was discovered that myriads of animalcula infested much of the water we drank, so now the microscope reveals "the gay motes that dance along a sunbeam" to be, in part, composed of multitudes of animal and vegetable forms of a very low grade, the germs of fermentation and putrefaction, and the probable sources of disease.
31.The best air filter? The remarks of Prof. Tyndall?
31.It is found that the best filter by which to separate this floating dust from the air is cotton wool, although a handkerchief will imperfectly answer the same purpose. In a lecture on this subject by Prof. Tyndall, he remarks that, "by breathing through a cotton wool respirator, the noxious air of the sick room is restored to practical purity. Thus filtered, attendants may breathe the air unharmed.In all probability, the protection of the lungs will be the protection of the whole system. For it is exceedingly probable that the germs which lodge in the air-passages are those which sow epidemic disease in the body. If this be so, then disease can certainly be warded off by filters of cotton wool. By this means, so far as the germs are concerned, the air of the highest Alps may be brought into the chamber of the invalid."
32.Carbonic acid in volcanic regions? In Java? At Lake Avernus? In mines?
32. Carbonic Acid in the Air.—We have already spoken of this gas as an exhalation from the lungs, and a source of impurity; but it exists naturally in the atmosphere in the proportion of one half part per thousand. In volcanic regions it is poured forth in enormous quantities from fissures in the earth's surface. Being heavier than air, it sometimes settles into caves and depressions in the surface. It is stated that in the island of Java, there is a place called the "Valley of Poison," where the ground is covered with the bones of birds, tigers, and other wild animals, which were suffocated by carbonic acid while passing. The Lake Avernus, the fabled entrance to the infernal regions, was, as its name implies, bird-less, because the birds, while flying over it, were poisoned by the gas and fell dead into its waters. In mines, carbonic acid forms the dreadedchoke-damp, while carburetted hydrogen is thefire-damp.
33.In the open air? Amount of carbonic acid exhaled by a man? A gas-burner? A room fire? From furnaces?
33.In the open air, men seldom suffer from carbonic acid, for, as we shall see presently, nature provides for its rapid distribution, and even turns it to profitable use. But its ill effects are painfully evident in the abodes of men, in which it is liable to collect as the waste product of respiration and of that combustion which is necessary for lighting and warming our homes. A man exhales, during repose, not less than one-half cubic foot of carbonic acid per hour. One gas-burner liberates five cubic feet in thesame time, and spoils about as much air as ten men. A fire burning in a grate or stove emits some gaseous impurity, and at the same time abstracts from the air as much oxygen as twelve men would consume in the same period, thus increasing the relative amount of carbonic acid in the air. From furnaces, as ordinarily constructed, this gas, with other products of combustion, is constantly leaking and vitiating the air of tightly-closed apartments.
34.Effects of inhaling carbonic acid alone? In small quantities?
34. Effects of Impure Air.—Carbonic acid, in its pure form, is irrespirable, causing rapid death by suffocation. Air containing forty parts per thousand of this gas (the composition of the expired breath) extinguishes a lighted candle, and is fatal to birds; when containing one hundred parts, it no longer yields oxygen to man and other warm-blooded animals; and is of course at once fatal to them. In smaller quantities, this gas causes headache, labored respiration, palpitation, unconsciousness, and convulsions.
35.Effects of the air in crowded and badly ventilated rooms?
35.In crowded and badly ventilated apartments, where the atmosphere relatively contains from six to ten times the natural amount of carbonic acid, the contaminated air causes dulness, drowsiness, and faintness; the dark, impure blood circulating through the brain, oppressing that organ and causing it to act like a blunted tool. This is a condition not uncommon in our schools, churches, court-rooms, and the like, the places of all others where it is desirable that the mind should be alert and free to act; but, unhappily, an unseen physiological cause is at work, dispensing weariness and stupor over juries, audience, and pupils.
36.A cause of consumption? How was the fact illustrated?
36.Another unmistakable result of living in and breathing foul air is found in certain diseases of the lungs, especially consumption. For many years the barracks ofthe British army were constructed without any regard to ventilation; and during those years the statistics showed that consumption was the cause of a very large proportion of deaths. At last the government began to improve the condition of the buildings, giving larger space and air-supply; and as a consequence, the mortality from consumption has diminished more than one-third.
37.How, in the case of the lower animals? Tendency of certain occupations?
37.The lower animals confined in the impure atmosphere of menageries, contract the same diseases as man. Those brought from a tropical climate, and requiring artificial warmth, generally die of consumption. In the Zoological gardens of Paris, this disease affected nearly all monkeys, until care was taken to introduce fresh air by ventilation; and then it almost wholly disappeared. The tendency of certain occupations to shorten life is well known; disease being occasioned by the fumes and dust which arise from the material employed, in addition to the unhealthful condition of the workshop or factory where many hours are passed daily.
38.Give the fact as set forth in the table.
38.The following table shows the comparative amount of carbonic acid in the air under different conditions and the effects sometimes produced:—
39.What can you state of the diffusive power of gases? The added influence of the winds?
39. Nature's Provision for Purifying the Air.—We have seen that carbonic acid is heavier than air, and is poisonous. Why, then, does it not sink upon and overwhelm mankind with a silent, invisible wave of death? Among the gases there is a more potent force than gravity, which forever precludes such a tragedy. It is known as the diffusive power of gases. It acts according to a definite law, and with a resistless energy compelling these gases, when in contact, to mingle until they are thoroughly diffused. The added influence of the winds is useful, by insuring more rapid changes in the air; air in motion being perfectly wholesome. The rains also wash the air.
40.How is the constant purity of the air secured? Explain the process?
40.We have seen that the whole animal creation is constantly abstracting oxygen from the atmosphere, and as constantly adding to it vast volumes of a gas injurious alike to all, even in small quantities. How, then, does the air retain, unchanged, its life-giving properties? The constant purity of the air is secured by means of the vegetable creation. Carbonic acid is the food of the plants, and oxygen is its waste product. The leaves are its lungs, and under the stimulus of sunlight a vegetable respiration is set in motion, the effects of which are just the reverse of the function we have been considering. Thus nature purifies the air, and at the same time builds up beautiful and useful forms of life from elements of decay.
41.What process occurs in the sea? How is the fact illustrated?
41.In the sea, as in the air, the same circle of changes is observed. Marine animals consume oxygen and give off carbonic acid; while marine plants consume carbonic acid and liberate oxygen. Taking advantage of this fact, we may so arrange aquaria with fishes and sea-plants, in their proper combinations, so that each supplies the needs of the other, and the water requires seldom to be renewed. Thisaffords us, on a small scale, an illustration of the mutual dependence of the two great kingdoms of nature; as well as of those compensating changes which are taking place on such a grand scale in the world about us.
42.Character of the external air? Of the air in our dwellings? What becomes imperative? Imperfect ventilation of our dwellings?
42. Ventilation.—Since the external atmosphere, as provided by nature, is always pure, and since the air in our dwellings and other buildings is almost always impure, it becomes imperative that there should be a free communication from the one to the other. This we aim to accomplish by ventilation. As our houses are ordinarily constructed, the theory of ventilation, "to make the internal as pure as the external air," is seldom carried out. Doors, windows, and flues, the natural means of replenishing the air, are too often closed, almost hermetically, against the precious element. Special means, or special attention, must therefore be used to secure even a fair supply of fresh air. This is still more true of those places of public resort, where many persons are crowded together.
43.What hints are given for the ventilation of our dwellings?
43.If there are two openings in a room, one as a vent for foul air, and the other an inlet for atmospheric air, and if the openings be large, in proportion to the number of air consumers, the principal object will be attained. Thus, a door and window, each opening into the outer air, will ordinarily ventilate a small apartment; or a window alone will answer, if it be open both above and below, and the open space at each end be not less than one inch for each occupant of the room, when the window is about a yard wide. The direction of the current is generally from below upward, since the foul, heated air tends to rise; but this is not essential. Its rate need not be rapid; a "draught," or perceptible current, is never necessary to good ventilation. The temperature of the air admitted may be warm or cold. It is thought by many that if theair is cold, it is pure; but this is an error, since cold air will receive and retain the same impurities as warm air.
44.State what Florence Nightingale says about inhaling night air?
44.Shall we open our bedrooms to the night air? Florence Nightingale says, in effect, that night air is the only air that we can then breathe. "The choice is between pure air without and impure air within. Most people prefer the latter,—an unaccountable choice. An open window, most nights in the year, can hurt no one. In great cities, night air is the best and purest to be had in twenty-four hours. I could better understand, in towns, shutting the windows during the day than during the night."
45.Warmth of the bird as compared with that of the air? Of the fish and the water? Heat in animals and plants? How illustrated with the thermometer?
45. Animal Heat.—Intimately connected with respiration is the production of animal heat, or the power of maintaining the temperature of the body above that of the medium in which the creature moves; thus, the bird is warmer than the air, and the fish than the water. This elevation of temperature is a result of the various chemical changes which are constantly taking place in the system. Although common to all animals, in a greater or less degree, heat is not peculiar to them; since plants also generate it, especially at the time of sprouting and flowering. If a thermometer be placed in a cluster of geranium flowers, it will indicate a temperature several degrees above that of the surrounding air.
46.Amount of heat in animals, how apportioned? As regards the birds? Frogs, and other sluggish animals? Arrangement made byzoologists?
46.Among animals great differences are noticed in this respect, but the degree of heat produced is always proportional to the activity of respiration and the amount of oxygen consumed. Accordingly, the birds, whose habits are extremely active, and whose breathing capacity is the greatest, have uniformly the highest temperature. Sluggish animals, on the contrary, as frogs, lizards, and snakes, have little need for oxygen, and have incompletelydeveloped lungs; these animals are cold to the touch, that is, they have relatively a lower temperature than man, and their positive temperature is but little above that of the external air. Accordingly, zoologists have so arranged the animal kingdom thatwarm-bloodedanimals, including man, the birds, and the quadrupeds, are classified together; while thecold-bloodedanimals, such as the fish, tortoise, frog, and all that have no vertebral column, are classed by themselves.
47.State what is said respecting the temperature of the human body.
47.The temperature of the human body is about 100° Fahrenheit, and remains about the same through winter and summer, in the tropics as well as in the frozen regions of the north. It may change temporarily within the range of about twelve degrees; but any considerable, or long-continued elevation or diminution of the bodily heat is certain to result disastrously.
48.Ability of man to adapt himself to different climates? In what does the power to resist cold consist? What is said about warm clothing?
48.Man is able to adapt himself to all extremes of climate; and, in fact, by means of clothing, shelter, and food, is able to create for himself an artificial climate where-ever he choses to reside. The power to resist cold consists chiefly in preventing the heat which is generated by the vital processes of the body from being lost by radiation. Warm clothing, such as we wear in winter, has, in reality, the same temperature as that which is worn in summer; but, by reason of being thick and porous, it is a bad conductor of heat, and thus prevents the escape of that produced by the body. If woollen fabrics were intrinsically warm, no one would wrap a piece of flannel, or blanket, around a block of ice to prevent its melting in summer.