Popular Education. Ira Mayhew
thus vitiated, not only by the subtraction of its oxygen and the addition of carbonic acid gas, but also by animal effluvia, with which it is loaded when returned from the lungs. In some individuals this last source of impurity is so great as to render their vicinity offensive, and even insupportable. It is this which gives the disagreeable, sickening smell to crowded rooms. The air which is expired from the lungs is rendered offensive by various other causes. When spirituous liquors are taken into the stomach, for example, they are absorbed by the veins and mixed with the venous blood, in which they are carried to the lungs to be expelled from the body. In some instances, when persons have drank copiously of spirits, their breath has been so saturated with them as actually to take fire and burn. An instance of this kind has recently been communicated to me by several reliable witnesses, in which the flame was extinguished by closing the mouth and nose, thus excluding the pure air that supported the combustion, until the unfortunate experimenter could remove the candle by which his breath had taken fire. This illustration will explain how the odor of different substances is frequently perceptible in the breath long after the mouth is free from them.
The lungs not only exhale waste matter, but absorption takes place from their lining membrane. In both of these respects there is a striking analogy between the functions performed by the lungs and the skin. When a person breathes an atmosphere loaded with the fumes of spirits, tobacco, turpentine, or of any other volatile substance, a portion of the fumes is taken up by the absorbing vessels of the lungs, and carried into the system, and there produces precisely the same effects as if introduced into the stomach. Dogs, for example, have been killed by being made to inhale the fumes of prussic acid for a few minutes. The lungs thus become a ready inlet to contagion, miasmata, and other poisonous influences diffused through the air we breathe.
From this general explanation of the structure and uses of the lungs, it is obvious that several conditions which it is our interest to know and observe are essential to the healthy performance of the important function of respiration. The first among these is a healthy original formation of the lungs. No fact in medicine is better established, says Dr. Combe, than that which proves the hereditary transmission, from parents to children, of a constitutional liability to pulmonary disease, and especially to consumption; yet, continues he, no condition is less attended to in forming matrimonial engagements.
Another requisite to the well-being of the lungs, and to the free and salutary exercise of respiration, is a due supply of rich and healthy blood. When, from defective food or impaired digestion, the blood is impoverished in quality, and rendered unfit for adequate nutrition, the lungs speedily suffer, and that often to a fatal extent. The free and easy expansion of the chest is also indispensable to the full play and dilation of the lungs. Whatever interferes with or impedes it, either in dress or in position, is obviously prejudicial to health. On the other hand, whatever favors the free expansion of the chest equally promotes the healthy action of the respiratory organs. Stays and corsets, and tight vests and waistbands, operate most injuriously, compressing as they do the thoracic cavity, and interfering with the healthy dilation of the lungs.
The admirable harmony established by the Creator between the various constituent parts of the animal frame, renders it impossible to pay regard to the conditions required for the health of any one, or to infringe the conditions required therefor, without all the rest participating in the benefit or injury. Thus, while cheerful exercise in the open air and in the society of equals is directly and eminently conducive to the well-being of the muscular system, the advantage does not stop there, the beneficent Creator having kindly so ordered it that the same exercise shall be scarcely less advantageous to the important function of respiration. Active exercise calls the lungs into play, favors their expansion, promotes the circulation of the blood through their substance, and leads to their complete and healthy development. The same end is greatly facilitated by that free and vigorous exercise of the voice, which so uniformly accompanies and enlivens the sports of the young, and which doubles the benefits derived from them considered as exercise. The excitement of the social and moral feelings which children experience while engaged in play is another powerful tonic, the influence of which on the general health ought not to be overlooked; for the nervous influence is as indispensable to the right performance of respiration as it is to the action of the muscles or to the digestion of food.
The regular supply of pure fresh air is another essential condition of healthy respiration, without which the requisite changes in the constitution of the blood, as it passes through the lungs, can not be effected. To enable the reader to appreciate this condition, it is necessary to consider the nature of the changes alluded to.
It is ascertained by analysis that the air we breathe is composed chiefly of the two gases nitrogen and oxygen, united in the ratio of four to one by volume, with exceedingly small and variable quantities of carbonic acid and aqueous vapor. No other mixture of these, or of any other gases, will sustain healthy respiration. To be more specific—atmospheric air consists of about seventy-eight per cent. of nitrogen, twenty-one per cent. of oxygen, and not quite one per cent. of carbonic acid. Such is its constitution when taken into the lungs in the act of breathing. When it is expelled from them, however, its composition is found to be greatly altered. The quantity of nitrogen remains nearly the same, but eight or eight and a half per cent. of the oxygen or vital air have disappeared, and been replaced by an equal amount of carbonic acid. In addition to these changes, the expired air is loaded with moisture. Simultaneously with these occurrences, the blood collected from the veins, which enters the lungs of a dark color and unfit for the support of life, assumes a florid hue and acquires the power of supporting life.
Physiologists are not fully agreed in explaining the processes by which these changes are effected in the lungs. All, however, agree that the change of the blood in the lungs is essentially dependent on the supply of oxygen contained in the air we breathe, and that air is fit or unfit for respiration in exact proportion as its quantity of oxygen approaches to, or differs from, that contained in pure air. If we attempt to breathe nitrogen, hydrogen, or any other gas that does not contain oxygen, the result will be speedy suffocation. If, on the other hand, we breathe air containing too great a proportion of oxygen, the vital powers will speedily suffer from excess of stimulus.
The chief chemical properties of the atmosphere are owing to the presence of oxygen. Nitrogen, which constitutes about four fifths of its volume, has been supposed to act as a mere diluent to the oxygen. Increase the proportion of oxygen in the atmosphere, and, as already stated, the vital powers will speedily suffer from excess of stimulus, the circulation and respiration become too rapid, and the system generally becomes highly excited. Diminish the proportion of oxygen, and the circulation and respiration become too slow, weakness and lassitude ensue, and a sense of heaviness and uneasiness pervades the entire system. As has been observed, air loses during each respiration a portion of its oxygen, and gains an equal quantity of carbonic acid, which is an active poison. When mixed with atmospheric air in the ratio of one to four, it extinguishes animal life. It is this gas that is produced by burning charcoal in a confined portion of common air. Its effect upon the system is well known to every reader of our newspapers. It causes dimness of sight, weakness, dullness, a difficulty of breathing, and ultimately apoplexy and death.[12]
Respiration produces the same effect upon air that the burning of charcoal does. It converts its oxygen, which is the aliment of animal life, into carbonic acid, which, be it remembered, is an active poison. Says Dr. Turner, in his celebrated work on chemistry, "An animal can not live in air which is unable to support combustion." Says the same author again, "An animal can not live in air which contains sufficient carbonic acid for extinguishing a candle." It will presently be seen why these quotations are made.
It is stated in several medical works that the quantity of air that enters the lungs at each inspiration of an adult varies from thirty-two to forty cubic inches. To establish more definitely some data upon which a calculation might safely be based, I some years ago conducted an experiment whereby I ascertained the medium quantity of air that entered the lungs of myself and four young men was thirty-six cubic inches, and that respiration is repeated once in three seconds, or twenty times a minute. I also ascertained that respired air will not support combustion. This truth, taken in connection with the quotations just made, establishes another and a more important