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 truth, viz., that air once respired will not further sustain animal life. That part of the experiment by which it was ascertained that respired air will not support combustion is very simple, and I here give it with the hope that it may be tried at least in every school-house, if not in every family of our wide-spread country. It was conducted as follows:
I introduced a lighted taper into an inverted receiver (glass jar) which contained seven quarts of atmospheric air, and placed the mouth of the receiver into a vessel of water. The taper burned with its wonted brilliancy about a minute, and, growing dim gradually, became extinct at the expiration of three minutes. I then filled the receiver with water, and inverting it, placed its mouth beneath the surface of the same fluid in another vessel. I next removed the water from the receiver by breathing into it. This was done by filling the lungs with air, which, after being retained a short time in the chest, was exhaled through a siphon (a bent lead tube) into the receiver. I then introduced the lighted taper into the receiver of respired air, by which it was immediately extinguished. Several persons present then received a quantity of respired air into their lungs, whereupon the premonitory symptoms of apoplexy, as already given, ensued. The experiment was conducted with great care, and several times repeated in the presence of respectable members of the medical profession, a professor of chemistry, and several literary gentlemen, to their entire satisfaction.
Before proceeding further, I will make a practical application of the principles already established. Within the last ten years I have visited half of the states of the Union for the purpose of becoming acquainted with the actual condition of our common schools. I have therefore noticed especially the condition of school-houses. Although there is a great variety in their dimensions, yet there are comparatively few school-houses less than sixteen by eighteen feet on the ground, and fewer still larger than twenty-four by thirty feet, exclusive of our principal cities and villages. From a large number of actual measurements, not only in New York and Michigan, but east of the Hudson River and west of the great lakes, I conclude that, exclusive of entry and closets, when they are furnished with these appendages, school-houses are not usually larger than twenty by twenty-four feet on the ground, and seven feet in height. They are, indeed, more frequently smaller than larger. School-houses of these dimensions have a capacity of 3360 cubic feet, and are usually occupied by at least forty-five scholars in the winter season. Not unfrequently sixty or seventy, and occasionally more than a hundred scholars occupy a room of this size.
A simple arithmetical computation will abundantly satisfy any person who is acquainted with the composition of the atmosphere, the influence of respiration upon its fitness to sustain animal life, and the quantity of air that enters the lungs at each inspiration, that a school-room of the preceding dimensions contains quite too little air to sustain the healthy respiration of even forty-five scholars three hours—the usual length of each session; and frequently the school-house is imperfectly ventilated between the sessions at noon, and sometimes for several days together.