Page:Popular Science Monthly Volume 7.djvu/617

Rh as it becomes tainted, can insure perfect salubrity. Dr. Dalton estimated the average respiration of a man to be 24 cubic inches, and the average number per minute to be 20: consequently, 400 cubic feet pass through the lungs of an ordinary man in twenty-four hours; while the fallacy to which we have alluded assumes that a supply of 400 cubic feet in the room, in twenty-four hours, insures sufficient ventilation. Certainly, if any one would draw breath out of one bag, and discharge the tainted air from his lungs into another, he would always breathe good air. But it is calculated that a man will taint and render unwholesome by mixture 17,500 cubic feet of air in the twenty-four hours; for every respiration not only robs the imbibed 24 cubic inches of a certain portion of its oxygen, but it has mixed with it a quantity of carbonic-acid gas and some vapor; and theoretically, at least, the second respiration, drawn from a room in which the air is stagnant, begins the process of blood-poisoning.

The first rule, therefore, to be laid down in reference to perfect ventilation, prescribes the entire removal of the whole stratum of air tainted in a room by each respiration; for by no less a movement do we conceive it possible to take away the polluted air. This removal must be effected no less than twenty times per minute. Part of the expired air being rarefied by the heat of the lungs will rise, and part—the carbonic-acid gas—will fall. Twenty-four cubic inches, thus spread, may be assumed to taint a stratum, at or about a mouth of an occupant, of 18 inches. Any lateral movement would, in the case of several occupants, simply sweep the air breathed by one person close by the lips of some other; and hence we hold, as a corollary to this rule, that the prescribed movement should be either up or down, not lateral.

But the preceding calculation is based upon the minimum consumption of each person during quiescence. When talking, laughing, singing, walking, or dancing, the average respirations are, relatively, quickened, the consumption of air increased, and the necessity for a rapid change of atmosphere further enhanced. The amount of air inspired has been found to be as follows:

The above-ascertained accelerations of the respiratory organs sufficiently indicate the effect produced by all kinds of in-door exertion,