Page:Popular Science Monthly Volume 10.djvu/676

656 that continuous work, which goes on day and night—a never-ceasing bellows-blowing, by which the organ of our life is kept in play. Of course, the quantity of air flowing round the surface of the human body is much greater than that. Do not object, that air is something so light that it need not be taken into account. It has some weight; water, certainly, is 770 times heavier, but our daily 2,000 gallons have for all that a weight of 25 pounds avoirdupois. Still, as it is not my intention to dwell here upon the subject of our oxygen-alimentation, I will to-day consider only the second use we make of the air, the cooling of our working machine.

You all know that life is bound up with chemical processes, kept in continual activity through the ingestion of solid and liquid food, and of oxygen from the air. One of the conditions for the normal performance of these processes is a definite temperature, above and below which they (although not brought to a standstill) go on differently—they leave off performing the functions of normal life—they lead to disease or death. With man this uniform temperature of his organs is one of the most essential conditions of his life. The blood of the negro living in the torrid zone of the equator is not by one-fifth degree warmer than that of the Esquimaux in the highest north at the coldest time of the year—it is always 99° Fahr. The extremes of temperature under which human life exists are 95 to 104° Fahr. in the tropics, and 57° to 84° under freezing-point in the polar regions. There are even differences of 72° in the mean monthly temperatures of some countries, and yet the organs of man are everywhere of the same temperature.

By what means is man enabled to meet such colossal differences? What are his weapons for sustaining this gigantic struggle?

Let us look a little nearer into the absolute quantities of heat the living organism has to manage. The chemical processes going on in an adult person, within the space of twenty-four hours, produce about 12,000 caloric units. By caloric unit natural philosophy designates that quantity of heat which is necessary to raise the temperature of one pound avoirdupois of water by one degree of Fahrenheit. By the heat produced by one person during one day about 660 gallons of water could be made warmer by nearly two degrees, or 7 gallons could be heated from freezing to boiling point, from 32° to 212° Fahr.

Under certain conditions man produces more or less heat; for instance, according to the quantity of food he takes, or the degree of muscular exertion he undergoes, such deviations from the mean amounting at times to 50 per cent. of the whole quantity; but it is always the task of the body, and a strict condition for the maintenance of health, to keep the heat of the blood substantially the same, or at least within two degrees.

We have to look upon ourselves as warm and humid bodies placed