Page:Popular Science Monthly Volume 2.djvu/418

402, the temperature of deep vessels and the cavities of the heart. He showed that blood, in passing out from the kidneys, is warmer than when it enters, and the same is true of blood passing through the liver, lie ascertained, too, that the vital fluid is chilled in going through the lungs, and consequently the temperature of the left cavities of the heart is lower than that of the right, by an average of two-tenths of a degree. The last fact clearly proves that the lungs are not the furnace of animal heat, and that the blood, in the act of revivification, grows cool instead of warm.

Ancient physiologists supposed that life has the power of producing heat; they conceived of a kind of calorific force in organized beings. Galen imagined that heat is innate in the heart—the chemic-physicians attributed it to fermentations, the mechanic-physicians to frictions. Time has dispelled these errors of supposition, and it is proved now that the heat of animals proceeds from chemical reactions taking place in the interior of the system. Lavoisier must be credited with the demonstration of this truth by experiment, As early as 1777 he discovered that air, passing through the lungs, undergoes a decomposition identical with that which takes place in the combustion of coal. Now, in the latter phenomenon, heat is thrown off; "therefore," says Lavoisier, "there must be a like release of heat in the interior of the lugs, during the interval between inspiration and expiration, and it is doubtless this caloric, diffusing itself with the blood throughout the animal economy, which keeps up a constant heat in it. There is, then, a constant relation between the heat of the living being and the quantity of air introduced into the lungs, to be there converted into carbonic acid." Such is the first capital fact brought to light by the creator of modern chemistry; but he did not rest there. He undertook to examine whether the heat theoretically produced in a given time by the formation of a certain amount of carbonic acid, that is to say. by the combustion of a certain quantity of carbon in the organism, is exactly equal to the amount of heat developed by the animal in a corresponding time. This quantity was estimated by the weight of ice melted by the animal placed in a calorimeter. Lavoisier ascertained in this way that such equality does not exist, nor was he long surprised at this, for he soon discovered that, of 100 parts of atmospheric oxygen absorbed, only 81 are thrown off by the breath in the form of carbonic acid. He concluded then, from this observation, that the phenomenon is not a simple one, that a part of the oxygen (nine per cent.) is consumed in burning hydrogen, to form the vapor of water contained in the expired air. Animal heat must be accounted for, then, by a double combustion: of carbon first, then of hydrogen; and respiration regarded as throwing off out of the animal carbonic acid and vapor of water.

Lavoisier's experiments have been repeated and varied, and his conclusions' discussed in many ways for nearly a hundred years.