Page:Popular Science Monthly Volume 2.djvu/417

Rh extended analysis has thus resulted in an instructive synthesis, which is one of the most signal acquisitions of the experimental method.

All animals have a temperature above that of the gaseous or fluid media in which they live; that is to say, they all possess the faculty of producing heat. Warm-blooded animals maintain an almost constant temperature in all latitudes and all climates. Thus, in polar regions, man, mammals, and birds, mark only one or two degrees less than they do at the tropics. The mean temperature of birds is 41° (cent.), and that of mammals 37°. Those animals called cold-blooded produce heat also, though in a less degree; but their temperature follows the variations of that of the surrounding medium, keeping, however, a temperature a few degrees higher than it. In reptiles, this excess varies from 5° to half a degree; in fish and insects, it is still smaller; and, in the wholly inferior species, it rarely reaches half a degree. In fine, with animals that vary in temperature, the power of resistance to external causes of refrigeration increases in proportion to the perfection of the organization. It is observed, too, that in these-beings vital activity and the force of respiration have a direct relation, to the thermometric state; thus, in a medium of 7°, lizards consume eight times less oxygen than at 23°. With animals of constant temperature, the reverse is the case; the colder it is, the more active is their respiration: a man, for instance, who, in summer, consumes only a fraction over an ounce of oxygen an hour, in winter consumes, more than an ounce and a half. Apart from the state of the surrounding medium, many different circumstances exert a perceptible influence on animal heat, and produce tolerably regular variations in it. The seasons, the times of day, sleep, digestion, mode of nourishment, age, etc., are thus constant modifiers of intensity of combustion/ in breathing; but there are such order and harmony, such foresight, one may say, in the organization of the system, that its temperature continues definitively nearly the same in the physiological state.

The temperature of the human body, at the root of the tongue or under the armpit, is about 37° (cent.); this figure expresses the mean found in taking the temperatures of different points of the body, for there are certain slight variations in this respect in passing from one organ to another. The skin is the coolest part; and the more so the nearer we come to the extremities. The temperature rises, on the contrary, with increasing depth of penetration into the organism; cavities are much warmer than surfaces. The brain is-cooler than the viscera of the trunk, and the cellular tissue cooler than the muscles. Nor does the blood have the same temperature in. all parts of the body. The labors of Davy and Becquerel established the fact that the blood is warmer the nearer to the heart examinations are made. Claude Bernard measured, by methods of equal ingenuity and