Animal Heat

All animals po e a certain amount of heat or temperature which is nece ary for the performance of vital action. The only cla es of animals in which a constantly-elevated temperature is kept up are birds and mammals. The bodily heat of the former varies from 39.4° to 43.9° C., and of the latter from 35.5° to 40.5° C. The mean or average heat of the human body is about 99° F., and it never falls much below this in health. Below birds, animals are named 'cold-blooded', this term meaning in its 173 strictly-physiological sense that their temperature is usually that of the medium in which they live, and that it varies with that of the surrounding medium. The temperature of 'warm-blooded' animals is remarkably constant, although there are individual variations. In man this variation is slight, amounting only to fractions of a degree. The cause of the evolution of heat in the animal body is referred to the union (by a proce resembling ordinary combustion) of the carbon and hydrogen of the system with the oxygen taken in from the air in the proce of respiration.