Animal Heat

Animal Heat, the heat produced in animal bodies as the result of the processes of chemical decomposition which take place in them. The oxygen absorbed by the lungs in combining with certain elements, and again, the food in undergoing certain changes within the body, are mainly accountable for the heat evolved. In some animals, which are therefore called warm-blooded, the temperature of the body only varies within very narrow limits. Thus the body temperature in man, whether he dwell at the equator or in the arctic regions, never deviates in health far from the standard, which is 98.6° F. It is usually somewhat higher in the afternoon, and falls to its lowest point in the early morning; again, it rises a little after food or exercise. Cold-blooded animals, however, do not possess this power of maintaining a constant body temperature. Indeed, their temperature differs but little from that of the medium, whether air or water, in which they live. Roughly speaking, among vertebrates mammals and birds belong to the class of warm-blooded, and fish, reptiles, and amphibia to that of cold-blooded animals. The regulation of the body heat in those animals whose temperature remains constant is largely effected by variations in the amount of heat given out. Thus in a warm atmosphere the capillaries of the skin are dilated, and much heat is lost by perspiration, while the exposure to cold air produces a diminution of the blood supply to the skin and a consequent diminution in loss of heat. But a second factor which is concerned in maintaining a constancy of temperature is variation in the amount of heat produced. The parts of the body in which chemical changes resulting in heat production are most active are the muscles, the liver, and the brain. The kind of food again has an influence in this matter. Fats are eminently heat giving foods, and it is noteworthy that much fat is consumed by dwellers in cold or temperate regions, while it is avoided as an article of diet in tropical countries.