572. _Animal heat is modified by the proportion of digestible carbon which the food contains, and by the quantity consumed._ As the kind of fuel that contains the greatest amount of combustible material evolves the most caloric when burned, so those articles of food that contain the greatest quantity of carbon produce the most heat when converted into blood. The inhabitants of the frigid zones, and individuals in temperate climates during the cold season, consume with impunity stimulating animal food, that contains a large proportion of carbon, while the inhabitants of the tropical regions, and persons in temperate climates during the warm season, are more healthy with a less stimulating or vegetable diet. _Observation._ When we ride or labor in cold weather, an adequate amount of nutritious food will sustain the warmth of the system better than intoxicating drinks. 573. _Age is another influence that modifies the generation of animal heat._ The vital forces of the child being feeble, less heat is generated in its system than in that of an adult. The experiments of Dr. Milne Edwards show that the power of producing heat in warm-blooded animals, is at its minimum at birth, and increases successively to adult age; and that young children part with their heat more readily than adults, and, instead of being warmer, are generally a degree or two colder. After adult age, as the vital powers decline, the generation of heat is diminished, as the energies of the system are lessened. Hence the young child, and the debilitated aged person, need more clothing than the vigorous individual of middle age. -=-=-=-=-=-=-=-=-=-=-=-= 571-585. _Give the hygiene of animal heat._ 571. State some of the influences that modify the generation of animal heat. 572. What element of the food influences the generation of heat? When and where can animal food be eaten with impunity? Give the practical observation. -=-=-=-=-=-=-=-=-=-=-=-= 574. _Exercise is an influence that modifies the generation of animal heat._ As carbon and hydrogen enter into the composition of the organs of the body, whatever increases the flow of blood in the system, increases also the deposition of new material, and the removal of the waste particles. This change among the particles of matter is attended with an elevation of temperature, from the union of oxygen with the carbon and hydrogen of the waste atoms. For this reason, a person in action is warmer than in a quiescent state. Consequently, the amount of clothing should be increased, when exercise or labor is diminished or suspended. 575. On the other hand, whatever impedes the circulation and the interchange of the atoms of matter, diminishes animal heat. Common observation shows, that the extremities are not as warm when tight gloves or boots are worn as when they are loose. One reason is, the circulation of blood is impeded, which is attended with less frequent change of the particles of matter.