570. As the primary object of the different processes of nutrition is to supply animal heat, so the action of the different nutritive organs is modified by the demands of the system for heat. When heat is rapidly removed from the body, the functional activity of the organs of nutrition is increased. When the system is warmed by foreign influence, the activity of the nutritive organs is diminished. This leads to the natural, and, we may add, instinctive change in the quality and quantity of food at different seasons of the year.
569. When is heat radiated from the body? When is it greatest? 570. What is the primary object of the different processes of nutrition? When is the activity of the nutritive organs increased? When diminished? To what does this lead?
CHAPTER XXVIII.
HYGIENE OF ANIMAL HEAT.
571. The amount of heat generated in man and inferior animals depends upon the quantity and quality of the food, age, exercise, the amount and character of the respired air, condition of the brain, skin, and general system.
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. 262 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.