Part 37 (2/2)

_Observations._ 1st. The first discovery of the use of free evaporation of the perspiration from the skin in reducing the heat of the body, and the a.n.a.logy subsisting between this process and that of the evaporation of water from a rough porous surface, so constantly resorted to in warm countries, as an efficacious means of reducing the temperature of the air in rooms, and of wine and other drinks, much below that of the surrounding atmosphere, was made by Franklin.

2d. In all ages and climes, it has been observed that the increased temperature of the skin and system in fevers, is abated as soon as free perspiration is restored. In damp, close weather, as during the sultry days of August, although the temperature is lower, we feel a disagreeable sensation of heat, because the saturation of the air with moisture lessens evaporation, and thus prevents the escape of heat through the lungs and skin.

3d. It is on the principle of the evaporation of fluids that warm vinegar and water, applied to the burning, aching head, cools it, and imparts to it a comfortable feeling. The same results follow if warm liquids are applied to the skin in the hot stage of fever; and this evaporation can be increased by constant fanning.

568. What are the princ.i.p.al means by which a uniform temperature of the body is maintained? On what does the quant.i.ty of heat abstracted from the system depend? What discovery relative to animal heat is due to Franklin? What is said of free perspiration in fevers? What occasions the disagreeable sensation of heat in damp, close weather?

4th. It is frequently noticed, in very warm weather, that dogs and other domestic animals are seen with their tongues out of their mouths, and covered with frothy secretions. This is merely another mode of reducing animal heat, as the skin of such animals does not perspire as much as that of man.

569. Under some circ.u.mstances, a portion of the heat of the system is removed by radiation. When cold air comes in contact with the skin and mucous membrane of the lungs, heat is removed from the body, as from a stove, to restore an equilibrium of temperature. The removal of heat from the body is greatest when we are in a current of cold air, or when a brisk, cold wind is blowing upon us.

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 quant.i.ty 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 quant.i.ty 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 quant.i.ty 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 quant.i.ty 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.

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