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.
576. The quantity of air which is inhaled modifies the heat of the system. In the generation of heat in a stove, air, or oxygen, is as essential as the wood or coal. It is equally 263 so in the production of animal heat. The oxygen of the inspired air should be in proportion to the carbon and hydrogen to be consumed. This requires voluminous lungs, together with free movements of the ribs and diaphragm. A person whose chest is small, and whose apparel is worn tight over the ribs, suffers more from the cold, and complains more frequently of chilliness and cold extremities, than the broad-chested and loosely dressed.
What do the experiments of Dr. Milne Edwards show? 574. Why does exercise influence animal heat? 575. What is the effect when the circulation of blood is impeded? Give examples. 576. Why do those persons that have broad chests and voluminous lungs suffer less from cold than the narrow-chested with small lungs?
Observation. Fishes that breathe by means of gills, as the cod, pike, &c., depend solely on the small quantity of oxygen that is contained in the air mixed with the water. Their temperature is not much greater than the medium in which they live. Whales, dolphins, &c., breathe by means of lungs, and the inhalation of atmospheric air makes their temperature about 100°, independent of the heat of the element in which they live.
577. The quality of respired air influences the generation of animal heat. In vestries, and other public rooms, when crowded with an audience, where the ventilation is inadequate, the lamps will emit but a faint light, because the oxygen is soon expended, and there is not enough of the vivifying principle to unite with the oil and disengage light. In the human body, when the respired air has lost some of its life-giving properties, the combustion that takes place in different parts of the system is not so complete as when it contains a proper proportion of oxygen; and hence less heat is disengaged. For this reason, those persons that breathe impure air, either in the daytime or night, require more clothing, than those that work and sleep in well-ventilated rooms.
578. The condition of the brain and nervous system affects 264 the generation of animal heat. If the brain is diseased, or the mind is absorbed in thought, depressed by sorrow, or aroused from fear, the breathing becomes slow and scarcely perceptible, and a chilliness pervades the body, particularly the extremities; while, on the contrary, if the mind and nervous system are excited by joyous and agreeable emotions, the circulation of blood is quicker, and the system more powerfully resists external cold. During sleep, when the brain is partially inactive, less heat is generated than when awake.
What is said of those fishes that breathe by means of gills? Of those that breathe by means of lungs? 577. Why do lamps give but a faint light in crowded, unventilated rooms? What effect on animal heat has impure air? 578. Mention the effects of some of the mental emotions on animal heat.
Observation. The preceding remark explains why an individual who sleeps in the same clothing that was adequate to prevent chills while awake, contracts a cold, unless he throws over him an additional covering.