ANIMAL HEAT. 151 



in the course of twenty-four hours by a rise to the normal or a degree 

 beyond. During childhood the temperature approaches that of the 

 adult ; in aged persons the temperature remains about the same, 

 though they are not so capable of resisting the depressing effects of 

 external cold as adults. A diurnal variation of the temperature 

 occurs from 1.8 F. to 3.7 F. (Jiirgensen) ; the maximum occurring 

 late in the afternoon, from 4 to 9 P. M. ; the minimum, early in the 

 morning, from i to 7 A. M. 



Exercise. The temperature is raised from i to 2 F. during 

 active contractions of the muscular masses, and is probably due to 

 the increased activity of chemic changes ; a rise beyond this point 

 being prevented by its diffusion to the surface, consequent on a 

 more rapid circulation, radiation, more rapid breathing, etc. 



Food and Drink. The ingestion of a hearty meal increases the 

 temperature but slightly ; an absence of food, as in starvation, pro- 

 duces a marked decrease. Alcoholic drinks, in large amounts, in 

 persons unaccustomed to their use, cause a depression of the tem- 

 perature amounting to from i to 2 F. Tea causes a slight elevation. 



External Temperature. Long-continued exposure to cold, espe- 

 cially if the body is at rest, diminishes the temperature from i to 2 

 F., while exposure to a great heat slightly increases it. 



Disease frequently causes a marked variation in the normal tem- 

 perature of the body, which rises as high as 107 F. in typhoid fever 

 and 105 F. in pneumonia; in cholera it falls as low as 80 F. 

 Death usually occurs when the heat remains high and persistent, 

 from 106 to 110 F. ; the increase of heat in disease is due to 

 excessive production rather than to diminished elimination. 



The source of heat is to be sought for in the chemic decomposi- 

 tions and hydrations taking place during the general process of 

 nutrition, and in the combustion of the carbonaceous compounds by 

 the oxygen of the inspired air ; the amount of its production is in 

 proportion to the activity of the internal changes. 



Every contraction of a muscle, every act of secretion, each exhibi- 

 tion of nerve force, is accompanied by a change in the chemic com- 

 position of the tissues and an evolution of heat. The reduction of 

 the disintegrated tissues to their simplest form by oxidation, and 

 the combination of the oxygen of the inspired air with the carbon 

 and hydrogen of the blood and tissues, results in the formation of 

 carbonic acid and water and the generation of a great amount of 

 heat. 



