CHAPTER XIII. 



ANIMAL HEAT. 



General considerations Limits of variation in the normal temperature in man 

 Variations with external temperature Variations in different parts of 

 the body Variations at different periods of life Diurnal variations Rela- 

 tions of animal heat to digestion Influence of defective nutrition and in- 

 anition Influence of exercise, mental exertion, and the nervous system, 

 upon the heat of the body. 



THE process of nutrition in animals is always attended 

 with the development of heat, and produces a temperature 

 more or less independent of external conditions. This is true 

 in the lowest as well as the highest animal organizations ; 

 and analogous phenomena have even been observed in plants. 

 In cold-blooded animals, nutrition may be suspended by a 

 diminished external temperature, and certain of the functions 

 become temporarily arrested, to be resumed when the animal 

 is exposed to a greater heat. This is true, to some extent, 

 in certain warm-blooded animals that periodically pass into 

 a condition of stupor, called hibernation ; but in man, and 

 nearly all the warm-blooded animals, the general tempera- 

 ture of the body can undergo but slight variations. The 

 animal heat is essentially the same in the intense cold of the 

 frigid zones and under the burning sun of the tropics ; and 

 if, from any cause, the body become incapable of keeping up 

 its temperature when exposed to cold, or moderating it when 

 exposed to heat, death is the invariable result. 



The production of animal heat is so closely connected 

 with nutrition, that in serious pathological modifications of 



