ANIMAL HEAT. 185 



plies this necessity by the difference of food, and of digestion, 

 of the inhabitants of these diverse regions. The principal 

 diet of the people within the torrid zone is of vegetable ori- 

 gin, while the inhabitant of the frigid zone lives mostly 

 upon flesh ; and the people who inhabit the countries in the 

 temperate zones, between these, have a mixed diet, in which 

 the meat predominates as they approach the arctic circle, 

 and the vegetable predominates towards the tropics. 



CHAPTER V. 



Other Influences may affect Supply of Heat. Some Diseases in- 

 crease, some diminish it. Fatigue and Exhaustion lessen Evo- 

 lution of Heat. Infants and old Men have less Heat. Less 

 Heat evolved in Sleep. Carbon consumed and Heat evolved in a 

 Day. Heat must be carried out of the Body through the Skin. 

 Evaporation of Perspiration carries off Heat. Greater Internal 

 Fire in cold than in warm Climates. Winter and Summer Con- 

 stitution. Animals cool more rapidly in Summer than Winter at 

 same Temperature. 



432. THIS chemical explanation of the origin of animal 

 heat is shown at length in Liebig's Animal Chemistry. 

 There are doubtless other influences that affect the develop- 

 ment of internal heat, beside the supply of carbon, hydrogen, 

 and pure air. It is ascertained by the later physiological 

 chemists that this process of combustion or combination 

 of oxygen with carbon and hydrogen accounts for only a 

 part of the heat that is developed in the animal body. " An- 

 imal heat is a phenomenon which results from the simulta- 

 neous activity of many different processes, taking place in 

 many different organs, and dependent, undoubtedly, on 

 different chemical changes in each one." * 



433. Even when the body is well supplied with both good 

 food and pure air, there is not an equal development of heat 

 in all states of the system. In some diseases, such as fever, 



* Dalton, Human Physiology, p. 263. 

 16* 



