HEAT AND FORCE 185 



perature may be looked upon as being a fairly constant 

 quantity. It varies scarcely at all with variations of exter- 

 nal temperature, so long as the heat-regulating apparatus is 

 in order. An external (dry) temperature of 212 F., or the 

 extremely low temperature of some regions, can be borne 

 with very slight fluctuations in that temperature of the body. 

 The actual limits of internal temperature consistent with the 

 preservation of life are given by Flint as 83 and 107 F. 

 These temperatures cannot be long endured. 



The fundamental fact to be kept constantly in mind is 

 that there is a continual production and a continual dissipa- 

 tion of heat, in ways to be indicated presently. These two 

 processes are known as thermogenesis (heat production) and 

 thermolysis (heat loss) respectively. The preservation of 

 the proper balance between heat production and heat dissipa- 

 tion is known as thermotaxis. 



Supply of Heat and its Relation to Force. It is a matter 

 of common observation that the burning (oxidation) of 

 any substance, as a piece of wood or an article of diet, is ac- 

 companied by the evolution of heat. It is also known that 

 heat may be converted into force may be made to do work. 

 The burning of a fat or a sugar produces CO2 and H2O ; the 

 burning of a proteid produces CCte and H2O, and additional 

 substances. The final products, and the amount of heat 

 evolved, are precisely the same whether the oxidation be 

 rapid or slow. Now, the oxidation of food is exactly what 

 occurs in the human organism, though that of the proteids is 

 not completely effected ; CO2 and H2O are produced from 

 them, and the "additional substances" mentioned are repre- 

 sented by urea. This process, then, is the source of body 

 heat. To the supply thus furnished may be added a little 

 from reactions between non-energy producing materials in 

 the body, from warm foods and drinks, and from friction in 

 the vessels, joints, etc. 



The foods thus possess a certain potential energy, an en- 

 ergy which may be converted directly or indirectly into heat, 



