SOURCE OF ANIMAL HEAT. 17 



moderation in eating, and men can bear hunger for a 

 long time under the equator ; but cold and hunger united 

 very soon exhaust the body. 



The mutual action between the elements of the 

 food and the oxygen conveyed by the circulation of the 

 blood to every part of the body is THE SOURCE OF AN- 

 IMAL HEAT. 



III. All living creatures, whose existence depends 

 on the absorption of oxygen, possess within them- 

 selves a source of heat independent of surrounding 

 objects. 



This truth applies to all animals, and extends, be- 

 sides, to the germination of seeds, to the flowering of 

 plants, and to the maturation of fruits. 



It is only in those parts of the body to which arterial 

 blood, and with it the oxygen absorbed in respiration, is 

 conveyed, that heat is produced. Hair, wool, or feath- 

 ers do not possess an elevated temperature. 



This high temperature of the animal body, or, as it 

 may be called, disengagement of heat, is uniformly and 

 under all circumstances the result of the combination of 

 a combustible substance with oxygen. 



In whatever way carbon may combine with oxygen, 

 the act of combination cannot take place without the 

 disengagement of heat. It is a matter of indifference 

 whether the combination take place rapidly or slowly, at 

 a high or at a low temperature ; the amount of heat 

 liberated is a constant quantity. 



The carbon of the food, which is converted into car- 

 2* 



