SECTION XIII. 

 Animal Heat. 



It has been seen that the income of the animal body is represented 

 by complex combinations of carbon, hydrogen, nitrogen, and oxygen, and 

 the introduction of free oxygen in respiration ; the outgo of the body, 

 on the other hand, is represented by similar combinations of the same 

 elements in the form of carbon dioxide, water, and urea. 



The conclusion is thus evident that the absorbed oxygen has within 

 the body undergone combination with carbon and hydrogen with the 

 production of carbon dioxide and water, and that the substances intro- 

 duced as food have all in different degrees united with oxygen. In other 

 words, the nutritive processes in the animal body are represented by a 

 series of oxidations by which the organic food-products are restored to 

 the inorganic form. Oxidation of any kind will invariably be accom- 

 panied by a production of heat, and we thus see that one of the principal 

 sources of the heat of the animal body is to be looked for in such pro- 

 cesses of oxidation. It is a well-established fact that the combustion of 

 any body, whether rapidly or slowly produced, is accompanied by the 

 evolution of a fixed quantity of heat, provided the energy be not other- 

 wise employed. Thus, the complete combustion of one gramme of sugar 

 invariably corresponds to the development of four heat-units.* 



If this combustion takes place in the animal body, it is evident that 

 the same amount of heat must be developed, no matter what may be the 

 character of the substances developed between the starting point and the 

 final termination of the process of oxidation. 



In the animal body, however, such processes of combustion are 

 rarely as complete as would occur in the incineration of food-stuffs 

 outside of the body. Thus, for example, in albumen the process of 

 oxidation results in the formation of urea, which itself is capable of 

 still further oxidation. Nevertheless, it may be stated with a tolerable 

 degree of accuracy how much heat is set free in such processes of 

 oxidation of the food-stuffs in the animal body. Knowing the amount 

 of heat developed in the oxidation of one gramme of albumen and 

 the amount developed in the oxidation of a proportionate quantity of 

 urea, deducting the latter from the former will evidently represent the 



*By this term, heat-unit, is meant that amount of heat which is required to raise one 

 kilogramme of water from 0° C. to 1° C. 



(693) 



