ANIMAL HEAT. 263 



ingredients of the urine and the perspiration are discharged in larger 

 quantit y than usual. An increased supply of food also is required, 

 as well as a larger quantity of oxygen; and the digestive and 

 secretory processes both go on, at the same time, with unusual 

 activity. 



Animal heat, then, is a phenomenon which results from the 

 simultaneous activity of many different processes, taking place in 

 many different organs, and dependent, undoubtedly, on different 

 chemical changes in each one. The introduction of oxygen and 

 the exhalation of carbonic acid have no direct connection with each 

 other, but are only the beginning and the end of a long series of 

 continuous changes, in which all the tissues of the body successively 

 take a part. Their relation is precisely that which exists between 

 the food introduced through the stomach, and the urinary ingre- 

 dients eliminated by the kidneys. The tissues require for their 

 nutrition a constant supply of solid and liquid food which is intro- 

 duced through the stomach, and of oxygen which is introduced 

 through the lungs. The disintegration and decomposition of the 

 tissues give rise, on the one hand, to urea, uric acid, &c., which are 

 discharged with the urine, and on the other hand to carbonic acid, 

 which is exhaled from the lungs. But the oxygen is not directlv 

 converted into carbonic acid, any more than the food is directly 

 converted into urea and the urates. 



Animal heat is not to be regarded, therefore, as the result of a 

 combustive process. There is no reason for believing that the 

 greater part of the food is " burned" in the circulation. It is, on 

 the contrary, assimilated by the substance of the tissues ; and these, 

 in their subsequent disintegration, give rise to several excretory 

 products, one of which is carbonic acid. 



The numerous combinations and decompositions which follow 

 each other incessantly during the nutritive process, result in the 

 production of an internal or vital heat, which is present in both 

 animals and vegetables, and which varies in amount in different 

 species, in the same individual at different times, and even in 

 different parts and organs of the same body. 



