OF ANIMAL HEAT. 87 



fecula or sugar, may be transformed into carbonic acid and 

 water, leaving no residue ; but the vital combustion of azotized 

 matters gives rise to other products ; and these compounds by 

 losing carbon become richer in azote, and constitute peculiar 

 organic principles, such as urea and uric acid.* 



173. Chemistry seems to prove that it is vegetables 

 which fabricate the combustible matters destined to be 

 consumed in animal bodies, plants alone having the power 

 thus to fix carbon under the form of organic compounds.f 



The carbonic acid gas and water escape by respiration ; the 

 more solid products, as the urea, by the urine. In the adult 

 animal it would thus seem, that there may be found nearly 

 the whole of the elements introduced into the system by the 

 food or by respiratory absorption, in the products of the respi- 

 ration and urinary secretion, the alvine dejections being com- 

 posed almost wholly of the indigestible residue of the food, 

 mingled with various secretions. 



Before the growth is completed, all the alimentary matter 

 is not burnt or consumed in this way ; a part is found in the 

 organism when the carbonaceous matters taken in exceed the 

 power of the oxygen to consume, the result being the deposi- 

 tion of fat, which may afterwards be consumed according to 

 the exigencies of the animal. 



To complete this sketch of the phenomena of nutrition, all 

 that remains is to speak of the sources of animal heat. 



OF ANIMAL HEAT. 



174. Animals vary so much in their different heat-pro- 

 ducing powers, that although all produce heat, some are 

 called cold-blooded animals with reference to others. The 

 difference may be shown by comparing the amount of heat 

 produced by a fish and a rabbit, placed in a vessel surrounded 



* When the tartrate, malate, or citrate of potass has been absorbed or 

 injected into the veins, and, so absorbed, carbonate of potass is found in the 

 urine, thus proving the combustion of the vegetable acid entering into their 

 composition. 



t According to the recent experiments of Dumas, Boussingault, and 

 Payen. 



J The fat is not deposited indifferently in every part of the body. It is com- 

 posed of two substances, oleineand stearine, the proportions of which vary in 

 the fat of different animals. It is abundantin animals which hybernate at the 

 commencement of winter, but disappears towards the close of that season. 

 The fat is supposed to be useful as a cushion for certain organs, as a reser- 

 voir to meet the consuming powers of the oxygen taken into the body, and as 

 a preservative of the heat of the body. 



