RELATIONS OF ANIMAL HEAT TO NUTRITION. 425 



tion. They are. completely destroyed in persons who, from 

 habitual muscular exercise, have very little adipose tissue. 

 "When their quantity in the food is large, they are not of 

 necessity entirely consumed, but may be deposited in the 

 form of adipose tissue. This, however, may be made to dis- 

 appear by violent exercise, or under an insufficient diet. 



There can be no doubt that the non-nitrogenized class of 

 alimentary principles is craved by the system in long-con- 

 tinued exposure to extreme cold. This is particularly marked 

 with regard to the fats. In all cold climates, fat is a most im- 

 important element of food ; and in excessively cold regions, 

 while the nitrogenized elements are largely increased, there is 

 a very much larger proportional increase in the quantity of 

 fat. These facts are very significant. If the non-nitrogen- 

 ized elements of food which are not always indispensable, 

 though often very necessary articles do not form tissue, are 

 not discharged from the body, and are consumed in some of 

 the processes of nutrition, it would seem that their change 

 must involve the production of carbonic acid, perhaps also of 

 water, and the evolution of heat. It is so difficult to ascer- 

 tain the exact quantities of carbonic acid, watery vapor, etc., 

 thrown off by the lungs, skin, and other emunctories, and to 

 estimate the exact amount of heat produced and lost, that it 

 is not surprising that calculations of the calorific power of 

 different articles of food should be frequently erroneous; 

 particularly as we have no means of knowing the exact calo- 

 rific value of the nitrogenized principles. 



Though we may assume that the non-nitrogenized ele- 

 ments of food are particularly important in the production 

 of animal heat, and that they are not concerned in the repair 

 of tissue, it must be remembered that the animal tempera- 

 ture may be kept at the proper standard upon an exclu- 

 sively nitrogenized diet ; and we cannot, indeed, connect 

 calorification exclusively with the consumption of any sin- 

 gle class of principles, nor with any single one of the acts 

 of nutrition. 



