RELATIONS OF ANIMAL HEAT TO NUTRITION. 



far been possible, only, to divide the food into different 

 classes. Of these leaving out oxygen we will consider, 

 in this connection, the organic matters, divided into nitro- 

 genized and non-nitrogenized. The inorganic salts are al- 

 ways combined with nitrogenized matter, and seem to pass 

 through the organism without undergoing any considerable 

 change ; and there is no evidence that they have any connec- 

 tion, of themselves, with the production of heat. 



What is the relation to calorification of those processes of 

 nutrition which involve the consumption of nitrogenized 

 matter and the production of the nitrogenized excrementi- 

 tious principles ? 



We cannot study these phenomena alone, isolated from 

 the other acts of nutrition. We may confine an animal to 

 a purely nitrogenized diet, and the heat of the body will be 

 maintained at the proper standard ; but at all times there 

 is a certain quantity of non-nitrogenized matter (sugar and 

 perhaps fat) produced in the system, which is only formed to 

 be consumed. We may starve an animal, and the tempera- 

 ture will not fall to any very great extent until a short time 

 before death. Here we may suppose that the process of de- 

 position of nutritive matter in the tissues from the blood is 

 inconsiderable, as compared with the transformation of the 

 substance of these tissues into effete matter ; and it is almost 

 certain that non-nitrogenized matter is not produced in the 

 organism in quantity sufficient to account, by its destruction 

 in the lungs, for the carbonic acid exhaled. It seems beyond 

 question that there must be heat evolved in the body by oxi- 

 dation of nitrogenized matter. When the daily amount of 

 food is largely increased for the purpose of generating the 

 immense amount of heat required in excessively cold cli- 

 mates, the nitrogenized matters are taken in greater quan- 

 tity, as well as the fats, although their increase is not in the 

 same proportion. When, however, we endeavor to assign 

 to the nitrogenized matters a definite proportion of heat-pro- 

 ducing power, we are arrested by a want of positive knowl- 



