SOUKCES OF ANIMAL HEAT. 517 



far been possible, only, to divide the food into different classes. Of these, leaving out 

 oxygen, we shall consider, in this connection, the organic matters, divided into nitrogen- 

 ized-and non-nitrogenized. The inorganic salts are always combined with nitrogenized 

 matter, and they seem to pass through the organism without undergoing any considerable 

 change ; and there is no evidence that they have any connection, 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 the phenomena of calorification 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 quan- 

 tity of non-nitrogenized matter (sugar and perhaps fat) produced in the system, which is 

 formed only to be consumed. We may starve an animal, and the temperature will not fall 

 to any very great extent until a short time before death. Here we may suppose that the 

 process of deposition 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 oxidation 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 climates, the nitro- 

 genized matters are taken in greater quantity, 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-producing power, we are arrested by a want of 

 positive knowledge with regard to the metamorphoses which these principles undergo ; 

 and it is equally impossible to fix the relative calorific value of the deposition of new 

 material in repair of the tissues and the change of their substance into effete matter in 

 disassimilation. From these facts, and from other considerations that have already been 

 fully discussed under different heads, it is evident that the physiological metamorphoses 

 of nitrogenized matter bear a certain share in the production of animal heat ; although, 

 in connection with inorganic matter, their chief function seems to be the repair of the 

 tissues endowed with so-called vital properties. 



What is the relation of the consumption of non-nitrogenized matter to the production 

 of animal heat ? 



It has been impossible to treat of the relations of the non-nitrogenized elements to 

 nutrition without considering more or less fully the part which these principles bear in 

 the production of heat ; and we must refer the reader to the previous pages for a discus- 

 sion of certain of these points. In this connection, we shall simply state the relations 

 that this class of principles is known to bear to calorification, and the facts upon which 

 our statements are based. 



It has been pretty clearly shown that both sugar and fat are actually produced in the 

 organism, even when the diet is strictly nitrogenized in its character ; but we shall con- 

 sider only the relations of the non-nitrogenized elements introduced into the body, assuming 

 that the principles of this class appearing de now in the organism are the result of a trans- 

 formation of nitrogenized substances. 



As far as the destination of the amylaceous, saccharine, and fatty elements of food 

 is concerned, we only know that they are incapable, of themselves, of repairing muscu- 

 lar tissue, and that they cannot sustain life. They are never discharged from the body in 

 health in the form under which they enter ; but they are in part or completely destroyed 

 in nutrition. They are completely destroyed in persons who, from habitual muscular exer- 

 cise, have very little adipose tissue. When their quantity in the food is large, they are not 

 of necessity entirely consumed, but they may be deposited in the form of adipose tissue. 



