MECHANISM OF THE PRODUCTION OF HEAT. 455 



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

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

 discussed, it is evident that the physiological metamorphoses of nitrogenized 

 matters bear a certain share in the production of animal heat. The carbo- 

 hydrates and fats are not concerned in the building up of tissues and organs, 

 except as the fats are deposited in the form of adipose tissue. Their addition 

 to the food saves the nitrogenized tissues, which latter must be used in heat- 

 production in starvation and in a restricted diet deficient in non-nitrogenized 

 matters. If the non-nitrogenized constituents of food 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 

 carbon dioxide and water and the evolution of heat. 



Although it may be assumed that the non-nitrogenized constituents 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 temperature may be kept at the proper standard upon a nitrogen- 

 ized diet ; and it is not possible to connect calorification exclusively with the 

 consumption of any single class of alimentary matters or with any single 

 one of the acts of nutrition. 



The exact mechanism of the oxidation-processes in the body is not under- 

 stood. All physiologists, however, are agreed that the quantity of heat pro- 

 duced by oxidation is the same, whether the combustion be rapid or slow. 

 The fact that fats are never discharged, but are either consumed entirely or 

 are deposited in the body as fat, leaves their oxidation and discharge as oxi- 

 dation-products the only alternative. The oxidation of albuminoids has 

 already been considered. As regards the carbohydrates, if it can be shown 

 that alcohol normally exists in the blood, even in very small quantity, the 

 idea that these matters are slowly passed from the liver as sugar, into the 

 general circulation, and are then converted into alcohol which is promptly 

 oxidized, is worthy of serious consideration. Such a theory would explain 

 the destination of the carbohydrates and their relations to calorification. 

 There can be no doubt that in certain cases of fever, alcohol administered in 

 large quantity may be oxidized and " feed " the fever, thus saving consump- 

 tion of tissue. 



In a series of observations made in 1879 (Flint), it seemed impossible to 

 account for the heat actually produced in the body and expended as force in 

 muscular work etc., by the heat- value of food and of tissue consumed. The 

 estimates of heat-production, made by the direct method, were then adopted; 

 but even the indirect estimates, which were much less, presented difficulty, 

 though in a less degree. In these observations, it was shown that water was 

 actually produced in the body in quantity over and above that contained in 

 food and drink, during severe and prolonged muscular exertion. It was 

 also shown that water was produced in considerable quantity during twenty- 

 four hours of abstinence from food. It has been shown by Pettenkofer and 

 Voit that " the elimination of water is very much increased by work, and 

 the increase continues during the ensuing hours of sleep." As regards the 



