MECHANISM OF THE PRODUCTION OF ANIMAL HEAT 405 



As regards the processes of combustion that take place in the 

 living organism, the oxidation of the constituents of food produces car- 

 bon dioxide and water ; but it is probable that the quantity of heat pro- 

 duced bears a definite relation to the total consumption of oxygen, the 

 heat, so far as this is concerned, being the same whether the oxygen 

 unite with carbon or with hydrogen. This relation between the quan- 

 tity of oxygen consumed and the production of heat seems to be dis- 

 turbed by muscular work ; but it has thus far been found impossible to 

 estimate accurately the quantity of heat represented by the force 

 expended in muscular work, circulation, respiration etc. 



The heat-producing processes undoubtedly are represented mainly 

 by the exhalation of carbon dioxide and water and to a less degree by 

 the discharge of urea, the quantity of heat produced by other chemical 

 changes being comparatively small. It is also true that the fats are 

 much more important factors in calorification than the proteids ; but 

 it seems beyond question that there must be heat evolved in the body 

 by oxidation of nitrogenous matters. When the daily quantity of food 

 is largely increased for the purpose of generating the heat required in 

 excessively cold climates, nitrogenous matters are taken in greater 

 quantity, as well as 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 meta- 

 morphoses of proteids have a certain share in the production of animal 

 heat. The. carbohydrates and fats are not concerned in the building up 

 of tissues and organs, except as fats are deposited in the form of adi- 

 pose tissue. Their addition to the food saves the nitrogenous tissues, 

 which latter must be used in heat-production in starvation and in a 

 restricted diet deficient in non-nitrogenous matters. If the non- 

 nitrogenous 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-nitrogenous constituents 

 of food are specially important in the production of animal heat and 

 that they are not concerned in the repair of tissue, it must be remem- 

 bered that the body-temperature may be kept at the proper standard on 

 a nitrogenous diet ; and it is not possible to connect calorification exclu- 

 sively with the consumption of any single class of alimentary matters. 



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

 understood. All physiologists, however, are agreed that the quantity 

 of heat produced by oxidation is the same, whether the combustion be 

 rapid or slow. The fact that fats are never discharged, but are either 



