ANIMAL HEAT. 451 



THE PRODUCTION 0.1? THE BODY HEAT. 



The heat which is produced in the body arises from the metabolic 

 changes of the tissues, the chief part of which are of the nature of oxida- 

 tion, since it may be supposed that the oxygen of the atmosphere taken 

 into the system is ultimately combined with carbon and hydrogen, and 

 discharged from the body as carbonic acid and water. Any changes, 

 indeed, which occur in the protoplasm of the tissues, resulting in an 

 exhibition of their function, are attended by the evolution of heat and 

 the formation of carbonic acid and water. The more active the 

 changes the greater is the heat produced and the greater is the amount 

 of the carbonic acid and water formed. But in order that the proto- 

 plasm may perform its function, the waste of its own tissue (destructive 

 metabolism), must be repaired by the due supply of food material to be 

 built up in some way into the protoplasmic molecule. For the 

 production of heat, therefore, food is necessary. In the tissues, 

 as we have several times remarked, two processes are continually 

 going on: the building up of the protoplasm from the food (constructive 

 metabolism) which is not accompanied by the evolution of heat, possibly 

 even by its storing, and the oxidation of the protoplastic materials 

 resulting in the production of energy, by which heat is set free and 

 carbonic acid and water are evolved. 



It is not necessary to assume that the combustion processes, indeed, 

 are as simple as the bare statement of the fact might seem to indicate; 

 and, we have indicated, in treating of muscular metabolism, the process 

 appears to consist first of all of building up of the oxygen into the 

 molecule. But complicated as the various stages may be, the ultimate 

 re&nlt is as simple as in ordinary combustion outside the body, and the 

 products are the same. 



This theory that the maintenance of the temperature of the living 

 body depends on continual chemical change, chiefly by oxidation of 

 combustible materials in the tissues, has long been established by the 

 demonstration that the quantity of carbon and hydrogen as supplied as 

 food, which, in a given time, unites in the body with oxygen, is sufficient 

 to account for the amount of heat generated in the animal within the 

 same period : an amount capable of maintaining the temperature of the 

 body at from 36.8-3.87 C. (98-100 F.), notwithstanding a large 

 loss by radiation and evaporation. This estimation depends upon the 

 chemical Lxiom that when a body undergoes a chemical change the 

 amount of energy set free is the same, supposing the resulting products 

 are the same, whether the change takes place suddenly or gradually. If 

 a certain number of grammes of different substances are introduced as 

 food, and if they undergo complete oxidation, the amount of kinetic 



