Physiology of Animal Heat, 



206. Sources of Heat. 



Sources. The heat of the body is an uninterrupted evolution 

 of kinetic energy, which we must represent to ourselves as due to 

 vibrations of the corporeal atoms. The ultimate source of the heat 

 is contained in the potential energy taken into the body with the 

 food, and with the of the air absorbed during respiration. The 

 amount of heat formed depends upon the amount of energy liberated 

 (see Introduction). 



The energy of the food-stuffs may be called "latent heat," if we 

 assume that when they are used up in the body, chiefly by a process 



of combustion, kinetic 

 energy is liberated only 

 in the form of heat. As 

 a matter of fact, how- 

 ever, mechanical energy 

 g and electrical energy are 

 developed from the poten- 

 tial energy. In order to 

 obtain a unit measure for 

 the energy liberated, it is 

 advisable to express all 

 the potential energy as 

 heat-units. 



The Calorimeter. This 

 instrument enables us to 

 transform the potential 

 energy of the food into 

 heat, and, at the same 

 time, to measure the num- 

 ber of heat-units pro- 

 duced. 



Favre and Silbermann used a 



water-calorimeter (Fig. 166). 



The substance to be burned 

 is placed in a large cylindrical 

 combustion chamber (K), sus- 

 pended in a large cylindrical vessel (L) filled with water (w), so that the combustion 

 chamber is completely surrounded by the water. Three tubes open into the upper 



Eig. 166. 

 Water calorimeter of Favre and Silbermann. 



