262 



GENERAL PHYSIOLOGY 



the air of the chamber is expanded by the heat given off by the 

 animal, and from the amount of the expansion the quantity of 

 heat produced may readily be computed. Partly by one method 

 and partly by another, Dulong, Desprez, Helmholtz, Rosenthal, 

 and Rubner, have determined the quantity of heat produced by 

 the animal body. Since all such heat is derived from the chemical 

 energy of the food introduced into the body, and since all the 

 energy of the body, in case the latter performs no work, is 



Fig. 117. — Diilong's "water-calorimeter. A box with double walls ; the wide space between the 

 two walls contains water, through which a tube runs in spiral coUs to the interior of the box 

 for the admission of air from the outside at D to the animal, and for the removal of the used 

 air through D'. At T and T' are thermometers. (After Rosenthal.) 



transformed finally into heat, the quantity of chemical energy 

 that is introduced into the body with the food, expressed in 

 calories, must according to the law of the conservation of energy 

 be equal to the quantity of heat given off from the body to the 

 outside. As a matter of fact, in the experiments this result has 

 been attained with all desired exactness, and thus the validity of 

 the law of the conservation of energy for the living body has been 

 experimentally confirmed. 



4. The Production of Electricity 



As with heat, so thus far the production of electricity cannot be 

 proved upon the single cell, because even our most delicate 

 apparatus is too gross. Here also masses of cells are required. But 

 the production of electricity can be perceived without special means 

 of aid in far fewer cases than the production of heat, since all homo- 



