THE ENERGY EQUATION. 395 



The number of calories furnished by burning i gm. of sub- 

 stance in each case is given. 



TABLE OF HEATS OF COMBUSTION. 



Hydrogen 34,200 Cane sugar 4,000 



Carbon 8,100 Starch 4,200 



Ethyl alcohol 7,060 Casein 5,7oo 



Glycerol 4,200 Egg albumin 5,7oo 



Mannitol 4,000 Urea 2,500 



Palmitic acid 9,300 Uric acid 2,700 



Stearic acid 9,400 Leucine 6,500 



Fats, average 9,400 Tyrosine 6,000 



Hexoses 3,7oo Creatine, anhyd 4,250 



These values are for complete combustion, but as the proteins 

 in the body are not oxidized to leave water, carbon dioxide 

 and nitrogen, we must subtract from the given values the 

 heats of combustion of the urea, uric acid, creatine and other 

 products found in the urine, in order to secure the physiolog- 

 ical heats of combustion with which we are practically con- 

 cerned. 



DISTRIBUTION OF FOOD ENERGY. 



With these preliminary considerations we are able to look 

 at the manner in which the energy of the consumed food is 

 distributed. On the one side we have the substance burned, 

 on the other the products, which may be represented diagram- 

 matically in this way : 



Potential energy of 



Food. 



Potential energy of 



Flesh gained. 

 Feces. 

 Urine. 



Perspiration. 

 Kinetic energy of 



Work. 

 Heat. 



Experimentally, the whole of the kinetic energy may be 

 made to take the form of heat, which simplifies the observa- 

 tions materially. It is practically possible to determine the 

 heat liberation in the large respiration calorimeters already re- 

 ferred to, and the use of such apparatus will be explained 



