192 AN AGRICULTURAL WAR PROBLEM 



the body. For instance the heat of combustion of 

 protein per gram is 5*80 cal. The difference be- 

 tween this figure and the nett value of 4-70 cal. is 

 due to the fact that when protein is burned outside 

 the body it is burned completely, but when it is 

 oxidized in the body the oxidation is not complete, 

 only proceeding as far as urea, uric acid, hippuric 

 acid and similar compounds. The difference be- 

 tween the gross heat of combustion of 5-80 cal. and 

 the nett heat value of 4*70 cal. is the heat value 

 left in these incompletely oxidized compounds. 

 The animal is able to obtain practically the whole 

 of the heat value of the fats in its food: the gross 

 heat of combustion and the nett heat value to the 

 animal are the same. Carbohydrates are subject 

 to fermentation in the digestive organs of the 

 animal. Marsh gas and similar products are pro- 

 duced and cause a loss of about 10 per cent, of the 

 heat value of these nutrients. The difference be- 

 tween the gross heat of combustion of carbohy- 

 drates, 4* local, per gram, and the nett value to 

 the animal, 3-76 cal. per gram, is due to this 

 cause. The last column in Table III gives the 

 relative nett heat values to the animal of proteins 

 and fats, the nett value of carbohydrates being 

 taken as unity. 



From these figures it is possible to calculate the 

 starch equivalent of any food from its content of 

 digestible nutrients. Thus the starch equivalent 

 will be the sum of the percentage of digestible 



