FUEL VALUE OF FOODS 



119 



stances is burnt in oxygen the quantities of heat 

 produced are as under : — 



Heat Value of Poods to Animal. — The amount of 

 heat produced by a food in the animal body may be 

 found by first ascertaining the quantity of heat pro- 

 duced when the food is burnt outside the body, and 

 then subtracting from this the heat produced by burn- 

 ing the soHd matter of the animal excrements obtained 

 during the consumption of the food by the animal. 

 The difference represents the net energy which 

 the body has received as the result of the feeding. 

 Besides the unburnt matter contained in the faeces 

 and urine, we must also in some cases take into 

 account the unburnt gases which escape from the 

 intestines, and also from the paunch of ruminant 

 animals, these gases consist of methane (CH^) with 

 a little hydrogen. The gases in question are not 

 produced from the albuminoids, or from the fatty 

 constituents of the food ; they are formed by the 

 fermentation of the carbohydrates. Those carbo- 

 hydrates which are quickly digested and absorbed, as 

 sugar and starch, yield a smaller proportion of methane 

 than cellulose, which remains longer in the intestines. 

 To estimate the unburnt gases given off by an animal 

 receiving a fixed ration, the animal must be placed 



1 This, and all other values for gluten, includes Kellner's subsequent 

 corrections in 1901. The gluten is reckoned at 16 per cent, of nitrogen. 



