150 MAIXE AGRICULTURAL EXPERIMENT STATION. 



hydrogen to water. The nitrogen is left uncombined. When 

 protein is consumed in the body the oxidation is not complete. 

 The nitrogen is left in urea, uric acid and other allied com- 

 pounds, all of which contain carbon and hydrogen, together with 

 some oxygen. In estimating the actual fuel value of the 

 digested ingredients which an animal can utilize, allowance 

 must be made for these unconsumed residual products, which 

 are excreted by the kidneys. Urea is usually the most abundant 

 of these excretory products, and it is here assumed that all of 

 the nitrogen of the digested protein is excreted as urea. The 

 fuel value of urea as determined by Stohmann and Berthelot is 

 2.53 Calories per gram. 



'■'The method used in the calculations here has been as follows : 

 Urea rCOXoH^) contains 46.67 per cent of nitrogen. Hence 

 nitrogen multiplied by the factor 2.143 equals urea. The pro- 

 tein as here estimated is the nitrogen multiplied by 6.25. Hence 

 dividing the protein by 6.2^ and multiplying the quotient by 

 2.143 gives tlie equivalent urea. Assuming that all of the 

 digested protein is excreted as urea, the number of grams of 

 urea multiplied by 2.53 the fuel value of one gram of urea, gives 

 the total fuel value of the urea equivalent to the digested pro- 

 tein. But (protein divided b}- 6.25) X2. 143X2. 53-proteinX -87 

 This last expression, protein X-87, therefore, represents the fuel 

 value of the urea equivalent to the digestible protein." 



Combustions of urine have shown that the fuel value of the 

 organic matter of urine is higher than that of urea, ^^'hen 

 sufficient data have accumulated to warrant its adoption, an- 

 other factor will need to be employed; imtil then it is probably 

 better to use that for urea. As the total fuel value of the urea 

 and other organic materials found in urine is small in compari- 

 son with the fuel value of the food ingested, the error in the 

 assumption here involved is not a large one. 



