39 



body, however, the oxidation is not so complete. The nitrogen is 

 excreted in the urine largel}' in the form of urea, but with some uric 

 acid and other allied compounds which also contain small amounts of 

 carbon and hydrogen together with some oxygen. In estimating the 

 actual fuel values of the digestible nutrients, allowance must be made 

 for these incompletely oxidized residual products which are excreted by 

 the kidneys. Urea is the most abundant of these products, and in 

 lack of determinations of the actual heats of combustion of these 

 incompletely oxidized products, estimates have sometimes been made 

 on the assumjition that all of the nitrogen excreted in the urine 

 is thus combined, and allowance has been made for the heat of com- 

 bustion of the amount of urea corresponding to the amount of nitro- 

 gen found in the urine or in the digestible protein in the food 

 consumed. On this supposition 0.87 calorie of the energy latent in 

 each gram of digestible ijrotein would be lost to the bodj^ in the urea 

 corresponding to the nitrogen of such protein. In a considerable 

 number of actual determinations of the ratio of the nitrogen to heat 

 of combustion in urine of healthy men, the average heat of combus- 

 tion of the organic matter in the urine corresponding to 1 gram of 

 digestible protein was found to be considerably greater than 0.87 

 calorie, and in the digestion work of the nutrition investigations of 

 this Office it has been decided to use for the present, and until a 

 more accurate factor has been ascertained, the factor 1.25 calories as 

 more nearly corresponding to the energ}^ of the urine for a gram of 

 digestible protein. The figures given in the tables for the proportion of 

 energy actually available to the body in the food eaten were obtained, 

 therefore, by deducting from the total energy of the digested food the 

 energy lost to the body in organic matter of the urine as determined 

 by multiplying the total amount of digestible protein by 1.25. 



Digestion Experiment No. 463. 



Kind and amounts of food. — A mixed diet with large amounts of 

 baked beans, corned beef, biscuits, etc. 



Subject. — A. F. 



Age. — Twentj'-three years. 



Weight {until clothing). — At the beginning of the experiment, 162 

 pounds. 



Duration. — Six days, with 18 meals, beginning with dinner Decem- 

 ber 3, 1902. 



The daily menu, as well as the amounts of the individual foods 

 eaten at each meal, was as follows : 



