FOODS ANIMAL PRODUCTION. 



781 



experiments with single food materials and a mixed diet were made 

 under the direction of the author by the usual methods, which have 

 been described in detail in a previous publication. 1 



The fuel value of the food, urine, and feces was determined. The 

 fact is pointed out that the fuel value of the food minus the fuel value 

 of the l'eces does not represent the energy which is available lor the 

 organism, since nitrogen is excreted in the form of urea. 



"Assuming that nil of the digested nitrogen excreted from the body is in the form 

 of urea, we may roughly calculate the amount of the potential energy of protein 

 which thus fails to he transformed into kinetic energy in the body. 



" Urea contains 4li.fi7 per cent nitrogen, hence N.'x 2.143=urea. N. X 6.25 = pro- 

 tein. Hence protein divided by 6.25 X 2.143 = the urea corresponding to the protein. 

 The heat of combustion of 1 gm. of urea is 2.53 calories. The fuel value of the urea 



corresponding to 1 gm. of protein would therefore be ~ -,j~ X 2.141! x 2.53, or 0.87 



calories. 



"According to this computation, which is theoretical and but approximately cor- 

 rect, there would be for each gram of digested protein 0.87 calories of energy in the 

 unconsumed urea and other compounds. Subtracting this value from the total fuel 

 value of the digested nutrients the remainder may be assumed to represent the pro- 

 portion of the total energy of the digested nutrients which becomes actually avail- 

 able to the body. This is designated in the tables as 'net fuel value of the food 

 digested.'" 



The results of the experiments are briefly shown in the following 

 table: 



Coefficients of digestibility of a number of foods by man. 



Subjects and food materials. 



Protein. 



Fat. 



Carbohy- 

 drates. 



Net fuel 

 value. 



Laboratory janitor. 



Milk 



Do 



Ito 



Wheat bread 



Do 



Bread and milk 



Beef round, milk, butter, oatmeal, bread. BUgar 



Beef round, eggs, butter, cheese, milk, crackers, bread, pota 

 toes, sugar. .V 



Do... 



Chemist. 



Beef round, eggs, butter, milk, bread, potatoes, apples 

 peaches, pears, sugar 



Physicist. 



Beef round, butter, milk, white bread, brown bread, oat 

 meal, beans, potatoes, apples, sugar 



Three chemists. 



Mixed diet (meat, eggs, bread, vegetables, fruit, etc) , 



Percent. 



88.1 

 90.9 



05. 6 

 91.9 



82.3 

 97. G 

 94.4 



95.9 

 91.8 



Per rent. 

 97.0 

 95. :> 

 98.1 



98. 



0G. 7 



07.4 

 97.1 



/'. reent. 



si. I 

 85.0 

 89.5 



(10. 4 



OS. 7 



o-.:. 



97.0 



OS. i 



89. 4 

 89.3 



94. G 

 02. 4 



95. 2 

 93.3 



03.2 

 92.6 



"The results of the first ~> experiments are not entirely reliable indications of the 

 actual digestibility of milk and bread as ordinarily eaten, partly because of defects 

 in the experiments themselves, and partly because of the probability that these 

 materials, taken by themselves, are not digested as completely as when they form a 

 part of a mixed diet. . . . 



U. S. Dept. Agr., Office of Experiment Stations Bui. 21 (E. 8. R., 7. p. 148;. 



