NORMAL PROCESSES OF ENERGY METABOLISM 553 



countries outside of the United States the mean heat value to the body 



4.27 X 40 + 3.98 X 60 

 would be: - =4.100 Cal. which is the average 



value given by Rubner. 



The physiological heat values of fat and carbohydrate are found by the 

 Atwater method in the same manner except that no deduction is made for 

 the urine. The average utilization in the human subject for animal fat 

 being 95 per cent and for vegetable fat 90 per cent, and the bomb values 

 being 9.5 Cal. and 9.4 Cal. respectively, the value to the body is 9.02 and 

 8.46 Cal. for the two or 8.75 Cal. for food fats in general. For carbohy- 

 drates the factors are 4.2 CaJ. per gram bomb value, and 98 per cent utili- 

 zation. Therefore, the value to the body is 4.1 Cal. 



Both Rubner and Atwater have justified the heat values of the several 

 foodstuffs to the body by direct calorimetric experiments upon the dog and 

 man respectively. Rubner(/) hit upon a very clever method of confirming 

 his heat values with the aid of his calorimeter. In one experiment he fed 

 a dog a large amount of protein and a small amount of fat; in another 

 just the reverse. The metabolism was as follows: 



1st Exp. N elim. 10.09 gm. 



C. of fat oxidized 9.06 " 



Total Calories 379.50 Cal. 



2nd Exp. N. elim. 2.95 gm. 



C. of fat 19.12 " 



Total Calories 311.0 Cal. 



Let x be the heat value of a gram of nitrogen and y the heat value of a gram 

 of C from fat. Then, 10.09x + 9.06y = 379.5 Cal. 



2.95x+19.12y = 311.0 " 

 From which x = 26.70 Cal. 



y = 12.15 " 

 Now 1 gram of N corresponds to 6.49 grams pure protein of meat 



O A ^7 C\ 



hence 1 gm. = - - = 4.05 Cal. One gram C corresponds to 1.3 gm. 

 6.49 



12 15 



pure fat; hence 1 gm. = Cal. = 9.31 Cal. 



1.3 



Atwater in a series of 27 studies on human subjects, 14 of which were 

 carried out in the calorimeter devised by Rosa, found a difference between 

 the direct measurement of heat eliminated and the theoretical heat produc- 

 tion as calculated from his factors of less than 1 per cent, which may be 

 taken as satisfactory proof that these values for the human subject are 

 substantially correct. 2 



3 The only difference of any consequence between Rubner's and Atwater's values 

 applies to fat. Modern authorities who have been most under the influence of the 



