THE ENERGY OF THE METABOLISM 185 



to have involved these materials rather than protein and 

 fat. The supposition has already been entertained and 

 may now be made a basis for indirect calorimetry. From 

 p. 180 we copy the amounts of protein and carbohydrate, 

 multiplying by 4.1, the value common to both: 



100 grams protein 410 Calories. 



430 carbohydrate J_763 " 



Total 2173 . " 



Comparing this sum with the 2489 Cal. previously de- 

 termined, we see that for a given production of carbon di- 

 oxid the evolution of heat will be greatest when fat is the 

 exclusive non-protein source, and least when the metabo- 

 lism is as nearly as possible on a carbohydrate footing. 

 The difference is some 15 per cent. 



If both carbohydrate and fat had participated in the 

 decomposition underlying the observed excretion, the heat 

 of the metabolism might have had any value intermediate 

 between 2173 and 2489 Cal. The figure obtained by 

 direct calorimetry might in such a case of mixed metabolism 

 be used to determine the part borne by carbohydrate and 

 fat respectively. How this could be done, roughly at least, 

 may be shown here. Suppose the total heat production to 

 be 2300 Cal. (The data regarding excreta are still as- 

 sumed to be as before, 16 grams of nitrogen and 225 grams 

 of carbon.) We can first deduct from 2300 the 410 Cal. 

 necessarily assigned to the protein metabolism. The 

 remainder, 1890 Cal., stands for the heat released in the 

 oxidation of glycogen and fat. We can now write simul- 

 taneous equations as below: 



Let x = the carbon from fat. 



y " carbohydrate. 



Then x + y = 172 (carbon from non-protein sources, page 171). 

 Also 1.3 X 9.3z -f- 2.5^ X 4.1 = 1890 (remembering that by mul- 

 tiplying the carbon in 

 fat by 1.3 we obtain the 

 fat represented, and that 

 by multiplying this re- 

 sult in turn by 9.3 we 

 get the calories. The 

 case of the carbohydrate 

 is parallel). 



