92 



METABOLISM AND NUTRITION 



If we consider the faeces as pure loss (cf. page 90), the body has dis- 

 posed of (94.4 g. ingested 5.4 g. excreted =) 89.0 g. proteid containing 

 (16.2 - 2.0 =) 14.2 g. N, besides (82.5 - 3.7 =) 78.8 g. fat, and (289.8 - 

 3.2=) 286.6 g. carbohydrates. In the urine 16.2 g. N" were given off; but 

 2.0 g. of the N have come from the body itself i. e., (6.25 X 2 =) 12.5 g. 

 of the body's proteid has been lost. The total proteid metabolism, therefore, 

 has been (89 g. + 12.5 =) 101.5 g. (or 16.2 X 6.25). 



The ratio of N" to C contained in proteid is 1 : 3.28. In the proteid de- 

 stroyed by this man therefore there were 3.28 X 16.2 = 53.1 g. C. The total 

 quantity of C eliminated in the respiration and in the urine was 219.5 g. ; 

 there remain 166.4 g. which must have been derived from nonnitrogenous food. 



Of carbohydrates 286.6 g. (289.8 ingested 3.2 excreted) were absorbed 

 from the intestine, and this by calculation was found to have contained 124.7 

 g. C. Now we shall see later that carbohydrates burn in the body more easily 

 than fat. We therefore deduct first the C belonging to carbohydrate. This 

 leaves 41.7 g. C (166.4 124.7) which must have come from fat i. e., since 

 the fat used contained about seventy-six per cent C, 54.6 g. fat were burned 

 in the body. 



We conclude that the body has decomposed a mean quantity of 101.5 g. 

 proteid, 54.6 g. fat and 286.6 g. carbohydrate per day. Comparison with the 

 ingesta, having regard to the C resulting from proteid destroyed, shows that 

 the body has lost 12.5 g. of its proteid but has stored up 24.2 g. fat, containing 

 12.2 + 6.5 g. C. 



2. POTENTIAL ENERGY OF THE FOODSTUFFS 



The energy stored in a combustible substance is measured by the quantity 

 of heat generated in its combustion, and is constant for every individual 

 substance. The heat values of the substances most important for our present 

 purpose, as determined by the calorimeter, are given in the following table. 

 All data are for 1 g. of the substance and the heat values here, as elsewhere 

 in this discussion, are expressed in large Calories (Cal.). 



When fat or carbohydrates are burned in the body, they are completely 

 oxidized into carbon dioxide and water. If, therefore, the principle of con- 



Meat extracted with water, alcohol, and ether. 



