458 BIOLOGICAL AND SANITARY MATTERS. 



nitrogen of proteins is not excreted as nitrogen, but as com- 

 pounds, of which urea may be taken as the type. 



Strohmer calculates that 1 gramme of average protein yields 

 O3428 gramme of urea, the heat of combustion of which is 

 2,537 calories per gramme ; the heat of combustion of the urea 

 from 1 gramme of proteins is, therefore, 869-7 calories, or, in 

 round figures, 15 per cent, of the total heat of combustion. It 

 is necessary, therefore, to deduct 15 per cent, of the heat of 

 combustion of proteins in calculating iso -dynamic metabolic 

 ratios. 



In round figures, the following will be the calories per gramme 

 developed in combustion of the three constituents in the human 

 body : 



Calories. 



Fat, 9,230 



Sugar, 3,950 



Proteins, . . . . . . 4,970 



These figures are in the ratio of 2-38 : 1 : 1-26. 

 The author proposes calculating the ratio between the various 

 constituents as follows : 



Anabolic ratio = fat : sugar : proteins. 



Metabolic ratio fat X 2 ' 38 + sugar + P roteins X 1<26 



Instead of the figures 2-38 and 1-26, the round figures 2-5 and 

 1 '25 may be used without appreciable error. The author believes 

 that the above ratios will give a truer idea of the porportionate 

 value of different constituents than the usual nutritive ratio, 



, . , . fat x 2-5 + sugar 

 which is - . 



protein 



Pood Value. We may now consider the food value of various 

 milks. 



The ratios for human milk are 



Anabolic ratio, . . . ,. . 2-2:4-5:1 

 Metabolic ratio, . . . . . 11-3 



For cow's milk 



Anabolic ratio, . . , . . 1*15:1 '14:1 

 Metabolic ratio, . v . . 5-54 



The marked difference of the two milks, due to the smaller 

 amount of proteins in human milk, is very apparent. 



It is assumed in calculating these ratios that the constituents 

 are all digestible ; this is true approximately with human milk. 



