874 



METABOLISM. 



Heat value of foodstuffs. A most important determination to be 

 made regarding any diet is its caloric (calorific) value. This is arrived at 

 by multiplying the number of grammes of its several organic constituents 

 by a number, determined by exact experiment, representing the amount 

 of heat produced by the oxidation of 1 grm. of the carbohydrate, fat, or 

 proteid to water and carbon dioxide and to urea. Such calorimetric 

 experiments were first carried out systematically by Frankland, 1 who 

 determined the caloric value of various articles of diet, and his results 

 have since been extended and confirmed or amended by various 

 observers, 2 using improved calorimetric methods. 



According to Eubner, the average caloric value of the proteid of the 

 aliment is 4124 calories, i.e. I grm. proteid oxidised to urea yields 4124 

 grm. degrees (or 41 kilogram-degrees) of heat ; of the fat, 9321 calories 

 (9-3 kilogram-degrees); and of the carbohydrate (starch), 4116 calories 

 (41 kilogram-degrees). Applying these numbers to Voit's diet (see 

 next page), we obtain in round numbers 



105 grms. assimilated proteid x 41 = 430 



56 fat x 9-3 - 520 



500 carbohydrate x 41 = 2050 



= 3000 kilo-calories, 



or 3,000,000 calories, as the energy value per diem of the food of a man 

 of about 70 kilos., doing hard muscular work. 



This amount is probably a little too high, since the whole of the fat and 

 carbohydrate of a mixed diet is not assimilated. Rubner estimates the actual 

 production at 2,843,000 calories. Hultgren and Lantergren, however, found 

 that Swedish workmen, of an average weight of only 67 kilos., consumed on an 

 average per diem 159 grms. proteid, 93 grms. fat, and 570 grms. carbohydrate, 

 which, even allowing for the non-assimilation of a certain proportion of each, 

 would still give a higher caloric value for the total foodstuffs. Probably, 



1 "On the Origin of Muscular Power," London, Edinburgh, and Dublin Phil. Mag., 

 London, 1866, vol. xxxii. p. 182. 



2 Stohmann, Journ. f. prakt. Chem., Leipzig, 1879, Bd. xix. S. 115 ; Ztschr. f. Biol, 

 Miinchen, 1894, Bd. xxxi. S. 364 ; Danilewsky, Arch. f. d. gen. Physiol., Bonn, 1885, Bd. 

 xxxvi. S. 237 ; Rubner, Ztschr. f. Biol., Miinchen, 1883, Bd. xix. S. 313; 1885, Bd. xxi. 

 S. 250 u. 337 ; 1886, Bd. xxii. S. 40 ; 1894, Bd. xxx. S. 73. 



