METABOLISM WITH A MIXED DIET. 913 



admitted, the amino-acids can serve in the building up of the proteins, 

 then there is no use denying that their amides can also be used by the 

 animal body. 



Recently GRAFE, ABDERHALDEN 1 and their collaborators have carried 

 on investigations on the value of ammonia and of urea as protein sparers 

 and protein formers. These investigations have shown that ammonia 

 or urea under special conditions of experimentation may cause a nitrogen 

 retention, but we are not justified in believing that a synthesis of protein 

 from ammonia takes place. 



Metabolism on a Diet Consisting of Protein, with Fat or Carbohydrates. 

 As the various foodstuffs can replace each other as sources of energy in 

 the food it follows that the non-nitrogenous foodstuffs can be used 

 instead of the proteins and can reduce the catabolism of these. Thus 

 the fat cannot completely arrest or prevent the catabolism of proteins, 

 but it can decrease it and so spare the proteins. This is apparent from 

 the following table by VoiT. 2 A is the average for three days, and B 

 for six days. 



Food. Flesh. 



Meat. Fat. Metabolized. On the Body. 



A 1500 1512 -12 



B 1500 150 1474 +26 



According to VOIT the adipose tissue of the body acts like the food- 

 fat, and the protein-sparing effect of the former may be added to that of 

 the latter, so that a body rich in fat may not only remain in nitrogenous 

 equilibrium, but may even add to the store of body proteins, while in a 

 lean body with the same food containing the same amount of proteins 

 and fat there would be a loss of proteins. In a body rich in fat a greater 

 quantity of proteins is protected from metabolism by a certain quantity 

 of fat than in a lean body. 



Like the fats the carbohydrates have a sparing action on the proteins. 

 By the addition of carbohydrates to the food, carnivora not only remain 

 in nitrogenous equilibrium, but the same quantity of meat which in 

 itself is insufficient and which without carbohydrates would cause a loss 



her., 27, and Zeitschr. f. Biologie, 39; Pfluger's Arch., 113; Kellner and Kohler, Chem. 

 Centralbl., 1, 1906; Voltz, Pfluger's Arch., 107, 117, with Yakuwa, ibid., 121; v. 

 Strusiewicz, Zeitschr. f. Biol., 47; Rosenfeld and Lehmann, Pfluger's Arch., 112; 

 Lehmann, ibid., 115; M. Miiller, ibid., 117; Henriques and Hansen, Zeitschr. f. physiol. 

 Chem., 54. 



1 Grafe, Zeitschr. f. physiol. Chem., 78, 82, 84, with Schlapfer, ibid., 77, with 

 Turban, ibid., 83; Voltz, ibid., 74; Abderhalden with Hirsch or Laupe, ibid., 80, 

 82-84; Peschek, Bioch. Zeitschr. 45. 



2 Voit, in Hermann's Handb., 6, 130. 



