506 DIGESTION. 



the coagulable proteins are constructed by synthesis. In support 

 of the theory of a protein synthesis from amino-acids we have a series 

 of experiments where deeply split or completely split proteins were 

 fed. In these experiments by LOEWI, HENDERSON and DEAN, HEN- 

 RIQUES and HANSEN, and especially by ABDERHALDEN and his co-workers 1 

 on dogs, mice and rats, it was possible to keep the animals in nitrogenous 

 equilibrium or indeed nitrogen retention for a long time with the cleavage 

 products of proteins besides non -nitrogenous food-stuffs and salts. Espe- 

 cially important are certain experiments of ABDERHALDEN and RONA 

 and ABDERHALDEN with OLINGER, MESSNER and WINDP.ATH with com- 

 pletely decomposed meat. 



The results of the experiments are generally considered as proof of 

 the ability of the animal body to construct proteins from amino-acids 

 by synthesis, and in the present state of our knowledge we can hardly 

 draw other conclusions from them or advance any simpler theory. It 

 is nevertheless true that a nitrogen retention is not synonymous with 

 a new formation of protein, and we must not overlook the fact that 

 LuTHJE 2 observed a nitrogen retention on feeding with one amino- 

 acid and abundance of carbohydrate, a condition where we can hardly 

 speak of a synthesis of protein. Still these experiments do not seem 

 to be conclusive enough to discard the above-mentioned experiments 

 and for the present, as above stated, we must admit that these experi- 

 ments give proof as to the synthesis of protein. With this we naturally 

 do not explain the occurrence or the extent of such a synthesis under 

 normal conditions. 



Where does the protein synthesis take place? If it were positively 

 sure that the amino-acids did not pass into the blood then we would have 

 transferred this synthesis to the intestinal walls. Otherwise we must 

 think in the first place of the liver; but this organ does not seem to play 

 an important role in this synthesis. ABDERHALDEN and LONDON 3 made 

 an experiment on a dog with an ECK fistula (see page 376), feeding the 

 dog with decomposed protein, and they found that this animal behaved 

 exactly like a normal animal, as it was kept for eight days not only in 

 nitrogenous equibrilium but also in nitrogen retention. According to 

 them the liver has no special function in the protein synthesis and the 

 theory is more reasonable that the protein synthesis takes place in 

 the intestine. 



1 Loewi, Arch. f. exp. Path. u. Pharm., 48. See also Henderson and Dean, Amer. 

 Journ. of Physiol., 9; Abderhalden and Rona, Zeitschr. f. physiol. Chem., 42, 44, 47, and 

 52; Henriques and Hansen, ibid., 43, 49; Henriques, ibid., 54; Abderhald'en with 

 Olinger, ibid., 57, with Messner and Windrath, ibid., 59. 



2 Pfliiger's Arch., 113. 



3 Zeitschr. f. physiol. Chem., 54. 



