ABSORPTION OF PROTEINS. 529 



of the leucocytes taking up the proteoses and fixing them, it seems, in 

 the cell substance. 



It is for the present impossible to say with certainty whether or 

 not and to what extent the proteoses, as such, are absorbed and to give 

 their further fate thereafter in the intestine. The present view is prob- 

 ably as follows: That they do not pass as such into the blood, and 

 that they are transformed into amino-acids in part in the intestinal 

 contents and in part in the intestinal mucosa, and then from these amino- 

 acids the coagulable proteins are constructed by synthesis. In sup- 

 port 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, 

 HENRIQUES and HANSEN, and especially by ABDERHALDEN and his 

 co-workers l 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. According to the recent experiments of ABDERHALDEN 

 the organism can build up proteins from amino-acids when the indi- 

 vidual amino-acids are supplied in proportions as they exist in the cell 

 proteins. Certain, sometimes absent amino-acids seem to be capable 

 of being produced within the organism (for example, glycocoll, proline) 

 while other (tryptophane) cannot be produced. This explains why 

 gelatine which does not contain any tryptophane cannot replace protein 

 in the food. 



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. 



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 2 

 made an experiment on a dog with an ECK fistula (see page 397), 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 equilibrium but also in nitrogen retention. On 



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; Abderhalden with 

 Olinger, ibid., 57, with Messner and Windrath, ibid., 59; Abderhalden, ibid., 77, 22, 

 78, 1 (1912). 



2 Zeitschr. f. physiol. Chem., 54. 



