PROTEIN METABOLISM 77 



mere trace is excreted through the kidney. How and where 

 this utilisation takes place is as yet unknown. 



The classical work of Miescher on the Rhine salmon demon- 

 strated the fact that the body can change one protein substance 

 into another without the intervention of the intestinal wall. 

 This observer stated that after the fish entered the fresh water 

 they ceased to take food, and yet in spite of this, great anabolic 

 changes took place in the salmon body. These changes con- 

 sisted in the marked growth of the generative organs, which 

 was shown to take place at the expense of the muscular 

 system. 



As regards the absorption of native proteins from the 

 intestine, the old work of Voit and Bauer, 1 which showed 

 that absorption of undigested proteins such as serum and egg 

 albumen could take place, has been extended and confirmed 

 by Heidenhain, 2 Friedlander, 3 Waymouth Reid, 4 and others. 

 Ascoli, 5 with the newly introduced biological methods of testing 

 for the presence of proteins, has been able to prove that the 

 protein taken up is unchanged, and can give the precipitin 

 reactions significant of the protein introduced. The absorption 

 of unchanged protein can hardly, however, be said to occur 

 under normal conditions. In the experiments referred to the 

 protein was introduced in excess into the intestine. This 

 absorption would seem also to be dependent to some extent 

 on an increased permeability of the intestinal wall, such as 

 is found in the very young. Another factor which plays an 

 important part in this form of absorption is the presence of 

 water, or salt solution. Friedlander (I.e.) has shown that after 

 all the water or salt solution has been taken up, absorption 

 of the protein, to all intents and purposes, comes to a 

 standstill. 



The objection which has naturally been raised to these 

 various experiments is that, although the observers say that 

 the intestine used in the experiment was thoroughly washed 

 out previous to the introduction of the protein, yet there may 

 have been sufficient trypsin left to act on the protein, and 



1 Voit and Bauer, Zeit.f. Biol. v. 536, 1869. 



2 Heidenhain, Pfliiger's Archiv, 56, 1894, 579. 



3 Friedlander, Zeit.f. Biol. 33, 1896, 264. 



4 Waymouth Reid, Phil. Trans. Ser. B. 192, 1900, 21. 



5 Ascoli and Vigan, Zeit.f. physiol. Chem. 39, 1903, 283. 



