48 THE AMINO ACIDS 



INTESTINAL ABSORPTION 



From extensive experimentation it would appear that 

 the small intestine is capable of absorbing unchanged 

 native proteins and their decomposition products the 

 proteoses peptones and amino acids. 



Absorption of Undigested Protein 



It was pointed out by Voit and Bauer in 1869 that 

 undigested proteins such as serum or natural egg albu- 

 min may be absorbed by the small intestine, an obser- 

 vation which has been repeatedly confirmed by others. 

 It has been suggested that this is not the manner in 

 which most of the absorption takes place, only enough 

 protein being absorbed to replace worn-out tissue, the 

 excess being oxidized without ever having entered into 

 the tissue metabolism proper. Various explanations 

 have been offered to account for the fact of absorption 

 of undigested protein. The most obvious assumption 

 to make is that enzymes must have been present in the 

 intestine resulting in hydrolysis to amino acids and 

 hence their absorption. This point, however, is not 

 valid since the absorption was too rapid to admit the 

 possibility of such an hypothesis. Again, it has been 

 assumed that the experimental conditions rendered the 

 intestinal wall unusually permeable, thus allowing 

 protein to pass. It is possible that these results may 

 later be explained on grounds other than that of ab- 

 sorption, for Abderhalden, Funk, and London after 

 introducing excessive amounts of protein into the 



