DIGESTION AND ABSORPTION OF PROTEIN 9 



can rapidly digest caseinogen giving rise to various amino acids and 

 tryptophane, whereas the real gastric juice, when tested under like 

 conditions, cannot do so. They also found that " pancreatin " will 

 break down many polypeptides which are resistant to the action of 

 natural pancreatic juice. This substantiates the contention of many 

 writers that there is a considerable danger in drawing far-reaching 

 conclusions as regards intravital action from mere test-tube experi- 

 ments, important and useful though the latter be. 



Intestinal Absorption. 



It was not until the experiments of Salvioli, Hofmeister and others 

 were carried out that a new explanation of the mode in which the 

 proteins were absorbed from the intestine was sought. Salvioli (353) 

 and Hofmeister (196) almost contemporaneously made the discovery 

 that, if peptone were left in contact with the living intestinal wall, it 

 disappeared or at any rate was so altered that it no longer gave the 

 reactions by which it was characterized. Hofmeister concluded that the 

 peptone on absorption was taken up by the leucocytes of the intestinal 

 wall and by means of these was converted into protein and at once 

 conveyed to the tissues (197). Heidenhain (179) repudiated this hypo- 

 thesis, but both he and Shore (373) inclined to the view that the pep- 

 tone was converted into protein, and that in this change the epithelial 

 tissues of the intestine probably played an important part. In addi- 

 tion to this Hofmeister (195) and Neumeister (305) have shown that, if 

 peptone were injected into the blood, it was wholly or in greater part 

 excreted from the body as waste material, and further that no trace of 

 peptone was ever found in the tissues, blood or lymph of animals even 

 at the height of digestion. 



It will be noticed that, although this expression of opinion as to 

 the fate of peptone brought into contact with the living intestinal 

 epithelium was practically unanimous, no definite direct proof of that 

 fate was produced. Neumeister (305) again took up the question and 

 again found that the peptone brought into contact with the intestinal 

 mucous membrane lost its characteristic reaction, but whether this was 

 due to the production of a higher product, a regeneration, or whether it 

 was due to further decomposition he did not definitely conclude. He 

 certainly found two decomposition products of protein, leucine and 

 tyrosine which suggested that further breakdown had taken place. 



