32 THE PHYSIOLOGY OF PROTEIN METABOLISM 



soon after the commencement of digestion and which reached its 

 maximum between the fifth and sixth hour and then gradually de- 

 creased. He thought that the change was brought about by a 

 proteo-synthetic enzyme but he did not think that rennin played a 

 part, in other words, the product which he obtained was not " plas- 

 tein ". Other observers, however, have criticized these observations of 

 Glaessner and have offered other explanations of his findings. Embden 

 and Knoop (117) repeated Glaessner's work using intestinal mucous 

 membrane (a tissue which had also been previously used with success 

 by Hofmeister). They, however, could find no trace of protein re- 

 synthesis, either in the natural intestine or in an intestine freed from 

 trypsin by previous ligature of the pancreatic duct to prevent digestion 

 of any newly formed material. At the same time they found no 

 evidence of the further breakdown of the proteose. Cohnheim (96) 

 believed that the difference found by Glaessner between the amounts 

 of proteose present in the two parts of the stomach, depended, to a 

 certain extent at least, on the fact that fresh tissue coagulated only 

 with difficulty. It is questionable if this argument is valid. Salaskin 

 (347) suggested that the changes which were observed might depend 

 on the alterations which take place in the cells during the resting 

 period that the apparent synthesis was nothing more or less than 

 the normal cell restitution. Neither of these series of experiments is 

 very convincing, but on the whole the evidence from digestion and 

 absorption experiments generally does not indicate the occurrence of 

 any marked resynthesis in the stomach wall, at least during normal 

 digestive processes. 



Synthetic Experiments in vitro. 



Not only have the above workers maintained that a synthesis took 

 place in the gastro-intestinal mucous membrane when proteose and 

 peptone are brought into contact with it, but a purely synthetic action 

 has been assigned to pepsin and trypsin as another phase of their 

 activity. A. E. Taylor (392), for example, stated, that if the con- 

 centrated products of the tryptk digestion of protamine were subjected 

 to the further action of fresh trypsin for five months reformed pro- 

 tamine could be obtained. It is true that the amount of resynthetized 

 product was not large, as from the digestion products <of 400 grms. 

 protamine he obtained only 2 grms. of synthetized material. The 

 trypsin employed was obtained from the liver of clams. In a later 



