144 PHYSIOLOGY OF ALIMENTATION. 



As proof that the formation of "plastein " indicates that a 

 proteolytic ferment has synthesized from the proteose solu- 

 tion a substance or substances which lie nearer the original 

 protein than the proteoses, the following may be said : 



We became familiar on p. 131 with SPRIGGS' observation 

 that a protein solution undergoing digestion under the in- 

 fluence of acid-proteinase (pepsin) and hydrochloric acid 

 suffers a decrease in viscosity, and that this decrease occurs 

 rapidly at first and then more slowly. When a solution of 

 proteoses and peptones (ordinary commercial " peptone ") 

 has added to it an artificial gastric juice the mixture is found 

 to increase in viscosity, at first only slowly and then very 

 rapidly. We have, in other words, exactly the reverse of what 

 occurred before. This seems to justify the conclusion that 

 acid-proteinase (pepsin) is able not only to catalyze the 

 analysis of a protein but also to catalyze its synthesis from 

 the products of digestion. What has been said holds not 

 only for acid-proteinase (pepsin) but also for alkali- and 

 ampho-proteinase (trypsin and papain). 



If the above is true and the formation of "plastein " is 

 really to be looked upon as representing a synthesis of 

 protein which occurs under the influence of a proteolytic 

 ferment, then we should expect that the same external con- 

 ditions which favor or hinder the activity of a proteolytic 

 ferment in hastening the analysis of a protein should favor 

 or hinder in the same way the activity of this ferment when 

 it is hastening the synthesis of a protein. Thanks to the 

 researches of WEINLA-ND,* we are familiar with a substance, 

 antiproteinase (antitrypsin, antipepsin) , which retards (prac- 

 tically prevents) most markedly the activities of the pro- 

 teolytic ferments. The addition of a small amount of 

 anti-pro teinase, obtained, for example, from the body of the 

 intestinal worm ascaris, to a digestion mixture of protein and 

 proteolytic ferment practically prevents the latter from act- 



1 See p. 133. 



