COAGULOSES AND PLASTEINS 437 



The question remains as to why this synthesis is not achieved, 

 or, at least, does not result in the production of a visible pre- 

 cipitate, when Merck's pepsin is substituted for Gruebler's prep- 

 aration. While a positive answer to this question cannot as yet 

 be advanced with confidence, it would appear to offer no very 

 valid reason, especially in view of the experiments of Gay and 

 Robertson, for deciding that enzymatic synthesis does occur 

 under defined conditions in mixtures of Gruebler's pepsin and 

 solutions of the products of the complete peptic hydrolysis of 

 casein. It would appear, on the contrary, to afford additional 

 justification for the view, expressed above, that the active agent 

 in the reversion is not identical with the active agent in hydrolysis. 

 The former substance is present in Gruebler's pepsin, but is 

 absent from Merck's preparation. 



The occurrence of synthetic processes (i.e., the reverse of 

 hydrolyses) in mixtures of pepsin and concentrated solutions of 

 the peptic split-products of proteins has also been demonstrated, 

 in quite a different manner, by Henriques and Gjaldbaek (27). 

 These observers have shown that if pepsin be added to an acid 

 and concentrated solution of the peptic split-products of a protein, 

 a synthetic process (union of COOH and H 2 N groups) occurs, 

 as indicated (a) by a progressive increase in the substances pre- 

 cipitable by tannic acid, and (6) by a decrease in the groups 

 (H 2 N ) which are capable of reacting with formaldehyde. The 

 process occurs at all temperatures lying between 5 and 70 degrees. 

 The more completely split the material in the digest is to begin 

 with the less complex are the products which result, but at the 

 same time their mass is greater. The most complex substances 

 which are formed in consequence of this reversion do not contain 

 much more formol-titratable nitrogen than the original proteins. 

 They have, moreover, shown (28) that the synthesis is reversible, 

 more dilution leading to a progressive increase in the formol- 

 titre. Furthermore, a decrease in the formol-titre also occurs 

 when trypsin is added to a concentrated solution of the products 

 of the peptic hydrolysis of protein. 



2. The Probable Nature of the Coaguloses and Plasteins. 

 It will be observed, on referring to the analytical data obtained 

 by Robertson and Biddle (55), that the carbon content of the 

 paranucleins (49-50 per cent) is considerably lower than that 

 of the proteins (51-55 per cent). In this, and in other respects, 



