( 2ss ,) 



outset the enzym in the extract of rennet is quite proof against 

 neutralizing, but after having been digested for a few days at 37° C. 

 this power of resistance becomes smaller, and then diminishes quickly. 

 Now, if the neutralized liquid, in order to determine the curdling 

 power, is mixed with milk, the reaction remains neutral and no 

 curdling arises. However, if it is rendered acid again, soon after the 

 neutralisation, a sufficient quantity of enzym is left to digest protein. 

 Also if the not heated solution of the enzym, before being neutra- 

 lized, is sufficiently diluted with 0.2% HC1, neutralisation herein 

 causes a rapid decrease and at last an annihilating of the curdling 

 power. Thus the curdling time of such a solution was, 8 times 

 diluted, 10 seconds, directly after the neutralisation 2 l /, to 4 minutes, 

 whilst the milk, mixed in the same proportion with the solution 

 half an hour after the neutralisation, was not yet curdled after 20 

 minutes. 



In all experiments, on the other hand, at which the noxious action 

 of alkali was avoided, the curdling and proteolytic power of the 

 enzym solutions appeared to keep pace with each other. 



Summing up the result is therefore that not a single reason is left 

 to assume a difference between pepsin and chymosin. 



No more is there any reason to stick to the opinion of Nencki 

 and Sieber, which I formerly shared, according to which pepsin 

 should be considered as a molecule, which, through different groups 

 of atoms, on the one hand should have a proteolytic, on the othei 

 hand a curdling action. The basis for such an idea, the opinion 

 that the activity in one direction could be preserved, whilst that in 

 the other direction was lost, I must now consider as having lost its 

 foundation. The opinion defended by Sawjaloff, is far more acceptable, 

 who considers the alteration of caseine, of which the formation of 

 cheese is the consequence, as the beginning of digestion, of proteolysis 3 ). 

 This opinion has, I believe, become more probable by the experiments 

 made of late about the alterations caseine undergoes under the 

 influence of rennet, particularly by the investigation made some time 

 ago in my laboratory by Miss Van Herwerden '). From these it 

 has appeared that caseine, at a very weak acid or neutral reaction 

 and at a temperature not much lower than 37° C. in a solution 

 of rennet — either a preparation of commerce or pepsin purified 

 as well as possible — soon falls asunder into paracaseine, which 

 when it does not directly become insoluble as a lime-compound, 

 cheese, continues to change, and other substances, among which 



i) Zeitschr. f. Physiol. Ghem. Bd. XLVI, S. 307. 

 2) Ibid, Bd. Lil, S. 184. 



