434 CHEMICAL DYNAMICS 



per cent of PzO?>, thus agreeing closely with paranuclein A and 

 with the substance synthesized at 36 degrees from the concen- 

 trated products of the hydrolysis of paranuclein. 



Furthermore, the change in the refractive index of AT/50 KOH 

 which is brought about by the introduction of one per cent of 

 this synthetic substance is identical with that which is brought 

 about by the introduction of one per cent of paranuclein, para- 

 nuclein A or of the substance synthesized at 36 degrees, namely 

 0.00140 for sodium light (54). 



A reversion of hydrolysis can be brought about, therefore, 

 even in the diluted products of the complete peptic hydrolysis 

 of N/10 solutions of the alkali caseinates (diluted, since varying 

 amounts of pepsin solutions were added to the solution of products) 

 by the addition of 0.5 cc. of 15 per cent pepsin to 10 cc. of 

 products (final concentration of pepsin 0.75 per cent) and keeping 

 the mixture for 24 hours at 65 degrees, while it requires 15 cc. 

 of 10 per cent pepsin in 100 cc. of mixture (final concentration 

 of pepsin 1.5 per cent) to bring about, in 24 hours, reversion of 

 the hydrolysis at 36 degrees in a solution of products which has 

 been concentrated four or five times. 



It is an extremely significant fact that the synthesis which 

 occurs at 65 degrees does so at a temperature from 10 to 15 de- 

 grees in excess of that at which, according to the majority of 

 authors, pepsin is rapidly and completely deprived of its proteo- 

 lytic activity.* True, the destruction even, at this temperature, 

 must be a matter of time, and one might be inclined to believe 

 that a short period of very intense action at 65 degrees produced, 

 in the above experiments, a similar result to the much more pro- 

 longed but weaker action of pepsin at 36 degrees. The facts are 

 not in favor of this view, however, since the appearance of the pre- 

 cipitate which marks a certain stage in the reversion does not occur 

 (if the pepsin is not too concentrated) until the solution has been 

 standing at 65 degrees for two or three hours, and it progressively 

 increases in amount for over 24 hours. It appears that the active 

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



* Cf. Oppenheimer (45).- From the determinations of Schwarz (64) it 

 appears that concentrated (10 per cent) solutions of pepsin are deprived of 

 their power of accelerating protein hydrolysis and at the same time acquire 

 considerable power of inhibiting the activity of unaltered pepsin after having 

 been heated to 60 degrees for 5 minutes. 



