494 SCIENCE PROGRESS 



At the present time it is perhaps advisable to regard the 

 identity of the "synthetic paranuclein" as an open question, 

 especially in view of the recent experiments of Bayliss. 1 



The latter investigator has thrown considerable doubt on 

 the second point at issue in relation to this reaction, viz. its 

 chemical nature. His experiments point definitely to a colloidal 

 precipitation between the enzyme and a colloid present in the 

 peptic digest owing to the method of its preparation. If this 

 other colloid is first removed from the digest, for instance by 

 addition of hydrochloric acid up to a concentration of 0*5 per 

 cent, then upon subsequent filtration and neutralisation it is 

 impossible to get this precipitate formed upon the addition of 

 the enzyme. On the other hand the precipitate given by the 

 acid, upon redissolving in the smallest possible quantity of 

 alkali, is readily reprecipitated by the addition of pepsin. 



This suggests that the appearance of this precipitate is due 

 to the precipitation of oppositely charged colloids, a view which 

 is supported by the comparative rapidity with which it is 

 brought about. Bayliss strengthens the evidence for this hypo- 

 thesis by showing that a similar precipitation may be produced 

 in the products of the peptic hydrolysis by the additions of other 

 substances than pepsin, that is to say, by other colloids which 

 are not enzymes. 



It is therefore unnecessary at the present time to do more 

 than glance at the interesting hypothesis of reciprocal catalysis 

 put forward by Robertson 2 to reconcile in the simplest manner 

 these apparently new types of enzyme catalysis with the Van 't 

 Hoff view that enzymes, behaving as normal catalysts, must, 

 given proper concentration conditions, accelerate synthetic 

 actions. Robertson suggests that at high concentration the 

 enzyme may be present in a dehydrated form and that this 

 form, which is stable at higher temperature than the normal 

 enzyme, may be responsible for the catalysis of the synthetic 

 reaction. 



If further investigation should show the necessity for it, this 

 ingenious hypothesis will certainly deserve serious consideration. 

 But it cannot be too strongly emphasised that advance in a 

 complex series of problems such as these will probably be 

 facilitated by a rigid adherence to the simplest possible 



1 Journ. of Physiology, xlvi. p. 236. 



2 Journ. of Biol. C&em., v. p. 510. 



