566 Dr. Armstrong and Prof. Armstrong. Studies on [June 13, 



acceptor together with an agent. According to this view, an enzyme is a 

 composite agent in which the functions of a catalyst such as platinum black 

 are combined with those of an acid catalyst. 



It appears to us that the only interpretation that can be placed upon the 

 facts as they are now known to us* is that the acceptor is a radicle which is 

 very closely allied to, if not identical with, a dominant group in the hydrolyte. 



For example, we incline to the belief that the enzymes which cause the 

 hydrolysis of the glucosides — the glucases — are themselves glucosides. 



With regard to the agent, as the only hydrolytic agents known to us are 

 either acids or alkalies and the latter act only on ethereal salts, not on 

 etheric compounds such as the sugars, we are of opinion that, in all 

 probability, the agent is an acid radicle so situated with reference to the 

 acceptor that when the hydrolyte is attached to this latter it is in immediate 

 or compatible proximity with it, a conducting path being formed between 

 agent and acceptor by their association with the solvent and it may be also 

 with a sufficient amount of some " salt " to render the intervening liquid an 

 electrolyte. 



In the case of enzymes which condition the hydrolysis of the carbohydrates 

 and glucosides, the agent may well be the carboxyl radicle, CO.OH. It may 

 be objected that the carboxylic acids are too weak — that the rate at which 

 hydrolysis is effected by enzymes is far too great to be accounted for on the 

 assumption that carboxyl is the effective catalyst. We shall discuss this 

 point later on, merely remarking that we should not regard such an objection 

 as a valid argument against the sufficiency of our postulate. 



The efficiency of an enzyme depends, however, not only on the effective 

 conjunction and simultaneous operation of the two elements we have termed 

 acceptor and agent but also on its colloid character. 



Manner in which Enzymes Act. — It is so generally held that the enzymes 

 are colloids that we think it unnecessary to restate the arguments on which 

 this conclusion rests but shall deal only with considerations derived from our 

 own work. 



In virtue of their colloid character, they are present in a liquid in 

 suspension — their solubility being only apparent : results such as those 

 obtained with urease, for example, cannot well be accounted for in any 

 other way. 



When hydrolysed by this enzyme, urea affords carbonic acid and ammonia. 

 When the hydrolysis is effected in presence of an excess of either of these 

 products, the rate is approximately a linear function of the time* : whereas, 



* E., XIX, p. 334. 



