1913.] Processes Operative in Solutions and Enzyme Action. 571 



pointed out, there is reason to suppose that when the sugars are hydrolysed 

 by means of acids the proportion of acid effectively associated with the 

 hydrolyte at any one moment is probably very small — as both are attracted 

 by the solvent and therefore subject to constant separation at its call. 

 Presumably, therefore, the efficiency of acids, though relatively very low, is 

 actually very high (S. VII, XXIV). 



The colloid is little subject to such attraction and only the hydrolyte is 

 specially attracted by the water ; but owing to the fact that the colloid is 

 present in an excessively finely divided state, the hydrolyte tends to 

 accumulate at its surface and probably the attractive influence of the solution 

 as a whole is largely overcome. A relatively large proportion of the hydrolyte 

 is therefore brought into effective conjunction with the acid radicle ; con- 

 sequently this is placed under specially favourable conditions. The argument 

 is applicable to enzymes generally whatever the nature of acceptor and agent. 



Our hypothesis is one which renders it unnecessary to assume that enzymes 

 obtained from a variety of sources which all function in a particular manner are 

 one and the same substance ; it is probable that the same acceptor and agent 

 may be differently attached so long as they are appropriately placed to act in 

 conjunction. It is conceivable, in fact, that a variety of enzymes may exist 

 which are all capable of hydrolysing only one particular compound or type of 

 compound but differ in activity. If, as appears to be the case, a given enzyme 

 will act on compounds so different as say /3-methyl glucoside and the 

 corresponding /3-methyl glucosamine derivative, it is clear also that a series of 

 equivalent acceptors may give rise to corresponding enzymes which would all 

 function similarly though probably with different degrees of readiness. 



Our point of view is also one which admits of the existence of several 

 classes of enzymes : for example, of enzymes which are compatible with the 

 whole of the molecule they attack — it is not improbable that invertase belongs 

 to this class — as well as of enzymes in which the acceptor is a group compatible 

 with the one or the other section of the glucoside or other compound which it 

 can hydrolyse. 



Specific Character of the Enzymes. — The rigidly selective activity of the 

 enzymes is in itself sufficient proof of their essentially specific character. 



The fact that enzymes are known, such as «- and /3-glucase (derived from 

 yeast and the almond fruit respectively), each capable of hydrolysing a series 

 of glucosides, is in no way subversive of this argument ; it is easily accounted 

 for by the assumption that each such enzyme carries an acceptor compatible 

 with a group common to all the members of the series of glucosides and is, 

 indeed, a corollary of the hypothesis. 



Our conception of an enzyme is embodied in the two diagrams, figs. 2 



