OOTOBEK 15, 1915] 



SCIENCE 



513 



or brought about by a homogeneous catalyst 

 such as aeid. This consideration was 

 brought to my notice by Professor Hopkins, 

 and requires experimental investigation. 

 We know, indeed, that in some cases there 

 is such a difference in the position of the 

 equilibrium position, for which various ex- 

 planations have been suggested. But it 

 would be a matter of some interest to know 

 whether this difference has any relation to 

 different degrees of adsorption of the com- 

 ponents of the system. 



At the same time, adsorption is under 

 the control of so many factors, surface ten- 

 sion, electrical charge, and so on, that the 

 possibilities seem innumerable. There are, 

 moreover, two considerations to which I 

 may be allowed to direct your attention. 

 Hardy has pointed out that it is probable 

 that the increased rate of reaction at the 

 interface between phases may be due, not 

 merely to increased concentration as such, 

 but that in the act of concentration itself 

 molecular forces may be brought into play 

 which result in a rise in chemical potential 

 of the reacting substances. In the second 

 place, Barger has shown that the adsorption 

 of iodine by certain organic compounds is 

 clearly related to the chemical composition 

 of the surfaces of these substances, but that 

 this relationship does not result in chemical 

 combination or in abolition of the essential 

 nature of the process as an adsorption. It 

 would appear that those properties of the 

 surface, such as electric charge and so on, 

 which control the degree of adsorption, are 

 dependent on the chemical nature of the 

 surface. This dependence need not cause 

 us any surprise, since the physical proper- 

 ties of a substance, inclusive of surface ten- 

 sion, are so closely related to its chemical 

 composition. 



There is one practical conclusion to be 

 derived from the facts already known with 

 regard to enzymes. This is, that any simple 



application of the law of mass action can 

 not lead to a correct mathematical expres- 

 sion for the rate of reaction, although at- 

 tempts of this kind have been made, as by 

 Van Slyke. The rate must be proportional 

 to the amount of substrate adsorbed, and 

 this, again, is a function both of the concen- 

 tration of the substrate and of that of the 

 products. It is, then, a continuously vary- 

 ing quantity. Expressed mathematically, 

 the differential equation for the velocity 

 must be something of this kind : 



dC 



dt 



= KC» 



where n itself is an unknown function of C, 

 the concentration of the substrate or prod- 

 ucts. 



The hypothesis of control by adsorption 

 gives a simple explanation of the exponen- 

 tial ratio between the concentration of the 

 enzyme and its activity, which is found to 

 be different numerically according to the 

 stage of the reaction. At the beginning, 

 it may be nearly unity ; in the middle it is 

 more nearly 0.5, as in the so-called "square 

 root law" of Schiitz and Borissov, which 

 is, however, merely an approximation. 

 Simple explanations are also given of the 

 fact that increasing the concentration of the 

 substrate above a certain value no longer 

 causes an increased rate of reaction. This 

 is clearly because the active surface is 

 saturated. Again, the effect of antiseptics 

 and other substances which, by their great 

 surface activity, obtain possession of the 

 enzyme surfaces, and thereby exclude to a 

 greater or less degree the adsorption of the 

 substrate, receives a reasonable account. In 

 many cases, the depressant or favoring ac- 

 tion of electrolytes, including acid and 

 alkali, is probably due to aggregation or 

 dispersion of the colloidal particles of the 

 enzyme, with decrease or increase of their 

 total surface. It is to be noted that such 



