146 REPORTS ON THE STATE OF SCIENCE.—1918. 
familiar fact that a surface may become saturated ; so that, above 
a certain concentration of the substrate, no more can be adsorbed 
at a given moment of time. On other hypotheses explanation is 
very difficult. Data showing the fact in the case of enzymes are 
numerous ; those of Frankland Armstrong (1904) with lactase may 
be particularly mentioned. 
When attempts are made to express in mathematical formulae 
the velocity of reaction with enzymes, starting with the usual expres- 
sions based on mass action, it is found that numerous empirical factors 
have to be introduced in order to obtain adequate expressions. Since 
we do not know the meaning of these factors, it seems to the writer 
that very little is gained by such procedures. The difficulty is to 
know exactly what is the active mass at any moment. It is clearly 
some function of the concentration of the substrate, because this 
determines the amount adsorbed, but it is also related to the 
adsorbing capacity of the enzyme surface, which is itself affected 
by numerous influences, probably changing during the progress 
of the reaction itself. 
According to the theory of Nernst concerning reactions in 
heterogeneous systems, there are three stages—diffusion of the 
reagents to the surface, adsorption on this surface, and finally 
chemical reaction with each other or with the constituents of the 
surface itself. The stage of adsorption is very rapid when the 
reagents have reached the surface ; so that, since the rate of the 
reaction as'a whole is that of its slowest component, the process 
of adsorption itself does not control it. When one of the phases is 
a large mass, the time taken for the reagents to diffuse to it is an 
important component and usually longer than the actual chemical 
reaction itself. In such cases, the temperature coefficient of the 
reaction as a whole is that of diffusion, and is a low one. In the 
case of a colloidal dispersion, such as an enzyme in solution, the 
solid phase is evenly distributed throughout the system, so that the 
paths travelled by the substrate to reach the surfaces of the enzyme 
particles are very short, and the rate of the reaction is that of the 
chemical component, with the temperature coefficient of a chemical 
reaction. It seems likely that the coarsely heterogeneous systems 
of urease or emulsin in alcohol would be found to have the tem- 
perature coefficient of diffusion, but they have not been investigated 
from this point of view. The failure to realize these various facts 
has led to confusion of statements regarding the impossibility of an — 
adsorption process having the high temperature coefficient of a 
chemical reaction. The temperature coefficient of an enzyme 
reaction is naturally that of whatever chemical change occurs, and it 
gives us no information as to the other components of the total — 
process. 
We know from numerous investigations that when a substance is 
strongly adsorbed it is capable of displacing another substance to a _ 
greater or less degree from its position on the surface. Many of the 
substances found to retard the rate of enzyme action are of this kind. 
The alcohols, urethane, saponin and so on lower surface energy 
markedly. It was natural. therefore, that Meyerhof (1914) should 
suggest this as an explanation of their action, which was found in a 
