642 Professor W. M. Bayliss [March 24, 



the position taken by van't Hoff in the work with which he was 

 engaged at the time of his death. AVijat is required, then, is a means 

 by which the cell is enabled to change the available water at the 

 disposal of reactions occurring therein. We do not as yet know the 

 precise nature of such mechanisms, but there is reason to believe that 

 they are provided by changes in the surface area of colloidal consti- 

 tuents or in the power of imbibition possessed by certain contents 

 of the cell. 



We here come across an interesting problem which cannot be 

 said to be solved satisfactorily at present. We have seen that the 

 equilibrium position of an ester system when reached rapidly under 

 the action of a soluble catalyst is the same as the spontaneous one. 

 But there is a certain difference when a heterogeneous catalyst, or 

 enzyme, is used. Nevertheless, the equilibrium is a true one, being 

 in the same position when approached from either end. The amount 

 of butyric acid combined as amyl ester in a particular system under 

 acid catalysis was found by Dietz to be 88 per cent, of the total ; 

 under the action of the enzyme lipase it was only 75 per cent. This 

 fact has given rise to various suggestions, and has troubled people's 

 minds because it appears to give a possibility of evading the second 

 law of energetics. Now, it was pointed out to me by Prof. Hopkins 

 that, on the hypothesis of a rapid attainment of equilibrium by 

 condensation on the surface of the enzyme, it is necessary, if the 

 natural equilibrium is to be unaltered, that adsorption of all the 

 components of the system should be the same proportion of each, 

 because the position of equilibrium must be the same on the surface 

 of the enzyme as that which results in the body of the solution. In 

 the presence of a large excess of water, it does not seem likely that a 

 difference of equilibrium owing to this cause could be detected. 

 But this should be possible when the equilibrium position is nearer 

 the middle, so to speak, and I am at present engaged in experiments 

 on the question. At any rate, difference in adsorption may be the 

 cause of the phenomenon of Dietz. It would simply imply that 

 water is adsorbed by the enzyme in relatively larger proportion than 

 the other constituents of the system. It should be remembered that 

 the solvent in these experiments was amyl alcohol containing about 

 8 per cent, of water, and, as Arrhenius has shown, all substances 

 present are adsorbed, although the laws governing the relative 

 proportion of these various substances are not yet completely 

 worked out. 



We see, by consideration of the facts relating to the action of 

 enzymes, how important a part is played by changes in the rate of 

 reactions, and there are two further points to which attention has 

 been directed by Prof. Hopkins. Take, first, a series of reversible 

 reactions in which the products of one form the starting-point of the 

 next following : — 



Ar:B;^C;^D7! etc. 



