1904.] on Ionic- Dissociation Hypothesis and Vital Change. 539 



the solutions being perhaps conditioned by the slight viscosity of the 

 solvents. On the other hand, it is highly probable that in many cases 

 in which slight conductivity has been observed insufficient care has 

 been taken in the purification of the materials used. 



In discussing the nature of chemical change in my Presidential Address 

 to the Chemical Society in 1895,* I specially drew attention to the diffi- 

 culty of explaining the behaviour of enzymes — particularly their selective 

 action — as hydrolytic agents by the ionic-dissociation hypothesis : the 

 view was then advocated that their function consists in bringing water 

 into conjunction with the carbohydrate by combining with both. The 

 evidence brought forward in the two previous papers! on enzyme 

 action appears to me to be of consequence in this connection : and I 

 venture to think that the case is very materially strengthened by the con- 

 siderations advanced by E. F. Armstrong and E. J. Caldwell in discussing 

 the action of acids on the sugars, f The selective character of the effect 

 produced by enzymes, which has now been demonstrated in several 

 ways, may almost be regarded as final proof that action is determined 

 by association — not by dissociation. And if in such a case we are led 

 to admit that change is the immediate consequence of effective 

 association, there can be no difficulty in regarding chemical changes 

 generally as of this character. 



In their behaviour towards acids, the sugars exhibit peculiarities 

 which are so little in accordance with the ionic-dissociation hypothesis 

 that we are almost compelled to admit that in this case also hydrolysis 

 is dependent on association. The explanation which this latter view 

 affords of the great influence which temperature changes have on the 

 rate of change is in itself striking evidence in its favour — especially as 

 the explanation set forth in their paper by E. F. Armstrong and 

 R. J. Caldwell is applicable to chemical changes generally. 



In advancing proof that the enzymes are built of dimensions which 

 enable the molecule to become associated at several points with the 

 carbohydrate molecule, E. F. Armstrong has carried a step further the 

 argument which I advanced in explanation of fermentation proper in 

 1895. % The statement then made was as follows : — " Supposing that the 

 protoplasmic hydrolyst were to condition the formation of a conducting 

 circuit in which any two of the carbon systems (CH^OH, CHOH or 

 COH) of the glucose molecule and water molecules were included, if 

 the total hydrolytic change which could take place in such a circuit 

 were exothermic, even if the change affecting the one group involved 

 an expenditure of energy, water could be electrolysed and its hydrogen 

 would effect the withdrawal of OH from the one group and its 

 displacement by hydrogen, while oxygen would be added to the other 



* ' Chem. Soc. Trans.,' vol. 67, p. 1122. 

 t Supra, pp. 526 — 537. 

 X Loc. cit., p. 1137. 



2 r 3 



