tgii] Chemical Interpretation of Vital Phenomena. ^77 



vital activity, as the cause of the chemical transformations of living 

 matter, the idea that these transformations are manifested in virtue of 

 the catalytic properties of definite substances that come together when 

 living things grow, properties that are of the same nature as those ex- 

 hibited by common substances that may be shown to operate wherever 

 there is matter. 



How far this clue may really lead, it is impossible of course to say. 

 But it stands the first test of scientific hypothesis. It has set the world 

 at work upon experiments that certainly shed light, confident that these 

 will be followed by those that bear fruit. The catalytic action of metals, 

 such as platinum, iron, manganese, the power they have of bringing 

 into evidence changes that otherwise appear not to take place, is made 

 manifest in chemical changes similar to those that we know are effected 

 in plants and animals but which cannot be detected without the inter- 

 vention of catalytic agents. What are the properties of these metals 

 that confer on them this power? In the case of platinum and also of 

 some other catalysts it seems clear that the action is one that takes place 

 on the surface of the metal. The action varies not with the mass of 

 the platinum but with the amount of surface it presents, so that exceed- 

 ingly minute weights of platinum in the finest state of division that can 

 be attained, in the form of what is called a collodial solution of the metal, 

 may act very strongly. This reminds us of what is one of the most strik- 

 ing characteristics of enzymes. Their activity in producing chemical 

 change is all the evidence we have of their existence. No one has ever 

 weighed an enzyme because no one has ever separated one out in a pure 

 state. But we know that the amount of active substance must in some 

 cases be less than a hundred thousandth part at any rate, probably less 

 than a millionth of thi weight of substance that it can transform. And 

 we know too that the amount of substance transformed is not deter- 

 mined by the amount of enzyme. Small quantities of enzyme, if they 

 are given time enough, can effect as much change as larger quantities. 

 There are even reasons for thinking that the explanation of these proper- 

 ties of enzymes is the same as that in the case of a colloidal solution of 

 platinum — that it may be, on the surface of minute particles suspended 

 in a colloidal state, that the influence on the velocity of the reaction is 

 felt. Enzymes are colloidal substances, their solutions are not like the 

 solutions of the common salts; the ultimate particles in solution are 

 apparently units of a different nature from molecules, and it is pos- 

 sible that the surface presented by such units as in the case of the par- 

 ticles in a colloidal solution of platinum should be regarded as the seat 

 of changes in the physical distribution of other substances present in 

 the solvent about them. That at any rate is one of the ideas that underlie 



