1912] Chemical Interpretation of Vital Phenomena. 275 



reactions. And these reactions, as we have seen, are in the main such as 

 cannot under the conditions obtaining in living organisms occur where 

 there is no life. But now since the time of Buchner's discovery of the 

 enzyme that causes alcohoUc fermentation, partly, it maybe, as the re- 

 sult of the stimulus it gave, more and more of these reactions of meta- 

 bolism have been found to be due to the action of enzymes. A large 

 number of other enzymes have been shown to exist within the cells like 

 the zymase of yeast, and our conception of the use made of enzymes in 

 nature has had to be considerably extended. 



The position into which we are thus brought is this : in so far as the 

 chemical changes underlying the phenomena of life are the result of the 

 action of enzymes, tjiese reactions are due to the presence of chemical 

 substances in no sense alive, and are not therefore caused by life, or by 

 the activities of living matter. 



The question then that at once arises is this : how far would the oper- 

 ation of enzymes account for those differences that make it at first sight 

 inconceivable that the laws which govern the reactions of metabolism 

 are the same as the laws of chemical change that we learn of in inanimate 

 nature? 



To answer this we have first to consider what we understand by an 

 enzyme. We have seen that Berzelius compared fermentation to the 

 catalytic action of certain substances which could bring about chemical 

 changes, that otherwise were not observed, without themselves parti- 

 cipating in those changes. Berzelius of course did not know that yeast 

 was a living organism, and the significance of his comparison was lost 

 sight of when this came to be understood. But when the fermentative 

 activity of yeast was found to be due to an enzyme, the analogy drawn 

 by Berzelius between fermentation and catalytic action was realized, and 

 acquired for common mortals the luminous import that it had had for 

 the prophet. 



At the same time the nature of catalytic action had been further 

 studied and more closely defined. In many cases at any rate it can be 

 shown that in catalysis chemical reactions are not initiated but merely 

 accelerated. This holds, for instance, in the case of the decomposition 

 of hydrogen peroxide, the original instance given by Berzelius. At the 

 ordinary temperature a solution of hydrogen peroxide is converted into 

 water and oxygen very slowly, but in the presence of a catalytic agent the 

 change is very greatly accelerated. And the acceleration effected may 

 be so great that the reaction that results may appear as one that does 

 not otherwise take place. Hydrogen and oxygen can exist side by side 

 at the ordinary temperature without appearing to unite, though the union 

 takes place rapidly in the presence of finely divided platinum. But the 



