FERMENTS AND ENZYMES 109 



the chemical change produced is specific, is of one kind, and of one kind 

 only. In each case too it is effected apparently without any expenditure of 

 energy, although to produce similar changes in our laboratories we have to 

 resort to very powerful means such as the employment of high tempera- 

 tures, intense chemical reactions, and, in many cases, we cannot reproduce 

 the changes at all. An instance will make these two points clearer. In 

 plants, starch is converted into sugar by the enzyme diastase without 

 apparent effort, whilst in the laboratory we can only cause this change 

 by boiling with mineral acids. But, whereas boiling with acids will 

 effect very many other changes, diastase is powerless to perform any but 

 the one alteration of starch into sugar. We can convert sugar into lactic 

 acid by heating with alkalies ; the lactic bacteria can do the same by their 

 fermentative power, but are unable to produce butyric acid. Some of the 

 biochemical processes of micro-organisms, the conversion of sugar into 

 alcohol for instance, cannot be exactly imitated by chemical means. 



Finally, neither enzyme nor organic ferment disappears in effecting 

 such changes, as a reagent disappears in a chemical reaction. There is no 

 definite relation between the quantity of ferment used and the quantity 

 of substance fermented, an enzyme like pepsin, or a yeast, being able to 

 ferment a hundred or a thousand times its own weight of fermentable sub- 

 stance. 



The chief and fundamental difference between enzymes and organized 

 ferments lies of course in the fact that the latter are living beings able to 

 grow and multiply, increasing the more rapidly the more food and ferment- 

 able material are placed at their disposal. This the enzymes cannot do, for 

 they are lifeless chemical compounds, although they have, it is true, many 

 points of resemblance to the proteids. They are extremely unstable com- 

 pounds, and when dissolved in water their fermentative power is destroyed 

 by a short exposure to 50 6oC., just the lethal temperature of most 

 sporeless micro-organisms. But towards protoplasm poisons their behaviour 

 is quite different from that of the organized ferments. Arsenious acid, 

 phenol, salicylic acid, ether, and chloroform in concentrations which paralyze 

 the organized ferments leave the enzymes unaffected. Chloroform however 

 seems to affect some enzymes in a short time. 



As regards the nature of the chemical change produced by enzymes 

 and organic ferments respectively, there is a broad and fundamental difference 

 between the two. The enzymes exercise solely a hydrolytic influence. That 

 is to say, they cause the molecules of insoluble compounds to take up 

 water and to separate into less complex molecules of a different constitution, 

 the resultant substances being soluble in water. Diastase, for instance, con- 

 verts one molecule of starch into one molecule of grape sugar : 



