WHAT ARE ENZYMES? 77 



When we consider that life is possible only because of 

 continued cellular activity, and when we bear in mind that 

 this activity is largely the result of chemical changes 

 brought about by these enzymes, the paramount impor- 

 tance of these substances becomes manifest. 



Alcoholic fermentation in yeast, the souring of milk, 

 processes of putrefaction, and various other examples of 

 changes in organic materials with, often enough, the ac- 

 companying liberation of bubbles of gas, had long been 

 known. The epoch-making researches of Pasteur had 

 shown that fermentations and putrefactions were inaugu- 

 rated by the presence of living organisms. Then later ex- 

 tracts from the saliva and the gastric mucosa of the stom- 

 ach were obtained which also had the power of bringing 

 about chemical changes in carbohydrates and proteins. 

 This led to the classification of ferments into those which, 

 like yeast and certain bacteria, acted because of certain 

 vital processes (organized ferments), and those which, 

 like the extracts from the saliva and stomach, were pre- 

 sumably "non-living unorganized substances of a chemi- 

 cal nature" (unorganized ferments). Kiihne designated 

 the latter "enzymes." This classification was generally 

 accepted, and the "vitalists" held absolute sway until Emil 

 Buchner, in 1897, overthrew the whole theory by a series 

 of researches which, in their influence, were only second 

 in importance to those of Pasteur in an earlier genera- 

 tion. One of Buchner's classical experiments consisted 

 in grinding yeast cells with sand and infusorial earth, and 

 then subjecting the finely pulverized material to a pres- 

 sure of 300 atmospheres a pressure far more than 

 enough to destroy yeast, or any other cells. The liquid 

 so obtained had all the fermentative properties of the 

 living yeast cell. Obviously, then, the living cell could 

 not be responsible for the fermentation. On the other 

 hand, this experiment did suggest that cellular activity 

 gives rise to some substance which, once produced, exerts 

 its influence whether the cell is alive or dead. All subse- 



