38 BACTERIOLOGICAL CHEMISTRY 



and the unorganised ferments. The discussion was 

 virtually brought to an end when, in 1897, Buchner ground 

 up yeast with sand, submitted the mixture to high pres- 

 sure, and obtained a non-living cell-free juice which was 

 capable of converting glucose into alcohol and carbon 

 dioxide in just the same way as the living yeast with 

 which he started. It is as a result of this investigation 

 that the term enzyme (Greek: en=m; zyme=yeBBt) 

 has come into being as the general term for all such 

 substances. Since that time many other similar active 

 preparations have been obtained from diverse biological 

 systems, usually by the maceration of the organism or 

 tissue in water and precipitation of the enzyme as an 

 amorphous powder by addition of alcohol or acetone. As 

 a result of this and later work it has become an accepted 

 fact that although enzymes are only produced by the 

 living cell, once they have been so produced the cell is no 

 longer necessary for their action, which can occur quite 

 independently of the life of the cell that brought them 

 into being. Both Pasteur, who maintained that 

 fermentation only occurred if a living organism was 

 concerned, and Liebig, who argued that fermentation 

 could occur in the absence of life, were correct up to a 

 point, but neither went far enough to complete the 

 story. Life is necessary to bring about the formation 

 of the enzyme, but the enzyme may remain active 

 after the death of its parent cell and still cause fermen- 

 tation. 



Enzymes as Catalysts. — Enzymes can be regarded as 

 biochemical, organic catalysts which are produced by 

 living organisms. All living cells contain enzymes of one 

 sort or another, often a large variety of them. A catalyst 

 is a substance which changes the rate of a chemical 

 reaction, usually, although not always, accelerating it ; 

 in some cases a catalyst may act by removing some 

 inhibiting factor, thus enabling a reaction to proceed 



