70 THE ACTION OF ENZYMES 



extract an enzyme or lifeless compound from yeast 

 capable of decomposing sugar into alcohol and carbon- 

 dioxide failed, and the alcoholic fermentation was 

 assumed to be the result of the activity of living yeast 

 cells only. About 1896, however, Buchner ground up 

 yeast with very fine sandy material in order to rupture 

 the cells, and then subjected the dough-like mass to 

 heavy pressure. By this means he extracted a juice 

 which, in the complete absence of living cells, decom- 

 posed small amounts of sugar into alcohol and carbon- 

 dioxide : the juice was found to contain an enzyme 

 which he named zymase. This result brings the 

 alcoholic fermentation by yeast into line with the 

 changes produced by unorganized ferments or enzymes. 

 More recently, lifeless products have also been obtained 

 from lactic bacteria which are able to produce lactic acid 

 from sugars, and, similarly, enzymes have been obtained 

 from the acetic bacteria which are able to oxidize alcohol 

 to acetic acid just as the living organisms do, except 

 to a smaller extent. The view, therefore, is gradually 

 gaining ground that fermentations of all kinds, whether 

 associated with living cells or not, are due to structureless 

 non-living enzymes, and that it is perhaps better to speak 

 of intra-cellular or endo-enzymes and extra-cellular ferments 

 or ecto-enzymes, the former term being applied to enzymes 

 which ordinarily carry on their work within the cells in 

 which they are produced, while the latter is reserved for 

 those which are excreted and are able to act independ- 

 ently of the cell. It must, however, be noted that there 

 are still many fermentations which do not take place 

 except in the presence of living organisms ; with many 

 of these we shall be specially concerned later. 



4. It will be useful here to notice briefly some of the 



