572 THE POPULAR SCIENCE MONTHLY 



living in a liquid medium in order to secure sufficient oxygen procured 

 it from the sugar, thus, as we have said, producing from the latter C0 2 

 and alcohol. The production of alcohol hence resulted as a product 

 of metabolism in the body of a living organism. 



It has been more recently shown, however, that the active cause of 

 fermentation is to be found not in the yeast itself, but in a ferment (or 

 enzyme) produced by the yeast cell. This ferment Buchner has suc- 

 ceeded in freeing from the cell, so that it is now possible to produce 

 alcoholic fermentation without the presence of the living yeast. 



But this discovery does not detract from the work of Pasteur, to 

 whom is due the great credit of definitely showing the importance of 

 living organisms, the yeasts, in the production of alcohol, since without 

 the yeast cell the ferment or enzyme would not be produced. 



The nature of the experiments by which Pasteur demonstrated the 

 importance of the yeast is of interest. In the first place he showed 

 that grape juice filtered and kept from contact with the air is not 

 subject to alcoholic fermentation. In the second case he demonstrated 

 that grape juice sterilized by heat is, if similarly protected, unferment- 

 able. In the third case he showed that if the yeasts caught on the filter 

 used in the first series of experiments be added to the sterile juice of 

 the second series, fermentation ensued. 



Pasteur was asked the origin of the yeasts which make the alcohol 

 in wine. The question was answered by an experiment. Taking the 

 grapes and completely removing from them the fuzz or " bloom," he 

 extracted the juice free from contact with the air. No fermentation 

 followed, consequently no alcohol resulted. From this it was learned 

 that the yeasts necessary for the production of the alcohol of wine live 

 in nature in the air and are found in abundance on the outside of the 

 grape. If the grapes be crushed the sweet juices serve as food for the 

 yeast plants. These when well fed grow rapidly and, by a simple 

 process of budding, produce myriads of yeast plants. These, like their 

 parents, give rise to ferments which break down the sugar into C0 2 

 and alcohol. 



It was later found that although these yeasts may increase greatly 

 in numbers, a strong percentage of alcohol is impossible in nature. 

 This is due to the singular fact that when the strength of alcohol 

 increases perceptibly the organisms forming it are unable to thrive in 

 their own product. Hence they increase more slowly. "When a strength 

 of 12 per cent, of alcohol is reached reproduction is manifestly checked, 

 and at 14 per cent, all cell activity ceases. 



To increase the strength and purity of the alcohol thus formed in 

 nature, man, as we have seen, has resorted to the processes of distilla- 

 tion and rectification by which alcohols practically free from impurities 

 may be obtained in concentration. 



