88 BACTERIA, YEASTS, AND MOLDS 



As Friends. Yeasts must usually be looked upon as 

 servants rather than as enemies. They are the aUies of 

 the housewife in a number of directions. We have noticed 

 above that when they grow in sugar solutions they give rise 

 to two new substances, carbon dioxide and alcohol, and 

 in various domestic and industrial processes sometimes the 

 one, sometimes the other, and sometimes both of these 

 products are utiUzed. 



The Use of Yeasts as a Source of Alcohol 



The alcohol produced by yeasts is the foundation of the 

 fermentative and distillery industries, for common yeasts 

 are the agents which produce the alcohol found in all 

 alcohohc beverages. The fermentative industries, which 

 were important in this country before prohibition and are 

 still of immense extent all over the rest of the world,, are 

 dependent upon yeasts. In the manufacture of fermented 

 and distilled liquors these little plants are used in all cases 

 for the production of alcohol out of various sugar solutions. 

 The struggle with gigantic evils resulting from these in- 

 dustries forms one of the greatest problems of civilization. 

 This, however, is a matter which does not belong to our 

 immediate subject. 



In breweries and distilleries some material containing 

 sugar (molasses, preparations from rye, com, barley, etc.) 

 is inoculated with a quantity of yeast, a species being 

 chosen which experience has shown to be well adapted to 

 the purpose. The mixture is warmed slightly and a vig- 

 orous fermentation is started. The fermented mass may 

 subsequently be used directly for a beverage — fermented 

 drinks, like beer, ale, etc. — or the water may be partly 



