240 INTRODUCTION TO GENERAL SCIENCE 



12. Farmers' Bulletin No. 317:27-28. "Starters" for Ripening 



Cream. 



13. Farmers' Bulletin No. 348. Bacteria in Milk. 



a. 1401 : 336-344. Parasites. 



b. 1404:361-408. Plants which cause Fermentation, De- 



cay, and Disease. 



c. 1502 : 457-477. Flowerless Plants. 



d. 1611 : 183-226. Friends and Foes of the Plant. 



e. 1902 : 9-21. General Character of Bacteria. 



/. 1903 : 13-25. General Characteristics of Bacteria. 

 g. 1903 : 168-174. Nitrification due to Bacteria. 

 h. 1904:18-20. Bacteria. 



174. FERMENTATION YEASTS 



Yeasts are small plants which live upon starches and 

 sugars, changing them into alcohol and carbon dioxide. 

 The highest amount of alcohol which can be produced by 

 yeasts is about 14 per cent, as yeasts cannot grow if there is 

 more than this percentage of alcohol present. If a larger 

 percentage of alcohol is desired, as in whisky or brandy, the 

 fermented material must be distilled. The above is called 

 alcoholic fermentation. 



Yeasts reproduce themselves by budding; that is, a small 

 bud appears upon the main cell and, becoming larger, breaks 

 off, as a perfect plant. 



There is another kind of fermentation which is called acid 

 fermentation. Bacteria are the cause of this, and examples 

 of bacterial fermentation are the souring of milk and the 

 changing of cider, or wine, to vinegar. 



References : 



1. 1407:231-232. Fermentation. 



2. 1501 : 41-48. Fermentation and Alcohol. 



3. 1503 : 166-168 Yeasts and Fermentation. 



