THE YEAST PLANTS 



organisms living on decaying matter. Among the 

 microscopic forms of this order are the Saccharomyces 

 (Torula cerevisia); the well-known yeast plant, the cause 

 of alcoholic fermentation ; the Lactic acid ferment, 

 whose germs are not destroyed by ebullition at 212 

 F., that causes the souring of milk ; and the various 

 varieties of mucor or mould plants. These germs 

 are met with everywhere, and seize greedily upon 

 dead organic matter for their food and development. 

 The yeast plant germs are present upon grapes and 

 other fruit, so that when they are crushed the juice 

 enters rapidly into fermentation. The growing plant 

 takes from the molecules of grape sugar in solution 

 such atoms thereof as it needs for its own nourish- 

 ment. The atoms remaining divide themselves into 

 nearly equal proportions by weight of alcohol and of 

 carbon dioxide, the latter escaping in the gaseous form 

 in effervescence. Small quantities of succinic acid 

 and of glycerine are at the same time formed. The 

 yeast plant multiplies or grows both by gemmation 

 or throwing out buds, as well as by the formation of 

 spores. The former is essentially the same as the 

 process of division among the bacteria, but the new 

 cellules usually remain connected with their parent 

 cell, though the slightest pressure suffices to part 

 them. At a temperature below 43 F. the growth is 

 almost exclusively by gemmation ; the process is slow 



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