THE BIOLOGY OF MICROBES, ETC. 177 



cerivisice it retards the action of the true beer 

 ferment. 1 



Saccharomyces mycoderma. The cells are oval, 

 elliptical, or cylindrical (Fig. 39, 9), measuring 

 about 7 fi long and about 2 //, thick. They are 

 united in richly-branched colonies ; and the cells 

 are often elongated, so as to resemble a hyphal 

 filament. This organism forms the scum on the 

 surface of beer, wine, sauerkraut, and fruit-juices. 

 It has nothing to do with the alcoholic fermenta- 

 tion; and is not identical with Bacterium aceti 

 (Mycoderma aceti), which is the microbe of the acetic 

 fermentation in wines and beers. 



Saccharomyces vini. This organism is the true 

 wine-producing ferment, for it is the cause of the 

 alcoholic fermentation of grape-juice. Its cells are 

 elliptical, slightly smaller than those of S. cerevisiw. 

 It forms spores, and is very common in the atmo- 

 sphere. 2 



It should be borne in mind that fermentation is 

 not a chemical, but a vital process; for the 

 researches of Pasteur and others have shown that 

 every fermentation has its specific ferment; in all 

 fermentations in which the presence of an organised 

 ferment has been ascertained the ferment is neces- 

 sary. 



1 See Martinand and Reitsch's paper in the Comptes Rendus, 

 t. 112 (1891). 



2 For further information concerning the yeasts see Jorgensen's 

 Micro-Organisms of Fermentation ; Pasteur's Etudes sur la Biere, 

 Etudes sur la Vin ; Engel's Les Fermentes Alcooliques ; and the 

 papers of Hansen. 



