248 



MICRO-ORGANISMS AND FERMENTATION. 



ellipsoideus kept alive in the earth for more than three 

 years. 



Thus, it has been proved, that these fungi may also winter 

 in the earth. Whether this is their only mode of circulation 

 in nature, has not as yet been ascertained. 



In antithesis to these direct observations of HANSEN, is 

 PASTEUR'S view that the wine-yeasts are unablQ to live in the 

 soil from one season to the next. Where the yeasts come 

 from which are found on grapes at the time of ripening, 

 PASTEUR was unable to say. MUELLER-THURGAU arrived at 

 the same results as HANSEN. 



MYCODERMA CEREVISI.E AND VINI. 



It is characteristic of these species that they very readily 

 form films on various alcoholic liquids. Under these names 



FIG. 79. Mycoderma cerevisise from Copenhagen breweries. (HOLM.) 



are included a number of different species, some of which may 

 excite a feeble alcoholic fermentation ; they behave differently 

 towards lager beer, some causing disease whilst others do not. 



The Mycoderma cerevisice (Fig. 79) examined by HANSEN, 

 which is very generally met with in Copenhagen breweries, 

 forms variously-shaped cells. The cells are usually transparent 

 and less refractive than the true Saccharomycetes ; to each cell 

 there are generally one, two, or three highly refractive particles, 

 which often have a quivering, rolling motion. This micro- 

 organism forms a dull, greyish, wrinkled film on wort and beer, 



