292 MICRO-ORGANISMS AND FERMENTATION. 



entirely alter its character. On these lines no starting point 

 can be found for an analytical examination of yeast to determine 

 its purity. 



A peculiar group of yeasts, the Schizo-saccharomycetes, are 

 distinguished from others by the formation of daughter cells 

 through division of the mother cell, a cross-section being 

 formed in the latter. 



Film Formation. It is well known that fermenting and! 

 fermented liquids are covered with film growths. It was. 

 first shown with certainty that Saccharomyces (in the strict 

 sense) are able to form films by Hansen's observations on 

 cultures derived from single cells. 



The universally occurring Mycoderma species form films 

 easily and rapidly. Some also give fermentation phenomena ; 

 others do not. Such a film is greyish on beer and wort, with 

 a dry appearance, and in its later stages wrinkled and lighter 

 in colour. Amongst the cells there is a considerable admixture 

 with air. Similar films are formed by a few of the Torula- 

 cells. The film of Chalara Mycoderma is gelatinous, and has 

 a bright appearance. In the case of Monilia, which may occur 

 with budding cells, the film formation is peculiar. During- 

 the vigorous fermentation, a film forms on the froth, which, 

 gradually spreads over the whole surface, and is occasionally 

 wrinkled. The cells in the flask form a deposit, produce- 

 a vigorous fermentation, and rise with bubbles of carbon 

 dioxide to the surface again, where they begin a new stage of 

 development. If sterilised lager beer is inoculated with this 

 fungus, no fermentation takes place, and a thin dusty film is- 

 formed, but under other circumstances the fungus forms white, 

 floury, and woolly layers like Oidium. 



The films of true Saccharomyces differ somewhat from these. 

 As a rule, they are produced in the following way : If cultures 

 are allowed to stand undisturbed for a longer or shorter period 

 in wort at room temperature, it will be found that small 

 specks of yeast appear on the surface of the liquid at th& 

 completion of the primary fermentation. These collect to- 

 gether at a later stage to form islands of varying size and shape, 

 with a flat upper and arched lower surface. Finally these 

 fuse together to form a light greyish-yellow and slimy film,. 



