138 MICRO-ORGANISMS AND FERMENTATION. 



Hansen has treated a large number of films, and amongst 

 them several forms which are most closely related to different 

 species of Saccharomyces Mycoderma, which do not produce 

 endogenous spores. According to de Seynes, Reess, and 

 Cienkowski, these Mycoderma-species do yield ascospores ; it 

 is, however, highly probable that these investigators were 

 dealing with impure films, containing an admixture of true 

 Saccharomycetes. It is, indeed, a matter of no little diffi- 

 culty to determine the purity of such a culture if one 

 does not start from a single cell ; for if Mycoderma 

 cerevisice is cultivated as sedimentary yeast, the cells 

 assume an entirely different appearance ; they become filled 

 to a greater extent with plasma, whilst the cells of the film 

 are, as is known, poor in plasma and contain strongly- 

 developed vacuoles. Such forms, whicli are generally re- 

 garded as Mycoderma cerevisice, readily and quickly form 

 films ; some simultaneously exhibit distinct signs of fermen- 

 tation, whilst others do not. On beer and wort these films 

 are grey and dry in appearance ; afterwards they become 

 .wrinkled and lighter in colour; air is found freely inter- 

 mixed between the cells. Some of the varieties of Torula 

 investigated by Hansen yield similar films ; the film of 

 Chalara Mycoderma, on the other hand, is glutinous, tough, 

 and slightly lustrous ; in the case of Monilia which, as 

 previously mentioned, can occur with budding cells, and 

 directly ferments cane-sugar the film formation is peculiar : 

 even during vigorous fermentation a film forms on the bub- 

 bles of foam, spreads gradually over the whole surface, and 

 sometimes becomes wrinkled. Thus, the cells in the flask first 

 sink to the bottom as sedimentary yeast, set up a vigorous 

 fermentation, and again rise with the bubbles of carbonic acid 

 to the surface, where they enter upon a new phase of develop- 

 ment. If sterilised lager-beer is infected with this fungus, no 

 fermentation sets in, and only a thin film resembling dust is 

 developed ; under other conditions the fungus forms a white, 

 floury, wool-like layer, as in the case of Oidium. 



