200 MICRO-ORGANISMS AND FERMENTATION. 



or on thin pulled-out tufts of cotton-wool, which were then 

 allowed to dry, protected from the sun. In less than twenty- 

 four hours all the cells had perished. It is self-evident that 

 the isolated cells lying on the unripe fruits are still more un- 

 favourably placed than in the experiment. If, however, thick 

 layers of the cells are wrapped in cotton-wool or filter-paper, 

 they will continue to live for a long time, as they do in the 

 earth in filter-paper, for instance, over eight months. 



No complete investigations have been published on the 

 life-history of other alcoholic ferments. Saccharomycetes 

 occur very generally on fruits containing a sweet juice. 

 For several years Hansen has carried on experiments similar 

 to those described, with species of Saccharomycetes which 

 often occur in fruit gardens, namely Sacch. Pastorianus /., 

 Sacch. ellipsoideus /., also with Carlsberg bottom-yeast No. 1, 

 and with some top -fermentation beer-yeasts. He always 

 found that the yeasts sown in the soil in September were 

 still alive after a year. Some species had formed spores at 

 the surface of the soil. Further experiments will probably 

 show that the true Saccharomycetes also have their habitat on 

 fruits during the summer and in the soil during the winter. 



In antithesis to these direct observations of Hansen, is 

 Pasteur's statement that the wine-yeasts are unable to live 

 in the soil during the period from one season to the next. 

 Where the yeasts come from which are found on the grapes 

 at the time of ripening, Pasteur was unable to say. 



MYCODERMA CEREVISLE AND VINI. 



It is characteristic of these species that they very readily 

 form films on various alcoholic liquids. Under the above 

 names are included a number of different species, some of 

 which can excite a feeble alcoholic fermentation ; they 

 behave differently towards lager beer, some causing disease 

 whilst others do not. 



The Mycoderma cerevisice (Fig. 54) examined by Hansen, 

 and which is very generally met with in the Copenhagen 



