84 RESEARCHES ON YEASTS. 



mena ; these appeared, however, as soon as the cultivation 

 was carried out at the ordinary room-temperature, or at 25 C., 

 and the yeasts always behaved in the same manner, even when 

 they were examined the last time after 10 years' cultivation. 



When it is desired to revive an enfeebled high yeast so 

 that it will again manifest high-fermentation phenomena, this 

 can be more readily effected when, in addition to growing it 

 at a favourable temperature, the liquid medium is also vigor- 

 ously aerated. 



For the reasons stated above, the experiments just 

 described are the only ones hitherto carried out which afford 

 any proof, and the results which they have yielded show that 

 the transformation of high into low yeasts and vice versd 

 cannot, as some believe, be brought about under the condi- 

 tions mentioned. That the low-fermentation yeasts cannot, 

 as Pasteur appears to assume, develop forms of high-fermenta- 

 tion yeast by means of their film growths, has been proved in 

 my treatise on film-formation in the Saccharomycetes. In 

 this treatise I have also stated how, after a certain treatment, 

 low-fermentation yeasts are able to exhibit high-fermentation 

 phenomena during a few fermentations, after which they 

 resume their normal properties. We can bring about tem- 

 porary changes, but as yet we cannot effect permanent 

 transformations. Whether we might, however, attain this by 

 varying the experiments, and exposing the cells to the same 

 action for a longer period than in the experiments described 

 above, is another question ; facts alone are dealt with here, 

 and these, at all events, show that such transformations 

 cannot, within a measurable time, take place in the brewery. 

 The only explanation that can be offered with reference to 

 the experiments of Reess and Pasteur is, that these investi- 

 gators must have been dealing with mixtures of high and low 

 yeasts, which may easily have been the case, considering the 

 time when their experiments were made. 



The high-fermentation yeast mentioned, Sacch. cere- 



