284 MICRO-ORGANISMS AND FERMENTATION. 



experiments which were undertaken with the hope of dis- 

 covering the conditions causing variation, and of experi- 

 mentally bringing about the formation of new races, and if 

 possible new species, He has since published additional work 

 on the subject. 



(a) He found in the case of typical Saccharomyces that 

 when their cells were cultivated in aerated wort * at a tem- 

 perature above the maximum for their spore-formation, and 

 near the maximum for their vegetative growth, they were 

 affected in such a manner that they lost their power of forming 

 spores and films (Asporogenesis). This was also true of the 

 innumerable generations successively formed in new cultures 

 under the most varied conditions. The starting point was 

 always a growth which showed not the slightest trace of 

 asporogenous cells. For example, it may be noted that 8. 

 Past. I. loses its power of forming spores by treatment at 

 32 C. In the case of the wine yeast, Johannisberg II., this 

 occurs at 36 C. In the seventh culture of S. Past. I. all the 

 cells were asporogenous. Hansen succeeded also in bringing 

 about a transformation by cultivation on solid media. Such 

 asporogenous growths were formed in the case of S. Past. I. 

 on wort-gelatine at 32 C., when inoculations were made at 

 shorter intervals, as is commonly the case when liquids are used. 



In some of the species treated in this way, it was also 

 observed that they yielded a more abundant crop of yeast in 

 wort-cultures, but a slower fermentation. This was, for 

 instance, the case with Carlsberg low-fermentation yeast 

 No. 2. The newty-formed variety attenuated more slowly 

 and weakly than the original species ; but at the same time 

 the clarification was better. 



Rayman and Kruis have shown that the cells present in 

 films possess the power of oxidising alcohol produced during 

 fermentation, into carbon dioxide and water. Hansen's 

 varieties, while completely losing the power of forming films, 

 are rendered incapable of performing this oxidising action. 

 Thus, while a flask, containing the original species, which had 

 developed a luxuriant film after six months' standing, showed 

 only 1-5 per cent, by volume of alcohol, a parallel flask, which 



* By repeated shaking of the successive cultivations. 



