ALCOHOLIC FERMENTS. 153 



species must be assumed. If colonies of each kind are 

 separately introduced into flasks containing wort, growths 

 are again obtained which consist partly of egg-shaped 

 and partly of " Pastorianus " cells. Reinserts experiments 

 showed that when these latter cultures were repeatedly re- 

 cultivated in fresh flasks the cells still partly retained their 

 sausage-shape for a lengthened period. When such a culture 

 was introduced into a yeast-propagating apparatus, the growth 

 obtained from it still showed an admixture of these cells ; 

 these disappeared, however, after the yeast from the propa- 

 gating apparatus had been introduced into an ordinary 

 fermenting vessel. In this case, therefore, the variation is 

 more strongly rooted, and only disappears after the yeast has 

 been propagated through a series of fermentations. 



Another example in the same direction is that of a species 

 of Sacch. cerevisice (a bottom-yeast) which, after a lengthened 

 and difficult development, was subsequently cultivated in 

 wort at a temperature of about 27 C. when the cells obtained 

 exhibited their ordinary appearance ; when cultivated at 

 7*5 C., however, grouped colonies with mycelium-like 

 branches were obtained. This is an interesting example of 

 the influence of temperature on the form of yeast cells. 



3. As an example of a much more deeply-rooted change 

 in the nature of the cells, Hansen's observations on Sacch. 

 Ludivigii may be mentioned. When single individuals taken 

 from an absolutely pure culture are again separately cultivated 

 as pure cultures, it is possible to obtain growths which exhibit 

 great differences in their power of forming spores. By a 

 methodical choice of single cells Hansen succeeded in obtaining 

 growths which, under the known conditions, completely failed 

 to yield spores; on the other hand, he found that when, starting 

 from the same original growth, a yeast speck which had 

 sprung from a spore-yielding cell was chosen and further 

 developed, a growth was obtained which was forthwith capable 

 of yielding an abundance of spores. By such methodical 

 selection, three varieties were separated from this species, one 



