ALCOHOLIC FERMENTS. 177 



more slowly and more sparingly than usual. If, however, 

 such cultures are subsequently treated in the manner first 

 described, the culture again assumes its normal condition. We 

 have here, therefore, an example of a very feebly-rooted 

 variation. 



2. In a gelatine culture of " Carlsberg bottom-yeast No. 1 " 

 both oval and elongated, sausage- shaped cells are often found, so 

 that, according to EEESS, the presence of two 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. 

 HANSEN'S experiments showed that when these latter cultures 

 were repeatedly re-cultivated in fresh flasks the cells partially 

 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 

 propagating 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. 



As early as 1883 HANSEN showed that the limits drawn by 

 EEESS in the characterisation of his species do not exist, because 

 in the case of each pure culture we are able to develop the 

 different species as defined by EEESS. Shape and size of the 

 yeast-cell are very variable. The sausage-shape (Sacch. Pastori- 

 anus Eeess) readily passes into the oval shape (Sacch. cerevisice 

 ellipsoideus exiguus Eeess), and conversely. 



Another example of a similar character 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 



