154 MICRO-ORGANISMS AND FERMENTATION. 



of which was characterised by its high capacity of forming 

 spores ; in the second this property had nearly disappeared, 

 whilst the third did not form spores at all. After numerous 

 cultivations in wort, the third form returned, but only slowly, 

 to its original condition, in which it was able to form spores ; 

 when it was cultivated in a solution of dextrose in yeast- 

 water, however, this property was immediately re-acquired. 



Another example of physiological transformation is the 

 following : The three species described under the group 

 Saccharomyces Pastorianus form under certain conditions a 

 dough-like sediment similar to those of the other Saccharo- 

 mycetes, under other conditions, however, a film-like, wrinkled, 

 or a caseous sediment consisting of small lumps (Pasteur's 

 levure caseeuse), that is to say, sediments of very different 

 appearance, and yet produced by the same species. In the 

 last-mentioned cage, the fermenting wort also assumes a very 

 characteristic appearance, and, contrary to what ordinarily 

 occurs, remains bright throughout the fermentation, so that 

 the yeast flakes can be observed to rise from the bottom to 

 the surface and to again sink. If this curious sedimentary 

 yeast is repeatedly cultivated by new fermentations in wort, it 

 can be again transformed into the dough-like form. 



A similar physiological transformation occurs in the^m- 

 formations of the Saccharomycetes (p. 137). 



4. At the beginning of the year 1889, Hansen published 1 

 the results of a series of experiments which were undertaken 

 with the view to discover the conditions causing variation, and 

 by experiment to bring about the formation of new races, and 

 if possible new species. These studies are being continued 

 in his laboratory. The following account is taken partly from 

 the source mentioned and partly from more recent publica- 

 tions. 



Hansen found in the case of several Saccharomyces species, 

 that when their cells were cultivated in aerated wort at a 



1 Centralbl. f. Bakt. u. Parasitenk. Bd. V., p. 665, 1889. 



