82 RESEARCHES ON YEASTS. 



It is necessary to refer to these results here, since, as 

 mentioned above, they form the groundwork of my practical 

 studies. 



2. HIGH AND Low YEASTS. 



As is known, widely different views prevail as to whether 

 the high and low yeast of breweries consist of one or several 

 species. Reess distinctly expresses the opinion that they 

 constitute two varieties of the same species Sacch. cerevisice 

 and that the one can be transformed into the other ; he 

 especially emphasises that high ale-yeast becomes trans- 

 formed into a typical low yeast after a few days' cultivation 

 in wort at 4-6 C. 



Pasteur, as previously pointed out, takes no definite stand- 

 point on the questions relating to the Saccharomycetes ; he 

 confines himself to the discussion of different possibilities ; 

 nevertheless, he is in the main inclined to assume that low 

 brewery yeast can be readily transformed into high yeast, and 

 that this transformation likewise occurs even in breweries. 



Other writers have also occupied themselves with this ques- 

 tion, but no conclusive experiments have been made ; true 

 pure cultures were not made use of, and in most cases it was 

 not even ascertained whether the yeasts employed belonged 

 to the Saccharomycetes or not. The question must, in fact, 



ness of Juhler's observations was confirmed by Jorgensen, who afterwards stated 

 that he had made similar observations in the case of other species of Aspergillus, 

 and also in the case of Dematium ('Centralbl. f. Bakteriologie,' Zweite Abt. 

 1895, pp. 16, 65, 321, and 326). Klocker and Schionning repeated the experi- 

 ments with Aspergillus Oryza, but without being able to observe any development 

 of yeast cells. The whole question must at present still be regarded as an open one. 

 These investigations have, of course, hitherto had no effect with reference to 

 the systematic analysis of yeast. For this it is also necessary to make experiments 

 with the yeast-cells themselves, and in such a way that we may be able to identify 

 the corresponding parent form in every case. I have frequently laid stress upon 

 the importance of experiments of this kind, and several years ago I made the first 

 positive contributions in this direction in that I proved that typical Saccharo- 

 mycetes can develop a mycelium with distinct septa, and also forms similar to 

 Oidium and Dematium (see my figures given in 'Zopf's Handbuch der Pilze,' 

 1890, p. 703 ; also the plates in ' Compte-rendu des travaux du laboratoire de 

 Carlsberg,' 1886). 



