RESEARCHES ON YEASTS. 81 



that the organisms under discussion consist of only a single 

 cell. If we are to regard them, however, as species, the 

 differences found should be constant. In order to ascertain 

 how far this is the case, it again became necessary to make 

 special experiments, and to expose the cells, which for the 

 time being we have assumed to represent different species, 

 to different conditions for some length of time, partly each 

 separately in the form of a pure culture and partly several 

 mixed together, and therefore under the influence of com- 

 petition. In the course of the last twelve years I have 

 carried out a large number of such systematic experiments, 

 especially with the six species which I described in 1883, 

 and subsequently also with some others, including also 

 brewery yeasts. The results obtained showed that it was 

 comparatively easy to produce temporary, and in some 

 respects even great variations, but by suitable cultivation 

 these again disappeared, and the respective species returned 

 to their original condition ; new species or varieties could 

 only be obtained by a certain treatment continued for some 

 length of time ; some particulars concerning this will be 

 given subsequently. It is of practical interest that species 

 which were cultivated uninterruptedly for several years in 

 wort were subject to only slight modification ; this has been 

 confirmed not only by laboratory experiments, but also by 

 an experience extending over nearly eleven years in different 

 breweries in which pure yeast culture has been thoroughly 

 carried out. In short, my experience indicates that we have 

 as much right to assume the existence of species in the 

 case of these lower fungi as in that of the higher.* 



* It has quite recently been pointed out by Takamine that the Aspergillns 

 Oryza employed in the preparation of Japanese sake develops yeast-cells which 

 produce a very vigorous alcoholic fermentation. Juhler obtained the same result 

 with his cultures, and he states further that these yeast cells formed endospores, 

 and that in their properties they agreed with the Saccharomycetes. Juhler's 

 statements led to the revival of the view held by Bail, Hoffman and others 

 nearly fifty years ago, and which has ever since had some advocates namely, 

 that the Saccharomycetes originate from the ordinary mould fungi. The correct- 



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