RESEARCHES ON YEASTS. 83 



formerly have been a difficult one to treat, when we remem- 

 ber that the ordinary low-fermentation yeast of breweries 

 frequently contains high yeasts and vice versa. Under these 

 circumstances, the conclusions drawn from observations made 

 in the brewery itself are naturally valueless. At most, dif- 

 ferent possibilities could be suggested, and in the literature of 

 the subject, and even in an important work like Pasteur's 

 1 Etudes sur la Bttre] we thus find contradictory views ex- 

 pressed without any possibility of ascertaining which is correct. 



Since the commencement of 1884 I have carried out 

 systematic experiments bearing on these questions. Abso- 

 lutely pure cultures were made use of in all cases, and these 

 were grown in Pasteur flasks containing sterile wort. The 

 low-fermentation yeasts with which I experimented were 

 Sacch. Pastorianus /., Sacch. ellipsoideus /., Sacch. ellip- 

 soideus //., Carlsberg yeasts No. I and No. 2, and also some 

 other low-fermentation yeasts which had been tested in prac- 

 tice. The experiments were made at the ordinary room 

 temperature, and the wort was frequently renewed, so that 

 numerous generations were produced at the temperature 

 employed in high fermentation, and at intervals the cultures 

 were grown at a still higher temperature namely, 25-30 C 

 High-fermentation phenomena did not, however, manifest 

 themselves, and the forms of the low-fermentation yeasts 

 remained constant ; in the case of some species these experi- 

 ments were continued over eleven years. 



Similarly, since the beginning of 1884, I have cultivated 

 at the low-fermentation temperature 5-7 C. two yeasts 

 Sacch. cerevisice I. and Sacch. Pastorianus HI. both of 

 which exhibit high-fermentation phenomena in a high degree. 

 In these experiments the nutrient liquid was renewed every 

 fortnight. So long as the flasks were exposed to the low 

 temperature mentioned, the fermentation was very feeble, 

 especially in the case of the first-named yeast, and there 

 were, therefore, no indications of high-fermentation pheno- 



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