HO WHAT IS THE PURE YEAST OF PASTEUR? 



number of flasks containing beer wort were inoculated : in addition to 

 this the colonies themselves were submitted to a microscopic examina- 

 tion. The growths which developed in the last-mentioned flasks of wort 

 were also examined microscopically, and in all cases for the properties 

 which I knew beforehand characterised the respective species. It is 

 self-evident that in all cases sterilised liquids and gelatine were em- 

 ployed, and that the work was carried out with the care necessary to 

 guard against infection from without. 



The result arrived at was that out of the six species of 

 yeast which were sown in the three flasks containing the 

 solution of cane sugar and tartaric acid at the commence- 

 ment of the experiment, only two species had survived, 

 namely, Sacch. ellipsoideus //., and Sacch. Pastorianus I. ; 

 the former of these survived in all the flasks, the latter only 

 in one, or perhaps in two of them. Sacch. Pastorianus I. 

 could only be detected with certainty in one of the flasks, 

 and then only after cultivation in the solution of dextrose 

 in yeast-water. Sacch. ellipsoideiis II. proved, therefore, to 

 be the strongest species wider the conditions of cultivation 

 described ; bnt not even in the case of this species was tJiere 

 any certainty that the method had yielded a pure culture. 



Experiment II. This was carried out in the same manner as the first 

 experiment ; whilst, however, in the latter the cultivations employed 

 were ten days old, in this case the growths made use of were quite young 

 and were obtained by cultivation in wort for twenty-four hours at 25 C. 

 Otherwise the method was the same, and the end result of the experi- 

 ment was likewise the same. 



Experiment HI. This was conducted in essentially the same manner 

 as the two previous experiments, but with only one flask as the starting- 

 point. The yeast sown consisted of Carlsberg bottom yeast No. I, Sacch. 

 cerevisia L and Sacch. Pastorianus III. 



The mode of experimenting differed from that adopted in the two 

 previous experiments in that the cultivation in the solution of cane sugar 

 and tartaric acid was carried out in the course of only four weeks, 

 and during this period four consecutive growths were obtained at about 

 equal intervals, and in the manner described. On then examining as to 

 which species were still living, it was found that Sacch. cerevisice I. 

 and Sacch. Pastoriamis III. had survived. The former species was 

 especially noticeable on cultivation in beer wort, whilst the latter was 

 only found after cultivation in a solution of dextrose in yeast-water. In 

 this case also a pure cultivation was, therefore, not obtained. 



