STUDIES ON FERMENTATION. 227 



phenomena are to be explained mucli more simply. The Dutch 

 veast employed being very impure must have contained traces 

 of foreign ferments, especially of mccharomyces pastorianus. 

 Reduced to a dry powder on December 17th, 1872, the two 

 or more varieties of cells comprising it had preserved their 

 vitality in consequence of the plaster, and this vitality had 

 continued at all events until July 25th, 1873. Subsequently, 

 when cultivated in wort, they had multiplied in that medium. 

 The saccharomyces had revived like the rest, but its quantity, 

 compared with the high Dutch yeast, was so small that the 

 microscopical observations made on August 2nd, when the flask 

 was decanted, failed to discover its presence. Between August 

 2nd and November I5th the high yeast must have perished 

 entirely : the cells of saccharomyces, on the contrary, still 

 maintained their vitality, and these alone multiplied in the 

 flask of wort impregnated on November 15th. Here we have 

 an example of the separation of alcoholic ferments, through 

 the unequal resistance they sometimes ofier to adverse con- 

 ditions to which they may be subjected. We may also conclude 

 that if we had prepared a quantity of beer with the ** high " 

 yeast, which in our experiment of August 2nd, 1873, seemed to 

 have developed in a state of entire purity, this beer when made 

 and stored in cask or bottle could not have failed to undergo 

 a secondary fermentation, in consequence of a development 

 of saccharomyces pastorianus. 



Let us take, as another example of purification of the same 

 kind, the case of the different ferments of the vintage. When 

 must begins to ferment the apiculated ferment invariably 

 appears, and becomes afterwards associated, more or less, with 

 the saccharomyces pastorianus, in the presence of which the 

 multiplication of the apiculated ferment soon ceases. Saccha- 

 romyces pastorianus, in its turn, is gradually displaced by the 

 ferment which we have termed the ordinary ferment of wine, 

 and which Dr. Rees has named saccharomyces elKpsdideus. On 

 the subject of these changes in the proportion of the ferments 

 of wine, the Note which we published in 1862 in the Bulletin 



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