xii FERMENT A TION. 



CHAPTER V. 



WHAT IS THE PURE YEAST OF PASTEUR f 



1. The old method which I made use of in 1880 for the preparation 



of my pure cultures of Sacch. apiculatus .. .. .. 130 



Duclaux's statement as to the efficiency of Pasteur's method of 



pure culture 132 



Theoretical objections raised by Miquel, Jb'rgensen, Denamur 

 and myself ., .. .. .. .. .. .. .. 133 



Duclaux's lectures at the Brewers' Congresses at Paris and Lille 



in 1889 and 1890 135 



Velten's attacks against my method of pure culture .. .. 136 



His statement that Pasteur's method is the right one for purify- 

 ing brewers' yeast .. .. .. .. .. .. .. 136 



The experiments of Messrs. Jacobsen at Old and New Carlsberg 137 



2. Pasteur's method of pure culture is tested 138 



The first four experiments .. .. .. .. .. .. 139 



Results 141 



The fifth and sixth experiments were specially carried out in order 



to test Velten's statements 142 



In Pasteur's method, as recommended by Velten and Duclaux, 

 there is no certainty of obtaining a pure culture, and with 

 regard to brewery yeast it even brings about a suppression of 

 the desired "culture" yeast, whilst the disease yeasts present 

 are even caused to develop more strongly .. .. .. 145 



New objections raised by Velten in 1891 146 



Jorgensen's investigations .. .. .. .. .. .. 147 



The new objections are disproved by the seventh and eighth 

 experiments .. .. .. .. .. .. .. 148 



3. The objections to the employment of tartaric acid apply also to 



hydrofluoric acid and other antiseptics 149 



Cultivation in a nutrient solution containing tartaric acid in the 

 analysis of yeast 151 



4. What Pasteur meant by a pure brewery yeast 153 



Pasteur's work and my work rest upon two quite different stand- 

 points ' 154 



