146 WHAT IS THE PURE YEAST OF PASTEUR f 



vation in the sugar solution must therefore be considered not 

 only with reference to the bacteria, but also with very special 

 regard to the species of disease yeast mentioned. Regarded 

 from this point of view, not only are the results of the fifth 

 and sixth experiments opposed to Velten's statement, but 

 this is really also the case with the first four experiments. 

 Pasteur's method for the purification of brewery yeast recom- 

 mended by Velten and Duclaux effects therefore no purification 

 whatever as regards the disease yeasts, but on the contrary it 

 brings about a more vigorous development of the disease-pro- 

 ducing ferments. This holds good for the experiments with 

 both high and low fermentation yeasts. Pasteur's method is 

 consequently absohitely useless in the brewery. Where it is 

 introduced it will lead to great loss and difficulties. 



The sixth experiment likewise showed that in the manner 

 employed the method does not with certainty lead to a pure 

 culture. 



The above experiments were published in 1891 in the 

 ' Compte-rendu des travaux du laboratoire de Carlsberg.' It 

 might have been expected that in view of such facts, opposi- 

 tion would have ceased, especially as my opponents were not 

 able to detect any error in my experiments or in the con- 

 clusions which I drew from them. This, however, was not 

 the case. Velten tacitly recognises that my experiments are 

 correct, and he therefore cannot oppose the results obtained 

 under the given conditions ; but then he introduces new 

 objections ('La Gazette du Brasseur,' 1891) that the disease 

 yeasts were present in my yeast mixtures^ in too high a pro- 

 portion in comparison with the brewery yeasts, and further, that 

 the experiments should have been conducted at a lower temperature 

 than 25 C. t which I in part employed. If I had experimented 

 as he suggests, I should, he states, have obtained quite a 

 different result, and he designates Pasteur's method as simpler 

 and more rational than my method, which, as is known, starts 

 with a single cell. In the detailed description of Pasteur's 



