SYSTEMATICALLY SELECTED YEASTS. 13 



directions, but nothing was proved, and the truth still 

 remained undiscovered. 



Pasteur got essentially no further in this field. This was 

 due not only to the position of the science at the time, but to 

 the fact that a botanical treatment of the problem did not 

 occur to him. Nowhere in his work does he make an attempt 

 to distinguish between the Saccharomycetes and the non- 

 SaccharomyceteS) all yeast cells exhibiting the ordinary bud 

 formation and capable of producing a fairly pronounced 

 alcoholic fermentation, were grouped together and described 

 sometimes as Saccharomyces, sometimes as lev-tires, ferments 

 alcooliques, &c. ; he had not any exact methods of pure culti- 

 vation, and sharp characteristics did not occur to him. Under 

 these circumstances there could consequently be no question 

 either of analysis or of a systematic selection of species. 

 Where Pasteur speaks of yeast, all possibilities are discussed, 

 but no definite scientific standpoint was arrived at. As an 

 example, it will suffice to mention his statements with 

 reference to the transformation of high brewery yeast into 

 low yeast, and vice versa. Whilst his observation mentioned 

 on p. 189 seems to indicate that this does not take place, 

 he comes to the conclusion later on (p. 213) that such may 

 occur, and in the note on p. 333 he gives instructions as to 

 what brewers must do if they wish to guard against their low 

 yeasts becoming converted into high yeast ; and it must be 

 pointed out that he is here not speaking of a temporary trans- 

 formation. I have elsewhere proved that such a change as 

 that assumed by Pasteur does not really occur. 



The above criticisms do not apply to Pasteur's justly 

 famous work, but to his pupils who still cling to the vague 

 standpoints, and with partiality revive obscure points in order 

 to find in them that which is not there, and which could 

 scarcely have been there, considering the time when the book 

 was published. 



The investigations of Nageli, published during 1877-1879, 



