WHAT IS THE PURE YEAST OF PASTEUR? 135 



present, together with the latter, which require approximately 

 the same conditions of nourishment. The principles of such 

 a cultivation method are of a purely physiological nature, 

 and, indeed, imply the assumption that the characteristics of 

 the species which are being dealt with are known beforehand ; 

 but since we are dealing with unknown factors in by far the 

 greater number of cases where we wish to prepare pure cul- 

 tures, it is clear that the methods under discussion can, as a 

 rule, give no certain results. They can, indeed, only be 

 employed in such rare cases of species which possess 

 sufficiently definite characters that they cannot easily be 

 mistaken for others, and where there is the possibility of a 

 control. A case of this kind is described at the beginning of 

 this memoir in the account of my earlier studies of Saccharo- 

 myces apiculatus. 



After the publication of the memoir mentioned in the 

 ' Annales de ITnstitut Pasteur,' Duclaux again attacked the 

 question, namely, at the French Brewers' Congress at Paris in 

 1889 (' Le genie civil,' p. no), and at the Congress at Lille 

 in 1890 (' La Gazette du Brasseur,' p. 447, No. 141, 1890). 

 He acknowledges that my method implies a real advance, and 

 that my researches have brought about a reform in fermenta- 

 tion in the brewery. He only concedes this, however, with 

 reference to low fermentation, and for high fermentation he 

 still advocates the adoption of the old methods of Pasteur. 

 These lectures appeared in journals which have only a limited 

 circulation, and consequently his views of the question of pure 

 culture are known to most readers only through the * Annales 

 de ITnstitut Pasteur.' If my famous colleague had also 

 published his new views in the last-named journal, I might, 

 perhaps, have refrained from again entering into the dis- 

 cussion of this old question. 



The question as to whether my method is applicable or 

 not to high fermentation has been answered in the affirmative, 

 in Denmark by the experiments of Alfred Jorgensen, in 



