132 WHAT IS THE PURE YEAST OF PASTEUR? 



after I had succeeded in this that I was able to really attack 

 those questions which, for me, formed the main problem.* 



In my first memoirs relating to the alcoholic ferments I 

 confined myself to giving an account of the new results which 

 I had obtained, and it did not then occur to me that it might 

 be necessary to call attention to the errors of previous ex- 

 perimenters and to bring into relief the advance brought about 

 by my researches. I have gradually learnt from my opponents 

 that the manner in which I stated my results is not sufficient 

 when it is a question of promoting advance in a new direction. 

 In recent years I have again been reminded of this by the 

 attacks directed against me, and more especially by Duclaux 

 and Velten. 



Duclaux f attempts to prove the sufficiency of the methods 

 described by Pasteur more than sixteen years ago for the 

 preparation of pure cultures of yeast, and he particularly 

 dwells upon the method of procedure, which consists in culti- 

 vating the yeast in a 10 per cent, solution of cane sugar to 

 which a little tartaric acid has been added. In order to 

 furnish proof of the correctness of his statement, he examined 

 some of Pasteur's old flasks which contained yeast growths, 

 partly in beer wort, and partly also in the tartaric acid and 

 sugar solution ; they had remained in the laboratory ever since 

 Pasteur gave up these studies in 1876; some of the cultures 

 were seventeen years old at the time they were examined. 

 Duclaux found that out of 19 flasks examined, 14 contained 

 pure cultures ; in the case of three flasks he was not quite 

 certain, but he assumed that each of these likewise contained 

 one species only ; in two flasks, containing brewery yeast, he 

 states that mixtures of two species were present. He con- 

 siders, therefore, that by means of these old flasks the method 

 under discussion is shown to be an exact one for the prepara- 



* For my methods for the preparation of pure cultures, see p. 5. 

 t E. Duclaux: " Sur la conservation des levures." ('Annales de PInst. 

 Pasteur/ 1889, p. 375.) 



