SYSTEMATICALLY SELECTED YEASTS. 5 



by Hansen's researches, and in our opinion this marks a great 

 advance, which we joyfully admit." 



At first I naturally had to take up the dispute single- 

 handed, but was subsequently supported by pupils and 

 colleagues, and I was then better able by new and elaborate 

 investigations to devote myself to the elucidation of the 

 question from different sides. This is, indeed, the only way 

 in which an investigator who belongs to a small nation will 

 be able in the long run to maintain his standpoint against 

 his powerful adversaries abroad. Politics, unfortunately, also 

 still play their part in science. Most of the authors have 

 taken my side, and the vigorous attacks have been gradually 

 silenced. Feeble attempts are, however, still frequently made 

 to minimise the importance of my work, and often the same 

 arguments are brought forward which have previously been 

 completely refuted. I have thus learnt that the same truth 

 must be repeated again and again if we wish it to prevail in 

 the end. In most cases, however, I have purposely avoided 

 directly addressing my replies and corrections to the 

 respective critics, as personal disputes were always distasteful 

 to me. 



2. MY METHODS OF PURE CULTIVATION. 



The methods for the preparation of pure cultures which 

 were in vogue when, in 1880, I undertook experiments ex- 

 pressly in this direction, were far from giving a sufficient 

 degree of certainty. In 1878 Lister had indeed stated the 

 manner in which he had obtained a pure culture of a lactic 

 acid bacterium by means of a dilution method. By counting, 

 he determined the number of bacteria present in a drop of 

 the liquid under examination, and he then diluted this with a 

 sufficient quantity of sterilised water, so that, in accordance 

 with the calculation, each drop of the mixture should contain 

 on an average less than one bacterium. After inoculating a 



