SYSTEMATICALLY SELECTED YEASTS. 9 





other investigators. Thus, Miquel found 134 different kinds 

 of bacteria in 100 colonies prepared by Koch's plate method. 

 In Holm's experiments with yeast cultures and wort gelatine, 

 the average number obtained was that 100 colonies had 

 sprung from 108 cells, whilst in the most unfavourable case 

 100 colonies were produced from 135 cells.* 



Koch's method of plate culture is essentially in agreement 

 with the dilution methods of Lister and myself; it is the 

 same except that in one case gelatine, and in the other 

 liquids, are employed. The various methods of obtaining 

 pure cultures, which were elaborated in the course of time, 

 can only be regarded as modifications of one another ; there 

 was no sudden development. The reason why the dilution 

 methods with liquids are now but seldom made use of, is that 

 working in this manner is more tedious and difficult than 

 working with gelatine. 



In the case of yeast there are no special difficulties in 

 carrying out the principle of pure cultivation from one cell, 

 and it is indeed generally conceded that my exact method 

 should be followed in the case of purely scientific experi- 

 ments ; on the other hand, there are still some zymotechnolo- 

 gists who are disposed to take the matter more easily when 

 it is a question of preparing a pure yeast for the brewery. 

 They do not consider the risk which is thus incurred of 

 introducing a dangerous disease yeast together with the 

 good brewery yeast. My warning here, as always, is: The 

 best is not too good for practice. 



The differences between Koch's and my methods are 

 at present no doubt acknowledged by most experts ; my 

 opponents have therefore of late turned to Brefeld. He 



* Just. Chr. Holm, " Sur les methodes de culture pure et specialement sur la 

 culture sur plaques de M. Koch, et la limite des erreurs de cette methode " 

 ('Compte rendu du Laboratoire de Carlsberg,' 2 vol. I livr., 1891). In this 

 treatise a historical account of the matter and an exact bibliography is to be found. 

 See also Jorgensen's 'Micro-organisms and Fermentation,' new edition, London, 

 1893, P- 32. 



