26 MICRO-ORGANISMS AND FERMENTATION. 



If, now, we ask, whether it is advisable to employ any of 

 the various methods mentioned above for the purification 

 of an unknown impure yeast-mass, the answer must accord- 

 ingly be in the negative ; and this will be the case whether 

 the culture is intended for purely scientific or for industrial 

 purposes, for the danger will always remain of furthering the 

 growth of species other than the desired one. And, the 

 starting-point being uncertain, it necessarily follows that the 

 result must be so too. In fact, all such methods must now be 

 regarded as antiquated, and will, whenever resorted to, prove 

 utter failures. Yet in certain cases they may have some 

 value when employed preparatory to the preparation of a 

 pure culture. In the different branches of the fermentation 

 industry there is only one way that will lead to the goal, 

 namely, the application of the same principles which have 

 for many years been followed in agriculture and horticulture 

 the selection, by means of methodical experiments, of 

 the particular species or type which gives the best results 

 under the circumstances, and which is therefore to be sown 

 alone, without any admixture of other types. The only 

 possible way of effecting this is, however, by the adoption 

 of the methods discovered by Hansen, which will come 

 under consideration later on. 



(/3) Dilution methods. The second group of methods 

 employed for physiological purposes embraces the dilution 

 methods, or the so-called "fractional cultivation," the 



an impure yeast-mass, whether brewers' or distillers' yeast, as proposed by 

 Effront, will give rise to the same dangers as were mentioned above in 

 the case of tartaric acid. In fact, a long series of methodical experi- 

 ments made in the laboratory of the author of this book have shown that 

 by the treatment of impure yeast according to Effront's method the wild- 

 yeasts and Mycoderma species will develop far more actively than culti- 

 vated yeast ; and our experiments have also shown that in many cases 

 even such a dangerous species as Bacterium aceti cannot be suppressed at 

 all by this treatment of the ye<ist-mass ; on the contrary, it was found to 

 multiply much more actively when treated with hydrofluoric acid or 

 fluorides. 



