126 METHODS OF PURE CULTURE. 



as the dilution method, Lister in 1878 prepared a pure culture of 

 Bacterium lactis, which was (chronologically) the first bacterial 

 pure culture, and FRITZ (VII.) also employed the same method 

 in his studies on fermentation by fission fungi. The first six 

 .species of the Saccltaromycetes studied by E. Chr. Hansen, and 

 which stand out so prominently in the literature of fermentation 

 physiology, were also isolated by the aid of an improved form of 

 the dilution method, further mention of which will be made in 

 the second volume. 



The so-called fractional method of culture, as it was afterwards 

 styled by Klebs, was employed in particular in Pasteur's experi- 

 ments on fermentation. It consists in taking from a sample of 

 fermenting liquid that has attained its maximum of development 

 a small aliquot portion and transferring this to a new, sterile 

 medium. By recalling the remarks made in the paragraphs of 

 Section II. dealing with symbiosis, it will be understood that, at 

 the period of highest fermentation in a natural liquid and there- 

 fore one rich in different species that species which is the cause 

 of the fermentation in question will preponderate. Therefore, if 

 merely a single droplet thereof be placed in a medium analogous 

 in composition to the original habitat, this species will be favour- 

 ably situated from the outset, and will increase at a relatively 

 quicker rate than its associates. By repeating this transference 

 (''re-inoculation") several times over, cultures will finally be ob- 

 tained wherein impurities, i.e. extraneous species, can only be 

 detected by more searching methods of separation, such as are 

 described in the next paragraph. 



These subjugated species will, however, come to the front 

 again if the (apparently pure) bacterial culture be inoculated in 

 .a different medium forming a favourable environment for their 

 development. Mention of this has already been made in a pre- 

 vious section, when referring to the older evolutionary labours 

 of Lister, Lankester, Hallier, Billroth, and others. We are now 

 in possession of another more convenient method for the pur- 

 poses of pure cultivation, which will be described in the succeeding 

 paragraph, and consequently a criticism of the dilution method 

 can be omitted. 



At present, only a couple of words will be devoted, as supple- 

 mentary to the remarks already made, to the examination of 

 brewery water for the presence of dangerous organisms. For the 

 brewer those water bacteria alone are important that develop in 

 wort and beer and are capable of producing injurious changes 

 therein. Consequently, sterilised samples of both these liquids 

 -are employed in the biological analysis of brewing water. The 

 method employed was first proposed by E. OH. HANSEN (IV.), 

 according to whom fifty small Freudenreich flasks are used, 

 twenty-five of them being charged with 15 c.c. of sterilised wort 

 .apiece and the remainder with a similar quantity of sterilised 



