50 MICRO-ORGANISMS AND FERMENTATION. 



HANSEN has further shown, that in zymotechnical analyses 

 of water and air, it is a mistake to employ gelatine at the 

 outset, and then to transfer the colonies that have been formed 

 into wort. Thus, he demonstrated by experiments that several 

 of the bacterial germs existing in atmospheric dust and in 

 water are capable of developing in nutritive gelatine, but not 

 in wort; but several of these species become invigorated to 

 such a degree after having formed a new growth in the 

 gelatine, that they are then enabled to develop in the less 

 favourable medium, wort. In such cases the experimenter is 

 therefore deceived. Another, and a still greater, objection to 

 the gelatine method is, that several important organisms do not 

 develop at all when transferred directly to the gelatine in the 

 enfeebled condition in which they generally occur in atmos- 

 pheric dust and in water. 



Based upon these observations, HANSEN devised the following 

 method : Small quantities of the water, either in its original 

 state or diluted, are added to a series of Freudenreicli flasks 

 containing either sterilised wort or beer. 1 After incubation at 

 25 C. for fourteen days the contents of the culture-flasks are 

 submitted to examination. If only a part of them show any 

 development, the rest remaining sterile, it may be assumed 

 with approximate certainty that each of the flasks belonging to 

 the former set has received only one germ. Information is 

 thus gained concerning the number of germs capable of de- 

 velopment existing in a determinate volume, and the different 

 germs are also under more favourable conditions for their free 

 development. An exact examination will show to what 

 species these germs belong. 



Although, in this method, the wort-cultures give a very 

 small number of growths in comparison to the plate-cultures, 

 yet in many cases the number of wort-growths will still be too 

 high, for these growths are able to develop in the flasks 

 undisturbed and without hindrance from other organisms, but 

 when wort is mixed with good culture-yeast in the fermenting 

 vessel, many of these germs will be checked. Further, the 

 flasks which show a formation of mould will have no impor- 



] In the analyses of air the germs are aspirated into water, or first into 

 cotton-wool and then transferred to water. 



