EXAMINATION OF AIR AND WATER. 49 



method is, that several important organisms do not develop 

 at all when transferred directly to the gelatine in the en- 

 feebled condition in which they generally occur in atmospheric 

 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 

 Freudenreich flasks containing sterilised wort and beer. 1 

 After incubation at 25 C. for fourteen days the contents 

 of the culture-flasks are submitted to an examination. If 

 only a part of them show any development, the rest re- 

 maining 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 development 

 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 numbers of wort-growths will be too 

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

 undisturbed and without hindrance from other organisms; 

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

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

 the flasks which show a formation of mould will have no 

 importance for the brewery, but only for the malt-house. 

 By way of a nearer approach to practical requirements, 

 Hansen proposes the following method of procedure. The 

 flasks containing a development of yeasts and bacteria are 

 divided into two groups : (1) those in which the growths soon 

 appeared, and (2) the remainder, in which they made their 



1 In the analyses of air the germs are introduced directly, by means 

 of an aspirator, into water, or first into cotton-wool and then into 

 water. 



