72 MICRO-ORGANISMS IN WATER 



in the fermentation-cellar, although, as a rule, they are 

 not able to develop in the beer during its sojourn in the 

 store-cellar ; but when the beer is drawn off, and thus 

 aerated, and placed in bottles or small casks and exposed 

 to a higher temperature, such bacteria may multiply 

 with astonishing rapidity and cause great damage. 



A slight modification of Hansen's method has been 

 introduced by Wichmann 1 in order to give some- 

 numerical expression to the different vital energy 

 possessed by the micro-organisms present in various 

 waters. For this purpose he takes twenty-five small 

 flasks, each containing 10 c.c. of sterile malt-wort, and 

 twenty- five containing the same quantity of sterile beer ;, 

 into twenty of each kind one drop ( = '025 c.c.) of the 

 water under examination is added, 2 whilst four further 

 flasks of each kind receive respectively '25, *50, *75,. 

 and 1-0 c.c. of the water, whilst the twenty-fifth tube- 

 of each kind is kept for control. The following arbi- 

 trary standard is then adopted to represent the relative 

 fitness or unfitness of the water : A water which ren- 

 ders the above four flasks of wort turbid in twenty-four 

 hours, and the four flasks of beer within three days,, 

 is represented as possessing a degree of impurity 100. 

 Lesser degrees of impurity are calculated from the 

 length of time elapsing before each of the above four- 

 dilutions becomes turbid, by multiplying the number 

 of the dilution by a constant factor, according to the 

 time, and then adding these products together. Thus,, 

 in the case of the wort, if the turbidity appears on the 

 first day the factor is ten, on the second day eight, on 



1 ' Biologische Uiitersuchtmg des Wassers fiir Brauereizwecke,' Mit~ 

 tlieilungen der Oesterr. Versuclisstation fur Braucrci mid Miilzerei* 

 Heft 5, 1892. (CentralUatt fiir Bakteriologie, vol. xiii., 1898, p. 207.) 



2 These twenty flasks, to which one drop of w r ater has been added 

 respectively, are intended to serve for Hansen's method as described on 

 p. 68. 



