176 MICRO-ORaANISMS IN WATER 



terpretation also, for the internal sterile broth, on 

 examination, was found to be incapable of supporting 

 the growth of typhoid bacilli, doubtless because the 

 products of the growth of the typhoid bacilli in the ex 

 ternal broth had diffused through the porcelain into the 

 internal broth, unfitting the latter for the nutriment of 

 typhoid bacilli ; for, as is well known, this bacillus will 

 not develop in media which have already supported 

 growths of typhoid bacilli. It must be regarded, there- 

 fore, still as an open question whether pathogenic 

 organisms, such as typhoid bacilli, can or cannot grow 

 through the pores of the Chamberland filter ; and until 

 this question has been answered in the negative it is 

 obvious that in using these filters the cylinders should 

 be frequently cleaned and sterilised, which is, in fact, 

 also necessary on the ground of the rapid reduction 

 in the yield of water which takes place. 



Berkefeld Filter. — One of the most imiDortant of the 

 modifications of the Chamberland filter which has been 

 introduced is the Berkefeld filter.^ It is constructed 

 upon exactly the same principles as the Chamberland 

 filter, but instead of biscuit-porcelain baked infusorial 

 earth (Kleselguhr) is used. It yields, in the first in- 

 stance, sterile water, and can be easily cleaned and 

 re- sterilised, when necessary, by placing it in a vessel 

 containing cold water, and allowing it to boil for three- 

 quarters of an hour. The material being somewhat 

 brittle, care must be used in handling it, and for the 

 same reason, for cleansing purposes, it should not be 

 placed, to begin with, in boiling water, but gradually 

 heated as described. It may also be cleansed by rub- 

 bing the cylinder with a loofah under running water ; 



^ * Ueber Wasserfiltration durch Filter aus gebrannter Infusorienerde/ 

 Nordtmeyer. Zeitschrift filr Hygiene, vol. x. p. 146, 1891 ; also loc. cit. 

 p. 155^ a paper by Bitter on the same filter. 



