PURIFICATION OF WATER FOR DRINKING PURPOSES 179 



special object of ascertaining its power of retaining 

 typhoid bacilli, purposely introduced with the latter as 

 small a quantity as possible of nutritive material into 

 the sterilised water which was to be filtered, thus re- 

 ducing the chances of multiplication and subsequent 

 growth of the organisms through the pores of the filter. 

 Observing this precaution, a filter fed with sterilised 

 distilled water infected with typhoid bacilli yielded, 

 when preserved at a temperature of from 19-26° 0, 

 a sterile filtrate for a period of sixteen days, similar 

 results being also obtained when sterilised tap water 

 containing typhoid organisms was used. 



In another experiment, 7 litres of a well-water rich 

 both in bacteria (2,960 per c.c.) and organic matter was 

 first passed through the cylinder, in order to obtain a 

 depo,sit of organic material and so possibly to favour 

 the growth of the typhoid bacilli ; the cylinder was then 

 sterilised and typhoid-infected water passed through, 

 but although during the twenty- four days over which 

 the investigation extended fresh typhoid bacilli were 

 introduced no less than twelve times, none were dis- 

 coverable in the filtrate. In this, as in the previous 

 experiments, there was obviously not sufiicient food 

 material present to permit of the growth and multipli- 

 cation of the typhoid bacilli. A further experiment 

 was made using very impure canal water (182,000 

 bacteria in 1 c.c), receiving indeed a large part of the 

 raw sewage of Vienna; 4 litres of this were passed 

 through a Berkefeld cylinder to coat it with an organic 

 deposit. The cylinder was then sterilised and filtration 

 continued from July 3-15, 1893, using the same canal 

 water to which on July 3, 6, 9, 11, and 14, typhoid 

 bacilli were added, the filtrate remaining however quite 

 sterile until after the addition of bouillon (5 c.c. per 

 60'0 c.c. water) on July 15, which addition was followed 



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