i>6'8 BACTERIOLOGICAL EXAMINATION OF WATER. 



the conclusion that the filtrate was not completely germ free 

 for a longer period than one day. He also tested the possibility 

 of pathogenic organisms passing through the filter. Broth 

 cultures of cholera vibrios, typhoid bacilli, and staphylococcus 

 pvogenes aureus were filtered through the bougie into a glass 

 vessel, in which there was a negative pressure of 500-600 mm. of 

 mercury ; one hour after the commencement of the experiment, 

 and then every twenty-four hours, a drop of the filtrate was 

 plated out in gelatine. Cholera vibrios and staphylococci were 

 found in large numbers in the filtrate received after twenty-four 

 hours, the typhoid bacilli, however, did not appear until after 

 seventy -two hours. A further experiment was then made by 

 adding 1.00 c.c. of a broth culture of cholera vibrios to one 

 litre of water which contained 30,000 bacteria per c.c., and 

 then filtering the mixture through a Berkefeld candle ; cholera 

 vibrios were again found in the filtrate at the end of twenty- 

 four hours. A similar experiment was made with B. typhosus, 

 and this organism was detected in the filtrate at the end of 

 forty-eight hours. Kirchner then concluded that the Berkefeld 

 filter operated in exactly the same manner on pathogenic as, on 

 non-pathogenic bacteria. Gruber criticised Kirchner's work, 

 and pointed out that, in the filtration of water, only those 

 bacteria could grow through a filter which found sufficient 

 nutriment in water to enable them to multiply in the pores of 

 the filter material. He considered that ordinary drinking- 

 water did not contain sufficient nutriment to enable pathogenic 

 bacteria to multiply in this manner. In Kirchner's experi- 

 ments pure broth cultures, or broth cultures diluted ten-fold 

 with water, were employed, and Gruber contends that in this 

 manner an amount of nutriment was supplied which enabled 

 the pathogenic organisms to multiply in the filter; such an 

 amount of nutriment he believes would never be found in an 

 ordinary drinking water. Gruber also considers that the 

 counting of the bacteria in the filtered and unfiltered water is 

 not a good test of a filter, and recommends the following points 

 for consideration when examining the power of a bougie to 

 prevent the passage of bacteria. The direct passage of 

 microbes must be sharply differentiated from the gradual 

 growth of bacteria through the material composing the filtering 



