ACTION AND UTILITY OF FILTERS. 2ti7 



and twenty-two days were found quite sterile. It appeared, 

 therefore, that, under the conditions of the experiments, the 

 B. typhosus was not able to grow through the walls of the 

 filtering candle. Freudenreich believed that the failure was 

 due to the products secreted by the B. typhosus passing through 

 the bougie and exerting a negative chemiotaxis on the typhoid 

 bacilli, which were thus prevented from growing through the 

 walls. This explanation appeared probable, as it was found 

 that when some of the filtrate was inoculated with a fresh 

 culture of B. typhosus the bacilli were unable to grow in it. 



Thirty experiments were made with water filtration, fifteen 

 at a temperature of 35 C., when the water filtrate remained 

 sterile after periods of filtration varying from two to fourteen 

 days, and fifteen at a temperature of 22 C.,in the latter experi- 

 ments the filtrate was sterile after from seven to eighteen 

 days filtration. Experiments were also made at 15-18 C. ; at 

 these temperatures the filtrate remained sterile after fifteen to 

 twenty-one days. These results also showed that water 

 bacteria were able to grow through the walls of the filtering 

 candle, but the rate of growth depended on the temperature. 

 Freudenreich stated that when typhoid bacilli were present in a 

 water supply, negative chemiotaxis would not be exercised by 

 the products present in the filtrate ; but in any case the typhoid 

 bacilli would never grow through the filtering candle more 

 quickly than water bacteria ; consequently, at ordinary room 

 temperatures, the Pasteur-Chamberland could be depended upon 

 to produce a germ-free filtrate for about eight days. 



With regard to the Berkefeld filter, the results of the various 

 experiments have caused bacteriologists to express diametrically 

 opposite opinions as to the usefulness of the filter. Nordtmeyer 

 and Bitter considered that the Berkefeld filter gave a germ-free 

 filtrate for a longer time than the Pasteur-Chamberland filter. 



O 



Prochnick found the filtrate from the Berkefeld filter to be 

 germ free after the filter had been in continuous use for thirty- 

 eight days. Weyl, as the result of his experiments in Berlin, 

 stated that the Berkefeld filter produced a germ-free filtrate for 

 three days, and when the candles were brushed the filtrate 

 remained sterile for six days. In 1893, Kirchner made a large 

 number of experiments with the Berkefeld filter, and arrived at 



