CHAPTER XV. 



THE MODE OP ACTION AND UTILITY OP THE 



PASTEUR-CHAMBERLAND AND BERKEFELD 



FILTERS. 



THESE filters have a very trifling influence on the chemical 

 composition of water which is passed through them. They 

 are supposed, however, to prevent the passage of bacteria by 

 exercising a molecular influence on the microbes during the 

 transit of the fluid containing them through the materials of 

 the filtering candles. Numerous investigations have been made 

 on the efficacy of these filters. In 1890 Kiibler tested the 

 Pasteur-Cham berland filter and arrived at the conclusion that 

 this filter only delivered a germ-free filtrate for a period of four 

 days. In his first series of experiments water, containing from 

 6160 to 126,720 bacteria per c.c., was passed intermittently 

 through the filter, suction being applied by the mouth. Up 

 to the fourth day the filtrate was sterile ; on the fifth day 

 twenty-four bacteria per c.c. were counted, and on the eighth 

 day the bacteria were innumerable. In the second series of 

 experiments, employing continuous filtration, a sterile filtrate 

 was only obtained up to the third day. In the third series 

 of experiments the surface of the filter was brushed every day, 

 but a sterile filtrate was only obtained up to the end of the 

 first day. Kiibler noticed that the first bacteria to appear in 

 the filtrate were the fluorescent motile bacteria ; two days later* 

 other species appeared. He accordingly came to the conclusion 

 that the bacteria grew through the filtering candle owing to 

 their power of multiplying in water, and this idea was supported 

 by the fact that when the filtration was maintained at C., 

 a temperature unfavourable to the multiplication of micro- 

 organisms, a permanently sterile filtrate was obtained. 



