9 6 



PATHOGENIC BACTERIA. 



for the sterilization of the unstable toxins and anti- 

 toxins, which are destroyed by heat. Various substances 

 have been used for filtration, as stone, sand, powdered 

 glass, etc., but experimentation has shown porcelain to 

 be the only reliable filter against bacteria. Even this 

 material, whose interstices are so small as to allow the 

 liquid to pass through with great slowness, is only cer- 

 tain in its action for a time, for after it has been used 

 considerably the bacteria seem able to work their way 

 through. To be certain of the efficacy of such a filter 

 the fluid first passed through must be tested by cultiva- 

 tion methods. The complicated Pasteur-Chamberland 

 and the simple Kitasato and Reichel filters are shown in 

 Figures 12, 13, and 14. 



After having been used a porcelain filter must be dis- 

 infected, scrubbed, dried thoroughly, and then heated in 

 a Bunsen burner or blowpipe flame until all the organic 



FIG. 13. Kitasato's filter: a, por- 

 celain bougie ; b, attachment for suc- 

 tion-pump; c, reservoir; d, sterile 

 receiver. 



FIG. 14. Reichel's bacteriologic filter 

 of unglazed porcelain : A, sterile re- 

 ceiver; B, porcelain filter; c, d, attach- 

 ments for pump. 



matter is consumed. In this firing process the filter first 

 turns black as the organic matter chars, then becomes 



