182 



Sterilization and Disinfection 



sand, powdered glass, etc., but experimentation has shown 

 unglazed porcelain to be the only reliable filtering material 

 by which to remove bacteria. Even this material, whose 

 interstices are so small as to allow the liquid to pass through 

 with great slowness, is only certain in its action for a time, 

 for after it has been repeatedly used the bacteria seem 

 able to work their way through. To be certain of the efficacy 

 of any filter, the fluid first passed through must be tested 

 by cultivation methods to prove that all the bacteria have 

 been removed. The complicated Pasteur-Chamberland and 

 the simple Kitasato and Reichel filters are shown in figures 

 29, 30, and 31. 



The porcelain bougies as well as their attachments must 

 be thoroughly sterilized before use. 



Fig- 3 2 - Apparatus for the rapid filtration of toxins, etc.: a, Filter 

 flask; 6, Woulff bottle to guard against regurgitation of water from 

 the pump; c, reservoir for the filtrate; d t water vacuum pump. 



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 

 matter is consumed. In this firing process the filter first 

 turns black as the organic matter chars, then becomes 

 white again as it is consumed. The porcelain must be dry 

 before entering the fire, or it is apt to crack. 



It should not be forgotten that the filtrate must be received 

 in sterile receivers and handled with care to prevent sub- 

 sequent contamination. 



The filtration of water, peptone solution, and bouillon 

 is comparatively easy, but gelatin and blood-serum pass 

 through with great difficulty, and speedily gum the filter. 



A convenient apparatus used by the author for the rapid 



