170 



PATHOGENIC BACTERIA. 



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 as it is consumed. The greatest care must be 

 exercised in cleansing, and especially must care be taken 

 that the porcelain is dry before entering the fire, as it 

 will certainly crack if moist. 



Before using a new filter it should be sterilized by dry 



Fig. 15. — Kitasato's filter: a, por- 

 celain bougie ; b ; attachment for suc- 

 tion-pump; c, reservoir; d, sterile 

 receiver. 



Fig. 16. — Reichel's bacteriologic filter 

 of unglazed porcelain : A, sterile re- 

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

 ments for pump. 



heat, then connected with receivers and tubes, also care- 

 fully sterilized. It should not be forgotten that the fil- 

 tered material is still a good culture-medium and must be 

 handled with the greatest care. 



While the filtration of water, peptone solution, and 

 bouillon is comparatively easy, gelatin and blood-serum 

 pass through with great difficulty, and speedily gum the 

 filter, so that it is useless until fired. 



A convenient apparatus used by the author for the rapid 



