STERILIZATION AND DISINFECTION. 



II 



an autoclave (Fig. 12). Here under a pressure of two or 

 three atmospheres sufficient heat is generated to destroy 

 the spores. The objections to this method are that it 

 sometimes turns the agar-agar dark, and that it is likely 

 to destroy the gelatinizing power of the gelatin, which 

 after sterilization remains liquid. 



Liquids may also be sterilized by filtration i. e. by 

 passing them through unglazed porcelain or some other 

 material whose interstices are sufficiently fine to resist the 

 passage of the bacteria. This method is largely employed 



FIG. 15. Kitasato's filter : a, por- FIG. 16. Reichel's bacteriologic filter 



celain bougie ; b, attachment for sue- of unglazed porcelain : A^ sterile re- 



tion-pump; c, reservoir; d, sterile ceiver; B porcelain filter ; c, <i, attach- 



receiver. ments for pump. 



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 



