172 



Sterilization and Disinfection 



and the vacuum be slowly relieved. If the valve be opened suddenly the fluids 

 boil rapidly and the cotton plugs maybe forced into the tubes or flasks by the 

 air pressure. The chief objection to the use of the autoclave is that the high 

 temperature sometimes brings about chemic changes in the media by which the 

 reaction is altered. 



Sterilization by Filtration. — Liquids that cannot be subjected 

 to heat without the loss of their most important qualities may 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 bacteria. This method is largely 

 employed for the sterilization of the .unstable bacterial toxins that 

 are destroyed by heat. Various substances have been used for 

 filtration, as diatomaceous earth (Berkefeld filters), stone, 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 porcelain bougies as well as their 

 attachments must be thoroughly sterilized 

 before use. 



After having been used, a porcelain 

 filter must be disinfected, 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 subsequent 

 contamination. 



The filtration of water, peptone solution, and bouillon is com- 

 paratively easy, but gelatin and blood-serum pass through with 

 great difficulty, and speedily gum the filter. 



III. The Disinfection of Instruments, Ligatures, Sutures, the 

 Hands, etc.^ — There are certain objects used by the surgeon that 

 cannot well be rendered incandescent, exposed to dry heat at iSo°C., 



Fig. 39. — Modern 

 autoclave. 



