STERILIZATION. 49 



CHAPTER II. 

 STERILIZATION. 



By sterilization is meant the killing of all microorganisms 

 found on or in any body or substance. It is possible to sterilize 

 objects by the use of bichloride of mercury (corrosive sublimate), 

 carboUc acid and other chemical agents, but their value in 

 practice is often overrated. Sterihzation is usually accom- 

 phshed by heat. The most effective sterilization is that done 

 by steam and by boiling; they are not, however, suitable for 

 all kinds of material. 



The naked flame of the Bunsen burner or the alcohol lamp 

 is used largely for the sterihzation of small articles. It is 

 evident that no more efficient way of sterilization could be de- 

 vised than by burning objects, or subjecting them to a red heat. 

 The uses of this method will at once suggest themselves; for 

 instance, surgical dressings that have become soiled with dis- 

 charges and similar materials can be most easily disposed of by 

 simply burning them up. In laboratory work the flame is con- 

 stantly employed for the sterihzation of the platinum wire, 

 forceps, pipettes and cover-glasses; occasionally test-tubes are 

 sterilized in this manner. 



Hot-air Sterilization. — Hot air, at a temperature of 150° 

 C, or higher, maintained for an hour, is very valuable for some 

 materials, although less effective than steam. It has been found 

 that the spores of certain bacteria are not killed even by expo- 

 sure to this temperature, but it is sufficient for ordinary con- 

 ditions. Hot-air sterihzation is employed for glassware such as 

 Petri dishes, flasks and test-tubes. Flasks and test-tubes are 

 generally plugged with raw cotton. The heating should not be 

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