CHAPTER III. 

 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 subli- 

 mate), carbolic acid and other chemical agents, but their value 

 in practice is often overrated. The most effective sterilization 

 is that done with heat, either by direct application of the Bun- 

 sen burner, or by heated air, or by steam, or by boiling. 



The naked flame of the Bunsen burner or the alcohol lamp 

 is used largely for the sterilization 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 sterilization 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 

 exposure to this temperature, but it is sufficient for ordinary 

 conditions. Hot-air sterilization 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 allowed to go to the extent of scorching the 



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