SECTION II 

 LABORATORY METHODS AND TECHNIC 



CHAPTER VI 



STERILIZATION 



STERILIZATION is the process whereby glassware, media, or 

 any of the materials or apparatus used in the laboratory are 

 entirely freed from living organisms. It is evident that in the 

 study of bacteria it is necessary that we deal with pure cultures, 

 that is, that one kind of organism only be present in the material 

 which we are studying. It is quite impossible to determine from 

 mixed cultures which of the organisms present bring about 

 observed changes. Bacteria are present upon the surface of 

 all laboratory apparatus, in the dust, in soil, upon the hands 

 they are ubiquitous, hence the necessity for sterilization. 



Sterilization may be accomplished by physical or chemical 

 means. In practice the latter is generally called disinfection, and 

 is rarely used in the laboratory. The term sterilization, there- 

 fore, as commonly used, indicates the destruction of micro- 

 organisms by physical processes. 



Sterilization by the Flame. The platinum wire used in the 

 transfer of bacteria in the laboratory is sterilized by heating to 

 a red or white heat in the flame of the Bunsen burner. Similar 

 methods are sometimes used in the sterilization of other small 

 pieces of laboratory apparatus, such as cover-glasses and slides. 



Sterilization by Hot Air. Glassware is commonly sterilized 

 by subjecting it to a temperature of 150 to 170 in a hot-air 

 oven for an hour. All bacteria will be destroyed at this tempera- 

 ture providing the material to be sterilized is of a nature such that 

 the heat can penetrate readily to all parts. This method cannot be 



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