176 



Sterilization and Disinfection 



150 C. or 302 F. in an appropriate hot-air oven. This 

 temperature is fatal to all forms of microscopic life. 



Rubber stoppers, corks, wooden apparatus, and other 

 objects which are warped, cracked, charred, or melted 

 by so high a temperature must be sterilized by exposure to 

 streaming steam or steam under pressure, in the steam 

 sterilizer or autoclave, before they can be pronounced 

 sterile. 



It must always be borne in mind that after sterilization 



Fig. 24. Hot-air sterilizer. 



has been accomplished the original sources of contamination 

 are still present, so that it is necessary to protect the sterilized 

 objects and media from them. 



To Schroder and Van Dusch belongs the credit of having 

 first shown that when the mouths of flasks and tubes are 

 closed with plugs of sterile cotton no germs can filter through. 

 This discovery has been of inestimable value, and has been 

 one of the chief means permitting the advance of bacteri- 



