Sterilization in the Autoclave 



207 



The media to be sterilized should be placed in the autoclave, the top 

 firmly screwed down, but the escape-valve allowed to remain open 

 until steam is freely generated within and replaces the hot air. The 

 valve is then closed, and the temperature maintained for fifteen min- 

 utes or longer if the media be in bulk in flasks. The apparatus should 



Fig. 41. Pasteur-Chamberland filter arranged to filter under 

 pressure. 



be permitted to cool before the valve is opened, and the vacuum be 

 slowly relieved If the valve be opened suddenly the fluids boil rap- 

 idly and the cotton plugs may be 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. 



