Sterilization in the Autoclave 



161 



developed bacteria are also killed. Eventually, the process 

 is repeated a third time, lest a few spores remain alive. 

 When properly sterilized in this way, culture media will 

 remain free from contamination indefinitely. 



In popular parlance, the intermittent exposure of the 

 culture media to steam is spoken of as sterilization; a 

 prolonged single exposure to lower temperatures (6o-7o C.), 

 as Pasteurization. 



Pasteurization is employed for the destruction of bacteria 



Fig. 26. Modern autoclave. 



in milk and other fluids that are injured -or coagulated by 

 exposure to 100 C. It is appropriate only when the 

 organisms to be killed are without spores and without 

 marked resisting powers. 



Sterilization in the Autoclave. If it should be desir- 

 able to sterilize a medium at once, not waiting the three 

 days required by the intermittent method, it may be done 

 by superheated steam under pressure in an autoclave (Fig. 



