STERILIZATION 



I0 9 



Sterilization of culture media is accomplished in steam steril- 

 izers of two patterns; of these, the autoclave, using steam under 

 pressure, is the most satisfactory and is most generally used at 

 present. 



The baskets containing the culture media are placed in the 

 autoclave after sufficient water has been put in it. The instru- 



FIG. 22. Autoclave. 



ment must never be allowed to run without water. The lid is 

 screwed down and the flame started; free flowing steam should 

 escape from the valve before the latter is shut. When the 

 pressure has risen to i atmosphere (15 pounds) or i2oC. and 

 held there for twenty minutes, all bacteria are destroyed, and 

 the media can be safely assumed to be sterilized. If media 

 containing sugar or gelatine are to be sterilized, the temperature 

 should not run above noC., since, if this is done the gelatine will 



