STERILIZATION 97 



clave after two quarts of water have been put in it. 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 one atmosphere (15 pounds) or 120 C. for twenty 

 minutes, all bacteria are destroyed, and the media can be safely 

 assumed to be sterilized. If media containing sugar or gelatine are 



FIG. 23. Autoclave. 



to be sterilized, the temperature should not run above 110 C., since, 

 if this is done the gelatine will not solidify when cold, the sugar is 

 caramelized and the media blackened. 



Potato tubes are hard.er to sterilize a times, and it is safer to 

 repeat the operation in twenty-four hours. 



Fractional method of sterilization, or Tyndallization, is accom- 

 7 



