82 METHODS USED IN THE STUDY OF BACTERIA 



almost universally used in this country, is the Arnold steam 

 sterilizer (Fig. 34). This has the advantage of being prac- 

 tically automatic, since the steam which is produced is con- 

 densed and reheated. 



Steam under Pressure. Steam under pressure has been 

 used by the French school for a good while and is now coming 

 into general use. Here a temperature of 105 to 120 C. is 

 ^ <X. maintained for fifteen minutes, 

 the latter temperature is de- 

 structive of all forms of germ 

 life and may be depended upon 

 as a certain means of steriliza- 

 tion. This method of sterili- 

 ' * zation is made possible by the 



FIG. 34. A simple steam sterilizer 



consisting of a galvanized iron pail. USC of a Special piece of appa- 

 a is the cover and b a false bottom. ratus knQwn ^ ^ autodave> 



which is essentially a copper vessel that can be hermetically 

 sealed, provided with a thermometer and steam gauge. In 

 practice it is not found necessary to use a thermometer, since 

 the temperature has a definite ratio to the pressure, provid- 

 ing, however, that the atmosphere within the autoclave is 

 saturated with water, and this can be accomplished by 

 leaving a pet-cock open until steam escapes freely. 



On account of the quickness with which materials can be 

 sterilized in the autoclave, this method is becoming deservedly 

 popular. At first it was thought that the high temperature 

 injured the culture media, but it has been found that the 



