METHODS OF STUDY 



21 



o o o 



plished by means of an autoclay e, which is a strong 

 iron cyUnder standing upright, closed at the 

 bottom and furnished with a tight- ^ 



fitting Ud, and provided with a ther- 

 mometer, a steam valve, a safety 

 valve, and a gauge whereby the tem- 

 perature and pressure may be regu- 

 lated, heat being furnished by Bunsen 

 gas burners or by indirect steam from 

 a central boiler. Foii ^culture.. media - 

 ifl>tabes an _exposure_ of fivejninutes 

 ail2 Q° 0.^ (248° F.) ^_suflaaientja 

 ^egtroXjllJiacterivbut for media in 

 bulk an exposure of fifteen minutes fio.6. 

 is necessary. 



Certain culture media are injured 



by exposure to great heat 

 under pressure, and this fact, 

 together with the extraordi- 

 nary resistance of the spores 

 of certain species of bacteria, 

 led to the employment of frac- 

 tional or discontinuous sterili- 

 zation. The ordinary Arnold 

 steam sterilizer used in the 

 Fig. 7. - Bunsen burner, kitcheu f or the stenlization of 



- Autoclave. 



a. Safety-valve. 

 6. Blow-off pipe, 

 c. Gauge. 



