12 



GENERAL BACTERIOLOGY 



steam gauge, safety and outlet valve. A thermo-regulator is also 

 desirable. The following table gives the temperature correspond- 

 ing to atmospheres of pressure indicated on the gauge : 



TABLE OF TEMPERATURES CORRESPONDING TO STEAM- 

 PRESSURES. 



This table is true only when all of the air in the 

 apparatus is replaced by steam, and hence the steam 

 must ie allowed to escape freely before the outlet 

 valve is closed. A single exposure of 20 minutes at 

 a temperature of 120° C. (one additional atmos- 

 phere) is sufficient to kill all germ life. After the 

 proper exposure, care must be taken not to allow the 

 steam to escape too rapidly, otherwise the culture 

 media may be forced against the plugs owing to the 

 unequal pressure. 



General Directions. Ordinary media may be 

 sterilized by either method. In case of gelatin and 

 sugar media the temperature should not exceed 

 110° C. for 15 minutes. 



SI ^ 



References. 

 166; P. 218. 



. , ^^ „ _ Fig. 4. Autoclave; 



A. 59-77 ; H. 37 ; M. & R. 29 ; McF. a. safety valve; 6, 



blow-off pipe; c, 

 gaugre ;" (Muir & 

 Ritchie). 



Special Directions. Sterilize bouillon pre- 

 pared in 4 for 20 minutes in a steam sterilizer on three consecutive 

 days, or in the autoclave at 120° C. for 20 minutes. Rule V. 



N. B. Some time is required to raise the temperature of the 

 media to that of the steam, especially if the vessels are large. 



All media should ie carefully examined every day for a week or 

 more, and if "specks" or the least cloudiness appears, the medium is 

 not sterile and the process of sterilization must ie repeated. 



