STERILIZATION BY HEAT 



47 



greater penetration secured by having the steam under 

 pressure. 



The accompanying figure shows a common type of 

 steam steriHzer. 



Fig. 22. — A pressure steam sterilizer. The steam jacket entirely 

 surrounds the chamber, to which the steam is admitted through a 

 valve. Pressure may be continued on the jacket while the dressings 

 are removed. The safety-valve is set to relieve at 15 pounds. 



The teacher should demonstrate the use of heat for sterilization 

 by inoculating six broth tubes with a well sporulated culture of hay 

 bacilli, and heating two in an Arnold sterilizer for five minutes, two 

 others in a pressure steam sterilizer for five minutes (pressure of 

 15 pounds), leaving two unheated. After this, all six tubes are 

 placed in an incubator over night. 



