54 



MANUAL OF BACTERIOLOGY. 



cotton; but a faint light browning of the outside is permissible, 

 and is an indication that the sterilization is effectual. Glass- 

 ware should be placed within the sterilizer when it is cold, and 

 after heating should be allowed to cool gradually in order to 

 avoid breaking. Hot-air sterilization is never used for culture- 

 media. 



The apparatus used for hot-air sterilization consists of a box 



FIG. ii. Hot-air sterilizer. 



made of sheet-iron, the walls being double, with an air-space 

 between them. On one side is a door. There are openings at 

 the top to secure the circulation of air in the air-chamber. A 

 thermometer passes from the top into the interior of the sterili- 

 zer so that one may read off the temperature that is being at- 

 tained. The sterilizer should be placed so that there will be 

 no danger of its setting fire to inflammable articles, as the heat 



