46 STERILIZATION AND DISINFECTION. 



burner or alcohol lamp a few times, or by holding them in 

 the flame for a few seconds. The platinum inoculating needle 

 is held in the flame until it is incandescent. The glass handle 

 should also be sterilized for at least half its length. Every 

 time this needle is picked up and before it is laid down again 

 it should be sterilized. This is very important, because it not 

 only insures its being sterile, but it also protects the bacteri- 

 ologist from infection. Steel instruments should not be held 

 in the flame for any length of time, as it affects the temper of 

 the metal. They can be passed through the flame a few times. 



FIG. 11. 



Hot-air chamber. (Leitz.) 



Dry heat: This also has a very limited application ; a very 

 high temperature is required, 150 C., and an exposure of at 

 least one hour. This will kill all known bacteria and their 

 spores. Its application is limited to the sterilization of glass- 

 ware used in the laboratory. Articles made of rubber, wood, 

 or crockery cannot be sterilized by dry heat. 



The tubes, dishes, and flasks are well washed and scrubbed 



