STERILIZATION AND DISINFECTION 6o 



the spores of certain species. Dry heat is applied by the use- 

 of the direct flame and by heated air chambers. 



(a) Direct flame. In laboratory work the direct flame, 

 of a gas burner or of an alcohol lamp is used to sterilize cer- 

 tain articles, such as platinum needles for making cultures 

 and sometimes for instruments used for making cultures 

 at post mortem and occasionally instruments used for slight 

 operations. The method consists in holding the instrument 

 in the flame until it is heated sufficiently to kill all organ- 

 isms that may be upon it. In practice this is usually deter- 



Fig. 32. Hot air sterilizer, Lautenschlager pattern. These 

 ovens can be heated to a temperature of 150C in about 20 minutes. 



mined with small articles like the platinum wire or loop by 

 the red or white heat of the metal. 



(b) Hot air. Many articles, can not be sterilized in 

 the direct flame but can be by the application of air heated 

 to the temperature of 135 to 170C. for from one to two- 

 hours. This is accomplished by means of the hot air steril- 

 izer, which is a metal chest heated by means of a gas flame. 

 In using it the material or apparatus to be sterilized is placed 



