Methods of Sterilization 



169 



it is, therefore, best to employ a temperature high enough to kill 

 all with certainty. The apparatus is known as a " hot-air sterilizer." 

 Platinum wires used for inoculation are sterilized by being held 

 in the direct flame until they become incandescent. In sterilizing 

 the wires attention must be bestowed upon the glass handle, which 

 should be flamed for least half its length for a few moments. 

 Carelessness in this respect may result in the contamination of the 

 cultures. 



Fig. 37. — Hot-air sterilizer. The gas Jets are inclosed within the space 

 between the outer and middle walls, C, and can be seen at F. That heat ascends, 

 warming the air between the two inner walls, which ascends between the walls, 

 K, then descends over the contents, /, and escapes through perforations in the 

 bottom, B, to supply the draft at F, and eventually escapes again at S; R, gas 

 regulator; T, thermometer. 



Knives, scissors, and forceps may be exposed for a very brief 

 time to the direct flame, but as this affects the temper of the steel 

 when continued too long, they are better boiled, steamed or 

 carbolized. 



All articles of glassware are to be sterilized by an exposure of 

 one-half to one hour to a sufficiently high temperature — iSo°C. or 

 302°F. — -in the hot-air sterilizer. This temperature is fatal to all 

 forms of microscopic life. 



Rubber stoppers, corks, wooden apparatus, and other objects which 

 are warped, cracked, charred, or melted by so high a temperature 



