172 



SteriKzation and Disinfection 



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 repect may result in the contamination of the 

 cultures. 



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 



Fig. 31. — Hot-air sterilizer. The gas jets are inclosed within the space be- 

 tween the outer and middle walls, C, and can be seen at F. The heat ascends, 

 wanning the air between the two inner walls, K, then descends over the contents, 

 /, and escapes through to supply the draft at F, perforations in the bottom, B, 

 and eventually escapes again at S; R, gas regulator; T, thermometer. 



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 

 must be sterilized by exposure to streaming steam or steam under 



