6 



STERILIZATION BY DRY HEAT 



Technique of sterilization by hot air. 



(a) Carefully wash and rinse in a large volume of water all apparatus, 

 whatever its nature, until all traces of organic matter have been removed. 

 Unless the cleansing of glass for example be very thorough, black stains, 

 due to the charring of organic matter during the heating process, will be 

 found on the surface after sterilization. After washing allow the apparatus 

 to dry, being specially careful in the case of glass, to avoid subsequent break- 

 age during heating. When dry, treat each article in the manner already 

 described, either plugging with wool, wrapping in paper, or packing in a 

 metal box, according to its nature and use. 



FIG. 3. Hearson's hot air sterilizer. 



(b) Place the articles in the sterilizer, taking care that neither wool nor 

 paper touch the floor or sides, for these substances will char if they come in 

 contact with the heated metal, and a tarry product rich in antiseptic sub- 

 stances will be deposited on the sterilized vessels, which will interfere with 

 the subsequent growth of organisms. If by accident charring should take 

 place, the articles which have been soiled must be washed, first in alcohol, 

 then in water, dried and re-sterilized. 



To avoid charring and breakage, it is advisable to place one or two fire 

 bricks on the bottom of the sterilizer to keep the contents from touching the 

 heated metal surface. 



(c) Close the sterilizer and place the thermometer in position, pushing 

 the latter well down into the interior. 



