STERILIZATION OF APPARATUS 7 



heating (allowing the temperature to rise gradually) until the outer 

 part of the wool is slightly singed over the whole of the exposed 

 surface. 



The special sterilizer which is used in the bacteriological 

 laboratory consists of a copper or iron oven with double walls 

 and perforated metal shelves. There is a hole in the top, which 

 is fitted with a perforated cork, through which the thermometer 

 passes. The oven is mounted on a stand, and heated by means 

 of a large Bunsen or Fletcher's burner. 



An efficient sterilizer may be made out of a cubical biscuit box, 

 but it will not stand much usage unless the joints are brazed 

 instead of being soldered : this can be done by any tinsmith. It 

 is much better to have the bottom of the box replaced by a sheet 

 of copper, and a sterilizer made in this way will answer every 

 purpose and be fairly durable. A circular hole is cut through the 

 centre of the lid and fitted with a cork bored so as to admit the 

 thermometer. A false bottom or a shelf an inch or so from the 

 bottom will keep the articles which are being sterilized from 

 the heated surface ; the false bottom may be made from a sheet 

 of tin 2 inches longer in two of the sides than the bottom 

 of the box. The extremities of the shorter sides are to be 

 turned down for a length of an inch, and several holes cut in 

 the plate. 



Lastly, the kitchen oven may be pressed into service if no 

 other sterilizer is at hand in an emergency. The apparatus to be 

 sterilized is to be placed on a layer of cotton-wool on one of the 

 shelves, and the temperature is observed by means of the thermo- 

 meter, which should be thrust through the little window which 

 permits of the regulation of the temperature ; or the heat may 

 be continued until the cotton-wool is singed over the whole of 

 the exposed surface. This method is very convenient for prac- 

 titioners sending materials to a laboratory for bacteriological 

 examination, 



A gas oven is even more convenient, as the temperature can 

 be regulated to a nicety. 



All glass apparatus must be thoroughly cleansed and dried 

 before sterilization. The remaining steps differ somewhat in the 

 different cases. 



Flasks are plugged lightly with cotton-wool before being placed 

 in the sterilizer. Bottles may be sterilized in the same way ; 

 they may also be sterilized by boiling. Test-tubes are treated in 



