STERILIZATION OF APPARATUS, ETC. 5 



over the whole of the exposed surface. This method is very 

 convenient for practitioners 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. Test-tubes are treated in 

 the same way as flasks. Petri 

 dishes are wrapped round with 

 tissue-paper or filter-paper before 

 being sterilized. 



Before removing glass appara- 

 tus from the sterilizer remember 

 to let the temperature fall gradu- 

 ally, or the vessels may crack. 



If a sterilized test-tube be re- 

 quired in a hurry (as often hap- 

 pens), plug a clean tube with cot- 

 ton-wool, and hold it with forceps, 

 one blade being" inside and one 

 outsi'de the open end. Then heat 

 every part of the tube thoroughly 

 in the flame, taking care the heat 

 is great enough to scorch the 

 plug. 



Petri dishes and similar ves- 

 sels can be sterilized extempor- 

 aneously as follows : Fill each part with i in 20 carbolic pre- 

 viously raised to the boiling-point. Allow it to act for a few 

 minutes, pour it away, and wash it out with several lots of 

 absolute alcohol or good methylated spirit. Apply a light, 

 and let the spirit which remains in the dish burn off. This 

 procedure can be relied on, unless the vessel has contained 

 material in which there are numerous spores. 



In many cases it will be sufficient to "flame" them over a 

 Bunsen or spirit-lamp. 



Cotton-wool is sterilized by being spread out in thin layers 



FIG. 3. STEAM STERILIZER. 



