8 



CLINICAL BACTERIOLOGY AND H.EMATOLOGY 



Before removing glass apparatus from the sterilizer remember 

 to let the temperature fall gradually, or the vessels may crack. 



If a steriHzed test-tube be required in a hurry (as often happens), 

 plug a clean tube with cotton-wool, and hold it with forceps, one 

 blade being inside and one outside 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 vessels can be sterilized extemporane- 

 ously as follows : Fill each part with i in 20 carbolic previously 

 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 re- 

 mains in the dish burn off. This 

 procedure can be relied on, unless 

 the vessel has contained material in 

 which there are numerous spores. 



Cotton-wool is sterilized by being 

 spread out in thin layers on the 

 shelves of the apparatus, and the 

 heat is continued until the outside is 

 singed. 



Metal insfniments (knives, scissors, 

 etc.) may be sterilized in the same 

 way and at the same time. They 

 should be wrapped loosely in cotton- 

 wool, and should not be removed 

 from their wrapping until the 

 monient at which they are to be 

 used. 

 Steam is chiefly used for the sterilization of culture media 

 before use, and for the destruction of cultures when they are done 

 with. The latter purpose, however, is accomplished more speedily 

 and safely by the addition of a few drops of commercial formalin 

 to each tube, or the tubes may be filled with i in 20 carbolic ; 

 neither method can be relied on to kill spores. 



The proper steam sterilizer consists of a metal cylinder with a 

 perforated diaphragm 6 or 8 inches from the bottom. It is 

 enclosed in a thick layer of felt or other non-conductor of heat, 

 and is provided with a lid. The space between the bottom and 



Fig. 7. — Steam Sterilizer. 



