10 BACTERIOLOGICAL DIAGNOSIS. 



in the same way and are sometimes requisite for the 

 transmission of fluids to a public laboratory for an 

 examination which the practitioner is unable to carry 

 out at home. They may also be sterilised by boiling. 

 Test-tubes are treated in the same way as flasks. Petvi 

 dishes are wrapped round with tissue-paper or filter 

 paper before being sterilised. 



Before removing glass apparatus from the steriliser 

 remember to let the temperature fall gradually, or the 

 vessels may crack. In the case of a proper steriliser or 

 of a biscuit tin heated by a burner the gas is turned out 

 and the whole apparatus allowed to cool before the door 

 is opened. In the case of a kitchen oven the best plan 

 is to let the fire go out, or to open the door* very 

 gradually. 



Cotton-wool is sterilised by being spread out in thin 

 layers on the shelves of the apparatus, and the heat 

 is continued until the outside is singed. 



Metal instruments (knives, scissors, &c.) may be steril- 

 ised 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 moment 

 at which they are to be used. 



STEAM is chiefly used for the sterilisation 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 ad- 

 dition of a few drops of commercial formalin to each 

 tube. 



The proper steam steriliser consists of a metal 

 cylinder with a perforated diaphragm six or eight 

 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 the 



