10 



CLINICAL BACTERIOLOGY AND 



A : dry-heat sterilizer consists of a double-jacket square box, 

 usually made of strong sheet steel, with a copper bottom and 

 two movable perforated shelves. On the top is a regulating 

 slide and two holes, one for the insertion of a thermometer, 

 and the other for a thermo regulator. The sterilizer is 

 fixed on a raised metal stand about a foot in height, the 

 heat being supplied by a Bunsen burner or by a power- 

 ful oil lamp. The articles sterilized by dry heat are 

 glass flasks, plates, test-tubes, pipettes, cotton-wool, etc. 



Fig. 4.— Dry Heat Sterilizer. 



To completely sterilize any of these, a temperature of 

 150° C. must be maintained for three-quarters of an hour. 

 When glassware is being sterilized, care must be taken to 

 allow the sterilizer to cool before removing any of its con- 

 tents ; otherwise they are liable to crack when exposed to 

 a lower outside temperature. 



Steam or moist - air sterilizers consist of a water-bath 

 over which is a cylinder with a perforated diaphragm fixed 



