20 



BACTERIOLOGY. 



burner. It is employed for sterilising nutrient 



media in tubes or flasks, 

 for cooking potatoes, or 

 hastening the filtration 

 of agar-agar. When 

 the thermometer indi- 

 cates 1 00 C. the lid is 

 removed, and test-tubes 

 are lowered in a wire 

 basket by means of a 

 hook and string, and 

 the lid quickly replaced. 



FIG. 2.-HOT-AIR STERILISER. p ota toes Or Small flasks 



are lowered into the cylinder in a tin receiver with 

 a perforated bottom, which rests fc-ii L*_i_A_A_ A 

 upon the grating and admits of 

 its contents being exposed to 

 the steam. 



Hot-air Steriliser. A cubi- 

 cal chest of sheet iron with 

 double walls, supported on four 

 leors ; it may also be suspended 

 on the wall of the laboratory, 

 with a sheet of asbestos inter- 

 vening (Figs. 2 and 3). It is 

 heated with a rose gas-burner 

 from below, and the temperature 

 of the interior indicated by a 

 thermometer inserted through 



i i ^i e FIG. 3. SECTION 



a hole in the roof ; in a second O p HOT-AIR STERILISER. 



