16 



BACTERIOLOGY 



the purpose of regulating the temperature. This arrange- 

 ment is suited for the sterilisation of instruments, apparatus, 

 glassware, &c. (fig. 9). 



To prevent flasks and test-glasses from becoming re- 

 infected after sterilisation they must be closed with a plug 

 of cotton-wool before being placed in the steriliser, as such 

 a plug, while allowing the air to enter the vessels, keeps 



back the organisms floating in it. 

 The plug can be further covered 

 with a cap of indiarubber. 



Instead of plugging with 

 cotton, Staff- surgeon Schill re- 

 commends the use of double 

 test-glasses, consisting of two 

 test-tubes made of stout glass 

 and with smooth even edges, one 

 of which is pushed over the 

 other as a cover. The for- 

 mer should be only so much 

 wider as to leave a space the 

 thickness of a sheet of paper 

 between the two, and should 

 be but half as long as the lower. 



Sterilisation by steam. Articles which cannot be ex- 

 posed to so high a temperature are sterilised by the 

 vapour of boiling water at 100 C. For this purpose a 

 cylindrical vessel of sheet copper is used, measuring nearly 

 a metre in height and about 20 cm. in diameter, covered 

 with felt or asbestos to prevent loss of heat, and capable of 

 being closed with a lid similarly protected. The latter is 

 provided with an opening for the introduction of a ther- 

 mometer, and does not fit quite air-tight (fig. 10). The 

 bottom of the vessel is double, the inner bottom consisting 

 of a grating fixed about 30 cm. above the outer, and the 



FIG. 9. HOT-AIR STERILISER. 



