STERILISATION OF APPARATUS. 7 



necessary to sterilise all vessels and other apparatus, 

 and all culture media before use. The methods which 

 are adopted all depend upon the action of heat ; 

 chemical antiseptics are rarely used in the bacterio- 

 logical laboratory for the sterilisation of apparatus, for 

 it would be impossible to remove them completely, and 

 the traces which might remain would prevent the 

 development of those germs which we wished to 



FIG. 5. Slot Air Steriliser (simple form). 



cultivate. Two chief methods are in use, sterilisation 

 by dry heat and by steam; we exclude sterilisation by 

 steam under pressure as this requires special and 

 expensive apparatus. 



DRY HEAT is used to sterilise all glass vessels (flasks, 

 Petri dishes, test-tubes, pipettes, &c.,) cotton-wool, and 

 metal instruments. The heat must be continued for at 

 least an hour and must not fall below 150 C. as indi- 



