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 
Fic. 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 HET 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- 
