62 A MANUAL OF BACTEEIOLOGY 



145 C. and maintained at this for at least an hour. 

 Above 150 C. cotton- wool becomes brown and brittle.. 

 It is a common practice to use various coloured wools 

 for the different culture media, especially the carbo- 

 hydrate ones, so that they are readily distinguishable by 

 the eye. The coloured wools may be purchased, or the 

 ordinary white wool may be dyed with household dyes. 



Glass vessels. The vessels (usually test-tubes, flasks, 

 and dishes) are thoroughly washed and rinsed in water, 

 then rinsed with 25 per cent, hydrochloric acid, and 

 afterwards washed well with tap-water and drained. A 

 final rinse with distilled water or alcohol is an advantage, 

 as no deposit then occurs on drying. The cleansed vessels 

 should be dried before sterilising, either in the air or by 

 placing in the hot-air steriliser for half an hour. When 

 dry, the vessels are plugged with a firm plug of the 

 sterilised cotton-wool, and are placed in the hot-air 

 steriliser, the temperature of which is then raised to 

 about 150 C. They should remain at this temperature 

 for not less than half an hour, after which the steriliser 

 and its contents are allowed to cool slowly. 



Petri dishes for plate cultures, graduated pipettes, etc., 

 are cleaned in the same manner. They may be sterilised 

 and kept in sheet-iron or copper boxes of appropriate 

 size and shape, or may be wrapped in paper and sterilised. 



If tubes, flasks, pipettes, etc., are required in a hurry 

 they may be rapidly sterilised as follows : After washing 

 in water they are rinsed with 5 per cent, carbolic, then 

 with absolute alcohol, and finally with ether, and are then 

 well flamed over a Bunsen flame, being held in a suitable 

 forceps or holder. The ether evaporates and burns at 

 the mouth, and when dry, a pledget of cotton- wool is 

 held in the forceps and singed in the flame, and, while 

 burning, the tube or flask is plugged with it. 



When thick glass vessels, such as measures, etc., have 



