BACTERIOLOGICAL TECHNIC 



3. Again use tube brush, and soap and water if 

 necessary. 



4. Rinse again in water to remove every trace of 

 acid or soap. 



5. Place the tubes in a wire basket, mouth down, and 

 heat in a hot-air sterilizer for 20 minutes or longer 

 until dry. 



All other glassware should be treated in the same 

 manner, excepting fermentation tubes, which should 

 not be heated in the hot-air oven, as this would be 

 likely to cause breakage. 



The tubes should be plugged with cotton. Non- 

 absorbent cotton is suitable for this purpose. The 

 cotton plug allows free communication with the air, 

 admitting oxygen, which is necessary for the growth 

 of many bacteria; at the same time the admitted air is 

 filtered germ-free and contamination of cultures is 

 avoided. 



Various methods for plugging tubes are employed 

 in different laboratories. The simplest method is as 

 follows: Take a small amount of cotton and push it 

 gently into the tube with a -glass 

 rod. The cotton should reach 

 into the tube for about f of an 

 inch and be sufficiently firm to 

 support the weight of the tube 

 (Fig. 2). The cotton may also be 

 rolled into a cylinder of thickness 

 equal to that of the tube and then 

 pushed into the mouth. 



The plugged culture tubes ^^^ ^ 



should be placed in a hot-air oven Plugged culture Tube 



