GENERAL BACTERIOLOGY 73 



along the needle track. If held in a vertical position, 

 contamination from the air may take place. 



3. Remove the cotton stoppers by taking hold of 

 the singed portion, and hold also by the singed part 

 between the other fingers. If the portion of cotton 

 from the inside of the tube is touched by the fingers, or 

 accidentally falls on the table or the floor, it becomes 

 contaminated and must be singed before replacing. 



4. Sterilize the straight platinum needle in the 

 flame, holding it like a pencil. The platinum wire 



Fig. 27 

 Method of laoculating Media 



should be heated until red hot, and the glass end passed 

 slowly through the flame once or twice. 



5. After cooling the needle by plunging into the 

 medium, take up a small portion of a colony or culture 

 on the end of the needle by a lateral movement, and, 

 when removing it from the tube, take care not to touch 

 the walls of the tube. If any cotton accidentally sticks 

 to the mouth of the tube, it should be burnt off with a 

 hot platinum needle, and then the mouth of the tube 

 passed through the flame before inserting the needle. 



