40 LABORATORY GUIDE IN BACTERIOLOGY 



that the end of the tube rests on one edge of the hand 

 (Fig. 22), holding them at an angle of about 45. If held 

 horizontally, the condensation water, always present at 

 the lower end of the agar medium, will moisten the surface 

 and destroy a characteristic growth along the needle-track. 

 If held in a vertical position, contamination from the air 

 cannot be avoided. 



FIG. 22 

 Method of Inoculating Media 



3. Remove the cotton stoppers by taking hold of 

 the singed portion only, and hold also by the singed part 

 only 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 con- 

 taminated and must be singed before replacing. 



4. Sterilize the straight platinum needle in the flame, 

 holding it like a pencil. The platinum wire 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 

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



