42 LABORATORY GUIDE IN BACTERIOLOGY 



contents of the loop are then spread over the whole sur- 

 face. 



Describe the appearance of the colonies as to — 



1. Naked-eye appearance: 

 Color. 



Shape. 



Border. 



Size (approximately in millimeters). 



2. Appearance under low power of microscope. 



3. Give the approximate number of colonies on the 

 plate. 



4. Examine as to motility in the hanging-drop. 

 Preparation of a hanging-drop (Fig. 23) : 



Fig. 23 



Hanging-Drop 



(After Muir and Ritchie) 



1. Clean a cover-slip in alcohol. Pass several times 

 through the flame so as to burn the last traces of grease 

 off the surface. 



2. Place a loopful of pure water on the center of the 

 cover-slip. 



3. Flame the straight platinum needle, and, after 



