36 LABORATORY GUIDE IN BACTERIOLOGY 



it into focus. It is then easy to feel if the lens touches 

 the glass, and a moving object is seen much more easily 

 than a stationary one. 



1 8. Use the plain mirror in combination with the 

 condenser, and the concave mirror without the condenser 

 or with artificial light. 



19. In preparing stained preparations, it often hap- 

 pens that a small amount of stain remains on the upper 

 side of the cover-slip. Care must be taken to focus for 

 a plane below this. 



