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. 



i8. 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. 



