CH. VI] THE PROJECTION MICROSCOPE 199 



(3) If the slides have many sections upon them, as in a series, 

 then the slide should be masked by putting some orange paper over 

 the cover glass with openings for the sections to be shown; then 

 these can be found quickly and with certainty (fig. 120, 3i2a). 



(4) Indicate in some way which edge of the slide should be up. 

 This will save time, and add to the respect for the exhibition. 



FIG. 1 20. SLIDE TRAY WITH MASKED PREPARATIONS TO BE USED IN A DEMON- 

 STRATION. 



(From Optic Projection). 



(5) It is often a great help to have stated on the preparation the 

 objectives best adapted to bring out the special feature desired. 



(6) For holding the specimens, a slide tray may be used (fig. 120) 

 or one of the slide boxes. In any case they must be so that the 

 slides can be easily grasped. 



(7) It is for many lecturers easier to manipulate the projection 

 microscope themselves and to use a pointer held out in the cone of 

 light. The pointer appears as sharply as when put on the screen. 



