12 THE FROG 



cover glass, balsam or water used in mounting the object, or 

 anything else except lens paper used in cleaning the lens. 

 Never remove or insert a slide while working with the high 

 power. Be especially careful not to touch the lenses with 

 the fingers. If the image is not clear this is usually due to 

 dirty lenses. To clean a lens, breathe on it and wipe it dry 

 with lens paper; if this is not sufficient speak to the in- 

 structor. (Balsam may be removed with xylol which should 

 be wiped off with a clean soft cotton cloth.) 



5. While working with the microscope, keep both eyes 

 open; this will lessen eye strain. 



6. While working with the high power you should use 

 the fine adjustment almost constantly. This will save 

 straining the eyes in an effort to see details out of focus, and 

 will reveal the finer structures. 



7. Careful adjustment of the diaphragm and manipula- 

 tion of the mirror so as to throw some shadow into the field 

 will often reveal structures that in too bright light are lost 

 sight of. Oblique illumination is often useful. 



8. If the microscope is equipped with a sub-stage con- 

 denser the plane mirror only should be used. In the absence 

 of a condenser (which is usually not furnished for micro- 

 scopes used in elementary work) the plane mirror should be 

 used only when working continuously with the low power, 

 with a bright light. 



9. In putting away the microscope see that the object 

 slide is returned to the tray and not left on the stage or on 

 your table. See that the low power objective is in position 

 for use and that the clips are in place. In carrying the 

 microscope grasp it by the base, or the handle if one is pro- 

 vided. Be sure to return the microscope to the place on the 

 shelf indicated by its number. 



