THE FROG 7 
working with the high power keep the fingers on the fine adjust- 
ing screw and turn it very slightly, alternating the direction so as 
to focus on all depths of the object. 
D. The following points should be especially noted: 
1. The object to be examined should usually be mounted in a 
liquid and covered with a cover glass—especially if it is to be 
studied with the high power. 
2. Always study the object first with the low power in order 
to obtain a general view. Never use the high power when the 
low power will do—there are many disadvantages attending the 
use of the high power. 
3. Never focus downward with the coarse adjustment while 
the eye is at the tube—the result usually is to smash the slide 
and perhaps also to injure the lens. 
4. Do not allow the objective to come in contact with the 
cover glass, balsam or water used in mounting the object, or any- 
thing else except lens paper used in cleaning the lens. Be espe- 
cially 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 instructor. (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 the fine adjustment 
should be used 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 manipulation 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. Better results can be secured if the stage is kept level. The 
use of the clips for clamping the object slide in place is, as a rule, 
to be avoided, since it interferes with delicate manipulation of the 
slide. 
