THE FROG I I 



the tube slowly until the object comes clearly into view; 

 finish the adjustment with the fine screw. Re-adjust mirror 

 and diaphragm until best results are obtained. While work- 

 ing with the high power keep the fingers on the fine adjust- 

 ment screw and turn it very slightly, alternating the direc- 

 tion so as to focus on all depths of the object. 



C. Examination of an Object by Reflected Light. 

 The above directions are intended for the examination of an 

 object by transmitted light. Sometimes it is desirable to 

 examine the general surface of a small opaque object by 

 light reflected from the object itself; this is usually prac- 

 ticable only with the low power. Mount the object (e. g., 

 the head of a honey-bee) on a microscopical object glass, 

 without water or cover glass, and place it in position on the 

 stage. Close the diaphragm completely, to cut off all light 

 coming from the mirror, and focus with the low power. 

 Compare the result with that obtained by using transmitted 

 light. 



D. Rules for the Use of the Microscope.- -The follow- 

 ing 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 crush 

 the slide and perhaps also to injure the lens. 



4. Do not allow the objective to come in contact with the 



