4 PHYSIOLOGY FOR THE LABORATORY. 



B. The Use of the Microscope. 



1. The stand is used with the ends of the horseshoe-foot 

 pointing away from the student. It is always kept in this 

 position, and any change in the light is overcome by a 

 change in the position of the mirror. 



2. The light is obtained by turning the mirror so that 

 it will reflect the light from the sky upward through the 

 draw-tube ; the amount of light may be regulated by the 

 diaphragm. The sun should never be allowed to shine 

 directly on the mirror or on any other part of the microscope. 



3. The proper focus is found by two adjustments. 



a. The coarse adjustment is used first with both low and 

 high power to find the approximate focus. It is accom- 

 plished most easily by slowly twisting the entire draw-tube 

 while sliding it upward or downward with the fingers. 



b. The fine adjustment is used to focus exactly, so that 

 the object shall be perfectly clear and distinct. It is 

 effected by turning the milled head on the upper end of 

 the pillar. 



c. Never focus downward with the eye at the microscope, 

 as there is danger of touching the slide with the lens and 

 injuring both the slide and the lens. 



d. If the object cannot be brought clearly into view by 

 the adjustment, test the illumination by changing the 

 position of the mirror, examine the objective to make sure 

 that it is not wet, and finally examine the cover-glass. 



e. Learn to keep both eyes open ; the strain upon them is 

 far less than if one eye is closed. If the object does not 



