102 MICROSCOPY 



removing stubborn spots that should never have been there if the micro- 

 scope had had proper care. If fresh material is to be examined, it can be 

 mounted in a drop of water on a slide, covered by a cover glass, and 

 placed on the stage. A permanent slide might need a little cleaning but 

 otherwise is ready for use. If the microscope is equipped with a mechani- 

 cal stage, the slide fits into a rectangular opening and is held in place by 

 a metal finger and spring. The controls of the mechanical stage are then 

 turned until the object is more or less centered over the hole in the stage. 



Illumination may be provided by a substage lamp or by a mirror and 

 separate lamp. Adjust the light source and focus the condenser until the 

 object looks bright when viewed from the side. Further adjustment in 

 lighting will have to be made later. 



If the object is new and unfamiliar, start with the lowest power objec- 

 tive (10 X or lower). It is even desirable to use a low power eyepiece, say 

 5 X, because it gives a wider field. Watching from the side, turn the ob- 

 jective lens down with the coarse focal adjustment until the lens is 

 about a centimeter from the slide. Look through the eyepiece and slowly 

 raise the objective with the coarse adjustment until the object comes into 

 focus. Make final focal adjustments with the fine adjustment knob. Move 

 the slide around, varying the fine adjustment more-or-less continually, 

 until you find the part of the specimen that you want to examine more 

 closely. Then the 10 X eyepiece can be used to give greater magnifica- 

 tion (but not improved resolution). Before switching to the 43 X objec- 

 tive, place the desired object in the center of the field because the higher 

 power lenses have a much smaller field of view. Turn the revolving nose- 

 piece until the higher power objective snaps into place. The microscope 

 is parfocal, which means that both lenses will be in focus at the same 

 position. Only minor focusing with the fine adjustment may be neces- 

 sary. 



Clear images depend upon optimum illumination, and focusing of the 

 condenser and regulation of the iris diaphragm should be varied until 

 the best image is obtained. Never focus downward with the coarse ad- 

 justment without watching from the side. More than one objective lens 

 has been driven through a slide. The slide may be easily replaced, but 

 a scratch on the objective lens is serious. 



To use the oil-immersion lens, first center the object in the field of the 

 43 X objective. Raise the body tube and place a drop of immersion oil 

 on the center of the slide. Watching from the side, slowly lower the 

 oil-immersion objective. As the lens approaches the drop of oil, the oil 

 seems suddenly to jump across the gap, making a bridge between the 



