158 Animal Microloyy 



the neck. Sit as upright as possible. If the instrument is 

 inclined it should set farther in on the table than if it is in the 

 upright position. 



3. With a piece of old linen, a chamois skin, or a bit of lens 

 paper, carefully clean the eyepiece to be used and put it in place. 

 Always use the low-power eyepiece first. 



4. Likewise clean and attach the objective (low-power first) 

 after elevating the tube far enough above the stage for this pur- 

 pose. Guard particularly against screwing the objective in 

 crooked, as this will injure the threads. It is best to swing the 

 objective between the first and second fingers of one hand and 

 bring the screw squarely into contact with the screw of the tube 

 (or nosepiece) ; with the thumb and forefinger of the other 

 hand it is then screwed into place. 



5. Bring the draw-tube to the standard length (see tube-loigtJi ) 

 for which the lenses are corrected. If a nosepiece is used, allow- 

 ance must be made for its height. 



6. Place the slide which bears the object on the stage with 

 the object over the central opening of the latter, and clamp it in 

 place by means of the spring clips. While looking at the object 

 from one side, turn the mirror until a flood of light shines up 

 through the center of the stage. 



7. Lower the tube until the objective nearly touches the cover- 

 glass, then look through the eyepiece and slowly raise the tube 

 by means of the coarse adjustment until the specimen to be 

 examined is plainly visible. Focus accurately by means of the 

 fine adjustment. If a high-power objective is being used, since 

 it must come very near the cover, the operator should lower his 

 head to the level of the stage, and look toward the light between 

 objective and cover-glass in order to prevent actual contact. This 

 is of great importance, for otherwise the objective or the object 

 is liable to injury. Remember that in focussing -up the lowest 

 part of the object comes into view first, the highest part last. 



8. The higher the power, the more difficult it is to find an 

 object or a particular part of it. For this reason the finding is 

 usually done by means of a low-power objective, or a low-power 



