DIRECTIONS FOR USING THE MICROSCOPE. 29 



low-power objective. The body of the microscope should be 

 about vertical, so as not to interfere with mounting in fluid 

 media. 



2. The object mounted on a glass "slide" in a suitable liquid 

 and covered with a "cover glass" is brought to the center of the 

 diaphragm and focused by means of the coarse adjustment in 

 the following manner : Using the left thumb and forefinger to 

 adjust the slide, with the right hand the objective is brought 

 down so that it all but touches the cover glass, then, while 

 looking through the eye-piece, slowly raise the tube by the coarse 

 adjustment until the object is in view ; from this point the 

 exact focus can be made by turning the fine adjustment screw. 



3. Never lift the slide from the stage, but, having raised the 

 objective, especially in case of high powers, slide it off the stage 

 without upward movement. 



4. Accustom yourself to use both eyes indifferently and 

 always keep both eyes open. It is preferable to observe with 

 the left eye, as it is more convenient in making drawings. 



5. To mount an object, place it in the center of a slide in a 

 drop of liquid, say water, ; rest a cover glass on its edge near the 

 object in a slanting position and gradually lower it by means 

 of a teasing needle or forceps, in order to avoid entrapping air 

 bubbles. The cover glass should be previously cleaned with a 

 soft rag or lens paper and then handled by the forceps only. 

 Any superfluous water on the slide is taken up by a camel's hair 

 brush or blotting paper. 



6. Cleanliness should characterize all the work of the micro- 

 scopical laboratory. All apparatus, slides, cover glasses, etc., 

 should be kept scrupulously free from dirt. The glasses of the 

 objectives and eye-pieces should never be touched with the fin- 

 gers. Whenever they need cleaning, breathe upon them and 

 wipe with a soft, clean linen rag or a piece of Japanese filter 

 paper. 



7. All objects observed should be drawn. Drawings are use- 

 ful, not only in explaining to others the structures observed, 

 but they are themselves great aids also to accurate observation, 

 and are equally helpful in giving vividness and permanency to 

 knowledge. 



Each student should provide himself with a drawing book 

 and a medium pencil. It is excellent practice to keep a record 

 in writing of work done in the laboratory, besides making 

 drawings. 



SOME ACCESSORY APPARATUS NECESSARY IN HISTOLOGICAL WORK. 



1. Micrometer, preferably metric scale. Convenient scale is 

 hundredths of a millimeter. 



2. Section razor, flat on one side, slightly hollow on the 



