MICROSCOPIC TECHNIQUE AND REAGENTS. 751 



seeds, may be softened by soaking in solutions of potassium 

 hydrate. 



SOME PRACTICAL SUGGESTIONS. The following are some 

 of the rules which should be borne in mind by the student 

 when using the microscope in the examination of microscopic 

 material : 



1. Always mount the sections (including powdered material) 

 in water or other suitable reagent prior to examination; never 

 attempt to examine dry material except in special cases. 



2. Use sufficient of the mounting medium or reagent to cover 

 the specimen, but avoid an excess or more than will be held under 

 the cover-glass. 



3. Always endeavor to have the object properly illuminated 

 by making use of the concave mirror. 



4. Always be particular about having the eye-piece and objec- 

 tives clean. 



5. In examining a microscopic object, always use the low- 

 power objective first. 



6. The edge of a section is always the thinnest, and this part 

 being the best for study, should be brought to the center of the 

 field. 



7. When the object is properly centered, raise the objective, 

 swing it to one side, bring the high-power objective into its place, 

 and cautiously lower it until it is brought to about the distance 

 of a millimeter from the cover-glass. Then holding the slide 

 with the left hand, the proper focus of the object is obtained by 

 making use first of the coarse adjustment and then of the fine 

 adjustment, the right hand being used for this purpose. In exam- 

 ining the object always hold the slide with the left hand, and 

 use the right hand for maintaining the proper focus by means of 

 either the coarse or fine adjustment. 



8. In all cases where practicable make drawings of the sections 

 examined. 



9. In some cases it is desirable to apply a reagent after the 

 material has been mounted, as in the addition of an iodine solution 

 to a section to determine the presence of starch, and this is accom- 

 plished by placing a drop or two of the reagent, by means of a 

 pipette or dropper, near the edge of the cover on one side and 



