14 PRACTICAL BOTANY 



New cover-glasses are sometimes difficult to clean : heating 

 them with very dilute sulphuric acid, and subsequently washing 

 with water, will usually be found successful. Old slides may 

 often be cleaned with ease with water only : if this be unsuccess- 

 ful try washing with turpentine, or heating in a potash solution, 

 or if that does not do, in dilute sulphuric acid. 



3. In mounting, whatever the fluid may be, take 

 only so small a drop of it as shall just suffice to fill the 

 space between the slide and the cover-glass, and extend to 

 the margin of the cover: judgment as to the quantity 

 necessary can only be acquired by practice. If too 

 much fluid has been used the excess must be soaked 

 up with slips of blotting-paper, or filter paper. 



4. The practice of scrupulous cleanliness cannot be too 

 strongly impressed upon students as the basis of all suc- 

 cessful work with the microscope, and it is in the use of 

 fluid reagents that the greatest care is necessary ; if 

 too large a quantity be used it is apt to extend to the 

 lower surface of the slide, and so to the stage of the 

 microscope ; or to be smeared over the upper side of the 

 cover-slip, and may then gain access even to the objec- 

 tive ; it is absolutely necessary that both the front lens of 

 the objective, and the upper side of the cover-slip be per- 

 fectly clean and dry, also the lower surface of the slide and 

 the stage of the microscope. 



5. Having taken a sufficiently small drop of the 

 mounting medium, and having placed the object in it, 

 bring down the cover-glass obliquely upon the drop so 

 that one edge of it is first wetted by the medium, then let 

 down the slip gently, so as to allow the medium time to 

 spread out under the cover-slip ; this may be done 

 either by holct'ing the cover-slip in a pair of clean 



