THE STAINING OF COVER-GLASS PREPARATIONS. 9S 



If this can be clearly seen through a depth of 5 cm. 

 of the staining solution in the middle of the watch 

 glass, the solution is of the right strength. This, of 

 course, only holds as a general rule ; occasionally it 

 is necessary to use a. somewhat stronger or weaker 

 solution. 



Either a few drops of this staining solution is carried 

 with a small pipette to the cover-glass, or the latter 

 is laid face downwards upon the surface of the liquid, 

 so that it floats. The second method frequently re- 

 sults in a failure at first, but with practice the student 

 soon succeeds with it. The best plan is to take the 

 cover-glass up by its edges with the forefinger and 

 thumb, to bring it as close as possible to the surface 

 of the staining solution, and then to drop it suddenly. 

 By this method fewer stain rings are , formed on the 

 edge of the cover-glass than by the other ; these rings 

 prove themselves very troublesome later on when the 

 cover-glass is washed. The first method is certainly 

 the simpler ; the surface of the cover-glass must be 

 completely covered up with the liquid. 



If solutions of fuchsine, or gentian violet, are used, 

 as is generally preferable, then the preparations are as 

 a rule sufiiciently stained in from five to ten minutes ; 

 if methylene blue is employed, they take rather longer. 

 Vesuvin is only used in certain cases, which will be 

 mentioned later on. 



If it is desirable to hasten this process of staining. 



