INTRODUCTION. 13 



liquid sufficiently to prevent the cover floating when 

 the slide is inclined. 



VI. APPLYING REAGENTS. 



Stains are most conveniently applied by placing a 

 drop of the liquid at the edge of the cover, and allow- 

 ing it to run under, hastening the process when desired 

 by placing a strip of filter paper at the opposite edge. 

 If the stain does not reach all parts of the specimen, 

 the cover glass may be slightly raised. It is quite 

 important in many cases to watch the action of reagents. 

 In such a case they should be applied with the stage of 

 the microscope horizontal. Time may be saved when 

 it is necessary to examine specimens in potash, by 

 placing a drop of potash on the slide, and mounting 

 directly in that medium. In all cases, as soon as the 

 specimens have become clear, the potash should be 

 washed out with water: otherwise the cell walls swell 

 excessively, and many points become indistinguishable. 

 It should be remembered in examining specimens 

 treated with potash that many cell walls are somewhat 

 swollen, and that the longer they remain the greater 

 the swelling becomes. 



Glycerine is one of the most useful media for clear- 

 ing, and at the same time preserving specimens for 

 prolonged examination. Whenever it becomes desir- 

 able to preserve specimens from one day to another, a 

 drop of glycerine should be applied to the slide, so 

 that it just touches the edge of the cover, and the slide 

 laid away in a horizontal position. As the water or 

 alcohol evaporates, the glycerine will run under the 

 cover. The excess may be wiped off with a damp rag 



