54 



155. Mounting in glycerin-jelly. The preparation should 

 be mounted from some aqueous solution. Warm the slide gently 

 and put it upon the centering card; in the center of the slide place 

 a drop of warmed (melted) glycerin- jelly. Remove the object from 

 the water or aqueous solution and arrange it in the glycerin -jelly. 

 Grasp a cover-glass with the fine forceps, breathe on the lower side, 

 gradually lower it upon the object and gently press it down. Allow 

 the glycerin-jelly to set, keeping the slide horizontal meanwhile. 

 Scrape away the superfluous glycerin- jelly around the cover-glass 

 and seal with shellac ( 163). 



156. Preparation of shellac mounting cells. Place the slide 

 upon the turn-table and center it (i. e., get the center of the slide 

 over the center of the turn-table). Select a guide ring on the turn- 

 table which is a little smaller than the cover-glass to be used; take 

 the brush from the shellac, being sure that there is not enough 

 cement adhering to it to drop. Whirl the turn-table and hold the 

 brush lightly on the slide just over the guide ring selected. An 

 even ring of the cement should result. If it is uneven, the cement 

 is too thick or too thin or too much was on the brush. After a ring 

 is thus prepared, remove the slide and allow the cement to dry 

 spontaneously, or heat the slide in some way. Before the slide is 

 used for mounting, the cement should be so dry when it is cold 

 that it does not dent when the finger nail is applied. A cell of con- 

 siderable depth may be made with shellac by adding successive lay- 

 ers as the previous one dries. 



157. Mounting in balsam: by desiccation. Certain prepara- 

 tions may be mounted in balsam, by drying, the method of desiccation 

 ( 147), e. g., cover-glass preparations of bacteria, stained cover-glass 

 preparations of blood, etc. For this is it only necessary that the prep- 

 aration be absolutely dry, a small drop of balsam placed upon it or 

 upon the under side of the cover-glass, which is carefully placed 

 over the specimen and pressed down. 



Mounting in balsam: by displacement. Mounting in balsam by 

 desiccation is serviceable for but few preparations in histology, and 

 in most cases the removal of the water by a series of displacements is 

 resorted to ( 147). For this the following steps are necessary: 

 Dehydration, Clearing, Mounting in balsam. 



158. Dehydration. The sections are entirely freed from 

 water by the use of 95% or absolute alcohol. The slide or free sec- 



