AND HOW TO USE IT. 29 



such that a piece can be stamped out nearly the size of the cell, 

 no gum will be necessary to keep it in its place ; but should the 

 object be very small, or with branches, it will be necessary to put 

 a small spot of gum (and the gum must be rendered safe from 

 fungoid growth by the addition of a few drops of carbolic acid) on 

 the slip at the junctions of the cell and glass, so that it may not 

 be seen. The object being placed in the cell, and the gum, if 

 gum be used (| gr. saHcylic acid to every ounce of gum, or a little 

 carbolic acid to keep it), being quite dry, the slide should again 

 be placed upon the turn-table, and the top of the cell-wall coated 

 with brown cement. In a few minutes, a warmed cover-slip may 

 be put down upon the cell, a clip placed upon it ; it may then be 

 put on one side, to be finished at leisure. For objects having 

 only one side to be inspected, we would always recommend a 

 black ground, of asphaltum if a bright one is preferred, or of matt 

 black if the ground is desired dull. This ground being thoroughly 

 dry, the objects may he^ placed on it, and the slides finished as last 

 described. It is much better to paint the asphaltum on the top of 

 the slide than under, as it is less Hable to be scratched off.* 



Mounting" in Canada Balsam, etc.— Some preparations which 

 it is desired to keep are usually mounted in Glycerine or in 

 solutions of Canada Balsam or Gum-Dammar. The solvent of 

 the last two substances evaporates and leaves a clear, hard edge, 

 so that no cement is required as in the case of Glycerine. The 

 mounting medium should be quite admixable with that from 

 which the specimen is last taken, it being necessary in some 

 cases to use several fluids to obtain this result. 



Tissues and sections, both stained and unstained, are, as a 

 rule, kept in spirit, so the following order should be carried out : — 



For mounting in Glycerine. — The objects should be removed 

 from Spirit into Water, and then into Glycerine. 



For mounting in Canada Balsam or Gum-Dammar, they must 

 be removed from Spirit to Absolute Alcohol, then into Turpen- 

 tine 4 parts. Creosote i part, or Oil of Cloves or Oil of Cajuput, 

 and finally into Canada Balsam, or Balsam and Benzole, or Gum- 

 Dammar. 



* We think there is really no need for any dark-ground cell, because by 

 proper management such a dark ground can be formed outside the glass. — Ed. 



