COLLECTION OF SPECIMENS 177 



cell is sealed with Canada balsam, a second and 

 even a third coat being added later in order to 

 guard against the escape of the glycerine. It 

 is much better, with this method of mount- 

 ing, to use square cover-glasses, as the sealing 

 of a round cell on the turn-table is a matter of 

 considerable difficulty, to say the least. There 

 are certain drawbacks to the employment of 

 glycerine which greatly detract from its useful- 

 ness as a mounting medium, though its preserving 

 powers are undeniable. In the first place, the 

 fact that it cannot be used with objects of 

 any thickness, as is possible with glycerine 

 jelly, is a distinct disadvantage. Then, too, if 

 the slide is accidentally jarred, as when it is 

 dropped too suddenly into its place in the cabinet 

 drawer, the Canada balsam with which the cell 

 is sealed is often liable, especially when old, to 

 crack, or chip off; this will cause the glycerine 

 to escape and the mount is spoiled, while with 

 glycerine jelly an additional coat of varnish soon 

 remedies any such defect. 



Deane's Gelatine was formerly more frequently 

 used than at present ; it has practically been 

 superseded by glycerine jelly, which it closely 

 resembles in composition, honey being sub- 

 stituted for glycerine to prevent the gelatine 

 hardening. I have frequently used it, prepared 

 from the following recipe : Take one ounce 

 (by weight) of gelatine and four of water; soak 



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