PREPARING AND MOUNTING. 219 



the method by which objects are mounted in balsam ; 

 there are, however, some specimens, the mounting of 

 which, in balsam, would render them almost invisible, in 

 which case — if not suitable for dry-mounting — they should 

 be placed in fluid in cells, the size and depth of which 

 must be regulated by the proportions of the object. If 

 it be the scale of a fish, or the pollen of a flower, a very 

 shallow cell will suffice, and it may be formed of " Bruns- 

 wick black" in the manner already described. When the 

 cell is quite dry, take the object (which should have been 

 some time previously soaked in the fluid in which it is to 

 be mounted to dispel the ah- from its substance), place it in 

 the middle of the circle, fill the space quite full of the 

 mounting fluid, and cover it with a glass circle ; place the 

 edge down first, and bring the whole surface of the circle 

 very gradually upon the cell as pointed out in the former 

 case. Some of the fluid will immediately escape under the 

 edge ; this may be absorbed by a piece of filtering paper. 

 Should too much escape, a bubble will make its appearance 

 in the cell ; in this case the process must be repeated. 

 When this has been performed successfully, secure the glass 

 circle in its place with a small spring-clip ; then take a 

 camel' s-hair brush, charged with varnish, and carry it 

 round, and slightly over the edge of the cover. Allow the 

 first layer to dry before another is added, and continue to 

 add more gradually until the cell is made perfectly air-tight. 

 Glass or metal cells must be employed for those objects 

 whose bulk renders the method just described inadmissible. 

 Glass-cells may be fastened to the glass-slide either by 

 Canada balsam, by Jefferey's marine glue, or Brunswick 

 black ; the latter will be rendered very durable by mixing 

 it with a small quantity of India-rubber varnish (made by 

 dissolving small strips of caoutchouc in gas-tar). The pro- 

 cess of mounting in glass-cells is similar to that employed 

 in making varnish-cells, except that a somewhat larger 

 quantity of cementing medium is required on account of 

 the greater weight of the cell. Objects mounted in this 

 way should always be kept in the horizontal position, and 

 a little fresh varnish applied now and then, if the cement 

 show any tendency to crack. 



In mounting objects in balsam, great care should bo 



