106 THE MICROSCOPICAL NEWS. 
wasp’s or blow fly’s head for example, and place it upon the 
previously warmed balsam, arranging it in the required position. 
Now take a clean cover glass, the diameter of which should be a 
little less than that of the cell, and holding it between the points 
of a pair of forceps, place a large drop of balsam in its centre, and 
allow it to fall upon the object. The edge of the cover B should 
rest upon the three beads. If the quantity of balsam under the 
cover glass is not sufficient to fill up the whole of the space between 
it and the slide, a little more must be allowed to run in, and if the 
object has become displaced, it may be re-arranged by means of a 
fine blunt needle, introduced beneath the cover glass. A clip 
should be used during the last operations, but only to prevent 
displacement of the cover. The slide must now be put aside in a 
Fig. 34. 
warm place, until the balsam is hard enough to allow the super- 
fluous portion to be removed safely. Sufficient balsam should be 
left to form a sloping edge around the cover glass; and I always 
re-harden it for a few days after cleaning. Be sure that the balsam 
is quite hard before applying brown cement. The ease with which 
an object can be re-arranged, or a chance air bubble removed, 
without disturbing the cover glass, constitutes the chief advantage 
of using beads. A supply of different sizes should be kept, and 
the size used must be regulated by the thickness of the object. 
I always use pure balsam in collapsable tubes, which I strongly 
recommend, on account of the nicety with which the quantity of 
balsam required for mounting a slide can be regulated. The neck 
of the tube should be wiped with a clean cloth moistened with 
benzole before the screw-cap is re-placed, in order to prevent the 
possibility of a little balsam hardening in the screw, and so pre- 
venting the easy removal of the cap when next required. 
