Microscopical Society of Victoria. 
59 
done; but if enough is expelled to make a passage nearly or quite 
through the cement wall there will be a liability of leakage. The 
best safeguard against this mishap is to be cautious that the 
cement is not run in till the whole of the fluid has evaporated 
from outside the cell, or even till the thin film between the 
covering glass and the upper surface of the cell has commenced to 
dry. When this occurs the cover will generally be drawn down 
as closely as is necessary, and the cement may be applied with 
reasonable security. 
The result of this operation is to secure a double cell;, the 
inner part consisting of the paper or whatever material may be 
used, and the outer of a solid wall of cement firmly uniting the 
slide and cover, and as wide as may be required. I use a cell 
about one-eighth of an inch less in diameter than the cover, giving 
a margin of one-sixteenth all round. Care must be taken in 
finishing slides mounted in this manner, as 1 have found one 
commence to run in on the application of varnish, after being 
mounted some months, the fresh varnish having softened the 
original cement. This difficulty woidd probably be obviated by 
using a rapidly--drying varnish, and only applying a thin layer at 
once, or by making a narrow circle of gum round the margin of 
the cover and allowing it to dry before using the finishing 
material; or by using paper covers, and thus dispensing with 
varnish entirely. There can be no doubt that slides mounted in 
this way will have almost the permanency of balsam mountings, so 
far as freedom from external influences can secure it. 
A modification of the above process may be used with media, 
which will not evaporate to dryness, such as glycerine and castor 
oil. In this case it will be advisable to place the object in the 
centre of the cell, in a quantity of the medium so small that on 
pressing down the cover the drop will not quite fill the cell, and 
consequently none will be forced out. The cement may then 1x5 
run in under the margin, as above described. If the medium be 
thin and likely to spread over the floov of the cell before the cover 
can be applied, it will be better to suspend a small drop from the 
centre of the cover, and bring it down upon the object; and in 
any case the cover should be moistened with the medium before 
applying it. 
