58 
Journal of the 
the covering glass, so that when the cover is in position it projects 
beyond the cell for about one-sixteenth or one-twelfth of an inch 
on every side. The cells may be made of any suitable material— 
thin tissue paper will serve for minute objects, and common 
cardboard for those of considerable thickness. The cell may be 
attached to the slide, or simply placed in the position which it is 
to occupy, without being cemented. The objects are immersed in 
the fluid in the centre of the cell and the cover pressed gently 
down, forcing out the fluid which is in excess of the capacity of 
the cell ; and after it is ascertained, by examination under the 
microscope, that the object requires no re-adjustment, the fluid 
must be removed from the space between the cover and the slide 
outside the cell wall. This is easily accomplished by simply 
allowing the slide to stand till the superfluous fluid has evaporated, 
or where the cell is thick enough, blotting paper may be inserted 
under the margin of the cover to absorb it. If this plan be 
adopted, eare must be taken, after the fluid is removed, to allow 
the slide to stand for a minute or two till the slide and the under 
surface of the cover-margin are quite dry, otherwise the cement 
will not adhere. Two or three drops of thin balsam or gold size 
are then to be applied at different points of the edge of the cover, 
when it will run in by capillary attraction and fill the space 
outside the cell and beneath the cover. Directly this cavity is 
filled any superfluous cement remaining on the slide must be 
-removed, otherwise the running-in process will extend too far, and 
the cement will enter the cell. The slide may then be put aside 
to harden. It will often be found after a day or two, especially 
with cells of considerable thickness, that the cement will be so 
shrunk from evaporation as no longer to quite fill the space 
destined for it, when a little more may be applied at the edges till 
this space is refilled, care of course being taken to scrupulously 
remove the superfluous cement as soon as the requisite amount 
has run in. It occasionally happens that some of the fluid is 
forced out of the cell in process of drying and occupies part of the 
space which should be filled only by the cement. This “running- 
out ” is no doubt caused by the shrinkage of the cement drawing 
the cover down more closely, and if the fluid extends only a very 
slight distance beyond the outer margin of the cell no injury is 
