6 THE PREPARATION OF MICROSCOPIC OBJECTS. 
VIL—THE PREPARATION OF MICROSCOPIC OBJECTS. 
In mounting microscopic objects be careful that your slides 
and coverslips are thoroughly clean. Slides should be labelled 
as soon as they are prepared, and should be kept im a box or 
cabinet in which they can lie flat. 
A. Methods of Mounting. 
There are various media in which objects may be mounted. 
The method of procedure is much the same with all. Puta 
small drop of the fluid in the middle of the slide, place the 
object in the middle of the drop, and arrange it with needles in 
any position that may be desired. Then place the coverglass 
carefully on the top, letting it rest by one edge on the slide 
and supporting the opposite edge by a needle, which is gradually 
withdrawn so as to let the coverglass down slowly and drive 
out any air-bubbles there may be in the fluid. If any air- 
bubbles still remain, leave them alone, as they will probably 
work out by themselves. Be careful not to use too large a 
drop of your mounting medium, and above all things be care- 
ful not to let any of it get on the top of the coverglass ; should 
this happen, the cover must be removed at once and the speci- 
men mounted again with a clean coverglass. 
The most important mounting media are :— 
1. Normal Salt Solution. A 0:75 per cent. solution of com- 
mon salt in water. This is very useful for the examination of 
fresh specimens of animal tissues, as, unlike water, it has practi- 
cally no action whatever on them. It cannot be used, however, 
for making permanent preparations. 
2. Glycerine. Can be used either pure or diluted with its 
own bulk of water. If the preparations are intended to be 
permanent, a narrow ring of cement must be painted round 
the edge of the coverglass to fix it to the slide. 
3. Canada Balsam. The most generally useful; requiring 
no cement. Specimens that are to be mounted in balsam must 
first be deprived of all water they may contain by placing for an 
hour or so in absolute alcohol, and should then, before mounting, 
be soaked for a few minutes in a mixture of creosote and turpen- 
tine in order to clear them, 7.e., render them permeable by the 
balsam. Canada balsam, if too thick, may be diluted with 
chloroform, turpentine, or benzole. 
