Owing to their want of adhesiveness, they are, however, usually mounted on glass as microscopic slides, either in glycerin jelly, Canada balsam or some other suitable medium.
If we take a thin layer of natural Canada balsam and heat it strongly for a little time most of the volatile oils are driven out of it.
The tissues, in fact, are preserved just as they would be in Canada balsam.
Microscopic sections of some of the more coherent clays and shales may be prepared by saturating them with Canada balsam by long boiling, and slicing the resultant mass in the same manner as one of the harder rocks.
