OF MICROSCOPIC OBJECTS. {21 
dried, burn it upon thin glass until all appears white, when 
it must be carefully mounted in balsam. I think, however, 
it is better to leave it in strong acid until all the substance, 
except the required portion, is removed; but this will take 
a length of time, varying according to the mass of the 
plant. Of course, when this latter method is used, the 
skeleton must be washed from the acid, &c., before being 
mounted in balsam. 
These siliceous cuticles are readily found. The straws of 
most of the cereals, wheat, oat, &c.; the husks, also, of some 
of these; many canes; the equisetum, as before described ; 
and some of the grasses. Many of these are everywhere 
procurable, so that the student can never want material for 
_a splendid object for the polariscope. 
In Chapter III. the scales (or hairs) which are often found 
upon the leaves of plants were mentioned as beautiful objects 
when mounted dry; but some of these when detached from 
the leaf—which is easily done by gently scraping it, when 
dried, with a knife—present brilliant starlike and other 
forms, if mounted in balsam and used with the polariscope. 
There is a little danger, when placing the thin glass upon 
the balsam, of forcing out the scales in the wave of matter 
which is always ejected; this may be overcome by applying 
to the slide, previously to placing the objects upon it, an 
extremely thin covering of balsam diluted with turpentine 
as before mentioned, letting it dry more or less with the 
objects placed in it, and then, after the addition of a little 
more balsam, putting the cover on, and thus giving them 
every chance of adherence; or by using the balsam with 
chloroform, as before noticed. This method is peculiarly 
successful in cases where it is desired to arrange severai 
objects symmetrically on a slide, and to obviate their sub- 
sequent disturbance by placing the cover on. ‘Type slides 
with several parts of an insect displayed upon them, scales 
of fish, or of plants, &c., may thus be shown, so that the 
number of slides may by this plan be seriously diminished. 
