OF MICROSCOPIC OBJECTS. 143. 
that the transparency is somewhat increased by this last 
operation. 
Corals are often treated in this way, in order to reveal 
their structure. Except, however, the student has had 
much practice, he will often find this a most difficult task, 
as many of them are exceedingly brittle and hard. THe wil! 
find the method before described equally applicable here, 
and should take both horizontal and vertical sections. 
Coat.—This substance is one of the most interesting 
objects to the microscopist. It is, of course, of vegetable 
origin; and though it is in many cases in such minute 
separate portions as to have lost all appearance of vegeta- 
tion, yet it is very frequently met with in masses, bearing 
the form, even to the minute markings, of wood, in various 
directions. To see this and prepare it for microscopic re- 
search, a suitable piece of coal must be obtained; but in 
every case the cutting and preparation of these sections 
require great care and skill. Sometimes the coal is first 
made smooth on one side, fastened to the glass, reduced to 
the requisite degree of thinness, and finished in the method 
before described. This mode of treating it is sometimes, 
however, very tantalizing, as, at the last moment, when the 
section is about thin enough, it often breaks up, and so 
renders the trouble bestowed upon it fruitless. The dark 
colour and opacity of coal render an extraordinary thinness 
necessary, and so increase the liability to this accident. 
Mr. Slade recommends that the piece of coal, having been 
smoothed on one side, be cemented on that side to a glass 
slip by marine-glue of the best quality, quite free from 
undissolved or foreign matter. Great care must be taken 
to press out all air-bubbles, the coal breaking up at such 
places as it gets thin, a hole resulting. It may then be 
reduced in the usual way, and when thin enough mounted 
in Canada balsam and covered by thin glass. 
Perhaps the best method which can be pursued is that 
recommended in the Micrographic Dictionary, which is 
as follows :—% The coal is macerated for absut a week in a 
