OF MICROSCOPIC OBJECTS. 141 
must be examined from time to time to ascertain whether 
the necessary degree of thinness has been reached. When 
this is the case the section should be washed thoroughly and 
dried. It must then be covered, which is best done by using 
ordinary Canada balsam, as recommended in Chapter [V.; 
or, if the section is to be mounted dry, it must be freed from 
balsam by washing, or soaking if necessary, in turpentine 
or other solvents. 
Sections of some exquisitely beautiful objects are cut with 
much less trouble than the above. The Orbitolite, for 
instance, may be prepared in this manner. Take the object 
and by pressure with the finger rub the side upon a flat and 
smooth sharpening stone with water until the portion is 
reached which it is wished to show. The strength of the 
object will easily allow this to be accomplished with ordinary 
care. This side may then be attached to the glass slide 
_ with heated balsam, as above described, and the object may 
then be gently rubbed down to the degree of thinness re- 
quired to show it to the best advantage. After removing 
all disengaged matter from the object by washing and 
thoroughly drying, it may be mounted in balsam in the 
usual manner, when it is equally beautiful as a transparent 
or opaque object. From this it will be seen that in many 
instances where a smooth stone is found sufficient for the 
work (which is often the case when the section is mounted 
in balsam) the final process of polishing advised above may 
be dispensed with, as in the Orbitolite, Nummulite, &., &c. 
It is quite necessary that the stones on which the objects 
are rubbed be perfectly flat, otherwise one side must be 
acted upon before the other, and it will be found impos- 
sible to attain anything like uniformity. Where it is not 
practicable to cut a section, and the object is very thick, a 
coarse stone may be first used to reduce it and the smoother 
afterwards. 
The consideration of the cutting of sections from shells 
would scarcely bedeemed complete without some mention of 
what Dr. Carpenter terms the decalcifying process. Muriatic 
