92 PREPARATION AND MOUNTING 
penetrate, the substance more than necessary. Sections of 
teeth are amongst these, but they will be noticed in another 
place, and some insects (see Dr. Carpenter) when required 
to show the ramifications of the trachee. 
Having freed the object, then, from these two enemies— 
dampness and air—we now proceed to mount it. 
The slide must first be cleaned; then on the centre a 
quantity of balsam must be placed with a bluntly-pointed 
glass rod, according to the size of the object about to be 
mounted. ‘To this a slight heat must be applied, which 
will cause any bubbles to rise from the surface of the slide, 
so that they may be readily removed with a needle. The 
object having been freed from all air by steeping in turpen- 
tine, as before described, and then from superfluous liquid 
by a short drainage, or touch upon blotting-paper, is to be 
carefully laid wpon, or where it is practicable thrust into, 
the balsam just prepared on the slide. In the former 
case, or where the balsam has not totally covered the object, 
a small quantity must be taken, warmed, and dropped upon 
it, and any bubbles removed by the needle as before. To 
cover this, the thin glass must be warmed, and beginning 
at one side, allowed to fall upon the balsam, driving a 
small “wave” before it, and thus expelling any bubbles 
which may remain. This is quite as safely performed (if 
not more so) by making a solution of balsam in turpentine 
of the consistency of thick varnish or by the use of chloroform 
and balsam, as mentioned in Chapter IJ. The thin glass cover 
may be slightly coated with this, and will then be much 
less liable to imprison any air, which frequently happens 
when the cover is dry. Bubbles, however, will sometimes 
make their appearance in spite of all care; but when the 
object is comparatively strong, they may be removed by 
keeping the slide rather warm, and working the cover a 
little, so as to press them to one side, when they should be 
immediately removed with a needle point, otherwise they 
are again drawn under. 
Where the slide requires keeping warm for any length of 
