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 tracheae. 



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 upon, 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 

 email " 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 IT. 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 



