66 The Microscopical Preparations. 



possibly adherent particles, the section may be declared suitable 

 for mounting. 



Before proceeding to this step, a few precautions are necessary 

 about particular sections. Transverse sections of teeth or bone 

 should be dried, after the preliminary washing, between glass, in 

 order to avoid the disadvantage of warping. Very porous parts, 

 such as cancellated bone, or fragile bodies, such as the poison 

 fang of serpents, require that the whole structure, or the canals, be 

 saturated with glue and dried. Sections may now be cut with a 

 saw, ground in oil, and cemented to the holding-glass subsequent 

 to immersion in chloroform. 



Mounting. — Spread a sufficient quantity of old Canada balsam, 

 or of that thickened by heat (not boiling), upon a slide, and, 

 when cold, impose the section. Have ready a spatula bearing a 

 quantity of equally inspissated balsam warmed until it flows, 

 with which cover the specimen, and then immediately warm the 

 slide, being careful to employ the least possible heat. Now 

 carefully depress the section and withdraw every air bubble with 

 a stout needle set in a handle towards the ends of the slide : put 

 on the cover glass, slightly warmed, not flat, but allowing one 

 edge to touch the balsam first, press out superfluous balsam, and 

 the specimen is safe. The slide may now be cleaned with a warm 

 knife, spirits of wine, and ammonia. 



This communication would be incomplete without some very 

 important hints concerning " cover glass." It is easy to clean 

 small covers, but very thin glasses or large ones, one or two 

 inches in length, are not so safely handled. All danger of break- 

 ing is, however, avoided by placing a cover upon a large clean 

 slide, and wiping one side only with a bit of linen damp with 

 aqua ammonia, and then with a dry piece. The other side may 

 be cleaned alter the mounting. 



In the next place, all preparers are aware of the difficulty at- 

 tending the use and application of large covers. I beg leave to 

 assure the inexpert that the following method will insure success. 

 Having prepared the cover glass, and superposed it, let it first be 

 gently pressed downwards at many points, with the flat end of a 

 lead pencil : it will be found, however, almost impossible to flatten 

 it without breaking, consequently too much balsam will overlie 

 and underlie the section. Let now a piece of thin paper be laid 

 over the cover and upon this a thick slide; if a moderate heat 

 be applied to both the slides, over and beneath the specimen, direct 



