WITH THE MICROSCOPE. 77 



air cannot be removed in this manner, the preparation immersed in 

 turpentine, may be placed under the receiver of an air pump. As 

 the pressure is removed the air rises to the surface and the fluid 

 rushes in to supply its place. A convenient and simple form of air 

 pump is represented in pi. XX, fig. 129. 



When the specimen has been thoroughly dried, and the air 

 removed, it may be slightly moistened with turpentine before it is 

 placed in the balsam. 



In mounting a thin section of bone or other hard dry texture in 

 Canada balsam, the following steps are taken : the glass slide having 

 been warmed upon the brass plate, a small quantity of Canada 

 balsam is removed upon the end of a piece of iron wire. By gently 

 warming it, it becomes perfectly fluid, and may be allowed to drop 

 in its proper place upon the glass slide. Or the metal pot contain- 

 ing the Canada balsam may itself be warmed, and a drop of the 

 fluid balsam placed upon the slide. The preparation is now taken 

 with a needle and placed in the drop of balsam, so that it may be 

 thoroughly wetted by it in every part, or a solution of Canada 

 balsam in chloroform may be dropped upon the specimen, 95. 

 A few air-bubbles may perhaps collect upon the surface of the 

 balsam, and by moving the slide from side to side, with a slight 

 rotatory movement while the balsam is quite fluid, the bubbles may 

 be seen to collect in one spot upon the surface. They may be made 

 to burst by the application of a warm needle, or completely removed 

 by touching them with a cold wire to which the balsam including 

 them will adhere. All bubbles having been removed, the thin glass, 

 which has been perfectly cleaned and slightly warmed on the brass 

 plate, is taken in a pair of forceps, and gently allowing one side of 

 it to come in contact with the balsam, is permitted to fall very 

 slowly upon the specimen, in such a manner that the balsam 

 gradually wets the thin glass, without including air-bubbles. It is 

 then pressed down slightly with a needle, and the slide placed in a 

 warm place. The superabundant balsam may be scraped away, and 

 the preparation when cold, cleaned with a little turpentine, and a 

 soft cloth, or piece of wash-leather. 



The feet and hard parts of the fly and other insects, and the 

 ova of small insects may be mounted in Canada balsam. The shells 

 and hard parts of the covering of many of the lower animals, the 

 palates of various mollusks, such as the limpet, and many fresh- 

 water species, the coriaceous coverings of insects, their antennae, 

 stings, eyes, feet, wings, and scales of their wings, the trachea? pene- 

 trating every part of their organism with their spiracles or external 

 openings, and in some cases the entire insects themselves, the scales 



