OF THE MICROSCOPE. 227 



Very laborious to get the air out of this by means of the air 

 pump, while by soaking successively in water, alcohol, and tur- 

 pentine, it can be mounted with great ease without a bubble. 



Let us now take the case of an object mounted in fluid in a 

 cell. Suppose it is the so-called tongue of a fly, which of course 

 has been soaked for some time in the liquid in which it is to be 

 finally mounted, viz., dilute glycerine. We make a cell of suita- 

 ble thickness, which in this case may be made with shellac 

 dissolved in alcohol. Several coats will be required, and as 

 shellac alone does not adhere well to glass, we prefer to lay on 

 first a coat of gold size or Japan, and when this is thoroughly 

 dry, to lay the shellac on it. No difficulty will be found in 

 making a cell of sufficient depth. The cell is now to be filled 

 with the liquid, the object placed in it, and the whole carefully 

 examined for air bubbles, which must be removed if they exist. 

 The cover is now applied, all superfluous fluid removed by 

 means of a camel hair pencil, which has been moistened and 

 then squeezed dry, and finally the edge of the cover is to be 

 coated with a thin layer of cement. After a day or so another 

 layer of cement should be laid on, and this process repeated 

 until at least three layers have been applied. 



We give no directions for the construction and use of very 

 deep cells as this is work that will hardly be attempted by be- 

 ginners. 



When opaque objects are to be mounted either in balsam, or 

 in fluid, the process required is the same as that employed for 

 transparent objects. Very many opaque objects are, however, 

 mounted dry, and in this case all that is needed is to attach 

 them to a slide, and see that they are properly protected. 

 When thin they may be readily mounted in cement cells, and 

 this is altogether the neatest and most secure plan where it can 

 be used. Thicker objects require deeper cells, which may be 

 made of card, ebonite or electrical cement. (3 parts resin, and 

 1 of wax, colored with ochre or any similar matter). Cells of 

 card are made by first punching out a disc like a gun wad, 

 and then punching a hole in this so as to leave a ring. The 

 ring is to be cemented to the glass slide and carefully var- 

 nished. 



Wooden slides with a cell bored in the centre, are recom- 



