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spirit-lamp, a portion of it is dropped on the slide (which should 

 also be previously warmed) by means of a warm glass tube. The ob- 

 ject is then taken up, with the needle-point or forceps, and placed in 

 the fluid medium, beginning at one end, and gently lowering it till 

 it is finally adjusted. If any bubbles appear they will rise to the 

 surface, and may be skimmed off with the edge of a pen-knife. If 

 any bubbles are in the vicinity of the object after the cover is on, 

 they may be removed by placing the slide aslant, keeping it warm, 

 with the bubble end uppermost, and they will gradually rise from the 

 object. If the cover is placed on immediately it will sometimes 

 throw the object out of place ; therefore it is best to allow the me- 

 dium to get cool, so as partly to congeal ; the cover is then held in 

 the forceps, warmed over the lamp, and placed over the object ; and 

 when cold it will remain firmly in its place. If the object is hard 

 and unyielding it will be advisable not to press the cover close down 

 upon it, but to allow a little of the medium to be between the object 

 and cover, which will lessen the risk of damage as the shrinking 

 takes place. It is a convenient way to cut out a piece of the 

 medium, and melt it on the slide ; but this increases the risk of 

 bubbles. 



Fresh animal or vegetable structures containing their natural 

 juices require little or no preparation before mounting in this sub- 

 stance. Those contained in water, such as Desmidise, Crustaceans, 

 &c, may be taken out of their native element, placed on a proper 

 slip of glass previously warmed, the superfluous water removed with 

 a piece of clean cambric or blotting-paper, and then mounted at 

 once, by dropping a little warm medium upon them with the glass 

 tube, and covering with thin glass. 



Animalcules mounted in this way do not appear to alter either in 

 colour or dimensions. The latter may be accounted for in this way, 

 — viz., that the contraction of the medium takes place entirely in 

 thickness, and the pressure of the cover prevents any alteration 

 taking place in the object laterally. It is probable that some ani- 

 malcules may be better shown if some moisture be allowed to remain 

 in the medium, the evaporation of which may be stopped at any 

 stage, by filling around the edge of the cover with gold-size, varnish, 

 or even boiled linseed-oil. 



For many delicate objects this has a great advantage over Canada 

 balsam, in not possessing the high refractive power of that substance ; 

 and the minute hairs and other parts of insects, that are quite obli- 

 terated with the balsam, are beautifully shown in the new medium. 



