252 MOUNTING PREPARATIONS \_CH.IX 



cover is in place, if the preparation is to be studied for some time, it is better 

 to avoid currents and evaporation by painting a ring of castor oil around the 

 cover in such a way that part of the ring will be on the slide and part on the 

 cover (Fig. 210). 



FIG. 197. To show the 

 method of putting a cover- 

 glass upon a microscopic 

 preparation. The cover is 

 grasped by one edge, the 

 opposite e dg e is then 

 brought down to the slide, and the cover gradually lowered upon the object. 



\ 342. Permanent Mounting. There are three great methods of making 

 permanent microscopic preparations. Special methods of procedure are 

 necessary to mount objects successfully in each of these ways. The best 

 mounting medium and the best method of mounting in a given case can only 

 be determined by experiment. In most cases some previous observer has 

 already made the necessary experiments and furnished the desired information. 



The three methods are the following : (A) Dry or in air ($ 343); (B) In 

 some medium miscible with water, as glycerin or glycerin jelly ($ 348) ; (C) 

 In some resinous medium like Canada Balsam (\ 353). 



343. Mounting Dry or in Air. The object should be thoroughly dry. 

 If any moisture remains it is liable to cloud the cover-glass, and the specimen 

 may deteriorate. As the specimen must be sealed, it is necessary to prepare a 

 cell slightly deeper than the object is thick. This is to support the cover- 

 glass, and also to prevent the running in by capillarity of the sealing mixture. 



\ 344. Order of Procedure in Mounting Objects Dry or in Air. 



1. A cell of some kind is prepared. It should be slight!}* deeper than 

 the object is thick ( 346). 



2. The object is thoroughly dried (desiccated) either in dry air or by the 

 aid of gentle heat. 



3. If practicable the object is mounted on the cover-glass ; if not it is 

 placed in the bottom of the cell. 



4. The slide is warmed till the cement forming the cell wall is somewhat 

 sticky, or a very thin coat of fresh cement is added ; the cover is warmed and 

 put on the cell and pressed down all around till a shining ring indicates its 

 adherence (\ 347). 



5. The cover-glass is sealed. 



6. The slide is labeled. 



7. The preparation is cataloged and safely stored. 



\ 345. Example of Mounting Dry, or in Air. Prepare a shallow cell 

 and dry it ( 346). Select a clean cover-glass slightly larger than the cell. 

 Pour upon the cover a drop of 10%' solution of salycilic acid in 95",, alcohol. 

 Let it dry spontaneously. Warm the slide till the cement ring or cell is some- 



