CH. VII] MOUNTING AND LABELING. 147 



§ 230. Permanent Mounting. — For making permanent micro- 

 scopical preparations, there are three great methods. Special meth- 

 ods of procedure are necessary to mount objects successfully in each of 

 these ways. The best mounting medium and the best method of mount- 

 ing in a given case can only be determined by experiment. In most 

 cases some previous observer has already made the necessary experi- 

 ments and furnished the desired information. 



The three methods are the following : (A) Dry or in air (§ 231) ; 

 (B) In some medium miscible ?vith water, as glycerin or glycerin jelly 

 (§ 2 35) I (C) I }1 some resinous medium like dammar or Canada balsam 

 (§ 240). 



§ 231. 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. 



ORDER OF PROCEDURE IN COUNTING OBJECTS DRY OR IN AIR. 



i. A cell of some kind is prepared. It should be slightly deeper than 

 the object is thick (§ 233). 



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 some- 

 what 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 (§ 234). 



5. The cover-glass is sealed (§ 234). 



6. The slide is labeled (§ 292). 



7. The preparation is cataloged and safely stored (§ 293, 296). 



§ 232. Example of Mounting Dry, or in Air. — Prepare a shal- 

 low cell and dry it (§ 233). Select a clean cover-glass slightly larger 

 than the cell. Pour upon the cover a drop of a \o c /o solution of sali- 

 cylic acid in 95% alcohol. Let it dry spontaneously. Warm the slide 

 till the cement ring or cell is somewhat sticky, then warm the cover 

 gently and put it on the cell, pressing down all around (§ 231). Seal 

 the cover, label and catalog (§ 234, 292, 293). 



A preparation of mammalian red blood corpuscles may be made very 

 satisfactorily by spreading a very thin layer of fresh blood on a cover 



