152 MOUNTING AND LABELING. \_CH. VII. 



§ 239. Example of Mounting in Glycerin Jelly.— For this select 

 some stained and isolated muscular fibres or other suitably prepared 

 objects. (See under isolation § 244). Arrange them on the middle of 

 a slide, using the centering card, and mount in glycerin jell}' as 

 directed in § 223. Air bubbles are not easily removed from glycerin 

 jelly preparations, so care should be taken to avoid them. 



§ 240. Mounting Objects in Resinous Media. — While the media 

 nhscible with water offer many advantages for mounting animal and 

 vegetable tissues the preparations so made are liable to deteriorate. In 

 many cases, also, they do not produce sufficient transparency to enable 

 one to use high enough powers for the demonstration of minute details. 



By using sufficient care almost an) - tissue ma} 7 be mounted in a resin- 

 ous medium and retain all its details of structure. 



For the successful mounting of an object in a resinous medium it 

 must in some way be deprived of all water and all liquids not miscible 

 with the resinous mounting medium. There are two methods of bring- 

 ing this about: (A) By drying or desiccation (§ 241), and ( B) by 

 successive displacements (§ 243). 



§ 241. Order of Procedure in Mounting Objects in Resinous 

 Media by Desiccation : 



1. The object suitable for the purpose ( fly's wings, etc. ) is thorough- 

 ly dried in dry air or by gentle heat. 



2. The object is arranged as desired in the center of a clean slide on 

 the centering card (Fig. 126). 



3. A drop of the mounting medium is put directly upon the object or 

 spread on a cover-glass. 



4. The cover-glass is put on the specimen with fine forceps (Fig. 

 123), but in no case does one breathe on the cover as when media mis- 

 cible with water are used. 



5. The cover-glass is pressed down gently. 



6. The slide is labeled (§ 292). 



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



8. Although it is not absolutely necessary, it is better to seal the 

 cover with shellac after the medium has hardened round the edge of 

 the cover (§ 238 C). 



§ 242. Example of Mounting in Balsam by Desiccation. — Find 

 a fresh fly, or if in winter, procure a dead one from a window sill or a 

 spider's web. Carefully remove the fly's wings, being especially care- 

 ful to keep them the dorsal side up. With a camel's hair brush remove 

 any dirt that may be clinging to them. Place a clean slide on the cen- 

 tering card, then with fine forceps put the two wings within one of the 



