73 MOUNTING AND LABELING. 



sealing preparations in balsam or other resinous media unless the solvent 

 of the cement is not a solvent of the balsam, etc. Otherwise the ce- 

 ment will soften the balsam and finally run in and mix with it, and 

 partly or wholly ruin the preparation. Shellac is an excellent cement 

 for sealing balsam preparations, as it never runs in, and it serves to 

 avoid any injury to the preparation when cedar oil, etc., are used for ho- 

 mogeneous immersion objectives. 



§ 170. Order of Procedure in Mounting Objects Dry or in Air. 



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

 than the object is thick (§§ 166, 167). 



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 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 (§ 168). 



5. The cover-glass is sealed (§ 168). 



6. The slide is labeled (§ 179). 



7. The preparation is cataloged and safely stored (§§ 181-183). 



MOUNTING OF OBJECTS IN MEDIA MISCIBLE WITH WATER. 



§ 171. Many objects are so greatly modified by drying that they must 

 be mounted in some medium other than air. In some cases water 

 or water with something in solution is used. Glycerin of various 

 strengths, glycerin jelly and Farrant's solution are also much em- 

 ployed (§§ 189, 190). All these media keep the object moist and there- 

 fore in a condition resembling the natural one. The object is usually 

 and properly treated with gradually increasing strengths of gly- 

 cerin or fixed by some fixing agent (See Part II) before being perma- 

 nently mounted in strong glycerin or either of the other media. 



In all of these different methods, unless glycerin of increasing 

 strengths has been used to prepare the tissue, the fixing agent is 

 washed away with water before the object is finally and permanently 

 mounted in either of the media. 



For glycerin jelly or Farrant's solution no cell is necessary unless the 

 object has a considerable thickness. 



§ 172. Order of Procedure in Mounting Objects in Glycerin. 



1. A cell is employed if the object is of considerable thickness. 



2. The suitably prepared object (§ 171) is placed on the center of a 



