CH. VII] 



MOUNTING AND LABELING 



169 



| 249. Sealing the Cover-Glass for Dry Objects Mounted in Cells. When 

 an object is mounted in a cell, the slide is warmed until the cement is slightly 

 sticky or a very thin coat of fresh cement is put on. The cover-glass is warmed 

 slightly also, both to make it stick to the cell more easily, and to expel any re- 

 maining moisture from the object. When the cover is put on it is pressed down 

 all around over the cell until a shining ring appears, showing that there is an in- 

 timate contact. In doing this use the convex part of the fine forceps or some 

 other blunt, smooth object ; it is also necessary to avoid pressing on the cover 

 except immediately over the wall of the cell for fear of breaking the cover. When 

 the cover is in contact with the wall of cement all around, the slide should be 

 placed on the turn-table and carefully arranged so that the cover-glass and cell 

 wall will be concentric with the guide rings of the turn-table. Then the turn- 

 table is whirled and a ring of fresh cement it painted, half on the cover and half 

 on the cell wall (Fig. 165.) If the cover-glass is not in contact with the cell wall 

 at any point and the cell is shallow, there will be great danger of the fresh cement 

 running into the cell and injuring or spoiling the preparation. When the cover- 

 glass is properly sealed, the preparation is put in a safe place for the drying of the 

 cement. It is advisable to add a fresh coat of cement occasionally. 



FIG. 138. Centering Card. A card with stops for the slide and circles in the 

 position occupied by the center of the slide. If the slide is put upon such a card it 

 is very easy to arrange the object so that it will be approximately in the center oj 

 the slide. The position of the long cover used for serial sections is also shown 

 (Fig. 162}. (From the Microscope, December, 1886). 



250. Mounting Objects in Media Miscible with Water. Many objects are 

 so greatly modified by drying that they must be mounted in some medium other 

 than air. In some cases water with something in solution is used. Glycerin of 

 various strengths, and glycerin jelly are also much employed. All these media 

 keep the object moist and therefore in a condition resembling the natural one. 

 The object is usually and properly treated with gradually increasing strengths of 

 glycerin or fixed by some fixing agent before being permanently mounted in 

 strong glycerin or either of the other media. 



