254 



MOUNTING PREPARATIONS 



[CIT. IX 



\ 347. 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 intimate contact. In doing this the 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. 210). 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 spoil- 

 ing the preparation. When the cover-glass is properly sealed, the prepara- 

 tion is put in a safe place for the drying of the cement. It is advisable to add 

 a fresh coat of cement occasionally. 



Fig. 199. 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 easy to arrange the object so that it will be approximately in the 

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

 also shown. (From the Microscope, December, 1886). 



I 348. 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. 



