CH. X] MOUNTING MICROSCOPIC OBJECTS 325 



rings are easily cut out with gun punches. These rings are fastened to 

 the slide by using some cement like the shellac. 



504. 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 remaining 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 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 break- 

 ing 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 is painted, half on the cover and half on the cell 

 wall (fig. 204) . 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 prepara- 

 tion. 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. 



505. 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. 



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. 



