OF MICROSCOPIC OBJECTS. 95 



cell with Canada balsam and leave behind no air-bubbles ? 

 I replied in the negative ; but now I can state how to 

 accomplish this. Fill the cell with clear spirit of turpentine, 

 place the specimen in it, have ready some balsam just fluid 

 enough to flow out of the bottle when warmed by the hand ; 

 pour this on the object at one end, and gradually inclining 

 the slide, allow the spirit of turpentine to flow out on the 

 opposite side of the cell till it is full of balsam ; then take 

 up the cover, and carefully place upon it a small streak of 

 Canada balsam from one end to the other. This, if laid on 

 the cell with one edge first, and then gradually lowered 

 until it lies flat, will drive all the air before it, and prevent 

 any bubbles from being included in the cell. It can be 

 easily put on so neatly as to require no cleaning when 

 dry. If the cover be pressed down too rapidly, the balsam 

 will flow over it, and require to be cleaned off when 

 hardened, for it cannot be done safely while fluid at the 



Sometimes with every care bubbles are enclosed in the 

 balsam, injuring objects which are perhaps rare and valuable. 

 If the object will not be injured by heat, carefully warming 

 the slide over a lamp will often set loose and remove these 

 pests ; but should heat be objectionable, or the bubbles too 

 closely imprisoned, the whole slide must be immersed in 

 turpentine until the cover is removed by the solution of the 

 balsam ; and the object must be cleansed by a similar steep- 

 ing. It may then be remounted as if new in the manner 

 before described. 



The balsam and chloroform described in Chapter II. is 

 thus used; and where the object is thin, the mounting is 

 very easily accomplished. When the object is laid upon the 

 slide with a piece of glass upon it, and the balsam and 

 chloroform placed at the edge of the cover, the mixture will 

 gradually flow into the space betwixt the glasses until the 

 object is surrounded by it, and the unoccupied portion filled. 

 The chloroform will evaporate so quickly that the outer edge 

 will become hard in a very short time, when it may be 



