312 



MANIPULATION. 



lessened if the slides be coated with paper. Ether is the best 

 solvent of Canada balsam, but the cost of it prevents its fre- 

 quent use; in some delicate operations, however, it is indis- 

 pensable. 



The best form of vessel for keeping 

 Canada balsam in, is the one represented 

 in fig. 209; the glass cover should be 

 sufficiently taU to enclose the rod for 

 taking out the balsam, and should fit over 

 the neck of the bottle, its upper surface 

 may be ground flat, as shown at a, so that 

 it may stand steadily when taken off. 



Other points to be particularly at- 

 tended to in the mounting of different 

 classes of objects will be mentioned in 

 the part of the work devoted to the de- 

 scription of the mode of preparing them ; 

 the rules above laid down will, however, 

 be apphcable to by far the greatest ma- 

 jority of objects, and only certain modi- 

 fications of these wUl require separate 

 mention. 



Method of Mounting Objects in Media 

 containing Gelatine. — The various plans 

 recommended for mounting objects in 

 Canada balsam, will apply equally well to the media de- 

 scribed in page 282, but the chief difficulty consists in getting 

 rid of the air bubbles, or the vacuities that occur in conse- 

 quence of the evaporation of the water. The specimen to be 

 mounted, if in a moist state, should be placed in a little of 

 the medium dissolved in a watch glass or smaU ceU by the aid 

 of a gentle heat before it is placed on the slide, and care taken 

 to exclude any bubbles that may be present before the cover 

 is put on. The cover should not be pressed down hard, as 

 many objects have a tendency to curl, and wiU lift it up, 

 and air wiU rush in. The copper vessel described in page 

 310, and the air pump will be generally found requisite for 

 the perfect exclusion of all the bubbles. 



Fig. 209. 



