14 The Microscope. 



hours, the alcohol should be changed ; and this process repeated, 

 according to the size of the insect, until ail the water in its body has 

 been replaced by alcohol. Then a small quantity of oil of cloves 

 should be placed in the cell with the alcohol and allowed to remain 

 for several hours, at the end of which time the cell should be filled 

 with the pure oil, which should be allowed to remain several days. 

 Now, the cover should be taken ofP and the entire slide immersed in 

 very pure turpentine, and the length of time of the immersion will 

 depend upon the natural opacity of the insect. If, however, the 

 insect should be very transparent at the start, it may not be at all 

 necessary to use turpentine, but at once pour out the oil of cloves 

 and fill the cell with Canada balsam- 

 Sealing a fluid balsam mount is not always as easy as it looks, 

 and if not properly done at first may have to be done over again. 

 For this reason it is well not to get in a hurry, but be siu'e of every 

 step before another is taken. The balsam used should be rather 

 thick. Never use balsam containing benzole or chloroform for cells, 

 as these solvents are extremely volatile and it is difficult to seal them 

 so that they will not eventually leak. After pom-ing out the oil of 

 cloves or turpentine, as the case may be, carefully fill the cell round- 

 ing full of the balsam and set the slide away out of dust for some 

 time. This will give the bubbles a chance to come to the sm-face 

 and get out. In putting on the cover, do not conclude that because 

 the cell is rounding full there will be no danger of enclosing bubbles. 

 The surface balsam will have become somewhat " skinny," and if 

 the cover be lowered upon that the chances are that several bubbles 

 will be enclosed, which may require considerable work to remove 

 them. This danger, however, may be prevented by patting a small 

 di'op of turpentioe upon the top of the balsam or under side of the 

 cover, and lowering very carefully. The'cover'^should not be pressed 

 down immediately, but allowed to remain upheld by the balsam till 

 satisfied that all bubbles are out, when it may be carefully pressed 

 down and the surpkis balsam which has exuded from around the 

 cover may be scraped away with small pieces of cardboard, and 

 subsequently cleaned by a piece of cloth and chloroform, or alcohol. 

 Never use turpentine for cleaning ofP balsam, as it is liable to pene- 

 trate the cells. When thoroughly clean allow the slide to stand, at 

 an average temperature, for several hours, and then seal with shellac 

 (in alcohol). After the shellac has become thoroughly dry, any 

 cement may be put on and the slide finished in modest black. Or 



