OP THE MICBOSCOPE. 175 



and great care must be taken to close the cell all round in this 

 way. It is true, this point is not of so much consequence with 

 the particular object under consideration, but with some ob- 

 j ects it would be quite important. The scales are now mounted 

 dry, and may be kept for any length of time; no dust can soil 

 them, and they are not liable to be injured by contact with 

 other bodies. It only remains to label and " finish " the slide 

 as hereafter directed. 



Next to the above in simplicity is the mounting of such ob- 

 j ects as the wings of insects in balsam. Suppose we wish to 

 mount one of the smaller wings of a bee or wasp, so as to show 

 the curious hooks with which it is armed: Place the warm slide 

 on the centering card, drop a little balsam on the centre, and 

 again warm the slide, so that any air that may be present may 

 collect in fine bubbles which can be removed by means of a 

 cold mounting needle. When the air-bubbles have been re- 

 moved, seize the wing (previously well cleaned with a camel 

 hair brush) with a pair of fine forceps, and lower the tip of it 

 i nto the warm balsam. Then slowly lower the wing until it is en- 

 tirely immersed. Drop, very little more balsam on it, warm 

 the slide again (slightly this time), and remove air bubbles if 

 there should be any. Then take a clean cover in the cover for- 

 ceps, make it quite warm, and place it over the object by allow- 

 ing it to first touch one edge of the balsam, and then to grad- 

 ually fall down so as to exclude all air bubbles. In the case 

 of the bee's wing it does not answer to apply much pressure as 

 this would tend to distort the hooks. Press the cover into 

 place as much as it will bear and no more, lay the slide in a 

 warm place for some time until the balsam hardens, and then 

 clean and finish the slide. 



In mounting objects in balsam and fluids, the great difficulty 

 to be encountered is the presence of air bubbles. Careful and 

 j udicious management, however, readily enables us to avoid 

 them. In the first place see that they are entirely removed 

 from the balsam on the slide. This is much more easily done 

 before immersing the object in the balsam then afterwards. 

 Next see that the air is expelled from the object. In the case 

 of the wing, this is effected by slowly immersing the object in 

 the balsam. Lastly see that no air enters with the cover. To 



