52 PREPARATION AND MOUNTING 



mends the use of Canada balsam (Chapter III.) as rendering their 

 structure more definite when illuminated with Wenham's para- 

 bolic reflector. Some advise other methods, which will be men- 

 tioned in Chapter IV. As most insects when undissected are 

 mounted in Canada balsam, the different modes of treatment 

 which they require will be stated in another place. 



In mounting blood of any kind to show the corpuscles, or, as 

 they are often called, globules, which are round or oval discs, it is 

 but necessary to cover the slide on the spot required with a coat- 

 ing as thin as possible and allow it to dry before covering with 

 the thin glass. There is a slight contraction in the globules when 

 dried, but not enough to injure them for the microscope. The 

 shape of these varies in different classes of animals, but the size 

 varies much more, some being many times as large as others. 

 Some of the larvce skins are beautiful objects; but, like many sec- 

 tions of animal and other fragile matter, are difficult to extend 

 upon the slide. This difficulty is easily overcome by floating the 

 thin object in clear water, immersing the slide and when the ob- 

 ject is evenly spread gently lifting it. Allow it then to dry by 

 slightly raising one end of the slide to aid the drainage, and cover 

 with the thin glass as other objects. The tails and fins of many 

 small fish may be mounted in a similar manner, and are well worth 

 the trouble. 



A few objects which are best shown by mounting dry may be 

 here mentioned as a slight guide to the beginner, though some of 

 them have been before noticed ; many of the Foraminifera as 

 elsewhere described. Some crystals are soluble in almost any 

 fluid or balsam, and should be mounted dry; a few, however, 

 deliquesce or effloresce, which renders them worthless as micro- 

 scopic objects. 



The wings of butterflies and gnats, as before noticed, afford 

 many specimens wherewith to supply the cabinet of the young 

 student. A great variety also may be found amongst the ferns ; 

 indeed, these alone will afford the student occupation for a long 

 time. On the under-side of the leaves are the reservoirs for the 

 " spores," which in many instances somewhat resemble green vel- 

 vet, and are arranged in stripes, round masses, and other forms. 

 The spores are usually covered with a thin skin termed the indu- 



