84 PREPARATION AND MOUNTING 
oval discs, it is but necessary to cover the slide on the spot 
required with a coating as thin as possible and allow it to 
dry before covering with thin glass. There is a slight con- 
traction in the globules when dried, but not enough to in- 
jure them for the microscope. The shape of these varies in 
different classes of animals, but the size varies much more, | 
some being many times larger than others. Perhaps it will 
not be out of place to say a few words concerning the detec- 
tion of blood. Wherever the stains are, they must be care- 
fully scraped away and immersed for a few hours in a weak 
solution of bichloride of mercury. With a thin tube the 
more solid portion may then be removed to a glass slide and 
examined with a somewhat high power. A slight knowledge 
of the microscopic appearance of blood-discs will show us 
whether the suspicion of blood is correct. 
Some of the skins of larve are beautiful objects; but, like 
many sections of animal and other fragile matter, are diffi- 
cult to extend upon the slide. This difficulty is easily over- 
come by floating the thin object in clear water, immersing 
the slide, and when the object 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 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 microscopic objects. 
The wings of butterflies, gnats, and moths will afford 
many specimens wherewith to supply the cabinet of the 
young student. A great variety of scales also may be found 
amongst the ferns; indeed, these alone will afford the 
student occupation for along time. On the under-side of 
