84 PREPARATION AND MOUNTING 



oval discs, it is bat 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 larvcB 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 render* 

 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 a long time. On the nnder-side of 



