ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 715 



larger slides are occasionally of use when it is desirable to mount 

 whole sections of thick rhizomes, roots, and similar preparations. 



Some German workers prepare their slides by cementing very 

 narrow strips of glass across the two ends of the slides, so that when 

 the slides are laid upon each other, these strips prevent one slide 

 from injuring the next one, and the slides may be packed away with- 

 out having the ordinary grooved boxes. These slides, however, says 

 Dr. Wall, " are not often employed in this country, for while it is 

 true that they offer some practical advantages, they are anything but 

 pretty in appearance, and it seems to be a pity to mount a good 

 preparation in such a shabby manner." 



" Some ornamental effects in mounting are obtainable by using 

 coloured glass for the slides. For opaque mounts, slides of very 

 dark-blue glass (pot-metal) present a fine background. A pretty 

 effect is produced with some opaque objects mounted on these dark- 

 blue slides, by illuminating with the bull's-eye lens, and at the samo 

 time reflecting the light upwards with the mirror, thus showing the 

 brightly illuminated object on a rich blue ground. This method is 

 very pleasant to the eyes. If the light is not reflected upwards with 

 the mirror, such slides appear perfectly opaque and black. 



Another pretty kind of slide may be made by cutting the slides 

 from coloured glass (flashed metal), and then painting a heavy circle 

 with varnish on the centre of the slide on the flashed side by the aid 

 of the turntable, and then, when dry, placing a drop of hydrofluoric 

 acid in the centre of the ring, and making a circular spot of clear 

 glass on which the preparation may be mounted. By having slides 

 of red, yellow, blue, purple, and other colours, prepared in this 

 manner, quite a pleasing variety may be given to the appearance of a 

 collection of mounted specimens. The roughness of the glass pro- 

 duced by the acid disappears when the preparation is mounted in 

 balsam, and, in fact, this kind of slide should only be used for balsam 

 mounts for low powers. 



Still another, and very pretty slide, may be made by giving one 

 side of a plain glass slide the appearance of ground glass, by grinding 

 on a slab of plate glass with emery flour and turpentine. The 

 preparation is to be mounted on the ground side with balsam. This 

 kind of slide, like the last, is only to be used for objects for low 

 powers. For some preparations, which should not be subjected to 

 pressure, glass slides may be obtained, on one side of which de- 

 pressions are ground, in which the object may lie when the cover- 

 glass is put on. These slides are to be preferred to cells for fluid 

 mounts in many cases, but as they are expensive, they are not as 

 frequently used as they would be if they were sold at more reasonable 

 prices. This might readily be done, we should think, as the grinding 

 and polishing of these depressions is not so very expensive. Tho 

 writer once had such depressions ground in a few hundred slides at 

 Itj cents per slide ; and even at twice or three times this price they 

 would still be cheap compared with the prices commonly asked for 

 them. As they are so convenient for many purposes, it is to be 

 hoped that they may be obtainable at more reasonable prices." 



