ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 377 



(6) Miscellaneous. 



Mounting Diatoms.*— J. Gr. E. Powell gives the following method 

 for mounting filamentous diatoms so as to display them in that beauty 

 of pattern which they lose by boiling. They are mounted between two 

 thin covers, so that they can be examined either as transparent or opaque 

 objects. The slips for this purpose are made of card, wood slips being 

 more costly. 



Cut 3 in. by 1 in. blanks, in one set punch f in., in the other about 

 \ in., and gum together. When thoroughly dry ring the hole with 

 black sealing-wax varnish, and cement in a f cover, ringing on a 

 varnish cell of about \ in. These slips, with their cells, are" best pre- 

 pared at odd moments in advance. The filamentous diatoms are found 

 as waving chocolate-coloured wisps in running streams, ditches, drains, 

 and springs. They should be lifted carefully out into a small, wide- 

 mouthed bottle with distilled water, and brought home with as little 

 skake as possible. Transfer them gently to a saucer of distilled water, 

 have ready some clean covers (say ^ No. 2), each cover with a drop of 

 distilled water on it. Cut off a tiny portion of the filament, and let it 

 settle on a cover in the drop, removing the superfluous water when 

 it has settled. Dry the covers thoroughly, and then burn them. Place 

 these diatoms upward on a flat slip of platinum or a bit of very thin 

 tin, and gently lower them into the flame of a Bunsen burner till 

 all vegetable matter is destroyed. Now very lightly retouch one of 

 the prepared cells with cement, and lay on the cover diatoms down- 

 ward, sealing down after a few hours. This last is a ticklish job, as the 

 cement has a tendency to run in and spoil the mount. The cement 

 should be thick, and only just touched. Brown's cement is good for the 

 first layers. Slides so mounted are glorious objects under incident light, 

 one side being best for this purpose ; and the other, on which the diatoms 

 are in optical contact with the cover, is better for transmitted light. 

 But this method obstructs the light for Lieberkuhn and paraboloid. 

 The burnt cover may be mounted on a ring of Canada balsam or 

 dammar in chloroform. These gums, separate or mixed, dry quickly, 

 are not so liable to run in, and do not obstruct the light. If the diatoms 

 on the cover are rather crowded, the cover may be fastened to a slip, 

 diatoms upward, with a tiny drop of ordinary balsam, heated till not 

 quite hard, and then the cover gently melted down. Then a tin ring of 

 proper size can be cemented just outside it, and a f or f cover put on, 

 One or two mounts of the burnt covers should be put up in the ordinary 

 balsam method. Run a drop of spirit of turpentine on to the diatoms, 

 followed by a tiny drop of ordinary balsam, and give them time to mix. 

 Then lay the cover on the thin slip, balsam upwards, heat gently over 

 say a benzoline lamp till the balsam when cool is not hard. Care ;is 

 needed to avoid bubbles. Centre a glass slip with an ink dot, touch the 

 other side with a very little fresh balsam, lay the cover balsam down- 

 ward, and warm gently till the two balsams mix, and run under the whole 

 cover. If the mounter has been successful, the cover when cool will 

 stand rubbing, and no finishing is required. Label with plain inch 



* English Mechanic, lxxix. (1904) p. 123. 



