It was before stated that the diatoms when cleansed might be preserved in small phials of distilled water. When required for mounting, shake the phial, and with a thin glass tube or rod take up a drop of the fluid and spread it upon the surface of the slide in the desired position. This must then be allowed to dry gradually, or by the aid of the lamp if necessary, without being shaken or interfered with, otherwise uniformity of dispersion will be prevented. When _thoroughly_ dry, a thin ring of one of the adhesive varnishes--gold-size will be found as good as any--may be drawn round the diatoms, and allowed to dry in a slight degree. The slide and thin glass cover should then be warmed and the latter gently pressed upon the ring of varnish until the adhesion all round is complete. As some of the diatoms require object-glasses of extremely high power, and, consequently, short focus, to show them, they must be as close to the outer surface of the cover as possible. For this reason they are sometimes placed upon the under side of the thin glass, as follows. Clean the surfaces of the slide and cover, and with the rod or pipe place the liquid containing the diatoms upon the thin glass, and dry as before. Trace the ring to receive the cover upon the slide, and when almost dry, warm both and proceed as above. Whichever of these methods is employed, the outer ring of coloured varnish may be applied as elsewhere described and the slide finished. The diatoms are also sometimes mounted betwixt two thin glasses, as described in Chapter I., so that the light by which they are examined may receive as little interference as possible, and that an achromatic condenser may be brought into focus under the slide. Of the various modes of cleaning and mounting the Diatomaceæ, I believe that the following may be safely recommended as affording results of the very best quality. My friend, Mr. T. G. Rylands, gave it to me as that which he prefers, and I can safely say that his numerous slides are at least equal to any I have ever seen. I will give it just as I received it from him, though there may be some little repetition of what has been said elsewhere, as he does not appropriate any part of it as his own. He says:--In this branch of mounting, general rules alone can be laid down, because the gatherings may contain iron, lime, fine silt, or vegetable matter under conditions for special treatment, and consequently the first step should be to experiment on various kinds.