_Cells for Mounting._--The minuter forms of life should be mounted in thin cells, which may be readily made with Japanners’ gold size, dammar or asphalte, and a Shadbolt or Walmsley’s turntable. The glass slide being placed under the metal springs in such a manner that its two ends shall be equi-distant from the centre (a guide to the position is afforded by the circles traced out on the brass), take a camel’s hair pencil and dip it into the Japanner’s gold-size, holding it firmly between the finger and thumb, and set the wheel in motion, when a perfect circle will be formed; put it aside to dry, or place it in the warm chamber to harden. To cut cover-glasses place a sheet of thin glass under the brass springs, and substitute for the pencil a cutting diamond. A cutting diamond is not only useful to the microscopist for the above purpose, but also for writing the names of mounted objects on one end of the slide. It will be found convenient to make a number of such cells, and keep a stock ready for use. There are many objects whose structure is very transparent. These should be mounted dry. Scales from the wings of butterflies and moths, of the podura and lepisma, and some of the diatomaceæ are of this class. All that is necessary in preparing objects for dry mounting is to take care that they are free from extraneous matter, and fix them permanently in the position in which their structure will show to the best advantage. For mounting specimens of greater thickness it is desirable to use deeper cells. It will then be found convenient to make a second or a third application of the gold-size, allowing sufficient time between applications for the varnish to dry. Cells of a still deeper kind are made up by cementing rings of glass or metal to the glass-slides with marine glue or Brunswick black. The latter will be rendered more durable by mixing in a small quantity of indiarubber varnish (made by dissolving small strips of caoutchouc in gas-tar). The process of mounting in glass-cells is similar to that employed in making varnish-cells, except that a somewhat larger quantity of cementing medium is required. Objects mounted in this way should be kept for a time in the horizontal position, and a little fresh varnish must be applied if the cement shows a tendency to crack. In mounting objects in balsam, care must be taken to have the specimen _quite dry_ before transferring it to turpentine. Objects mounted in cells should become _perfectly saturated_ with the mounting fluid before being finally cemented down. [Illustration: Fig. 263.--Glass-cells for Mounting.] It is preferable to mount and preserve specimens of animal tissues in shallow cells, to avoid undue pressure on the preparation. Cells intended to contain preparations immersed in fluid must be made of a substance impervious to the fluid used, such as here represented (Fig. 263). The surface of the fixed glass-circle should be slightly roughened before applying the cement.