1890.] MICKOSCOPICAL JOURNAL. 249 



A ring of some hard varnish, such as that made of gum dammar, dis- 

 solved in benzole, is made on a glass slide by means of a turn-table, and 

 when sufficiently hard, the object may be mounted within it. The 

 cover-glass being chosen rather smaller than the ring, may then be 

 fastened on with the wax and Canada balsam before a permanent 

 cement is put on, or there is great danger of the cement being drawn 

 in by capillary attraction, and the preparation spoiled. Neat glass cells 

 may be constructed in the following manner: Take a brass plate hav- 

 ing circular apertures in it of the size the cells are required to be, and 

 with marine glue cement a square of thin glass over one of the selected 

 holes. When the glue is quite hard, give a smart puncture in the 

 centre of the glass with a small rat-tail file, when the brass will be 

 starred, the cracks, however, not proceeding beyond the edge of the 

 aperture. The glass may then be filed out under water to the edge of 

 the aperture. Great care must be exercised afterwards, in warming 

 and removing the glass from the plate, though if a simple fracture 

 should occur, it is of no great consequence, as the cell joins again 

 readily when cemented to the glass slide. 



It may sometimes be useful to cut a hole through the slide itself, 

 which may be accomplished in this fashion : Take a hard steel drill, 

 having a spear-headed point, dip it in turpentine, and drill partly 

 through the surface of the slide at the point opposite to that in which 

 the cell is to be made ; then attack the other surface, so that the hole 

 made shall correspond to that already begun, and by the application of 

 fresh supplies of turpentine, continue the drilling until the point comes 

 out at that first commenced, when the drill comes through without 

 cracking the glass or starring its surface. Having got the hole, it may 

 be enlarged by the use of the rat-tail file under water, to the dimensions 

 required. Where it is desirable to examine test objects through thin 

 glass, this may be cemented over such a hole, and the test object 

 mounted on it in the ordinary way, and covered with a similar piece 

 of cover-glass. 



Glass rings, corresponding in dimensions with the diameters of the 

 most generally employed circular covering glasses, are exceedingly 

 valuable for mounting opaque objects. They may be cemented to the 

 glass slide with marine glue ; their surfaces being left rough from the 

 cutting afibrd a firm attachment for the glue, which diminishes the risk 

 of the ring coming ofi^ the slide with too energetic wiping. Rings of 

 pure tin or zinc can also be obtained, and are useful from the 

 ease with which they can be reduced in depth by filing, should they 

 be too deep for the object to be mounted. Rings of gutta-percha, vul- 

 canite, and millboard, have found favor with some ; but their 

 qualifications for making a sound and secure mount have been 

 so deficient that they have been discarded by all good mounters. 

 Brass rings are not suitable as the copper in them stains the mounting 

 medium green after the preparation has been set up a short time. There 

 are some cells termed ground-out cells, which can be highly recom- 

 mended to those who mount small insects as transparent objects ; they 

 may be had of difierent sizes, to suit difi'erent objects. They are as 

 the name implies ground out from the surface of the slide, and after- 

 wards polished. For mounting those objects which show their points 

 of interest to the greatest advantage without pressure, they are most 



