210 DRY-MOUNTING OPAQUE OBJECTS. 



however, it be large, and the part of it to he attached have an 

 irregular surface, it is desirable to afford a ' bed ' to this by Gum 

 thickened with Starch. If, on the other hand, it should be desired 

 to mount the object edgeways (as when the mouth of a Foramini- 

 fer is to be brought into view), the side of the object may be 

 attached with a little gum to the wall of the cell. The complete 

 protection thus given to the Object is the great recommendation of 

 this method. But this is by no means its only convenience. It 

 allows the slides not only to range in the ordinary Cabinets, but 

 also to be laid one against another and to be packed closely in 

 cases or secured by elastic bands ; which plan is extremely conve- 

 nient not merely for the saving of space, but also for preserving the 

 objects from dust. Should any more special protection be required, 

 a Thin Grlass cover may be laid over the top of the cell, and secured 

 there either by a rim of gum or by a perforated paper cover 

 attached to the slide ; and if it should be desired to pack these 

 covered slides together, it is only necessary to interpose guards of 

 card somewhat thicker than the glass covers. In cases in which it 

 is desired to retain the power of examining the object without the 

 intervention of a glass cover, a thin disk of Bone or Vulcanite may 

 be attached to the slide (as suggested by Mr. Piper, ' ' Trans, of 

 Microsc. Soc." Vol. xv. p. 18) by means of a split metal rivet 

 passing through a hole near its edge, and attached to the slide 

 near the edge of the cell by clenching it on the under side before 

 the cardboard-bottom is attached. The rivet acts as a pivot on 

 which the disk turns, so that it may either cover the cell or may 

 be moved to one side ; and the disk may be conveniently made to 

 carry a label for the description of the object. For objects which it is 

 desired to examine under different aspects, Morris's Object-holder 

 (Fig. 76) will be found very convenient : full advantage can only 

 be taken of this, however, when the objects are mounted on de- 

 tached disks ; and in such cases Beck's Dish-holder (Fig. 77) is 

 decidedly preferable. 



156. Objects to be viewed by LieberTciihn illumination, however, 

 require a different mode of mounting, in order that the light may be 

 allowed to pass up around them from the mirror to the speculum. 

 If they are of moderate size, the Wooden slide may still be conve- 

 niently employed for them, its aperture being made as large as it 

 will bear, and its cardboard -bottom being replaced by a thin ordi- 

 nary glass slide ; and the object may either be mounted on a small 

 disk punched out of blackened card, or it may be attached directly 

 to the glass, to the under side of which a spot of black varnish or 

 a disk of black paper should be then affixed. Small and delicate 



about 1-lOth part of Glycerine to thick Gum-mucilage ; for the gum is 

 thereby prevented from hardening so completely as to become brittle, 

 and the bodies attached by it are less likely to be separated by a jarring 

 shock ; whilst, on the other hand, if it should be desired to remove the 

 object from the slide, the gum is more readily softened and dissolved by 

 the addition of a drop of water. 



