44 OBJECTS AND THEIR MOUNTING, 



36. MOUNTING OPAQUE OBJECTS. The smallest glass sliders, 

 of which we have spoken, (section 33,) are exclusively used for opaque 

 objects. On to one side of them is cemented, near the end, a piece 

 of soft leather or cork, punched out into circles of a convenient 

 size ; the leather or cork being previously blackened, or covered with 

 black paper. A pin run through the leather, holds the object con- 

 veniently. Sometimes these cylinders are made of ivory, but in all 

 cases it must be remembered, that in order to render them fit as a 

 back ground, they must be blackened. The darker the object the 

 more black and sombre must be the mounting, to heighten the brilliancy 

 of the object by the contrast. The best means of fixing the objects 

 in this mounting, is a solution of isinglass and gum arabic in spirits of 

 wine, which affords a strong and tough glue. 



37. Mr. Cooper, the editor of the Microscopic Journal, remarks, 

 that the plan of mounting opaque objects on a dead back ground, 

 generally black paper is objectionable, on account of the small fibres 

 on the surface of the paper reflecting some considerable portion of 

 light. The plan he recommends for mounting minute objects, to be 

 viewed either opaque or transparent, is simply by placing them on a 

 piece of crown glass with a little weak gum-water, and surrounding 

 them to the extent of a quarter of an inch or more with a rim of card- 

 board sufficiently thick to prevent the object being removed or broken 

 when another slide is placed either intentionally or otherwise upon it. 

 By using the stop of the diaphragm the object is made opaque, and an 

 even and uniform dark -coloured field is by this means obtained. 



38. MOUNTING IN PRESERVATIVE FLUIDS. Some objects, more 

 particularly the microscopic infusoria, are generally deemed only to be 

 interesting when seen alive, because from their peculiar structure 

 they cannot be preserved for occasional inspection in the usual ways. 

 This difficulty, however, may be removed, by preserving them in 

 alcohol or other preservative fluid a valuable resource, as it enables 

 us to retain, with little injury, their general structure. By this means 

 creatures which are new may be saved from entire demolition, and 

 secured until their genus, nature, or usual habitat can be ascertained. 



39. The method of mounting in alcohol or spirit of wine, is as 



