PREPARING AND MOUNTING. 221 



mar the beauty, but possibly interrupt a clear view of a 

 very splendid and delicate object. Then, again, if the 

 microscopist prefers to cut and grind his own glass slips, 

 he should be very careful that there are no sand-specks or 

 air-bubbles in the centre of the slide, or of the glass- 

 cover : many a good object has been spoiled from neglect 

 of this precaution. A good light by which to work is 

 also highly important. In using the ordinary microscope, 

 the microscopist should keep both eyes open, the practice of 

 closing the eye not in use being injurious to the sight 

 of both. The beginner who is about to purchase a micro- 

 scope, will do well to procure a binocular, the price of 

 which has been reduced so much as to bring it within 

 the reach of those of even moderate means. 



The preservation of objects is a matter of much im- 

 portance. They ought to be kept in a cool and dry 

 place. Sections of bone, the pollen of plants, and the 

 scales of the podura and butterflies, become spoiled if 

 kept in a damp atmosphere. Objects mounted dry should 

 be carefully protected from dust, which will find its way 

 into crevices and corners where one might hardly suppose 

 it could possibly enter. 



Some opaque objects require dry mounting ; others 

 show best in fluid ; the elytra of some beetles are mag- 

 nificent objects when mounted in balsam. Cells punched 

 out of thick mill-board, or turned in some hard wood, or 

 Mr. Suffolk's metal-rings, are much lighter and more con- 

 venient than glass for such objects, and also for those 

 mounted dry. In mounting objects in fluid, the glass-cover 

 should come nearly, but not quite, to the edge of the cell ; 

 a slight margin must be left for the cement, which ought 

 to project slightly over the edge of the cover, in order to 

 unite it securely to the cell. In cells, however, that con- 

 tain balsam, there is no necessity for cement, and the 

 appearance of the slide will be improved by choosing a 

 cover of exactly the same size as the cell. 



There are some objects which require considerable dex- 

 terity and patience to prepare them for mounting. The 

 petal of the pelargonium is one of these. It is necessary 

 to split, it in order to show its structure to perfection. 

 This is effected by dividing the base of the petal with a 



