ON MOUNTING OBJECTS. 77 



screws. A handle of wood is fixed into the upper part of one, for the 

 purpose of turning it round, the motion being communicated to the 

 other by an endless band of catgut running in the grooved edge of 

 each. On the upper surface of the wheel, under the right hand, are 

 fixed, by means of screws, two strips of brass, which serve as springs 

 for securing the glass-slip ; a camel's-hair pencil previously dipped in 

 japanners' gold-size is then taken between the finger and thumb, and 

 held as represented in the woodcut, when the wheel is put in motion, 

 and a perfect circle is rapidly formed ; the cell is then removed, and 

 put aside to dry. In the same way, by securing a sheet of thin glass 

 under the brass springs, and substituting for the pencil a cutting 

 diamond, a circular cover may be readily cut out. A cutting diamond 

 is not only useful to the microscopist for the above purpose, but also 

 for writing the names of mounted objects on the ends of the glass slides. 

 A glazier's diamond for cutting glass slides is both convenient and 

 economical : the mode of using it may be learned in any glazier's shop. 

 On mounting and preserving Objects. Microscopic objects are 

 usually mounted on slips of glass three inches by one inch, either dry 

 or immersed in some fluid. The minute structures, such as the tissues 

 of animals, parts of insects, vessels of plants, &c., must be preserved in 

 thin cells, made as directed above, with a small amount of fluid.* 

 Clean the glass with a weak solution of ammonia or potash from all 

 grease, and wipe it dry with a piece of chamois leather or cotton velvet ; 

 cloth generally leaves behind it small filaments, which are always un- 

 sightly when seen near the object. Let fall a drop of the preserving 

 fluid or Canada balsam on the centre of the glass; then place the object 

 in it with a small pair of forceps, and spread it out very carefully with the 

 point of one of your fine needles. Select a thin glass cover, previously 



fig. 61. 



cleaned, touch its edges with cement, and let it fall gently and gra- 

 dually down upon the object, as represented in fig. 61 ; press it lightly 



* Cells for microscopic purposes may be purchased of Mr. Bender, 6 Brunswick 

 Place, City Road, or of Mr. Baker, 244 High Hoiborn. 



