448 PKEPAKATION, MOUNTING, AND COLLECTION OF OBJECTS 



in order to secure the firm adhesion of the glue ; and this is readily 

 accomplished, in the first instance, by pushing each, as it is finished, 

 towards one of the extremities of the plate. If two plates are in 

 use, the heated plate may then be readily moved away upon the ring 

 which supports it, the other being brought down in its place ; and as 

 the heated plate will be some little time in cooling, the firm attach- 

 ment of the cells will be secured. If, on the other hand, there be 

 only a single plate, and the operator desire to proceed at once in 

 mounting more cells, the slides already completed should be carefully 

 removed from it, and laid upon a wooden surface, the slow conduc- 

 tion of which will prevent them from cooling too fast. Before they 

 are quite cold, the superfluous glue should be scraped from the glass 

 with a small chisel or awl, and the surface should then be carefully 

 cleansed with a solution of potash, which may be rubbed upon it 

 with a piece of rag covering a stick shaped like a chisel. The cells 



should next be washed 

 with a hard brush and 

 soap and water, and 

 may be finally cleansed 

 by rubbing with a little 

 weak spirit and a soft 

 cloth. In cases in which 

 appearance is not of 

 much consequence, and 

 especially in those in 

 which the cell is to be 

 used for mounting large 

 opaque objects, it is de- 

 cidedly preferable not 

 to scrape off the glue 

 too closely round the 

 edges of attachment, as 

 the ' hold ' is much 

 firmer, and the proba- 

 bility of the penetra- 

 tion of air or fluid much 



less, if the immediate margin of glue be left both outside and 

 inside the cell. To those to whom time is of value, it is recom- 

 mended that all cells which require marine glue cementing be 

 purchased from the dealers in microscopic apparatus, and it is 

 well to note that all cells cemented with marine glue should be 

 well ' payed,' as the nautical expression is, or well surrounded 

 with shellac varnish or gold-size as indicated by the nature of 

 the enclosed fluid. Many media, saline fluids especially, work their 

 way between the cell and the slide, and at length destroy the marine 

 glue. 



Plate-glass Cells, Where large shallow cells with flat bottoms are 

 required (as for mounting zoophytes, small medusce, &c.), they may be 

 made by drilling holes in pieces of plate-glass of various sizes, 

 shapes, and thicknesses (fig. 376, A), which are then cemented 

 to the slide with marine glue. By drilling two holes at a 



D 



FIG. 376. Plate-glass cells. 



