228 



SUNK AND PLATE-GLASS CELLS. 



concave bottom is free from scratches and roughness. — Where 

 shallow cells are required with flat bottoms, they may be made by 

 drilling apertures of the desired size in pieces of plate-glass of the 

 requisite thickness, and by attaching these with marine-glue to 

 glass-slides (Fig. 105). Such holes may be made not merely cir- 

 cular (a), but oval (c) ; and a very elongated perforation may be 



Fig. 104. 



Sunk Cells. 



made by drilling two holes at the required distance, and then con- 

 necting them by cutting out the intermediate space (b). Deep 

 Cells, such as are required for mounting preparations of consider- 

 able thickness, may be made by drilling through a piece of thick 

 Plate -Glass, and cementing it in the usual way (d). These opera- 

 tions, however, can scarcely be performed by any but regular glass- 

 cutters, and, being troublesome, are expensive ; hence the Plate- 

 glass cells have been generally superseded, either by Tube- Cells or 

 by Built-up Cells. 



169. Tube-Cells. — These are made by cutting transverse sections 

 of thick- walled Glass tubes of the required size, grinding the sur- 



