230 



TUBE-CELLS. — BUILT-UP CELLS. 



Ayr stone, after they have been cemented to the glass-slides ; and 

 this will be found the best preventive against the running-in of the 

 Gold-size, which often takes place with Glass-tube cells in conse- 

 quence of their inequality of surface. 



Fig 



Tube-Cells, Round and Quadrangular. 



170. Built-up Cells. — When Cells are required of forms or 

 dimensions not otherwise procurable, they may be built-up of 

 separate pieces of Glass cemented together. Large shalloio Cells, 

 suitable for mounting Zoophytes or similar fiat objects, may be 

 easily constructed after the following method : — A piece of Plate- 

 Glass, of a thickness that shall give the desired depth to the cell, is 

 to be cut to the dimensions of its outside wall ; and a strip is then 

 to be cut off with the diamond from each of its edges, of such 

 breadth as shall leave the interior piece equal in its dimensions to 

 the cavity of the cell that is desired. This piece being rejected, 

 the four strips are then to be cemented upon the glass-slide in their 

 original position, so that the diamond-cuts shall fit together with 

 the most exact precision ; and the upper surface is then to be 



