MOUNTING CELLS 



449 



suitable distance, and cutting out the piece between them, any 

 required elongation of the cavity may be obtained (B, C, D). 



Sunk-cells. This name is given to round or oval hollows, exca- 

 vated by grinding in the substance of glass slides, which for this 



purpose should be 



thicker than ordinary. 

 They are shown in fig. 

 377, A, B, C. Such A 

 cells have the advan- 

 tage not only of com- 

 parative cheapness, but 

 also of durability, as 

 they are not liable to 

 injury by a sudden jar, 

 such as sometimes 

 causes the detachment 

 of a cemented plate or 

 ring. For objects whose 

 shape adapts them to 

 the form and depth of 

 the cavity, such cells 

 will be found very con- 

 venient. It naturally 

 suggests itself as an 

 objection to the use of 

 such cells that the con- 

 cavity of their bottom 

 must so deflect the 



light-rays as to distort or obscure the image ; but as the cavity is 

 filled either with water or some other liquid of higher refractive 

 power, the deflection is so slight as to be practically inoperative. 

 Before mounting objects in such cells the microscopist should see 

 that their concave surfaces are free from scratches or roughnesses. 



Built-up Cells. When cells are required of forms or dimensions 

 not otherwise procurable, 

 they may be built xp of 

 separate pieces of glass 

 cemented together. Large A 

 shallow cells, suitable for 

 mounting zoophytes or 

 similar flat 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 FIG. 378. Built-up cells, 



dimensions of its outside 



wall ; and a strip is then to be cut oft' 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. 



G G 



FIG. 377. Plate-glass sunk-cells. 



