BUILT-UP CELLS. 



231 



ground flat with emery upon the pewter plate, and left rough as 

 before. The perfect construction of large deep Cells of this kind, 

 (Fig. 107, a, b), however, requires a nicety of workmanship which 

 few amateurs possess, and the expenditure of more time than 

 Microscopists generally have to spare ; and as it is consequently 

 preferable to obtain them ready-made, directions for making them 

 need not be here given. A plan of making deep cells, however, 

 has been introduced by Dr. L. Beale ; which, though it does not 

 give them side walls possessing the same flatness with those of the 

 built-up cells, adapts them to serve most of the purposes for which 

 these are required, and makes them more secure against leakage ; 

 whilst it has the advantage of being so easy and simple that any 

 one may put it into practice. A long strip of Plate-Glass is to 



Fig. 107. 



Built-up Cells. 



be taken, whose breadth is equal to the desired depth of the cell, 

 and whose length must be equal to the sum of the lengths of all its 

 sides. This strip is to be carefully bent to a right angle in the 

 blow-pipe flame, at three points previously indicated by marks so 

 placed as to show where the angles should fall ; and the two ends, 

 which will thus be brought into contact at right angles, are to be 

 fused together. Thus a large square well, slightly rounded at the 

 angles, will be formed; and this being very brittle, should be allowed 

 to cool very gradually, or, still better, should be annealed in an oven. 

 It must then be ground quite true on its upper and lower edges, 

 either on the lead-plate with emery, or on a flat stone with fine 

 sand ; and it may then be cemented to a Glass-Slide in the usual way. 

 171 . Mounting Objects in Cells. — In mounting an object in a 

 Cell, the first attention will of course be given to the cleanness of 

 the interior of the cell, and of the glass-cover which is to be placed 

 on it : this having been secured, the cell is to be filled with fluid 



