. 1893] NEW-YORK MICROSCOPICAL SOCIETY. 41 



flame to the melting point, a small lump (say nut size) of the 

 balsam-cement is added, and the whole digested at gentle heat, 

 with frequent stirring, for about an hour, until the saturation of 

 the paraffin by balsam is shown by a slight yellowish tinge. 

 This colored paraffin contains less than five per cent, of balsam 

 and is now ready for use; a supply is poured into a shallow porce- 

 lain capsule with broad bottom, of about thirty cubic centimetres 

 capacity. When needed, this is heated upon the mounting-table 

 over a very low flame and kept just at the melting point. Over- 

 heating should be avoided, indicated by the escape of vapors, as 

 it tends to break up the paraffin into softer forms and also to 

 volatilize the diffused balsam-cement. At long intervals it may 

 be desirable to add a little more of the original hard stock to 

 the capsule, and a very small lump of balsam-cement. A com- 

 mon camel's-hair brush (extra sup. No. 2) is used to transfer 

 the paraffin, and, on account of the low melting point (63° C), 

 the brush needs no cleaning after use, and, if not allowed to re- 

 main too often in contact with the hot bottom of the capsule, it 

 lasts almost indefinitely. In use, the turn table should be placed 

 as near as possible to the cai)sule, and, if convenient, on the same 

 level. The glass slides on which the cells are to be spun should 

 also be kept warmed upon the mounting-table. If very shallow 

 cells are needed, mere films, suitable for mounting bacteria in 

 potassium acetate, the slides should be hot, and even a slight 

 warming of the turn-table may be of advantage if the room 

 should be cold. Cells may be thus spun at a single twirl of the 

 brush, shallow or deep, in proportion to the load of paraffin on 

 the brush and the mode of its application. 



A paraffin cell is immediately ready for use after it is spun ; 

 this is one great advantage of the material overall others. Paraf- 

 fin cells spun in this way are well suited for dry mounts, as they 

 are free from moisture and do not give off the oily vapors whose 

 condensation, in cells made from sheet wax, has been found in 

 time to obscure the under surface of covers. 



In using a paraffin cell for a mount with a liquid preserva- 

 tive, the first step is to flatten the top of the cell, which, if 

 the cell is deep, is apt to be convex. This can be done with a 

 stroke of a fine flat file, taking care to remove any loose particles 

 which might be thrown into the cell. This flattened surface 



