36 MICROSCOPICAL RESEARCH 



The method of building up a cell for a balsam mount is much 

 more simple than the above. Balsam is placed in the cavity ; then the 

 specimen is arranged in position, a tin ring is cut across and each half 

 arranged round the cavity with a small space left between them (Fig. 22). 

 A cover slip is placed on the ring and the whole held in position by a 

 spring clip. If the cell is not already full of balsam more may be run 

 under the cover slip through one of the openings in the ring. The 

 preparation must be allowed to dry slowly ; and after the superfluous 

 balsam is removed, the cell should be protected with several layers of 

 brown cement, and ultimately finished off with zinc oxide. 



Fig. 22. — Tin ring divided for building up balsam mounts. 



Cleaning, Ringing, and Finishing the Slides. 



Balsam preparations are dried by being placed in a water-oven for 

 sixteen hours at a temperature of 140 degs. Fahr., or in the absence 

 of the water-oven, should be put aside in a warm place for a few days to 

 evaporate the benzol and set the balsam. If the water-oven be used for 

 this work, the slides, after drying, must remain in it until it has 

 gradually cooled down; they should then be taken out, the spring clips 

 removed, and the superfluous balsam cleaned off with the "hot-knife." 

 The hot-knife may be made out of an old table-knife by reducing the 

 point end to a chisel edge, which must be square. This is heated in 

 the bunsen flame and then lightly passed round the edge of the cover 

 slip carrying the balsam with it (Fig. 23 A). 



