Making Wholemounts 



117 



Fig. 83. Balsam wholemount ready for drying. The phosphor-bronze clip prevents 

 the coverslip from moving. 



cavity has been ground, it is desirable to hold the coverslip in place with 

 a clip while the balsam is hardening. This process is seen in Fig. 83; the 

 type of clip there shown is made of phosphor-bronze wire and is far 

 superior to any other type. 



The description above presumes the use of natural Canada balsam, un- 

 questionably the best resinous medium in which to prepare wholemounts. 

 If a solution of dried balsam in xylene is used, a very different technique 

 will have to be adopted. In the first place, most of these solutions are so 

 thin that it is almost impossible to apply the coverslip as shown in Fig. 81, 

 and the technique shown in Fig. 82 must be adopted. This difficulty may 

 be avoided by placing the object on the slide, putting a drop of the 

 medium over the object, and then setting the slide in a desiccator until 

 most of the solvent has evaporated. A second layer is placed on top to 

 build up a large drop or, rather, a thick coat of varnish over the speci- 

 men. A coverslip is applied, and the slide is warmed until the resin be- 

 comes fluid. 



The best use for solutions of balsam in making wholemounts is in 

 dealing with a very large number of objects. The method in this case is to 



