10 THE CALIFORNIA SPECIES OF MEALY BUGS 



do not become unduly heated, as this destroys their staining qualities, 

 the resulting preparation being of a uniform bluish color and showing 

 little or no differentiation between the various parts. It is for this 

 reason that a weak solution of caustic potash should be used, for it ap- 

 pears that the boiling point of a strong, "soupy" solution is somewhat 

 higher than the critical point. 



It is especially noteworthy that the method outlined above may be 

 used for the purpose of rendering old mounts suitable for study. The 

 results obtained are sometimes not as good as with fresh material, but 

 they are usually very much worth while. The specimens should be re- 

 moved from the mount if possible without the use of heat, or if heat is 

 necessary, it should be very carefully applied. The specimens should 

 then be freed from the medium in which they have been mounted, the 

 method of doing so depending upon what medium has been used. If the 

 medium is balsam they should be soaked in carbol-xylene or a similar 

 reagent, if glycerine jelly they may be boiled in caustic potash. In any 

 case this boiling should not be omitted, as it renders the specimens flex- 

 ible. Following this the treatment proceeds in the usual manner. The 

 only risk encountered in attempting to stain old mounts lies in the pos- 

 sibility that they may have been overheated when they were originally 

 made and this can only be discovered by experiment. However, this risk 

 may partially be avoided by staining but a part of the specimens con- 

 tained in the mount. 



