MOUNTS AND MOUNTANTS 



MoHR AND Wehrle's Medium: 



37 



Camsal is a viscous fluid produced by the mutual solution of equal quanti- 

 ties of camphor and phenyl salicylate (salol). It is well to make up more of 

 this than is required for the preparation of the medium, since it may be used 

 for clearing whole objects which are intended for mounting in a medium of 

 this type. There is a superstition that a variety of euparal, known as green 

 euparal, preserves the color of hematoxylin stains better than does the plain 

 material. The formula given above may be turned into an imitation of green 

 euparal by adding as much of a solution of copper oleate in eucalyptol as 

 needed to produce the required color. 



The most usual resinous mounting medium is Canada balsam. This is the 

 natural exudate of the balsam tree (Abies balsamea). Unfortunately, commercial 

 samples are often contaminated with the exudates of other resinous trees, 

 which render the material less suitable for the preparation of microscope 

 mounts. This balsam, as all other balsams, is a solution of a "resin" in turpen- 

 tine and contains, in addition, a series of higher-boiling-point hydrocarbons, 

 which serve as "plasticizers" to render it less brittle when it dries. The material 

 is commercially obtainable in two forms. "Natural balsam" is the thick sticky 

 material as it comes from the tree and should always be used in the prepara- 

 tion of wholemounts. The other form is "dried balsam" which has been 

 heated to the extent that the turpentines are driven off, but the natural plas- 

 ticizers remain. This material is dissolved in xylene to a suitable consistency 

 and is used for mounting sections. The dried balsam, unfortunately, is often 

 carelessly prepared by suppliers who heat it to the point where the natural 

 plasticizers, as well as the turpentines, are driven off. This results in a very 

 brittle coriipound, and slides made with it are quite likely to flake off the 

 coverslip a year or two after they have been mounted. Therefore, specimens 

 purchased should be examined carefully by pressing them with the thumb 

 nail. If, on pressure with the thumb nail, one of the pieces of dried balsam 

 cracks into a powdery material, the sample should be rejected. The desirable 

 consistency is that in which the thumb nail will just manage to mark a piece 

 without any shattering. It is usually worth while to prepare one's own dried 

 balsam from the natural balsam by tipping a pound or two into a shallow 

 metal container (a baking dish is excellent) and placing this on a hot plate. 



