106 The Preparation of Microscope Slides 



the atmosphere is commonly humid, it would be well to reduce the 

 quantity of chloral hydrate to 60 g. 



RESINOUS MEDIA 



There are two main types of resinous mounting media: (1) those into 

 which the object may be placed directly from alcohol; and (2) those for 

 which the object must first be cleared. The former type of medium is com- 

 monly referred to as a "neutral" mountant and is used almost exclusively 

 for mounting stained blood films, which are sensitive to the acid that 

 inevitably develops in balsam mounts. The best known of these neutral 

 mountants is a proprietary compound of secret composition known as 

 euparal. This may be obtained commercially, but for those who prefer 

 to prepare their own solutions an excellent substitute is: 



MOHR AND WeHRLe's MEDIUM: 



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

 quantities 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 to clear whole objects before 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 is needed to produce the required tint. 



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, like all other balsams, is a solution 

 of a "resin" in turpentine and contains, in addition, a series of higher- 

 boiling-point hydrocarbons that serve as "plasticizers" to render it less 

 brittle when it dries. Canada balsam is commercially obtainable in two 

 forms. "Natural balsam" is the thick sticky material as it comes from the 

 tree and is best used in the preparation of wholemounts. The other form 

 is "dried balsam," which has been heated to the extent that the turpen- 

 tines are driven off, but the natural plasticizers remain. This material, 

 when dissolved in xylene, is used for mounting sections. Dried balsam, 



