116 Sl(n)ii)ig Procedures (chap. 11) 



sections (unless technician is left-handed) (Fio. 25); ease cover olass into 

 place slowly to allow air to displace from imder cover glass; press firmly 

 from center outwards, to evenly distribute the medium. An alternate 

 method is to apply mounting medium along one edge of sections on 

 slide; rest one edge of cover glass adjacent to moimting medium and 

 lower gradually to ease out air without bubble formation; press gently 

 in place. 



If, during microscopic examination of stained and mounted slides, 

 dull black spots replace nuclear detail, the clearing solution partially 

 evaporated out of the sections before the cover glass was in place. Re- 

 turn such slides to xylene, dissolve all moimting medium to allow the 

 air to leave the sections, and remount. If the slides appear dull, almost 

 milky, instead of crystal clear, water is present. Remove all mounting 

 medium in xylene and return slides to absolute alcohol, preferably a 

 fresh solution. Clear and remount. 



Mounting Media (mountants) 



Formerly natural resins were used as mounting media: Canada bal- 

 sam, composed of terpenes, carboxylic acid and esters; gum damar, 

 composed of unsaturated resin acids and a little ester; or gum sandarac, 

 an unsaturated acid resin. These dried slowly, were variable in compo- 

 sition and impredictable in behavior. Some developed acidity and faded 

 stains, would turn yellow and crack after a few years. One still used, 

 particularly for blood smears, is Euparal, refractive index 1.483, a 

 eutectic (melts at low temperature) mixture of oil of eucalyptus, gum 

 sandarac, salol, paraldeliyde, menthol and camphor. Euparal Vert 

 (green because of copper salt content) is claimed to intensify hematoxy- 

 lin stains. Dried smears may be mounted directly in Euparal, but 

 sections must be carried into 95% alcohol, and then into Euparal 

 Essence before mounting. (If alcohol is carried into the Euparal, sec- 

 tions will fade.) Drain off excess Essence and apply Euparal. 



The synthetic resins now available have proven superior to natural 

 resins in most respects. The composition of synthetic resins can be con- 

 trolled and they are stable and inert. They dissolve readily in xylene or 

 toluene, do not require long drying, and adhere tightly to glass. They 

 have the correct refractive indices, are pale in color, and do not yello^v 

 \vith age. 



The most widely used synthetics are the ^-pinene polymers — terpene 

 resins, such as Permount [Fisher Scientific Company) and Piccolyte 



