SECTION THREE 



NON-AQUEOUS MOUNTING MEDIA 



CANADA BALSAM 



Strictly speaking " Canada balsam " is natural Canada balsam, 

 a pale-yellow viscous fluid obtained from the balsam fir, indigen- 

 ous to Canada: this fluid is useless as a histological mounting 

 medium. "Canada balsam, dried " is the natural Canada balsam 

 which has been dried by heat until it has become a brittle solid. 



" Canada balsam in xylol " (or in benzene or other suitable 

 solvents) is prepared by dissolving the dried natural balsam in 

 xylol, etc. When an histologist sees the words " Mount in 

 Canada balsam " (or simply " balsam ") he takes it to mean, and 

 correctly so, that the preparation is to be mounted in Canada 

 balsam in xylol. However, the term " Canada balsam " can be 

 misleading to those who are new to the language and customs of 

 histology, and such workers have been known to mount in true 

 Canada balsam: i.e. natural Canada balsam, and with most un- 

 satisfactory results. It is for this reason that this definition of 

 " Canada balsam " is given here. 



Although Canada balsam in xylol is still used extensively it 

 has a serious disadvantage in that it is prepared from a natural 

 resin which is uncertain and variable in chemical composition, 

 usually somewhat acid in reaction, and while it may be neutralized, 

 will revert to an acid reaction after a time, however careful one is 

 in handling and storing the mountant. For this reason it is better 

 to employ a synthetic mountant of definite and unvarying chemical 

 composition. Short descriptions of mountants of this kind are 

 given below: they also have the advantage of being considerably 

 less costly than Canada balsam. 



CLEARMOUNT 



(Edward Gurr) 

 Refractive ifidex 1-515 



A colourless, neutral, synthetic mountant, with a drying time 

 approximately the same as Canada balsam in xylol. This mount- 

 ant, which remains neutral indefinitely and does not cause the 

 fading of even the most delicate stains, is miscible with xylol, 

 absolute alcohol, benzene, toluol, dioxane and many other solvents. 



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