MOUNTING OF SPECIMENS 21 



preserved without special treatment. A further dis- 

 advantage of temporary mounts is that they cannot 

 be readily transported. 



The permanent mounting media include glycerin 

 jelly, Canada balsam and solutions of various resins. 

 Glycerin jelly is used in most instances because it is 

 readily miscible with the aqueous or alcoholic media 

 generally used for the preservation of stock specimens. 

 Glycerin jelly is prepared with gelatin, glycerin and 

 water with a trace of phenol as a preservative (refer 

 to Appendix). Specimens mounted in glycerin jelly 

 will last at least five years if kept under favorable 

 conditions. Canada balsam is a liquid oleoresin 

 obtained from the tree Abies balsamea. It is a thick 

 liquid of pale yellow color and when used as a mount- 

 ing medium is usually mixed with xylol. As it is 

 immiscible with water it cannot be used unless the 

 specimens are dehydrated by being passed through 

 increasing strengths of alcohol and finally through 

 xylol or chloroform. The balsam gradually solidifies 

 and forms a varnish. The mounts are absolutely 

 permanent, but crystals of resin acids may separate 

 from the balsam and obscure the specimen. The 

 refractive index of Canada balsam is less than that 

 of glycerin jelly; therefore when working with very 

 delicate objects mounted in balsam it is customary 

 to stain or color the specimens so that clearer views 

 may be had. 



PREPARATION OF GLYCERIN JELLY MOUNTS 



Materials required: 



Slides and cover-slips. 



Knife. 



Needles. 



