142 HISTOLOGY OF THE TEETH. 



Another method is to grind the section till thin. Place it 

 between two plates of ground glass with water and a pinch of 

 levigated pumice powder, and by a rotatory motion of the upper 

 glass gradually rub the section down till it is thin enough for exa- 

 mination with even the highest powers of the microscope. But 

 great care must be used when finishing, as an extra turn of one of 

 the glasses may ruin the whole section (old polished glass is now 

 the best to finish with), and when sufficiently thin mount in 

 Canada balsam. Canada balsam is not, strictly speaking, soluble 

 in alcohol, but is converted by it into a white, pulverulent condi- 

 tion. Therefore, the plate having the thin section attached to it 

 (first method) may be placed in alcohol, and in a few hours the 

 section is easily detached without a fracture, but will be found 

 coated with the altered balsam, every particle of which must be 

 removed with a clean camel-hair pencil, kept constantly wet with 

 spirit. If this is not done, the specimen will appear muddled and 

 messy when mounted. Having got it quite clean, it may be placed 

 with the other, which has been rubbed down between the glasses, 

 in clean absolute alcohol till you want to mount it. Some will say 

 this camel-hair ])encil work might be dispensed with by placing 

 the section into some complete solvent of balsam, such as chloro- 

 form, benzole, or turpentine, etc. ; but be it remembered that by 

 so doing we should bring about the very thing we have been 

 trying to avoid — i.e., to mount our section without the highly- 

 refractive balsam rendering it invisible, and that is why the alcohol 

 is recommended. 



Mounting Teeth and Bone in Balsam.— There are two good 

 methods for doing this : — 



(i) Take your section out of the absolute alcohol, and let it 

 dry ; ])artially protect it from the dust, etc. When nearly dry, 

 give it a good soaking in filtered, distilled water, that the tubules, 

 lacuncC, and canaliculi may become filled with water ; then dry 

 its surfaces by wiping with a clean, warm finger, so that all 

 moisture is taken from them, when the section may be mounted 

 in rather firm balsam without the structure being destroyed. 



(2) Plunge the section for a moment into an alcoholic solution 

 of white shellac and quickly withdraw it. The alcohol evaporates, 



