ON THE PREPARATION OF TOOTH SECTIONS. 201 



Of all the media recommended, none fulfil the requirements 

 in so satisfactory a manner as Canada balsam if certain precautions 

 are observed, of which I shall speak presently. Canada balsam 

 is not, strictly speaking, soluble in alcohol, but is converted by it 

 into a white pulverulent condition. Therefore the plate, having 

 the thin section attached to it, may be placed in alcohol, and, 

 after a few hours' soaking, the thin section is easily detached with- 

 out fracture, but will be found coated with this altered Canada 

 balsam, every particle of which must be removed with a clean 

 camel-hair brush kept constantly wetted with spirit. Unless this 

 is done, the section will look messy and muddled when it is 

 mounted permanently. Having got it quite clean, it may be 

 placed in clean absolute alcohol till you want to mount it. It 

 might be considered that all this camel-hair-pencil work could 

 have been dispensed with by placing the section into some com- 

 plete solvent of the balsam, such as chloroform, benzole, or 

 turpentine ; but it must be remembered that, by so doing, we 

 should bring about the very thing we have been trying to prevent. 

 We want to mount our section without the highly refractive balsam 

 running into the minute structure and rendering it invisible ; and 

 that is the reason I recommend the treatment by alcohol. 



There are two good methods of mounting bone and teeth in 

 Canada balsam, which, while securing the advantage we are 

 desirous of attaining, also preserve, in the highest degree, the 

 visibility of their histological details. That which I practice is 

 the simpler. Take your section out of the absolute alcohol and 

 let it partially dry, carefully protecting it from dust or other con- 

 tamination. When nearly dry, give it a good soaking in filtered 

 distilled water, that the tubular structure, or any minute spaces 

 like lacuna or canaliculi, may become filled with water; afterwards 

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

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

 in rather firm balsam, with very little fear of the structure being 

 swallowed up in translucency. The reason blotting paper is not 

 used for preliminary drying is, that the fibres from it adhere to 

 your section and disfigure its appearance. 



The second method of mounting is to plunge the section for 

 a moment into alcoholic solution of white shellac, and, quickly 



International Journal of Microscopy and Natural Science. 



Third Series. Vol. V. p 



