HISTOLOGY OF THE TEETH. 143 



leaving tlie porous structure completely occluded and protected 

 from the balsam, however liquid it might be. By either method 

 specimens of abnormal dental histology may be satisfactorily 

 preserved. 



To Exhibit in a recently-extracted tooth the state of relation- 

 ship existing between its dentinal tubuli and the pulp. — These 

 can only be made after decalcifying the tooth and harden- 

 ing the pulp. Picric acid is often used, but for a ready solution 

 that is generally to hand, there is none so effectual as a saturated 

 solution of common alum, with about \ drachm hydrochloric 

 acid added to each ounce of solution. Steeping the tooth in this 

 for about three weeks leaves the tooth with a consistency of cork. 

 If now it is soaked in glycerine for a few days, it may be 

 embedded and cut into thin sections by any of the usual instru- 

 ments. I think this method is preferable to either picro or 

 chromic acid because it does not stain the hands, and (what is 

 more important) does not produce so nmch granularity as they do. 

 The section can now be stained and mounted. 



Staining. — I now propose to consider the manner of using some 

 of the different re-agents employed in staming^ and will begin 

 with Logwood, as it admits of almost universal application. The 

 solution is best filtered just before using, and sections will be more 

 advantageously coloured if the ordinary fluid is diluted, and the 

 immersion consequently prolonged. If, on examination, it is found 

 that the tissues are so deeply pigmented as to render them opaque, 

 the excess may be removed by soaking in methylated spirit or in 

 a half per cent, solution of alum. 



Carmine. — The preparation recommended by Dr. L. Beale is, 

 perhaps, the best. If, however, any of the carmine on keeping is 

 found deposited, it may be again dissolved by adding a drop or two 

 of ammonia. Leave the sections in it for at least twelve hours ; 

 but if found too deeply stained they should be washed with i per 

 cent, solution of hydrochloric or glacial acetic acid. The acid 

 brightens the colour. Tissues stained in carmine are best 

 mounted in glycerine jelly. 



The Gold Chloride Method will be found above (p. 140). The 

 hard sections will, if stained with this re-agent, show fairly well 



