THE TEETH. 75 



mucus accumulates, it hardens and forms the tartar of the 

 teeth, which consists, according to Berzelius, of earthy phos- 

 phates 79 0, mucus 12*5, ptyalin 1*0, organic matter, soluble 

 in hydrochloric acid, 7*5. 



The best mode of examination of the teeth is by making fine 

 sections and preparations softened in hydrochloric acid. To ob- 

 tain good specimens of the former it is necessary to employ only 

 young and fresh teeth, as the enamel otherwise readily breaks off. 

 A longitudinal or transverse slice should be first taken off with 

 a fine saw, and may then be rubbed down, first upon a coarser 

 and then upon a finer stone, as thin as possible; the section 

 should then be cleaned and polished between two glass plates, 

 until its surface is as smooth and shining as it can be made, 

 and finally washed with ether in order to remove any impurities 

 it may have contracted. When well polished and dried, all 

 the dentinal canals and lacuna will be filled with air, and the 

 section may be preserved without further addition under a glass 

 plate, cemented by some thick and quickly solidifying varnish. 

 Such polished sections are preferable to any others, which, on 

 account of their irregular surface, require to be covered with 

 different fluids, as Canada balsam, oil of turpentine, &c, in 

 order to be examined by high magnifying powers. It almost 

 always happens, in fact, that some portion of these fluids 

 enters the dentinal tubules, which then become quite clear and 

 indistinct and invisible in their finer ramifications. A very 

 viscid varnish alone is of any service. In preparing these 

 sections of the teeth, the slices may also first be affixed to pieces 

 of glass with Canada balsam, and then be rubbed down with a 

 file and polished, on one side first, and then by warming the 

 balsam and turning the section round, upon the other. "When 

 such a section has been washed with ether and dried, it is as 

 good as one prepared with water only. Two sections made 

 perpendicularly to one another through the middle of the 

 crown and fang of a tooth, from before backwards, and from 

 right to left, are sufficient to exhibit the most important features 

 of the teeth ; but sections ought also to be prepared, showing 

 the surface of the pulp cavity and that of the enamel; and 

 also different oblique and transverse sections through the com- 

 mencement of the dentinal canals of the fangs, to exhibit the 

 anastomoses of their branches. The dental cartilage is easily 



