206 



THE MICROSCOPE. 



and their short diameter in the other. In all doubtful 

 cases, the better plan is to examine a number of fragments, 

 both transverse and longitudinal, taken from the same 

 bone, and to form an opinion from the shape of bone-cell 

 which most commonly prevails. 



The Teeth. The best mode of examining teeth is by 

 making fine sections. Specimens should be taken, both 

 from young and old teeth, to note 

 the changes. A longitudinal or 

 transverse slice should be first 

 taken off; a circular saw. fitted to 

 the lathe, fig. 143. cuts sections 

 very quickly then rub down, first 

 by the aid of the corundum-wheel, 

 which should also be fitted to 

 the head-stock of the lathe, then 

 finish them off between two 

 pieces of water-of-Ayr stone, and 

 finally clean and polish between 

 plates of glass, or on a polishing 

 strap with putty powder. The 

 section requires to be washed in 

 ether, to remove all dirt and im- 

 purities j when well polished and 

 dried, it may be preserved under 

 thin glass, and cemented down 

 with gold-size or varnish. 



Such polished sections are preferable to many others 

 which, on account of their irregular surface, require to be 

 covered with fluids, as Canada-balsam, turpentine, &c., in 

 order to fit them for examination with high powers. It 

 almost always happens, that some portion of these fluids 

 enters the dentine, which then becomes indistinct, and 

 almost invisible in its ramifications. 



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 suffi- 

 cient to exhibit the more 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 likewise 

 various ohlkiue and transverse sections through the dentine 



Fig 1436 Small Lathe for 

 polishing. 



