498 SPECIAL HISTOLOGY. 



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 perpendicu- 

 larly 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 commencement of the dentinal canals of the fangs, to exhibit the 

 anastomoses of their branches. The dental cartilage is easily demon- 

 strable by maceration in hydrochloric acid, a process which requires a 

 longer or shorter time according to the concentration of the acid and 

 its more or less frequent renewal, taking 34 days in strong acid and in 

 dilute, from 5-8. If it be desired to soften the tooth so much that the 

 tubules may be isolated, it must be left for about eight days in con- 

 centrated hydrochloric acid ; in thin sections of dental cartilage 12-24 

 hours' treatment with sulphuric and hydrochloric acid, and a few hours 

 with dilute solutions of caustic potassa and soda, are sufficient for this 

 purpose. It is very instructive also to macerate thin sections of teeth 

 in acid and to examine them upon glass plates at intervals, until they 

 entirely break up. The enamel prisms are readily isolated in develop- 

 ing enamel ; the transverse lines are seen best when the object is mois- 

 tened with hydrochloric acid, and the transverse sections of the prisms 

 are seen exceedingly well in longitudinal sections, in some layers. The 

 early development may be studied in embryos of two, three or four 

 months with the simple microscope and in transverse sections of parts 

 hardened in spirit ; the structure of the dental sac, and the development 

 of the dental tissues in foetuses of four, five, and six months, and in 

 new-born infants, both in fresh subjects and, if it be desired to recognise 

 the relations of the enamel organ, in spirit-preparations also, in which 

 its structure is very well retained. The pulp of mature teeth is obtained 

 by breaking them in a vice, and their nerves are best seen on the addi- 

 tion of dilute solution of caustic soda. 



Literature of the Teeth. L. Frankel, " De penitiori dentium human- 

 orum structura observationes," Vratislav, 1835 ; and Retzius, " Be- 

 merkungen liber den innernBau der Zahnen," in Mull. " Arch.," 1837; 

 J. Tomes, " A Course of Lectures on Dental Physiology and Surgery," 

 London, 1848; R. Owen, " Odontography," London, 1840-45, 1 vol., 

 with atlas of 150 plates; and article "Teeth," in "Cyclopaedia of 

 Anatomy," IV. p. 864 ; Krukenberg, " Zur Lehre vom Rbhrensysteme 

 der Zahne und Knochen," in Mull. " Archiv," 1849, p. 403 ; J. Czer- 

 mak, " Beitrage zur mikroskopischen Anatomic der menschlichen Zahne, 



