76 SPECIAL HISTOLOGY. 



demonstrable by maceration in hydrochloric acid, a process 

 which requires a longer or shorter time according to the concen- 

 tration of the acid and its more or less frequent renewal, 

 taking 3 — 4 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 

 concentrated hydrochloric acid; in thin sections of dental 

 cartilage 12 — 24 hours' treatment with sulphuric and hydro- 

 chloric 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 developing 

 enamel ; the transverse lines are seen best when the object is 

 moistened 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 micros- 

 cope 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 addition of dilute solution of 

 caustic soda. 



Literature of the Teeth, — L. Frankel, ' De penitiori dentium 

 humanorum structura observationes/ Vratislav, 1835 ; and 

 Retzius, l Bemerkungen iiber den innern Bau der Zahnen/ in 

 Mull. ' Arch./ 1837; J. Tomes, ' A Course of Lectures on 

 Dental Physiology and Surgery/ London, 1848; It. 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 Rohrensysteme der 

 Zahne und Knochen/ in Mull. 'Archiv/ 1849, p. 403; J. 

 Czermak, l Beitrage zur mikroskopischen Anatomie der mensch- 

 lichen Zahne, in Zeitschr. fiir. wiss. Zool/ 1850, bd. II. p. 295 ; 

 Arnold, in 'der Salzburger med. Zeitung/ 1831, p. 236; 

 Easchkow, f Meletemata circa dentium mammalium evolutionem/ 



