214 TOMES, ON THE DEVELOPMENT OF THE ENAMEL. 



that a membrane can be raised from the surface of the 

 enamel, at any period during growth, by the addition of an 

 acid ; the membrane being external to the enamel fibres 

 already formed, and internal to the enamel organ — in fact, 

 lying between and separating the two tissues. This mem- 

 brane Mr. Huxley regards as the membrana preformativa of 

 authors. He describes it as perfectly clear and transparent, 

 and as being continued over the dentine in those parts where 

 enamel has not been formed, and over the dentinal pulp where 

 dentine has yet to be developed, giving it in fact the position 

 vi^hich the basement membrane of the mucous membrane of 

 the mouth would occupy when the tooth-pulp is in the folli- 

 cular stage, and consequently in the sacular stage, supposing 

 such membrane to exist in the one case, and that it has not 

 disappeared in the other. These points are shown in the 

 figures illustrating Mr. Huxley's paper. 



M. Lent, a pupil of KoUiker's, published a paper on the 

 development of the dental tissues, which was subjected to the 

 Professor for revision.* Hence it must be regarded as ex- 

 pressing to some extent the opinions of M. Kolliker as well as 

 those of M. Lent. The account there given of the development 

 of the enamel is in the main but a confirmation of Mr. Huxley's 

 statements, the points of difference being unimportant. 

 M. Lent describes the so-called membrana preformativa as 

 structureless, but as it were indented with the ends of the 

 enamel fibres. His figure shows a surface impressed with 

 minute square depressions. Mr. Huxley gives a similar 

 figure. The latter author says : " Neither the capsule nor 

 the enamel organ take any direct share in the development of 

 the dental tissues, all three of which — viz., enamel, dentine, 

 and cement — are formed beneath the membrana prefoj'mativa, 

 or basement membrane of the pulp." In another place he 

 says : " Neither the capsule nor tlie ' enamel organ,' which 

 consist of the epithelium of both the papilla and the capsule, 

 contribute directly in any way to the development of the 

 dental tissues, though they may indirectly." 



M. Lent believes that the enamel organ exerts some 

 direct influence in the formation of the enamel, and puts 

 forward the following hypothesis, viz., that the cells of the 

 enamel organ secrete a fluid, which passes through the mem- 

 brana preformativa and there forms enamel, and he assumes 

 that the secretions of individual cells are independent, each 

 one forming or corresponding to an enamel fibre. 



* ' Uebei' die Entwicklung des Zahnbeins und des Sclimelzes,' von 

 Eduavd Lent, Stud. Med. aus Hamm.' ' Zeitschrift fiir Wissensclial'tlicLs 

 Zoologie Sechster Band,' p. 121, 1855, 



