MEMOIRS. 



On the Nature of the Cuticula Dentis (Nasmyth's 

 Membrane). By Charles S. Tomes, M.A. Oxon., 

 Lecturer on Dental Anatomy and Physiology at the 

 Dental Hospital of London. (With Plate XVII.) 



Since it was discovered by Nasmyth that by the use of 

 acids a membrane could be raised from the surface of the 

 enamel in a perfected but as yet unworn tooth, numerous 

 and irreconcilable views have been propounded as to its 

 nature and homologies. Nevertheless, if the preparations 

 which serve to illustrate this paper are to be trusted, the 

 theories of its origin which are set forth in the most recent 

 histological text-books cannot be accepted. 



When the crown of the unworn tooth is submitted to the 

 action of an acid a thin membrane peels off the surface of the 

 enamel ; this membrane is characterised by its great power 

 of resistance to the action of reagents, and, when burnt, gives 

 off a smell like that of burning horn, leaving behind it a 

 spongy ash. 



By Professor Huxley it was considered to be identical 

 with the membrana preformativa of Raschkow, whilst 

 Professor Kolliker^ holds that it is merely a continuous layer 

 round the exterior of the enamel, which has been shed out 

 by the enamel-cells in common after the completion of the 

 sejjarate enamel-fibres ; in other words, that it is a sort of 

 varnish furnished by the enamel organ as a finish to its work 

 of forming the fibrous enamel. This similar origin has been 

 ascribed to it by Professor Rolleston^ who speaks of " the 

 '^ cuticidar dentis^'' being the last result of the process of 

 induration, as taking place in the enamel organ." 



In the opinion of Waldeyer,^ Nasmyth's membrane is 

 derived from the external epithelium of the enamel organ, 

 the cells of which become closely applied to the surface of 

 the enamel after the enamel-prisms are completed in length, 

 and he believes that these cells become cornified. 



^ KoUiker, 'Handbuch der Gewcbelelire,' 5th Aufl. 



" ' Transactions of the Odontological Society/ June, 1871. Report of 

 discussion, vol. iii, p. 245. 



' Strieker's ' Handbook of Human and Comparative Histology.' Sydeu" 

 ham Society's Translation. 



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