TOMES, ON THE DENTAL TISSUES. 103 



Observations on the Structure of the Enamel. 



Without going: fully into the structure and development of 

 the enamel, and into the citations of the opinions published 

 upon the subject, I wish to take this opportunity of recording 

 certain observations which I have made upon that structure. 

 The transverse striation of the enamel fibres has been fre- 

 quently remarked, but the cause of these markings has not 

 been determined. If sections from a number of teeth be 

 examined, it will be found that the striae are much more 

 strongly pronounced in some specimens than in others, and 

 most especially so in those in which parts of the tissue have a 

 brown colour when seen by transmitted light. 



The markings crossing the direction of the fibres are of 

 two descriptions. The one arranged in contour lines, and 

 situated at irregular distances from each other, uncertain in 

 number and extent, and sometimes altogether absent. The 

 other kind minute and regular, extending from fibre to fibre, 

 and strongly resembling the transverse markings in voluntary 

 muscle. In the present instance my remarks will be confined 

 to the latter kind of markings. 



In unhealthy subjects the permanent teeth, when they 

 appear through the gums, are not unfrequently destitute of the 

 brilliant white colour common to the finely-developed organs 

 of a healthy child ; on the contrary, they have an opaque 

 yellow colour. If such teeth be selected for examination, we 

 shall find that the sockets, when reduced sufficiently thin to 

 be seen by transmitted light, present in the enamel a confused 

 opaque appearance ; but if a tolerably high power be used 

 (such as the quarter or eighth object-glass) in conjunction 

 with a strong light, the dark appearance will resolve itself into 

 a series of lines ; the one set marking the course of the fibres, 

 the other taking the direction of the transverse stria. The 

 two sets of lines crossing each other at right angles leave inter- 

 spaces approaching a square form. These interspaces are 

 fitted with granular masses, having the appearance of cells. 

 By treating the section carefully with dilute hydrochloric 

 acid, these appearances become more distinct, and we then 

 have series of parallel fibres composed of distinct sheaths, 

 each containing a line of granular cells or meshes arranged 

 in a single series, presenting a strong resemblance to the 

 ultimate fibrilea of muscles. That such is the true structure 

 of enamel is, I think, satisfactorily proved by specimens in 

 my collections, some of which show the cells or granular 

 masses ; whilst others show the sheath, with the contents 

 removed. Other specimens, again, show the enamel fibres in 



