TOMES, ON THE DEVELOPMENT OF THE ENAMEL. 215 



I have latterly been occupied with this subject, but have 

 for the most part confined my investigation to young and foetal 

 teeth of the human sulrject. I must, thei'efore, be understood 

 to speak of the enamel of human teeth. 



The method of investigation has been that indicated by 

 Mr. Huxley and M. Lent ; and in the pursuit of the subject I 

 have endeavoured to trace the development of the tissue with- 

 out reference to its homological relations, under the belief 

 that the structure and development of a tissue should be per- 

 fectly understood before assigning its place among other 

 structures. 



The investigations were commenced upon the lower jaw of 

 a nine-months' foetus, which had been in spirit for some weeks. 

 On placing an incisor under the microscope, the surface was 

 seen to be covered by the enamel organ : the addition of a 

 drop of dilute hydrochloric acid (one part of acid to eleven of 

 water) at once produced the appearance described and figured 

 by Mr. Huxley ; that is, a membrane seemed by degrees to 

 swell up from the whole surface of the enamel, the outer 

 surface having adherent to it, by their proximal ends, the 

 columns of the enamel organ. The covering glass was then 

 removed, the acid taken up with blotting-paper, and dilute 

 spirits of wine substituted. The next step in the investiga- 

 tion was the removal of the membrane raised by the acid, in 

 order to submit it to separate examination. This end was 

 effected by the aid of needles ; but in the operation the part 

 became torn in several places, so that its sac-like form was 

 lost. On returning the specimen to the microscope it was 

 seen that the membrane had a strong tendency to roll up in an 

 opposite direction to its normal position on the tooth, the out- 

 side thereby becoming the inside of the rolls. This dispo- 

 sition offered facilities for examination : had it been otherwise 

 there would have been some difficulty in obtaining a good 

 view of the torn edge — an inspection of which, with the 

 quarter of an inch object-glass, showed the conditions given 

 in fig. 1, PI. XV. It will be observed, on examining this 

 figure (which is an accurate representation of a preparation 

 which I have succeeded in preserving), that we have on the 

 concave side the columns of the enamel organ, while on the 

 convex side the decalcified enamel fibres remain. I have failed 

 to discover anything like a distinct membrane interposed be- 

 tween the two parts. A point may be recognised where the 

 two graduate into each other ; but this part cannot be re 

 garded as a membrane, as the forming-enamel fibres clearly 

 pass through it. 



The columns of the enamel organ are, however, very readily 



Q 2 



