DEVELOPMENT OF THE ENAMEL 175 



organic material in suspension. The persistence of part 

 of this colloid as a permanent * gel ' in the finished tissue 

 is not, it appears, consistent with what we know of the 

 physical processes involved in calcification. Uncalcified 

 substances in the finished tissues are usually protoplasmic, 

 and it is difficult, moreover, to see how the junction of this 

 ' gel ' substance, which he considers composes these fibrils, 

 is effected with the living protoplasmic dentinal fibrils. 

 The evidences of the actual presence of tubes in marsupial 

 enamel are, however, so complete that it is very difficult 

 to allow Mr. Carter's contention. 



The passage of coloured fluids from the dentinal tubes 

 along channels in the enamel, and the fact that in dried 

 specimens these fluids run out again unless due precautions 

 are taken, seems conclusive evidence of their tubular nature. 

 In this method of staining applied to teeth in which the soft 

 parts have been fixed, the fluid does not run out, but is 

 retained by the tube contents which we have considered 

 to be of a protoplasmic nature. 



Mr. Carter says there are no spaces between the prisms, 

 not even at the dentine junction, but figs. 96 and 97 scarcely 

 support this contention. The author denies the existence of 

 Tomes' processes of the ameloblasts and says, ' there is not 

 the slightest evidence of any cytoplasmic structures such as 

 Tomes and Mummery believe to be present ' ; and again, 

 ' in forming marsupial enamel there is no trace of the exis- 

 tence of such prolongations of the cytoplasm of the amelo- 

 blasts as those on which Tomes has based his theory of 

 enamel development '. 



In his own investigations the present author has traced 

 the cytoplasmic threads of the ameloblasts distinctly into 

 these processes, and also can see them in numerous prepara- 

 tions Becoming incorporated in the forming enamel as 

 shown in figs. 86 a.nd 87. From these appearances it seems 

 impossible to accept Mr. Carter's explanation of them as 

 a colloidal deposit, and there is every evidence they are of 

 an organic nature and a portion of the ameloblast cell, and 

 that Mr. Tomes's view that they enter into the formation 

 of the prisms is correct. It would appear that these processes 

 being proved to be prolongations of the cell, the whole of 



