HISTOLOGY OF ENAMEL ORGAN 391 



of the stratum intermedium play the most important part in the 

 selection from the blood of the materials for the constitution 

 of enamel is correct in a general sense, but I am unable to detect 

 any histologic evidence, such as presence of secretory gran- 

 ules, that this layer is actually a 'highly differentiated secreting 

 tissue.' 



The stratum intermedium is most probably to be interpreted 

 as the result of mutually opposing pressures on the part of the 

 growing tooth, with the lengthening ameloblasts, against the 

 softer tissue of the enamel pulp. These opposing pressures of 

 necessity involve primarily the cells of the original stellate reticu- 

 lum next the outer ends of the ameloblasts. The modified charac- 

 ter of the cells of the stratum intermedium, including cuboidal, 

 ovoid, and stoutly fusiform types, and their closely packed con- 

 dition, result from the operation of the mechanical factor of 

 pressure, preventing a separation and the coincident differentiation 

 characteristic of the cells of the stellate reticulum. The differen- 

 tial acidophilic staining reaction may be correlated with the 

 homology of these cells with the cells of the rete mucosum of 

 the epidermis. Their specific function in amelogenesis is, as far 

 as can be judged from their cytology, not essentially different 

 from that of the cells of the stellate reticulum as a whole. Amelo- 

 genesis cannot be dependent upon a specific stratum intermedium, 

 for, as Williams admits, enamel formation begins before the layer 

 is differentiated. Moreover, amelogenesis may be initiated and 

 maintained in certain teeth in the absence of such a sharply 

 defined layer. 



d. The stellate reticulum 



As regards the question of the function of the stellate reticu- 

 lum in connection with amelogenesis, I can confirm Williams' 

 observation of the formation of globules at the central ends of 

 the ameloblasts; but I can discern no indication that these glob- 

 ules are derived from the nucleus. Of the derivation of an 

 albuminoid mineral substance from the 'ameloblastic cells' of 

 the stratum intermedium as described by Williams, I have seen 

 no evidence in the sets of slides included in this study. However, 

 in a previous study I ('21) described in the stellate reticulum 



