DEVELOPMENT OF THE ENAMEL 147 



commenced, these cells, as has been shown, are cut off from 

 the ameloblast layer by a separating membrane, so that 

 it seems more reasonable to suppose that the principal 

 recuperating effect they have on the ameloblast cells must 

 be due to osmosis and the passage of nutrient material and 

 lime salts through this membrane, although, as stated in 

 discussing the inner ameloblastic membrane, the penetration 

 of this separating layer by processes of the cells is quite 

 comprehensible . 



A very distinct function is, however, assigned by Leon 

 Williams to the cells of the stratum intermedium in the 

 later stages of enamel formation, when the stellate reticulum 

 has disappeared and the external epithelium is in contact 

 with the cells of the stratum intermedium. 



He describes blood-vessels in the stratum intermedium 

 at this stage, and that there are blood-vessels in this layer 

 is fully evidenced by the photographs in illustration of his 

 paper. 



When, however, this author speaks of the incorrectness 

 of the statements of Wedl and the majority of observers 

 that no blood-vessels are seen in the cells of the enamel 

 organ proper, he scarcely conveys the true meaning of their 

 statement. In the early stages of enamel formation, when 

 the stellate reticulum intervenes between the external 

 epithelium and the stratum intermedium, no blood-vessels 

 are seen in the enamel organ except vestiges of them in the 

 stellate reticulum of marsupials, and at the outer border 

 of the stellate reticulum in man (see figs. 70 and 72). It 

 is only in the later stages of calcification that this supply of 

 blood-vessels can be seen, when the stellate reticulum has 

 disappeared and the external epithelium is in contact with 

 the stratum intermedium, and the abundant vessels of the 

 connective tissue of the follicle are in intimate relation with 

 this layer of cells. He has shown, and one cannot but think 

 very conclusively, that in the rat blood-vessels enter the 

 stratum intermedium in these later stages very abundantly, 

 and that they have a special arrangement with regard to 

 the cells. 



In this later stage of calcification he says that the charac- 

 teristic forms of the cells of the stratum intermedium have 



L 2 



