HISTOLOGY OF ENAMEL ORGAN 383 



These cells are in intimate structural relation with both the 

 ameloblasts and the cells of the stellate reticulum. The stellate 

 reticulum is composed of widely separated stellate cells, the 

 intercellular spaces being filled with a basophilic tissue fluid. 

 This so-called enamel pulp resembles somewhat the gelatinous 

 connective tissue of the young umbilical cord. In contrast 

 with the basophilic staining reaction of the stellate reticulum, 

 the stratum intermedium has an acidophilic reaction, staining a 

 deep pink or light red color in the eosin counterstain. The 

 outer enamel epithelium is likewise acidophilic in staining reac- 

 tion. In the tooth of the cat the stratum intermedium is present 

 as a layer of compact cuboidal or ovoid cells along the entire 

 extent of the enamel organ except in the extreme radicular 

 portions. 



Great importance has been ascribed by Williams and others 

 to the so-called papillary layer. It becomes necessary to des- 

 cribe this layer in some detail. Though much better developed, 

 and therefore more conspicuous, in the rat's incisor tooth (fig. 6), 

 it is clearly present also in the teeth of the kitten (figs. 1 and 2). 

 At the stage here considered it occurs only over the surface of 

 the crown. It consists simply of a collection of irregular pro- 

 jections and ridges (resembling papillae in sections) on the outer 

 surface of the enamel organ of the dental crown. It involves 

 both the outer tunic of enamel epithelium and a variable depth 

 of the peripheral portion of the stellate reticulum. It is there- 

 fore not a distinct layer, but simply a modified peripheral 

 portion of the enamel organ. This modification, consisting of 

 an alternation of irregular grooves and ridges, results from the 

 operation of the mechanical factor of unequal pressure, causing 

 indentations, in certain regions. This pressure factor inheres 

 in the abundant blood capillaries which abut upon the surface 

 of the enamel organ. In short, blood vessels produce numerous 

 indentations in the coronal surface of the enamel organ, effecting 

 thus a modification in the peripheral portion, to which the name 

 'papillary layer' has been applied by Williams. 



The intimate relation of these circumdental capillary blood 

 vessels to the enamel organ must be further considered. These 



