658 BERTHA E. MARTIN 



stratum intermedium and inner enamel epithelium, as shown in 

 figure 5. During the period when the enamel is forming there 

 is present over the ameloblasts a compact layer of cells which 

 probably consists of outer enamel epithelium and stratum inter- 

 medium, the stellate reticulum having entirely disappeared, as 

 stated above. The reason that, with the exception of Spurgin, 

 previous investigators found no enamel is obvious. Tomes 

 found none because none had been deposited. He lays great 

 stress on the fact that none would have been deposited because 

 the inner and outer epithelia are in contact, and that there is no 

 trace of a stellate reticulum. But as I have said before, this con- 

 dition of the enamel organ is reached before any trace of enamel 

 can be seen. Rose said that enamel is not deposited, but that 

 in its stead there is secreted a thin structureless membrane, 

 which corresponds to Nasymth's membrane. The enamel be- 

 fore calcification (fig. 4, LE) does have the appearance of a thin 

 structureless membrane, and Rose must have seen the first 

 formed layer of enamel before calcification had taken place. 

 That the enamel is by no means a structureless membrane can 

 be readily seen by a glance at figure 4, FE. 



The reason that Ballowitz found no enamel is that he had a 

 stage which was far too young for enamel deposition to have 

 occurred. In his younger specimens, the four layers of the 

 enamel organ were still intact. In his older stages, Ballowitz 

 describes the disappearance of the outer enamel epithelium and 

 stellate reticulum, and concludes that, since these have disap- 

 peared, enamel deposition would never have occurred, in spite 

 of the fact that Tomes' processes were present. Had he exam- 

 ined a slightly older stage, he undoubtedly would have found 

 enamel. 



Spurgin is apparently the only one who has previously described 

 enamel in connection with these teeth. He states that the first 

 deposition of enamel takes place before the disappearance of the 

 stellate reticulum. As proof of this, he has shown a figure (fig. 

 3), which represents a cross section through the first back tooth 

 of the lower jaw. A shght deposition of enamel has taken place, 

 and the enamel organ is composed of a compact layer of cells 



