152 MICROSCOPIC ANATOMY OF THE TEETH 



described more especially by Arnell (2), Graf v. Spee (23), 

 Von Ebner (8), and Leon Williams. They are very evident 

 in the cells as soon as enamel deposition has commenced, 

 and that they do contain the calcifying elements there seems 

 to be very little doubt, although C. S. Tomes and others, 

 while quite convinced of the appearance of these bodies, 

 do not feel in a position to give any positive opinion as to 

 their nature. 



When calcification is about to commence, the ameloblast 

 cells become separated from the cells of the stratum inter- 

 medium by a delicate membrane, although prior to the 

 commencement of the process they show no signs of such 

 separation, but the cells of the stratum intermedium are 

 in many places seen to be lying between the ameloblasts as 

 shown in figs. 75 and 77. 



This membrane once formed, no such intermingling of the 

 cells of the two layers can ever be seen, but they remain 

 quite distinct from one another. 



At the same time another delicate membrane-like layer 

 is formed between the ends of the ameloblasts and the 

 forming enamel. These two membranes, called by Leon 

 Williams the outer and inner ameloblastic membranes 

 respectively, are supposed to take an important part in the 

 calcifying process, and to act as dialysing membranes to 

 separate the lime salts from the albuminoid material con- 

 tained in the cells. As shown in the experiments with 

 inorganic solutions above referred to, such a process takes 

 place through the membranes of precipitation formed in 

 the solution of silicate of potash, the lime salts contained 

 in the water being separated by dialysis and deposited on 

 the distal side of the membrane as calcospherites. 



Professor Huxley, as previously stated, described an inner 

 ameloblastic membrane under the name of membrana 

 preformativa, and he also considered that the calcification 

 of enamel took place ' by the transference of crystallizable 

 products through a membrane '. 



In a recent paper, referred to more fully on p. 174, Mr. 

 Thornton Carter denies the existence of an outer amelo- 

 blastic membrane, but fig. 78 will, we think, give a clear 

 indication of its existence. Whether these membranes are 



