OF DENTAL ENAMEL. 359 



descending to supply the loops which pass round the ends of the 

 papillffi lying next the ameloblasts (Fig. 2). 



At the commencement of enamel-formation in the teeth of the 

 mouse there is but little indication of a special secretory organ, as 

 may be seen by referring to Fig. 4. We see here that the outer 

 ameloblastic membrane is not structureless, but is apparently com- 

 posed of very tine fibres. 



Method of Formation of Enamel. 



Several observers of distinction — notably Dr. R. R. Andrews 

 and Professor Spee — have described the development of enamel 

 as a process in which the tissue is formed by the deposit of drop- 

 lets or spherules of calcoglobuliii. This view is undoubtedly 

 correct, but, as stated by the writers mentioned, it does not include 

 all the phenomena that may be observed. The ultimate structure 

 of completely formed enamel shows that it is built up by the 

 deposit of bodies which are of very nearly uniform size. There 

 is, as we shall see, no uniformity in the size of these masses of 

 calcoglobulin, neither is there anything in their structure which 

 corresponds with that of formed enamel ; in fact, under the finest 

 lenses that are made they show as highly refractive masses without 

 definite structure. Although they are usually more numerous at 

 the inner ends of the ameloblasts, next to the forming enamel, 

 they may be seen throughout the entire length of these cells, and 

 I have often seen them lying close up to the membrane which 

 separates the ameloblasts from the stratum intermedium. Occa- 

 sionally I have espied them when they seemed to be actually in, 

 or emerging from, this membrane. Such appearances are shown 

 in Fig. 5. It is possible, and I think highly probable, that this 

 substance, although appearing in the ameloblasts, is really formed 

 in the more specifically secreting cells of this stratum intermedium. 

 These masses probably consist of calcoglobulin, an albumin-like 

 substance holding calcific material in solution. Its function, I 

 believe, is not the building up of the enamel rods as has hereto- 

 fore been supposed, but the formation of the interprismatic or 

 cement substance which binds the enamel rods together. 



It is clearly shown in Fig. 6 that the enamel rods are formed 

 by the superposition or continuous deposition of bodies which are 

 spherical when they leave the enamel cells, but by compression or 



