Development, &c. of Dental Enamel. By J. L. Williams. 265 
truth. Enamel seems to be produced by an infiltration of the inner 
ends of the ameloblasts with the albumen-like calcific material which 
is secreted from the blood by the cells of the stratum intermedium. 
It appears as though the more liquid portion of the cell structure is 
replaced by the albumen-like substance containing the lime salts. 
When the inner ends or sections of the ameloblasts become completely 
infiltrated, so as to form in appearance a series of globular bodies, they 
are shed off or become partially separated from the cells, and melt 
more or less completely into the surface of the forming enamel. 
I say partially separated, because there appears never to be a complete 
break in the continuity of the cytoplasmic strings or network con- 
stituting the organic substructure of enamel. The cytoplasmic strings 
or fibres pass without break from the ameloblasts into the forming 
•enamel. The process of ripening and shedding off of the globular 
bodies appears to occur simultaneously over the entire surface of a 
forming tooth ; and in this simultaneous or rhythmic action we 
probably have a complete explanation of the lines of stratification 
seen in formed enamel. The Retzius bands are due to pigmentation, 
and not to imprisoned air entering the ground-off ends of enamel rods, 
as claimed by Von Ebner. This is very clearly shown in fig. 8, where 
the enamel rods are seen to pass without break in their continuity 
completely through the dark bands. 
It would perhaps be going too far afield to enter upon a discussion 
•of the methods by which this harmony of cell action is secured. It is 
one of the great problems of biology ; and I shall do no more on the 
present occasion than to suggest that in this particular instance 
simultaneous cell action may be secured through the medium of the 
protoplasmic processes or threads which, passing from one cell to 
another, are everywhere seen to unite not only the ameloblasts but also 
the cells of the stratum intermedium. 
The organic substructure of enamel is formed by the continual 
outward growth of the ameloblast, the cells as they grow outward 
continually shedding off their infiltrated inner sections, so that the 
length of the ameloblast is maintained with considerable regularity 
throughout the entire process of enamel formation. There are, how- 
ever, not infrequently to be seen marked exceptions to this rule ; the 
ameloblasts over a certain area sometimes appear to become rapidly 
engorged with the calcific material, and the ends of these particular 
cells are shed off more rapidly than are those of the surrounding cells, 
and more rapidly than the outward growth of the cell can occur ; so 
that the result is that these particular cells are for the time made 
much shorter in appearance than the neighbouring cells. 
The “stellate reticulum” has always been represented as com- 
posed of triangular or stellate-shaped cells united by long processes. 
►Such an arrangement leaves a large amount of space between the 
cells unaccounted for. The stellate appearance in this tissue, as 
shown in ordinary balsam-mounted specimens, is largely produced by 
