Development , &c. of Dental Enamel. By J. L. Williams. 267 
The threads of the meshwork or reticulum have often been observed 
to be granular ; and this appearance has led to another theory, which 
has been especially developed by Altman n, teaching that these 
granules (now generally termed microsomes) are actually bioblasts or 
organic units capable of assimilation, growth, and division, and consti- 
tuting the elements out of which the fibres or threads are formed. 
The suspicion that these various features may to a considerable extent 
be due to the action of the reagents used in the treatment of the 
tissues has stood in the way of a complete acceptance of the views 
mentioned. Prof. Wilson, in treating of the structural basis of the cells, 
says of these granular fibres, “ The difficulty is to determine whether 
this appearance represents the normal structure, or is produced by 
a coagulation and partial disorganisation of the threads through 
the action of the reagents. ... It is very difficult to determine this 
point in the case of the cyto-microsomes, owing to their extreme 
minuteness. The question must, therefore, be approached indirectly 
by way of an examination of the nucleus and its relation to the cyto- 
plasm. Here we find ourselves on more certain ground, and are able 
to make an analysis that in a certain measure justifies the hypothesis 
that the cyto-microsomes may be true morphological elements having 
the power of growth and division like the cell-organ formed by their 
aggregation.” It will be seen from this quotation that Prof. Wilson 
is strongly inclined to regard the granular appearance of the cyto- 
plasmic threads as a true structural feature. 
Van Beneden, in speaking on the same subject, expresses himself 
in a much more positive manner. He says, “ In my opinion every 
fibrilla, though it appear under the Microscope as a simple line devoid 
of varicosities, is formed at the expense of a moniliform fibril composed 
of microsomes. ,r 
I believe my studies of the structure of the enamel rod enable me to 
throw a little light on these difficult problems. We have seen in the 
calcified organic matrix composing the basis of the enamel rod, every 
structural feature to be observed in the cytoplasm of the ameloblast ; 
and we may conclude, as I have previously remarked, that this calci- 
fied matrix faithfully represents the cytoplasmic structure of the cells. 
There is here no question about effects produced by chemical reagents. 
The calcification of the cement substance of the enamel has most, 
perfectly preserved the minutest structural features of the cytoplasm. 
With the finest lenses and an amplification of from 2500 to 3000 
diameters, we are able in nearly every instance to resolve the fibres 
composing the calcified organic matrix of the enamel rods into a con- 
tinuous thread of granules. And we observe further that, although 
these granular threads form a fairly constant feature in the structure' 
of the enamel rod, yet there is aside from these a very great variety in 
the structural appearances of the organic matrix even within the 
limits of normality. Prof. Wilson, in speaking of the varied appear- 
ance of the cytoplasmic network, suggests that it represents different 
