RAINEY, ON DENTAL TISSUES. 219 
coalescence. Where the rods are imperfectly formed, being 
made up partly of globular portions, then the passages run- 
ning between them will partake of the same form, and an 
appearance of anastomosis will result. If the fibres should 
take a flexuous course, then the contour of the quadrilateral 
areas will be more or less curvilinear. In fact, it is certain 
that, if a body were made up of square rods placed side by side, 
and so inclined towards one another as to assure all directions 
between a vertical and horizontal axis, ani if, at the conflux 
of every four, there was a minute space, which passed more or 
less deeply between each adjoining pair, such sections made 
through this body, as have been directed to be made through 
the decalcified dentine, would exhibit the same appearances. 
The appearance presented in transverse sections of dentine, 
of rings with a dark point im the centre, has been too exclu- 
sively regarded as satisfactory proof of the existence of dis- 
tinct tubes. It is well known, however, that this appearance 
is delusive, and not to be depended upon. In proof of this I 
have only to adduce the structure of the silicious cuticle of 
the common cane, and the appearance which it presents under 
the microscope. This is best seen in cuticle which has been 
boiled in nitric acid. The structure is made up of hexagonal 
blocks of silica (fig. 1 a, 6), each block having within it a 
flask-shaped cavity, with the narrow part uppermost (fig. 1 ¢) ; 
and at the conflux of every three such blocks there is a space 
extending from its superficial surface down to the layer of 
cellular tissue upon which the portions of silica rest. Now 
these spaces, of the true nature of which no one who has 
examined them can entertain a doubt, present exactly the 
same forms and appearances as have been described in the 
dentine, namely, the annular, arrow-shaped, and linear forms, 
according to the direction and position in which they are 
viewed. Also a too great anxiety to account for all appear- 
ances on the cell-hypothesis has contributed much to the 
idea of the tubular nature of dentine, and thus these imagi- 
nary tubules have been attributed to “ certain filiform pro- 
longations of dentinal cells,’ or to their elongated nuclei. 
For between cells and tubes there is considerable analogy, so 
that an erroneous idea originating in the one is easily propa- 
gated to the other. In this manner, probably, the fibres of 
the crystalline lens have been thought to acquire a tubular 
form, and hence these also are now described by Professor 
Kolliker as tubes—an error which will be seen to be corrected 
in my account of the structure and development of that 
organ. But the chief cause of fallacy on this point is to be 
traced to the erroneous notion generally entertained of the 
VOL. VII. T 
