30 
MR. C. S. TOMES ON THE STRUCTURE AND 
If the pulp be withdrawn from a tooth, and slightly teased out, capillaries filled 
with blood and clothed upon their surfaces with odontoblast cells may be abundantly 
found ; the odontoblast cells are apparently seated directly upon the capillary, no 
connective tissue nor other cells intervening (see fig. 7) ; by the calcification of these 
odontoblasts the capillary vessel would obviously become closely embraced by hard 
dentine. 
And this is a strong argument in favour of what is known as the “ conversion 
theory ” of the development of dentine ; supposing these odontoblasts to be calcified 
and themselves converted into dentine, there is no difficulty in seeing how the 
capillary comes to be enclosed in a tube of dentine having the same calibre as itself. 
But if the odontoblast cells “ secrete ” the dentine, as maintained by Hertz and 
others, how is the process to be completed when there is no longer room for an entire 
odontoblast or the half of an odontoblast between the rigid wall of already formed 
dentine and the capillary ? One can hardly conceive a secreting cell going on 
shedding out from its end its secretion when it has been reduced to, say one-tenth, of 
its length ; and unless one is prepared to accept such a conception, this observation 
of the structure of a Hake’s tooth-pulp becomes fatal to any “secretion” hypothesis 
of the formation of dentine. 
There is not much difficulty in procuring sections which show the relations of the 
pulp and the dentine in situ, if the teeth and their contents be hardened and 
decalcified in chromic acid ; I have found immersion in ^ per cent, solution for ten 
days to be effectual in decalcifying them sufficiently to enable sections to be cut 
with a razor, and much longer treatment with the acid decidedly injures the pulp 
tissues. A transverse section prepared in this way is represented in fig. 4 ; in cutting 
the sections the pulps have been to a slight extent dragged away from the dentine, 
but this is rather an advantage than not, as it renders the figures clearer than they 
would otherwise be. 
In fig. 4 several capillaries (cp) are seen stretching across from the pulp and 
entering the substance of the dentine, each one fringed with its layer of odontoblast 
cells ; in the axial portion of the pulp are seen the cut ends of the numerous blood- 
vessels which make up so large a part of its bulk. In fig. 9 the distribution of the 
odontoblast cells is also seen ; they clothe the whole surface of the pulp, and where 
there is a capillary at the surface they clothe it, so that when they calcify the 
capillary becomes solidly embedded in dentine. 
The capillary plexus does not extend quite to the surface of the original formative 
pulp, so that the outermost layers of the dentine are formed from the continuous 
sheathing of odontoblasts which invests the pulp, and hence contain none of the 
larger capillary canals. A portion of the thin decalcified dentine cap taken from 
a tooth-sac in which calcification had only just commenced is shown in fig. 6. It will 
be seen that the rods, so to speak, of dentine formed from the several odontoblast 
cells have not entirely coalesced, and show a tendency to separate from one another ; 
