are proceeding, the calcareous salts of the surrounding plasma begin
to be accumulated in the interior of the cells, and to be aggregated
in a semi-transparent state around the central granular part of
the elongated nuclei, which now present the character of secondary
cells,, and the salts occupy, in a still clearer and more
compact state, the interspaces of such cells (ih e-) : the elongated
granular matter of the terminally confluent secondary cells
establishes the area of the tubes, by resisting, as it would seem,
the encroachment of the calcareous salts ; the nuclear tracts (ih. ĥ)
receiving a smaller proportion of the salts, in the condition of
minute disgregated particles, which are usually arranged in a
linear series of nodules, and contribute to cause the white colour
of the moniliform area, of the tube when viewed by reflected
light, and its opacity when viewed by transmitted light. Thus
the primitive existence of the granular nuclei, their multiplication in
the primary or parent cell, their elongated form, their serial arrangement
end to end, and terminal confluence, are indicated in the calcified
pulp by the areæ of the dentinal tubes (fig. 2, c) ; the interspaces of
the metamorphosed nuclei being occupied by calcareous salts in a
clearer and more compact state, with evidence, however, of a distinctness
of the nucleolar membrane or secondary cell (fig. 2, b) from
the cavity of the common containing cell, which sustains the interpretation
of the proper parietes of the dentinal tube. The indications of the
primitive boundary or proper parietes of the parent-cell (fig. 2, a) are
in like manner more or less distinctly retained, through a modification
of the arrangement of the calcareous salts in the boundaries and in
the interspaces of the cells. The salts are sometimes blended with
the blastema in these interspaces in a disgregated condition which
renders them almost as opake as the arese of the tubes. "When
a layer of the calcified cells is carefully detached, the exposed
uncalcified surface of the pulp (fig. 3, b) presents the appearance
of a net-work, the meshes being formed by the exposed cells, and
the intervening very thin layer of blastema. Each mesh, however,
which gives a transparent or bright contour to the cell, when
viewed by transmitted light, instead of presenting a single stellate
nucleus, shows by well directed light under a higher power, several
points, each of which is the centre of one of the meshes of a
finer network : these points are the ends of the granular elongated
nuclei, (1) which have been torn from the cavities of the dentinal
tubes in the displaced cap of dentine. A piece of the thin transparent
margin of the cap of a growing tooth, which may be cut off
with a pair of fine scissors, easily affords the means of demonstrating
the corresponding structure in that calcified part of the pulp. A slight
change of focus is required to bring the ends of the tubuli in view,
from that in which the clear outline of the dentinal cell is best seen.
In proportion as the progress of calcification approximates the
cells, and as these have undergone the changes in their nucleolar
contents, preparatory to the proper arrangement of the hardening
salts within, the proportion of the basal substance in the interspaces
of the cells to the enlarged cells themselves decreases, and
the cells become more readily detached and seemingly independent,
when torn out in the displacement of the cap of dentine. Although
they are" less adherent laterally to the basal substance of the pulp,
they are more coherent with the cells of the same linear series : the
tubes of the calcified cell accepting or effecting an union with the
peripheral ends of the elongated granular nuclei or nucleolar cavities
(1) The term ‘granulation des aréoles/ used by the French Academicians in referring
to my observations in support of the theory of centripetal calcification of the pulp, expresses
the appearance produced by the nuclei, which are converted into the dentinal tubes, as seen
in the area of their parent dentinal cell.