seat of the calcifying processes.(1) Here, as in the dentinal and
enamel pulps, the calcareous salts are selected and arranged by
the assimilative, selective, or intus-susceptive, properties of the cell-
walls and by the repulsive power of their nuclei. (2)
The blastema or fundamental tissue of the capsule is, at first,
semitransparent and of a pearly or opaline colour ; but is soon richly
ornamented by tlieplexiform distribution of the blood-vessels, (PI. II).
As the period of its calcification approaches, which is later than
that of the dentinal pulp, it becomes denser, and exhibits numerous
nucleated cells. The blastema itself (PI. I. fig. 5, ri) presents more
evidently a fine cellular or granular structure in which the calcareous
salts are impacted in a comparatively clear state constituting the framework
(«•) of the cemental tissue. The characteristic features of this
tissue are due to the action of the proper nucleated cells (ib. m) upon the
salts of the plasma diffused through the blastema in which those
cells are imbedded. The cells being characterised by a single large
granular nucleus (ib. p) which almost fills the clear area of the cell
itself. If, when the formation of the cement has begun in the incisor
or molar of a Colt, one of the detached specks of that substance, with
the surrounding and adhering part of the inner surface of the
capsule in which it is imbedded, be examined, these nucleated
cells are seen, closely aggregated around the calcified part, in concentric
rows; the cells of which are further apart as the rows
recede from the field of calcification. Those next the cement (ib. o)
rest in cup-shaped cavities in the periphery of the calcified part just
as the first calcified cells of the thick cement which covers the
(1) This has led me to doubt whether the altered blood-discs of the capillaries of the
dentinal pulp are converted into the cells of the pulp which occupy the place of the capillaries in
the calcifying field.
(2) It might be supposed that the cell-membrane and the surface of the nucleus were in
different electrical states.
crown of a complex molar are lodged in cavities on the exterior
of the enamel. These exterior cavities of the cement are formed
by centrifugal extension of the calcifying process in the blastema
in which the cells are imbedded. The calcareous salts penetrate
in a clearer and more compact state the cavity of the cell, but
their progress is arrested apparently by the nucleus which maintains
an irregular area, partly occupied by the salts in a subgranular
opake condition, hut chiefly concerned in the reception and transit
of the plasmatic fluid which enters and escapes by the minute
tubes which are subsequently developed from the nucleolar cavity
as calcification proceeds. The radiated cells or cavities (p1) thus formed,
are the most common characteristic of the cement, hut not the
constant one. The layer of the capsule which surrounds the crown
of the Human teeth and of the simple teeth of Quadrumana and
Carnivora, consists simply of the granular blastema, without nucleated
cells, and the radiated corpuscles are, consequently, not
developed in the cement which results from its calcification. In
the thicker parts of the inflected folds of the capsule of the
complex teeth of the Herhivora traces of the vascularity of that
part of the matrix are persistent, the blastema calcifying around
certain of the capillaries and forming the medullary canals. The
varieties of these canals are traversed by minute tubules continued
from or communicating with the radiated, cells. These tubules, and
the more parallel ones which traverse the thickness of the cement in
many Mammalia, are the remains of linear series of the minute
granules of the blastema.
In the deep sockets of the teeth of persistent growth the
matrix is maintained by the constant additions of new blastema
and cell-material to the bases of the dentinal, enamel and cemental
pulps. I have demonstrated the partial growth of the enamel pulp