It is, therefore, obvious that any inference as to the structure of the
pulp’s surface, or the nature of its previous connection with the transitional
cells and the superincumbent layer of dentine, which may be
founded on appearances observed under the circumstances above mentioned,
is liable to the objection that the natural relations of the parts
observed have been destroyed. If the dentine be the ossified pulp,
as Dr. Schwann was disposed to believe, then the calcified part of
the growing tooth has been violently displaced from the uncalcified
part, and the part of the pulp which thus presents itself for examination
is a lacerated and not a natural surface.
But to the observer who regarded the dentine as a secretion
from the pulp’s surface, every modification which he might detect
on that surface after the displacement of the dentine, would appear
natural, and be perhaps described as such with the vieyv to the elucidation
of the secreting process. Thus the cells which might be
observed in progress of ossific transition into dentine would appear as
independent parts, and the products of a secreting property; their detached
condition being, all the while, a necessary result of the artificial
displacement of the new-formed cap of ivory, and the consequent
laceration of the pulp’s substance.
In the terms of the £ excretion theory ’ the exposed surface of
the pulp over which the cells lie scattered is a ‘ formative surfaces ;
the nucleated cells are naturally £ detached,’ and the ivory or dentine
resulting from their calcification and metamorphosis, is, in
respect to the pulp, £ altogether a distinct formation, and by no
means an ossification of the pulp.’
Such is the interpretation which an advocate of the excretion-
theory has given to the true phenomena of dental development first
observed and described by Purkinje, Raschkow and Schwann.
Observations on the pulp, in its various stages of conversion into
dentine, whilst in undisturbed connection with the calcified portion,
in the thin, transparent, lamelliform teeth of a fetal Shark (Carcharias),
first yielded me unequivocal demonstration of the organic continuity
of the cap of dentine with the supporting vascular pulp ; they also
indicated some stages of the progress of the conversion of the pulp
into dentine, and produced that clear idea of the nature and relations
of dental development, which is expressed in the ‘ Theory of dentification
by centripetal calcification of the pulp’s substance,’ submitted
to the French Academy in December, 1839.(1)
The following are the progressive steps of the calcifying processes,
according to my microscopic researches on the formation of
the different substances which compose the more complex teeth of
Reptiles and Mammals, pursued in various species of both classes,
but chiefly in the higher organized domestic animals.
Three formative organs are developed, as already described,
for the three principal or normal dental tissues. The dentinal pulp
(PL 122 a, figs. 5, 6, 7 & 8, d), or pulp proper, for the dentine ; the
1 capsule’ (ib. c) for the cement, and the ‘ enamel-pulp’ (ib. e) for
the enamel. The essential fundamental structure of each formative
organ is cellular ; but the cells differ in each organ, and derive
their specific characters from the properties and metamorphoses of
their nucleus, upon which the specific microscopical characters of
the resulting calcified substances depend.
(1) The general results only of this communication were given in the ‘ Comptes Rendus,’
183S, p. 784. The Commission appointed by the French Academy to report on a subsequent
Memoir on the same subject advert to some of the phenomena previously communicated by me.
“ Quant aux preparations qui montrent l’aréohté de la pulpe, non seulement nous les avons
reproduites avec succès, mais de plus nous avons constaté, à l’état frais, la granulation
des aréoles signalée par M. Richard Owen,” loc. cit. 1842, p. 1063.