subject are as follows : after observing that the blood-vessels of
true bone are confined to the medullary canals, and that the
presence or absence of blood-vessels in a tissue occasions no essential
difference in its mode of growth ; he proceeds to classify teeth
with bones in an order of tissues, characterized by the parietes of their
primordial cells becoming confluent either with each other, or with the
intercellular substance(l).
Dr. Schwann identifies the pulp-granules of Purkinje with his
nucleated cells, and asks, “ In what relation does the dentine stand
to the cells?” He then proceeds to say, “ I must confess, at the
outset, that I am unable to answer this question with certainty, and
that my observations are not mature. Purkinje and Raschkow describe
the formation of the dentine as follows :—“ Primordio substantia den-
talis e fibris multifariam curvatis convexis lateribus sese contingentibus
ibique inter se concrescentibus composita apparet.—In ipso apice istse
fibrse aequaliter quamcunque regionem versus se diffundunt, attamen
parietes laterales versus directio longitudinalis prsevalet, dum fibrse
sinuosis flexibus sequalique modo se invicem contingentes ibique ubi
concavse apparent lacunas inter se relinquentes, ab apice coronali
radicem versus ubicunque procedunt. Nonnisi extremi earum fines
tunc molles sunt cseterse autem partes brevissimo tempore indurescunt
. .Postquam... .fibrarum dentalium stratum depositum est, idem
processus continuo ab externa regione internam versus progreditur,
germinis dentalis parenchymate materiam suppeditante.... Convexse
fibrarum dentalium flexurse, quse juxta latitudinis dirnensionem cres-
cunt, dum ab externa regione internam versus procedunt, sibi 1
(1) Microskopische Untersuehungen iiber die Uebereinstimmung in der Struktur und dem
Wachsthum der Thiere und Pflanzen. 8vo. 1839, p. 117»
invicem appositse continuos canaliculos effingunt, qui ad substantiae
dentalis peripheriam exorsi multis parvis anfractibus ad pulpam
dentalem cavumque ipsius tendunt, ibique aperti finiuntur, novis ibi,
quamdiu substantiae dentalis formatio durat, fibris dentalibus aggre-
gandis inservientes.”—Raschkow, 1. c. p. 6.
“ I must confess,” Dr. Schwann proceeds to say, jj£ that there
is much obscurity in this description. If I rightly understand it, the
dentine consists of fibres, formed layer-wise out of material afforded
by the pulp, which become confluent with each other but leave interspaces
which are the dentinal tubes. But these tubes cannot be
mere interspaces between fibres, since Müller has proved them to possess
distinct parietes... If a young tooth be removed from its capsule
and steeped for one day in not too much diluted muriatic acid, the
animal basis of the dentine, which, at the first removal of the earth,
was of cartilaginous hardness, becomes quite soft, so that one can
only detach small pieces from it by the forceps. If this pultaceous
mass be examined, it will be seen to consist of fibres, which can be
separated from one another. These fibres are too thick to be merely
the walls of the canals ; they constitute the whole substance. Neither
can they be a mere artificial product, since the acid penetrating the
canals first dissolves the immediately contiguous substance, and then
the intertubular substance remains as a fibre; besides, they are too
regular and smooth. It appears, moreover, that the dentine is composed
of these reciprocally united fibres, since they are identical with
the fibres which, according to Purkinje and Raschkow, form by their
confluence the dentinal cartilage; and this confluence of the fibres
is not so complete but that they can be again artificially separated.
The fibres in the human teeth run in the same direction as the canals.
I could not discern the canals in their interspaces. The peripheral
c