which characterize the structure of true bone : and he observed in
one instance that this bone-like substance was continued upon the
enamel of the crown of a human incisor.
This fact I have confirmed(l) as regards the human teeth and
the simple teeth of many mammals and reptiles. The layer of
coronal cement varies in thickness ; its tenuity is extreme in the teeth
of man and the quadrumana.
Purkinjé also found that the third substance, crusta petrosa or
cement of compound teeth, as those of the horse and ox, was
in like manner characterized by the presence of numerous bone-
corpuscules or cells; and thus proved that the difference between
the so called simple and compound teeth depended, not on the presence
of a third and additional substance in the latter, but on its
greater abundance and different disposition in the tooth.
At the time that these observations were being made at Breslau
and Berlin, it appears that similar investigations had been set on foot
at Stockholm. Professor Retzius of the University in that city
informs us that he had been led by tbe iridescence of the fractured
surface of the substance of a tooth to conceive that that appearance
wTas due, as in the crystalline lens, to a fine fibrous structure, and
that he communicated his opinions as to the regular arrangement of
these fibres to some of his colleagues in 1834; and that the University
having obtained, in the summer of 1835, a powerful microscope,
by Plessl of Vienna, he commenced a series of more exact
researches on the intimate structure of the teeth in man and the
lower animals. He operated on thin sections of teeth both before, and
after, the removal of the earthy matter by means of acid, and atten-
(1)Trans. Brit. Assoc. 1838, vol. vii. p. 136.
tively examined the fractured and polished surfaces of the ivory part:
he determined the exact arrangement, course, and size of the
tubuli in the teeth of different animals, and detected the finer ramifications
given off by the tubuli during their divergence, (1) and the
anastomoses of their finest terminal branches with the cells in the
intertubular, or as it is sometimes termed, interfibrous tissue.
Retzius also claims to have discovered the radiated or purkin-
jian corpuscles(2) in the dentine ; and to have thus succeeded in displaying
a far greater identity between tooth-bone and proper bone
than had been before anticipated.
He exhibited the preparations and drawings illustrative of these
interesting observations to Berzelius, Urede, and Professor Wahlberg
at the latter end of 1835; being then unacquainted with the discoveries
of Purkinje; and communicated his researches to the Royal
Academy of Sciences at Stockholm on the 13th of January, 1836.
They were published in the same year in those Transactions and in
the following year as a distinct treatise (3).
At the early part of that year, 1837, I received from Mr. Darwin
(1) Leeuwenhoek appears to have suspected the existence of such branches ; he says,“ upon
examining the tubuli round about this small cavity (the pulp-cavity1) I perceived that they all
arose from thence and spread themselves all round towards the circumference. I endeavoured
to examine still farther, beyond the part where this cavity ended, in order to discover whether
from these first-formed tubuli others might not arise or branch forth; but this part of nature’s
work was inscrutable to me.” Hoole’s Leeuwenhoek, 4to. p. 113.
(2) I have not yet been able to detect the radiated cells or corpuscles in the dentine of the
horse’s tooth, in which they are described by Retzius; but they are very numerous and conspicuous
at the peripheral portion of the dentine of the dugong’s grinder, pi. 94.
(3) Mikroskopiska Undersokningar ofver Jadernes sardeles Tandbenets struktur: Stockholm,
1837*