Page 121 - My FlipBook

BIOLOGICAL STUDIES ON THE BACTERIA OF THE MOUTH. 95

recent experimeuts had demonstrated the presence of iron in a
variety of tissues where it had not previously been detected.
This discovery led to the thought that iron might be present in
the dental pulji, and that in such case the black color of the
putrid pulps might be accounted for by the formation of the sul-
phide of iron. I made a few preliminary experiments relating
to this question, the results of which I here give. The tests Avere
made in the following manner A tooth was cracked in a porce-
:
lain mortarjSO as to thoroughly expose the pulp, and then placed
in a mixture of dilute hydrochloric acid, to which was added a
small proportion of a 10 per cent, solution of ferrocyanide of
potassium. The hydrochloric acid, as well as the water used
for diluting it, must be fi'ee from iron ; neither must any iron
instrument be brought in contact with the ti-eshly-broken sur-
faces of the tooth. Those parts of the tooth containing iron,
even in minute quantities, will, after an exj:>osure of from one to
sixty minutes, assume a blue color—Prussian blue being formed.
One source of error is introduced in the necessary use of an iron
instrument in extracting the tooth, but this will only affect those
points on the external surface of the tooth with which the forceps
come in contact, and may therefore be easily eliminated.
I have found iron (1) constantly in Xasm\i:h's membrane
(probably only as a deposit from external sources) ; (2) in the
dental pulp, though not constantly; (3) in carious dentine almost
constantly, a bright lilue line often forming on the border
between the decalcified and normal tissue,—a rather remarkable
appearance for which I can at present attempt no explanation ; (4)
in enamel, particularly around the margin of cavities of decay.*
It seems, consequently, not impossible that the sulphide of iron
which would be formed during putrefaction of the i)uli> may have
something to do with the discoloration of the same. AVhether
sulphide of iron may be formed through decay of the dentine or
enamel in sufficient quantity to aid in discoloring the same, I
cannot say ; at present I doubt it. Further experiments may
furnish an answer to this question.

* Traces of iron have been detected (as is well known) ly chemical analysis
in both dentine and enamel.