Page 168 - My FlipBook

142 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

"When gold plates with clamps of baser metal are put into the
mouth, a weak electric current is produced through which acid
may be liberated upon the clamp. This, in course of time, may
have a marked injurious eiFect upon the tooth with which
it
comes in contact. This action may be demonstrated by the
following experiment : I attached a bicuspid by means of a plat-
inum wire, twisted around the neck of the same, to the positive
pole of a Siemen's battery of three cells, and a second bicuspid
in the same manner to the negative pole. The teeth were then
placed one in each arm of a U-shaped tube which was filled with
a 0.75 per cent, solution of chloride of sodium. The circuit con-
tained, for observing the current, a galvanometer possessing a
multiplicator of 1000 turns and a resistance of 200 Siemen's
units. On closing the circuit there followed a deflection of the
needle amounting to thirty-one degrees ; after two weeks, the
deflection had decreased to eight degrees. On removing the
teeth from the solution it was found that the wire, by virtue of
the acid liberated upon its surface, had cut a groove about | mm.
deep around the neck of the anode tooth. At the kathode tooth
no change was observed.
Electric currents may therefore occur in the mouth (1) when
a metallic filling has not the same density throughout (2) when
;
two fillings of different metals touch (3) when a plate is com-
;
posed of different alloys.
Dentine being, as shown by these experiments, an absolute
non-conductor of electricity, all these electric currents between
different parts of the teeth or between filling and tooth-substance
can have only an imaginary existence, and the results obtained
by Chase in the experiments referred to above must be erro-
neous. That they are utterly so may be easily determined by a
few carefully made experiments of the same nature.
I have made in all over twenty such experiments, with dif-
ferent substances and under varying conditions.^"" The results
of ten of these experiments are given below, and each one may
draw- his own conclusions from them. These ten were not
selected from the whole number, but each alternate one was
taken in the order in which they were made. The first series of
experiments I made with ivory, the second with dentine taken