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140 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.
If, as we have stated, tlie conductivity of the living tooth for
electric currents depends entirely upon the liquids contained in
its pores, then dentine, which is more porous than enamel, should
show a less resistance than the latter; furthermore, a section of
dentine which cuts the canaliculi at right angles or nearly so
would have less resistance than one parallel with them, and
finally the resistance would increase with that of the liquid with
which the section is moistened.
In order to determine whether the resistances of dentine and
enamel, of cross-sections and longitudinal sections, in reality bear
the relations to each other demanded by the above condition, the
following tests were made
The section whose resistance was to be determined was held
between the ends of two amalgamated zinc wires, which had a
diameter of 1.9 millimeter, under a constant pressure of about
two grams to the square millimeter. The
section of dentine, ^^ of a millimeter thick,
was moistened with a concentrated solution
of sulphate of zinc.
The arrangement of the apparatus for de-
termining the resistance may l)e seen in the
accompanying figure (Fig. 56).
Here JS denotes two Siemen's elements;
B, a mirror galvanometer after Wiedemann,
with 16,000 turns of wire and a resistance of
5000 Siemen's units, having an aperiodized
magnet ring after E. du Bois-Reymond ; Bh, the rheostat ; Wx,
the resistance to be determined ; 0, 1, II, HI, IV, denote the
connections with a round compensator after E. du Bois-Eeymond
with the modifications of Christiani.
As result of the large number of experiments, I fonnd that a
section of dentine -^^^ millimeter thick, cutting the canali-
culi at right angles, had a resistance of about 1700 Siemen's
units ; that a similar section, parallel or nearly so with the canali-
culi, had a resistance at the beginning of about 8050 Siemen's
units. As the piece l)egan to dry, the resistance rapidly increased,
till it soon became infinitely great.
"When the same sections were moistened with water, the re-
140 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.
If, as we have stated, tlie conductivity of the living tooth for
electric currents depends entirely upon the liquids contained in
its pores, then dentine, which is more porous than enamel, should
show a less resistance than the latter; furthermore, a section of
dentine which cuts the canaliculi at right angles or nearly so
would have less resistance than one parallel with them, and
finally the resistance would increase with that of the liquid with
which the section is moistened.
In order to determine whether the resistances of dentine and
enamel, of cross-sections and longitudinal sections, in reality bear
the relations to each other demanded by the above condition, the
following tests were made
The section whose resistance was to be determined was held
between the ends of two amalgamated zinc wires, which had a
diameter of 1.9 millimeter, under a constant pressure of about
two grams to the square millimeter. The
section of dentine, ^^ of a millimeter thick,
was moistened with a concentrated solution
of sulphate of zinc.
The arrangement of the apparatus for de-
termining the resistance may l)e seen in the
accompanying figure (Fig. 56).
Here JS denotes two Siemen's elements;
B, a mirror galvanometer after Wiedemann,
with 16,000 turns of wire and a resistance of
5000 Siemen's units, having an aperiodized
magnet ring after E. du Bois-Reymond ; Bh, the rheostat ; Wx,
the resistance to be determined ; 0, 1, II, HI, IV, denote the
connections with a round compensator after E. du Bois-Eeymond
with the modifications of Christiani.
As result of the large number of experiments, I fonnd that a
section of dentine -^^^ millimeter thick, cutting the canali-
culi at right angles, had a resistance of about 1700 Siemen's
units ; that a similar section, parallel or nearly so with the canali-
culi, had a resistance at the beginning of about 8050 Siemen's
units. As the piece l)egan to dry, the resistance rapidly increased,
till it soon became infinitely great.
"When the same sections were moistened with water, the re-
