The stimulations employed were light blows from the cork tip of a
hammer actuated by an electric current. These instruments, of which
there were two, exactly alike in construction, were similar in
principle to the acoustical hammers employed by Estel and Mehner. Each
consisted essentially of a lever about ten inches in length, pivoted
near one extremity, and having fastened to it near the pivot an
armature so acted upon by an electromagnet as to depress the lever
during the passage of an electric current. The lever was returned to
its original position by a spring as soon as the current through the
electromagnet ceased. A clamp at the farther extremity held a small
wooden rod with a cork tip, at right angles to the pivot, and the
depression of the lever brought this tip into contact with the dermal
surface in proximity with which it had been placed. The rod was easily
removable, so that one bearing a different tip could be substituted
when desired. The whole instrument was mounted on a compact base
attached to a short rod, by which it could be fastened in any desired
position in an ordinary laboratory clamp.

During the course of most of the experiments the current was
controlled by a pendulum beating half seconds and making a mercury
contact at the lowest point of its arc. A condenser in parallel with
the contact obviated the spark and consequent noise of the current
interruption. A key, inserted in the circuit through the mercury cup
and tapping instrument, allowed it to be opened or closed as desired,
so that an interval of any number of half seconds could be interposed
between successive stimulations.

In the first work, a modification of the method of right and wrong
cases was followed, and found satisfactory. A series of intervals,