Connect 8 dry cells in series (the carbon of
one cell to the zinc of the next, etc.). Coupling
in this way enables the electromotive force of
each cell to be added with slight loss to that of
the others, provided the resistance in the circuit
outside the cells is so great that the internal
resistance of the battery disappears in compari-
son, as is the case where living tissues form part
of the circuit. Connect the terminal zinc and
carbon pole through a pole-changer (with cross-
wires) to a small and a large electrode covered
with cotton thoroughly wet with strong saline



STIMULATION OF MUSCLE AND NERVE 95

solution. Place the small electrode over the
ulnar nerve between the internal condyle and
the olecranon, a little above the furrow. Make
and break the current. If no contraction is
secured, add cells to the battery until contraction
occurs.
It will be found that the first contraction
occurs on closure with the cathode over the
nerve. With this strength of current the opening
contraction will be absent.
Turn the pole-changer so as to bring the anode
over the nerve and increase the intensity still
further.
A strength will be reached at which closure
with the anode over the nerve will cause contrac-
tion, but the opening of the current will still be.
