1. The relation between the E. M. F. and the minimal duration of an activating current has been determined for passive iron wires in nitric acid under varying conditions of concentration of acid, duration of recovery period, and presence of surface-action compounds.

2. The characteristic intensity-duration curves resemble those of irritable living tissues with moderate speeds of response to stimulation (with chronaxies of the order of 10 to 30σ).

3. The intensity of the current required for activation, as well as its minimal effective duration for a given intensity, increases rapidly with increase in the concentration of HNO3.

4. The responsiveness of the iron wire to brief currents is low immediately after activation and returns progressively to the original level during the immediately following period, at first rapidly and then slowly, following a time curve resembling the corresponding curve of living tissues during the relative refractory period.

5. Surface-active compounds decrease reversibly, to a degree dependent on concentration, the responsiveness of iron wires to brief currents.

6. Conditions are described under which the iron wire is activated by the break of an already flowing constant current.

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