The Effects of Polarization upon the Steel

In this series of experiments steel wires in a bath of 65 per cent nitric acid have been submitted to polarization by somewhat the same technique as that applied to nerve (Bishop and Erlanger, 1926), in the hope of further elucidating both the functioning of nerve and of the metastable steel-acid system itself. Similarities between this model and nerve have been studied particularly by Lillie (1926) who, on the basis of rather striking analogies, has inferred that nerve and other protoplasmic systems function by reason of a passivating film, of the nature of an oxide film, which covers the cell membrane. When this film is disturbed, particularly when it is electrochemically reduced, the local circuit between the reduced region and adjacent oxidized regions reduces or activates the latter, and in this manner the negative wave is propagated over an initially uniform cell surface without decrement. Refractoriness consists in the reestablishment of this film to a stable condition, due to reactions within the nerve, after which, by a partial reduction, the film becomes less stable, i.e. more reactive, during the relatively refractory state, until complete recovery of irritability subvenes. The mechanism of passivity in metals has not been satisfactorily explained. Evans (1922) concludes that the surface is protected by a layer, perhaps monomolecular, of a metastable oxide not of any recognized composition and possibly of activated oxygen itself. Bennett and Burnham (1917) suppose that an unstable superoxide is adsorbed on the iron surface, and is in this condition relatively stable.