Hermann's phenomenon

In 1887, Hermann published an account of some experiments from which he drew the conclusion that when an electric current passed from a dilute solution of a salt, such as sodium sulphate, to one more concentrated, a liberation of acid took place at the boundary layer between the two fluids; also, that when the current passed in the opposite direction alkali was liberated at the same place. This experimental difficulties were considerable, but the facts were firmly established, though it is only to he expected that their repetition and amplification to-day should suggest another interpretation to that put for ward 27 years ago. Strangely enough, although these phenomena were cited by early physiologist as affording an explanation of the "electrical taste," they have quite escaped all the later text-hoofs and articles on physico-chemical subjects. Rosenthal's experiments, which showed that the "electrical taste" was not to be attributed directly to electrolytic phenomena, may have led to a general but mistaken impression that Hermann's observations were faulty. In explaining the habits of certain free-swimming protocoa, however, vale has attributed the directive stimuli to these boundary effects. The cogency of these speculations is in striking contrast to the earlier applications of Hermann's experiments to physiological problems. In a paper on the cataphoresis of ferments, too, V. Henri has alluded to the liberation of alkali and acid at the boundaries of the ferment solution and distilled water when an electric current is passed. This, as he remarks, cannot he avoided by the use of non-polarisable electrodes, but may he overcome by dialysing the enzyme solution until it has the same conductivity as the distilled water employed. It may be pointed out, in passing, that this undesirable restriction to the experimental conditions is not necessary; it is only essential that the specific conductivities of the two solutions should be the same. But, since the published work in which this precaution has not been taken would otherwise he not properly understood, it was decided to investigate the significance of these boundary complications in their relationship to transport experiments generally.