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Review of


Knight Dunlap

Psychological Bulletin, 1910, 174-177.



         The recent article by Dr. Sidis (1) on the so-called psycho-galvanic phenomena is in some respects so remarkable as to warrant the consumption of the BULLETIN'S space and the readers' time in criticism thereof. The fact that Sidis' work is typical of all that has been done in this line of experimentation gives us still more justification.

         Dr. Sidis claims that the results obtained by other experimenters in psycho-galvanism can be explained as due (a) to variations in the resistance offered to the electric current at the points where it passes from the electrodes to the skin or other tissues, or (6) to local chemical action between the electrodes and the bodily secretions, or the bodily fluids, where the electrodes are inserted, thus setting up a difference of potential between the two electrodes. This explanation would be quite satisfactory it we were confronted with the results of the psycho-galvanic experiments alone, but the electrocardiograms which have been so successfully obtained by Waller (2), Einthoven (3), Krause and Nicolai (4), Noyons (5), and others (6-8) cannot be so lightly brushed aside. These physiologists obtain records of the galvanometric deflection which represent faithfully the phases in the contraction of the heart, from electrodes applied to the exterior of the body, preferably by immersing tile hands or hand and foot in jar­electrodes. This method for obtaining cardiograms has been found serviceable in diagnosis of cardiac troubles. Now it is possible that the periodic variations in potential-difference which the electro-cardiogram records give are due to periodic variations in the volumes of the members immersed in the saline solutions, or to other strictly local effects of the pulse. The physiologists, however, adopt the somewhat naive theory that the electric potentials of the heart itself are in some mysterious way projected to the periphery of the body, the potential of the apex to the left side of the body, and the potential of the base to the right side.

         Dr. Sidis thinks that he has discovered proofs of the existence of electric currents of intra-bodily origin, which can withstand reasonable objections. He bases his conclusions on results obtained with platinum electrodes within the tissues, assuming, apparently, that no chemical action takes place between the platinum and the bodily fluids, and that since no battery or other extraneous source of current was employed, mere variations in resistance cannot account for the galvanometric deflections. Under the conditions of Sidis' experiment deflections occurred (a) immediately upon the insertion of the electrodes, decreasing to zero a short time thereafter, and (6) upon muscular activity of the members or parts of the body in which the electrodes lay.

         The platinum electrode for work of this sort was discarded by physiologists a quarter of a century ago, and for cause. I am informed by Dr. Pfund, of the Johns Hopkins Physics Department, that if it were possible to secure a piece of platinum so homogeneous that when divided and the two halves used as electrodes in the same solution―as on the tip of the tongue―a sensitive galvanometer connected with them would show no deflection, the mere bending of one of the pieces, thus changing the internal stresses, would so differentiate the two that deflection would be found. Heating the two unequally would produce the same result. Not only is platinum polarizable, but it acts definitely on organic substances.

         That platinum electrodes in contact with organic fluids can produce an E. M. F., is shown by one of Sidis' own experiments. "If now we take cotton and saturate it with the secretions from the arm pit, and then let the cotton soak in a small beaker filled with distilled water and immerse one of the platinum electrodes in the beaker and the other platinum electrode in another beaker with pure distilled water, the galvanometric deflection is found to be of the same order of magnitude and in the same direction as in the experiment on the arm pit and shoulder." (Sidis' italics.) If the electrodes, when in separate beakers, one of distilled water and the other of dilute animal secretion, show a difference of potential, we need not be surprised if they show a potential-difference when lying in the living tissues.

         That the deflection attendant upon the insertion of the electrode quickly disappears, and that muscular action of the members in which the electrode lies renews it, go to confirm the conclusion that the phenomena observed by Sidis are due simply to local action on the electrodes. The fact that Sidis was able to get the galvanometer deflections by causing passive movements of the tissues in which the electrodes lay, supports this interpretation. The record of the experiment in which the electrodes were moved in the tissues is not convincing. Apparently, the movements were made before the galvanometer deflections had become zero. Whether the difference in potential between the electrodes when in the body depends on a difference between the fluids at the two points, or on differences between the electrodes themselves, might have been determined by interchanging the electrodes (but without heating them in the gas flame!)

         The striking thing about all the work on psycho-galvanism is that the enthusiasts have either been unable to conceive of the simplest and most obvious check experiments, or have been unwilling to carry them out. The topography of the potential differences has not even excited their curiosity. Sidis, for example, does not show that the two electrodes when placed an inch apart would not give the same deflection as when in opposite limbs. Again, the experimenters seem to have ignored the vast amount of physiological work which has been done on the electric currents produced in nerve, in muscle, and in the skin; all of which has direct bearing on the problem they are attacking, and which must be considered before any headway can be made. Perhaps the greatest lack on the part of the experimenters is a comprehension of the simple principles of electric phenomena. Even some physiologists who are working with electro-cardiograms do not realize that the polarized electric waves which they suppose to radiate from the heart are not ordinary electric 'currents.'

         If a difference in potential does exist between two bodily members at a given moment, it is possible that it is due to unequal motor discharges from the nervous centers. The differences should be investigated from that point of view, for a justification thereof would open up an important means of studying motor discharges.

         As for the alleged psycho-galvanic phenomena, they do not seem to have progressed beyond the stage of allegation. The experiments up to date can be explained as showing that mental activity is accompanied by muscular activity and by variations in animal secretions. Perhaps something may be done in the future to establish the usefulness of the psycho-galvanic experiments, but it will be done by physiologists who are skilled physicians, and with the string-galvanometer.




1. SIDIS, B., & NELSON, L. Psychol. Rev., 1910, XVII., 98-146.

2. WALLER, A. D. Jour. of Physiol., 1887, VIII., 233-234. Philos. Transacts. Roy. Soc., 1889. CLXXX, B, 169.

3. EINTHOVEN, W. Pflügers Arch., 1895, LX., 101-123; 1900, LXXX., 139-160; 1903, XCIX., 472-480; 1908, CXXII., 517-584. Arch. Internat. de     Physiol., 1906, IV., 132-164.

4. KRAUSE, P. & NICOLAI, G. F. Berlin. kl. Wochenschr., 1907, XLIV., 765-768, 811-818.

5. NOYONS, A. K. M. Amsterdam Kkl. Akad., Proceedings, 1908 (1909), XI., 273-277, 723.

6. BAYLISS & STARLING. Internat. Monatschr. f. Anat. u. Physiol., IX., 276­281.

7. HERING, H. E. Deutsche med. Wochenschr., 1909, XXXV., 7-9.

8. STRUBEL, A. Deutsche med. Wochenschr., 1908, XXXIV., 1842-1846.


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