Bio-Electric Potential Gradients in the Chick

Gradients of many kinds have been described in a variety of living organisms, including invertebrates as well as vertebrates. The extensive studies of Child and his co-workers have shown rather wide differences in physiological activity between apical and basal poles in certain invertebrates and between head and tail in longitudinally organized animals. The rates of 02 consumption and CO2 formation, as well as reaction to destructive agents, have been used as indices of these differences. Moreover, there seems to be good experimental evidence that these physiological gradients, whether they be axial, radiate, or surface-interior, in some way exert a controlling influence on differentiation. In numerous papers, Child8 has suggested that bio-electric factors might be important in determining these physiological gradients. Direct evidence for this hypothesis was presented by Mathews."4 Studying electrical polarities in Hydroids by means of a capillary electrometer, Mathews showed that in the stem of Parypha with the cut surfaces placed on two zinc-zinc sulphate, clay electrodes moistened with Y8 n. sodium chloride solution, the polyp surface was electro-negative to the stolon surface. The current was probably about 5 millivolts. Moreover, Mathews related regeneration to these bio-electric phenomena and in an illuminating sentence presented a far-reaching generalization. He said, "Every excess of action, every change in physical state of the protoplasm of any organ, or of any area in the embryo or in the egg produces, it is believed, an electrical disturbance." And again: "These currents probably play a larger part in the determination of rates of growth, in the orientation or polarization of the cells, and the differentiation of the organism, in its polarity, in other words, than has been supposed." (p. 297)