Threshold densities of the electric current for inhibition and orientation of growth in Obelia.

Abstract

If an electric current of proper density is passed lengthwise through an internode cut from the stem of the common hydroid Obelia, then the polyp on the end turned toward the cathode can be prevented from growing while a normal polyp will grow on the end turned toward the anode. The inhibition toward the cathode is reversible. The threshold density of electric current in the sea water for reversible inhibition on apical internodes is close to 66 microamperes per square millimeter of cross section. If an electric current of proper density is similarly passed through the internode at right angles to its long axis, then normal growth of a polyp occurs at each end, but the axis of symmetry in the regenerating tissue is deflected toward the anode. The magnitude of the angle of deflection depends in a certain definite quantitative manner upon the density of the electric current. The threshold density of the electric current in the sea water for a barely perceptible deflection of the growth axis is between 6 and 13 microamperes per square millimeter of cross section.

Intensities slightly above the threshold for orientation exert no apparent effects, other than orientation, upon the growth process.

The occurrence of a definite type of quite constant bioelectric potentials in the stem of Obelia has already been demonstrated. 1 Recently it has become possible to measure these electrical potentials of internal origin. The results show that the magnitude of these inherent potentials is many times greater than would be required for the orientation effects in the growth process and consequently demonstrate the possibility that the living cells of the tissue possess a mechanism which might be brought into action in the rôle of a mechanism for cell correlation in growing tissues. The detailed experimental facts at the basis of the above suggestion will be presented in full elsewhere.