Response to electricity in Volvox and the nature of galvanic stimulation

Summary

• 1. Volvox orients fairly precisely in a constant galvanic current.

• 2. It is positive to the cathode whenever it is photopositive and positive to the anode whenever it is photonegative. Anything which causes reversal in the direction of orientation in light causes reversal in the direction of orientation in a galvanic current, e. g. light, temperature, chemicals, hydrogen-ion concentration.

• 3. Galvanic orientation is due to cessation or diminution in the activity of the flagella on the side of the colony toward which it turns. Photic orientation is brought about largely, if not entirely, by change in the direction of the stroke of the flagella due to change in the amount of light received by the photosensitive tissue in the eyes, owing to rotation on the longitudinal axis.

• 4. When the circuit is closed the activity of the flagella in colonies which are not rotating, diminishes or ceases on the surface facing the pole toward which the colonies are positive, but the decreased activity continues only a few seconds after which the activity increases to that which obtained before the circuit was closed. If the circuit is now opened a similar response is obtained on the opposite side.

• 5. If the colonies are positive to the cathode the flagella on the cathode side respond after the circuit is closed and those on the anode side after it is opened. If they are positive to the anode the reverse obtains.

• 6. The galvanic response in the individual zooids in Volvox is only momentary. But in colonies which are swimming freely and rotating on the longitudinal axis the galvanic response on the side toward which they turn is continuous, owing to the continuous transfer of zooids to this side, from the opposite side, i. e. from the side where they are not affected by the current to the side where they are affected.

• 7. Reversal in the direction of galvanic orientation is probably accompanied by a change in the electric charge of the colonies. Colonies which are positive to the cathode usually drift cataphoretically toward the anode, indicating a negative charge; and those which are positive to the anode usually drift toward the cathode, indicating a positive charge. This has, however, not been unequivocally established.

• 8. A galvanic current induces in the lower organisms various chemical and physical changes at the anode and at the cathode surfaces but the changes induced at these two surfaces differ greatly. In some the changes at the surface toward the cathode are followed by certain conspicuous phenomena, e. g. reversal in the direction of the stroke of the cilia in Paramecium; in others those at the surface toward the anode are followed by equally conspicuous but different phenomena, e. g. contraction in Amoeba and bioluminescence in ctenophores; and in still others those on one side are followed by the same conspicuous phenomena if the organisms are in a given state, as those on the other side, if the organisms are in different state, e. g. decrease in the effectiveness of the stroke of the flagella in Volvox.

• 9. The reversal in galvanic response observed in Volvox is not in accord with Pflüger's law. Whether or not the responses observed on the anode side in amoeba and ctenophores also violate this law, depends upon its interpretation.

• 10. Galvanic stimulation in Volvox is probably associated with decrease in surface polarization and decrease in water-content.