The galvanotropic reactions of Polycelis nigra were investigated in constant and "intermittent" (that is, a current showing slight commutator ripple) electrical currents, varying in strength from one to about ten milliamperes. Galvanotropic reactions were most readily forthcoming at about 2 m.a. constant current, higher current strengths producing signs of discomfort or rigor, and intermittent current being slightly more effective in producing such disturbances than constant current.
As a rule, Polycelis places itself longitudinally, with head facing the kathode, and moves thither by means of looping, its normal gliding motion being in abeyance. If facing the kathode on application of the current, it simply loops forward, but if moving parallel to the electrodes it turns its anterior end first, and then movesmore or less directly towards the kathode. If previously facing the anode, a turn in the direction of the kathode is usually accomplished only after more or less headwaving and apparent difficulty or hesitation.
Decapitate animals, if facing the anode in the current, at some time or other almost invariably loop backwards to the kathode, tail foremost, for a varying number of times, before turning their anterior end to the kathode and orientating normally. This was never observed in normal animals. Decaudate animals behave like unmutilated individuals. Decapitate-and-decaudate Polycelis (middle-pieces) reactin the same manner as do decapitate specimens, i.e. show backward looping. Longitudinal halves of Polycelis are usually curved towards the injured side, and show little or no movement, either in or out of the current; it is supposed that this curvature is mechanical and the result of the injury.
Higher amperages (above 2 m.a.) produce, progressively, cessation of forward movement with twisting and apparent discomfort, and, finally, flattening of the kathodic end of the body. This last reaction is often accompanied by various postures, presumably the result of arrested movement.
An explanation of these reactions, in normal and unmutilated animals, is attempted, based on the supposed interaction of the experimental current with the external portion of an inherent electrical circuit. If this inherent circuit be obstructed it is suggested that the metabolic activities, with which it is apparently correlated, are to some extent upset. Further, that to avoid this derangement, and concomitant malaise, the animals orientate themselves so that the experimental current does not flow counter to the external portion of their inherent circuit; that the turning mechanism of the flanks which affects this orientation can be explained upon similar grounds; finally that backward looping can be explained as a transference of control or dominance to the tail end, due to the combined inhibitory action of mutilation and of a contrary experimental current upon the normal physiological gradients at the anterior end.
A variety of points related to the theory, and some cases of galvanotropism bearing on the work, together with their theoretical explanations, are discussed.