Repetitive Potentials Following Brief Electric Stimuli in a Hydroid

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Abstract
1. Electrical pulses (amplitude -0.05 to -15 mV.; duration 20-120 msec.) have been recorded from the stolon of Cordylophora lacustris following stimulation. These pulses are propagated with an average velocity of 2.7 cm./sec. at 22° C. 2. Brief electric shocks of little more than threshold intensity can evoke bursts of pulses. The number of pulses in a burst increases with stimulus intensity, but the shape and size of individual pulses do not. 3. Repetitive stimulation causes facilitation of both size of single pulses and number of pulses in a burst. Refractory period, if present, is variable. The minimum interval between two pulses is about 200 msec. 4. Mechanical stimulation evokes pulses identical to those evoked by electrical stimulation. 5. The greater the number of pulses recorded in the stolon near a polyp, the greater and faster is the contraction of that polyp. 6. The number of pulses, but not their individual sizes, decreases with increasing distance from the point of stimulation. 7. It is concluded that conduction in the stolon and the electrical pulses are due to nervous activity and that the conducting system is a network having interneural junctions which sometimes require to be facilitated.

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