Membrane Properties of the Somatic Muscle (Obliquely Striated Muscle) of the Earthworm

1. The membrane properties of the longitudinal muscle fibre of the earthworm Pheretima communissima were investigated by intra- and extracellular stimulating methods. 2. The membrane potential was -35.4 mV., and spontaneous discharges with overshoot (mean +18 mV.) and after-hyperpolarization (-60 mV.) were recorded. 3. Tetrodotoxin (10-7 g./ml.) blocked nervous activity but did not influence the spontaneous discharges or the spikes elicited in the muscle fibre by intracellular stimulation. 4. The critical membrane potential required to elicit a spike was not constant, and the falling phase of the spikes was markedly dependent on the level of the membrane potential. 5. The chronaxie, measured from the intensity-duration relation to elicit a spike by intracellular stimulation, was 55 msec. 6. When nervous activity was excluded the propagation of excitation in longitudinal muscles was decremental.