Importance of Ca Ions on the Excitable Membrane

　Recently it was found that the Ranvier node of toad's nerves can generate action potentials in sodium free isotonic solution of choline chloride, CaCl₂，KNO₃ or even in sucrose solution, when an adequate intensity of hyperpolarizing current is applied to the nodal membrane^1）．Similar observations to those of the Ranvier node were made in the present investigation on the giant neurons in the supraoesophageal ganglion of a marine pulmonate mollusc, Onchidium verruculatum．