An application of a new method for recording the action potential of the single myelinated nerve fiber to detecting the cobalt-ion effect.

The action potential of the single myelinated nerve fiber has been heretofore recorded as a current flow along the longitudinal axis of the fiber, using the so-called Tasaki's bridge insulator method. In this method a great magnification of the amplifier is required as the current thus led is extremely small. Stampfli (1), Tasaki and Frank (2) devised a new recording method capable of obtaining a height of the spike as great as that obtained by the intracellular recording technique. Their method is the same in principle as the intracellular microelectrode technique. The use of the intracellular microelectrode was proved not always suitable by several authors (3, 4, 5), since the impairement by the insertion of the electrode into such a small fiber is great. The authors adopted a new method of recording the action potential extracellularly using the pre-amplifier made for the intracellular microelectrode. The new method enables us to record the potential as great as the source of the action potential itself. It was .found that some heavy-metal ions have specific action on the node of Ranvier. In this paper the abnormal prolongation of action potential of the single myelinated nerve fibers of toad and heavy-metal ion effects on them is mainly dealt with.