1. Strength-duration data for the giant fiber of the great stellar nerve of the squid (Loligo pealii) can be approximately described by several mathematical formulations.
2. Excitation time constants for isolated giant fibers are essentially the same as constants of the giant fibers in the intact nerve.
3. The strength-duration curves of the fibers in the intact nerve lie higher on the voltage axis than those of the isolated fibers. It is concluded that the principal effect of other fibers upon the excitation of one fiber in a nerve trunk is that of shunting the stimulating current.
4. Deterioration of the nerve shifts the curve upward and to the left, resulting in shorter time constants.
5. Decreasing interelectrode distance also shifts the curve upward and to the left.
6. Excitation time constants of the giant fibers are larger with plate electrodes than with wire or pore electrodes.
7. The strength-duration curves of the smaller fin nerve fibers lie consistently to the right of, and the time constants are longer than those of the giant fibers.