Effects of “paralytic shellfish poison” on frog nerve and muscle

A purified extract of toxic lamellibranchs, Saxidomus giganteus (Deshayes), containing “paralytic shellfish poison,” has been tested for its effects on conduction and contraction in frog nerve and muscle. The poison was very toxic and concentrations within the range 0.025 to 0.1 μg/ml. paralysed isolated muscle preparations, with abolition of the muscle action potential. The poison did not readily penetrate the perineurium, but in desheathed sciatic nerves the conduction of nerve impulses was rapidly blocked by concentrations of 0.05 to 0.1 μg/ml. There was no evidence that the poison had any specific curarizing action at the neuromuscular junction, and the paralysis was not accompanied by any appreciable depolarization of the muscle membrane.