1. A crude preparation of toxin was extracted from a sample of mussels Mytilus edulis, part of a batch responsible for many cases of
paralytic shellfish poisoning.2. The
crude extract was partially purified by absorption on
sodium Amberlite ion-exchange resin. Two toxins were recovered by elution from the
Amberlite, and purified further by gel filtration.3. One toxin closely resembled
saxitoxin in its behaviour on
Amberlite and in its
biological effects.4. The other toxin behaved quite differently on the
Amberlite. Its molecule was small, comparable in size with
saxitoxin. It was not
tetrodotoxin. Its
biological effects were similar, but not identical, to those of
saxitoxin: it paralysed muscular contraction and inhibited conduction along nerves; it caused death of experimental animals by producing a peripheral
paralysis of respiration; it did not depolarize the membrane of frog skeletal muscle fibres, but acted by preventing a stimulus from initiating a conducted action potential.5. The
biological effects of the second toxin suggest that, like
saxitoxin and
tetrodotoxin, it is an inhibitor of inward
sodium ion movement through electrically excitable membranes.