1. Extracts of the sea anemones, Calliactis parasitica and Metridium senile, have been prepared and their effects on the neuromuscular response of these anemones tested. The presence of extract sensitizes the organism so that a response is given to a single stimulus, whereas normally this occurs only on the second and subsequent stimuli. No other significant effects were observed.
2. The sensitizing effect of the extract differs from the effect of a sensitizing drug like tyramine; it appears more quickly, more regularly, and it is rarely accompanied by an increase in the size of the muscular contraction.
3. The fact that a substance with sensitizing properties has been detected in anemones supports the view that a ‘sensitizer’ or ‘facilitator’ exists and takes part in neuromuscular transmission in these animals. Nevertheless, the extract, like the sensitizing drugs, lacks some of the properties that would be expected of a true ‘sensitizer’ or ‘facilitator’.