1. The action of a number of drugs which affect the neuromuscular systems of vertebrates has been examined on the sea anemone, Calliactis parasitica. In contrast to their action in vertebrates, no drugs directly cause contraction in the muscles of the anemone.
2. Some drugs of the group which act at cholinergic junctions in the vertebrates, including acetylcholine itself, were ineffective on Calliactis. Atropine and nicotine, of the same group, had depressant effects.
3. Some drugs of the group which act at adrenergic junctions in vertebrates, including adrenaline itself, were ineffective on Calliactis. On the other hand, tyramine, tryptamine and 933 F enhanced and sensitized the response to nervous excitation. Thus responses to single stimuli occurred, whereas normally responses only follow the second and subsequent stimuli. Cocaine enhanced and ergotoxme depressed the responses of Calliactis in a manner analogous to their effects in vertebrates.
4. No significant effects were observed with other substances, including strychnine, veratrine, histamine, betaine and tetramethylammonium hydroxide.
5. The limitation of the drug effects to enhancement and sensitization supports the view that neuromuscular transmission in Calliactis cannot be a simple chemical process as in the vertebrates. In general the results support the hypothesis that there is a separate process of sensitization which must precede the excitation of the muscle in these animals. On the other hand, the drugs which have sensitizing effects on Calliactis do not possess all the properties that would be expected of a natural ‘sensitizer’ or ‘facilitator’ carrying out this process of sensitization at the nerve ending.