1. The previously reported effect of anemone extracts, the occurrence of quick closing responses to single electrical stimuli in Metridium, has been re-investigated. In standardized tests it was found that whereas hundreds of stimuli are required for each response to a single stimulus in untreated animals, after anemone extract the incidence of such responses is one per nine stimuli.
2. The incidence of these responses falls off with decreasing doses of extract and the effect disappears when less than 1/500th of the material from a single large Metridium is administered. There is no evidence that extracts from ‘stimulated’ and ‘unstimulated’ (i.e. anaesthetized or quick-frozen) anemones differ in potency. Extracts from divided animals show greater activity in the ‘sphincter-disk’ fraction.
3. The incidence of the responses also falls off in time and is highest from 15 to 30 sec. after beginning the treatment. The effect is sporadic and short-lived and responses to two or more successive stimuli are exceptional.
4. A number of treatments, such as drastic changes in pH, KCl(K+ x 8), tetramethylammonium hydroxide (1 : 100), NH4C1 (1 : 340) and especially bile salt and saponin, have similar effects. Drugs with neuro-muscular effects elsewhere (acetylcholine, adrenaline, tyramine, histamine, etc.) were generally ineffective except at very high doses. Food stimulants too were ineffective.
5. From the time relations and other aspects of the responses to single stimuli it is concluded that the effect should not be attributed to a substance with the function of a ‘facilitator’ in the living animal.
6. While the effects are consistent with the passage of occasional adventitious impulses in the nerve net, there is a singular absence of spontaneous or post-stimulus contractions. Certain implications of this feature of the results are discussed.