The action of factor I on certain invertebrate organs.

Factor I, prepared from beef brain, has been applied to a number of invertebrate organs and physiological preparations. It was found to antagonize the effect of acetylcholine in some preparations while it imitated it in others. The discussion of the results of this investigation as well as of previous findings leads to the assumption that factor I may be classified with the many pharmacological agents which affect cholinergic mechanisms and that it is likely to be a transmitter substance of inhibitory neurons.