The peripheral terminations of motor nerves in muscle appear to be irritated by certain poisons, so that the excised muscle exhibits fibrillary twitchings. This might be due to irritation of the muscular structure itself, but as they are gradually abolished by curare they are supposed to depend upon irritation of the terminations of motor nerves. The poisons which produce this effect are: aconitine, camphor, guanadine, nicotine, pilocarpine, pyridine. Physostigmine produces it most markedly in warmblooded animals, but does not seem to cause it in frogs.