In an earlier paper (1931) we described a quantitative method of comparing the curariform properties of quaternary ammonium salts. We have now extended our studies to quaternary onium salts derived from phosphorus, arsenic, sulphur and iodine, and to quaternary salts of pyridine and quinoline. Our object has been to obtain fresh light on tire anomalous behaviour of tetraethylammonium salts. The rapid loss in curariform activity which attends the successive replacement of methyl groups in the cation Me 4 N by ethyl groups was studied in detail by Marshall (1914) and is clearly illustrated in fig. 1. A, which gives the time-action curves obtained by us for the series Me n Et 4-n N. The unique properties of these ethylammonium ions are in striking contrast with the quantitative equivalence of ions so varied in structure as tetramethylammonium phenylbenzyldimethylammonium and octylquinolinium (fig. 1B).