FOUR FIGURES IKTEODUCTIOSIn 1880, Biedermann observed that, after having placed two leads with NaCl in contact with two points of an uninjured frog sartorius, a resting potential of the order of tens of millivolts develops, when NaCl on one lead is substituted by KC1. RC1 yields an electronegativity which is similar to that obtained when a muscle is cut. The KCl effect, however, is reversible. Twenty-five years later, Hober ( '05 ; Seo, '24) investigated the electromotive effect of a great number of other inorganic salts with the following result in regard to neutral alkali salts.With change in cation, the negativity decreased in the order: I<, Rb, NH,, Cs, Na, Li, while changing the anion yielded the order: SO,, Cl, Br, J, SCN. The anion effect was small in comparison to the cation effect. More recently, a corresponding effect of these salts on frog sciatic has been observed by Netter ('28), and on crab nerve by Wilbrandt ( '37) aind Cowan ( '34). There is only a quantitative difference in these tissues, the anions having still less effect on crab nerve than on frog muscle, while the effect on frog nerve is almost though not entirely lacking. All the electromotive effects mentioned are more or less reversible. The potential measurements on frog muscle, for the first time, provided evidence for a connection between the resting potential and excitability. The great and rapid decrease of excitability, produced by immersion of the uninjured muscle into different alkali salt solutions (Overton, '04; Schwarz, '07) is paralleled by the large and rapid increase of negativity caused by local application of the salts to the muscle. Preliminary reports have been published in the