For years it has been known that the effect of an inorganic salt on the irritability of nerve and muscle tissue is influenced by the presence of another salt in the solution. Ringer1 was the first to discover that the twitchings of a frog's muscle produced by immersing it in an isotonic solution of pure sodium chlorid, were abolished by the addition of a small amount of calcium. J. Loeb2 pointed out that the toxicity of a sodium chlorid solution was not due solely to the absence of calcium, but also to the presence of the sodium ion, since distilled water had no such toxic action. He also suggested that irritability depends on various ions, especially the metallic ions, Na, Ca, K and Mg, existing in definite proportion in the tissue.
But since the effect of an alteration in these proportions varies widely in different species of