The conducted action potential of mixed somatic nerve when recorded, after amplification, by the cathode ray oscillograph exhibits waves, the more constant and prominent of which, for the sake of convenience, have been designated alpha, beta, gamma and delta’in the order of their have been designated alpha, beta, gamma and delta’in the order of their appearance (Erlanger, Gasser and Bishop, 1924). These waves have always been confluent, with the exception of the one in the saphenous nerve of the dog, called delta, which, at sufficient distances of conduction, nerve of the dog, called delta, which, at sufficient distances of conduction, is separated from the waves preceding it by a stretch, labelled gamma is separated from the waves preceding it by a stretch, labelled gamma (Erlanger, 1927), lying almost, if not quite, at the level of zero potential. With the high amplification now used it turns out that an upward convexity of this “gamma” portion of the sa. phenous record, when present at all, vexity of this “gamma” portion of the sa. phenous record, when present at all, is insignificant in comparison with the other elevations of the action potential; evidently it was a mistake to dignify it with a special designation. 2 Recently a wave spaced similarly to the “delta” in the saphenous has Recently a wave spaced similarly to the “delta” in the saphenous has been found in other warm-blooded somatic nerves and in cold-blooded nerves; in addition, waves even later still have been found in the action potentials of both potentials of both warm-and cold-blooded nerve, somatic (Gasser and warm-and cold-blooded nerve, somati c (Gasser and Erlanger, 1929) and Erlanger, 1929) and autonomic. 3 auton omic. 3 The present pape The present paper deals primarily with r deals primarily with the waves of slow conduction as seen in somatic nerves and spinal roots.