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For many years neurologists have needed more precise methods for investigating the series of physiologic and pathologic changes that follow injury of the motor nerves. The familiar reaction of degeneration, as studied by means of faradic and galvanic currents, has proved rough and uncertain, and is all too often of little service in arriving at a satisfactory prognosis. Studies on nerve regeneration by means of accurate determinations of the time constants of excitation have, however, especially in the hands of Bourguignon (Chronaxie chez l'homme, Paris: Masson & Cie, 1923), proved enormously fruitful both as an aid in diagnosis and in the establishment of accurate prognosis. For the elucidation of the time factors of the excitatory process of nerve and muscle, the scientific world is indebted largely to the exhaustive investigations of Lapicque and his collaborators in the physiology laboratory at the Sorbonne. In the course of twenty-five years of unremitting