SPECIFIC AFFERENT IMPULSES AND CUTANEOUS SENSIBILITY

After reviewing literature indicating correlation between quantitative aspects of action potentials in afferent nerve fibers with specific sense modalities, a technique is described for obtaining electrical responses from single fibers supplying individual receptors in the skin of the frog. Records of action potentials from these fibers were made using a Matthews amplifier and oscillograph in conjunction with a loud speaker, a camera and a standing wave screen. Forty-five receptive endings in 20 frogs were examined: 32 responded only to light touch and not to 20% acetic acid or to crushing; 13 responded only to these latter stimuli but not to light touch. Ten endings in other series gave responses to both types of stimulation. The action potentials initiated by "touch" are typically (75% of the cases) of large amplitude and short duration; those initiated by stimuli which in man would be called painful are of small amplitude (3% to 50% of the amplitude of the "touch" type in about 75% of the cases) and travel at a much slower speed. In 25% of the cases this classification does not hold[long dash]there may even be a reversal in this classification of impulses. Thermal stimuli applied to the skin must be intense in order to initiate nerve impulses. The evidence suggests that the frog may possess protopathic and epicritic sensibility.