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1. Effects of various kinds of adequate stimuli such as touching, pinching, heating and cooling to various skin areas as well as repetitive electrical stimulations to a nerve branch innervating the skin areas upon the unitary discharges of the expiratory or the inspiratory muscle units of the intercostal muscles were studied on the spinal dogs. Effects of pinching upon the intercostal nerve action potentials elicited in reflex by single electrical shock to the adjacent intercostal nerve were also studied. 2. Excitatory skin area for the expiratory discharges roughly exhibits a triangle, one of whose vertex faces the sternum, the side against the vertex corresponds to the apical line of the spine and includes the spot from where the discharges of a muscle unit are led off. The triangular area is surrounded by a belt-shaped zone having no reflex response. All the other wide area is the inhibitory one. 3. Both the excitatory and the inhibitory skin areas for the discharges of the inspiratory muscle unit are exceedingly narrow in contrast to those for the expiratory discharge, having a tendency to be limited to the small localized area involving the spot from where the discharges are led off. In the other extensive area, however, any reflex effect is not provoked. 4. The more intense and noxious the adequate stimuli become, the more prominent the effect come to be. 5. When the repetitive electrical stimuli to the skin nerve innervating the excitatory area are weak in intensity or low in frequency, an increasing discharge of the respiratory muscle unit results, whereas when the stimuli are sufficiently raised in either of the two factors above described, a remarkable inhibition preceded by a momentary acceleration ensues. In the case of stimulation of the skin nerve innervating the inhibitory area, however, the inhibition alone is obtained throughout. 6. Reflex action potentials in the intercostal nerve elicited by single shock stimuli to the adjacent intercostal nerve show a shortening of latency and an increase in size by pinching the excitatory skin area, while the reverse effects to those above described are obtained by pinching the inhibitory one.