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PROCEEDINGS OF THE PHYSIOLOGICAL SOCIETY: March 19, 1904

1. The scratch reflex in the spinal dog. It was shown that the reflex can be elicited not only by mechanical stimuli applied to the skin of the appropriate receptive region, but that weak unipolar faradisation with the stigmatic pole at the receptive hairy skin also excites the reflex with great regularity and precision. Graphic records of the scratching movements were then demonstrated. These exhibited the following among other points. The scratching movement consisting of flexion at hip, knee and ankle is rhythmic with a frequence of about four per second. External conditions, e.g. rate of stimuli (break shocks, double shocks, etc.), intensity of stimulus, locus of stimulus, nature of stimulus (i.e. whether faradisation, break or make of constant current, mechanical rubbing or pricking), hardly appreciably affect the frequence of the rhythm. Intemal conditions, e.g. local fatigue, spinal shock, etc., often considerably modify the frequence of the rhythm, thus fatigue renders the rhythm slow. There is a tonic as well as a rhythmic contraction involved in the response of the muscles. The tonic element is more pronounced the nearer the locus of stimulus to the mid-dorsal line and the more it is posterior. The reflex arc concerned in the reflex appears to be disynaptic: the first synapse is in the same spinal segment as the locus of stimulation, the second lies in the spinal segment innervating the flexor muscle of the limb, i.e. of hip, or leg, or foot respectively. Fatigue can easily be induced by repeated stimulation of one receptive spot in receptive region, and is found to be of remarkably restricted local extent and