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 IV. ANTAGONISTIC REACTIONS. BY W. G. SMITH. IT is customarily assumed, with the ordinary arrangement of procedure in reaction experiments, that the subject, in trying to carry out the direction to lift his finger from the key as soon as he perceives the stimulus, actually does lift the finger. No doubt in the majority of instances this is the case. But there are some individuals who, instead of lifting the finger forthwith, make a preliminary depression before the lifting is carried out. It is clear that this fact has an important bearing on several problems, in particular on the problem of the exact measurement of reaction time. This mode of reaction, which we may term the antagonistic form, in contrast to the ordinary form in which the lifting of the finger is carried out at once, is the subject of the follow- ing paper. The experiments here recorded were begun in the hope of discovering an explanation of certain irregularities in the results of some measurements of reaction time made with the Hipp chronoscope. The first series, mainly quali- tative, was carried out partly in the Physiological Laboratory of Guy's Hospital, London, and partly in a private house where I was able to meet a larger number of persons willing to be tested : the second series, mainly quantitative, was undertaken in the Pathological Laboratory of the London County Asylums, Claybury, Essex. I am greatly indebted to Dr. Pembrey, Lecturer on Physiology, Guy's Hospital, and to Dr. Mott, Director of the Claybury Laboratory, for the liberal assistance they have given me in the course of the investigation, as well as to the many persons who have acted as subjects in the experiments. 1 The essential point of the experimental methods employed was the use of apparatus by which differences of pressure 1 The abstract of a communication given before the Physiological Society, 20th October, 1900, will be found in the " Proceedings of the Society," Journal of Physiology, vol. xxv., p. xxvi.