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LOMBARD :

Fig. 8.

April 2nd, 6.15 P.M.

M.M

knee-jerk at this examination was 23 mm., and the movement which occurred while the child was crying were 47 mm. and 46 mm. (Fig. 8.) The subject of the experiments was in no way interested in the child and was not conscious of making the slightest movement while it was crying.

Three explanations of the rein- forcement suggested themselves: One, that the subject had, without knowing it, made a voluntary move- ment ; another, that the sound had acted like other forms of sensory stimulation, which have been found to reenforce, and, finally, that it was possible that the cerebral processes, which accompany the turning of the attention into new channels had, in some way, influenced the action of the distant centres in the cord which control the extent of the knee-jerk.

When the attention of the subject had once been turned to studying the action of his mind, he began to recognize that the activity of his thoughts was not without an influence on the extent of the knee- jerk. It was soon noticed that noises which were not loud, and which could be only very weak sensory irritants, if of a kind to attract the attention, in- creased the extent of the phenomenon, while much louder sounds, if devoid of interest, had no appre- ciable effect. Thus, during the examination at 8 P. M., April 12, when the average knee-jerk was 29 mm., some one was heard coming up stairs, and the knee-jerks, which happened to be taken at the time,