This boy J. had always been "nervous," and affected with "nervous movements" of face or limbs. At the age of thirteen years, when playing in the house one day, he knocked himself against an open door and bruised the shoulder near the outer end of the left clavicle. Three or four days later all pain and discolouration had vanished, and the child's movements were perfectly unimpeded again. His tics continued as before. Two months after this little accident was over and forgotten, it was remarked that at the seat of the contusion there was a slight swelling, quite painless and scarcely even uncomfortable, but disquieting enough to the parents and thought to require applications of neapolitan ointment and the actual cautery. This line of treatment effected no alteration in the local condition, but it had other far-reaching consequences, for the boy noticed the anxious interest aroused by the singular exostosis, and began to devote attention to it himself. From the moment that his parents manifested their apprehension by words of pity and by solicitous examination, his tics developed a preference for the left shoulder, though continuing to exhibit themselves in the face and the right arm. He would unexpectedly elevate or depress his shoulder, would shrug it forwards or brace it back, accompanying the performance with inclination of the head or abduction of the upper extremity. He was very positive as to the painless nature of his affection; his sole complaint was of a certain stiffness in the joint, and at the thought of it came an impulse to move the shoulder which there was no resisting. The twitching would disappear for a time for no fathomable reason, and reappear again. By the exercise of a little circumspection he could temporarily overcome it, and during sleep it subsided entirely. The facts--duly controlled and confirmed by the parents--that involuntary shoulder movements preceded not merely the application of the counter-irritants, but the accident itself, and that the unique difference lay in the similarity of his shoulder tic to all his other tics before the trauma, and in its marked preponderance in degree and frequency after, especially subsequent to the treatment, are of weighty diagnostic significance. Plainly the injury and its sequelæ did not exert any causative influence on the tic, and while it is conceivable that the clavicle may have been cracked and an exostosis ensued, we must repeat that the pre-existence of the movements in question negatives the possibility of their being attributable to nerve irritation from a periosteal overgrowth. The only effect which the accident and its consequences had was to intensify the patient's preoccupation and to determine the incidence of the tic.