Among the confused varieties of spasm, clonus, hyperkinesis, etc., it is impossible not to recognise the obvious individuality of certain motor affections--certain movements of defence, of expression, of mimicry, certain gestures more or less co-ordinated for some imaginary end--all readily distinguishable from spasms, fibrillary contractions, and choreiform or athetotic movements. It is only logical to attribute a somewhat more complex origin to these varying gestures, in which the influence of the will, however unperceived in the end, is always to be detected at the beginning. While some convulsions and spasms are the product of special changes in muscle fibre, or motor nerve, or spinal cord, in medulla, pons, or basal nuclei, the synergic and co-ordinated muscular contractions of tic imply cortical intervention. The will may not play a conscious role therein, but the cortex alone is capable of initiating such acts. What part does it take in their genesis? For an instance, a simple blinking of the eyelids may form a tic. Considered in itself, it is a movement of defence against dust or light; but in the absence of irritation it becomes meaningless. How then are we to explain the abruptness and intensity of contraction of the orbicularis palpebrarum, and of this muscle alone? If it were due to stimulation at some point on the reflex facial arc, other facial muscles ought to be involved; if referable to isolated excitation of the orbicularis filaments of the facial nerve, why is the contraction bilateral? It is evident we are dealing here not with a simple reflex of bulbar origin, but with a movement at once premeditated and purposive, and it is this purposive element, presupposing, as it does, co-ordination of contraction, that indicates the cortical nature of the phenomenon. Such co-ordinated movements, however causeless and inopportune they may appear, cannot be identified with mere pathological reflexes or spasms. They are tics. Such, since the days of Trousseau and Charcot, has been the teaching of the Paris School of Medicine. Nevertheless, confusion remains, and in many text-books the unfortunate sacrifice of analytical accuracy to a premature desire for the schematic classification of disease has not tended to lessen it.