We all have met the young man who cannot strike a ball at tennis without protruding his tongue at the same moment; his partner bites his lips at any difficult stroke. At other times neither betrays the slightest grimace; neither is conscious of any effort in maintaining repose. The occurrence of these movements during active concentration of the attention, and the absence of either difficulty or distress in checking them, justify their classification as stereotyped acts, in subjects psychically normal. Tic is a pathological habit, to use Brissaud's phrase, and its description as a habit disease is in harmony with the facts. We must expect, of course, to meet every intermediate variety between the bad habit and the true tic, but this need not deter us from drawing the above-noted distinction, the application of which will be found not without value in the great majority of instances. TIC AND IDEA As we have already seen, a peripheral stimulus may originate a cortical reflex whose expression is a motor reaction, or the reaction may take place where the stimulus is entirely cortical; in other words, an idea may be the starting-point of a movement which may in its turn degenerate into a tic. All that has been already said of these phenomena is applicable to this movement of ideational origin. It too will be transformed into a tic when it is repeated without exciting cause and for no definite end, when its reiteration becomes imperious and irresistible, its suppression accompanied with malaise and its execution with relief. Tics of this sort are numerous enough. "To think an act," as Charcot used to say, following Herbert Spencer and Bain, "is already to accomplish it. When we think of the movement, say of extension of the hand, we have already sketched it in our minds; and, should the idea be too strong, we execute it." In this connection Grasset most appropriately cites the fact that the peoples of mid-France evince a peculiar aptitude for mimicking by suitable gesture the various ideas which occur in the course of conversation. "You will always succeed," he says, "with the following little experiment. In a drawing-room ask ten individuals consecutively to tell you what a rattle (_crécelle_) is. The answer will in every case be accompanied by a gesture expressive of an object that turns. To think an act is already to perform it; the thought and the gesture are wellnigh inseparable." The truth of this observation is not a question of geography. Examples are met with on every hand. It is a law, abundant evidence for which is furnished by all who tic. But however exuberant be accompanying movements of explanation, they must present the additional features of inappositeness and irresistibility to be denominated tics.