CHAPTER XI THE EVOLUTION OF TIC Tic is, from its nature, highly variable in its evolution; each tic has a development peculiar to itself. Mental differences among individuals have their counterpart in physical differences, in health as well as in disease, and a comprehensive sketch of the evolution of tic is therefore impracticable. We shall restrict ourselves accordingly to a few general remarks. In the great proportion of cases of tic the onset is an insidious one. We have already made a sufficiently detailed examination into the pathogenic mechanism to obviate any repetition in this place, but we may note how unsettled the earliest manifestations are, how a tic may pass from one muscle or group of muscles to another, and even when its exciting cause is patent an apprentice stage always precedes its final establishment. Of the truth of this the history of J. provides an excellent instance. Another one is from Pitres: A nine-year-old boy received a severe shock one day through being pounced on by some companions who were in hiding behind a wood pile, and though the emotion was of short duration, he commenced a few days later to exhibit involuntary muscular twitches of the upper part of his body, and to utter suppressed cries. The phenomena increased in violence and in frequency, and, in spite of treatment, a year later he was not freed of them entirely. For an unknown reason the tics renewed their activity when he was seventeen and continued so for the next three years, until a spell of Pitres' respiratory exercises effected a complete cure. An evolution such as the above may be considered more or less typical of the great majority of tics. We have seen that the tic may be localised indefinitely in one and the same muscle or muscular group, but its site may also vary from day to day. Two tics may co-exist and coincide, or a third may appear with the disappearance of the others. Unexpected resurrections may succeed periods of complete repose. Tic always shows a tendency to invade; regarded as a functional act, it moves in the direction of greater complexity. After involving the orbicularis, for instance, a tic will spread to neighbouring groups, in particular to those muscles whose synergic contractions form a special expression of countenance. That is why tics of the eyelids are associated with movements of the pyramidales, frontales, and corrugators. Tics of the lips or of the alae nasi very commonly extend to the corresponding elevators. It is not surprising that muscular groups accustomed to act in physiological unison should also be affected together (Noir). Moreover, the fecund imagination of the victim to tic is calculated to facilitate the invention of all sorts of modifications, complications, parodies, and caricatures of the functional acts on which his tics are grafted.