Even at the best, however, the disorder is always tedious, as is shown by the fact that its average duration is seventy days. It is very natural, therefore, that parents should be anxious when they see that their child has some awkward or ungainly habit, some odd trick or gesture never noticed before, lest it should be the beginning of this tedious ailment. Now it is well to remember that St. Vitus's dance does not begin with twitching of the muscles of the face, but that its earliest symptoms are involuntary movements of the arms and twitching of the fingers, and that contortions of the face do not come on till afterwards. Movements of this sort too, even when not limited to the face, vary in the course of a few days in the parts which they affect, and show themselves, now in winking the eyes, then in grimacing, in twitching of the muscles of the face or neck, or in some awkward gait or manner. These are all best left unnoticed, for they are almost invariably made worse if the child's attention is called to them. They are, or at least before the days of Board Schools they were, scarcely ever met with among the children of the poor, for they almost invariably depend on mental strain; not of necessity on undue length of the hours of study, or on the difficulty of the tasks imposed, but often on a child's anxiety to make progress and to keep up with his schoolfellows. In corroboration of this being their cause I may say that, contrary to the rule which obtains with St. Vitus's dance, these movements are more frequent in boys than in girls, for the over-mental strain of boys comes earlier; that of girls seldom occurs before the time of transition to womanhood, and its results are then different, though much graver. In cases of this kind, lessening the mental strain is almost always followed by a cessation of the movements; change of air, country amusements, and a generally tonic treatment perfect the cure, and dancing and gymnastics overcome the remains of any awkward habit. The movements in real St. Vitus's dance do not shift about as these do from one part to another, but tend to involve various parts in succession, without previously ceasing where they had begun.