Tics are constantly varying in amplitude, degree, and frequency; as O. remarked spontaneously, "We have our good days, and we have our _mauvais quarts d'heure_." The sedative effect of rest, solitude, silence, and obscurity may be contrasted with the detrimental results of fatigue, noise, fear of ridicule, etc. However incapable S. is of rotating his head to the right when requested to do so, the movement is executed with the utmost readiness should his attention be drawn in that direction. But if he hesitates, even momentarily, before looking round, he cannot then do so without the preliminary performance of all sorts of contortions, ending in a twist of his body through a half circle to the right. Sometimes he actually turns round two or three times, after the fashion of a dog chasing its tail. Let him have a pleasant visit, on the other hand, let him engage in a discussion, or be engrossed in a play, let him administer a rebuke to some one, and immediately his trouble is forgotten, his speech is accompanied with animated gestures, the vicious position of his head vanishes--in short, he becomes normal. An intercurrent affection may act either as a deterrent or as a stimulus; with convalescence, however, there is usually a re-establishment of the mischief. The most potent influence over the phenomena of tic is wielded by a sense of well-being, to employ Janet's discriminating expression. Well-being is a panacea for the _tiqueur_ no less than for the hysteric. The tic of the worried financier disappears, as we have had occasion to note, under the magic of a rise in stocks or a knowledge of solvency. The child's happiness is bound up in his freedom, which explains the cessation, in Tissié's little patient, of all convulsive movements during the holidays. Much evidence is forthcoming to support these points, but we must admit that the why and wherefore of a tic's amelioration or aggravation often escape us, nor must we forget that both in the child and the adult spontaneous cure is not unknown. As has been remarked, the evolution of tic does not lend itself to systematic description, but there are cases that form an exception, their course being regularly progressive. Strictly speaking, they are instances of Gilles de la Tourette's disease. GILLES DE LA TOURETTE'S DISEASE Under the title, "Study of a nervous affection characterised by motor inco-ordination, and accompanied with echolalia and coprolalia," Tourette[131] grouped together, in 1885, a certain number of cases presenting features in common and so enabling him to describe a morbid entity, specially remarkable for its progressive evolution. He was followed in the same line by Guinon, who supplied an account in nosographical form, and since then the disease has figured in all the text-books. To obtain a schematic picture of the condition we shall borrow from Tourette's[132] last communication on the subject: