As for the grave mental affections that sometimes are superadded to long-standing tics, it is unjustifiable to class them as complications; they are rather manifestations of psychical instability that have found a suitable medium for their evolution; in many instances they occur quite independently of the tics. It may, however, be remarked that the persistence of a tic entails ceaseless preoccupation on the part of the subject, and may thus pave the way for obsessions or hypochondriacal ideas. The motor disturbance reacts adversely on the mental state of which it is the outcome. Hence an obsession may give rise to a motor display that has all the appearance of a tic, while the motor act in its turn may become an actual obsession. CHAPTER XIV THE RELATION OF TICS TO OTHER PATHOLOGICAL CONDITIONS A vast number of disturbances of motility, distinguished as spasm, chorea, cramp, myoclonus, myotonia, etc., may be derived from the same pathological substratum as tic, and an equally vast number of psychical anomalies may spring from that psychopathic diathesis of which tic is merely the motor expression. The frequency of these associations is confirmed by innumerable clinical observations, many instances of which have been given already. That the relations between tic and other diseases of the nervous system are very intimate is patent from every-day experience; such and such a tic may be succeeded, in the same individual, by a much graver condition in the shape of mental disease, general paralysis, tabes dorsalis, etc. Inversely, some cases of chorea seem to terminate by leaving no trace of their occurrence beyond some little convulsive movement or tic. The position tic occupies is, then, a peculiarly interesting one, for it may be the starting-point of another affection, it may be an intercurrent phenomenon, or it may persist as the reminder of some previous disease. For this reason it well merits attentive study. In this chapter we shall examine the connections of tic with hysteria, neurasthenia, epilepsy, mental disease, and idiocy respectively. TICS AND HYSTERIA Our response to the question whether tics are hysterical in origin is a direct negative. Without attaching pathognomonic significance to stigmata, we may remark how seldom they are encountered among those who suffer from tic, and how rarely the latter exhibit any of the paroxysmal manifestations of hysteria. Modifications of general sensibility such as anæsthesia or hyperæsthesia are unknown; the special senses are intact; in particular, contraction of the visual fields is never met with. Though these signs are negative, their importance from the point of view of diagnosis is none the less real.