Should a fixed idea entail a motor reaction, it may give rise to a tic as ineradicable as the idea itself, and a series of fixed ideas may be accompanied by a succession of corresponding tics. The frequency with which obsessions, or at least a proclivity for them, and tics are associated, cannot be a simple coincidence. Without defining the word obsession, let us be content to recall the excellent classification given by Régis, according to whom they mark a flaw in voluntary power, either of inhibition or of action. On the one hand we have _impulsive obsessions_, subdivided into obsessions of indecision, such as ordinary _folie du doute_; of fear, such as agoraphobia; of propensity, such as those of suicide or homicide. On the other we find the _aboulic obsessions_, such as inability to stand up (ananastasia), or to climb up (ananabasia), or the astasia-abasia of Séglas, or the akathisia of Haskowec. Perhaps we ought also to place here sensory obsessions in the shape of topoalgia, and even hallucinatory affections. In all these varieties of obsession increase or diminution of volitional activity is undeniable. But this alteration in the function of the will is no less distinctive of tic, and if we compare the psychical stigmata of obsessional patients--the asymmetry of their mental development, their intellectual inequalities and lack of harmony, their alternating excitability and depression, their unconventionalities, eccentricities, and imaginativeness, their timidity, whimsicalness, sensitiveness, and all the other indications of a psychopathic constitution--if these are compared with the mental equipment of the sufferer from tic, we cannot but notice intimate analogies between the two, analogies corroborated by a glance at their symptomatology. An obsession may be of idiopathic origin, or it may be causally connected with some particular incident, sensation, or emotion. A conflagration may determine fear of fire, or a carriage accident amaxophobia. Further, the obsession is irresistible, as is the tic: opposition endures but for a moment, and is therefore vain. Nor is the inhibitory value of attention or distraction any less ephemeral. This feature of tic was noted as long ago as 1850 by Roth, who held its motor manifestations to be phenomena of "irresistible musculation." Consciousness is maintained in its integrity both before and after, but not during, an obsessional attack, and this is equally true of tic, as are the preliminary discomfort and subsequent satisfaction that attend the obsession. Noir makes the appropriate remark that idiots affected with krouomania, in whom sensory disturbance is awanting, so far from suffering pain through sundry self-inflicted blows and mutilations, seem, on the contrary, to be thus afforded a certain feeling of relief, if not of actual relish.