Should the cortex be functioning harmoniously, afferent impulse and efferent reaction stand in due proportion one to the other; but any disturbance of psychical equilibrium--_e.g._ the fixity of some idea combined with inhibitory weakness--will effect a corresponding disturbance on the motor side. Charcot used to speak of tics of the mind revealing themselves by tics of the body. Fear may elicit a movement of defence, to persist as a tic after the exciting cause has vanished. It is of course quite incorrect to say that each and every motor reaction to a pathological idea is a tic. The psychasthenic who in his fear of draughts shakes the door-knob a hundred times a day to make sure the door is shut, is not a martyr to tic; in spite of the absurdity of his action, it is logically connected with the idea that originated it, and it is the idea which is absurd. To make an involuntary movement of defence against some purely imaginary ill, on the other hand, and to continue when all fear is past, is to tic. In practice it may not always be a simple matter to uphold the distinction, but some such demarcation of the tic's limits is called for if we are to avoid its being applied to any act performed under the compulsion of a pathological mental state. In its mildest form the mental trouble may consist of an ordinary psychomotor hallucination, but if it be not projected as an objective phenomenon it does not deserve to be called a tic. One of Séglas's patients met a choreic woman undergoing electrical treatment in the same room as herself; on leaving she felt as though her own right arm were the seat of spasmodic movements similar to those of the choreic patient, but as they did not betray themselves by any external sign they cannot be considered tics. The exteriorisation of the hallucinatory phenomenon suffices at once to bring it within the scope of our definition. Innumerable tics arise in this way, provoked, mayhap, by some or other insignificant psychomotor hallucination. The attitude adopted by certain patients, as remarked by Séglas, is an index to the nature and seat of their hallucinations. Some keep their tongue firmly bitten between the teeth; others cram their mouth with pebbles, or compress their epigastrium tightly, under the impression that it is the source of their voice. Should such gestures persist while the hallucination does not, they may give rise to what we are in the habit of calling "tonic tics," or "tics of attitude," but we must repeat that the presence of a convulsive element is essential; however out of place or absurd the contractions are, if otherwise they are normal we are dealing with what Séglas designates stereotyped acts. To this question we shall return later. TIC AND CONSCIOUSNESS