If the patient be asked to open his mouth, the spasm of the left cheek remains in abeyance at long as it is open, but the platysma of the same side then begins to twitch spasmodically. Or if he be requested to shut his eyes, so long as they continue closed the cheek is quiescent; but, on the other hand, both orbiculares palpebrarum, as well as the pyramidal muscles and the adjacent fibres of the frontalis, are seen to contract irregularly. There is a sort of transference of spasm, and this is of peculiar interest, inasmuch at it affords evidence that the lesion is not so restricted as one might suppose. The explanation no doubt is to be sought in the law of the diffusion of reflexes, confirming the diagnosis of an irritative lesion at some point on the trigemino-facial reflex arc. In the differential diagnosis of spasm assistance may be obtained by a consideration of the following points: The extreme abruptness of the movement recalls the contractions produced by electrical stimulation. There is no purposive or co-ordinated feature in the spasm, which is confined to some nerve area anatomically limited. Volition, attention, distraction, emotion, all fail to effect any modification of the phenomena. No irresistible impulse precedes their manifestation, nor is it succeeded by a feeling of satisfaction. Sometimes the spasm is accompanied by severe pain. As a general rule the patient's mental state does not present the anomalies met with so frequently among those who tic. Important information may be gleaned from a scrutiny of the condition during sleep. Should the convulsive movement persist, it may be said with confidence to be a spasm; whereas if it completely disappear, it is probably a tic. Whether a spasm may vanish in sleep, however, is another question, which clinical observation has not yet satisfactorily answered, and if no other indication of organic disease be forthcoming, the problem must in the present state of our knowledge be left unsolved. A. Tic or Spasm of the Face In cases where the face is the seat of the convulsive movements this problem of diagnosis becomes one of the utmost nicety. That a distinction may be drawn, however, is universally admitted. Hallion,[170] for instance, specifically separates clonic spasms due to structural changes from the "nervous movements" of neuroses such as chorea or tic. Facial spasm is rigorously limited to the distribution of the nerve, and is commonly the result of some alteration in it effected by causes similar to those that occasion facial paralysis. Clonic spasms of the face are occasionally a sequel to local traumatism--that is to say, they are the result not of direct but of reflex excitation of the facial nerve. Tic douloureux belongs to this class. Tic non-douloureux also is sometimes merely a simple reflex spasm.