It is chiefly among the mentally infirm, such as idiots and imbeciles, that the phenomenon of salutation occurs, and as its rhythm is an element which is foreign to most ordinary tics, it is not likely to be confounded with them. These conditions apart, however, there is one highly specialised clinical type that merits separate study--viz. mental torticollis. MENTAL TORTICOLLIS The medical world has long been familiar with various kinds of permanent or intermittent torticollis presumably unconnected with muscular, articular, or osseous lesions of the neck, and been as long divided on the question of their tabulation. Instances of this affection, bearing such widely differing names as "hyperkinesis of the accessory of Willis," "spasmodic torticollis," "functional spasm of the neck muscles," "rotatory tic," etc., have abounded in medical literature ever since the days of Duchenne of Boulogne, Trousseau, and Charcot. Some twelve years ago now, the term mental torticollis was applied by Brissaud[79] to a type of convulsion of the neck musculature whose association with psychical disturbances justified its description as a tic, and his opinions have been abundantly confirmed by later observation. As a matter of fact, mental torticollis is a tic which the patient can ordinarily curb by some procedure of his own invention. It has its _raison d'être_ in his mental imperfection. To obviate misunderstanding, we must premise that the latter term is not synonymous with mental alienation. It merely signifies that lack of mental balance, to whatever extent, that is patent in all sufferers from tic. From the motor aspect the tic under consideration may be characterised as a functional disorder, consisting in the ill-timed, inapposite, unceremonious, and exaggerated repetition of the function of head rotation. Notwithstanding the large number of muscles involved, the various modifications of movement possible, and the consequent complexity of clinical types, each individual case is recognisable as a tic. Let but momentary cessation of the muscular spasm be effected, and the torticollis disappears without leaving a trace. Instantaneous and total prevention is in practically every case attainable by resort to some subterfuge, however vehement be the patient's contortions. This device, whatever it be, may be called the "efficacious antagonistic gesture," of which the simple placing of the index finger on the chin may be cited as an example. Its field of operation is not limited to mental torticollis, and we shall have opportunities of observing its working in greater detail in other tics; but in the former affection the constancy of its occurrence and the facility of its detection combine to enhance its diagnostic value.