The execution of a functional act at an inopportune moment constitutes another variety of functional disorder. A smile with no pleasant thought to correspond; a cry, a word, that betoken no precise idea; a gesture to relieve an irritation that does not exist; a chewing movement when the mouth is empty—all are examples of untimely, inappropriate functional acts, which merit the name of tics if in addition they are anomalous as regards rhythm, amplitude, and intensity.
Again, the performance of function is accompanied by antecedent desire and subsequent satisfaction. Authoritative proof of this law is furnished by the case of micturition and of defæcation, although momentary suspension of the function of nictitation or of respiration is also a sufficiently convincing mode of demonstrating its truth. In the case of locomotion and other motor functions a preliminary feeling of need may not be so imperative, but it is none the less constant.
Now, it has been observed already that these are equally conspicuous features in our conception of tic. In so far, then, as the latter is preceded by irresistible impulsion and followed by inordinate content, it may be considered a functional affection.
We cannot, however, dispose of each and every tic as an anomaly of some normal universal function. We have already had occasion to notice a large number of functional acts that are not of general distribution, so-called professional movements, which of course are liable to derangement. Such functional disturbances may be styled professional cramps, spasms, or neuroses; but are they identical with tics?
To attach the majority of them to the tics is, in our opinion, justifiable. They are the clinical expression of abnormalities supervening in a function that has by repetition acquired the automatism of genuine functional acts: they are germane to the tics. In certain points, however, the analogy is not absolute.
Professional cramps are motor phenomena distinguished by arrest of intended movement. Spasm signifies excess of motor reaction, cramp denotes its inhibition. It cannot, then, be said that they present the characteristic features of spasm as we have defined it: they are akin rather to a form of tonic tic of which we shall give instances later.
With this premise, we can identify the professional cramp as a functional anomaly recognisable by defective amplitude and force on the part of the motor reaction. Its most special character is its appearance exclusively during the exercise of the function of which it forms the anomaly. Writers' cramp manifests itself in the act of writing, dancers' cramp during dancing, and so on. We are ready to admit the close affinity of professional cramp to tic, with which it has an additional element in common in its occurrence among the psychically unstable. But, regarded as a tic, it is unique in its dependence on the casual exhibition of the professional act; as long as the telegraphist has no occasion to transmit messages, his occupation cramp will not incommode him in the least.
The great majority of genuine tics, on the other hand, are roused into activity by anything or nothing, and this distinction is fundamental.
With all due recognition, therefore, of the marked resemblances between the two, we shall be well advised in not confounding them under one designation. For want of a better word, we shall use the phrase professional cramp to specify functional disturbances taking place solely during the discharge of professional acts.
One other class remains to be dealt with, consisting of functional acts not merely superfluous but actually prejudicial to him who is at once their creator and their slave. The idea that induced them and the object they have in view are alike irrational.