CHAPTER III

THE PATHOGENY OF TIC

TIC AND SPASM

Our study of tic can be approached only after a preliminary understanding as to the meaning of two words too frequently confounded even in scientific literature--_tic_ and _spasm_. Let us explain, then, once for all, exactly what we intend by the latter.

Etymologically ([Greek: spasmos, spaô, I draw) the word signifies a twitch, but as it is unfortunately considered a synonym for convulsion, the two expressions are used indifferently in medical parlance, though the desirability of restricting the application of the former has more than once been indicated. Littré's definition--"an involuntary contraction of muscles, more particularly of those not under voluntary control"--may appear somewhat idle, as the contraction of muscles not under the influence of the will can scarcely be other than involuntary. His intention was, no doubt, to reserve spasm for convulsive phenomena in non-striped muscle fibres; but in this limited sense the term has not met with acceptance, and it remains equivalent to "involuntary muscular contraction," whatever that may mean. Thus interpreted, it is applicable to any and every involuntary muscular movement, physiological and pathological, to the inco-ordination of tabes, to chorea, athetosis, tremor, etc.

Rather than imagine a new substantive to characterise certain of these muscle contractions, we may retain the word in a somewhat wider though equally precise sense, and follow the distinction drawn by Brissaud[9] in 1893: "a spasm is the result of sudden transitory irritation of any point in a reflex arc; ... it is a reflex act of purely spinal or bulbo-spinal origin."

By definition, then, _a spasm is the motor reaction consequent on stimulation of some point in a reflex spinal or bulbo-spinal arc_. To differentiate between the reflex, which is physiological, and the spasm, which is pathological, we may add as a corollary: _the irritation provocative of the spasm is itself of pathological origin, and no spasm can occur without it_. The anatomo-pathological substratum of a spasm is, then, some focus of irritation on a spinal or bulbo-spinal reflex arc, which may be situated in peripheral end organ, in centripetal path, in medullary centre, or in centrifugal fibre. Whatever be its localisation, it will determine a spasm in our sense of the word.

Cortical or subcortical excitation, however, as well as peripheral stimuli, may provoke these bulbar and spinal centres to activity. Irritation of a point on the rolandic cortex, or on the cortico-spinal centripetal paths, is followed by a motor reaction exactly as with afferent impulses; the sole change is in the route taken by the centripetal stimulus; the reflex centre remains bulbo-spinal, and the efferent limb of the arc is as before.

The application of the word spasm to these motor responses to cortical or subcortical stimulation is quite justifiable. Developmentally the grey matter of the cerebral convolutions is ectodermic, as is the skin, and capable of functioning as a sensory surface; it may be considered the end organ of an afferent path that conducts to medullary reflex centres. According to our definition, then, provided the centre of the reflex arc be bulbo-spinal and the irritation pathological, the consequent motor phenomenon is a spasm.

A distinction most nevertheless be drawn between the two cases, inasmuch as in the one the afferent path is peripheral, in the other it is cortico-spinal, and there is a corresponding difference in the clinical picture. Jacksonian convulsions, consecutive to cortical stimulation, do not seem to bear much resemblance to spasmodic movements indicative of peripheral--_i.e._ sensory nerve--irritation. As a matter of fact, it is not always easy to differentiate the two, except by the aid of concomitant phenomena. The characteristic evolution of the Jacksonian convulsion is of course readily recognisable. We can similarly diagnose an irritative lesion of the internal capsule not so much from the objective features of the convulsive movements as from accompanying indications. In short, there need never be any occasion for confusion. Convulsive conditions attributable to irritation of cortico-spinal centripetal paths have long been described and analysed: they constitute well-recognised morbid entities, among which may be enumerated Jacksonian epilepsy, hemichorea, hemiathetosis, pre-and post-hemiplegic hemitremor, etc.

These clinical denominations for the affections under consideration it is at present desirable to retain. We shall not call them spasms; above all, we must not call them tics, else we shall end by confounding conditions absolutely distinct. The case recorded by Lewin,[10] under the title of "convulsive tic," of a three-year-old infant still unable to walk, who has daily attacks in which "all the muscles" twitch for about a minute at a time, is indeed a most singular tic. We were under the impression that such an attack is usually known as an epileptiform convulsion. Is the term "convulsive tic" quite a happy synonym?

Again, in the recent thesis of Cruchet the attempt has been made to base the pathological physiology of tic on researches of von Monakow and Muratow apropos of the occurrence of choreic, epileptoid, or athetotic movements after certain lesions of the cerebro-spinal axis, and to find an analogy in the action of various convulsion-producing substances (Richet and Langlois). Cruchet's conclusion is that convulsive tic is as often cortical or subcortical as spinal in origin; that it is, in short, a mere symptom, common to many cerebro-spinal conditions.

The same regrettable confusion is discernible in various treatises on neuropathology the work of German and other foreign authors.

As far as we are concerned, the outcome of the whole matter is simply this: if tic is doomed to be used indifferently for convulsion, its retention in scientific terminology is unjustifiable. Rather, then, than widen its application, we prefer to restrict it; we shall employ the term convulsion in its most general sense of "any anomaly due to excess of muscular contraction," of whatever variety or origin; and we shall limit the use of the word spasm to phenomena the result of irritation at any point on afferent or efferent reflex paths, or in reflex bulbo-spinal centres.

In thus indicating our position, we find ourselves once more in accord with generally received opinion since the days of Charcot. These views have been excellently expressed by Guinon:

Convulsive movements differ widely in kind. Some consist of localised spasms in the domain of a motor or mixed nerve, most frequently one of the cranial series--in especial the seventh--consecutive to some anatomical lesion, central or peripheral. The great majority of observers, French and foreign alike, are in the habit of designating such movements "tics." ... But they are only partial convulsions limited to the area of some one nerve, not true convulsive tics, differing alike in essential features and concomitant symptoms. From the anatomo-pathological standpoint, moreover, lesions are as constantly present in the one as absent in the other.

The opinion of Brissaud on the subject coincides with our own.

* * * * *

If we suppose now that the cortex ceases to act as a surface of peripheral excitation, and becomes itself a reflex centre, we note at once a complete change. The modification effected by the cortex on afferent impressions is obvious in altered motor reactions, which appear with the stamp of cortical intervention, herein differing from bulbo-spinal phenomena. To this category belong the tics; we shall soon see why and how.

Conformably, then, to convention sanctioned by usage, and especially by the teaching of Charcot and Brissaud, we have given a precise definition to the word spasm, and we can only solicit its general adoption.

To resume briefly the argument we have advanced in the foregoing paragraphs, we maintain:

If in a given motor phenomenon there is no evidence of actual or previous cortical intervention, it is not a tic.

If the motor reaction is consecutive to pathological irritation at any point on a bulbo-spinal reflex arc, it is a spasm.

If the cortex is or has been involved in its production, it is not a spasm.

Should it present, in addition to the fact of cortical participation, certain distinctive pathological features, it is a tic.

It is precisely these distinguishing characteristics that we shall now proceed to examine, preluding our study of them with one or two physiological considerations.

TIC AND MOTOR REACTIONS; REFLEX, CO-ORDINATED, FUNCTIONAL, AUTOMATIC, AND VOLUNTARY ACTS

The instantaneous muscular contraction that follows the application of a drop of sulphuric acid to the limb of a decerebrate frog is an example of a pure spinal reflex. With the persistence of the irritation contraction of the other limb and of the whole body ensues; the simple spinal reflex has become generalised. Observe the frog a little longer. Soon the sound foot approaches the affected limb and attempts by rubbing to remove the point of irritation. A movement of attack has succeeded the simple movement of defence, and indicates a complete change in the nature of the motor reaction. In the first case the limb is withdrawn briskly from the painful stimulus; in the second the animal performs a series of co-ordinated purposive movements. The first reflex is automatic, and so no doubt is the second, since the frog is decerebrate. But a co-ordinated movement is not of necessity automatic from the outset; its automatism may be the sequel to voluntary education. Co-ordination is often a manifestation of cortical activity.

Take, next, the case of the infant. His earliest muscular movements are pure spinal reflexes. Pinch his leg, and he withdraws it; continue the stimulus, and he moves the other leg, his arms, his whole body; he starts to cry. The original reflex is becoming generalised, yet he makes no attempt to remove the source of irritation. Should a particle get into his eye, his lids will blink so long as the pain persists, but he never rubs them to expel the foreign body. In Virchow's phrase, the newborn infant is a spinal animal, endowed with spinal reflexes only; his responses to stimuli are beyond voluntary control.

More complex motor phenomena, however, equally independent of cortical influence, characterise the early days of the infant's life. The contact of his lips with the breast at once elicits a reflex in the shape of sucking movements. These are obviously co-ordinated and adapted for a particular end; suction is a functional act. Yet the cortex plays no part therein; the act is automatic from the beginning. Peripheral excitation from tactile impression of nipple, teat, or finger is sufficient to provoke this reflex response.

Similarly with the functions of respiration and nictitation--their establishment follows the stimulation by air of the respiratory or conjunctival mucosa. The appropriate movements constitute the spontaneous reaction to afferent impulses; they are simple bulbar reflexes. Co-ordinated and purposive though they be, they do not come within the sphere of the will. The newborn child cannot voluntarily accelerate or retard his respiratory rhythm.

But a day comes when the formation of cortico-bulbar or cortico-spinal anastomoses renders possible the interaction of higher and lower centres; respiration may be made quicker or slower; the eyelid may be closed less rapidly, more often. In a word, cortical modification of function becomes a reality.

A further step in advance is soon taken.

Under the "law of least effort" the inhibitory power of the will reduces motor reaction for the attainment of a given object to a minimum. The infant begins to make more complicated movements, attempting the removal of a source of annoyance by direct attack, learning to scratch itself, to spit instead of swallow, etc.

The essential difference between these acts--a thousand other examples might be chosen--and the reflexes of the first group, is that the precise and regular execution of the former demands more or less prolonged education, repetition, and voluntary co-ordination.

It is true these co-ordinated acts are eventually performed with all the spontaneity of the simplest reflexes; voluntary co-operation is no longer indispensable; scratching, spitting, walking, can be effected without any actual intervention of the will. But we must not forget such muscular automatism entails a preliminary training in the shape of frequent repetition of purposive movements--a training which varies in duration with the individual and the nature of the particular movement. It is only after several years of volitional effort that such acts as locomotion or the expulsion from the throat of an irritant particle become really automatic.

The fact that the newly hatched chick is capable of walking has been advanced as an argument for the existence of congenital automatism. It is true that the chick's movements are very imperfect--it stumbles and falls, as does the infant, on the slightest provocation, and even without any apparent cause; but the rapidity with which certain animals acquire the faculty is so surprising that the latter almost appears to have been innate.

In all phenomena characterised as instinctive we cannot deny the existence of a certain congenital aptitude, the result possibly of ancestral education, owing to which some individuals learn infinitely more quickly than others, and in their case a period of preliminary education may seemingly be awanting. Probably the truth is, however, that this stage has been a very brief one. In man there is a gradual transformation of voluntary into automatic acts. Though no teacher be necessary, teaching is requisite. The infant learning to walk is really independent of his parents, and might, for that matter, be entirely self-taught; but the point remains, however automatic his walking subsequently become, that he begins by voluntarily co-ordinating the movements of his lower limbs and trunk towards a definite end.

Another advance is still to be made.

With increasing cortical development the individual is able, on stimulation no longer peripheral but central in origin, spontaneously to execute movements which frequent repetition has endowed with all the features of functional acts. Of these ideomotor phenomena physical exercises, games, manual trades, readily furnish instances. Swimming, for an instance, requires the rhythmical co-ordination of arm and leg, to attain which perseverance, retentiveness, and above all repetition are essential. At length the time arrives when the swimmer is surprised at the absence of any necessity for voluntary co-ordinating effort on his part. In fact, to reintroduce volition into this acquired automatism would be to court disaster. "What I do naturally," said Montaigne, "I can no longer perform if I attempt it expressly."

From these physiological considerations we are led to make the following classification of motor reactions:

1. Simple spinal reflexes, innocent of co-ordination or functional systematisation, on whose production or inhibition the will has no influence. To this division belong the movements known as spasms.

2. Functional motor acts. Among these we may distinguish:

_a._ Essential movements, _e.g._ respiration, suction, etc., appearing at birth, and co-ordinated in view of some definite function.

_b._ Acts such as locomotion, mastication, etc., whose acquisition is subsequent to a more or less prolonged period of education.

_c._ Non-essential ideomotor acts, acquired later in life, which soon assume all the characters of functional acts.

The movements belonging to the first group in this latter category may manifest themselves without any exertion on the part of the will, but its activity is essential to the perfecting of the second, and the originating of the third.

In this last division are placed the motor phenomena known as tics.

TIC AND CO-ORDINATION

We have thus come to see that a tic is a co-ordinated, systematised, purposive act. The majority of observers are satisfied on this point, although there exist various differences of opinion, more apparent than real, the inevitable result of disagreement as to the interpretation of certain expressions. It is imperative to obviate misunderstanding once and for all.

In his first contribution to the study of the disease which bears his name, Gilles de la Tourette gave the general description of _motor inco-ordination_ to the convulsive movements of his patients. It has been argued by Guinon, on the contrary, that they are really systematised, and that they reproduce, in an involuntary manner, the co-ordinated movements of everyday life. That this is sometimes the case Tourette subsequently admitted, but he still professed their frequent actual inco-ordination.

This divergence of opinion is entirely attributable to difference of interpretation. Littré's definition of muscular inco-ordination is, "A condition occurring in various diseases of the nervous system, in which the patient cannot co-ordinate the necessary muscular movements for walking, grasping an object, etc." In this sense the term is applicable indiscriminately to the gesticulations of choreic, athetotic, or tic patients; to the ataxia of tabetics and others; to the tremor of disseminated sclerosis or paralysis agitans, etc. An expression so general is not merely of no diagnostic value; it leads to positive confusion.

It is precisely in the type of inco-ordination that the difference lies. As rigorous a distinction must be drawn between the gestures of chorea and the gesticulations of the sufferer from tic as between the tremor of insular sclerosis and of Parkinson's disease.

In assigning an exact meaning to the term muscular inco-ordination, we cannot do better than quote the remarks of Guinon:

The tabetic who throws his legs to right and left, who as he sits at table cannot carry his spoon to his mouth, furnishes an instance of true motor inco-ordination. On the other hand, the subject of tic performs his voluntary actions with perfect assurance; though his infirmity occasion all sorts of ridiculous involuntary arm movements, he never brings his fork against his ear or his cheek, nor does he spill a drop from his glass; his walk may be interrupted by a sudden halt to bend his knees and kneel, or to strike his foot violently on the ground, but he never trips one leg over the other and never falls.

In his article in the _Dictionnaire Jaccoud_, Letulle distinguishes two kinds of tics:

The _convulsive tic_ consists of a series of partial convulsions, while the _co-ordinated tic_ is the expression of some complex act by a sequence of muscular contractions for that purpose. In the former case the resulting movement is irregular, abnormal, and useless; it is a muscular "shock" evolved without reason and continued without effect.... The normal individual usually possesses _in potentia_ all the elements for the genesis of a co-ordinated tic. Some little trick or mannerism, arising perhaps from the necessity of gaining time for reflection, or from the desire of concealing some innate timidity, or of dissimulating some preoccupation, becomes sooner or later involuntary and automatic, and though maintaining its regularity and co-ordination, passes insensibly into the realm of pathology.

The distinction, however, is far from being absolute. Letulle himself admits it is a question of degree rather than of kind; the co-ordinated tic differs from the first variety only in its greater extent, complexity, and duration. Now, the convulsive tic may be a local, partial, irregular, abnormal convulsion, yet these characteristics are not sufficient to differentiate it: biting the lips is classed by Letulle as a co-ordinated tic, but it is surely a local, partial, irregular, abnormal muscular act; and the explosive laryngeal "ahem!" he would similarly place, yet it cannot be said to be a phenomenon characterised by its extent, complexity, and duration.

According to Guinon, a further distinguishing feature of the convulsive tic is its frequent though inopportune reproduction of some reflex or automatic purposive movement of everyday life, whereas we have just seen that one of the elements in Letulle's co-ordinated tic is its purposiveness. In a word, these observers apply the same epithet to two varieties of tic which they are endeavouring to separate.

The explanation of the apparent contradiction is simple. A gesture which seems meaningless and useless to-day becomes intelligible and logical to-morrow, when we learn the reason for it. In the course of an attack of conjunctivitis a patient acquires the habit of winking his eye, and though the inflammation subsides, the habit persists. If we are ignorant of its cause, are we to call the tic convulsive since it appears to us needless? And if we do know its origin; can we say it is co-ordinated when one muscle only is involved in the contraction?

The distinction drawn by Letulle between the two groups may hold good in some cases, but certainly not in all, and in our opinion it is preferable to abstain entirely from the attempt to base a classification on variation in muscular contraction. Noir remarks very justly that intermediate forms occur which are difficult to place in one or other category. In face of the confusion to which an illogical division inevitably leads, we may safely leave this question aside. In our view, the motor phenomena of the disease are always systematic, co-ordinated movements, directed for the attainment of some definite object. We exclude all simple bulbar or spinal reflexes, and all spasms, since the cardinal feature in these conditions is the absence of any functional systematisation.

THE GENESIS OF TIC

We have seen how various purposive, co-ordinated movements may, by dint of education and voluntary repetition, become automatic and be automatically repeated should occasion arise. Imagine some such act recurring involuntarily without any apparent reason and for no apparent object; what does such an anomaly signify?

Take, for instance, the case of a young girl who inclines her head on her shoulder to relieve the pain of a dental abscess. The act is called forth by a real exciting cause; the muscular response is voluntary, deliberate, undeniably cortical in origin: the patient _wills_ to appease the pain by pressing and warming her cheek. Should the abscess persist, the movement will be repeated less and less voluntarily, more and more automatically; but as the why and the wherefore still remain, there is nothing pathological about it.

With the healing of the abscess, however, and the consequent relief of the pain, the girl still inclines her head on her shoulder from time to time, albeit cause and purpose have ceased to operate. Her primarily volitional, co-ordinate, systematic, motor reaction is now automatic, inopportune, and meaningless: it is a tic.

Charcot[11] has given us an excellent description of the process:

However complex and bizarre may appear the convulsive phenomena known as tics, they are not always as irregular, inco-ordinate, and contradictory as superficial examination might lead one to believe. On the contrary, they are, as a general rule, systematised; in a given case they recur always in an identical manner, reproducing, and simultaneously exaggerating, complex, automatic, purposive movements which are essentially physiological; they are in a sense the caricatures of ordinary acts and gestures. The tic is not in itself absurd; it appears so only because it occurs inappositely, without obvious motive. Source of irritation is absent, yet the patient scratches himself; he blinks, but no foreign body is to be detected in his eye.

Mere repetition does not, cannot, evolve a tic in every case. Not all who would may tic; psychical predisposition in the shape of volitional enfeeblement is a _sine qua non_.

Of the rôle played by mental insufficiency in the genesis of tic we shall have much to say later. The point we are desirous of emphasising now is that the first manifestations of tic have their origin in, and are dependent on, cortical activity, at least in a majority of cases.

Notwithstanding painstaking investigation, determination of the initial cause may no doubt be difficult in some instances, owing to the patient's ignorance or forgetfulness; for that matter, the observer may not know how to set about his task. Prolonged interrogation, however, and due consideration of the patient's environment, will generally enable him to reconstruct the pathogeny of the condition.

It has been our practice for some years now to examine with especial care into the mode of onset, and to scrutinise the reasons for the particular localisation, of any given tic; and we have been able, in practically every case, to rediscover the exciting cause, and consequently to explain the form taken by the tic in its earliest manifestations as a voluntary response to the stimulus. Time may have distorted the original movement, but a little patient analysis will facilitate its recognition even in the caricature made of it by the tic.

A few concrete instances will help us better to understand the nature of this psycho-physiological mechanism.

An individual is wearing a collar too small for him, and its frayed edge chafes his skin; the neck is at once abruptly inclined away from the irritating point--a simple spinal reflex movement of defence. Now that he is warned by the sensation of pain, he wishes to avoid it, which he does by bending his head to the opposite side. The act is similar to the preceding, but of a totally different nature; it is voluntary, not involuntary; cortical, not bulbo-spinal.

Next day the collar is replaced by another of ampler proportions. There is no further irritation of the skin, and accordingly no occasion for deviation of the head. Memory of the disagreeable sensation may perhaps incite him to verify the disappearance of the irritation by a few movements of the head, and in the normal individual the matter ends there. Even should the idea of repeating the gesture, now become meaningless, occur to him, he banishes it by an effort of the will.

With the candidate for tic things pass in quite a different fashion. Uncalled for though it be, he performs the brusque movement of yesterday perhaps with a view to satisfying himself that the pain is non-existent, but he is not thus satisfied. He does not limit his experiments to one or two attempts. He repeats it frequently and complacently. The original source of irritation is gone; the movement intended at first to relieve it persists. Soon the whole trouble is forgotten, but the reiterated gesture becomes habitual and automatic; it may have been rational yesterday, but to-day it is superfluous, if not actually prejudicial; it is a tic. In its evolution the cortex has had a part, and the very untimeliness of this cortical intervention indicates a certain disorder of psychical function.

Or again: a speck gets under my eyelid, and I wink--a spasmodic act independent of the cortex. The speck is removed, but the conjunctiva remains a little tender, and I wink again--still only a spasm. All trace of irritation vanishes, yet the blinking persists: it is degenerating into a tic.

Wherein consists the rôle played by the cortex in the production of such phenomena? It intervenes to order the repetition of the gesture provoked involuntarily, in the first instance, by peripheral excitation; and though one may not always be able later to discover evidence of this, one must at the least recognise the fact that the mere inopportune persistence of the movement bears witness to psychical imperfection.

It has been remarked by Guinon that patients suffering from tics of blinking attribute them to the presence of foreign bodies; he declares, however, that "if they bear a superficial resemblance to simple tic, they differ widely in essential characters and from the point of view of prognosis. They are really involuntary movements of reflex origin, occasioned by abnormal sensations, usually of pain." He cites as a typical instance the "tic douloureux" of the face.

The description is strictly accurate provided the pain continue; such acts are not tics, they are spasms. On the other hand, the perpetuation of the movement in the absence of all exciting cause and pain constitutes it a tic. In this way a spasm may be the forerunner of a tic, and in many cases no doubt a purely spasmodic motor reaction may determine the form and localisation which the latter will adopt; but, as we have said, its first manifestation is usually a voluntary act of definite causation, and directed to the accomplishment of a definite object.

The candidate for tic is mentally unstable. Indifferent perhaps to acute suffering, he may become entirely preoccupied by some trifling sensation of pain or by some source of petty annoyance, to rid himself of which he will resort to all sorts of tricks and assume all sorts of odd attitudes--tic germs quick to develop in suitable soil.

In many motor reactions of the class we are now considering the main object is the _avoidance of some abnormal sensation_, suppression of which, however, brings no relief to the patient's mind. He dreads its reappearance; he must assure himself of its absence. He taxes his ingenuity in the attempt to rediscover the sensation, and multiplies his gestures and attitudes until once again he experiences it. The satisfaction he felt originally in shunning the pain or the discomfort is paralleled by the satisfaction he now knows in its rediscovery. In each instance the motor phenomena are voluntary and co-ordinated, but their excessive repetition betrays unstable mental equilibrium.

Instructive examples of this pathogenic process are furnished by the history of O., and by the case of a young patient J., from which we extract the following:

In 1896, during the holidays, a tic, secondary to some slight nasal ulceration, made its appearance. The child learned the trick of wrinkling its nose and of puckering its upper lip, sometimes attempting by various facial grimaces to lessen the irritation due to the little nasal sore, sometimes, on the contrary, finding delight in deliberately seeking the unusual sensation. The sniffing soon became involuntary, and for the next two months, long after the ulceration was healed, this nasal tic continued.

Then another cause came into operation, occasioning a new gesture and entailing a new tic. Cracking of the labial mucous membrane during winter led to incessant licking and nibbling at the roughened surface. With the first excoriation the patient proceeded to moisten his lips with his tongue, whence fresh cracks, followed by the renewal of nibbling and licking movements.

In March, 1899, after a severe attack of influenza accompanied by fever and pains in the joints, he began to complain of stiffness and a sort of cracking in the neck, disagreeable rather than painful. To avoid this, or to reproduce it--as one sometimes amuses oneself by "cracking one's joints"--he quickly learned to make all sorts of bizarre head movements, and so a tic of the neck started which lasted several months.

Noir has directed attention to a tic of frequent occurrence among amaurotic idiots, consisting in rapid to-and-fro movements of the finger before the eyes. The explanation seems to be that their blindness is not absolute enough to prevent some faint appreciation of light by retinal stimulation, and the effect of the luminous impression is enhanced by the alternation of light and shade sensations produced by the waving of the fingers in front of the eyes. The tic is neither more nor less than a search after this effect.

Another case in point is reported by Dubois[12]:

The patient is a young woman twenty years old who has acquired the habit of beating her right elbow against her chest fifteen or twenty times a minute, until it happens to impinge with rather greater violence on a whalebone in her corset; this is accompanied by a slight guttural cry. It would appear the sole satisfaction in her tic is in the attainment of this object, since it is succeeded by temporary cessation of the movements. Their constant repetition has caused an insignificant erosion of the skin over a limited area on the elbow, and it is only when this particular spot is touched that the ejaculation is uttered and the tic arrested. If the elbow be at rest, the head is inclined from left to right several times a minute.

Evidently, then, in the subjects of tic the _impulse to seek a sensation_ is of very common occurrence, as is also the _impulse to repeat to excess a functional act_. It is precisely this exaggerated and inopportune multiplication of movement that is pathological.

The mother of one of Noir's patients was always tempted to repeat any simple purposive movement that she had made a moment before, even though the reason for the act no longer existed.

The imperiousness of these impulses, and the peculiar relief attendant on submission to them, accentuate the closeness of the resemblance between tic and obsession, to which reference will be made later; but it is necessary at this early stage to indicate the bearing of these psychical phenomena on the pathogeny and diagnosis of tic.

Many of the conditions with which we are dealing are characterised in addition by an emotional element. Dupré[13] believes an emotional shook is the exciting cause of tic, as it sometimes is of obsessions.

Apropos of this view, we may quote again from the history of the young patient J.:

During his holidays he improved sufficiently to enable him to resume his classes, but another attack of influenza in the beginning of 1900 was the occasion of a relapse. He began to complain of overpowering fatigue; became depressed and morbidly anxious about his future; had attacks of hysterical sobbing; suffered great mental anguish, accompanied by flushing and profuse perspiration; in short, he fell into a veritable state of _mal obsédant_.

At the same time, the slightest pain or annoyance was a pretext for his tics to exhibit themselves with redoubled vigour. Even the mere idea of his tics, the fear of them, incited him further in the same direction. He seems then to have set himself to invent new movements, and forgetting forthwith that he himself was their creator, became alarmed at them as sure signs of the aggravation of his disease.

Analogous details will be found in all cases which have been studied as well from the mental as from the physical side. For our part, we consider a tic cannot be a tic unless it be associated with a certain degree of mental instability and imperfection, indubitable evidence of which is furnished by a psychical abnormality of constant occurrence in this malady--viz. anomalies of volition.

TIC AND WILL.

It might be imagined that a tic would cease to exist as such were a voluntary element to enter into its constitution. The fact, however, that tic is the sequel to frequent repetition of a primarily voluntary act, and that it may be arrested, transformed, or aborted, is proof to the contrary of which there is no gainsaying.

The truth is, once a tic is established, it has all the appearance of an involuntary movement, but that nevertheless its manifestations may be either modified or inhibited by an effort of the will is patent from clinical observation. This is a fact of great importance.

Spasm knows no control (says Brissaud). Nothing will arrest the bolus of food as it passes into the pharynx, unless by the inversion of the whole function of deglutition.... As regards tic, however, inhibition is possible because the phenomenon is cortical. In almost every case, reinforcement of the will can momentarily at least check it.

Consensus of opinion admits diminution of will power to be the cardinal mental symptom of the tic patient. Inhibitory insufficiency, as Blocq and Onanoff say, allows the persistence of fixed ideas of movement which reveal themselves by involuntary acts. Noir has admirably supplemented the researches of Ribot in this direction:

The infant's activity is purely reflex, and manifested by a profusion of movements, to suppress or restrain the majority of which is the task of education. It is highly probable that any co-ordinated tic whose evolution can be traced at all has its origin in the infant's spontaneous muscular play. From this point of view the frequency of these movements in idiots is readily explicable, since their intellectual development never gets beyond the stage of childhood. The more confirmed the idiocy and the more rudimentary their mind, the more prone are their tics to be complex and inveterate.

These remarks are pertinent to the case not only of idiots, imbeciles, or backward children, but of all the subjects of tic. In them some degree of mental infantilism is of invariable occurrence. The tic patient has the weak and capricious will of the child; young or old, he does not know how to _will_; if his willing be sometimes excessive, it is never resolute. Were it otherwise, he might control his meaningless gestures, but his efforts are both feeble and ephemeral.

TIC AND HABIT

The view which regards tic as a "pathological muscular habit" provides emphatic illustration of the sinister influence of volitional infirmity.

This aspect of the question is of deep significance. If we define a habit, in the words of Littré, as a "disposition acquired by the repetition of the same acts," we can easily conceive how intimate is the relation between habit and automatism, and how constant rehearsal of the same movement in the same manner will create a mode of motor reaction independent of the function of the will. It has been made clear already that the phenomena of tic, regarded from the motor standpoint, reveal an identical process at work; but the fundamental difference between the habits of normal individuals and those of tic subjects is that the former can be checked or modified by voluntary effort, whereas the latter gradually acquire the pathological features of tenacity and irresistibility.

In a typical case of tic (says Dupré)[14] the establishment of a reflex sensorimotor diastaltic arc, viâ the cortex, between peripheral stimuli of whatever nature and corresponding muscular reaction, is a sign that predisposition has changed the physiological to the pathological, and transformed a habit into a tic.

Guinon argues, however, that tic ought not to be cited in the catalogue of diseases, since it is ultimately a deep-rooted "bad habit" only, not a pathological fact.

We are not prepared to maintain, of course, that all motor "bad habits" are tics, for a whole host of familiar gestures, tricks, and mannerisms do not merit the name, superfluous and even detestable though they may be. It is true they are the product of education, and become, since the will has less and less to do with their appearing, at the last purely automatic; they may thus developmentally bear a close resemblance to tics. As Letulle says:

The infant who is constantly sucking its thumb, the individual who never ceases picking his teeth, or rubbing his eyes, or lips, or chin, or ear, who is for ever scratching his head or his beard--all have no doubt, originally, been driven to the repetition of the trick by some real necessity in the shape of dental caries, or ciliary blepharitis, or pityriasis capitis; but removal of the cause is not followed by cessation of the gesture. A man will learn the habit of perpetually smoothing his hair, and will not desist from his favourite trick though he become absolutely bald.

But such automatic habits and mannerisms are not genuine tics so long as the movement executed conserves in form the characters of a normal gesture. Be it never so inopportune or absurd, it is not a tic. It comes rather under the heading of _stereotyped acts_, whose kinship with, and difference from, the tics, have been well demonstrated by Séglas.

While the stereotyped act has all the appearance of a normal movement, the tic, on the contrary, is a "corrupt" muscular contraction; its subject is irresistibly impelled to its performance, and any attempt at repression is painful, sometimes even agonising. Victory is perhaps not entirely impossible, but any arrest is, as a rule, only temporary, and entails suffering which well deserves to be considered pathological.

On the other hand, the thousand illogical and absurd mannerisms of which we have been speaking betray no irresistible imperiousness in their execution, and require no agonising struggle for their repression. They are not tics. The crucial point in the differential diagnosis is the presence or absence of mental suffering.

The distinction may be further elaborated. Concentration of the attention may diminish the intensity or even inhibit the occurrence of a tic; inversely, a simple bad habit is manifested preferably during this very concentration. In the heat of physical or intellectual labour, we have all our favourite and characteristic tricks: we curl our moustache, we twist our beard, we scratch our forehead, we rub our chin, we nod our head, we fidget with our fingers in reading, speaking, reciting--in any mental or physical exercise requiring our attention we reveal innumerable little oddities of movement; but let our thoughts be directed for an instant to these gestures of distraction, and they disappear forthwith, to reappear afresh when we are absorbed in our work again. Charcot used to twist his hair round his index finger so intricately that to disentangle the finger one day a lock of hair had actually to be cut off. It was a trick of his, not a tic.

In the case of the latter, leisure of mind and body is the signal for the apparition of the inopportune movements. Any form of effort demanding the attention will, as a general rule, lessen their frequency or abolish them altogether.

Trousseau quotes the case of a young girl afflicted with severe tic who could play through any piece on the piano without the slightest interruption. Guinon similarly has known cases, one of whom could juggle accurately with knives, and another whose infirmity did not prevent her from taking a successful part in operatic ballet. Young L. is passionately fond of dancing, but he never tics in the ballroom. O. is an excellent amateur billiard player and never handicapped by his tic when playing, or, for that matter, when fishing or fencing; but if his attention be not thus absorbed, it is only with the utmost difficulty that he can master his tic.

We all have met the young man who cannot strike a ball at tennis without protruding his tongue at the same moment; his partner bites his lips at any difficult stroke. At other times neither betrays the slightest grimace; neither is conscious of any effort in maintaining repose. The occurrence of these movements during active concentration of the attention, and the absence of either difficulty or distress in checking them, justify their classification as stereotyped acts, in subjects psychically normal.

Tic is a pathological habit, to use Brissaud's phrase, and its description as a habit disease is in harmony with the facts. We must expect, of course, to meet every intermediate variety between the bad habit and the true tic, but this need not deter us from drawing the above-noted distinction, the application of which will be found not without value in the great majority of instances.

TIC AND IDEA

As we have already seen, a peripheral stimulus may originate a cortical reflex whose expression is a motor reaction, or the reaction may take place where the stimulus is entirely cortical; in other words, an idea may be the starting-point of a movement which may in its turn degenerate into a tic. All that has been already said of these phenomena is applicable to this movement of ideational origin. It too will be transformed into a tic when it is repeated without exciting cause and for no definite end, when its reiteration becomes imperious and irresistible, its suppression accompanied with malaise and its execution with relief.

Tics of this sort are numerous enough. "To think an act," as Charcot used to say, following Herbert Spencer and Bain, "is already to accomplish it. When we think of the movement, say of extension of the hand, we have already sketched it in our minds; and, should the idea be too strong, we execute it."

In this connection Grasset most appropriately cites the fact that the peoples of mid-France evince a peculiar aptitude for mimicking by suitable gesture the various ideas which occur in the course of conversation. "You will always succeed," he says, "with the following little experiment. In a drawing-room ask ten individuals consecutively to tell you what a rattle (_crécelle_) is. The answer will in every case be accompanied by a gesture expressive of an object that turns. To think an act is already to perform it; the thought and the gesture are wellnigh inseparable."

The truth of this observation is not a question of geography. Examples are met with on every hand. It is a law, abundant evidence for which is furnished by all who tic. But however exuberant be accompanying movements of explanation, they must present the additional features of inappositeness and irresistibility to be denominated tics.

A case that has come under our own notice is worth mentioning because of its peculiarity and instructiveness. The patient was an artistic, well-educated, and well-travelled man, gifted to a remarkable degree with the faculty of assimilation. Apart from genuine tics in the shape of sudden jerks of face, arm, or leg, he had acquired the trick of accompanying his conversation with a peculiar mimicry of its content. Not satisfied with providing a gesture for nearly every word, he divided the words themselves into syllables for each of which he had an appropriate action, whence arose a series of mimicry puns of most unexpected effect.

For instance, during the enunciation of the following sentence, "We were on a paddle steamer, with captain, commissaire, and doctor," he first of all imitated the movement of paddles; he then put his hand, with three fingers apart, to his forehead (the captain's cap has three lace bands); to mimic the word commissaire he shook hands with himself (_commissaire_--_comme il serre_); to express the word doctor he pretended to touch imaginary breasts on his body (_médecin_--_mes deux seins_); and so on throughout all his conversation.

Voluntary execution of these puns had been succeeded by complete automatism, yet they were not tics, because, however singular the mimicry, it was appropriate; whereas his facial grimaces, the shrugging of his shoulders, the tapping of his heels, repeated every minute for no reason or purpose, were real tics.

If, when asked what a rattle is, we make a turning movement with our hand, or if when asked to explain the word _brandebourg_ we indicate an imaginary arrangement of braid on our coat--these two experiments always succeed--we are attempting to express an idea by mimicry at the actual moment of its arising in the mind; but the subject of a tic--which may primarily have been the representation by mimicry of an idea--continues the gesture long after the idea which provoked it has vanished.

A woman speaking with animation at a telephone will make with face or hand a thousand useless gestures, useless since her friend cannot see them, but they are not tics, even though they may be justly described as functional, automatic, superfluous, and inopportune. If we are normally constituted, we betray a pleasant idea by a smile, we express our conviction by an appropriate gesture of affirmation; if we smile or gesticulate with no motive for doing either, we have begun to tic. It is not sufficient that the act be untimely at the moment of execution; we must be persuaded that it no longer stands in any relation to the idea which called it forth at the first, and that its repetition is excessive, its inappositeness constant, its performance urgent, and its inhibition transient, before we can say it is a tic.

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

According to Guinon, proof that "convulsive" tic is conscious is furnished by the accurate description and rational explanation patients supply of their affliction. Similarly Letulle's "co-ordinated" tic is a conscious act, at least in its commencement; it is a "bad habit" which finally passes beyond the limit of consciousness.

Now, while no doubt most subjects show a keen appreciation of their tic when their attention is directed to it, they are none the less unconscious of it at the moment of its manifestation. This is the ground on which Letulle bases his statement that all tics, of whatsoever variety, are habitually outside the domain of consciousness. To this fact so much importance has been attached that the attempt has been made, more especially by Blocq and Onanoff,[15] to differentiate the conscious from the unconscious tic.

In our opinion, the distinction is ambiguous and tends needlessly to complicate our ideas on the subject. The patient with "convulsive" tic is conscious of it in the sense that he is well aware of its existence, yet how can the gesture be a conscious one if it is synchronous with mental preoccupation? On the other hand, the patient with "co-ordinated" tic may bite his lips unconsciously, but he is by no means ignorant of his little failing.

This divergence of opinion depends entirely on the possibility of regarding the phenomena at different moments during their production. The subject is in a position to appreciate his state both before and after the tic, not during it. In a sense it may be said that tic is alternately conscious and unconscious, in which respect it is comparable to the obsession; the close analogy between the two conditions we shall indicate more fully later. As a matter of fact, the same holds true for every variety of spasm.

We are not disposed to introduce here a term sacred to the psychologist and to speak of the tic as subconscious. Pierre Janet does not admit the absolute unconsciousness of habit; even when the latter has degenerated into a tic, it is not outwith the realm of consciousness. We prefer not to venture, however, into the perilous region of the subconscious, in spite of our appreciation of the happy results attributable to its careful and discerning exploration by observers such as Janet himself.

According to Cruchet, certain so-called psychical tics are always subliminal--for instance, the imitation tics common in children and in idiots.

But if the consciousness of the normal adult be, as it admittedly is, a most elusive conception to define, how infinitely more precarious is the task in the case of idiots or infants! Cruchet says it is impossible to be sure whether at any given moment a tic has been above the threshold of consciousness or not; and we do not think the question will be elucidated by the introduction of data so difficult to comprehend as the consciousness, unconsciousness, or subconsciousness of the tic patient. In any case, these conceptions are quite inadequate for the establishment of useful distinctions. All that we can say is that the participation of consciousness in the phenomena of tic varies in time and degree. To hazard farther would be to invite disaster.

TIC AND POLYGON

The proposal has been made by Grasset to apply his attractive hypothesis of the cortical polygon to the interpretation of the pathogenesis of tic. It is desirable, first of all, to recall briefly the significance of the word polygon in the sense adopted by that neurologist.[16]

At the central end of the physiological ladder is the superior or cortical system of perception neurons whose cells form the grey matter of the convolutions. Physiological and clinical research necessitates the subdivision of this system into two groups--the neurons of psychical automatism, and the neurons of superior (_i.e._ voluntary or free) cerebration. The former function is not of the same level as the ordinary reflex arc, since it is in relation to co-ordinated, intelligent, and in a sense conscious acts; at the same time it is to be distinguished assiduously from the latter, in which we include our personality, moral consciousness, free will, and responsibility.

Activity on the part of the inferior psychical neurons is seen:

1. In normal individuals--during sleep, dreams, and acts of distraction.

2. In the nervous--in nightmares, oniric states, table turning, thought reading, the use of the divining rod, automatic writing, cumberlandism, spiritualism.

3. In the diseased--in somnambulism, catalepsy, hysteria, certain phenomena of epilepsy, hypnotism, double personality; also in some cases of aphasia, and in such conditions as astasia-abasia. Every manifestation of this inferior psychism is characterised by spontaneity, herein differing from mere reflex acts, but not by freedom, which is the _propre_ of superior psychism.

The various neurons subserving the former or inferior function are cortical, and form the cortical polygon. Situated at a higher physiological level are those for the latter function, united in what I designate the centre O.

Grasset's general conception of tic is accordingly as follows:

In contradistinction to a pure reflex, a tic is a complex or associated act. There is, however, more than one centre for the elaboration of these complex or associated acts, notably the bulbo-medullary axis, and the cerebral polygon, as we call it. The former serves as centre not merely for simple reflexes, but for true associated acts also, such as conjugate deviation of the head and eyes, walking movements in the decerebrate animal, etc.

We can conceive, then, a first group of non-mental tics corresponding to and reproducing these movements of bulbo-medullary origin.[17]

Let us turn now to our polygon formed by the various centres of psychic automatism. Polygonal reactions, such as writing or speaking, exceed both simple reflexes and bulbo-medullary associated acts in complexity; they are to all appearance spontaneous and in a certain measure intellectual, but they are neither free nor conscious--attributes that distinguish the functions of the centre O, the seat of the personal, conscious, voluntary, responsible ego. The polygon consists of receptive sensory centres for hearing, vision, and general sensibility, and of transmitting motor centres for speaking, writing, and various body movements. They all communicate with each other, with O, and with the periphery, so rendering possible voluntary modification of automatic action. In some cases, on the contrary, there may be a sort of dissociation between O. and the polygon, when the activity of the latter becomes supreme, as during sleep--we dream with our polygon--or in distraction.

In states intermediate between the physiological and the pathological, pure independent polygonal action may reveal itself in the remarkable phenomena of nightmare, the divining rod, table turning, automatic writing, etc., while certain aphasias and agraphias, somnambulism, catalepsy, and various hysterical conditions constitute the pathology of the polygon.

The fact that all mental attributes and functions are situate in O definitely negatives, in my opinion, any classification in the category of mental diseases of such conditions as hysteria, so many of whose manifestations are polygonal alone.

Our second group of tics--polygonal tics, we may style them--are correspondingly associated, co-ordinated, and psychical, but not mental; they have nought to do with the superior psychism of O.

Finally, in direct and strict dependence on an actual idea is a third group of tics, the psychical tics properly so called.

We have reproduced Grasset's theory in some detail since it is one of the two most recent contributions to the study of the tic's pathogenesis. The other is that of Brissaud.

An apparent lack of harmony between the rival hypotheses is, we shall see, due rather to a difference in the interpretation of certain terms than to a real opposition of ideas.

Brissaud's view that the tic is a co-ordinated automatic act and consequently cortical is objected to by Grasset. Every automatic co-ordinated act is not of necessity cortical. Conjugate deviation of the head and eyes may be of bulbar origin; certain spinal movements even may be no less co-ordinated and automatic. The decerebrate animal's walk may be perfect in its co-ordination.

Careful analysis shows the divergence of opinion to arise merely from a differing significance attached to the word origin. Brissaud is considering the origin of the tic in time, at the moment of its appearance; Grasset its origin in space, at the seat of its production. Once the tic is constituted, its repetition each moment is a manifestation of polygonal activity, but it is none the less true that the movement which has degenerated into a tic had its source in cortical, _i.e._ psychical, activity.

Any one who appreciates the import of Grasset's ideas will readily understand his terminology; it is at the same time expedient that the possibility of ambiguity in the use of words etymologically synonymous should be avoided. Now, however judicious be the distinction he draws between psychical and mental, it is to be feared it is not always adequately grasped: we do not intend, therefore, to employ either mental or psychical tic in our vocabulary, still less "psycho-mental" tic (Cruchet). As for bulbo-medullary tic, it appears to us to be identical with spasm as we have defined it, unless indeed it is to be taken as signifying a tic begotten of a spasm, in which interpretation Grasset and Brissaud both acquiesce.

TIC AND FUNCTION

We must now pass on to elaborate our conception of tic as a disordered functional act.

The term function is employed to denote various biological phenomena differing widely in manifestation and design. Vegetative functions such as digestion, circulation, urination, etc., are regulated by a special unstriped muscle system, the mechanism of which cannot be suspended by cortical interposition; hence under no circumstances can its derangement bring a tic into being.

Other functions, subserved by striped muscles, come within the range of voluntary activity. Some--_e.g._ respiration--are essential to the maintenance of life, and scarcely to be differentiated from those we have called vegetative. Others, such as nictitation, mastication, locomotion, are no whit less important, since their cessation, in the absence of extraneous aid, would speedily have a detrimental effect on the organism. They too are in a sense vital.

Others, again, such as expectoration, are useful, though not indispensable. Some people labour under the disadvantage of being unable to expectorate, but it is not a fatal defect. The function is not universal.

Finally, let us take once more the case of the child.

As he grows up he passes by easy transitions from the voluntary to the automatic stage. He is taught to swim, and swimming soon rivals walking in the unconcern with which the movements are executed; he learns to write, and no less rapidly does the act become one of unconscious familiarity; his games, his exercises, the labour of his hands--be it digging or typewriting--all reach the level of regular automatism; in short, they are functional acts as truly as locomotion or even respiration, with the qualification of being neither essential nor general.

Such examples serve to illustrate the comprehensiveness of the term functional, and embody all the intermediate forms between what is inherently vital and what is purely acquired. When we have to deal in practice with a case of functional disease, discrimination is obligatory from the standpoint of prognosis. We are alarmed at our patient's respiratory embarrassment, not at his impaired caligraphy.

A distinction has also been drawn between _functional_ and _professional_ affections, profession being conceived as a function of the individual in relation to society. But the latter term has the drawback of being too exclusive. As a matter of fact, scriveners' palsy is met with in people who, so far from being professional writers, do not use the pen much at all. Nor is it necessary to be a professional pianist to develop pianists' cramp. It would be more accurate to speak of disturbances in "occupation acts," it being understood that these have by dint of repetition acquired the automatic characters of true functional acts.

* * * * *

Let us consider for a moment the salient features and component elements in our conception of function.

First and foremost is repetition. It is an absolute law, this of the periodicity of function, and strikingly exemplified in the case of the circulation, digestion, urination, etc. Regularity of rhythm is no less obvious in the muscular activity of mastication, locomotion, and respiration, and its degree seems to be in direct proportion to the duration and vital importance of the particular function.

The characters of this rhythm may be influenced by various extraneous causes. A painful stimulus makes us blink or quickens our respiration. The will may intervene, to accelerate or retard. The personal factor accounts for individual differences, but for each individual a certain rhythm and amplitude of movement, suited exactly to the end in view and conforming to the natural law of least effort, may be regarded as normal. It is only in pathological cases that this law admits of exceptions, and these we shall now proceed to investigate.

Disobedience to the law in the shape of exaggeration or redundance of purposive movement indicates functional excess. For instance, the object of the function of nictitation is to moisten the conjunctiva. In its evolution the child's unmethodical reaction gives place to the rhythmical automatism of the adult. Perfection is the fruit of education.

But the person whose impetuous and uninterrupted blinking far exceeds the demand of the eye for lubrication is plainly troubled with excess, with "hypertrophy" of function. Herein may consist a tic, and, in fact, a large number of tics are nothing more than functional derangements of this kind.

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.

An individual as he moves his arm one day becomes aware of a cracking feeling in his shoulder-joint, and from the unwonted nature of the sensation emanates the notion that he must have some form of arthritic lesion. Renewal of the gesture is attended with reproduction of the sound. The thought of a possible injury develops and extends until it is an object of constant preoccupation and becomes a fixed idea. Under its malign influence the movement is repeated a hundredfold and with growing violence until it passes into the field of automatic action. It is typically functional in its repetition, in the association of desire and satisfaction; but it originates in an absurd idea, and is actuated by a meaningless motive: its range is exaggerated, its performance irresistible, and its reiteration pernicious. In fact, it is a tic.

We may thus regard tic as an obsolete, anomalous function--a _parasite function_--engendered by some abnormal mental phenomenon, but obeying the immutable law of action and reaction between organ and function, and therefore just as prone to establish itself as any motor act of the physiological order.