Disease of the external nerve produces anæsthesia of the skin on the outer half of the sole, the little toe aud half the fourth, paralysis of the flexor accessorius, the muscles of the little toe, all the interossei, the two outer lumbricales, and the adductor of the great toe. The effect of this palsy (see p. 45) is serious, since the toes cannot take their proper share in propelling the body forward in walking, and they gradually become flexed at the last two joints and extended at the others, from the contracture of the opponents of the interossei,-aposition of the toes that causes serious inconvenience in walking.

DIAGNOSIS.-The diagnosis of diseases of the nerves of the leg is determined by the same general principles as those that have been mentioned as applicable to the nerves in general, and to the nerves of the arm in particular. The limitation of the symptoms to the functional areas of individual nerve-trunks, the evidence afforded by nutrition, irritability, and reflex action that the muscles are separated from the spinal cord, the implication of the sensory functions, and often the tenderness of the affected nerves, indicate, in most cases, the seat of the disease. To these signs, are often added other indications of a local cause, corresponding, in its position, with the nerve to which the symptoms point.

The relation of nerve-trunks to nerve-roots, although by no means simple, is certainly less complex in the case of the nerves of the leg than in those of the arm. This is especially the case in the lumbar plexus, and it leads to an occasional difficulty in diagnosis. Pressure on the spinal cord, for instance, at the level of the origin of the fourth lumbar roots, may cause symptoms identical with those of a partial lesion of the anterior crural nerve. For instance, I have known paralysis of the extensors of the knee, loss of the knee-jerk, with anesthesia in the frout of the thigh, to be the result of a gumma at the side of the cord at this level. But other evidence of a spinal lesion is rarely absent under such circumstances, and, in this patient a foot-clonus, due to the pressure on the pyramidal fibres, left no doubt as to the situation of the disease. Another difficulty arises from the long course of the nerve-roots in the cauda equina, disease of which may simulate that of the nerves of the leg. But the symptoms are commonly bilateral in consequence of the proximity of the nerve-roots of the two sides. In all cases in which symptoms are bilateral (unless there is evidence of a disease known to cause symmetrical lesions, such as multiple neuritis), the suggestion is that the disease is situated where the motor or sensory paths of each side are so near that they can be affected by a single lesion, i. e. that the disease is within the spinal canal. But here, as in other cases, we cannot reverse our diagnostic rules. Disease of the spinal cord does not always cause bilateral symptoms. A limited lesion of one anterior cornu may be so placed as to paralyse the muscles supplied by a single nerve, and a doubt may be felt as to the central or peripheral origin of such palsy. The muscles supplied by the anterior

crural nerve, and the muscles in the front of the lower leg supplied by the external popliteal, are those of which the central palsy most often leads to doubt. The mode of onset, the presence or absence of sensory symptoms, the rarity of acute spinal palsy except in childhood, and of nerve-lesions except in adult life, the wider initial prevalence of the palsy in acute, and its later extension in chronic, cornual disease,-these suffice as a rule to remove any doubt.

It is important to remember that the pressure of a growth may cause either a chronic or an acute affection of the nerves. The chronic symptoms result from compression; the acute from a neuritis set up by the pressure and irritation.

TREATMENT.-The treatment of disease of the nerves of the leg does not differ from that of disease of the nerves of the arm. More care, perhaps, is needed to avoid increasing present mischief, or inviting a relapse, by exposure to cold or by fatiguing exertion. More care is also needed to obviate the tendency to secondary contractures in the case of palsies of long duration, and in those attended by pain, in which the patient seeks ease in postures to which the muscles only too readily adapt themselves. The contraction of the hamstrings, from constant flexion of the knees, occurs very readily and is most troublesome; that of the calf muscles, which occurs when the flexors of the ankle are paralysed, also constitutes a serious obstacle to walking after recovery. A little timely care, by attention to posture, will often save a vast amount of later trouble. That of the calf muscles, however, which is due to the extension produced by the weight of the foot, as the patient lies, cannot always be entirely prevented, but may be lessened by a board or large sand-bag against which the feet can rest.

PRACHIAL NEURITIS.

Besides the forms of inflammation of the nerves of the arm already described, a primary inflammation of the brachial plexus occurs in a form as well defined as sciatica, and equally meriting a separate description. This, however, need only include its special features; those that are common to other forms of neuritis have been already described. It is so closely analogous to sciatica that it may be called "sciatica of the arm." It is essentially a perineuritis,-a primary inflammation of the sheaths of the branches that enter and form the brachial plexus.

Cases occur, however, in whicn the symptoms correspond in general character to the rest, but in which their distribution suggests that the nerve-roots rather than the plexus are the seat of the inflammation, and pain about the spine supports the opinion. This form may be called Radicular Neuritis. Although its existence has not been

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established by pathological evidence, the symptoms mentioned adinit of no other explanation. A knowledge of their significance is of great practical importance on account of the closeness with which they may simulate those of organic disease of the bones of the spine, or a growth in the spinal membranes.

CAUSES. The influence of gout in causing local neuritis is very conspicuous in the brachial form, with the special characteristic that this occurs chiefly late in life, very often from the inherited disease, and with greater frequency in females than any other form of neuritis; their liability is at least equal to, if not greater than, that of men. Five-sixths of the cases occur after fifty, and it may be met with up to extreme old age. In men there have usually been the ordinary manifestations of gout, but in women the tendency is often only indicated by the family history, and by previous muscular rheumatism, especially lumbago and sciatica,- which have seldom been absent in either sex. In one case the onset of the brachial neuritis occurred immediately after an attack of sciatica.

SYMPTOMS.-Pain, the great symptom of the inflammation of all mixed and sensory nerves, is greater in this than in most forms of neuritis. It is usually the first symptom, and lasts long after the inflammation is over; its severity, coupled with the age of most sufferers, renders the malady one of a peculiarly trying character. The first pain is often referred to a distance from the seat of the inflammation, perhaps because this begins at the plexus, where, at divisions, it is facilitated by motion, and the conducting fibres are readily reached and early irritated. Frequent seats for the first pain are the region of the scapula (sometimes beneath the bone) and the wrist or back of the forearm, with or without the hand. In other cases, however, the first pain is at the plexus itself, above the clavicle or in the axilla, and these are the places in which it is commonly most intense throughout the attack. As the pain increases it extends along the course of the nerves of the arm, which the patient will often accurately indicate with his finger when tracing the lines of pain.

The pain is sometimes sudden in onset and severe from the beginning; more often it is at first occasional, or felt on certain movements, but, as it increases, it becomes more continuous, with variations that soon rise to paroxysmal degree. Ultimately there is always more or less dull wearying pain in the whole arm, but especially in the region of the plexus, varied by attacks of great severity. In these the pain is acute and lancinating, or stabbing, or burning; it usually takes the course of the nerves, diffusing itself from them, and often passing to the side of the chest, and to the neck,- seldom to the head. pain often varies in character according to intensity; at the height of the paroxysm it may be sharp and stabbing, or such darting pains may be superadded to a more diffused burning pain, which lasts longer than the acute pain, and may be followed, as the paroxysm subsides, by general tingling of the skin of the whole limb. The paroxysms are

The

induced by movement or occur spontaneously. In slighter cases the pain is paroxysmal only, and then the relation to movement is a very conspicuous feature. Although it is seldom confined to movement, this never fails to induce severe pain, and the patient avoids the slightest use of the limb. Elevation of the arm especially causes distress.

With the pain there is usually undue sensitiveness of the skin, which may be much increased during and after the paroxysms. Loss of sensation is rare, and is met with only in cases that are not only severe but prolonged. The two may concur, as anesthesia dolorosa." The muscles usually present the flabbiness and slight wasting common in neuritis, but the damage to the motor fibres is seldom sufficient to cause considerable atrophy. Sometimes, however, there is enough damage to cause wasting of some group of muscles, with the reaction of degeneration. This is most frequent in the radicular form, in which the damage is to the upper part of the plexus and nerveroots. There may then be anesthesia of the skin over the affected muscles. It is difficult to ascertain the existence or the amount of motor weakness; effort induces pain so readily that the patient can seldom be induced to make an attempt to exert force. Power is often said to be almost lost, when it is probably greater than is believed. Besides the muscles, the subcutaneous tissue of the limb may also waste, and the skin may become thin and shining, and present the aspect already described. Subcutaneous cedema is also common. Arthritic changes in the joints of the fingers are almost constant in the cases that occur in later life; the adhesions may be permanent.

DIAGNOSIS. Few maladies, as a fact of experience, give rise to greater diagnostic difficulty. This is due to several causes: the affection is rare; its symptoms are sometimes equivocal; the subjects are usually in the degenerative period of life, when many obscure diseases attended with pain in the arm occur to the mind of the physician; and lastly, the distinction between neuralgia and neuritis is often difficult, although less so than is supposed. The last is indeed the most frequent source of error. The most severe and characteristic cases of brachial neuritis are frequently mistaken for pure neuralgia, on account of the paroxysmal character of the more severe pain, and because the characters of neuritis are unfamiliar. The points to determine the diagnosis are those described in the sections on neuritis and neuralgia; -the degree of persistent tenderness of the nerves and the influence of movement, together with the history of the attack, the locality of the pains, and especially any evidence of damage to the fibres. A history of neuralgia in the person or the family is of slight weight only; the tendencies to true neuralgia and to neuritis are often combined, and each is a frequent result of gout. A far greater difficulty is presented by the cases in which the inflammation remains slight and is confined to the plexus, affecting branches where the conducting fibres can be so irritated as to cause distant pain, which then becomes the leading symptom. This is often paroxysmal, and, when on the left side, may

radiate to the chest and be associated with disturbed action of the heart. Angina pectoris is often thought of in such cases; and here again the degenerative age may increase the difficulty by leading to the presence of some coincident disease of the heart, or by making true angina not unlikely. The distinction afforded by the nerve-tenderness is then of great importance, because the disproportionate amount of tenderness (compared with the amount of pain) is more emphatic in slight than in severe cases. Persistent tenderness with only paroxysmal pain should always suggest neuritis. When the position of the pain is carefully examined, its relation to the plexus and branches is often clear. It is important to remember that all nerve-pains in the brachial region on the left side have a tendency to resemble anginal pain in distribution, and to be associated with cardiac distress. Probably there is some peculiar tendency for pains in this part to disturb the action of the heart; a common physiological relation may underlie both the nerve-pains of cardiac angina and the cardiac symptoms of nerve-pains. Hence this secondary disturbance does not neutralise the significance of the special signs of neuritis. In some cases of the slighter class, the pains suggest the idea of an aneurism; in many cases of brachial neuritis this diagnosis has been made, and the patient has had to endure months of mental distress, for which no real cause was in existence. Such a suspicion, in the absence of special signs, such as pressure-symptoms, should only be entertained if the pains are persistently and increasingly severe, and unaccompanied by any considerable amount of tenderness. In all these cases, moreover, the presence of the gouty diathesis may be allowed weight in the diagnosis.

The muscular wasting, slight in degree, added to the arthritic changes, gives rise to a condition which may be mistaken for a primary joint affection with secondary "arthritic atrophy" of the muscles. It is only in the chronic stage that this error is possible. A careful attention to the history of the case will show its real nature, but without this attention the mistake is easy, and it is often made.

PROGNOSIS. Except in its most trifling degree, brachial neuritis is a tedious malady; the duration of every severe case is to be measured by months, and often more than a year elapses before the patient is free from pain. Post-neuritic pain is always more prolonged in the old than in the young, and the age of the subjects, together with the amount of damage to the nerves, causes suffering to last longer than in almost any other form. To these causes also must be added the degree of sensitiveness of the affected nerves, exceeded only by that of the fifth nerve, and also the mobility of the parts in which the plexus lies; this involves a continued cause of irritation, brought into play as soon as the diminution in the severer pain permits the patient to employ the long useless arm. Relapses, moreover, are not uncommon. Recurrence may take place after moderate attacks, but seldom occurs after those of extreme severity.