existence of neuritis, the wasting of the muscles and the anesthesia indicate structural damage to the nerve-fibres, and preclude any other explanation. There is every gradation between these severe forms and those which are slight, and the symptoms in the latter are identical with those of the earlier stage of the severe cases.

The symptoms find their explanation in the character of the morbid process, and the facts of neuritis in general, already described, apply to this disease in every point. It is primarily a perineuritis; the pain in the nerve and its tenderness are due to irritation of the sheathnerves. The pain referred to the distal portions of the nerve is due to the irritation of the proper fibres by the interstitial inflammation, while their greater damage explains the anesthesia and muscular wasting. DIAGNOSIS.-The diagnosis of sciatica rests on the position of the pain on the relation of this to the trunk of the nerve, and to its area of distribution. But the recognition of this relation does not alone suffice for the diagnosis. We have to consider the distinction from other pains in the sciatic area, to discriminate, if we can, sciatic neuritis from sciatic neuralgia, and to decide whether the affection of the nerve is primary, or is secondary to mischief outside it. It should be needless to say that pain felt only on the outer side of the thigh is not sciatica, although the name is sometimes applied to such cases, apparently because, some name being needed, that of the nearest affection is chosen.

Branches of the sciatic nerve and sacral plexus ramify over the hipbone, and pain in sciatica may be felt near the hip-joint; hence disease of this joint and sciatica may be confounded. The pain in simple disease of the hip-joint does not extend down the back of the thigh in the course of the sciatic, and there is no tenderness of the nerve. The danger of this error is not great if a careful examination is made, and has been much exaggerated by writers unfamiliar with the characteristic symptoms of true sciatica.

The distinction between a sciatic neuritis and a sciatic neuralgia is sometimes difficult, although less frequently than might be inferred from current accounts of these diseases, in which the history of the neuralgia has been written from the symptoms of the neuritis. If we recognise that all cases of sciatica with persistent tenderness of the nerve are really neuritic, cases of sciatic neuralgia become extremely rare. The two diseases occur usually under different conditions: the subjects of neuralgia have often suffered from neuralgia elsewhere, and are generally weakly and anæmic. The pain is from the first spontaneous; posture has little influence upon it; movement is not itself painful, although it may excite paroxysms of pain. The pain is referred to the branches and distribution of the nerve rather than to its trunk, or it darts up or down the trunk; and tenderness of the nerve, if it exists, is altogether subordinate to the spontaneous pain. Secondary sciatica is usually produced by disease of bone about the hip-joint, or of the joint itself, or by disease in the pelvis. In the

former case a careful examination (never to be omitted in any case of sciatica) at once reveals the mischief. When the disease is within the pelvis, the tenderness of the trunk of the nerve is slight in proportion to the pain, and this circumstance should always lead to a careful search for any indication of pelvic mischief. In any case of doubt a rectal examination should be made.

Sciatic pain occurs in some diseases of the bones of the spine, in lesions of the cauda equina, and occasionally in disease of the spinal cord itself. In these cases we have little or no tenderness of the nerve; the pain is chiefly peripheral, and very often bilateral. Double true sciatica is so rare that bilateral pain should always suggest disease of the nerve-roots. The pains of locomotor ataxy are often felt in the sciatic area, and occasionally follow the course of the sciatic nerve; but their wider range, their fugitive character, and their association with other symptoms of tabes, should prevent an error.

PROGNOSIS. The prognosis of sciatica, not dependent on disease outside the nerve, is always good as regards ultimate recovery. As a general rule, the probable duration of the disease is proportioned to the severity of the symptoms. The practicability of adequate rest is an important element in the prognosis. Irritating exertion may lengthen the duration of the disease by many months, and indeed relapse may follow each partial recovery until one or even two years may pass before the sufferer at last beco'nes free from pain. When the nerve is so sensitive that the patient cannot stand, the affection will continue for some months.

TREATMENT. The principles of the treatment of sciatica are those of neuritis already described, and only the points of special importance need be here repeated. In all cases rest to the limb is essential, and its urgency is proportioned to the acuteness and severity of the symptoms. Many slight cases are converted into severe ones by unwise exertion. All postures and all movements which increase pain should be avoided. The same principle applies to mechanical compression of the nerve by hard seats, and by strong contractions of the flexors of the knee. In more positive treatment the possible causes of the disease must be remembered. In gouty cases saline purgatives are often of signal service, and are distinctly useful in preventing attacks in those who are liable. In the acute stage of a severe attack, hot linseed-meal poultices should be applied along the course of the nerve. Counter irritation is of great value, and cannot be employed too early. A commencing attack may often be cut short in a few days by rest, and a series of mustard plasters or small blisters applied over the seats of pain, as this changes under their influence, chasing it, as it were, from one spot to another, until it disappears. Internally, whenever there is reason to believe that active inflammation exists, mercury should be given a grain of blue pill twice daily; nothing else seems distinctly to influence the process. Salicylate of potash or lithia and nitrous ether should also be given at the onset-soda salts being avoided. Sponta

neous pain can only be relieved by sedatives. Morphia is the surest, but it should only be used for the relief of severe spontaneous pain. In no malady has cocaine proved of more signal service. It should be injected pretty deeply at the seat of pain, but never into the nerve. One twelfth of a grain may be first used, increased rapidly to a third or half a grain. It relieves pain, although not in the same degree as morphia, but it has a powerful action in promoting the subsidence of the inflammation. as described in the account of neuritis. Morphia, although equally effective elsewhere, may also be injected with advantage over the inflamed part of the nerve, so as to combine the counter-irritation of cutaneous acupuncture with some local as well as general sedative influence. Simple acupuncture along the course of the nerve has been recommended; it gives temporary relief to the sciatic pain, as does any superficial pain, but the cases are very few in which it has a permanent effect. Sedative or counter-irritant liniments and ointments may also be applied along the course of the nerve; the most useful are belladonna liniment mixed with an equal part of chloroform liniment, and aconite ointment, rubbed in until distinct tingling is produced. Electricity is chiefly useful in the later stages; its method of use has been described in the account of the treatment of neuritis. In very obstinate cases, nerve-stretching has done good; sometimes, perhaps, by releasing the nerve from compressing adhesions, but probably more often by effecting an energetic counter-irritation, and enforcing a beneficial rest.

To prevent recurrence the causes should be carefully avoided, and any gouty state lessened by an appropriate regimen. Slight threatening pain should be met by more rest, counter-irritation by sinapisms, and the careful avoidance of sudden movements especially. If there is the sacro-lumbago that often precedes sciatica, the pain produced by rising from a seat may often be lessened by a few moments' rubbing.

MULTIPLE NEURITIS.

The term "multiple neuritis," or "polyneuritis," is applied to the condition in which many nerves are inflamed simultaneously or in rapid succession. This multiplicity is its most obtrusive feature. In most forms, moreover, the nerves affected are the same on the two sides; the neuritis is not only multiple, it is symmetrical; and when, as is sometimes the case, only a few nerves are involved, even one only on each side, the symmetry becomes a more salient feature than the multiplicity. Another important characteristic is its peripheral distribution; usually most intense at the extremities of the nerves, it lessens progressively towards the centre, commonly ceasing long before the nerve-roots are reached. Hence it has also been termed "peri

pheral neuritis," a name that is accurate but somewhat confusing, inasmuch as the term has been applied to affections of nerve-trunks generally, in distinction from central diseases causing similar symptoms.

The discovery that certain combinations of symptoms, formerly thought to depend on disease of the spinal cord, are really due to disease of the peripheral nerves, is one of the most important steps in the recent advance of pathology. It has profoundly modified many of our conceptions, not only of the processes of disease, but of the range and action of certain morbid influences, and has shown that much of our supposed knowledge of the central affections of corresponding aspect was erroneous, and the history of these maladies has to be reinvestigated.

The occurrence of multiple neuritis was first demonstrated by Duménil, of Rouen (1864), although the leprous form had been previously described by Virchow. Graves, indeed, long ago suspected that many cases of paralysis were due to disease of the nerves, but he based his opinion on the normal aspect of the spinal cord; and in most of the cases he describes it is probable that modern methods of examination would have revealed disease. Naturally, also, symptoms so peculiar had attracted the notice of clinical observers, and were described from time to time; first, perhaps (1822), by Dr. J. Jackson, of Boston, U.S.A., and, much later, but fully, by Duchenne (1858).* Duménil's observations attracted little notice, and it was not until fresh facts were brought forward by Joffroy (1879), Leyden (1880), and Grainger Stewart (1881), that attention was generally directed to the subject. During the last ten years a very large number of observations have been published, and the general history of the disease is now established on an adequate basis.

The peculiarities of distribution of multiple neuritis harmonise with what is known of its pathology. In isolated neuritis the primary affection is of the nerve-sheath and connective tissue-the neuritis is "adventitial;" in the symmetrical multiple forms the nervefibres themselves are almost always the seat of the primary process; the connective tissue and sheath suffer secondarily and in proportion to the acuteness of the process in the nerve-elements-the neuritis is "parenchymatous."

The forms of multiple neuritis which are thus characterised by their symmetry and parenchymatous nature are due entirely to a morbid blood-state having a direct influence on the nerve-tissue. Their cause is the presence in the blood of some virus, often an organic

The first ascription of a form of paralysis to this lesion was by Dr. Todd, in the case of lead palsy. "I believe that the muscles and nerves are early affected, and that at a later period the nerve-centres become implicated. The nervous system is thus first affected at its periphery, in the nerves, and, the poisoning influence continuing, the contamination gradually advances towards the centre" (' Clin. Lect., 1854, p. 9).

or inorganic chemical compound, to which the nerve-fibres are sus ceptible, just as they are susceptible to curara, or the motor-cells to strychnia, or the nerves for accommodation to atropia. It is an instance of what has been termed "selective action," the manifestation equally of a peculiarity in the acting virus and in the structures acted on. The peripheral distribution of the affection is probably due to the fact that the vital and nutritional energy of the nerve-fibres lessens with the distance from the cells of which they are part, and from which their vitality is derived. The relation to a blood-state as the cause explains also the symmetry of the affection, since the like structures on each side possess the same characteristics, and, being equally exposed to the morbid influence, there is no reason why the nerve-elements on one side should suffer alone, or even in less degree, than those on the other side.

Isolated neuritis may be caused in part by a constitutional or blood state, but is not due to this alone; some exciting cause is in operation, acting locally and determining the position of the affection. Hence it is rare for such neuritis to be multiple, and when more than one nerve is affected the distribution is irregular and not symmetrical. Gouty neuritis affords an illustration of this. Moreover, in these forms the connective tissue, and especially the sheath of the nerve, is the part primarily affected, and the nerve-fibres are damaged only in a secondary manner. Between the two chief forms of neuritis, the isolated or irregular adventitial and the parenchymatous symmetrical forms, there is thus an essential difference.

Between the two classes, however, certain forms seem to cccupy an intermediate position. These are the forms of multiple neuritis in which sometimes the one and sometimes the other element in the nerve seems to suffer most, or in which both are involved. We must, however, distinguish from these the cases in which mere acuteness of the process causes both elements to be involved; in which, for instance, a very acute parenchymatous neuritis causes some degree of adventitial inflammation, or acute adventitial inflammation involves the nerve-fibres. These cases conform in distribution to the type to which they belong; the primary parenchymatous neuritis, and it alone, being strictly symmetrical. But there are other cases in which the causes are combined. Alcoholism, for instance, the most common toxic cause, may be due to a mode of life that has also produced gout, and then isolated gouty perineuritis may accompany general polyneuritis of parenchymatous nature and symmetrical distribution. Exposure to cold, again, may cause a "rheumatic" perineuritis, either of a single nerve, or of a few nerves irregularly distributed; and it may also produce a blood-state allied to that of acute rheumatism, and thus a symmetrical parenchymatous polyneuritis. An important cause of neuritis is toxæmia due to the development of specific organisms in the blood, sometimes those that cause a definite disease, as diphtheria or smallpox. Such organisms seem occasionally