the back; any sign of deep edema among the muscles beside the vertebral column, in such a case, is probable evidence of commencing purulent inflammation extending from within, and the development of acute local inflammation in either the pleura, posterior mediastinum, back of the abdomen, or behind the pharynx, has the same significauce. It is important that the nature of such symptoms should be kept in mind, as otherwise their occurrence increases the perplexing character of the case. It is probable that the nature of many cases, which remain undecided during life, would be rendered clear by repeated careful observation.

PROGNOSIS.—The acute affection is exceedingly grave. Recorded cases have ended in death, but this termination has been a condition of the diagnosis; and it is possible that some cases which have recovered, in which the exact seat of the inflammation was uncertain, may have been instances of this form, and that the fatality of the disease may not be so great as published facts suggest. But on this point only future observations can throw light. Chronic external meningitis which results from caries is only serious in the compression it exerts on the cord. TREATMENT. The local form alone affords an opportunity for effective treatment. The first and most important element is the treatment of the original cause of the disease, the caries, &c., to which the meningitis is secondary. Any accessible collection of pus should be opened, and if acute local symptoms, in a case of bone disease, suggest the passage of pus into the vertebral canal, the propriety of immediate trephining should be considered. Rest, counter-irritation to the spine, especially the actual cautery, sedatives to relieve the pain, and tonics are the most important measures in chronic cases. So far as the acute form is open to treatment, the measures suitable are those for the internal variety. In a subacute case, a free exit should be afforded to the pus. An opportunity for this very seldom presents itself, but may perhaps be furnished by sufficiently frequent examination more often than has hitherto been the case.

INTERNAL MENINGITIS.

Internal meningitis, inflammation beginning within the dura-matral sheath, may be either acute or chronic. The acute form usually commences in the pia mater and arachnoid; the chronic forms may begin in these membranes, or in the inner surface of the dura mater. Little is known practically of any separate affection of the arachnoid.

ACUTE INTERNAL MENINGITIS.

Internal meningitis, for the reason already mentioned, has been termed "leptomeningitis," but the acute form only remains limited to those membranes when of slight degree. In some cases the inner surface of the dura mater is also inflamed. Frequently the inflammation extends rapidly to the cord, and to such cases the term "meningo-myelitis" is often applied; in other cases, strange to say, no extension to the cord takes place. The inflammation may be either simple or purulent, or it may be secondary to tubercle. It also occurs in conjunction with cerebral meningitis in the epidemic form. Acute simple spinal meningitis is a rare disease.

The immediate causes that have been traced are in part such as have a local action; in part they are general morbid influences, such as give rise to other internal inflammations, and have been effective in causing meningitis in consequence either of some personal predisposi tion, or in consequence of a peculiarity in the agent, which led to a specific action on these structures.

(A) The local causes may be-(1) Injuries to the spine, severe or slight, from fracture to simple dislocation; concussion; surgical procedures, such as an operation on the vertebral column, or the puncture of the sac in spina bifida. (2) The exposure of the back to cold has been the apparent cause in rare cases; and still more rarely the prolonged exposure of the spine to the sun, "spinal insolation," has seemed to be effective. (3) Adjacent inflammation has sometimes caused internal meningitis, but in such cases external meningitis has of necessity been first produced, and the inflammation has passed through the dura mater. Hence, all the causes of acute external meningitis are also occasional causes of the internal form. But, as already stated, such extension through the sheath is very rare, and there is some doubt as to the precise nature of many of the cases in which it has been supposed to occur. We have seen that in many of the instances in which external meningitis has been ascribed to adjacent suppuration, the latter has been secondary, and the meningitis has been the result of a primary blood-state. When in such cases there has been both internal and external meningitis, it is probable that the former has not been due to actual extension through the dura mater, but that both have been the simultaneous result of a general cause.

(B) In a few cases acute internal meningitis is due to the extension of inflammation from the cerebral membranes. Such extension is rarely traced, however, except in two classes of cases :-(1) Those in which slight meningitis is found in the upper cervical region, as far as gravitation favours the descent of solid particles in the cerebrospinal fluid as the patient lies in bed. The inflammation ceases when the spine becomes horizontal; for the most part symptoms are slight or absent in such cases. (2) In cases in which a general spinal

meningitis has been secondary in point of time to inflammation of the cerebral membranes the affection has generally been due to some cause capable of acting upon both, such as the local presence of tubercles or a morbid blood-state of the character to be immediately mentioned.

(c) The most acute and severe forms of internal meningitis are due to a morbid blood-state, either septicæmia or a virus allied to that which causes the cerebro-spinal form. Purulent meningitis occurs in cases of surgical and puerperal septicemia, both with and apart from a similar affection of the cerebral membranes. Acute inflammation, purulent when intense and prolonged, occurs also as an isolated malady, sometimes without apparent exciting cause, sometimes after exposure to cold. In such cases organisms have been found in the spinal fluids, analogous to those of the cerebro-spinal form, in connection with which the pathological relations will be more fully considered. It probably results from a blood-state not far removed from those which cause some other forms of internal inflammation, and which give rise to acute articular rheumatism. General exposure to cold must be assumed to cause so special an effect only through the agency of toxæmia, such as that which has been already considered as underlying the rheumatic form of acute polyneuritis. Such exposure has been apparently rendered effective in some instances by coincident menstruation, which may have produced a special susceptibility to the attack, or favorable conditions for the development of some organised virus, such as seems to be the essential factor in the causation of these forms. The exposure to cold that has been effective has presented all the variations that are met with in the case of other diseases thus produced, variations which are common to so many maladies that they can have no special relation to any one of them. Lastly, as a crucial example of this origin of the disease, is the important fact that it may follow, or occur in the course of certain acute specific diseases, as one consequence of the virus that produces them.

In the case of a precise level at

PATHOLOGICAL ANATOMY.-Internal meningitis is usually of wide extent, since the inflammation spreads readily in the loose tissue of the arachnoid. Probably also the movement of the cerebro-spinal fluid aids in the extension of local forms and in the descent of intracranial inflammation by conveying irritant material. patient who had been in bed for some time the which such slight descending meningitis ceases may be that at which the vertebral column becomes horizontal. In the earliest stage the only change is congestion in the pia mater, which is reddened from vascularity, and may be dotted with ecchymoses. The inner surface of the dura mater, and the substance of the spinal cord, may be similarly congested. When the inflammation is further advanced, in the stage in which the condition most often comes under observation, the pia mater and arachnoid are opaque and thickened, and an

"exudation" of inflammatory products, greyish yellow in tint, may cover the pia mater and occupy the meshes of the arachnoid, forming a layer over the cord. This exudation varies in its consistence, and may be semi-purulent in aspect; in the suppurative form the membranes are infiltrated with pus, which also covers their surface. The inner surface of the dura mater usually presents similar changes, and the inflammatory products may fill up the whole space between the dura and pia mater, thus connecting the two membranes and surrounding the nerve-roots (Fig. 90). The microscope shows abundant leucocytal elements, and the larger round and spindle cells that are common in all inflammatory products. The former corpuscles,

FIG. 90.-Purulent meningitis; portion of spinal cord and membranes; the space between the pia mater and dura mater is occupied by inflammatory products, pus, &c., in which the nerve-roots, n n, are embedded. a a. Cavities which had apparently been filled with liquid pus. From a case of septic origin, secondary to caries of the jaw.

FIG. 91. From the same; meshes of arachnoid infiltrated with pus-corpuscles. A nerve-root, n. r., although surrounded by pus, is perfectly normal; and so also are the pia mater, p. m., and the peripheral layer of the spinal cord, s. c.

which resemble, and are probably identical with pus-corpuscles, may be abundant, even when the exudation has not a distinctly purulent aspect; when it has, they constitute almost the whole of the material, lying among the fibres of the arachnoid (Fig. 91). The vessels are dilated, and their sheaths distended with cells. The spinal fluid is increased in quantity, and turbid from flocculi, or even purulent in aspect. The nerve-roots are covered with exudation, and are often swollen and reddened from invasion by the inflammation. But they do not always suffer, even in purulent meningitis, as Fig. 91 shows, in which a nerve-root is almost normal in aspect, and its sheath is unaffected, although it is surrounded by pus-cells. The spinal cord

is often invaded by the inflammation; it is then reddened, pale, and softened, and the microscope shows the tissue-changes common in other forms of myelitis. The change is always most marked in the periphery of the cord, and may occur in wedge-shaped areas, having the apex directed inwards, and coalescing at the surface. The peripheral arterioles come from the pia mater (see "Vessels "), and the continuation of their perivascular spaces with the lymphatic interstices of the membranes renders it easy to understand the invasion of the cord. Nevertheless, in some cases, especially of purulent meningitis, the pia mater itself is little affected, even when the arachnoid is filled with pus, and in these cases the spinal cord may be normal, as in the example shown in Fig. 90. If recovery takes place, the inflammatory products may undergo cicatricial changes, the membranes remaining opaque and adherent, and there may be a permanent excess of arachnoid fluid. The changes in the cord may lead to sclerosis, widely spread, or limited to certain spots, and from these secondary degenerations, ascending and descending, may develop.

The area affected varies in different cases; the membranes are involved in their whole extent in most acute forms. Usually the affection is greater on the posterior than on the anterior surface; probably on account of the influence of the recumbent posture, which determines the passage backwards of the lymphatic fluids containing material capable of exciting and increasing the inflammation.

In tubercular inflammation the amount of exudation is usually small, and it may be absent. It is often grey and gelatinous in appearance, and in it are scattered the greyish or whitish tubercular granulations. Similar granulations may usually be found in abundance upon the inner surface of the dura mater. Such grey granulations are often found upon the spinal membranes in cases of tuberculosis when there is no inflammation, even when the cerebral membranes are intensely inflamed. The arachnoid, especially that covering the cauda equina, may appear as if dusted over with grey particles, so abundant are the granulations.

In many cases, the signs of spinal meningitis are associated with those of inflammation of the membranes of the brain, especially of those about the base and posterior part of the brain. The continuity of the spinal and cerebral inflammation may be obvious or indistinct. In the latter case, the connecting inflammation has apparently been much slighter than that in the base of the brain or around the cord, so slight, indeed, as to have left no distinct traces, the inflammation having apparently extended in consequence of the passage of morbid material by the cerebro-spinal fluid. In cases of slight cerebral meningitis, in which the patient has been recumbent, signs of spinal meningitis, opacity of the arachnoid and its distension with slightly turbid fluid, may exist only in the cervical region, ceasing opposite the upper dorsal vertebræ, and thus extending as far as gravitation (the head being slightly raised on a pillow) favoured

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