cause, but this influence is exceedingly doubtful, except in the rare cases in which inflammation of a nerve ascends to the cord. In a considerable number of cases we are able to discover no cause to which myelitis can be ascribed. Many of these are probably due to a bloodstate which may have no other consequences or may also cause simultaneous inflammation elsewhere.

PATHOLOGICAL ANATOMY.-In recent acute inflammation of the cord, the pia mater, at the affected part, is usually red and vascular, and the cord itself may be slightly swollen. Its tissue is reddened and often marbled from distended vessels, and the distinction between white and grey matter is indistinct and lost.

The diminution of consistence which occurs in acute inflammation may be so great that the affected part is diffluent, like cream, and flows out when the pia mater is divided. It does not follow that the consistence is lessened to this degree during life; post-mortem softening occurs more readily at an inflamed part. When the vascular disturbance and extravasation are considerable, the condition is termed "red softening ;" so much blood may be effused into the tissue that the part looks as if there had been an actual hæmorrhage, and in some cases an extensive extravasation does actually exist; this form is termed "hæmorrhagic myelitis." If the inflammation has existed for some time, the effused blood is altered in tint, and the colour of the softened part may be rather chocolate than red. After a longer time the changes in the blood-pigment cause the colour to be lighter, "yellow softening." In many cases the breaking up of the nerveelements (partly, as just stated, post mortem) is out of all proportion to the extravasation of blood, so that the softening is "white." It is said that red and yellow softening may ultimately become white from the removal of the blood-pigment, but the evidence of this is inadequate. The period at which these changes of colour are found varies according to the amount of extravasation at the onset. At a later period the yellow or white opaque aspect is changed to a grey translucent appearance, from the absorption of the fatty products of degeneration, and an increase in the connective tissue. If the myelitis is very limited in extent, cavities may be formed within the cord.

The microscopical appearances in myelitis vary much according to the duration and form of the inflammation. In the fresh state the most conspicuous objects are the products of degeneration of the fibres, granules and masses of myelin, and granule corpuscles, with, in older cases, the peculiar bodies termed corpora amylacea " (Fig. 93, d). With these are numerous red blood-discs, leucocytelike corpuscles, and, after the first week, distinct cells, round, oval, spindle-shaped, or angular, with nuclei which resemble leucocytes in size, and are readily mistaken for them. Fragments of axis-cylinders may also be seen, granular in aspect, and with irregular swellings (Fig. 93, a).

The softened and even diffluent state of the tissue prevents us from learning much, by microscopical examination, of the condition of the parts in which the inflammation

is intense and diffuse, because the breaking up of the tissue and separation of the fragments renders it impossible to obtain sections of the hardened organ. It is only where the inflammation is less intense, or less uniformly diffused, that a thorough examination can be made. The products of degeneration are best seen in the fresh state or in sections mounted in glycerine (Fig 93). The fragments and globules of myelin in part occupy the position of the nerve-fibres from which they have come, in part are aggregated into

masses.

In sections rendered transparent in the ordinary way, the fatty products of the destruction of the nerve-elements are invisible, and the most conspicuous alterations are the dilatation of vessels, which is often

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FIG. 93.-Myelitis. a, an irregularly swollen axis-cylinder. b, section of nerve-fibre with swollen axis-cylinder. c, section of white substance, with granule-masses and atrophied nervefibres. d, corpora amylacea. (From Leyden.)

very great, and the accumulation of leucocytes and other cellelements in the tissue and especially about the vessels. In the white substance the larger vessels are conspicuous by their enlargement, and in the grey substance the dilated arteries and capillaries may occupy a considerable part of the tissue (Figs. 94, 95, A). The nuclei of the capillaries are large and numerous. The walls of the smaller arteries are encrusted with leucocytes in the early stage, and, later on, in both white and grey substance, are much thickened by cells, the nuclei of which are often elongated and more or less concentric to the lumen of the vessel (Fig. 98, D). Outside this thickened wall the perivascular sheath is enormously distended, at first by leucocytes, among which, afterwards, other cells are mingled, round, fusiform, angular, with leucocyte-like nuclei (Fig. 98). In transverse section this distended sheath may look, at first sight, like an enormously thickened wall. Red blood-corpuscles distend the vessels and are seen. also in the adjacent tissue, sometimes uniformly scattered through it (Fig. 98, F), sometimes aggregated in small extravasations due to the rupture of minute vessels. The grey substance is densely set with round corpuscles, staining deeply, many of which are the nuclei of

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small fusiform or angular cells (Figs. 95, A; 97. B) waile the intervening substance is much more granular than in neaith. The nervecells are much swollen and granular, often contain distinct globules, strongly refracting, and probably fatty. The cell-processes appear shrivelled or lost (Fig. 95, A). In slight cases the margins of the cells may be less sharply defined than in health, and the bodies then may contain large vacuoles, sometimes wholly within the cells, some

FIG. 94.-Subacute myelitis, lumbar region; both white and grey substance uniformly affected. In the latter the numerous distended vessels appear as lines; here and there a larger one is visible.

FIG. 95.-Portions of the section shown in the last figure, more highly magnified A, from the left ant. cornu; distended capillaries with numerous nuclei; larger vessels with slight distension of perivascular sheaths; numerous round and stellate cells; ganglion-cells, swollen, with shrivelled processes. C, from front of post. column; scattered nerve-fibres separated by amorphous material in which small cells can be seen, round and irregular, some distinct, others indistinct, vessels with thickened walls. B, from near the posterior surface, shows similar changes but with more open spaces from which nerve-fibres have perished. (From sections prepared by Dr. Money.)

times partly within and partly outside them in an adjacent albuminouslooking substance. In some cases, however, especially those of disseminated interstitial myelitis of moderate degree, the nerve-cells appear little changed in hardened and cleared specimens, although a granular condition can usually be seen in the recent state.

In the white substance, cleared sections show a great increase and alteration in the interstitial tissue. The change may be uniformly distributed, or greatest in the neighbourhood of the vessels (Fig. 98, c). The increase is due in part to an amorphous material, containing nuclei here and there, some of which belong to cells such as have been described in the grey substance; and these may constitute extensive tracts between the spaces where nerve-fibres once existed (Fig. 98). In older cases the tissue may have a fibrous aspect in places. The large cells, with many processes called "spider cells," or "cells of Deiters," are

often conspicuous objects (Fig. 96). The processes extend between the nervefibres. We have seen (p. 165) that their existence in the normal cord has been doubted, but in the inflamed cord, in which they are enlarged, their presence is distinct.

The changes in the nervefibres vary much. They always suffer destructive changes, but the products of their degeneration, above described, are scarcely to be seen in cleared specimens. The slightest change in the myelin appears to consist in an alteration in its chemical nature, in consequence of which it stains more readily than in health. Fibres are thus changed adjacent to any increase in the interstitial tissue, and they contrast with the unstained healthy fibres in the vicinity (Fig. 97, c). With or without this change in the myelin, there is an irregular swelling of the axis-cylinders, such as is seen on examination in the fresh state. If the fibres are divided transversely at the places where the axis-cylinder is swollen, this appears much larger than normal (Fig. 93, b). Examples of this will be found in most of the figures. These intense degenerative changes cause the breaking up of the myelin, and may involve the destruction of the fibre, the space occupied by it being left empty.

FIG. 96.-Subacute disseminated myelitis; part of the posterior column. Nerve-fibres separated by granular material and products of degeneration, and by numerous large spider cells. The myelitis in this case was attended by optic neuritis. (From a section lent by Dr. Dreschfeld.)

The significance of this vacuolation has been much discussed. It is probable that the vacuoles form after death, perhaps during the process of hardening, but that they do not form unless the cells have been altered by disease. They have thus some pathological significance.

In other cases, however, the axis-cylinder persists and remains surrounded by a narrow zone of myelin. Often a large number of such shrunken fibres may be found in a part which at first sight appeared devoid of fibres. This shrinking of the fibres occurs not only as the result of pressure on them by the connective-tissue elements, but also where there is little interstitial change and no compression.

FIG. 97.-Acute transverse myelitis, fatal in three weeks. Carmine preparations. A, section through most diseased part, at first lumbar segment. Foci of inflammation scattered through the whole area of this cord, most abundant in the posterior columns (the apparent enlargement of which is probably due to the direction of the section). Dilatation of the central canal. B, from the anterior cornu at A, b, a distended vessel; the tissue crammed with lymphoid and other cells, among which run normal nerve-fibres. C, from the posterior column, A,c. The areas staining deeply are seen to consist of thickened trabeculæ, lymphoid cell, amorphous tissue, and also of nerve fibres, the white substance of which stains with carmine while that of the neighbouring healthy fibres does not.*

I am indebted to Dr. Dreschfeld for the section from which these drawings are ade. The patient was a girl aged twenty-three; paralysis, motor and sensory, was complete at the end of two days; the application by her mother of hot bottles to the feet caused such extensive sloughing ulcers that amputation of one leg was deemed necessary three weeks after the onset, and the patient died the next day.