in which the least excusable errors in diagnosis occur, and in which their effects are often the most disastrous.

PROGNOSIS.-Chronic myelitis is a very grave disease, on account of the intractability of the morbid process, its frequently progressive tendency, and the persistence of damage which is slowly produced. But cases vary widely, especially in the two former features, and it is a disease in which general prognostic rules can scarcely be formulated. The observed tendency of an individual case is alone a trustworthy guide. Arrest of the disease is often obtained, but actual recovery is rare. The prognosis is little affected by the seat or extent of the process, except that the implication of the grey matter of the enlargenents is generally an unfavorable indication. The severity of the lesion, as shown by the degree of the symptoms, is significant chiefly in cases of long duration, and is subordinate to the course and mode of onset. If it can be arrested, the prospect of improvement is better the slower has been the development of the disease, and the shorter the time the symptoms have lasted. In general, moreover, the prospect is better, the fewer the foci of inflammation, in males than in females, and in cases of uniform than of recurrent or relapsing course. Preceding syphilis does not materially modify the prognosis; hence the great importance of the diagnosis from syphilitic growth, in which suitable treatment has a most certain effect. The ultimate danger to life is least in focal myelitis in the dorsal region; it is greatest in the disseminated form, especially in the less chronic cases with a tendency to sloughing of the skin, and in the more chronic forms with muscular wasting. The indications drawn from the invasion of the respiratory muscles, and from the presence of any of the complications that so often terminate life, are the same as in other diseases of the cord.

TREATMENT. The first and most important measure is the improvement of the general health, by rest, change of air, and tonies. All causes of physical and mental depression must, as far as possible, be removed. Over-exertion, and even fatigue, should be avoided, and the patient should be kept, as far as possible, from exposure to cold. Absolute rest for a short time is often useful at the outset of the treatment, especially when there has been a somewhat rapid development of symptoms. In cases of purely chronic course, absolute rest should not be maintained for more than a few weeks, or the patient may find it hard to regain his former muscular power. Counterirritation at the situation of the disease is often useful, and most so in cases in which there is spinal pain or tenderness. Repeated sina pisms or blisters may be employed, but a mild form of the actual cautery is on the whole the most useful. A superficial burn or even slight vesication is sufficient on each side of the spine opposite the affected part. It should be repeated as soon as the skin has healed, and if linear cauterisation is adopted the fresh line can be made beside the old one. A hot douche to the back, at a temperature of 103° or 104° F., applied

daily, has been strongly recommended by Brown-Séquard. Warm brine baths, and various thermal mineral waters, have been also said to do good. A sea voyage is often of service, combining as it does the maximum of fresh air with the minimum necessity for exertion. Drugs, unfortunately, often fail to influence the morbid process, but nevertheless they are occasionally useful, so as distinctly to justify their careful trial in most cases; and it is important to remember that those that are useless in one stage or period of the disease may yet be of unquestionable service at another stage. Tonics, as quinine and iron, should be given if indicated. Most of the measures recommended, and precautions advised, in the treatment of acute myelitis are needed in the chronic form, and it is therefore superfluous to repeat them. Those drugs that most deserve a trial are arsenic, small doses of mercury (such as gr. of the red iodide), and iodide of iron. Energetic mercurial treatment rarely does good, even when the patient has had syphilis, and sometimes it does harm. Iodide of potassium seems to have little influence on the disease. Nitrate of silver, ergot, and phosphorus have been recommended. Strychnia is chiefly useful in cases in which there is muscular wasting, but is of far less value than in the degenerative muscular atrophy. The treatment of other symptoms is that suitable in primary spastic paraplegia or progressive muscular atrophy, and described in the account of those diseases.

COMPRESSION OF THE SPINAL CORD.

Compression of the spinal cord is a common consequence of various morbid processes. Inflammation is almost always excited by the pressure, and interference with function occurs, partly from the pressure and partly from the resulting myelitis. The symptoms produced have, in different cases, many characters in common, although they vary according to the mechanism of the compression and the acuteness of the inflammation. It is only when there are indications that an acute myelitis has damaged the nerve-elements that we are justified in regarding the interference with function as an effect of the inflammation.

CAUSES. The morbid processes that may compress the cord are those that involve an encroachment on, or occupy part of, the vertebral canal. The chief are the following:-Disease of the bones of the spinal column, especially caries; growths in the spine; aneurism eroding the bones and then compressing the cord; growths in the membranes; thickening of the dura mater. These processes have usually only a small vertical extent, and the pressure they exert rarely extends over more than a few inches.

PATHOLOGICAL ANATOMY.

The cord usually presents evidence of the compres sion it has endured in considerable narrowing at the spot, where it may be indented and flattened, or cylindrical. Sometimes the reduction in size is extreme; for an inch or so the cord may be reduced to one third of its normal diameter, and it has even been found no thicker than a crow-quill. An example of flattening is shown in Fig. 106. On the other hand, there is sometimes very little narrowing to be discerned. At the compressed part the cord is usually grey in tint; its consistence is lessened in early cases, and increased in those of long duration. The change in colour and consistence is due to the inflammation of the substance of the cord which always results from pressure, and may often be traced for some distance above and below the compressed part. When there is much compression there is always much inflammation, but considerable myelitis may occur when the amount of compression is slight. The inflammation may be chronic and slow, developing in propor tion to the pressure, or it may be subacute or acute, even when the pressure is gradual. The signs of inflammation are very distinct on microscopical examination, and resemble those in other forms of myelitis. There is a general increase in the interstitial tissue; in this, at first,

FIG. 106.-Compression of the spinal cord and pres sure-myelitis, in a case of caries of the spine. D, mid-dorsal region, near the chief point of greatest compression; the cord is narrowed from before backwards, and is uniformly damaged by inflam mation, so that the grey substance can scarcely be distinguished. C, 1 inches higher up, shows a slighter degree of myelitis, still extending through the whole thickness of the cord. B, first dorsal; the myelitis is much slighter and the chief disease is in the posterior columns, in which ascending degeneration occupies the post.-median columns and extends outwards into the post.-external columns. E, 14 inches below the point of greatest pressure; inflammation still extending through all the elements of the cord. F, 2 inches lower down, shows only descending degeneration in the pyramidal tracts, anterior and lateral, and also the "comma-shaped" descending degeneration in the anterior part of the post.-external column. In G, at the lowest part of the dorsal region, the commashaped degeneration has ceased, and only that of the pyramidal tracts remains. (From preparations by Dr. F. G. Penrose.)

various cell-forms may be found, but it ultimately presents the appearance of a dense reticulum. The nerve-elements undergo degeneration, and abundant masses of myelin, granule corpuscles, and corpora amylacea are visible in the fresh state or in glycerine preparations of the hardened cord (Fig. 107, c). Many nerve-fibres persist, however, with a narrowed sheath of myelin, and it is probable that these regain the power of conducting, in spite of the persistence of considerable, and even dense sclerosis in the part. In extreme cases all the fibres seem to be destroyed at the point of chief compres

FIG. 107.-Pressure-myelitis; portions of the section D in Fig. 106 more highly magnified. A, from the grey matter, numerous angular and fusiform cells; vessels with walls thickened by a growth of cells, narrowing the cavity, which in some is obliterated. B, from the white columns; thickening of the interstitial tissue, nerve-fibres in part destroyed, in part narrowed; a vessel with thickened walls. C, glycerine preparation from white substance; abundant products of degeneration of the nerve-fibres, in part aggregated into granule-masses. D, section of a nerve-root passing by compressed area; increase of interstitial tissue, many nerve-fibres narrowed, some with swollen axis-cylinders.

sion, but there is never an actual division of the cord itself. The grey matter can scarcely be distinguished from the white, even with the microscope, and the ganglion-cells become shrunken and atrophied. The walls of the small vessels are often thickened by spindle-cells, disposed more or less concentrically to the cavity, which is encroached upon and may be obliterated (Fig. 107, A, B), a process that must add to the degree of damage to the cord. The signs of inflammation gradually lessen above and below the compressed part, but often

extend for some inches in each direction. Beyond its limits the usual ascending and descending degenerations may be traced (Fig. 106). The nerve-roots passing by the seat of compression suffer from the pressure, and from interstitial inflammation excited in them. They are usually grey in tint and ultimately waste, and may even be reduced to fibrous threads. The microscope shows increase of the interstitial tissue, wasting of many nerve-fibres (Fig. 107, D), and enlargement of some axis-cylinders.

SYMPTOMS.-The effects vary much according to the degree of pressure, its rapidity, its direction, the amount and character of the inflammation produced, the amount of damage to the nerve-roots, and the position of the disease. The symptoms in most cases enable the fact of slow compression to be inferred, even when there is no indication of the cause. They are of two classes: (1) interference with the function of the nerve-roots at the level of the morbid process; (2) interference with the functions of the cord itself. The cord symptoms consist chiefly in impaired conduction, manifested in the parts below the lesion. The central functions of the cord (reflex action, &c.) at the level of the lesion are abolished by the pressure, but the symptoms of this abolition are often lost in those of the damage to the nerve-roots.

Of the root symptoms the most constant is pain, extending along the course of the nerve-fibres, and through the area of their distribution. The seat of these pains depends on the position of the disease; they may be felt in the arms, around the thorax or abdomen, or in the legs. They are usually sharp pains, resembling neuralgia in character, sometimes accompanied by tender points. Occasionally, when felt in the limbs, they are referred especially to the joints. The pain may be intermitting or constant. It may exist alone, for a long time, in a disease that increases slowly, and sometimes may be the only symptom, although some compression of the cord occurs. With it there is usually hyperesthesia of the skin, often intense. After a time anæsthesia develops in irregular areas, in spite of the persistence of the pain,the condition termed "anesthesia dolorosa." Irritation of the motor nerve-roots may cause painful contracture of the muscles, but this is, on the whole, rare, and the chief motor symptoms are due to the interruption of the fibres-muscular weakness, gradual in onset, and accompanied by wasting. The rapidity of the atrophy varies much, and with it the electrical reaction. When slow, there may be merely a progressive diminution in irritability to faradism and voltaism; when rapid, there is often the degenerative reaction, and sometimes the "mixed form," from the partial damage to the fibres that supply a muscle.

These local root symptoms are usually the first, and to them are added, after a time, the indications of interference with the function of the cord itself. There is weakness in the parts supplied from the cord below the lesion. The loss of power is usually gradual, but