A lesion of sudden occurrence, the symptoms developing in the course of a few minutes, is almost always vascular, commonly hæmorrhage, sometimes perhaps vascular obstruction. But a vascular lesion may occupy a somewhat longer time in development-a few hours or days. In acute and subacute inflammation the symptoms come on in the course of a few hours, a few days, or a few weeks. Subacute and chronic inflammation occupies from a few weeks to a few months Degeneration, in which there is no adequate evidence of any inflammatory process, occupies many months, or it may be years. The symptoms produced by tumours which invade or compress, and by simple. pressure (traumatic causes excluded) are never sudden or very acute, and rarely very chronic, the time occupied by the development of the symptoms varying, according to the nature of the cause, from a fortnight to six months.

It is necessary to consider, however, not merely the whole time occupied by the development of the disease, but also the uniformity of its course. Two or more morbid processes may concur. An initial myelitis, for instance, may lead to a secondary degeneration; and, on the other hand, in degenerated tissues, sudden vascular lesions occasionally occur. Pressure produces local myelitis, which may be independent of the pressure in its development, and have an acute or subacute onset. The whole course of the disease must be ascertained before an inference is drawn, and the possibility of a double process must always be kept in view.

The onset and course of the symptoms thus sometimes enable us to decide at once that a lesion is of a given character, as that one which occurs instantly is vascular, or that one which takes years for its development is degenerative. More frequently they enable us to exclude certain morbid processes, and to restrict the possible lesion to two or three forms. For instance, a lesion which comes on in the course of a few hours must be either vascular or inflammatory. Between these we have to decide by attention to other indications.

In actual diagnosis it is convenient to consider next the indication afforded by the position and distribution of the disease. We consider what diseases occur in this situation, and then which of them have the mode of onset that has been ascertained. This indication involves a knowledge of the various diseases and their seat. The most important consideration is that a wide range of symptoms of uniform character

indicates the affection of a definite system of structure, and in most instances a disease commencing in the nerve-elements, and if the onset be chronic we may feel sure that it is a degeneration. On the other hand, the involvement of many functions suggests a random process, such as inflammation or pressure. But this indication is always to be subordinated to the mode of onset. Thus the limitation to a single structure does not exclude inflammation: this may affect, for instance, the anterior grey matter only, and cause corresponding symptoms.

The symptoms may indicate a morbid process limited to one half of the cord, but this does not materially modify the diagnostic method. Almost any process may, in rare cases, be thus limited. System degenerations and acute inflammations are least frequently unilateral, and they never reach a considerable degree of intensity on one side without some affection of the other side. On the other hand, tumours and foci of chronic myelitis are often one-sided, and still more often affect one half of the cord first and then the other.

Indication of disease outside the cord, irritation of certain nerveroots, causing severe local pain, often precedes the symptoms of compression, and is an important aid to diagnosis. It shows the existence of a morbid process outside the cord before the cord is involved. But we cannot use even this indication except in dependence on the mode of onset. A disease, as a growth outside the cord, may, as we have seen, not only compress the cord, and cause slow loss of power; it may excite inflammation and cause rapid palsy.

The last element in the pathological diagnosis is the detection of any influence which can be regarded as the cause of the disease in the spinal cord, or any associated condition which may indicate an active morbid process. We have seen that the mode of onset may help us to limit the disease to certain possible forms of lesion; the distribution of the affection may render it probable that it is one or other of these forms; and the detection of a cause and the knowledge of the lesion that cause produces may help us to carry the diagnosis still further. The most important general causes of disease of the cord, and the processes to which they chiefly give rise, have been already mentioned. The causal element in diagnosis is chiefly an application of those facts.

The morbid process outside the spinal cord that most closely simu lates its disease is, unquestionably, parenchymatous multiple neuritis. The diagnosis depends on a thorough knowledge of the varied symptoms of the latter, since its elements vary according to the different manifestations of the disease of the nerves. For these, and for any general diagnostic principles, the reader is referred to the account of that disease.

The only sure ground for diagnosis is a thorough knowledge of the various morbid processes and their symptoms; and the only safe plan is to work by these, from symptom to seat and onset to nature,

treating every case as a problem to be worked out to a definite diagnosis, and only then comparing the result with the types of disease. To one of these the case may or may not conform; if it does not, the comparison with types as a means of diagnosis will only leave the observer stranded and powerless.

The distinction of functional and nutritional disease from organic lesions may conveniently be postponed until the symptoms of the former are specially described.

SPECIAL DISEASES OF THE SPINAL CORD.

DISEASES OF THE VERTEBRAL COLUMN.

Diseases of the bones of the spine fall for the most part within the province of surgery. But there are few of these diseases that do not, among their most frequent effects, interfere with the functions of the spinal cord. Hence an account of the diseases of the cord would be incomplete without some mention of the morbid states that begin in its bony case.

INJURIES OF THE SPINE.

Injuries to the spinal column may consist of punctured wounds. (which need not be considered here), concussion (the effects of which on the cord will be considered later), and fracture or dislocation of the vertebræ. It may, however, be useful briefly to describe the more salient features of the last two conditions, their relation to the damage the cord sustains, and the symptoms thus produced.

DISLOCATION.

Simple dislocation occurs in the cervical region, most frequently at the fifth and sixth vertebræ. It may take place gradually or suddenly: gradual displacement is always secondary to disease of the bones; sudden displacement may occur in disease or from injury. The damage to the cord is always greatest in traumatic displacement of healthy bones, because the force needed to produce the dislocation is much greater, the displacement is more considerable, and the effect on the canal and the contained cord is greater. Displacement may occur in any direction: it usually involves both vertebral articulations, but, in rare cases, it is oblique, involving one articulation only. The common causes are violent blows or falls on the head, rarely sudden

rotation of the nead while a weight is carried upon it. The symptoms are a lateral or forward or backward displacement of the head, so that the chin is in contact with the shoulder or the chest, or the occiput with the nape of the neck. There is also irregularity of the vertebral spines, usually readily detected. The cord is damaged in most cases, and the symptoms are those of a total transverse lesion in the situation of the luxation. It may be merely compressed, especially in cases of disease, in which the displacement has occurred with little force. The symptoms of paralysis have been known to pass away, in such a case, on the reduction of the dislocation. More commonly the cord is also bruised, with extravasation of blood, and secondary myelitis occurs later. In such cases, if the patients live, there may be anaesthesia or hyperesthesia below the lesion, with total paralysis of the limbs, and excess of reflex action. In rare instances the cord has been completely divided. In still rarer instances of slight displacement it has not been injured.

Rupture of the transverse ligament which retains the odontoid process may permit the latter to compress the cord, and thus to cause instant death. This often results from sudden suspension by the head, as in criminal executions. One of the curiosities of surgical literature is a case related by Petit in which a man, playing with a neighbour's child, lifted it up by the head, and caused instant death. by rupturing the transverse ligament. The father of the child, entering at the moment, stabbed the man with a knife, the blade of which passed in between the first and second cervical vertebræ, divided the spinal cord, and the man also fell dead. Rupture of the ligament has also resulted from raising a heavy weight with the head. The treatment of dislocation is too purely surgical to be described here.

FRACTURE.

All organic diseases of the bones, weakening them, predispose to fracture. Among these, one is of special medical interest; the vertebræ, especially in the lumbar region, may share the rarefaction and weakening of the osseous tissues occasionally produced in tabes, and then a very slight traumatic influence, a blow or wrench, may cause fracture. The force needed is often so slight as to fail to cause displacement or other symptoms except local pain, and symptoms may only supervene at a somewhat later date. Apart from disease, the accident is most common in adults, the greater elasticity of the vertebral column in children giving to them a comparative immunity. Its cause is a blow or fall on the spine, or sudden forcible flexion. In extremely rare cases a fracture, usually slight, has resulted from a severe muscular exertion. This is an important fact, showing that muscular exertion may injure the spine, and may lead to symptoms

one the process is limited to structures that have the same function; the process begins as a degeneration of the nerve-elements, and the overgrowth of the connective tissue is a consequence of their wasting, the affection is essentially "parenchymatous." The so-called "secondary degenerations" are of this character; but similar changes are often primary, and affect the structures that have the same function, often through a considerable extent of the cord. Hence they are termed "system diseases." In the other type the morbid changes are not distributed according to function. They are apparently random in incidence, and involve adjacent structures in consequence of contiguity. These begin in the connective tissue and not in the nerve-elements, which suffer secondarily. They are essentially interstitial processes. Insular sclerosis is an example of this type.

The position of the islets of sclerosis has no relation to the function of the parts, and may involve parts of adjacent structures that have no common func tion. Areas of diffuse sclerosis are also met with which have not the sharp limitation of the insular form, and are regarded by some as of the nature of chronic sclerotic inflammation. If such a lesion is so situated as to involve fibres that undergo secondary degeneration, this necessarily results when the damage to the fibres is sufficiently great. We have then a combination of the random and systemic forms of sclerosis, but one that has no real pathological signifi

cance.

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There are, however, other relations between the two types that deserve attention. These will be considered in connection with the special morbid processes that present them, but a brief mention of them here may make some facts of other diseases more intelligible. The process of secondary degeneration and secondary sclerosis varies in its character, presenting in some greater amount of vascular disturbance than in others. It seems to partake of the character of the lesion causing it, as we have seen (p. 55) the process of secondary degeneration in the nerves may do. The same difference is seen in the primary degenerations, such as occur in tabes. This difference is analogous to that which, as already described, occurs in some varieties of multiple neuritis. We can indeed see the difference in the eye: tabetic optic nerve atrophy, in most cases, presents no sign of inflammation, while in others the early stage may be accompanied by distinct slight neuritis, to be seen with the ophthalmoscope. Secondly, the chronic inflammations, with the diffuse limitation, extending to adjacent structures irrespective of function, have yet sometimes a marked tendency to be localised in structures of definite function. Thus there is sometimes diffuse sclerosis of the lateral pyramidal tracts and posterior median columns, not sharply limited to these, and yet with a correspondence and symmetry not to be overlooked. Thus the two processes tend to meet; the systemic degeneration or sclerosis to be diffuse; the diffuse inflammation or sclerosis to be systemic; and it is sometimes not easy to say, from mere microscopic examination, to which class a lesion belongs. Lastly, there is a curious fact, which has been strangely overlooked although attention was first called to it by Charcot-that inflammation may extend from a primary lesion along a tract that undergoes secondary degeneration, but in the opposite direction to that of the degeneration. It is very common for the inflammation at a given place in the cord, especially that