which impressions from the muscles are conveyed to the posterior nuclei of the medulla and probably thence to the cerebellum (p. 205). The effect is to deprive the motor cortex of the guidance afforded by these impulses. The difference between this form and the slighter degrees of the first is that the muscle-reflex action is not lost, the knee-jerk being preserved. (3) Irregular compression of the motor fibres in the cord apparently causes the peculiar jerky inco-ordination seen in disseminated sclerosis, which is supposed to depend on unequal and irregular conduction along the fibres, due to their compression. This form, however, needs further study.

SENSORY SYMPTOMS.-Loss of sensation is a very common effect of disease of the spinal cord. It may be total, and involve all forms of sensibility, or partial, and affect only some forms. The statements made on pp. 8-10 regarding impairment of sensation generally, and the method of ascertaining it, apply to that which results from cord disease, and need not be here repeated. It has been also pointed out (p. 60) that loss of sensation occurs less readily than loss of motor power. In cord disease it is common for muscular paralysis to exist with intact sensibility. This may partly depend on the fact, ascertained by experiments on the effect of local anæmia of the cord, that the sensory fibres, of the nerve-roots at least, seem to have more resisting power than the motor fibres. Sensation may be impaired by disease of any part of the sensory path,-posterior roots, probably also the posterior cornua and commissure, or the conducting tracts up the cord. A division of the sensory path into upper and lower segments is conceivable, analogous to that of the motor path, although we have not the same clear ground for the distinction into simple segments of similar composition.

Disease of the posterior nerve-roots causes loss of reflex action as well as impairment of sensation, just as disease of the anterior roots interferes with reflex action as well as with motor power. Interruption of the sensory conducting tracts higher up leaves reflex action unaffected. But a focal lesion, such as transverse myelitis, may damage both the conducting tracts and the nerve-roots at the level of the lesion, or may affect only one of these. Disease outside the cord, compressing it, may have the same double effect. Hence it is important to test sensation at the level of the lesion, as well as in the parts below, and to remember that the "level of the lesion" may involve the limbs or the trunk. Areas of anesthesia may thus be found on the trunk when there is none on the legs, and may be of considerable diagnostic importance, e. g. in spinal caries.

Random disease of the nerve-roots outside the cord usually impairs all forms of sensibility, although slight damage may arrest the conduction of tactile impressions, and not those of pain, which are probably more energetic. Disease of the roots within the cord often causes only partial loss, because the fibres which conduct different impressions have a different course. But loss of one form of sensi

bility from disease of the root-fibres or nerve-fibres usually depends on the kind of disease, and is especially due to degenerative changes, the result of some present or past local influence. Disease higher up the cord still more frequently causes partial loss; either sensibility to pain or to touch may be impaired. That to temperature is rarely affected without that to pain. We do not yet know precisely the significance of this special form of loss, because, as we have seen, we are still uncertain as to the path for each form of sensibility. It is bighly probable, however, that loss of sensibility to pain is produced by disease of the antero-lateral ascending tract.

Disease of the posterior median column, and possibly that of the cerebellar tract, certainly impairs the conduction of impressions from the muscles. It probably abolishes the "muscular sense" of posture and movement, although this does not entail a distinct sensory loss. But there may be also a greater loss of muscular sensibility, so that the normal sensitiveness to pressure and passive extension (and even at last to electrical stimulation) may be impaired or lost. The "common sensibility" of muscles is probably lost only when the disease of the nerves is greater than suffices to abolish what is termed the "muscular sense." Interference with this path in the nerves or roots outside the cord abolishes muscle-reflex action, and also causes more pronounced symptoms (ataxy, &c.) than disease higher up the path within the cord.

Increased sensitiveness, hyperæsthesia and hyperalgesia, are also common in disease of the spinal cord, and usually depend on irritation of the conducting fibres in some part of their course. Probably the irritation produces the effect by intensifying the impulse as it passes, since the phenomena of stimulation of nerves show that their axiscylinders have some power of transforming other forms of energy into nerve-force, i. e. of evolving nerve-force, and therefore of increasing the strength of that which passes along them.

The term "hyperesthesia" is commonly used in the sense of "hyperalgesia." In the strict sense of the word, hyperæsthesia is seldom observed or even searched for.

When the sensibility to touch is "increased" there is some perversion of the sensation, not a simple increase. The sensation may be felt as "thrilling" or "shock-like sensations." When there is an extreme increase, pain may be produced by a touch, but it is more probable that the touch stimulates the over-sensitive nerves of common sensibility, than that actual pain is produced through the tactile nerves. A touch may cause pain when it is not felt as a touch, as in the condition termed "anesthesia dolorosa." Other forms of altered sensibility have been already described.

Pain, referred to the spine, occasionally present in organic disease of the cord, is more frequent in disease originating in the meninges or bones. But the frequency with which spinal pain is present in abdominal, especially gastric, disease, and in neuralgic affections,

lessens its significance when it exists alone. In meningitis, acute or chronic, and in meningeal growths, spinal pain is frequent, and in organic disease of the bones of the vertebral column it is an almost constant symptom, and is combined with local tenderness. The same combination of local pain and tenderness frequently occurs in cases of neuralgic pain, “rachialgia,”—a condition that is often loosely termed "spinal irritation," especially when it succeeds, as it often does, concussion of the spine. Such pain is usually felt through a considerable extent of the vertebral column, or has more than one place of chief intensity and tenderness. That which is due to organic disease is usually fixed and unchanging. In organic disease of the cord itself, pain is more often referred to the neighbourhood of the spine, to the loins or the sacrum, than to the spinal column itself.

Still more important are the pains that are referred to the parts to which the sensory nerves are distributed, and have hence been termed " "excentric or "radiating" pains. They are of two kinds: (1) those due to the irritation of the posterior nerve-roots in their passage through the intervertebral foramina, through the membranes, or through the posterior columns of the cord; (2) those produced by irritation of the sensory conducting tracts. The pains of the first class are called "root-pains," and are often intense. They correspond in level to the disease. Those of the second class are sometimes acute, especially in lesions that irritate the conducting tracts by pressure, e. g. growths. More often they are dull pains, closely resembling rheumatism, and frequently mistaken for rheumatism by the patients themselves and their medical attendants. The mistake is the more easily made, because other symptoms suggestive of spinal disease may be inconspicuous, and the rheumatoid pains in chronic cases may be influenced by weather, being much more troublesome in damp and cold than in fine and dry weather. In all cases, persistent rheumatic pains in the limbs should suggest the possibility of spinal disease, and watch should be kept for such symptoms as local loss of power, or alterations in reflex action. There is a third class of pains-resembling root-pains, which depend on degenerative changes in the nervefibres; the molecular alterations that result give rise to upward impulses of considerable intensity. They are met with in locomotor ataxy and in multiple neuritis, and may be dull as well as acute. The position in which these various radiating pains are felt-legs, trunk, or arms-depends upon the seat of the disease. Although often produced in the root-fibres, these pains may also be due to the peripheral nerves.

It is especially important to note that the root-pains are frequently felt as a sense of constriction, a painful sense of tightness, as if a band were tied tightly around the part-the "girdle-pain," as it is called. When there is transverse damage to the cord, at the lowest part of the healthy region there is a state of irritation of the sensory nerves, and this irritation (referred to the nerve-endings) causes the girdle

pain. It is named from its frequency at the level at which a girdle is worn, the middle of the trunk, which depends on the dorsal region being the most common seat of disease; but it may be felt lower down, about the groins or even the legs, or higher up, in the arms. In the limbs it is a mere sense of tightness.

The girdle-pain is a symptom chiefly of inflammatory and degenerative processes within the cord. Pressure on the nerve-roots usually causes acute pain, but the most severe root-pains are those met with in disease of the bones of the spine. These have also, more than any other kind, the characteristic that they are increased by movement, and in growths commencing in the bones (which are usually malignant) this feature is of considerable diagnostic importance. The suffering in such cases is so great as to have gained for the resulting symptoms the ominous designation of paraplegia dolorosa.

Spontaneous sensations, other than pain, are very common in disease of the spinal cord, and are often of considerable diagnostic importance, but suggestive rather of the presence of a morbid state than of its nature. They may present many varieties of character, but the familiar sensation produced by pressure on a nerve-trunk, when the part is said to be "asleep," or to have "pins and needles," is the most common and the most significant. It may occur in functional disturbance of the cord as well as in organic disease, and also is very common in peripheral neuritis. It depends on overaction of the sensory structures, but it has at present no special significance as to the locality of disease. It may be excited by contact when it is not spontaneous, and probably represents the highest degree of excess of impressions conveyed by the nerves of tactile sensibility. The still vaguer feeling called "numbness" is also common, and may occur, in slight degree, in diseases of which all other symptoms are purely motor. But this word is used in so many different senses that the meaning in which the individual uses it should always be ascertained as far as possible. Sometimes it signifies distinct loss of seusibility. More often a feeling as if there ought to be loss when there is not. Our sensations altogether transcend our vocabulary, but the observer must try (without leading) to ascertain the character of the sensation experienced.

REFLEX ACTION.-Loss of reflex action indicates an interruption of the reflex arc concerned. This interruption may be anywhere between the peripheral endings of the motor and sensory nerves, and thus is not necessarily within the spinal cord, or even within the spinal canal. It is as constant in peripheral neuritis as in any spinal disease. The position of the interruption must be determined by the associated symptoms; if it is in the centripetal portion of the reflex arc, there is impairment of sensation, since the interruption will equally arrest conduction to the brain. If it is in the centrifugal portion of the arc, there is a corresponding interruption in the path of the voluntary impulse, and loss of motor power. Moreover, disease of the motor centre

or inotor nerves causes also degeneration of the nerves, and wasting of the muscles. Any considerable disease of the nerves abolishes all reflex action from the part they supply, but disease limited to the motor structures may permit a reflex movement to take place at a distance, although preventing it at the part stimulated.

Disease of the motor centre or nerves causes loss of all forms of reflex action, the simple form and the muscle-reflex that underlies myotatic irritability. Partial disease of the afferent path may impair one and not the other, may abolish the muscle-reflex action (myotatic irritability) and not the superficial reflex action, since the afferent nerves for the two are distinct, coming in the one case from the muscles, in the other from the skin. When one only is lost it is generally the muscle-reflex action; the nerves for this seem more susceptible and to have less power of resisting morbid influences.

Loss of all reflex action may occur as a transient symptom, immediately after the onset of an acute lesion of the cord, apparently from irritative inhibition of the centres. Cutaneous reflex action may be lessened permanently in some cases of brain disease on the side of the motor palsy, even when the muscle-reflex action is increased. Indeed, this opposite change in the two forms of reflex action co-existing on the same side always suggests intra-cerebral disease. It may be well

again to remind the reader how difficult it often is to be sure whether the knee-jerk is present or is lost, on account of the readiness with which its occurrence may be prevented by inability to relax the muscles, and its presence may be simulated by a true reflex action (see p. 200). Excess of reflex action implies, of necessity, the integrity of the reflex arc concerned, and shows that organic disease, if it exists, is higher up the cord. Each form of reflex action is often increased. In some acute diseases, as acute meningitis, and probably also in some chronic diseases, the increase may be due to an irritation of the centres, but in most forms of chronic disease it is apparently the result of a loss of control, and indicates disease between the centre concerned and the brain. We have already considered (p. 202) the probable mechanism, and have seen that the excess of the muscle-reflex action is related to disease of the pyramidal fibres, and especially to the loss of the terminal part of these fibres, within the grey matter, adjacent to the centres concerned.* This is the significance of considerable excess. Degeneration of the terminal portions of the fibres is commonly due to a descending degeneration of the fibres themselves. It is possible, however, that the degeneration of the endings of the pyramidal fibres may be primary, as is that of the nerve-fibres. (See Primary Spastic Paraplegia.) The increase of reflex action is chiefly

It is interesting to note the analogy between the effects of degeneration of the termination of the two segments of the motor path. The increased activity of the muscle-reflex centres, which results from degeneration of the termination of the upper segment, presents some similarity to the increased voltaic irritability of the muscular fibres which results from degeneration of the termination of the lower segment.