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more especially since anatomical considerations seem plainly to indicate that, after passing through the grey substance, a large part of the fibres proceeding from the posterior roots emerge again into the fibrous columns of their own or the opposite side of the cord.
Supposing, however, M. Brown-Séquard's position to be conclusively established, it must not be thence inferred that the conduction of sensory impressions takes place by vesicular matter, to the exclusion of the tubular. For the grey substance of the spinal cord is by no means composed of the former only; being penetrated not merely in the transverse but in the longitudinal direction, by numerous fasciculi of nerve-fibres. These longitudinal fasciculi are probably composed in part of those fibres which appear in transverse sections of the cord to lose themselves in the central grey substance; whilst it would seem likely that they also include a portion at least of those fibres which pass into the grey substance, as already explained, after running for some little distance either up or down the posterior and lateral columns. Still, as M. Brown-Séquard justly remarks, the whole aggregate of these fibrous strands is too small to admit of our supposing that they are the exclusive channels of the transmission of sensory impressions as well as of motor impulses; and since it has been clearly shown that nerve-cells communicate with one another by filamentous prolongations analogous to those by which they connect themselves with nerve-tubes, there seems no à priori reason against the belief that the vesicular substance may share with the tubular in conducting power.
In his published lectures, M. Brown-Séquard enters into a very elaborate examination of the evidence furnished by Pathological observation in regard to the conduction of sensory impressions along the spinal cord, which want of time prevented him from discussing orally. Of this evidence, some appears contrary not only to his theory, but to every other; such, for instance, as that of cases in which voluntary motion and sensation were in great degree preserved, notwithstanding what appeared to be the disorganization of the entire substance of the cord. Few, as he justly remarks, who are acquainted with the present state of neurology, will now be disposed to accept either the hypothesis of Magendie that nervous transmission was effected through the membranes of the cord, or that of Hutin, who supposed that it took place through the serous fluid which replaced the cord; the more probable explanation of such anomalies being obviously that a great part of the alteration in the structure of the cord had taken place in these cases subsequently to the last examination of the patient, very likely in some of them after death. The rapid occurrence of post-mortem change in the nervous substance, especially in warm weather, and when the tissue has already undergone partial disorganization, is known to every pathologist; and its possibility must be always kept in view in the interpretation of phenomena of this class. It must be admitted that recourse to such an explanation affords an easy solution of many difficulties, a sort of cutting of the Gordian knot, which becomes very convenient when the recorded facts are inconsistent with hypothesis.
But as it is obvious from the cases just referred to, that its use must be occasionally admitted, we cannot consistently decline to accord it in other instances; and the question therefore stands thus ;-what hypothesis of the relative functions of different parts of the cord is most accordant with pathological phenomena, and leaves least to be explained away by this or any other kind of special pleading?
In interpreting the affections of sensibility which depend on lesions of the spinal cord, we are warned by M. Brown-Séquard to keep in mind the two following positions, which he has experimentally determined:-1st, that the smallest portion of the conducting zone of the cord contains elements capable of conveying sensory impressions from all the parts below it, so that partial division of the cord, instead (like partial division of a nerve) of extinguishing the sensibility of certain regions, leaving others but little or not at all affected, diminishes the sensibility of the whole region posterior to it, without destroying the sensibility of any one part; this diminution increasing with the extension of the division, but not increasing to complete anesthesia until the whole of the conducting zone has been cut through: and 2nd, that whilst simple section of the posterior columns induces hyperesthesia, extensive alteration of those columns is not attended with this result, the hyperæsthesia being antagonized by the partial anesthesia produced by the destruction of that portion of the posterior roots of the spinal nerves which at first enters into the composition of the posterior columns. It is also important to bear in mind that sensibility often persists after a structural alteration sufficient to destroy the power of voluntary movement; apparently because the sensorium is much more readily acted on by feeble impressions than is the motor apparatus. And thus it happens that complete anesthesia from lesions of the spine is a rare occurrence. Now in regard to the functions of the posterior columns, we believe that M. Brown-Séquard is justified in asserting that no case has yet been adduced in which there has been any considerable diminution of sensibility during life, and in which after death there has been found a lesion of the posterior columns strictly limited to them, and involving neither the posterior roots of the spinal nerves nor the central grey substance; whilst, on the other hand, there are many cases in which a notable diminution of sensibility accompanied disorganization of the anterior and central portions of the cord, the posterior columns remaining entire. Moreover, when the posterior columns have been alone affected in one spot or for a short distance (as by an incised wound, or by the pressure of a tumour or of a piece of bone), hyperesthesia has been an almost constant symptom; although a more extensive lesion does not produce any increase, but rather a diminution, of sensibility. In cases of alteration extending through a great length of the posterior columns, there is a notable diminution in the power of standing and of walking; and when the affection has lasted long, there may be a complete loss of those powers without any considerable impairment of the sensibility of the lower limbs.*
Of this we have a striking example in the well-known case recorded by Mr. Stanley
The causes of this weakness are said by M. Brown-Séquard to be:1st. That the posterior columns are the principal channels for the excitations which produce reflex movements, so that when they are altered there is a great diminution of those movements; and as these are absolutely necessary for the actions of standing or walking, it follows that the power of performing these actions must be diminished by an alteration of the posterior columns. 2nd. That after a time, when an alteration exists in these columns, the amount of power of action in the other parts of the spinal cord diminishes, as a consequence (we suppose M. Brown-Séquard to mean) of their diminished exercise. The following seems to us the most important case on record of the persistence of sensibility, notwithstanding the disorganization, in a certain portion of the cord, of all its fibrous columns, the central grey substance alone remaining; it is recorded by M. Laboulbène :
"A man, aged forty-four, after having had cramps, formication, weakness in the lower limbs, and paralysis in the upper limbs, for a long period, was admitted at the Charité. Sensibility to pinching, pricking, touching, tickling, the feeling of cold, and to muscular spasm excited by galvanism, existed everywhere. On the evening of November 1st the patient was able to walk with some aid. Sensibility remained everywhere to the last moment before his death on November 3rd.
Autopsy-Encephalon normal. There is an induration of the spinal cord from its upper extremity to the third dorsal vertebra, and from the sixth dorsal vertebra to the lower extremity. The tissue of the cord in those parts being cut was shining, looking like porcelain, hard and difficult to be crushed. The grey matter was also a little harder than normally, but of its usual colour. The anterior and posterior roots seemed normal. In the space between the third and sixth dorsal vertebræ the cord was softened, pultaceous, resembling a whitish or slightly rose-coloured pulp (bouillie), punctuated in some places. Put in water, many parts became disintegrated and formed a kind of emulsion. This alteration existed only in the white substance; the grey, on the contrary, seemed to have preserved its normal consistence. The microscope showed that the grey matter in both the softened and the indurated parts contained normal cells and fibres and normal bloodvessels; while the white substance in the softened region contained but rare fibres, which were altered, containing an oily matter and granulations. There was also a quantity of granulated corpuscles of inflammation, with many capillaries, oily drops, and amorphous matter. In the indurated white substance there was less alteration, and the fibres were normal and numerous."*
M. Brown-Séquard also enters at considerable length into the pathological evidence which may be opposed to the doctrine that the encephalic prolongations of the posterior columns constitute the special channels of common sensibility: but we do not think it requisite to dwell upon this, since this doctrine has never been advocated by any British physiologist of repute; and it was, in fact, the obvious anatomical connexion of the posterior columns with the cerebellum, through the restiform bodies, whilst the sensory tract of the medulla (Medico-Chirurgical Transactions, 1840), the symptoms of which had led to the confident expectation that the anterior portion of the cord was diseased, but in which the disease was found after death to involve only the posterior columns.
* Mémoires de la Société de Biologie. 1855.
oblongata (shown to be such by the origins of sensory nerves) passes on in close apposition with the motor in the crura cerebri, that led Sir C. Bell to modify his original idea of the sensory function of those columns.
III. Of all the results of M. Brown-Séquard's experimental researches on the nervous system, the most original and satisfactory appear to us to be those which appear conclusively to establish the Decussation of the Conductors of Sensory Impressions in the Spinal Cord itself, at a very short distance from their entrance into it. far as we are aware, this had never been previously suggested even as a possible hypothesis; certainly it had never been propounded as a deduction either from experimental enquiries or from pathological observation. It had been universally admitted that from the medulla oblongata downwards, each lateral half of the cord ministers to the sensibility as well as to the motility of its own side of the body; and as the phenomena cf ordinary cerebral paralysis clearly indicate that the conductors of sensory impressions, like those of motor influence, cross from one side to the other in their passage between the sensorimotor ganglia and the periphery of the body, it was currently supposed that a decussation of the sensory tract must take place either in or above the medulla oblongata. By Sir C. Bell it was affirmed that this decussation takes place in a part of the floor of the fourth ventricle, above and near the crossing of the anterior pyramids; but the appearances on which he founded this assertion have been shown by John Reid, Solly, and Valentin to be deceptive. By Mr. Solly it was thought that a decussation of the sensory columns could be shown to exist higher up than this-namely, during their passage through the pons varolii; and Dr. Radclyffe Hall arrived at a like result. Their statements, however, have not met with general acceptance; and by the greater number of anatomists and physiologists the problem has been considered as still waiting for its solution. Its difficulty was enhanced by the fact, that while, in cases in which sensibility and motor power are conjointly affected, the loss or impairment of both endowments usually affects the same side, cases every now and then occur in which the loss of sensibility occurs on the opposite side to that of the motor power; and although the idea of a decussation of the sensory tract at a point different from that of the motor tract seemed to offer a feasible explanation of this difficulty, yet its applicability to the supposed locality either of Sir C. Bell's or of Mr. Solly's decussation, so far from being established by pathological evidence, seemed to be negatived by it; and the only other possible solution seemed to be in the idea that some of the sensory fibres decussate, whilst others do not, and that one or other of these tracts might be separately affected. But this solution was far from satisfactory; since it did not account for the complete extinction of sensibility which is sometimes observable, either on the side paralysed to motion, or on that which retains its motor power, whilst the sensibility on the other side is unimpaired. As regards the course of the sensory impressions in the spinal cord, the only modification of the previously-current doctrine
that had been proposed before the researches of M. Brown-Séquard, was that put forth by Stilling, Schiff, and other German experimental physiologists; who, finding that a section of one entire half of the spinal cord is not followed by loss of sensation in the part of the same side posterior to the section, concluded that when the sensory impressions once reach the grey substance of the cord, they are (so to speak) diffused through it, and are thus conducted onwards to the sensorium through its undivided lateral half,—either lateral half being sufficient (according to this view) for the transmission of sensory impressions from both sides of the body.
It seems to have been quite overlooked, however, by these physiologists, that a complete transverse section of either lateral half of the cord, whilst entirely paralysing that side to all but reflex movement, paralyses the other side no less completely to sensation. The result of this experiment is the more remarkable, when the posterior columns have been first divided on both sides, so as to induce a hyperesthesia in the whole posterior part of the body; for if the lateral section be then made, it has no effect in reducing the hyperesthesia of the corresponding limb, whilst the sensibility of the opposite limb is entirely extinguished, the difference in the condition of the two being then rendered peculiarly conspicuous. In making experiments of this kind, it is necessary to be very careful in distinguishing the indications of sensibility from those which proceed from reflex movements; and it has been objected to M. Brown-Séquard's deductions, that what he regarded as signs of direct sensibility to painful impressions were really the results of reflex action, of which the animal became cognizant by the general disturbance produced in its body; whilst he accounts for some of the results advanced by his opponents in proof of the persistence of sensibility in parts alleged by him to be anaesthetic, by imputing them to the "recurrent sensibility" whose nature has already been inquired into. The following experiment which he has published since the delivery of his lectures, seems well devised to eliminate both sources of fallacy:
"In a vigorous young rabbit between two and a half and three months old, I lay bare the spinal cord through the whole length of the lumbar region, taking care to avoid wounding the large vessels. I then cover-up the wound with the skin, and leave the animal in tranquillity for an hour or two. After this long repose, I divide all the anterior roots of the nerves of the posterior members and of the other lumbar pairs; and again leave the animal in tranquillity for an hour or two. In examining the state of the sensibility of the hinder limbs, after this period of repose, I find that it exists there in a degree manifestly above the normal. It is unnecessary to say that there does not exist any trace of movement in these members, either reflex, voluntary, or convulsive: the hypersthesia is then obviously independent of those causes of pain which may proceed from muscles affected with spasmodic contractions. After having fully satisfied myself that the posterior members are both endowed with a high degree of sensibility, I divide one lateral half of the spinal cord (including the anterior, lateral, and posterior columns, and the corresponding portion of the central grey substance, of one side) at the level of the first lumbar vertebra. If this section has been made on the right side, I find that the right posterior member has an even yet greater sensibility than before, whilst the left posterior