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It further appears that, in the dorsal region, the various parts of the spinal cord, except the posterior columns-namely, the lateral columns, the anterior columus, and the central grey substance,—are employed in the conveyance of the will to the muscles; each of the last two seeming to have a greater share in this function than the first, and the grey matter appearing to have as great a share as the anterior columns.
The results of sections of the cord in the upper part of the cervical region, however, are notably different; for in that part it is the section of the lateral columns, and of the part of the grey matter situated between the anterior and the lateral columns, which most completely prevents the transmission of volitional power. Division of the anterior columns alone, when it has been effected without any considerable injury to the neighbouring parts, does not produce by any means a complete annihilation of the transmitting power. Hence it would seem that the conductors of the mandates of the will to the muscles are more limited in the upper part of the cervical region, than they are in the dorsal part of the cord, to the lateral columns and to the grey matter between these and the anterior columns; a result which harmonizes well with the anatomical fact already referred to. If the two anterior pyramids be divided, loss of all voluntary movement is the result; whilst if the olivary columns be divided, no very decided loss of motor power can be observed: these results again being in harmony with the structural continuity of the anterior columns with the olivary tracts and of the lateral with the pyramids. Further, if a section be made longitudinally just at the place of decussation of the anterior pyramids, so as to divide all the decussating elements, it is found that although the animal lives for some time after the operation, it has entirely lost the power of voluntary motion, just as when the pyramids were divided transversely; yet no impairment of voluntary power seems to proceed from the longitudinal division of the spinal cord in any part of its length. Hence we have the same experimental evidence of the decussation of the sensory conductors along the spinal cord, that we have of the decussation of the motor fibres in the medulla oblongata; the only difference being that the sensory fibres which decussate in any one segment of the cord, and which are consequently severed by longitudinal division of that segment, are only those of the parts immediately adjacent, in which alone the loss of sensation is observable; whilst, in the case of the anterior pyramids, as the entire aggregate of the motor fibres decussates at once, and is severed by a longitudinal section, there must necessarily be paralysis of all the parts to which they proceed.
It is well known that it has been doubted by many anatomists, physiologists, and pathologists, whether the decussation of the anterior pyramids includes all the motor fibres; the doubts in question being founded on considerations of three different kinds. Thus Foville, Valentin, and Longet have maintained that there is a complementary decussation of nerve-fibres connected with the olivary columns, all along the median line of the base of the encephalon. Again, Cruveilhier and
others have maintained that the small size of the anterior pyramids forbade the idea that they could contain all the fibres which communicate between the encephalon and the muscles. And further, the idea that the pyramidal decussation is the only one, seemed to be inconsistent with the fact that cases of paralysis occasionally present themselves, in which the loss of power is on the same side with the lesion of the encephalon. Against this theory of a complementary decussation, M. Brown-Séquard urges arguments derived from pathological phenomena which seem to us conclusive; the main point of these arguments being, that if there were a partial decussation between the fibres of the motor tract, either in the crura cerebri, the corpora quadrigemina, the pons varolii, or the upper half of the medulla oblongata, there must, whenever there is a lesion on one side of that tract, be a partial paralysis of both sides; the paralysis being greater on the side of the injury, or on the opposite side, according as the situation of the lesion is such that a larger proportion of the motor fibres has already decussated above it, or remains to decussate below it. Now this result, according to M. Brown-Séquard, is never witnessed; the effect of injury limited to one side of the motor tract being uniformly shown in muscular paralysis of one side only of the body, and that side being, as a rule, the one opposite to that of the lesion. (Of the exceptional cases, M. Brown-Séquard's explanation will be presently given.) It is only when the lesion affects the motor tract on both sides, or when it exists at the place of the pyramidal decussation, that it produces a paralysis of motion on both sides. If, then, it may be deduced from these facts that there is no decussation of motor fibres higher up than that of the anterior pyramids, it follows that, as no decussation of the motor fibres takes place in the spinal cord (at least in Man, though not so certainly in the lower animals), the conductors of the mandates of the will are entirely contained in the pyramidal bodies and in the grey matter associated with them, the olivary columns as well as the restiform being excluded by the fact that they certainly do not decussate in that region. A striking confirmation of the truth of this view is furnished by a class of cases (of which several are now on record) in which there has existed atrophy of one half of the brain and of the corresponding anterior pyramid, with paralysis and atrophy of both limbs on the opposite side, and also atrophy of the opposite half of the spinal cord, the restiform and olivary bodies remaining unaltered.
M. Brown-Séquard has collected fourteen examples of that curious class of cases of paralysis, in which the loss of power has existed on the same side with the encephalic lesion: and he states that all of them were characterized by the same features-namely, incomplete paralysis, no anesthesia (save in a single case), and frequent fits of vertigo; and that the lesion was of the same nature in all, having been the result of the existence of a tumour pressing upon the anterior surface of one of the crura cerebelli and the insertion of the trigeminal nerve. This paralysis may be explained in two modes; either by the supposition that it is the result of the destruction of some of the
conductors of volitional power; or by the hypothesis that it proceeds from the irritation of certain of the nerve-fibres in the peduncle, in the same way as a reflex paralysis is often occasioned by irritation of centripetal nerve-fibres in any viscus, in any membrane, or in any nerve-trunk that contains them. The former explanation requires the hypothesis that there are motor fibres that do not decussate, which is rendered improbable by the limitation of the paralysis to one side; and it seems to be disproved by cases in which the effect of the destruction of a large part of one of the crura has been muscular paralysis of the opposite side. The latter is favoured by the fact that reflex paralysis more frequently proceeds from irritation of the peripheric branches of the fifth pair, than from the like irritation of the branches of any other nerve; and that it usually affects the side of the body on which the irritation exists. The question is one of great interest; and the phenomena of every case in which this form of paralysis presents itself should be carefully observed and recorded, for the sake of the aid which a comparison of its symptoms and of its post-mortem appearances may afford to the determination of their real relation.
Some very interesting suggestions are offered by M. Brown-Séquard in the latter part of his course, in regard to the functional relations of the encephalic portion of the motor apparatus, as manifested in the effects of lesions in producing vertigo, convulsions, rotatory and rolling movements, &c. His views on these points, however, are so far from being completely stated, that we think it better to abstain at present from the discussion of them; merely mentioning that he thinks he has evidence that there is much nervous matter in the pons varolii, in the olivary tract, and in other parts about the base of the encephalon, which is not employed in the transmission either of sensory impressions, or of the orders of the will to muscles, but which is endowed with the singular property of producing, after even a slight irritation, persistent spasms or clonic convulsions in various parts of the muscular apparatus. It is through this part of the nervous apparatus, according to him, that the movements of rolling and rotation are produced; their source being sometimes a lesion or irritation acting directly on the tract in question, sometimes a change in its circulation produced by contraction either of its blood vessels or of those of some other part of the encephalon, but very frequently a reflex irritation conveyed through some other nerve, especially the auditory, as in the wellknown experiments of Flourens on section of the semicircular canals. This idea harmonizes well with the results of various pathological phenomena, especially the occurrence of convulsions on one side and of paralysis on the other from the same lesion, the convulsions being on the same side with the lesion, owing to the non-decussation of the olivary columns. But it cannot be doubted that this set of fibres and nerve-cells, supposing it to exist, must have some important normal or physiological function; and to the nature of this, M. Brown-Séquard at present gives us no clue whatever.
V. Although it cannot be said that M. Brown-Séquard's researches
into the actions of the Sympathetic System: have established any principle that is new to Physiologists, yet we are disposed to regard them as among the most practically-important of all his contributions to Neurology. For if they have not dispersed all the cloud of uncertainty that hung over this subject, they have made such openings through it as to afford us clear and definite glimpses of what was previously so misty and obscure as to present scarcely any appreciable form; and whilst they have thus given a character of reality to much that was before so vague and speculative that it could lay no claim to be accounted scientific truth, they offer many suggestions of the highest value in the interpretation of pathological phenomena, and in the selection and application of remedial means. Amongst the Physiologists, of our own country at least, who have most philosophically studied the functions of the Sympathetic system of nerves, we believe that those views had come generally to prevail which were formally taught by Dr. Alison, and explicitly set forth by him in the pages of one of our predecessors namely, that its special purpose is to bring the functions of Organic Life into harmony with those of Animal life, in virtue of the guiding and restraining influence which it possesses over the former; but that whilst it can either excite, modify, or retard the acts of Nutrition, Secretion, &c., those acts are in themselves independent of it, in the same sense that the actions of a horse are independent of those of the rider upon his back, who nevertheless controls and directs them at his own will. The evidence obtained by Valentin and other experimenters as to the power of the Sympathetic to excite contractions in the heart, the muscular coat of the alimentary canal, the walls of the great vessels, and other muscular organs immediately concerned in the maintenance of the organic functions, and as to the derivation of this power from the Spinal Cord, was generally accepted as rendering it probable that a part of its influence was exerted through its regulation of the calibre of the blood vessels; a modus operandi which was specially indicated on the one hand by the distribution of the Sympathetic upon their muscular walls, and on the other by the phenomena of blushing and other kinds of vascular turgescence arising from mental emotion. But although this regulation of the supply of blood accounted for much, there have seemed to be residual phenomena which indicate that the Sympathetic system has some direct relation with the operations of nutrition and secretion; in virtue of which it can excite, modify, or repress them, not by altering the supply of blood, in the first instance at least, but by affecting the uses to which the blood is put in its passage through the capillaries, and thus consecutively augmenting or diminishing the demand for blood in any particular organ.
has been thought that this agency might not unreasonably be attri buted to the system of fibres which has its central terminations in the vesicular matter of the ganglia of the Sympathetic itself, and which may be considered to constitute the essential part of that system, as
• British and Foreign Medical Review, vol. iii. p. 1 et seq.
distinguished from the portion which is directly derived from the Cerebro-spinal.
Such having been, as we believe, the doctrines currently taught, in this country at least, previously to the commencement of M. BrownSéquard's researches upon this subject, we shall now inquire how far they have been corrected, modified, or substantiated by the results of his investigations. The first point which he has established is the influence of the Sympathetic nerve upon the calibre of the ordinary bloodvessels, by the contraction it has the power of exciting in their muscular walls. In the latter part of 1851 and the commencement of 1852, M. Claude Bernard made public the results of his experiments on the effects of section of the cervical sympathetic; the most marked of these effects being besides the permanent contraction of the pupil, which had long previously been noticed by Pourfour du Petit, John Reid, and others an increased afflux of blood to the head, manifested in turgescence of the vessels of the inside of the ear, elevation of temperature, and augmented sensibility. Impressed, like many other physiologists, with the belief that these results (which might in some degree be likened to a state of persistent blushing) were all due to the paralysis of the muscular walls of the blood-vessels, M. Brown-Séquard considered that the normal state of things would be brought back if galvanism were employed to make them contract; and on making the experiment he found that the results were what he anticipated. These results, having been published in the Philadelphia Medical Examiner' for August, 1852, of course take precedence of those of similar experiments communicated a few months later by M. Claude Bernard to the "Société de Biologie," and of those obtained about the same date by Dr. Waller, whose experiments we had ourselves the opportunity of witnessing; and they obviously afforded the first decisive evidence of the influence exerted by the sympathetic system over the calibre of the blood vessels. Putting aside its action on the pupil, the principal results of section of the cervical sympathetic are clearly traceable to the increased afflux of blood to the head; and they may be very closely imitated by holding an animal suspended by its hind-legs for a short time, so as to produce congestion in the head. The chief antagonistic effects of section and of galvanization of the nerve may be thus contrasted:
Galvanization of the Nerve.
1. Contraction of Blood-vessels.
1. Dilatation of Blood-vessels. 2. Afflux of Blood. 3. Increase of Vital Properties. 3. Decrease of Vital Properties.
The source of what M. Brown-Séquard appropriately terms the vaso-motor fibres of the Sympathetic, distinctly lies (as does that of the fibres which dilate the pupil) in the Spinal Cord. Those preceeding to the vessels of the head come forth, according to him, by the roots of the last cervical and first and second dorsal nerves; but their place of real origin he believes to be partly the upper part of the spinal cord,