Billeder på siden

readers to the noble sentiment we have italicized, by way of preface to the enquiry through which we purpose to conduct them, as to the merits of the most important among the numerous sets of researches carried on by one of the most distinguished experimental physiologists of our time, -namely, those investigations into the Physiology and Pathology of the Nervous System, of which M. Brown-Séquard gave an account (with experimental illustrations) in a course of lectures delivered by him last summer at St. Bartholomew's Hospital, and afterwards repeated at the Royal College of Surgeons, by the special request of its Council. The slight notice which we have already given of the results of some of these investigations (vol. xvii., p. 407 et seq.) by no means relieves us from the responsibility of now critically examining into the value of the entire series; and we are sure that no one is more desirous than M. Brown-Séquard himself, that their merits should be tested by a careful scrutiny into the validity of his methods, the accuracy of his statements, and the justice of his deductions. If they prove able to bear such an ordeal, they are fairly entitled to take rank as physiological verities, notwithstanding their contrariety to much that has been previously received as true. We are not among those who are disposed to stand by a doctrine, merely because it is currently accepted, or because it has been taught by men whose authority we hold in the highest respect. Such reasons for upholding it are good against the slight assaults of such opponents as are themselves deserving of but little credit; but when a formal contradiction is given even to our most cherished beliefs, by men whose patient search for truth, and whose capacity for its discovery, command our highest respect, we do not see that any other honest course is left to us, than that of candidly weighing the new facts and arguments against the old, assigning to each its worth according to the best judgment we can form, and striking the balance without more regard to our previous conviction than is found to be justified by the stability of the base on which it rests.

Now, in endeavouring to form this kind of estimate of the merits of M. Brown-Séquard's doctrines, as compared with those which have been currently accepted in Physiology, we must confess in limine that we are not able to speak from personal experience as to more than a small part of his experimental results. But we feel scarcely less readiness to credit those which we have not ourselves witnessed, than to trust our own observation as to those which we have; so great is our confidence in M. Brown-Séquard's aptitude for observation, which allows no phenomenon to escape him, in the exactness with which he not merely performs his operations but subsequently determines the precise nature of the lesion he has inflicted, and in the scrupulous truthfulness with which he records every fact which bears upon the question at issue, whether or not it is favourable to his own view of the case. This confidence is founded in part on the careful watch we have ourselves kept on M. Brown-Séquard's scientific course, from the time when his researches first began to attract attention about twelve years ago, and on the estimate we have formed of his character from

the personal acquaintance which it was our good fortune to commence with him not long afterwards; and in part on the fact that several of his capital experiments have been performed before a Commission of the Société de Biologie, consisting of MM. Cl. Bernard, Bouley, P. Broca, Giraldès, Goubaux, and Vulpian, whose report drawn up by M. Paul Broca, bears the fullest testimony to the accuracy with which he has described both the operations and their results.

The Course of Lectures which M. Brown-Séquard has published in the columns of the Lancet,' is much fuller in detail than that which he actually delivered at the College, especially in regard to the evidence supplied by Pathological observation; still on many points it is far from being complete; and we think that we shall do most justice both to him and to our readers, by limiting our discussion of his doctrines to the following questions, which we shall take up in succession:

1. The relative functions of the Anterior and Posterior Roots of the Spinal Nerves.

2. The channel through which Sensory Impressions are conveyed from the Spinal Nerves to the Encephalon.

3. The Decussation of the Conductors of Sensory Impressions in the Spinal Cord itself.

4. The channel through which Motor power is conveyed from the Encephalon to the Spinal Nerves.

5. The motor action of the Sympathetic system on the walls of the blood vessels.

6. The action of the Nervous System (especially, though not exclusively, its Sympathetic division) upon the Organic functions of Nutrition and Secretion.

I. The first question to which we have to apply ourselves,-that of the Relative Functions of the Anterior and Posterior Roots of the Spinal Nerves,-is one which, although commonly supposed to have been conclusively settled by Sir C. Bell and his immediate followers, still presents certain points of difficulty. And it is obvious that until these shall have been elucidated, no conclusions regarding the functions of the different columns of the Spinal Cord can be satisfactorily drawn either from experiment or from pathological observation. It was early observed by Magendie, that although pain is obviously the principal result of irritation of the posterior roots, and muscular contraction the principal result of irritation of the anterior roots, yet that local movements are induced by irritation of the posterior roots, and that pain is obviously excited by irritation of the anterior; and hence he was for a time erroneously led to the conclusion that each set of roots is subservient to both functions, the posterior being chiefly but not exclusively sensory, and the anterior chiefly but not exclusively motor. Further enquiry, however, has served to demonstrate the erroneous nature of this conclusion; the movements excited by irritation of the posterior roots, and the pain induced by irritation of the anterior, being clearly due in each case to the participation of the nerve-roots not thus experimented on. For if, before irritating the posterior

roots, the operator divide the anterior, he can excite no movement by irritation of the former; and if, instead of irritating the posterior roots whilst connected with the spinal cord, he divide those roots, he finds that motion can only be excited by irritation of their proximal segment, no irritation of their distal segment having the least power of calling it forth. On the other hand, if, before irritating the anterior roots, the operator divide the posterior, he finds that irritation of the anterior no longer gives signs of pain; and if, instead of irritating the anterior roots whilst in connexion with the spinal cord, he divide those roots, he finds that signs of pain can only be excited by irritating their distal segment, no such indications being called forth by irritation of their proximal segment. It is obvious from these facts, that the movements excited by irritation of the posterior nerve-roots are in reality reflex actions; the irritation being first propagated by the afferent fibres to the central organs, and being thence reflected through the motor to the muscles. And it would at first seem equally obvious, that the sense of pain excited by irritation of the anterior roots is the result of the transmission of the effect of the irritation to the peripheral organs, through which it is reflected back, as it were, to the central.

Such was the explanation of the phenomenon that was originally adopted by Magendie, who designated this form of nervous activity as "recurrent sensibility." Owing, however, to the obvious difficulty attending Magendie's interpretation, another explanation proposed by Kronenberg and Pappenheim has met with much acceptance-namely, that the sensitiveness of the anterior roots is due to their containing fibres which pass back into them from the posterior at the point of junction of the two sets of roots, so that when they are irritated, the sensory current passes peripherally no farther than that junction, being then transmitted direct to the spinal cord through the posterior roots. But if this were the case, it is obvious that such transmission of the sensory current would not be interrupted by section of the trunk of the nerve beyond the junction of the two roots; whilst the fact has been demonstrated by the experiments of Magendie, Cl. Bernard, Volkman, Schiff, and Brown-Séquard himself, that the paininducing effect of the irritation proceeds as far as the peripheric extremity of the nerve-fibres, no signs of pain being given except when the continuity is complete between the part of the root or trunk irritated, and the muscles which that trunk supplies. Further, it appears from these experiments, that the amount of pain induced is proportional to the force of the muscular contraction called forth; and thus it seems obvious that the effect of the irritation is really transmitted along the motor fibres; and that the excitement of a current in the sensory fibres is consecutive upon the action of the muscles to which they are distributed.

A very ingenious mode of accounting for this excitement is proposed by M. Brown-Séquard. Every one is now acquainted with the phenomenon of "induced contraction", first discovered by Matteucci, in which the contraction of one muscle calls forth the contraction of a

second whose motor nerve has been dissected out and laid upon the first; and it is certain that, whether the excitation of the nerve-current be due, as maintained by Matteucci, to a sort of galvanic discharge in the contracting muscle, or, as asserted by Du Bois-Reymond, to a diminution of the ordinary muscular current at the moment of contraction, it results from some change in the electric state of the muscle. To this change M. Brown-Séquard considers that we may attribute the excitement of that current in the afferent nerves of the muscle itself, which makes us conscious of the state of its contraction, and thus affords the sensations by which our voluntary efforts are guided; whilst it is by a more intense excitement of the same kind, that the pain of cramp is produced. This pain, according to him, depends upon the degree of resistance which is opposed to the contraction; and he adduces the following well-known physiological and pathological phenomena in support of his doctrine:-the uterine pains are far more severe when the parturient efforts are antagonized by the rigidity of the os uteri or of the external parts, than they are when the contractions are effectual in overcoming the resistance; in cases of anal fissure, the pain due to the spasm of the sphincter is increased when there is a resistance to the contraction, and ceases when that resistance is destroyed by section of the sphincter; and in cases of painful contracture (by which we suppose is meant permanent contraction) of other muscles, the pain increases when the muscles are elongated, but disappears entirely or almost entirely when the resistance is completely or almost completely destroyed by division of the tendon. Two other facts occur to us, which harmonize well with this view. The experiments of M. Du BoisReymond, as we can ourselves testify, clearly show that the amount of electric disturbance depends, not on the amount of muscular contraction produced, but on the amount of contractile effort put forth; this effort being facilitated by using means to resist contraction, as by grasping in the hand a full-sized stick. So, again, it is well known that the reflex expulsive efforts of parturition, defecation, urination, &c., become more violent the more they are resisted; the explanation of which seems partly (at any rate) to be in the intensification of the contraction by the additional stimulation conveyed to the spinal cord through the afferent nerves of the contracting muscle itself. And we may further notice, that when the action of any set of muscles is ordinarily dependent upon guiding sensations originating out of themselves, but from defect of these is brought to depend upon sensations originating in themselves, those sensations are painful. Of this any of our readers may convince himself by attempting to rotate his eye-balls when he has completely excluded the light by closing the lids and covering them with his hand. And it is also a matter of experience, that when the deaf-mute is taught to speak, it is in the first instance at the expense of considerable uneasiness in the larynx; this uneasiness, in the well-known case of Dr. Kitto, having amounted to a degree of pain sufficient to induce him to abandon all attempts to speak for several years.

Whether or not M. Brown-Séquard's explanation of the pheno

[blocks in formation]


menon known as "recurrent sensibility" be correct, it may be taken as proved by experimental inquiry that the recurrence is only apparent, and that the pain occasioned by irritation of the anterior roots of the spinal nerves is really felt through the posterior, and is of the nature of the pain of cramp, being dependent on the muscular contraction which that irritation calls forth. "recurrent sensibility" does not furnish any more real objection to Sir Hence the phenomenon of C. Bell's doctrine of the distinctness of the motor and sensory nerves, than does the phenomenon of reflex movement; the excitation of either set of nerves producing a certain excitation of the other, in the one case through the peripheral organs, in the other through the central. There are certain results of experiments on frogs, however, which it seems difficult to explain except upon the hypothesis that some, at least, of the nerve-fibres which minister to the muscular sensations that serve for the guidance of movements, pass to the spinal cord through the anterior roots; but we are not sure that they necessarily require this inference, as we are disposed to think that the conditions of reflex and of voluntary movement as to this particular are very different, and that the actions cited by M. Brown-Séquard as having been performed after all the posterior roots of the spinal nerves had been cut, do not necessarily imply the existence of guiding sensations. At any rate, the harmonious results of the best-conducted experiments on birds and mammals appear fully to justify the conclusion, that the transmission of impressions which occasion pain takes place through the posterior roots alone.

II. From the study of the relative endowments of the anterior and posterior roots of the spinal nerves, M. Brown-Séquard naturally passes to that of the relative functions of the several columns of the Spinal Cord; and he makes it his first business to ascertain the channel through which Sensory impressions are transmitted to the encephalon. Every one who is acquainted with the history of Sir C. Bell's inquiries. must be aware, that when he had established the relative functions of the anterior and posterior roots of the spinal nerves, he at first attributed the corresponding functions to the anterior and posterior columns of Spinal Cord; regarding the latter as the conductors of sensory impressions upwards from the nerve-roots to the encephalon, and the former as the conductors of motor impulses downwards from the encephalon to the nerve-roots. But it is equally well known amongst his followers in this country, that he did not continue to entertain this idea; but that he was led, both by anatomical enquiry and by pathological observation, to consider the lateral columns as the parts of the cord chiefly if not entirely concerned in the transmission of sensory impressions, and partly also in that of motor impulses. Of late, however, the experiments of M.. Longet, who began by opposing the doctrines of Sir C. Bell, and ended by becoming more Bellian than Sir Charles himself, have been generally accepted, both in France and England, as justifying his reversion to Bell's former doctrine, notwithstanding the difficulty of reconciling it with pathological phenomena. The experiments of M. Brown-Séquard, however, have led him to.

« ForrigeFortsæt »