But there are exceptions to this: in some cases (and only in those in which there is more or less rigidity of the paralysed muscles) these muscles respond to the galvanic stimulus with more force and readiness than the sound ones. In these cases the palsied muscles are kept in a state of excitement by some irritant disease within the cranium, and this constant condition of more or less active contraction augments the nutrition, and therefore the irri tability of the muscles.
It seems, however, most probable that in all the cases of paralysis, the excitability of the muscles to the galvanic stimulus is dependent not so much upon any change in the condition of the muscles themselves as upon the state of the nerves. If the nervous force in the nerves on the palsied side be deprsed, the galvanic stimulus will produce little or no effect upon the muscles of that side, whilst those of the other side will be distinctly excited: but should the nerves participate in any excitement propa gated to them from disease within the cranium, as in red softening, or an imitating tumor, or a contracting cyst, they will then respond to the galvanic current more readily than those of the opposite side.' I have thus endeavoured to show that the spinal cord is a centre of nervous actions, men tal and physical, to all parts which derive nerves j'rom it, the mental actions, however, requiring its association with the brain. Whatever phy sical nervous actions occur in parts whose nerves are spinal, must be referred to the cord alone; and whatever mental nervous actions occur through the agency of spinal nerves inust be referred to the cord in conjunction with the brain.
Of the quire of the columns if the cord.—I shall now inquire whether the parts into which the anatomist can divide the spinal cord have special functions. These parts are, on each side of the median plane, an antero-lateral co lumn and a posterior column. It has been a very prevalent opinion that the anteto-lateral column corresponds in function with the ante rior roots of the spinal nerves, and that the pos terior column corresponds with the posterior roots. This doctrine might have had a good foundation if it could be proved that the posterior or sensitive roots were implanted solely in the! posterior, and the anterior roots solely in the an terior columns. Nothing, however, is more cer tain than that both roots are implanted in the an tero-lateral columns, and it is extremely doubt ful that the posterior roots have any connection at all with the posterior columns. Hence, as far as anatomy enables us to judge, this distinction of function between the two columns cannot be admitted. On the contmry, anatomy indicates that the antero-lateral columns are compound in function. Their connection with the corpora striata and optic thalarni, and with the mesocephale through the anterior pyramids and fasciculi innominati, their reception of both the anterior and posterior roots, and their size in each region of the cord bearing a direct proportion to that of these roots, denote that these columns with the associated vesicular matter are the seat of the principal nervous actions, botlr mental and physical, with which the cord is concerned.
This view of the office of the antero-lateral columns is confirmed by comparative anatoray, which shows that the bulk of the organ or the variety in the size of its various parts depends mainly on these columns.
Pathological observations are also in favour of this doctrine. They distinctly denote that
lesion of the antero-lateral columns impairs the sensitive as well as the motor power to an extent proportionate to the amount oflesion. It is worthy of note, however, that while a slight lesion of the cord appears sufficient to impair or destroy the motor power, it requires a considerable ex tent of injury or disease to impair in any very marked degree the sensitive povrer. Some lesions of these columns destroy the physical nervous actions of the diseased or injured part of the cord—augmenting those of the portion below the seat of lesion, doubtless by increasing its polarity ; this is seen especially in cases of injury to the cord by fractures or dislocations of the spine.
Direct experiments afford no aid in deter mining the functions of the columns of the cord. Attempts to expose this organ either in living or recently dead animals are surrounded with difficulties, which embarrass the experi menter and weaken the force of his inferences, if, indeed, they afford any premises from which a conclusion may be drawn. The depth at which the cord is situate in most vertebmte animals, its extreme excitability, the intimate connection of its columns with one another, so that one can scarcely be irritated without the others being affected, the proximity of the roots of its nerves to each other, and the diffi culty, nay the impossibility, of stimulating any portion of the cord itself without affecting either the anterior or the posterior roots, are great impediments to accurate experiments, and sufficiently explain the discrepancies which are apparent in the recorded results of experi ments undertaken by various observers. More over, the resultant phenomena, after experi ments of this kind, are extremely difficult of interpretation, especially with reference to sen sation. " The gradations of sensibility," re marks Dr. Nasse, " are almost imperceptible ; the shades are so delicately and so intimately blended, that every attempt to dbterrnine the line of tmnsition proves inadequate. There is a great deal of truth in an expression of Calmeil, that it is much easier to appreciate a hemi-pa ralysis of motion than a hemi-paralysis of sen sation. If the anterior fasciculi of the cord possess sensibility but only in a slight degree, the mere opening of the spinal canal and laying bare tbe cord must cause such a degree of pain as would weaken or destroy the manifestations of sensibility in the anterior Fasciculi. This has not been sufficiently attended to by expe sinienters. Again, the practice of first irritating the posterior fasciculi, and afterwards the ante rior, roust have had considerable effect in pro ducing the same alteration. It is plain, that in this way the relation which the anterior fasci culi bear to sensation ust be greatly obscured ; yet, with the exception of some few experiments, this has been the order of proceeding generally adopted."* All the experimenters agree in attributing to the antero-lateral columns more or less power of motion, but we gain no satisfactory infor mation from this source respecting their sensi tive power, and probably for the reasons so well expressed by Nasse in the passage above quoted. But, indeed, we do not need the appeal to experiment in reference to this que.s tion, although, if a distinct and unequivocal response could be elicited by means of it, the additional evidence would be of great value.