Some support is obtained for this view of the function of the posterior columns from the phe nomena of disease. In many cases, in which the principal symptom has been a gradually in creasing difficulty of walking, the posterior coIumns have been the seat of disease. Two kinds of paralysis of motion may be noticed in the lower extremities, the one consisting simply in the impairment or loss of the voluntary motion, the other distinguished by a diminution or total loss of the power of co ordinating movements. In the latter form, while considerable voluntary power remains, the patient finds great difficulty in walking, and his gait is so tottering and uncertain that his centre of gravity is easily displaced. These cases are generally of the most chronic kind, and many of then) go on from day to day with out any increase of the disease or improvement of their condition. In two examples of this variety of paralysis I ventured to predict dis ease of the posterior columns, the diagnosis being founded upon the views of their func tions which I now advocate ; and this was found to exist on a post-moitem inspection; and in looking through the accounts of re corded cases in which the posterior columns vvere the seat of lesion, all seem to have com menced by evincing more or less disturbance of the locomotive powers, sensation being af fected only when the morbid change of struc ture extended to and more or less involved the posterior roots of the spinal nerves.
Bellingeri put forward the opinion that the anterior columns of the spinal cord influenced movements of flexion, and the posterior co lumns those of extension ; to the grey matter he assigned the office of propagating sensitive impressions to the brain ; and the lateral co lumns, according to him, exercised an influ ence upon the organic functions of nutrition and circulation.
The views already referred to respecting the grey matter show that it cannot be legarded as devoted exclusively to one function of the ner vous system ; nor can it be viewed as capable of taking its part in nervous actions without the white or fibrous matter.
Valentin adduces some experiments not un favourable to the supposition that the nerves of extensor muscles pass towards the posterior part of the cord, and those of the flexor muscles to the anterior part. Ile found that if, in frogs, the posterior surface of the cord on one side of the posterior median fissure in the region of the sccond or third vertebra were irritated by the point of a needle, the anterior upper extremity of the same side was extended and drawn backwards. When the anterior surface was irritated, the limb was drawn forwards to the head. Irritation of the posterior column in the region of the sixth vertebra and below it caused extension of the posterior extremities, but they were thrown into flexion by irritation of the anterior columns.
These are remarkable results; they need, however, the confirmation of other observers. If they be correct, the fact of the connection of the nerves of extensor n)uscles with the posterior columns has an interesting relation with the supposed locomotive function, for there can be no doubt that movements of ex tension contribute largely to the ordinary attitudes and to the various modes of pro gression.
Valentin refers to cases in which the anterior columns having bees) the seat of tumor or of softening, more or less permanent flexion of the lower limbs had emued. These cases do not favour his view unless he can show that the lesion in all the cases was of the irritant kind, inducing a spasmodic contraction of the flexor muscles; for if the lesion be of a paralysing kind, the effeca would be to paralyse the flexor muscles and allow the extensors full sway. The explanation of the flexed state of limbs in cases of this kind is probably to be derived from a chronic state of contraction induced in the muscles themselves by the lesion of the nervous centre, and the state of flexion is as sumed rather than extension in consequence of the predominance of flexor muscles over ex tension.
Sir Charles Bell's doctrine, which assigned to that portion of the cord which is interme diate between the roots of the nerves, ( Iris middle column,) a special power over the move ments of respiration, has long ceased to gain attention from physiologists. It wanted the support of anatomy. The so-called middle column had no defined limits, nor could it be proved that any respiratory nerves were con nected with this region of the cord, excepting a few fibres of the spinal accessory nerve. The distinct anatomy of a respiratory system of nerves existed only in the imagination of the inventor of the doctrine. It could not he shown by experiment that the so-called nerves of respiration had any special respiratory func tion beyond that which they exercised as the motor nerves of certain muscles. And among the nerves which Sir C. 13ell had classed toge ther as nerves of respiration, were some which certainly had no necessary connection with that function. Of these the portio dura and the glosso pharyngeal are examples.
IVIlience of the spinal cord upon the organic functions.—The influence of the spinal cord upon certain organic functions has engaged a large share of the attention of experimental physiologists. It has been said to have a very dtrect control over the functions of circulation, calorification, secretion, especially that of the kid neys.