Of the.functions of the spinal cord.—It was long held that the spinal cord was no more than a bundle of nerves proceeding from or to the brain, and emerging at various points of the vertebral canal to be distributed to their destined regions." The anatomy of the organ, however, suffi ciently exposed the error of this opinion. The existence of a large quantity of vesicular matter in it varying in quantity according to the bulk of its segments showed that it was more than a mere fasciculus of nerves. Although the true office of the spinal cord was known to physio logists long before, to Prochaska for example, Call appears to have been the. first who ad duced the best proofs from anatomy to show that the spinal cord was not a mere appendage to the brain, but a special centre in itself. Ilis principal arguments were derived from the want of any constant proportion in bulk be tween it and the brain, the spinal cord being small with a large brain, as in man, and large with a small brain, as in the inferior mammalia and in other vertebrate, from the fact that it _ does not taper gradually in proportion as it gives off nerves, but on the contrary is alter nately large or small according to the number and volume of the nerves which are given off' from its various segments; and, lastly, from the ana logy which he indicated between the spinal cord of vertebrata and the ganglionic chain of articulata, the former consisting of a series of ganglia fused together, the latter remaining separate by reason of the peculiar disposi tion of the bodies of these animals in distinct segments.
The determination of the functions of the nerves which are intimately connected with or implanted in the spinal cord affords some clue to the solution of the problem as to its own office. There can be no doubt that as the nerves of sensation as well as those of motion of the trunk and extremities are all, to say the least, intimately connected with the cord, this organ must be the medium of the reception and propagation of the sentient impressions made upon the one, and of the mental or phy sical impulses which excite the others.
If, moreover, we look to the results of expe riments on the lower animals, or to the effects of injury or disease in the human body, we obtain the following important facts :-1st, that the perfect connexion of this organ, in all its integrity, with the encephalon is the essential condition for thefull and complete exerciseof the nervous force, whether for sensation or voluntary motion, as far as regards the trunk and extremi ties; 2nci, that division of the cord, so as com pletely to separate the lower from the upper segment, causes paralysis both of sensation and voluntary motion in the parts supplied with nerves from the lower segment; 3rd, if the section be made high up in the neck so as to separate the cord from the medulla oblongata, all the parts supplied by spinal nerves will be paralysed in the same way ; hy such an expe riment the spinal cord remains entire, but its continuity with the encephalon is interrupted.
In cases of injury to the vertebral column it may be laid down as the rule that the higher the seat of injury the more extensive will be the paralysis. A man who has received exten sive injury of the spinal cord high up in the neck is like a living head and a dead trunk, dead to its own sensations, and to all voluntary control over its movements. The same rule prevails with regard to the effects resulting from disease of the vertebrze or from any intra-spinal growth, or from a morbid state of the cord itself, there being only this difference, that where the morbid change is chronic, the paralytic effects are less marked than in injury or acute disease. In all cases the extent of the paralysis affords a correct indication of the seat of the solution of continuity.
If the spinal cord be divided partially in the transverse direction, there will be paralysis of parts on the same side with the injury. Dr. Yellowly has put on record an experi ment of Sir Astley Cooper's, in which he divided the right half of the spinal cord in a dog just above the first vertebra. The effect was paralysis of the motions of the ribs on the right side, and of the right posterior and pos terior extremities, with irritation of those of the left side.* A longitudinal section of the cord along the median line in frogs does not cause paralysis ; it gives rise, however, to a temporary disturbance of the functions of the cord which soon subsides.t Continuity of the spinal cord and encepha lon is then the condition necessary to establish the control of the former organ over the vo/utt tiny movements and sensations of the trunk. The disunion of the cord or any portion of it from the encephalon dissociates the cord or the separated segment of it from all participa tion in mental nervous actions. So long as the cord is united with the brain, it takes a certain share in mental nervous actions, in acts of sen sation and volition ; this, however, it loses when disease or accident separates the one from the other.
It is plain, then, that the spinal cord, although apart from the encephalon it takes no share in sensations and voluntary actions, (for then, indeed, these phenomena cannot take place as far as regards the trunk and extremities,) while united with the encephalon participates fully in sensori-volitional actions, and its integrity is quite necessary to the perfection of those actions.
I repeat that we are not justified in supposing that the mind localises itself exclusively in some or all of the gangliform bodies, the assemblage of which constitutes the encephalon ; but this we may assert, with perfect justice, that when the cord has been separated from the encephalon, the mind appears as it were to cling to the latter organ, and to lose all its connection with the former.