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Page:Popular Science Monthly Volume 21.djvu/190

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downward and backward into the cerebellum, which he supposed to be the center of volition; from this "it descends through the posterior columns of the spinal marrow, and expands through the posterior fasciculi of all the nerves, which are, therefore, the nerves of volition, toward the muscular system."

Thus, then, it is clearly Mr. Alexander Walker who must be credited with the first promulgation of the idea of the functional distinctness of the anterior and posterior roots of the spinal nerves, in virtue of what he supposed to be their connections with the cerebrum and the cerebellum respectively: but, working out this idea under a wrong conception of the relative functions of the two brain-centers, he was led to regard the anterior roots as sensory, and the posterior as motor; and, as he neither submitted nor proposed to submit this erroneous doctrine to the test of experiment, it fell unheeded to the ground.

Now, those who only know the history of Bell's work either directly or indirectly through Mr. A. Shaw's first account of it, will be considerably surprised to learn that (whether or not he was acquainted with Walker's speculations) he pursued, in the first instance, precisely the same anatomical track; and that, through his having followed this under the guidance of another wrong preconception as to the functions of the cerebellum (which had not at that date been elucidated by experiment), the physiological conclusion at which he arrived was even further from the truth than that of his predecessor.

A distinguished Edinburgh professor of the last century, Dr. Robert Whytt, who had studied with great care what he termed the "vital and involuntary motions" of the body, had argued with considerable ingenuity that, while the cerebrum is the center of sensation and the originator of voluntary motion, the cerebellum is the organ of such "vital and involuntary motions" as the action of the heart and the muscular walls of the alimentary canal, together with the movements of respiration. Now, Bell, brought up in the Edinburgh school, and commencing his investigations under the influence of this prepossession, was led by it in an entirely wrong direction; for the whole argument of his "Idea" is to the effect that the anterior roots of the spinal nerves minister both to sensation and voluntary motion, in virtue of their connection with the cerebrum, while the posterior roots "govern the operation of the viscera necessary to the continuance of life," in virtue of their connection with the cerebellum. He did institute experiments, indeed, both on the columns of the spinal cord and on the roots of the spinal nerves; but, under the influence of his anatomical preconception, he entirely missed the true meaning of their results, and deemed them to be confirmatory of his erroneous views:

"Experiment I.—I opened the spine, and pricked and injured the posterior filaments of the nerves; no motion of the muscles followed.