i8o THE POPULAR SCIENCE MONTHLY. 



downward and backward into the cerebellum, which he supposed to 

 be the center of volition ; from this " it descends through the poste- 

 rior 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 con- 

 siderably 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 eluci- 

 dated 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 con- 

 siderable 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 move- 

 ments of respiration. Now, Bell, brought up in the Edinburgh school, 

 and commencing his investigations under the influence of this pre- 

 possession, 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 in- 

 stitute 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. 



