DISCOVERIES OF MR. BELL. 137 



brain, along the nerves, to the parts to be affected, and 

 -may be called the stimulus of volition. 



Emily. Is this function also demonstrated by expe- 

 riment, like the last ? 



) r . B. It is well known, that if the nerves which 

 are distributed to a muscle, be divided, that muscle will 

 be found to be entirely beyond our control, however ea- 

 ger our wish, or strong our efforts to move it. 



Emily. 'It appears then, that when a nerve is divi- 

 ded, it is neither capable of transmitting the impressions 

 made on its extremities, nor of conveying the stimulus 

 of volition to its extremities. Now this double func- 

 tion of the same nerve puzzles me exceedingly, for 

 functions so different, one would imagine, would be ex- 

 ecuted by different instruments. 



Dr. B. This reasoning always had great plausibility, 

 and its truth has lately been most satisfactorily demonstra- 

 ted by Mr. Charles Bell. He was first led to correct 

 views of this subject, by thinking on the difference which 

 the nerves of the spine, and the brain, present in regard 

 to their origin, or as we have called it, their termination. 



The former, as we have already seen, are connected 

 with the spinal marrow by two roots, and each root with 

 a distinct track or column of nervous matter, three of 

 which columns compose each side of the spinal mar- 

 row, and may be easily distinguished through its whole 

 Bourse, and even in the brain itself. If any one of these 

 nerves be divided, both the sensation and the motion of 

 the part to which it leads, are lost. The nerves of the 

 brain, on the contrary, are connected by a single root 

 only, and the division of which, is found to occasion 

 the loss of but one of these powers. Thus, if the optic 

 nerves be divided, the sense of vision disappears, but 

 the motions of the eye are performed as readily as be- 

 fore. To ascertain now, whether this difference of pow- 

 er depends on the kind of connection which the nerves 

 maintain with the brain and the spinal marrow, he de- 

 termined to divide the roots of the spinal nerves singlv,, 

 12* 



