76 THIRD REPORT — 1833. 



ever, remained mere matter of conjecture until a recent period, 

 when it was unequivocally established by Sir Charles Bell. 

 From the original experiments of that most distinguished phy- 

 siologist, repeated and confirmed by Magendie, it follows that 

 the faculty of conducting sensations resides exclusively in the 

 two posterior columns of the medulla, while that of communica- 

 ting to the muscular system the motive stimulus impressed by 

 volition is the attribute of the two anterior columns. The same 

 limitation of function is found in the nervous roots which spring 

 from these separate columns. Thus each spinal nerve is fur- 

 nished Avitli a double series of roots, one set of which have their 

 origin in the anterior medullary column, and one in the pos- 

 terior. The spinal nerves are, in consequence of this anatomi- 

 cal composition, nerves of twofold function, containing in the 

 same sheath distinct continuous filaments from both columns, 

 and exercising, in the parts to which they are distributed, the 

 double oflice of conductors of motion and sensation. It will 

 afterwards appear, in our history of individual nerves, that all 

 those which spring from the brain, except the fifth and eighth 

 pairs, possess only a single function. 



Sufficient experimental proof of the foregoing propositions 

 has been furnished by Sir Charles Bell and by M. Magendie. 

 Thus, division of the posterior roots of the spinal nerves is uni- 

 formly followed by total absence of feeling in the parts of the 

 body to which the injured nerves are distributed, while their 

 motive power remains undiminished. Magendie has further 

 observed, that if the medullary canal be laid open, and the two 

 posterior cords be touched or pricked slightly, there is instant 

 expression of intense sufi^ering; whereas, if the same or a greater 

 amount of irritation be applied to the anterior columns, there 

 are scarcely any signs of excited sensibility. The central parts 

 of the medulla seem also nearly impassable *. They may be 

 touched, and even lacei*ated, according to Magendie, without 

 exciting pain, if precautions are taken to avoid the surrounding 

 medullary substance. In general, the properties of the spinal 

 marrow, and especially its sensibility, seem to reside mainly on 

 its surface ; for slight contact, even of the vascular membranes 

 covering the posterior columns, caused acute pain. 



The first experiment of Sir C. Bell consisted in laying open 

 the &pinal canal of a living rabbit, and dividing the posterior 

 roots of the nerves that supply the lower limbs. The animal 

 was able to crawl. In his second trial he first stunned the 

 rabbit, and then exposed the spinal marrow. On irritating the 



* Annales de Chimie et de Physique, torn, xxiii. p. 436. 



