668 OP THE FUNCTIONS OF THE NERVOUS SYSTEM. 



the Nerve-trunks and the Encephalic centres ; and in the second place, as itself 

 an independent centre of nervous power. As a mere conductor of nervous force, 

 its functions are the same as those of a nerve-trunk ; for, if it be divided, all 

 the parts of the body which are solely supplied by nerves coming off below the 

 point of section are completely paralyzed as far as regards sensibility and volun- 

 tary movement ; no impressions made upon them having the least power to 

 affect the consciousness, and no exertion of the will being able to determine 

 contraction of their muscles. This state of paraplegia, which may be experi- 

 mentally induced in animals, is frequently exhibited in Man as a result of injury 

 or of disease which seriously implicates the Spinal Cord ; and, as, it has been 

 shown that among the lower animals complete reunion of the Cord may take 

 place after complete division, as indicated by the entire restoration of its func- 

 tional powers and the complete redintegration of its structure ( 349), so have 

 we reason to believe that a similar regeneration may take place to a considerable 

 extent in Man, this being marked by the gradual return of sensibility and 

 power of voluntary movement in the lower limbs which had been at first com- 

 pletely paralyzed. This regeneration is of course less likely to occur in cases 

 of disease, when the parts around are in an unhealthy state, than when the 

 paralysis is due to injury, which all the restorative powers of the system are 

 engaged in repairing: but it is to be remembered that, as the injuries which are 

 likely to cause such lesions of the Cord are nearly always attended with severe 

 concussion (it being very rare for it to be accidentally wounded by the penetra- 

 tion of a sharp instrument between the vertebrae, in the mode in which experi- 

 ments are made upon animals), some of their first effects are attributable to the 

 shock which it has sustained; so that the partial recovery which takes place at 

 an early period must not be regarded as the result of regeneration of nervous 

 tissue, which requires a much longer time for its completion. 



704. The conducting power of the entire Spinal Cord being thus established, 

 we have next to inquire whether any difference in endowment can be shown to 

 exist in its several columns. By Sir C. Bell, it was supposed that the anterior 

 columns possess the same endowments as the anterior roots of the nerves, and 

 the posterior columns the same as the posterior roots } and this view is supported 

 by the experiments of Longet, 1 who deduces from them the conclusion, that 

 irritation of the posterior columns, as of the posterior nerve-roots, gives rise to 

 excruciating pain, without exciting any other movements than such as are called 

 into action in reflex respondence to the impression, and that irritation of the 

 anterior columns excites movements directly (or without reflexion), and is not 

 a source of pain. Again, he found that when the Spinal Cord was completely 

 divided, and time was allowed for the reflex activity of the cord to subside (this 

 disappearing rapidly in adult warm-blooded animals), the application of an 

 electric current to the posterior columns of the separated part occasioned no 

 movement whatever, whilst its transmission through the anterior columns called 

 forth vigorous movements. Moreover, he states that the effects of the reversal 

 of the electric current, transmitted through the anterior columns, were the same 

 as those of the same reversal when the currents were transmitted through the 

 anterior roots of the spinal nerves 1 ; whilst they differed from those produced by 

 the same change in the direction of the currents, transmitted through a nerve 

 of mixed endowments. The researches of Van Deen 3 lead on the whole to 

 the same conclusions : but they tend, in his opinion, to show that the conduct- 

 ing power both of the anterior and posterior columns is very imperfect, if their 

 white strands be completely separated from their gray matter. His experiments 



1 "Anatomic et Physiologie du Systeme Nerveux," 1842 ; and " Traite de Physiologic," 

 1850, torn. ii. pp. 184-8. 



2 "Traites et Decouvertes sur la Physiologie et la Moelle Epiniere," Leide, 1841. 



