FUNCTIONS OF THE SPINAL CORD. 627 



we' reason to believe that a similar regeneration may take place to a con- 

 siderable extent in Man, this being marked by the gradual return of sensi- 

 bility and power of voluntary movement in the lower limbs which had been 

 at first completely paralyzed. This regeneration is of course less likely to 

 occur in cases of disease, when the parts around are iu 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 the Cord to be acci- 

 dentally w r ounded by the penetration of a sharp instrument between the 

 vertebra?, in the mode iu which experiments 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. 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. 



500. The Spinal Cord considered as a Conductor of Sensory Impressions and 

 Motor Impulses ThePosterior Columns. The concurrent testimony of nearly 

 all observers shows that the posterior columns are highly sensitive, the 

 slightest irritation applied to their surface causing the animal to give indi- 

 cations of pain ; whilst, after division, irritation of their cut surfaces not 

 only causes pain, but in many instances convulsive movements also occur. 

 Experiments, moreover, can be made, which demonstrate that the pain is 

 attributable, not to the fibres of the columns themselves, but to the posterior 

 roots of the nerves which traverse them. Thus, if the Spinal Cord be ex- 

 posed, and a few minutes allowed to elapse to permit the effects of the mere 

 exposure to pass off, the sensibility of 

 the skin of the hind limbs may be FIG. 229. 



shown to be everywhere perfect. If a 

 section be now made through the pos- 



terior columns (c P, Fig. 229) bypass- {^s^^f^-^K^K^^^^fr^^^^^ s a 



ing a tenaculum from side to side, and 



Cutting down Upon it, and any nerve N.Nerve. GS, or SG, Gray Substance. 



(N) connected with a part of the cord PC, or CP, Posterior CAL, Antero-lateral 

 , / , , i . , , , Column. Column. 



below the section be stimulated as by 



pricking, the cries and movements of the animal show clearly that the con- 

 duction of sensory impressions is not materially interfered with. On the other 

 hand, if after the same preliminary proceed- FIG 93Q 



ings, the whole of the Spinal Cord be divided 

 transversely (caL, sg, Fig. 230), with the ex- 

 ception of the posterior columns (cp), it will 

 be found that the sensibility of the posterior 



limbs is entirely abolished. It is clear, therefore, that the posterior columns 

 do not constitute the continuation of the posterior roots. The circumstance 

 that after division of these columns the surface of both the caudal and 

 cephalic segments of the cord are acutely sensitive, is considered by M. 

 Brown-Sequard to be due to the fact that some of the sensory fibres of the 

 posterior roots (Fig. 238) ascend, whilst others descend a little way in these 

 columns before crossing to the opposite side. There is good reason, then, for 

 believing that the proper fibres of the posterior columns are insensitive, and 

 it seems not improbable that they consist essentially of commissural fibres 

 (F, Fig. 238), which run longitudinally, and bring different segments of the 



No. 45, and 1850, No. 30; also the Comptes Rendus de la Societe de Biologie, 1849, 

 1850. 



