286 NEKVOUS SYSTEM. 



trcmitics after complete section of the posterior white col- 

 umns. 1 



At the time the above-mentioned experiments were 

 made, our knowledge of the properties of the cord was very 

 incomplete, and it was difficult to understand how any of 

 its fibres could conduct sensory impressions and yet be in- 

 sensible to direct stimulation ; but now we know that the 

 gray matter does act as a conductor, and yet it is certainly 

 insensible. The simple questions now to be determined are 

 the following : 



1. Does or does not the white substance of the posterior 

 columns of the cord conduct sensory impressions to the 

 brain ? 



2. Does the entire gray substance of the cord act as a 

 conductor of sensation ? 



3. Do both the gray matter of the cord and the white 

 substance of the posterior columns act as conductors, or 

 does either one act to the exclusion of the other ? 



These questions may now be considered as definitively 

 answered by the most positive and unmistakable results of 

 experiments upon living animals, which, while they render 

 the precise function of the white substance of the posterior 

 columns a matter of conjecture, leave no doubt with regard 

 to t!he parts of the cord which act as conductors of sensory 

 impressions. This statement is based upon the researches 

 of Brown-Sequard, whose experiments upon this subject 

 have been often confirmed and never successfully contra- 

 dicted. 



The experimental answer to the first question is capable 

 of but one construction. If the white substance of both 

 posterior columns be divided, the sensibility of the posterior 

 extremities is not diminished, at least as far as can be shown 



1 BELLINGERT, De Medulla, Spinali Nervisgiie ex ea prodeuntibus, Annolationes 

 Anatomico-Physiologicce, Lectce a die Sjanuarii 1822 ad ZQjanuarii 1823, p. 237 ; 

 Experimenta Physiologica in Medullem Spinalem habita, Lecta die 13 junii 1824, 

 p. 311;' and LONGET, op. cit., tome iii., p. 341. 



