46 NERVOUS 



there may be a bridge, however small, between the gray sub- 

 stance of the right and that of the left, peripheral impression 

 can be perceived, and thus pain be caused (indifferent trans- 

 mission, Stilling, Vulpian). 



Brown-Sequard has even gone further in the analysis of 

 special conductors composing the columns of the spinal cord ; 

 according to him there are more numerous and even more 

 distinct conductors of sensibility than have been generally 

 supposed. Basing his opinion upon clinical observations of 

 anaesthesia, hyperaesthesia, and of special subjective sensa- 

 tions, he allows special conductors for the sense of touch, 

 tickling, temperature, and of pain ; all these conductors are 

 situated in the posterior columns and intercross or decussate 

 in such a manner that every portion of the conducting zone 

 in a posterior lateral half of the spinal cord contains conduc- 

 tors coming from every point of the opposite side. Besides 

 these four conductors contained in the posterior columns, 

 Brown-Sequard notices three others which form the antero- 

 lateral columns, and pursuing a direct course (at least in the 

 spinal cord) ; these are the conductors of voluntary move- 

 ments, vaso-motors, and conductors of the muscular sense (!) ; 

 these constitute a sum-total of seven special conductors com- 

 prised in the spinal cord. 



2. The Spinal Cord as a Nerve Centre ; Reflex Centres. 

 Up to this point we have considered the spinal cord only in the 

 light of a conductor ; but we have mentioned before in the 

 general study of nerve centres (vide p. 32) that, judging from 

 modern investigations, the spinal cord should be considered 

 the principal one of these centres. The globules of the gray 

 matter of the spinal cord establish in a more or less direct 

 manner the functional connection between the centripetal 

 fibres which go towards this centre, and the centrifugal 

 fibres which go from this centre; hence they preside over 

 the reflex actions. 



So the gray matter of the spinal cord suffices for the trans- 

 formation of sensibility into movement, and most often it 

 does this without the intervention of the cerebral function. 

 If a section of the spinal cord be made below the brain, the 

 peripheral portions by this interference cease from being in 

 communication with a reflecting nerve centre ; and yet in 

 such an instance a movement of the extremities may be pro- 

 voked, as for example by tickling the bottoms of the feet. 

 This same fact is also observed in certain paralyses, where, in 

 spite of alterations of the upper part of the spiual cord, a 



