DECUSSATIOX OF THE SENSORY CONDUCTOES. 293 



In treating of the cord as a conductor of sensory impres- 

 sions, we have already shown that this function is performed 

 by the gray substance alone. "We have also seen, in connec- 

 tion with the phenomena of conduction of the motor stimu- 

 lus, that this is effected by the antero-lateral columns, which 

 do not act as sensoiy conductors, except by virtue of their 

 gray matter. As it is impossible to divide the gray matter 

 with certainty without injuring the white substance, and as 

 we are fully acquainted with the motor properties of the 

 cord, we are prepared to comprehend the effects upon con- 

 duction of sensory impressions which follow division of one 

 or the other lateral half. In our detail of experiments, we 

 will not consider the phenomena of hypersesthesia, but con- 

 fine ourselves to the loss or diminution of sensibility. 



Brown-Sequard was the first to demonstrate decussation 

 of the sensory conductors in the cord itself ; and, although 

 his experiments upon this subject are almost innumerable, 

 and his writings, scattered, voluminous, and sometimes not 

 free from the obscurity due to unnecessary refinement and 

 elaborateness of detail, the main facts can be expressed in 

 a very few words ; and he may justly be said to have created 

 the physiology of the sensory conductors. 



Brown-Sequard repeated the experiments of Galen and 

 of Fodera, dividing the cord longitudinally in the median 

 line, producing complete paralysis of sensation on both sides 

 in all the parts below the section. By this operation, if the 

 section had been made accurately in the median line, the 

 only fibres that could be divided were those passing from 

 one side of the cord to the other. 



The second experimental proof of the decussation of sen- 

 sory fibres consists in transverse section of one or the other 

 of the lateral halves of the cord. If one lateral half of the 

 cord be divided, sensibility is abolished in the parts below 



cord in its posterior portion, see, BROWN-SEQUARD, Nouvelles recherches sur la 

 physiologic de la moelle epinere. Journal de la physiologic, Paris, 1858, tome i., 

 p. 139. 



