BROWN-SEQUARD ON THE CENTRAL NERVOUS SYSTEM. 277 



2ndly. If after having made first, a section 

 of a lateral half of the spinal cord in the dorsal 

 region on the right side, and after having 

 ascertained that the right posterior limb is 

 quite sensitive, the left lateral half of the spi- 

 nal cord is divided in the cervical region, 

 then the right posterior limb loses its sensi- 

 bility. This experiment shows that the sen- 

 sitive impressions coming along pr. (after 

 the lesion at 3) had first crossed to the other 

 side of the spinal cord, along which they 

 were transmitted until interrupted by the 

 2nd section, not represented in the diagram. 



3rdly. The spinal cord is laid bare in the 

 whole lumbar region, and a careful division 

 of the entire extent of the part of the organ, giving origin to the 

 nerves of the posterior limbs, is made directly along the middle 

 line, so as to separate the two lateral halves of the organ one from the 

 other. If this experiment could be executed perfectly, nothing 

 would be divided in the cord, except the commissures which unite the 

 right and left sides, and all the longitudinal elements of this centre 

 would be left uninjured ; but it is impossible not to cut more or less 

 on either side. However, when the operation has succeeded, i.e. 

 when the two lateral halves have been very little injured, a striking 

 result is obtained. Voluntary movements still exist in the hind 

 limbs, but sensibility is entirely lost in them. The animal has the 

 use of his two hind limbs ; he moves about pretty freely. The 

 loss of sensibility, therefore, must depend on the division of the 

 commissures of the spinal cord, or in other words on the elements of 

 this organ which cross each other in the median line, or rather, in 

 the median plane. 



If on comparing the results of these three experiments, and if, 

 after considering the many great difficulties already spoken of, which 

 attend all such experiments, the reader admits (as we ourselves 

 assuredly do) that the results may be accepted, then the inferences 

 from them are clear and undeniable ; so that it is unnecessary here 

 to point out how completely the third experiment disproves the no- 

 tion of some German physiologists, that the grey matter has the 

 power of transmitting impressions in every direction. 



* Diagramatic representation of the decussation of the conductors for voluntary 

 movements, and of those for sensation. Ar. anterior roots continued by dotted 

 lines in the spinal cord, where they decussate ; pr. posterior roots and their decus- 

 sation ; g. the ganglia; mo. the medulla oblongata; r. the right, and/, the leftside. 

 1, 2, 3 represent supposed lesions of one lateral half of the medulla oblongata and the 

 spinal cord ; 1 above, 2 at the level of the decussation of the voluntary motor con- 

 ductors, and 3 at some part below this decussation, say in the dorsal or upper 

 lumbar region. The arrows indicate the direction of the nervous action in the mo- 

 tor and sensitive conductors. — ( Copied from Dr. Brown- -Sequard'ft work.) 



