PATHS OF SENSATION IN THE CORD. 271 



ance of sensation, in the latter case, being dependent on painful reflex 

 movements. 



It is believed by Brown-Sequard, that different kinds of sensory 

 impressions have different channels, none of which are substitutes for 

 the others touch, pain, the sense of temperature, and the muscular 

 sense, each having its own channel. Schiff also states, that the higher 

 form of common sensibility, which is named tactile sensibility, as dis- 

 tinguished from a mere sense of pain, travels up along a different path 

 to that of ordinary sensation. According to him, tactile sensibility is 

 lost on the cut side, so that its path is in the white columns of the 

 same side, and does not decussate or pass over to the other side ; 

 whereas the path of common sensation is through the gray matter, in 

 which the impressions are diffused in various directions. He further 

 adds, that it is the common sensibility only, and not the other forms 

 of sensation, which is exalted on the same side, and diminished on the 

 opposite side ; and that this effect is only temporary. Some singular 

 results follow a median section down the spinal cord. According to 

 Brown-Se'quard, if the cord be cut along the middle line in the lumbar 

 region, sensation is lost, on both sides, in all the parts below the cut ; 

 but if the section be higher up, sensation is lost only in the parts sup- 

 plied by nerves from the corresponding piece of the cord, and not in 

 the parts lower down. These results appear to show that the decussa- 

 tion of the paths of sensation, in reference to all the parts below, takes 

 place in the lumbar enlargement of the cord, and that therefore both 

 sides are paralyzed as to sensation ; whereas, higher up, the decussa- 

 tion of the paths of sensory impressions from the parts below, has 

 already taken place, and so those arfc not cut in the median section, 

 which destroys only the decussation of the nerve roots or sensory paths 

 of the adjacent nerves. Other observers conclude that this decussa- 

 tion of the paths of sensation is not quite complete, but that some sen- 

 sory fibres may pass up in the gray matter, or in the posterior white 

 columns of their own side; for they have found that, after median 

 longitudinal division of the cord, some sensory impressions still pass 

 up on their own side. (Schiff.) It may be that the arrangement of the 

 fibres of the cord differs in the different species of animals, which have 

 been the subjects of experiment. It will immediately be seen, that a 

 median section down the spinal cord, does not paralyze the muscles, 

 or affect the voluntary movements. It has been found, that so per- 

 fect, or generally diffused, is the conducting power of the gray matter 

 of the cord for sensory impressions, that the smallest portion left, either 

 in a transverse or longitudinal direction, is sufficient to conduct, though 

 in a limited degree, sensory impressions across to the opposite side, or 

 in an upward direction. This facility of conduction caused Schiff to 

 compare the gray matter to a mass of fluid, in which vibrations are 

 transmitted equally in all directions. From the fact, that the gray 

 matter of the cord is itself insensible, though a conductor of sensory 

 impressions, he named it the cesthesodic substance, because it is the 

 path of sensory impressions (al'ffOy<rts, aisthesis, sensation, and Jfl?, odos, 

 a path), and yet not sensitive itself. 



The path of the voluntary motorial stimulus has next to be consid- 



