PATHS OF SENSORY IMPRESSIONS. 273 



the term aesthesodic has been applied by Schiff, as already mentioned, 

 to that substance of the cord, which is concerned in the conveyance of 

 sensory impressions, so, for similar reasons, the- term kinesodic 



kinesis, motion, and J<Wc, odos, a path), has been employed to desig- 

 nate the substance concerned in the conduction of motorial impulses, 

 a property, which, he likewise believes, it can exert in any direction. 



The sum of our information on the whole subject is this : First, 

 that the paths of sensory impressions reach the gray matter of the 

 cord, the interposition of which is regarded as an essential condition 

 of sensitive conduction; diffusing themselves in the gray matter, they 

 pass to the opposite side, and then ascend towards the brain ; so that 

 they decussate even at the lowest part of the cord. Secondly, that 

 the paths of voluntary motion descend from the brain, not through any 

 intervening gray matter, but along the white fibres of the anterior and 

 lateral columns, perhaps also through white fibres lying in the adjacent 

 gray matter of the same side of the cord, and that they do not decus- 

 sate in it. Numerous fibres certainly cross over from one side of the 

 cord to the other, in the anterior columns ; but these, which belong to 

 the anterior roots of the nerves, are perhaps concerned in the reflex, 

 and not in the voluntary movements. This difference in the paths of 

 sensory and motor impulses along the cord, and the decussation of the 

 former within it, explain cases of disease of the cord, in which there 

 are observed, muscular paralysis of one limb, and anaesthesia or pa- 

 ralysis of sensation in the other. 



Considered as an anatorriical question, it does not seem possible that 

 all the fibres, either of the sensory or motor roots of the spinal nerves, 

 can ascend directly up to the seats of common sensation and of voli- 

 tional impulse, in the brain ; for the mass of the cord is not increased 

 as it ascends, in proportion to the number of nerves which join it ; 

 indeed, most of the fibres of the nerves appear to end in the cord itself; 

 and many of its own longitudinal fibres appear to be commissural, 

 serving to connect the nerves with many segments of the cord, or its 

 own segments with each other. Many of the nerve-fibres appear thus 

 to be concerned in the exercise of functions dependent on the cord 

 itself, acting as a special nervous centre. The propagation upwards 

 of sensational impressions, is properly accomplished chiefly through 

 the gray matter, by indirect electrotonic changes excited in it ; whilst 

 the volitional impulses descend chiefly through longitudinal fibres, in- 

 directly excited from above. The conducting power of the gray mat- 

 ter, moreover, in both cases, seems now to be well established ; it con- 

 tains, however, many intermixed white fibres. It has been observed, 

 that the posterior columns of the cord are highly sensitive to stimuli 

 on their surface, but not in their interior ; whilst the antero-lateral 

 columns are not sensitive either on their surface, or in their interior 

 (Chauveau). 



The preceding experiments demonstrate the conducting properties 

 of the spinal cord, both as concerns its gray and its white substance, 

 and in reference both to sensory and to voluntary motor impressions ; 

 and they show, moreover, by the complete annihilation of voluntary- 

 power in the parts below a cross section through its substance, that it 



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