FUNCTIONS OF THE SPINAL CORD. 269 



in connection with the cerebrum, is followed by pain. The absence 

 of pain, on irritating the lower portion which is severed from the brain, 

 is held by most physiologists to be a sufficient proof that the cord itself 

 is not sensitive, but that it is a mere conductor of the effects of sensory 

 impressions. By a few others it is maintained, however, that when 

 the cord is entire, as in its natural state, it really does possess true 

 sensibility; but that, when divided, its sensations are not consciously 

 felt, because they cannot produce any effect in the cerebrum from 

 which the cord is severed. Seeing that the latter opinion is one which, 

 in the nature of things, cannot be proved, for unless a sensation be 

 consciously felt, it cannot be positively known to exist, it seems diffi- 

 cult to understand on what experimental grounds such an opinion can 

 be supported ; but we shall immediately have to consider certain phe- 

 nomena, which have been supposed to justify such a view. 



Secondly, as regards voluntary motion, experiments, or accidental 

 injuries or disease, illustrate the fact that, in this case also, the cord 

 is a mere conductor of the effects of the voluntary motorial stimuli, 

 and is not a centre of origin of such stimuli; for all the parts below a 

 division, injury, or disease of any portion of the cord, are completely 

 paralyzed, or beyond the least control of the will. Severe as such an 

 injury may be supposed to be, union of the divided cord, with complete 

 restoration of its functions, has been observed in animals experimented 

 upon, and, to a certain extent, in cases of injury or disease in man. 



The true sensorium, or the seat of the realization of sensations, and 

 so also the true seat or centre of volition, are situated higher up in the 

 cerebro-spinal nervous centres, indeed, somewhere in the cerebrum 

 itself. The effects of sensorial impressions and volitional stimuli, pass 

 up or down along the cord, to or from those chief centres. 



We have next to examine, what are the paths within the cord, which 

 these two sets of impressions pursue; in briefer phraseology, what are 

 the paths of sensation, arid what are the paths of motion, through the 

 cord. The gradual increase in quantity of the white matter of the 

 cord, from below upwards, favors the idea, that its longitudinal columns 

 are channels of conduction between the spinal nerves and the cerebrum ; 

 but the structure of these columns is very intricate, and the gray 

 matter, as well as the white, would seem to possess a certain conduct- 

 ing power for sensory impressions. The minute details of the arrange- 

 ment of the fibres in the spinal cord, have been studied, by making 

 sections of hardened cords, and then examining them under the micro- 

 scope. By such means, it has been found that, of the fibres of the 

 posterior or sensory roots, some ascend through the white posterior 

 columns; others cross through the gray matter of the posterior, and 

 even of the anterior, horn, then spread upwards, downwards, and hori- 

 zontally, and enter the posterior, lateral, and anterior columns of the 

 same side, many of them reaching the anterior roots of the same, or 

 of adjacent, nerves ; another set decussate in the transverse commis- 

 sure of the cord, cross over to the opposite side, and end, either in the 

 gray matter, or in the posterior, lateral, or anterior columns, and even 

 in the anterior roots of the opposite nerves ; finally, many terminate 

 in the gray matter, where they form loops, or become connected with 



