FUNCTIOXS OF SPINAL CORD 



Similarly in a nerve we may regard the stimulus as setting 

 up a change, whose nature we do not as yet understand, 

 at the point to which it is applied ; this change 

 sets up a similar change in the next neighbouring 

 particles of the nerve, and so on until it finally appears at 

 the furthest end of the nerve. But a nerve, unlike the 

 train of gunpowder, relays itself so long as it is alive, 

 as soon as the impulse has passed along it, whereas 

 the train of powder is "dead" after the passage of 

 the explosion, and must be artificially relaid for further 

 use. 



8. The Properties or Functions of the Spinal Cord. — 

 Up to thi.s point our experiments have been confined to 

 the nerves. We may now test the properties of the spinal 

 cord in a similar way. If the cord be cut across (say in 

 the middle of the back), the legs and all the parts 

 supplied by nerves which come oft" below the section, will 

 be insennble, and no effort of the will can make them 

 move ; while all the parts above the section will retain 

 their ordinary powers. 



When a man hurts his back by an accident, the cord is 

 not unfrequently so damaged as to be virtuallj' cut in two, 

 and then insensibility and paralysis of the lower part of the 

 body ensue. 



If, when the cord is cut across in an animal the cut 

 end of the portion below the division, or away from the 

 brain, be irritated, violent movements of all the muscles 

 supplied by nerves given ofi" from the lower part of the 

 cord take place, but no sensation is felt by the brain. On 

 the other hand, if that part of the cord, which is still con- 

 nected with the brain, or better, if any afferent nerve 

 connected with that part of the cord be irritated, sensations 

 ensue, as is shown bj^ the movements of the animal ; but 

 in these niovements the mnscles supplied by the nerves 

 coming from the spinal cord below the cut take no part ; 

 they remain perfectly quiet. 



Thus, it may be said that, in relation to the brain the 



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