FUNCTIONS OF THE SPINAL CORD. 497 



ends of divided anterior roots elicits signs of pain, as well 

 as producing muscular movements : the pain thus excited 

 is probably the result of cramp (Brown-Sequard). 



As an example of the experiments of which the preced- 

 ing paragraph gives a summary account, this may be 

 mentioned : If in a frog the three posterior roots of the 

 nerves going to the hinder extremity be divided on the left 

 side, and the three anterior roots of the corresponding 

 nerves on the right side, the left extremity will be deprived 

 of sensation, the right of motion. If the foot of the right 

 leg, which is still endowed with sensation but not with the 

 power of motion, be cut off, the frog will give evidence of 

 feeling pain by movements of all parts of the body except 

 the right leg itself, in which he feels the pain. If, on the 

 contrary, the foot of the left leg, which has the power of 

 motion, but is deprived of sensation, is cut off, the frog 

 does not feel it, and no movement follows, except the 

 twitching of the muscles irritated by cutting them or their 

 tendons. 



Functions of the Spinal Cord. 



The spinal cord manifests all the properties already 

 assigned to nervous centres (see p. 485). 



i. It is capable of conducting impressions, or states of 

 nervous excitement. Through it, the impressions made 

 upon the peripheral extremities or other parts of the spinal 

 sensitive nerves are conducted to the brain, where alone 

 they can be perceived by the mind. Through it, also, the 

 stimulus of the will, applied to the brain, is capable of 

 exciting the action of the muscles supplied from it with 

 motor nerves. And for all these conductions of impressions 

 to and fro between the brain and the spinal nerves, the 

 perfect state of the cord is necessary ; for when any part 

 of it is destroyed, and its communication with the brain is 

 interrupted, impressions on the sensitive nerves given off 

 from it below the seat of injury, cease to be propagated to 



KK 



