FUNCTIONS OF THE SPIXAL COED. 495 



muscular movements , irritation of the ends of the proximal 

 portions, which are still in connection with the cord, is 

 followed by no effect. Irritation of the distal portions of 

 the divided posterior roots, on the other hand, produces no 

 muscular movements and no manifestation of pain ; for, as 

 already stated, sensitive nerves convey impressions only 

 towards the nervous centres : but irritation of the proximal 

 portions of these roots elicit signs of intense suffering. 

 Occasionally, under this last irritation, muscular move- 

 ments also ensue ; but these are either voluntary, or the 

 result of the irritation being reflected from the sensitive to 

 the motor fibres. Occasionally, too, irritation of the distal 

 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 nerve centres (see p. 483). 



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



