502 THE NERVOUS SYSTEM. 



probable that consciousness or will lias any snare in 

 them. And so, in the human subject, or any warm- 

 blooded animal, when the cord is completely divided 

 across, or so diseased at some part that the influence 

 of the mind cannot be conveyed to the parts below it, 

 the irritation of any part of the surface supplied by 

 nerves given off from the cord below the seat of injur} r , 

 is commonly followed by spasmodic and irregular reflex 

 movements, even though in the healthy state of the cord, 

 such involuntary movements could not be excited when 

 the attention of the mind was directed to the irritating 

 cause. 



In the fact last mentioned, is an illustration of an impor- 

 tant difference between the warm-blooded and the lower 

 animals, in regard to the reflecting power of the spinal cord 

 (or its homologue in the Invertebrata), and the share which 

 it and the brain have, respectively, in determining the 

 several natural movements of the body. When, for ex- 

 ample, a frog's head is cut off, the limbs remain in, or 

 assume, a natural position ; resume it when disturbed ; and 

 when the abdomen or back is irritated, the feet are moved 

 with the manifest purpose of pushing away the irritation. 

 It is as if the mind of the animal were still engaged in 

 the acts/* But, in division of the human spinal cord, the 

 lower extremities fall into any position that their weight 

 and the resistance of surrounding objects combine to give 

 them ; if the body is irritated, they do not move towards 

 the irritation ; and if themselves are touched, the conse- 

 quent movements are disorderly and purposeless. Now, if 



* The evident adaptation and purpose in the movements of the cold- 

 1 dooded animals, have led some to think that the}' must be conscious 

 and capable of will without their brains. But purposive movements. 

 are no proof of consciousness or will in the creature manifesting them. 

 The movements of the limbs of headless frogs are not more purposive 

 than the movements of our own respiratory muscles are ; in which we 

 know that neither will nor consciousness is at all times concerned. 



