REFLEX FUNCTION OF THE SPINAL COKD. 503 



cited to motion as well as the upper portion : the tail may 

 be divided into several segments, and each segment, in 

 which any portion of spinal cord is contained, contracts on 

 the slightest touch ; even the extremity of the tail moves 

 as before, as soon as it is touched. All the portions of the 

 animal in which these movements can be excited, contain 

 some part of the spinal cord ; and it is evidently the cause 

 of the motions excited by touching the surface ; for they 

 cannot be excited in parts of the animal, however large, if . 

 no part of the cord is contained in them. Mechanical irri- 

 tation of the skin excites not the slightest motion in the 

 leg when it is separated from the body ; yet the extremity 

 of the tail moves as soon as it is touched. The same power 

 of the spinal cord in reflecting impressions will cause an 

 eel, or a frog, or any other cold-blooded animal, to move 

 along after it is deprived of its head, and when, however 

 much the movements may indicate purpose, it is not 

 probable that consciousness or will has any share 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 injury, 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 



