REFLEX FUNCTION OF THE SPINAL CORD. 397 



frog, or any other cold-blooded animal, to move along after it 

 is deprived of its head, and when, however much the move- 

 ments may indicate purpose, it is not probable that conscious- 

 ness or will has any share in them. And so, in the human 

 subject, or any warm-blooded animal, when the cord is com- 

 pletely divided across, or so diseased at some part that the in- 

 fluence 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 ani- 

 mals, 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 example, a frog's 

 head is cut off, the limbs remain in, or assume, a natural posi- 

 tion ; 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. 1 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 consequent movements are disorderly and purposeless. 

 Now, if we are justified by analogy in assuming that the will 

 of the frog cannot act more than the will of man, through the 

 spinal cord separated from the brain, then it must be admitted 

 that many more of the natural and purposive movements of 

 the body can be performed under the sole influence of the cord 

 in the frog than in man ; and what is true in the instance of 

 these two species, is generally true also of the whole class of 

 cold-blooded, as distinguished from warm-blooded, animals. 

 It may not, indeed, be assumed that the acts of standing, leap- 

 ing, and other movements, which decapitated cold-blooded 



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

 blooded animals, have led some to think that they 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. 



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