THE SPINAL CORD. 671 



however, among the phenomena described by different observers, to enable even 

 a probable statement to be hazarded in regard to the nature of this arrangement; 

 and it seems quite possible that it may vary in different animals, in accordance 

 with their respective modes of progression. As far as Man is concerned, we 

 have no evidence but that of pathological phenomena ; and we certainly may 

 find, in many forms of convulsive action, an indication that there is some com- 

 mon centre or tract of motor impulse for the extensor muscles generally, and 

 another such centre or tract for the flexors. 



706. We have now to consider the Spinal Cord as an independent centre of 

 nervous power, and to inquire whether the movements which are excited through 

 its "reflex activity really involve sensation. These movements are most cha- 

 racteristically displayed, when the Spinal Cord is cut off from communication 

 with the higher Nervous centres ; probably rather because the nerve-force ex- 

 cited by the impression reacts through the Spinal ganglion to which it is con- 

 veyed, when it can no longer pass on to the Encephalic centres ( 683), than 

 because (as some suppose) the impulse to reflex movement is ordinarily neutral- 

 ized and rendered inoperative by an effort of the will. It is true that those 

 reflex actions of the Spinal Cord which are necessary to the maintenance of 

 Organic life, and which are equally performed whether the Spinal axis be in 

 communication with the higher Encephalic centres or not, are continually modi- 

 fied or temporarily suspended by the Will; but this is only when we consciously 

 bring the Will to bear upon them ; and it is no less certain that we are not 

 continually making any such exertions, in order to antagonize movements, 

 which (as we learn from Pathological evidence), would be continually excited 

 but for this neutralizing influence, if such a doctrine were correct. The readiest 

 demonstration of the independent power of the Spinal Cord is derived from the 

 motions exhibited by the limbs of animals, when irritation is applied to them 

 after section of the Spinal Cord at some point above the entrance of their 

 nerves ; the fact that these movements are reflected through the Cord, and are 

 not the product of direct stimulation applied to the part irritated, being shown 

 by their complete cessation when the nerve-trunks are divided, or the substance 

 of the Spinal Cord is broken down. Further, it is to be observed that a slight 

 irritation applied to the peripheral extremities of the afferent nerves, is a more 

 powerful excitor of reflex action than a much stronger impression, which occa- 

 sions acute pain, applied to their trunks; thus, Mr. Grainger found that he could 

 remove the entire hind-leg of a Salamander with the scissors, without the 'crea- 

 ture moving, or giving any expression of suffering, if the Spinal Cord had been 

 first divided; yet that by irritation of the foot, especially by heat, in an animal 

 similarly circumstanced, violent convulsive actions in the legs and tail were ex- 

 cited. This fact is important, not only as showing the comparatively powerful 

 effect of impressions upon the cutaneous surface, but also as proving how little 

 relation the amount of reflex action has to the intensity of sensation. [When 

 the cutaneous surface is removed, reflex action can scarcely be excited at all by 

 impressions, even of the most irritating character, as we have seen repeatedly in 

 frogs whose inferior extremities have been denuded of cuticle. ED.] That the 

 movements executed by the limbs of the lower animals, when these are no longer 

 connected by the Spinal Cord with the Encephalon, but remain connected with 

 the Cord itself, do not take place through the intermediation of sensation, might 

 be supposed to be sufficiently proved by the simple fact that division of the 

 Cord, in Man, and hence by inference in the lower animals, reduces the parts 

 below to a state of complete insensibility. But, on the other hand, the very 

 performance, by decapitated animals of inferior tribes, of actions which had not 

 been witnessed in Man under similar circumstances, has been held to indicate 

 that the spinal cord in them has an endowment which his does not possess. The 

 possibility of such an explanation, however unconformable to that analogy 



