324 INNEEVATIOX. [CHAP. XI. 



sensation is entirely destroyed,, movements may yet be excited 

 without the consciousness of the individual. In such cases it is 

 supposed that the fibres of sensation and volition are alone para- 

 lysed, but that those of the true spinal cord remain free from injury 

 or disease, and therefore competent to perform their functions. 

 Sometimes, however, these fibres participate in the general shock 

 which the spinal cord or brain experiences at the onset of disease or 

 accident, and therefore reflex movements are not to be excited in 

 all cases in which the influence of the brain has been cut off by 

 disease of that organ, or of the cord itself. 



This hypothesis has very much to commend it ; and not the least 

 argument in its favour is that drawn from the compound nature of 

 spinal nerves, as proved by Bell, in which filaments of very different 

 endowments are bound together in the same sheath. If it be proved 

 that filaments of sensation and of motion may be thus tied together, 

 it is not going too far to conjecture the existence of another series 

 of fibres of distinct function. 



The movements of decapitated animals, of parts in connexion 

 with small segments of the spinal cord, of limbs paralysed to sensa- 

 tion and voluntary motion from diseased brain or spinal cord, are 

 satisfactorily explained by this hypothesis. But there are two phe- 

 nomena familiar to those who observe disease with a knowledge 

 the many interesting discussions now going on upon the nervous 

 system, which are not explained by it : these are, the movemenl 

 which may be excited by mental emotion in limbs paralysed to 

 the influence of the will, and the total paralysis of the sphincter 

 ani, which frequently accompanies diseased brain, whilst, at the 

 same time, the limbs are only affected to a partial degree. 



Cases occur sometimes in which hemiplegia arises from an apo- 

 pletic clot or other destructive lesion in one hemisphere of the brain. 

 The arnfand leg, or either of them are completely removed froi 

 the influence of the will ; yet, occasionally, under the influence 

 some sudden emotion, fear, joy, surprise, the palsied limb is rais 

 involuntarily with considerable force.* Mental emotions probabb 

 affect some part of the brain : if the only communication betweei 

 the brain and the limbs be by the fibres of sensation and volition, 

 it is impossible to understand how, in such a case, the emotional 

 influence could be conveyed through a channel which has long been 



* Even so slight a cause as yawning, which is an action of emotional charac- 

 ter, will excite a palsied limb. In the case of a patient now in King's College 

 Hospital with very complete hemiplegia, the arm is raised involuntarily every 

 time he yawns. 



