CHAP. XI.] PHYSICAL NERVOUS ACTIONS OF THE CORD. 313 



the cord are so independent of all mental influence, and so purely 

 physical in their cause, as well as in their nature, being provoked 

 by a physical stimulus, and consisting essentially in a physical 

 change in the centre, as well as in its afferent and efferent nerves, 

 that they may be distinguished from those of volition and sensa- 

 tion, in which the mind has a necessary share, by being designated 

 " physical." It has been already stated, that Dr. Marshall Hall 

 uses the not unobjectionable title of "excito-motory" in reference 

 to these actions. 



In general, when a stimulus is applied to the spinal cord, the 

 actions which are excited by it are confined to a part which derives 

 its nerves from that segment of the cord on which the stimulus falls. 

 In some instances, however, parts supplied from other and even 

 distant segments are thrown into action. Thus irritation of one leg 

 will cause movements of one or both of the upper extremities ; the 

 introduction of a catheter into the urethra will sometimes cause 

 forcible contractions of the muscles of all the limbs. No doubt 

 these effects are due to the extension of the irritation in the cord 

 beyond the point first stimulated ; and they may be regarded as 

 proofs that that peculiar state of physical change which nervous 

 irritation can excite in a centre may be propagated in the spinal 

 cord, upwards, downwards, or sideways from the seat of the primary 

 stimulation. 



Disease affords some striking instances in confirmation of this 

 remark. 



A wound in the sole of the foot, or the ball of the thumb, or in 

 some other situation favourable to the maintenance of prolonged 

 irritation, is capable of exciting a particular region of the cord, from 

 which the state of excitement spreads so as to involve not only the 

 whole cord, but part of the medulla oblongata also ; and in this 

 state a large proportion of the motor nerves participate, so as to 

 induce tonic contraction of the muscles they supply. This is the 

 rationale of the development of that fearful malady called tetanus. 

 It consists not in an inflammatory affection of the cord, or of its 

 membranes, nor in congestion of them, but simply in a state of 

 prolonged physical excitement, the natural polar force of the centre 

 being greatly exalted, and kept so by the constant irritation propa- 

 gated to it by the nerves of the wounded part. 



In cases of paraplegia from disease of the spinal cord, even when 

 the paralysis of sensation and of motion is complete, patients are 

 tormented with involuntary movements of the lower extremities 

 at night, which not only prevent sleep, but occasion considerable 



