310 INNERVATION. [CHAP. XI. 



ones which are capable of calling nervous power in to play,, such as 

 mechanical irritation, heat, cold, galvanism, chemical irritants. 



There can be no grounds for supposing that the will has any- 

 thing to do with these movements. An animal pithed, which is to 

 all intents and purposes in the same condition as one decapitated, 

 shews no sign of voluntary action, excepting perhaps for a short 

 time after the operation, whilst the irritation caused by the division 

 of the cord remains. He maintains one and the same position, 

 without evincing any sign of sense or motion, unless a stimulus be 

 applied to some part of the surface; and, after the movement which 

 such a stimulus excited has ceased, he resumes the same state of 

 inactivity. 



Comparing this state of a pithed or decapitated animal with the 

 phenomena which we know to take place in the human subject in 

 effect of particular forms of accident or disease, it is impossible to 

 regard these actions in any other light than as involuntary ones. 

 To refer once more to such a case as that cited in a former paragraph, 

 when, from the destruction of the cervical part of the cord, the trunk 

 appears as if dead, while the head lives, we find in many instances, 

 if the stunning effect have not been too great, that similar motions 

 to those described in the frog may be produced by the application 

 of mechanical or other stimuli to the surface. Tickling the soles of 

 the feet causes movements of the lower extremities : the intro- 

 duction of a catheter into the urethra, which is not felt by tl 

 patient, excites the penis to erection. Over these acts not only 

 have the patients no control, but they are absolutely unconscious of 

 their occurrence, as well as of the application of the stimuli by 

 which they were provoked. It is plain, then, that these move- 

 ments take place without the concurrence or even the cognizance of 

 the mind, whether as the recipient of stimuli, or as the source of 

 voluntary impulses. 



In hemiplegia, the result of diseased brain, when the paralysis i* 

 complete, the influence of the will over the paralysed side is alto- 

 gether cut off. In such cases, movements may be excited in the 

 palsied leg very rarely in the arm by stimuli applied to the sole 

 of the foot, or elsewhere ; and we often astonish the patient him- 

 self, who expresses his utter inability, by any effort of his will, to 

 move his leg, by exciting active movement of it on touching the 

 sole of the foot very lightly with a feather. It is proper to add, 

 that there is much variety as regards the extent to which these 

 actions take place in hemiplegic cases, owing to causes which are 

 not yet fully understood. Still, they do occur in a large proper- 



