PHYSICAL SENSIBILITY 327 



the impression received by the part affected should be transmitted to 

 the nucleus of the system of sensations ; but if the whole action 

 ended there, there would be no general effect, and no reaction would 

 be conveyed to the point which received the impression. As regards 

 the transmission of the original movement impressed, it doubtless 

 only takes place through the nerve which was affected and by means 

 of the nervous fluid moving in its substance. We know that, if by a 

 ligature or tight compression of the nerve, we intercept communica- 

 tion between the portion arriving from the part affected and that 

 passing on to the nucleus of sensations, no transmission of movement 

 is effected. 



The ligature or tight compression interrupts the continuity of the 

 soft substance of the nerve by binding together the walls of its sheath, 

 and thus suffices to intercept the passage of the nervous fluid ; but, as 

 soon as the hgature is removed, the elasticity of the nervous substance 

 permits of restoration of continuity in the nerve, and sensation can 

 then be produced again. 



Although therefore it is true that we only feel what is within our- 

 selves, yet the perception of the objects which affect us does not occur, 

 as has been held, in the nucleus of sensations, but at the extremity 

 of the nerve which received the impression ; and all sensation is thus 

 actually felt in the part affected, because it is there that the nerve of 

 this part terminates. 



But if this part no longer exists, the nerve, which ran there, continues 

 to exist although it is shortened ; if therefore this nerve receives an 

 impression a sensation is experienced which appears by illusion to be 

 in the part that is no longer possessed. 



It has been observed that people who have lost a leg, feel, when the 

 stump has healed, at changes of the weather, pains in the foot or leg 

 which they no longer possess. It is obvious that in these individuals 

 there is an error of judgment as to the actual site of their sensation ; 

 but this error is due to the fact that the nerves affected were just those 

 which were originally distributed in the foot or leg of these individuals ; 

 in reahty the sensation is produced at the extremity of the shortened 

 nerve. 



The nucleus of sensations only serves for the production of the general 

 disturbance set up by the nerve which received the impression, and for 

 bringing back into this nerve the reaction from all the rest ; hence 

 there results at the end of the affected nerve an effect, which all parts 

 of the body combine to produce. 



Cabanis seems to have had some notion of the mechanism of sensa- 

 tions, for although he did not work out the principles of it clearly, and 

 although he wrongly suggests a mechanism analogous to that by which 



