PHYSICAL SENSIBILITY 325 



travel without any discontinuity to their nucleus, always retaining 

 their individual sheaths. This does not prevent the nervous cords, 

 which arise from the junctions of several such threads, from having 

 their own sheath as well ; and the same applies to the still larger 

 cords formed by the union of several of these. 



Each nervous thread may thus be distinguished by the name of the 

 part where it starts, for it only transm'ts impressions made on that 

 part. 



We are here dealing exclusively with nerves serving for sensations : 

 those destined for muscular movement start apparently from some 

 other nucleus, and constitute a special system within the nervous 

 system, distinct from that of sensations ; in the same way that the 

 latter is distinct from the system providing for the formation of ideas 

 and acts of the understanding. 



It is true that in consequence of the close connection between the 

 system of sensations and that of muscular movement, paralysis usually 

 extinguishes both feeling and movement in the parts affected ; never- 

 theless cases are seen where sensibility is quite extinct in certain parts 

 of the body which still possess freedom of movement,^ and this proves 

 that the systems of sensation and movement are really distinct. 



The special mechanism which constitutes the organic act giving rise 

 to feehng, consists therefore in the following process : 



When an impression is received at the extremity of a nerve, the 

 movement thereupon set up in the subtle fluid of that nerve is trans- 

 mitted to the nucleus of sensations, and from there to all the nerves 

 of the sensitive system. But the nervous fluid immediately reacts 

 from all the nerves together, and brings back this general move- 

 ment to the common nucleus, where the only nerve which brought 

 no reaction receives the entire product of all the rest and transmits 

 it to the point of the body originally affected. 



For greater clearness let us take a special example of the details 

 of this mechanism. 



^ M. Hébréard recorda in the Journal de Médecine, de Chirurgie et de Pharmacie 

 that a man fifty years of age had suffered, ever since he was fourteen, from an absolute 

 insensibility in the right arm. Yet this limb retained its activity, size and usual 

 strength. A phlegmon grew upon it, causing heat, swelling and redness, but no pain 

 even when squeezed or pressed. 



While working, this man fractured the bones of his fore-arm in their lower third. 

 At first he only heard a crack, and thought that he had broken the spade which he 

 held in his hand ; but it was intact, and he only discovered his accident, because he 

 could not continue his work. The next day the site of the fracture had swollen, and 

 the temperature of the fore-arm and hand had risen : yet the patient experienced 

 no pain even during the extensions necessary for reducing the fracture, etc. 



The author concludes from this fact and from similar experiences by other doctors, 

 that sensibility is absolutely distinct and independent from contractility, etc., etc. 

 {Journal de Médecine pratique, I5th June, 1808, p. 540). 



