MODE OF ACTION OF THE SENSORY NERVES. 89 



leaving the parts supplied by the nerve insensible to direct 

 irritation. In cases of disease it is not unusual to note great 

 pain in parts of the skin that are insensible to direct impres- 

 sions. 1 The explanation of this is, that the nerves are par- 

 alyzed near their terminal distribution, so that an impres- 

 sion made upon the skin cannot be conveyed to the senso- 

 riuin ; but that the trunks of the nerves still retain their 

 conducting power and are the seat of diseased action, produ- 

 cing pain, which is referred by the patient to the periphery. 



In multiplying examples showing the mode of action of 

 the sensoiy nerves, we may refer to the sensations experi- 

 enced after certain plastic operations. In the very common 

 operation of restoring the nose by transplanting skin from 

 the forehead, after the operation has been completed, the 

 skin having been entirely separated and cicatrized in its new 

 relations, the patient feels that the forehead is touched when 

 the finger is applied to the artificial nose. After a time, 

 however, the sensorium becomes accustomed to the new 

 arrangement of the parts, and this deceptive feeling disap- 

 pears. 



There are certain curious nervous phenomena, that are 

 not without physiological interest, presented in persons who 

 have suffered amputations. It has been long observed that 

 after loss of a limb the sensation of the part remains and pain 

 is frequently experienced referred to the amputated member. 

 Thus a patient will feel distinctly the fingers or toes after an 

 arm or a leg has been removed, and irritation of the ends of 

 the nerves at the stump produces sensations referred to the 

 missing member. A few years since, we observed a very 

 striking example of this in a soldier who had suffered ampu- 

 tation of the leg. While this patient was walking about on 

 crutches, before the stump had entirely healed, on getting up 

 suddenly from his seat, he attempted to walk, and put the 

 stump to the ground, producing considerable injury. His 

 explanation was, that he felt the foot perfectly, and it was 



1 LONGET, Traite de physiologic, Paris, 1869, tome iii., p. 178. 



