FUNCTIONS OF NERVE-FIBRES. 479 



tion is applied to the end of the proximal portion, i.e., of 

 the portion still connected with the nervous centre, sensa- 

 tion is perceived, or a reflex action ensues ; but, when the 

 end of the distal portion of the divided nerve is irritated, 

 no effect appears. 



When an impression is made upon any part of the course 

 of a sensitive nerve, the mind may perceive it as if it were 

 made not only upon the point to which the stimulus is ap- 

 plied, but also upon all the points in which the fibres of the 

 irritated nerve are distributed : in other words, the effect 

 is the same as if the irritation were applied to the parts 

 supplied by the branches of the nerve. When the whole 

 trunk of the nerve is irritated, the sensation is felt at all 

 the parts which receive branches from it ; but when only 

 individual portions of the trunk are irritated, the sensation 

 is perceived at those parts only which are supplied by the 

 several portions. Thus, if we compress the ulnar nerve 

 where it lies at the inner side of the elbow-joint, behind 

 the internal condyle, we have the sensation of " pins and 

 needles," or of a shock, in the parts to which its fibres are 

 distributed, namely, in the palm and back of the hand, 

 and in the fifth and ulnar half of the fourth finger. W T hen 

 stronger pressure is made, the sensations are felt in the 

 fore-arm also ; and if the mode and direction of the pres- 

 sure be varied, the sensation is felt by turns in the fourth 

 finger, in the fifth, and in the palm of the hand, or in the 

 back of the hand, according as different fibres or fasciculi 

 of fibres are more pressed upon than others. 



It is in accordance with this law, that when parts are 

 deprived of sensibility by compression or division of the 

 nerve supplying them, irritation of the portion of the nerve 

 connected with the brain still excites sensations which are 

 felt as if derived from the parts to which the peripheral 

 extremities of the nerve-fibres are distributed. Thus, 

 there are cases of paralysis in which the limbs are totally 

 insensible to external stimuli, yet are the seat of most 



