AFFERENT NERVES 233 



the nerve is distributed. A person whose limb has been ampu- 

 tated often seems to feel pain in the extremity although it has 

 been removed from the body such pain coming from compres- 

 sion by the cicatrix (or otherwise) of the nerves which before 

 the amputation were distributed to the severed limb. Here, as 

 in the case of efferent nerves, division of the fibers between the 

 seat of impression and the center precludes the possibility of 

 any nervous manifestation. That is to say, no pain will be felt, 

 no matter how great the injury be, if the sensory fibers running 

 from the seat of injury be divided. Stimulation of the periph- 

 eral end of a divided afferent fiber produces no effect; but stimu- 

 lation of the central end is followed by the ordinary manifestation 

 by pain if the nerve stimulated be a common sensory one. 

 This remark, of course, applies only to those nerves which can 

 be thus directly stimulated typically to true sensory fibers. 



Impressions conveyed by nerves of special sense must be re- 

 ceived through the intervention of certain complex organs, con- 

 sideration of which belongs elsewhere. 



Although a division has been made of nerve fibers into afferent 

 and efferent, each with definite, proper and dissimilar functions 

 so far as the direction of conduction is concerned, it has been 

 impossible to discover any actual difference in the composition, 

 appearance, or other properties, of the actual fibers themselves. 

 In fact, it may be even considered as only an accident that one 

 fiber conveys a message peripherally and another centrally an 

 accident dependent upon the kind of center which with the fiber 

 is connected and the kind of termination it has in the periphery. 



Direction of the Current in Nerve Fibers. It has long been 

 understood that in no case will a fiber in situ convey a message at 

 one time in one direction and at another in an opposite one, that 

 no individual fiber can be both afferent and efferent; and so far as 

 practical action is concerned this is true, but "experiment has 

 shown that if a nerve trunk be stimulated at a given point, then 

 the nerve impulse can be demonstrated as passing away from the 



