EFFERENT NERVES 23! 



motor. It will likewise be seen that all sensory fibers are 

 centripetal or afferent, but not all centripetal or afferent 

 fibers are sensory. For impressions made upon the termina- 

 tions, or upon the trunk, of a centripetal nerve may cause 

 (i) pain, or some other kind of sensation; (2) special sen- 

 sation; (3) renex action of any kind; (4) inhibition. Simi- 

 larly impressions made upon a centrifugal nerve may (i) 

 cause contraction of a muscle (motor nerve) ; (2) influence 

 nutrition (trophic nerve) ; (3) control secretion (secretory 

 nerve) ; (4) inhibit, augment, or stop any other efferent ac- 

 tion (Kirkes). 



To these two classes, efferent and afferent, should be 

 added a third, the intercentral fibers which connect different 

 parts of the nervous centers. Most of these even can be 

 called either afferent or efferent. 



Characteristics of Efferent Nerves. In case of these 

 nerves a force is generated in the centers and conveyed by 

 the nerves to the periphery, where it manifests itself in one 

 of the ways mentioned above as characteristic of centrifugal 

 fibers. Division of these fibers, or interference with their 

 conductivity by disease or otherwise, renders impossible the 

 manifestation of nervous force generated in the center, for 

 the simple reason that the organ to which the fibers are di- 

 tributed cannot receive the message intended for it. For in- 

 stance, a muscle cannot, by the most persistent effort of the 

 will be made to contract if the motor fibers running to that 

 muscle are divided. In case, however, of division of effer- 

 ent nerves, if the peripheral end be irritated, thus roughly 

 counterfeiting normal stimulation, the ordinary effects of 

 normal stimulation will be brought about, provided (as is 

 usually the case) that particular nerve can be thus directly 

 stimulated. Stimulation, however, of the central end of 

 such a cut nerve produces no effect. No matter whether 

 such efferent nerves receive their stimulus directly from the 

 center or artificially, as by mechanical or electrical means, 

 the effect is produced in the end organs, whatever they may 



