THE PHENOMENA OF CONDUCTION IN NERVE 



127 



galvanometer. To adjudge this result correctly, it must of course be remembered 

 that the anterior roots of the cord are motor in their function; i.e., they conduct 

 under normal conditions in a centrifugal direction. Double conduction for the 

 afferent fibers was proved by stimulating the posterior root of the sciatic nerve 

 and observing the deflections of a galvanometer adjusted to the central end of the 

 peripheral portion of this nerve. The posterior roots of the spinal nerves are 

 sensory in their function and conduct under normal conditions in a centripetal 

 direction. 



n. 



FIG. 73. CONDUCTION IN BOTH DIRECTIONS IN NERVE. 



N, nerve; S, point of stimulation; A and B, galvanometers upon the two 



ends of the nerve. 



Another method of proving double conduction in nerve has been devised by 

 Ktihne 1 (Fig. 74). It has previously been stated that several of the long muscles, 

 such as the gracilis and sartorius, receive their nerve supply at a point about mid- 

 way between their two extremities. The nerve entering here divides into two 

 principal branches, which innervate the upper and lower ends of the muscle respec- 

 tively. If the muscular continuity is now broken by a transverse cut into the tip 

 of the triangle formed by these branches (<7), the upper and lower ends of the mus- 

 cle (A and B) will be practically isolated from one another save for the bridge of 





FIG. 74. CONDUCTION IN BOTH DIRECTIONS IN GRACILIS MUSCLE. 

 A and B segments of gracilis muscle divided by cut C; S, point of stimulation; 

 N, motor nerve and its branches. 



nerve-tissue. If the distalmost filaments of one of the branches of this nerve are 

 now stimulated (S), the muscular contraction immediately ensuing does not remain 

 confined to this half of the muscle (A) but also involves the other half (B). This 

 fact leads us to infer that the excitation advances first of all in a centripetal direc- 

 tion over the fibers of the corresponding branch (A) and then spreads over the 

 normally centrifugal fibers to the distant muscle-strip B. Thus, the normally 

 efferent] fibers innervating the end A, are temporarily converted into afferent 

 fibers. In order to meet the possible objection that this result may be caused by a 

 direct spreading of the electrical current from A to B, the stimulation may be 



1 Archiv fur Anat. und Physiol., 1859, 595. 



