ELECTRICAL PHENOMENA. 109 



the neurofibrils in the axis cylinder may represent the core or cores and the sur- 

 rounding neuroplasm the sheath, thus providing for the possibility of electro- 

 tonic currents in non-medullated fibers. As a matter of fact, the non-medul- 

 lated fibers in mammals give very slight electrotonic currents compared with 

 the medullated fibers.* 



According to the "core-model" explanation, the electrotonic currents 

 represent a purely physical phenomenon, which is dependent, however, upon 

 a certain structure of the nerve. That is, a completely dead nerve will not 

 show these currents, although an anesthetized nerve, hi the mammal (Waller) 

 at least, continues to show them, and, according to Sosnowsky, excised rab- 

 bits' nerves kept in a moist atmosphere may show them for several days. 

 While the core-model hypothesis has led to much investigation in physiology 

 and has been made the basis for a purely physical explanation of the nerve 

 impulse, it is still very uncertain whether it furnishes any positive informa- 

 tion concerning the processes that actually take place in the living nerve when 

 submitted to the action of electrical currents or other artificial stimuli. 

 *Alcock, "Proceedings Royal Society," 1904, 73, p. 166. 



