ELECTRICAL PHENOMENA. 103 



diagram, of a glass tube A-B, through the middle of which is stretched a 

 platinum wire, P, the rest of the tube being filled with a saturated solution 

 of zinc sulphate. The glass tube is provided with vertical branches by means 

 of which a polarizing current, p, can be sent into the solution of zinc sulphate 

 and the electrotonic currents be led off to galvanometers, g'. g, on 

 each side. Under these conditions a current similar to the anelectrotonic 

 current can be detected on the side of the anode (g'} and one equivalent to 

 the catelectrotonic current on the side of the cathode (g). The explanation 

 given to these currents is that as the threads of current pass into the platinum 

 core there is a polarization at the surface between the core and the zinc sul- 

 phate solution which extends to a considerable distance on each side of the 

 electrodes and causes diffusion currents from sheath to core. It is these 

 threads of current that may be led off as electrotonic currents. Hermann 

 suggested that in the nerve we have a structure essentially similar to that 

 of the core model. He thought that the axis cylinder might be considered 

 as representing the core and the myelin the less condu tive sheath as corres- 

 ponding to the zinc sulphate solution. Others (Boruttau) have suggested that 

 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, in 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. 



