108 



THE PHYSIOLOGY OF MUSCLE AND NERVE. 



Hermann* has suggested a relatively simple explanation of these currents. 

 He constructed a model consisting of a conductor surrounded by a less con- 

 ductive liquid sheath, and showed that such a model is capable of giving the 

 electrotonic currents. This model may be made as represented in the ac- 

 companying diagram, of a glass tube AB, 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 



ff 



Fig. 50. To show the action of the core-model: p, The polarizing current; g' and 

 g, the galvanometers with leading off electrodes to detect the anelectrotonic and cateleo 

 trotonic currents, respectively. 



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

 as representing the core and the myelin the less conductive sheath corre- 

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

 that the neurofibrils in the axis cylinder may represent the core or cores and 

 the surrounding neuroplasm the sheath, thus providing for the possibility of 

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

 medullated fibers in mammals give very slight electrotonic currents compared 

 with the medullated fibers.f 



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 curients, 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. 



* Hermann, "Handbuch der Physiologic," vol. ii, p. 174. 

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



