108 



THE PHYSIOLOGY OF MUSCLE AND NERVE. 



into a nerve. Whether the physiological and the electrical changes 

 have a causal connection or are two independent phenomena is 

 at present undecided. 



Bethe* has shown that during the passage of the polarizing current 

 the neurofibrils in the axis cylinder lose at the anode their power of stain- 

 ing with certain basic dyes (e. g., methylene blue), while at the cathode the 

 affinity for these dyes is increased. He assumes, that in the neurofibrils there 

 is an acid substance fibril acid and that at the anode the combination 

 with this body and the neurofibrils is loosened; hence the loss of staining 

 power. At the cathode the reverse change takes place. He assumes further- 



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

 Ivanometers with leadi 

 currents, respectively. 



g. the galvanometers with leading off electrodes to detect the anelectrotonic and' catelec- 

 trotonic 



more, that when the affinity between neurofibril and fibril acid is increased 

 at the cathode an electronegative ion is liberated (anion), while at the 

 anode at the time that the combination between fibril and fibril acid is dis- 

 sociated an electropositive ion (cation) is liberated. In this way he constructs 

 an hypothesis of a complex of neurofibril, fibril acid, and electrolyte which 

 is capable of accounting for the electrotonus, both as regards the electrical and 

 the physiological phenomena, and which refers both phenomena to a single 

 reaction hi the nerve. 



Another explanation, of the electrotonic currents which has been much 

 discussed is that first developed by Hermann. f This author constructed 

 a model consisting of a conductor surrounded by a less conductive liquid 

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

 currents. This model may be made as represented in the accompanying 

 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 (y). 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 conductive sheath corre- 

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



* Bethe, " Allgemeine Anatomic u. Physiol. des Nervensystems, " Leipzig, 

 1903. 



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



