102 



THE PHYSIOLOGY OF MUSCLE AND NERVE. 



trotonus. A similar current can be led off from the nerve on the 

 cathode side for a considerable distance beyond the cathode ; this 

 is known as the catelectrotonic current, and the electrical condition 

 leading to its production as catelectrotonus. Within the nerve 

 these electrotonic currents have the same direction as the battery or 

 polarizing current, as is shown in the diagram (Fig. 45). The terms 

 anelectrotonus and catelectrotonus are used, therefore, in physiology 

 to designate both the physiological and the electrical changes 

 around the poles when a battery current is led into a nerve. 

 Whether the physiological and the electrical changes have a causal 

 connection or are two independent phenomena is at present un- 

 decided. 



Bethe* has recently shown that during the passage of the polarizing cur- 

 rent 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- 



II 



Fig. 46. 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 catelec- 

 trotonic currents, respectively. 



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 electrotpnus, both as regards the electrical and 

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

 reaction in 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 



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

 1903. 



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



