102 



THE PHYSIOLOGY OF MUSCLE AND NERVE. 



such a character that if the nerve- is led off from two points on 

 the anode side a current will be indicated. The current can be 

 obtained at a considerable distance from the anode, and is known 

 as the anelectrotonic current, while the electrical condition in the 

 nerve that makes it possible is designated as anelectrotonus. 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 elec- 

 trical 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 undecided. 



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- 



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 electrotonus, 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. t 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 



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

 1903. 



tHermann, " Handbuch der Physiologic," vol. ii, p. 174. 



