284 ELECTRO-PHYSIOLOGY 



a single closure of the polarising current. From this it appears 

 that non-medullated nerve also exhibits an alteration initiated at 

 the anode of a polarising current, and connected with a develop- 

 ment of positive potential, which spreads with diminishing intensity 

 over a certain region beyond the poles, and is more widely diffused 

 in proportion with the strength of the polarising current. 



We cannot hesitate to compare this alteration (which is only 

 expressed galvanically) with the " anelectrotonus " of medullated 

 nerve, seeing that there is a fundamental conformity between 

 them. It is therefore the more remarkable that there should be 

 no sign of alteration in non-medullated molluscan nerve compar- 

 able with the (galvanic) katelectrotonus of mcdullated nerve. This 

 is most apparent in experiments in which the galvanometer 

 electrodes are isoelectrically arranged upon the nerve. With 

 a descending polarising current there is then, as a rule, no 

 effect ; the magnet remains absolutely at rest at and during the 

 closure of the exciting circuit, even when the galvanometer tract 

 is only a few millimetres distant from the part excited. This 

 shows that there is no spread of the polarising current by 

 current-escape of any kind, in the preparation in cp:iestion, beyond 

 the region immediately traversed. The effects at and during 

 closure of an ascending current, under similar conditions, are 

 therefore the more striking. If the galvanometer electrodes 

 (at uniform distance) are brought gradually nearer to the anode 

 of the polarising current, there is invariably an increasing 

 deflection in the sense of a rapidly augmenting anelectrotonus, 

 which may reach considerable proportions while still comparatively 

 remote from the anode. 



The magnitude of these positive effects of the ascending 

 current is determined not merely by its intensity, but also most 

 essentially by the excitability of the preparation. The effects are 

 always more distinct and more vigorous in proportion with the 

 vitality of the nerve. 



At a given position of the galvanometer electrodes, the 

 magnitude of the positive deflection increases with augmentation 

 of the ascending current only within a comparatively narrow 

 range, and there is no approximate proportion between the two. 

 The effect is generally maximal with the full current from two 

 Daniell cells, while further rise of current intensity produces only 

 an inconspicuous increase of deflection (Biedermann). This is true 



