548 



NER VE. 



the anodic lowering of excitability and the anelectrotonic current 

 appear simultaneously, 1 and there is good ground for the belief that 

 the further time relations of these two sets of changes are identical. 



The anelectrotonic current, like the anodic fall in excitability, attains 

 its maximum slowly, and subsides but little during closure ; the catelec- 

 trotonic attains its maximum rapidly, and may subside whilst the former 

 change is still increasing. The time relations of the development of 

 the electrotonic currents in the immediate neighbourhood of the poles 

 were expressed diagrammatically by du Bois-Eeymond, as shown in the 

 curves, Fig. 285, where the abscissae represent time after closure has 

 begun, and the ordinates the intensity of the respective electrotonic 

 currents. 2 The curves are constructed from a series of successive 

 observations, in each of which the galvanometer was connected with 

 the extrapolar region for a definite period after the closure of the 

 polarising current. 



The propagation of the electrotonic effects. — The electromotive changes 

 of electrotonus are undoubtedly present in the extrapolar regions, and 

 there appears to be a delay between the moment of closure and 



the commencement of the 

 electrotonic change, when 

 the distance between the 

 polarising and galvano- 

 metric contacts is suffi- 

 ciently increased. If this 

 delay is referred to the 

 propagation of the state, 

 then, according to Bern- 

 stein, the catelectrotonic 

 change is propagated in 

 nerve (15° C.) at a rate of 

 from 9 to 10 metres per 

 second ; the rate for the an- 

 electrotonic change varying 

 between 6 and 12 mm. per second. 3 These results are rendered incon- 

 clusive by the circumstance that the electromotive change at some 

 distance from the pole is much diminished, and thus any comparison 

 between a distant and a near point must be made under dissimilar con- 

 ditions. The later commencement in the distant region may be chiefly 

 an instrumental lag due to the smallness of the change. 4 A further 

 complication may be the presence of the excitatory negative variation. 



The rate of propagation of the electrotonic change has been investi- 

 gated also by the response of a nerve muscle preparation used as a 

 galvanoscope. If one of the two branches of the sciatic nerve of the 

 frog is dissected out and divided near its muscular termination, then, 

 on passing a galvanic current through this portion, the other branch is 

 excited, the excitation being indicated by a response in the supplied 

 muscles. This " paradoxical contraction " 5 is due to the electrotonic 



1 Pfiiiger, loc. cit. 



2 E. du Bois-Reyruond, Arch. f. Anat., Physiol, a. ivissensch. Med., 1867, S. 446; also 

 "Gesammelte Abhandl.," Bd. ii. 



3 Bernstein, Arch. f. Physiol., Leipzig, 1886, S. 197; also Tschiriew, ibid., 1879, 

 S. 545. 



r, tx 



Fig. 285. — A = anelectrotonic ; = catelectrotonic 

 T x , commencement of closure of polaris- 



effect. 



ing circuit ; T. 2 . 



extrapolar effect. 



commencement of observed 



4 Hermann, Arch. f. d. ges. Physiol., Bonn, 1880, B< 



5 E. du Bois-Eeymond, "Untersuclmngen," 1849 (1), 



Bd. xxi. S. 423. 

 Bd. ii. S. 528. 



