362 EFFECT OF IRKITATION OF A POLARIZED NERVE. 



transitory and that currents travelling in both directions act paretically, 

 his results were but confirmatory of those obtained by Nobili. 



The first who really sj^stematically investigated this subject was 

 Valentin,* This investigator applied the constant electrodes to the 

 ischiadicus, just at the entrance of this nerve into the gastrocnemius, 

 while the irritating electrodes were applied at the point of exit of the 

 nerve from the pelvis. Valentin found that when the constant current 

 was passing through the nerve the irritating current gave a weaker con- 

 traction than when this was not the case, or, at times, none. This author 

 also showed that the same diminution in the effect of the irritating current 

 occurred when this was placed between the constant current and the 

 muscle. This latter result, however, was produced in the experiments 

 of Valentin only when the current was ascending, and not when a de- 

 scending current was employed. 



Eckhardt confirmed the observations of Nobili and Valentin. He 

 found that an electrical irritation can be made to lose its effect when 

 between it and the muscle a constant current is made to pass through 

 a given portion of the nerve. Not only did he find this to be true for 

 electrical but also for mechanical and chemical irritants. This inhibi- 

 tory eftect was manifest when the polarizing or constant current was 

 made to i^ass in either an ascending or a descending direction, provided 

 that this current was of a certain strength (5-6 large Daniel elements). 

 This author also confirmed the statement of Valentin that when the irri- 

 tation (mechanical, chemical, or electrical) is applied to the nerve above 

 the point where this is being polarized the effect is no longer so constant. 



In his first paper Eckhard made the statement, which he afterwards 

 withdrew, that the "paretic" effect was most constant when an ascend- 

 ing polarizing current was used. 



In a second paper | Eckhard irritated by means of an induced current, 

 and measured the muscular contractions thereby produced by means of 

 a Helmholtz myograph. His previous observations were confirmed. 

 When the constant current was applied to the nerve above the irrita- 

 tion, ascending polarization only diminished the effect of the irritation, 

 thus showing adiminishedexcitability of the nerve between the positive 

 electrode and the muscle. When the descending current was employed 

 a state of augmented excitability of the nerve was produced between the 

 negative electrode and the muscle. 



Pflilger,§ whose exj)eriments and "laws" will frequently be referred 

 to in this paper, was the next investigator who devoted his atttention 

 to this field of research. He made use of weak currents, while the pre- 



* Lehrb. der Phys. des Menschen, B. ii, Abth. 2, p. 155. 



t Der galv. Strom als Hinderniss der Muskelzuckung. Zeitsclir. fiir rat. Med. , N. F. , 

 B. iii, p. 198. 



tUeb. den Einil. des const, galv. Stromes auf die Erregbark. der motor. Nerven, 

 Beitriige zur Auat. und Phys., H. 1, 1855, p. 25. 



$ Allgem. Centralzeit., 1856, Nov. 22, 1857. Unters. iiber die Phys. des Elektrotomis, 

 Berlin, 1859. 



