130 ELECTRO-PHYSIOLOGY CHAP. 



current. The ordinates above the abscissa correspond with 

 descending currents in the nerve, those below the abscissa with 

 ascending currents. The curve (cibcde) corresponds to an entire 

 revolution of the bridge. 



It is obviously easy to determine by this method the 

 amplitude, duration, and abruptness of the oscillation within wide 

 limits ; it is also possible to lead a current into the nerve which 

 shall correspond only with the tract (abc). The action of a 

 single linear oscillation of current was investigated by Fuhr 

 (15), using a similar apparatus to that of v. Fleischl. No special 

 differences from the ordinary method (in which current intensity 

 rises, as it were, with infinite steepness) could be detected in the 

 indirectly excited muscle-twitch. Von Fleischl always saw the 

 twitches first at a certain rate of rotation of the rheonome, i.e. at 

 a given pitch of current oscillation. They do not last throughout 

 the entire period of increase of intensity, but commence at a 

 certain pitch, and soon terminate, while the curve of oscillation 

 increases still further, and finally sinks abruptly. The sharp 

 turning-points (kinks) of the curve are not excitatory. The re- 

 action of the muscle during the entire period of current oscillation 

 is thus comprised in a single contraction. 



Von Kries subsequently constructed a "spring rheonome" on 

 an entirely different principle, by which he obtained linear 

 jfr variations of current of different steep- 



nesses, while the resulting intensity re- 

 mained constant, producing oscillations of 

 the form _^~ '. If ah (Fig. 183) 

 is a solid or fluid conductor traversed 

 by a constant current, there will at any 

 two points be a difference of potential 



proportional to the distance between them. If c and d are 

 then joined by a conductor, the resistance of which as compared 

 with the resistance of cd is very high (nerve, e.g.), it will be 

 traversed by a current of which the intensity can easily 

 be raised lineally as required, if as is the case in v. Kries' 

 apparatus one leading -off electrode is firmly attached to the 

 point c while the other slides with constant rapidity along 

 the wire ab, and is finally brought up at a certain point of the 

 conductor (Kries, like Fleischl, employed a trough of fluid) tra- 

 versed by the current. 



