134 ELECTRO-PHYSIOLOGY CHAP. 



remains to be seen whether this fact is sufficient to justify 

 Tschirjew's assumption. On purely theoretical grounds this is 

 a priori improbable, while experiments carried out under Her- 

 mann's direction by Albrecht and A. Meyer (16) are distinctly 

 against it. From the first point of view we have the fact that 

 both in the pseudopodia of Ehizopods (Actinosphaerium^), and also 

 in striated muscle, iiiexcitability to currents directed vertically 

 to the long axis of the cells is indubitably established. Since 

 there is general conformity between nerve and muscle in their 

 reaction to current, it would be surprising if there was any 

 exception in this particular. Albrecht and A. Meyer showed, 

 moreover, that with pure transverse passage of current through 

 the nerve, the strongest battery and induction currents had no 

 effect, although the least displacement of the nerve caused a 

 twitch. Starting with certain experiments already described on 

 locally alcoholised nerve (which indicate that excitability rises 

 within the tract involved, while conductivity is simultaneously 

 diminished), Gad and Piotrowsky (16) have recently reaffirmed 

 the transverse excitability of nerve, urging as proof that the local 

 increase of excitability from alcohol is more conspicuous in a 

 prepoiideratingly transverse passage of current (through a trough 

 between two clay strips connected with unpolarisable electrodes) 

 than with the longitudinal direction. Without entering into 

 detailed criticism it may be said that this experiment hardly 

 suffices to throw over the older conclusions as to transverse in- 

 excitability of nerve. 



The differences of excitatory effect, according as the current 

 flowing longitudinally through the nerve is directed to or from 

 the terminal organ, belong to a department which has been 

 explored from every point of view since the first days of 

 galvanism. A solution and a legitimate interpretation have, how- 

 ever, only recently been attempted. We know as a general law 

 that a constant electrical current flowing through a motor nerve 

 excites mainly at closure or opening of the circuit, although the 

 passage of current at constant density may also have an excita- 

 tory effect upon the muscle. Along with this fact we know that 

 the magnitude of make and break twitch, and even the appear- 

 ance of one or the other, is also conditioned by direction of 

 current in the nerve, i.e. whether it flows from a point proximal 

 to the muscle to a more distal point, or vice versa in a descend- 



