256 ELECTRO-PHYSIOLOGY CHAP. 



brates, the conditions required for a wider distribution of lines of 

 current in the proximity of the electrodes, and therewith also for 

 the effectuation of secondary electrodes, are a priori and unavoidably 

 present. The conspicuous thickness of all these parts is the reason 

 that the lines of current do not, even with bipolar excitation, adjust 

 themselves (as in the exposed nerve, or ureter) mainly in a direction 

 parallel with the long axis of the organ, between the two points in 

 contact with the electrodes, but that there is inevitably a further 

 distribution, and, so to speak, diffusion, of the current in the 

 proximity of the point where it enters, as well as that where it 

 leaves, the muscle. The most important result of these experi- 

 ments, in various parts of smooth muscular organs, is undoubtedly 



FIG. 92. 



the fact that in conformity with the law of polar excitation, as 

 established for striated muscle, the make excitation is ivithout excep- 

 tion discharged at the physiological kathode only, i.e. the true point 

 of exit of current from the contractile substance of the entire 

 muscle, and is seldom transmitted beyond this point; while, 

 on the other hand, excitation never appears at the physiological 

 anode itself on closure of the circuit, but where a state of tonic con- 

 traction is present, local inhibition of the existing excitability may 

 appear as a more or less obvious localised relaxation of the muscular 

 tissue, followed occasionally, lohen the current is opened, by a contraction 

 which in extension and character exactly resembles the persistent 

 kathodic closure contraction. While this last nearly always appears 

 as .a tolerably ivell-dejined swelling, a persistent closure contraction 

 of quite a different character may often be seen on both sides of the 



