in ELECTRICAL EXCITATION OF MUSCLE 233 



of the battery current is applied to any indifferent part of the 

 frog's body, while the other is in contact with the surface of 

 the ventricle, the closure of the circuit will, on stimulating with 

 a just effective current, without exception excite only when 

 contact with the heart is made by the kathode, never when it is 

 formed by the anode ; sometimes, however, the opening (at least 

 after a long closure) will also be effective. And if the validity 

 of the polar law of excitation is thus incontestable for cardiac 

 muscle, it can be demonstrated in appropriate cases for smooth 

 muscle also. 



As such, we may refer, inter alia, to the adductor muscle of 

 Anodonta, of which the response to current has already been fre- 

 quently quoted, and which, from its generally-speaking regular and 

 parallel-fibred structure, presents the best comparison with the 

 frog's sartorius. It was said above that a preparation of the 

 adductor muscle, as free from tonus as possible, persists in a 

 shortened state during the entire passage of the current. The 

 merest inspection will suffice to show that neither at closure nor 

 opening (where the latter is effective) of the current does the 

 entire intrapolar tract become persistently and uniformly con- 

 tracted, but in the first instance the kathodic, in the second the 

 anodic, half will be mainly affected. Undoubtedly this is a 

 phenomenon analogous with that of the transversely striated frog's 

 sartorius, where the corresponding localisation of the closing, or 

 opening, persistent contraction has long been known, and has 

 always been regarded as substantial confirmation of the law of 

 polar excitation by the electrical current. More exact conclu- 

 sions are obtained from the application of the graphic method 

 recording the separate contraction of either half of the muscle, 

 which is possible here as in the sartorius, by fixing the centre of 

 the muscle. But while in striated muscle, as a rule, at the 

 moment of closure, as also eventually at break of the cur- 

 rent, a wave of contraction is propagated from the kathode, or 

 anode, with great velocity through the entire length of the 

 muscle, producing on either side of the fixed centre an approxi- 

 mately equal twitch at closure or opening, in molluscan muscle 

 we find only a more or less localised persistent contraction, 

 corresponding with the persistent closing and opening contrac- 

 tion of striated muscle, which, like these, fails altogether if the 

 entrance or exit of the current is effected by a layer of dead con- 



