236 ELECTRO-PHYSIOLOGY CHAP. 



The excitation effects produced under similar conditions at 

 the point where the current enters are quite different. Here at 

 the point where the anodic electrode is in contact with the smooth, 

 even surface of the muscle, a more or less profound canal or furrow 

 arises at make of the current, and runs transversely over the 

 muscle ; its length and breadth correspond more or less with 

 the transverse swelling, which appears, or (with unipolar excita- 

 tion) would have appeared, under the same conditions at the 

 kathode. It is easy to see that the bulk of the muscle is pushed 

 over from the anodic side at the moment of closure, and, as it 

 were, flows away, while on either side of the hollowed canal a 

 swelling rises up, of similar aspect to the kathodic continuous 

 contraction. The changes of form in the muscle which ensue 

 may therefore be characterised as a deep hollow, rising up under 

 the electrode, marked off on either side by a transverse swelling. 



Under certain conditions yet to be considered, it appears as 

 though the two swellings were formed solely from the muscle- 

 substance dragged away from the anode. But if the experiment 

 is made with fresh, excitable preparations, it will be found, with- 

 out exception, that a conspicuous contraction appears on both sides 

 of the anode, and extends over comparatively wide tracts of the 

 muscle ; it is most evident in the immediate proximity of the 

 hollowed canal, and decreases on both sides of it. In other 

 words, at make of the current the muscle elongates itself close to 

 the anode by relaxing, while in consequence of the excitation 

 produced in the surrounding region, the muscle-substance presses 

 in towards the relaxed point. In this way there is often for the 

 whole muscle a more considerable, and always much more im- 

 portant, shortening, than in kathodic excitation. 



Since the flat longitudinal muscle-bands of Holothuria are 

 tolerably broad, the excitation effects described above can only 

 appear in one part of the fibres, when the electrode points are 

 applied to the centre of the muscle. The changes of form are, 

 however, much more striking, and can be seen at a greater dis- 

 tance, if the muscle is lightly stroked with the brush electrode at 

 right angles to the direction of the fibres. 



The same manifestations (as on the electrical excitation of 

 the longitudinal muscle-bands) appear in the thin bundles of the 

 circular muscles, although they are less striking owing to the 

 greater delicacy of structure. If a perfectly level point of the 



