in ELECTRICAL EXCITATION OF MUSCLE 245 



wise it would be difficult to come to any conclusions as to the 

 changes in the circular muscles, particularly with kathodic 

 excitation (Ftirst, 30). 



We have so far been investigating the manifestations of 

 excitation at closure only. It remains to add a few words as to 

 the polar effects that appear on opening the circuit. As in most 

 other cases, so here, it is found that stronger currents and pro- 

 longed duration of closure are essential to produce effective break 

 excitation. It need hardly be added that individual differences 

 of excitability in the preparation are also prominent factors. The 

 opening excitation effects, at least in Lumbricus, are never so 

 sharply defined as those at closure. The most definite appearance 

 is a contraction of the circular muscles similar to that of the 

 anodic closure at the previously kathodic segment, on opening the 

 circuit ; yet it is difficult to decide with certainty whether the 

 contraction spreads itself in this case, as in anodic make excitation, 

 on either side of a relaxed point. Yet more difficult is it to 

 determine the nature of the co-operation of the longitudinal 

 muscles, as appearing under certain conditions after strong anodic 

 excitation of a segment on breaking the current. It is partly due 

 to the comparatively slow equalisation of the excitation effects 

 after closure, which at least sometimes produces a superposition 

 of what may be taken as the antagonistic effects of closing and 

 opening the current, by which the question is further complicated. 



The effects of electrical excitation in the leech, and in 

 Arenicola (29) in particular, are quite as characteristic as in the 

 muscular integument of the earthworm. Here, too, the most 

 prominent effects at closure of the current are, on the one hand 

 (at the anode), contraction of the circular muscles of the segment 

 directly in contact with the electrode ; on the other hand (at the 

 kathode), the marked shortening of the same in consequence of 

 the contraction of the longitudinal muscles. Owing to the small 

 distance between the transverse furrows which encircle the worm's 

 body, the kathodic effects of excitation spread, more particularly 

 in the leech, over a large number of segments, whilst in a long 

 body-ring, e.g. at the anterior end of Lumbricus, the kathodic 

 contraction of the longitudinal muscles (at least with weak excita- 

 tion) is often only segmentally developed. The flat shape of the 

 body in the leech, moreover, brings out plainly the localisation 

 of effects of kathodic excitation to the dorsal surface excited. 



