240 ELECTRO-PHYSIOLOGY CHAP. 



The key to this somewhat startling fact seems to lie in the 

 reaction of the Holothurian muscles, as described above. We can 

 hardly doubt that in both cases there is complete conformity in 

 regard to kathodic effects of excitation. But even the seemingly 

 divergent effects in unipolar anodic excitation of Echinus muscles, 

 must really be traced back to changes analogous with those 

 so clearly expressed in the longitudinal muscles of the Holo- 

 thurians. Here at the very entrance of the current we found a 

 local relaxation, marked by the formation of an attenuated part 

 from which a contraction that is well marked in fresh speci- 

 mens develops on either side, and produces a considerable total 

 shortening of the muscle. Now if a short, fine muscle of identical 

 or similar properties were stretched between two points of in- 

 sertion, which in contracting can only be approximated within 

 certain limits, the effect of the kathodic closure excitation would 

 obviously be the same as in the yielding attachment of a Holo- 

 thurian muscle. 



With unipolar anodic excitation the effect is, however, quite 

 different. If the current enters at any point along the muscle, 

 and local relaxation appears after closure, or if the part in con- 

 tact remains unexcited while a marked contraction occurs on 

 either side of it, there must obviously, if the point of insertion 

 cannot be further approximated, be an interruption of continuity 

 at the point of least resistance. 



The tearing apart at the anode would on this assumption be 

 referred to the fact that in unipolar anodic excitation of the 

 muscle, relaxation occurs at the contact itself, but there is a 

 marked condition of tension on either side if the muscle, on 

 account of the given mechanical conditions, is unable to contract 

 further. This is also the reason why Echinus muscle stimulated 

 in situ does not, like Holothuria, exhibit a deep canal with walls 

 rising round it at the anode, but only a tension which is appar- 

 ently uniform at every point. 



The two last cases also interpret those more complicated 

 instances, where, e.g., in the muscular integument of many worms, 

 and also in the intestine of vertebrates, two systems of smooth 

 muscle-cells lie superficially directly over each other, so that the 

 direction of fibres in both is at right angles (30). If a large 

 earthworm, paralysed with dilute alcohol (5 to 7 per cent), is placed 

 on a leading-off stage, which is constructed of several layers of 



