in ELECTRICAL EXCITATION OF MUSCLE 247 



the anode remains un excited at the point of contact at the 

 instant of closure, or relaxed if there has been a previous tonus. 

 In this example a good indication of contraction, or relaxation, of 

 the circular muscles is afforded by the relative distance of the 

 fine transverse lines of the skin, through which each segment 

 vertical to the direction of fibres in the circular muscles exhibits 

 parallel striae. At every shortening of the circular muscles, 

 these stride approximate at the contracted, parts ; at every exten- 

 sion the space between them gets larger. This last occurs 

 unmistakably at closure of the current in the immediate proximity 

 of the anodic contact, together with a marked contraction, and 

 subsequent circular constriction, of the segments implicated. 

 This also applies, at the same point, to the longitudinal muscles, 

 which do not shorten at the electrode itself; the height of the 

 segment does not alter. On the other hand, as in the earthworm, 

 a more or less extensive contraction of the longitudinal muscles 

 appears in the segments implicated on either side of the circular 

 constriction, in proportion with the strength of the current ; this 

 is most developed in the immediate vicinity of the body-ring in 

 contact with the anode, and gradually decreases outwards. 



All these facts combine to show that the so-called smooth 

 muscles of very different invertebrate animals exhibit, as regards 

 their reaction to the electrical current, a wide, almost complete, 

 uniformity of behaviour. Here, too, the law of polar excitation 

 prevails in general, although certain effects appear which are 

 apparently without analogy in striated muscle. As a general 

 rule, the proposition still holds that at closure of a sufficiently 

 strong current, excitation and contraction follow at the physio- 

 logical kathode. Where at first sight there seem to be exceptions 

 (e.g. in the circular fibres of the muscular integument of worms), 

 more exact observation brings them under the same law. 

 Especially notable is the fact that the kathodic closure excitation is 

 localised in every instance to the point of exit of the current, and its 

 immediate proximity, in the form of a local " idio- muscular" 

 swelling (persistent closure contraction). In no case is an undulatory 

 propagation of the contraction to be detected. 



Further, in conformity with the law of polar excitation, 

 there is at closure of the current no localised excitation at the anode, 

 but rather an inhibition of a previously existing condition of ex- 

 citation, while an opening excitation, on the contrary, does occur 



