in ELECTRICAL EXCITATION OF MUSCLE 235 



end of the muscle and pushing it along the muscular band, 

 pressing it against the attachment. Excitation experiments can 

 then be tested on this isolated arid freely -stretched band of 

 muscle, just as in the muscle of Mollusca. In every instance 

 the protracted tonic contraction into which these muscles 

 usually fall, more especially after mechanical injury, is very 

 disturbing ; but after a period of rest under sea- water relaxation 

 sets in again sufficiently to make experiment possible ; a certain 

 degree of tonus, however, persists and must be taken into considera- 

 tion. If two fine pencil electrodes are then applied simultane- 

 ously to two points, not too close together, of a longitudinal 

 muscle-band, lying in situ or stretched between two corks, or if 

 one electrode is laid on some indifferent part of the preparation, 

 the other only being in contact with the muscle, there will, in 

 either case, be characteristic changes of form at the points where 

 current enters or leaves the muscle, differing widely at the two 

 poles (29). 



As soon as the circuit is closed, a small transverse swelling 

 arises at the kathode, exactly under the electrode in contact, and 

 extends thence at right angles to the direction of the fibres ; 

 under some conditions (not too weak a current) this swelling 

 spreads over the whole breadth of the muscle-band, and stands 

 out sharply from the region round it. This " idio-muscular," 

 kathodic swelling persists during the period of closure, and (what 

 is specially remarkable) never spreads beyond the point where it 

 originates. The total shortening of the muscle-band produced by 

 the localised contraction is always insignificant, since it is essen- 

 tially only the part of the muscle immediately adjacent to the 

 exciting electrode which contributes to the local expansion. It 

 also depends, of course, upon the strength of the current used for 

 excitation, so that within a certain range the kathodic swelling, 

 which undoubtedly corresponds with the persistent closure con- 

 traction of striated muscle, increases with the strength of the 

 current, and then includes a larger tract of the muscle. With 

 very weak minimal currents the upper layers of fibres only con- 

 tract locally, so that the kathodic swelling does not extend over 

 the whole thickness of the muscle. In all cases the sharp delimit- 

 ation of the kathodic continuous contraction is very remarkable, 

 it rises in a crest, descending sharply on both sides to the 

 surface of the muscle. 



