in ELECTRICAL EXCITATION OF MUSCLE 231 



the kathode no longer falls at the limit of moribund, i.e. less 

 excitable, muscle -substance on the one hand, and surrounding 

 fluid or dead cell-substance on the other, but lower down at the 

 border of living and dead cells, i.e. nt the demarcation surface. 

 Every polymerous striated skeletal muscle, as can easily be 

 demonstrated, exhibits the same reaction. The consideration of 

 the electromotive action of the heart (infra} further confirms 

 this theory. Another method of demonstrating the law of polar 

 excitation on cardiac muscle, when it is totally uninjured and 

 n 'mains in diastolic relaxation, is the so-called unipolar sfimu/"- 

 t in ii. Since excitation by the electrical current depends in the 

 first place upon its density at the point of ingress or egress, it is 

 l>rima facie evident that the diminution of the same at one pole, 

 with simultaneous maximal increase at the other, may furnish an 

 explanation of the law of polar current action. Thus, indeed, as 

 was pointed out by Klihne (28). we may obtain an electrical 

 excitation as weak as that formerly produced by mechanical 

 excitation. If two punctiform leading-in electrodes are imagined 

 upon the surface of any conductor, the whole interior of the 

 same will be traversed by lines of current, whose density is 

 greatest at the point of contact, and slowly diminishes outwards. 

 And if by employing a flat electrode, the density, and consequently 

 the efficacy, of the current is rendered minimal, or negative, at 

 the point where it enters, or leaves, the muscle, the other elec- 

 trode only will finally remain effective at the point of contact, and 

 may, as it were, be localised by limiting the surface of the con- 

 tact as much as possible. If, for example, the skin is removed 

 from the ventral surface of the thigh of a curarised frog, 

 the broad surface of one (the indifferent) electrode being 

 applied to the skin of the throat, while the other, the finest 

 possible pencil electrode, is in contact with any point of the 

 moist surface of the muscle, characteristic effects of excitation 

 appear, which differ widely, according as contact is effected at the 

 kathode or anode. In the first case, on sending in a weak 

 current, the bundles of fibres immediately under the point of the 

 electrode may be seen to contract at the moment of closing the 

 circuit, producing for a moment a small longitudinal furrow on 

 the smooth, even surface of the muscle, while at the actual point 

 at which contact is effected a small, sharply-defined transverse 

 swelling appears, which provided the contact is unbroken 



