232 ELECTRO-PHYSIOLOGY CHAP. 



persists unaltered throughout the entire period of closure. We 

 cannot doubt this to be a persistent kathodic closure-contraction. 

 If the intensity of the excitation current is strengthened, both the 

 twitch and the continuous contraction increase also, although the 

 latter never loses its localised character. This appears most 

 clearly if (as above) marks are affixed to the surface of the 

 muscle, which, by moving in opposite directions during contrac- 

 tion, are a measure of its spatial extension. The muscle investi- 

 gated may, e.g., be painted with sepia bands at right angles to the 

 direction of the fibres, so that the distance between each two 

 lines, drawn with a fine bristle, is about -J mm. Every contrac- 

 tion thus defined expresses itself therefore by a more or less 

 conspicuous decrease in one or several cross -bands, or the 

 uncoloured spaces between them. Within those tracts of the 

 muscle, on the other hand, which are only passive factors, the 

 coloured cross-bands, though variously distorted, do not become 

 smaller. It is undeniable that with the unipolar method of 

 excitation, as described (where the lines of current do not, gener- 

 ally speaking, pass in and out through the natural ends of the 

 muscle, but traverse the fibres in the most opposite directions, 

 oblique and tranverse, which must partially affect the current 

 action), the conditions of experiment are less easy to summarise 

 than with the customary bipolar method, and the results, 

 e.y., in regard to the possibility of action from secondary 

 kathodic or anodic points in the proximity of the exciting 

 electrode, often hard to interpret. Still this method has its 

 advantages in many cases where the bipolar method could not 

 well be brought into application. This occurs eniphatically 

 in many smooth muscular parts, and not less in cardiac muscle, 

 where the complex and intricate course of the fibres makes it 

 a priori impossible for the current to traverse all the individual 

 elements longitudinally. The cells thus fitted together in all 

 conceivable directions would more probably be traversed by the 

 lines of current in the most various directions, and at widely- 

 divergent angles. But as shown by the above, this is of little 

 importance to the final consequence. If the ventricle of the 

 frog's heart is arrested in diastole, according to Bernstein's 

 method, by squeezing it away from the auricle, it appears filled 

 out with blood, and reacts to every mechanical stimulus by 

 a powerful total contraction. If, once more, the broad electrode 



