iv ELECTROMOTIVE ACTION IX MUSCLE :;_". 



i.e. electromotive, muscle, and it is the more essential to bear in 

 mind these phenomena of interference between the artificial <n\<1 

 the natural current, since they involve facts which have led to 

 important theoretical conclusions. 



AYe have already cited, as a cogent proof of the validity 

 of the law of polar excitation, the characteristic response of a, 

 muscle with parallel fibres, injured at one end only, to longi- 

 tudinal passage of current ; as seen, e.g., in the fact that the 

 excitatory effect of closure or opening of a current is invariably 

 diminished or abolished, when it leaves or enters by the demarca- 

 tion surface. Since in the former case the direction of that 

 fraction of the muscle current which branches into the exciting 

 circuit is always opposed in direction to the battery current, 

 the latter is necessarily weakened by the former, and the 

 question arises whether this in itself would not be sufficient to 

 account for the diminished excitation at closure of the circuit. 

 Obviously in this case, if the muscles are introduced into the 

 same circuit, one behind the other, one of them being injured at 

 one end, the closure of the current would affect both muscles 

 equally, i.e. the make excitation with admortal direction of current 

 would be abolished or lessened, not merely in the muscle with an 

 artificial cross-section, but in the normal preparation also. Yet 

 this is not the case, and the theory is no less definitely refuted 

 by the fact that the death of the fibres at loth ends of a muscle 

 with parallel fibres, produces the same depression, or abolition, 

 of excitability towards the closure of ascending as of descending- 

 currents. On the other hand, it appears as if the augmented 

 effect which is often to be seen at closure of weak " abter- 

 minal " battery currents after injury to one end of the sar- 

 torius, is essentially caused by the deriving current from the 

 muscle superadded in this case, algebraically, to the exciting 

 current. 



Under certain conditions, to be discussed below, a spurious 

 break twitch appears in consequence of interference between the 

 demarcation current and an artificial excitation current, which 

 might easily be taken for the effect of a real break excitation, 

 and is in fact frequently confused with it. Given a leading-in 

 circuit of comparatively low resistance, so connected with a 

 curarised sartorius provided at the pelvic end with an artificial 

 cross-section, that the unpolarisable contacts are applied, on the 



