in ELECTRICAL EXCITATION OF MUSCLE 219 



the process of excitation is, as a rule, discharged only at the 

 kathode. If it is further remembered that the break shock 

 excites less strongly than the make shock, it is easy to compre- 

 hend the sequence of phenomena which are observed when a 

 curarised sartorius is stimulated with gradually-increasing make 

 and break shocks, sent in throughout the length of the muscle. 



It was shown above that the difference in current density, 

 due to the form of the muscle, at the points at which the current 

 leaves and enters, occasions the dissimilar effects of excitation in 

 the descending and ascending constant currents : this is equally the 

 case with the induced current, so that the polar action of the 

 latter may be taken as proven. The experiment is even more 

 convincing with muscles that have been injured at one end. 

 Both make and break induction currents, sufficient in intensity to 

 produce maximal excitation in the uninjured sartorius, when the 

 kathode lies at the end nearest the tibia, first produce excitation 

 after mechanical, thermic, or chemical destruction of the latter, 

 when the intensity of current has been strengthened by pushing 

 the coil up considerably further (26). If the injury of a muscle 

 with parallel fibres is not confined to one end, but both are 

 destroyed, excitation fails with both ascending and descending- 

 direction of current, so that a muscle-fibre bounded by two 

 artificial cross-sections, traversed in its total extension by parallel 

 lines of current of equal density, remains unexcited whether the 

 current axis is parallel with, or at right angles to, the axis of the 

 fibres. Under certain conditions, when there is any opportunity 

 for the arising of effective longitudinal components, excitation 

 will occur sooner than it does with pure longitudinal currents. 

 With the aid of the method of sending current transversely 

 through the muscle described above, these facts may easily be 

 verified, and serve to explain the frequent statement that the 

 transverse excitability of muscle is less than its longitudinal 

 excitability. This applies in particular to Giuffre's experiments, in 

 which bits of muscle were employed bounded on both sides by an 

 artificial cross-section. 



In interpreting the peculiar effect exerted by local injury 

 (death) of the ends of the fibres upon the excitability of 

 the muscle, with longitudinal passage of current, it is very 

 significant that total death of the fibre-ends is not essential, 

 certain chemical changes of the muscle - substance being all 



