382 ELECTRO- PHYSIOLOGY CHAP. 



exactly parallel with that derived from the second ; but 

 according to Bernstein this never is the case, the positive, being 

 always smaller than the negative variation. Accordingly, the 

 excitatory wave decreases in amplitude as it is propagated 

 along the muscle - fibres ; in other words (at least in excised 

 muscle), it is decremental. The double action current observed 

 after each single excitation in uninjured, currentless muscle 

 may be termed, after Hermann (27), the "phasic current of 

 action." The first phase is directed from, the second towards 

 the seat of excitation. If one of the leading- off contacts is 

 applied to an artificial cross-section, the corresponding phase will 

 make its appearance. Since the galvanometer magnet is much 

 too insensitive to respond by corresponding deflections to these 

 opposite currents (which follow with extraordinary rapidity in 

 tetanising excitation), we should anticipate that on leading off 

 without current from two points of the longitudinal section, 

 there would be no effect even during tetanus. That this is 

 actually not the case may be explained from the fact that the 

 excitatory wave decreases in amplitude during its transmission 

 through the muscle ; it follows directly that on leading off 

 from two longitudinal points of an uninjured, currentless, 

 parallel -fibred muscle, a difference in electrical potential must 

 appear between the two points, when one end is tetanised by 

 an ordinary induction coil : the longitudinal contact proximal 

 to the seat of excitation must always be negative to the distal 

 point, since the latter, owing to the decrement of the excitatory 

 wave, must always be less negative than (i.e. relatively 

 positive to) the former. Such an action current is in fact 

 present in tetanus, and has been confirmed by du Bois-Reymond 

 and Hermann. The latter found the E.M.F. of this current, 

 which he described, from reasons given above, as the " decre- 

 mental action current of tetanus," to be of considerable pro- 

 portions (0'002-0'02 Dan.) Du Bois-Reymond originally 

 believed that decremental action currents were only to be 

 observed on fatigued, moribund muscle, i.e. that the excitatory 

 wave only diminished in these cases. Hermann, however, 

 showed that the decrement obtains immediately after making 

 the preparation. Since the excitatory wave becomes smaller 

 in proportion as it is farther from the seat of excitation, the 

 individual transverse sections of a muscle tetanised at one end 



