428 THE PROPERTIES OF STRIPED MUSCLE. 



tion, because it associates itself so closely with ordinary polarisation, that 

 it is often difficult to distinguish the one effect from the other ; positive, 

 because it is in the same direction as the led-through current. The 

 significance of these characteristics becomes at once plain from the 

 moment that it is understood that this phenomenon is of the nature of 

 excitation. 



After the opening of a current flowing through a muscle, the 

 presence of the effect just described indicates that the region of the 

 anode, that is, the seat of disturbance, is itself relatively negative. If 

 the experimental current is strong, this effect is so immediate and 

 powerful that the polarisation effect proper is overpowered by it. If it 

 is weaker, a diphasic movement of the needle is observed, in which the 

 transitory true polarisation effect is followed by the other. If in a 

 succession of experiments the strength of the " polarising" or external 

 current is gradually increased, the brief duration remaining the same, 

 the effects which are at first opposed in direction to the external 

 current become diphasic (the movement due to polarisation being 

 followed by that due to the anodic disturbance), and eventually have 

 only the direction of the external current ; and this gradual change is 

 best seen when one galvanometer contact is at the anode. Perhaps the 

 best proof of the excitatory nature of the phenomenon is obtained 

 when, the muscle having been injured by heat so as to produce a 

 " thermal section " at its tibial end, one electrode is placed on the injured 

 part, the other on the natural surface at the pelvic end. In this 

 case, if the anode of the polarising current is on the injured surface, 

 the effect is scarcely perceptible, whereas with the polarising current 

 reversed (anode on the uninjured pelvic end) a descending after-current 

 is^observed. 



These experiments justify the application to the phenomena in question, 

 in preference to du Bois-Keymond's original designation (positive polarisation), 

 of the term "anodic after-effect" used by other writers, as denoting the 

 localisation of the effect at the anode and the time of its occurrence, without 

 suggesting any theory of its nature. Considering that relative negativity of 

 a part is a sign of the excitatory state, and that in nerve the anode is the 

 seat of the excitatory effects which take place at the opening of a current 

 led along it, it is not unreasonable to regard the effect as excitatory. The 

 reader will find that some difference of statement exists between leading 

 physiologists as to the degree in which the anodic after-effect is limited to the 

 anode. According to some observers, the whole of the anelectrotonic region 

 becomes relatively negative. 



The phenomena which have just been described are those which are 

 best known. The admission, however, that the anodic after-effect is 

 the result of a polar change, dependent on the cessation of the inflow 

 of the current, carries with it the suggestion that the cessation of the 

 outflow at the cathode may have a corresponding after-effect, that is, 

 one in which the cathodic region becomes relatively positive. 

 Phenomena which are in accordance with this surmise have been 

 observed by Biedermann in the sartorius ; but in order to make them 

 appreciable, one end of the muscle must be steeped in salt solution 

 containing veratrine. The part thus treated can be thrown by a single 

 instantaneous excitation into a state of continuous spasm of sufficient 

 duration to make it possible to examine its properties experimentally. 



