o 



14 PHYSIOLOGY OF MUSCLES AND NERVES. 



branch-currents of tlie electric current used for irritation, 

 which might easily lead to errors, are pre ent in the mul- 

 tiplier. 



13. Electrotonus. Secondary Pulsation effected by 

 Neryes. Paradoxical Pulsation (p, 221). 



The reason why it is impossible to examine the electro- 

 tonus of the intrapolar portions is purely physical. If the 

 constant current is transmitted through .the portion a k 

 (fig. 60, p. 220), and two points of this portion are con- 

 nected with the multiplier, then a part of this current passes 

 thi-ough the multiplier itself, so that the portion of the 

 nerve which is situated between these points is traversed 

 by a weaker current than are the adjacent portions. The 

 conditions are thus rendered so complex that it becomes 

 very hard to explain the phenomena. Other attempts to 

 study the character of the intrapolar region have as yet 

 afforded no clear results. 



If a nerve a is laid on a nerve h, in the way shown in 

 fig. 75, A, B, 6', so that the nerve b forms a diverting arch for 

 a portion of the nerve a, and if electrotonus is generated in 

 the latter by a constant current, then the electrotonic cur- 

 rent passes through the nerve 5, and can at its commence- 

 ment and cessation (closing and opening) excite the nerve b, 

 and cause pulsation in the muscle of the nerve. This is 

 spoken of as secondary 2^ulsation from the nerve. By rapidly 

 repeated closings and openings of the circuit, tetanus may be 

 elicited. But this secondary pulsation is caused only by 

 electrotonus and not by negative variation, so that it can 

 be more easily brought about by constant currents than by 

 inductive currents. It is thus distinguished from the secon- 

 dary 2ndsatio7i effected by muscle, which was described on 

 p. 209. Tlie negative variation of the nerve-current is too 

 weak to cause any noticeable effect in a second nerve. 



