426 



THE FUNCTIONS OF CROSS-STRIATED MUSCLES 



the anode, and the closing contraction is wanting. With- the descending cur- 

 rent the excitation started at the anode meets with a resistance at the cathode 

 which may or may not completely block it ; hence the opening contraction either 

 fails altogether or is greatly diminished. 



Exactly the same laws hold for the induction currents as for the constant 

 current. They also stimulate at the cathode as they appear and at the same 

 time produce a resistance at the anode. When they are strong enough, they 

 have a stimulating effect also as they disappear and then the stimulus starts 

 from the anode. 



The fact that the induction currents produce a resistance at their anode is 

 demonstrated by the following experiment: a nerve is stimulated with ascend- 

 ing' induction currents which, beginning with very weak shocks, are gradually 



FIG. 163. Stimulation of a nerve by a series of ascending make- and descending break-induction 

 shocks of increasing strength. To be read from right to left. The first contraction of each 

 pair was obtained by the ascending closing and the second by the descending opening 

 shock. There are no " gaps " in the latter series. 



increased in strength (Fig. 163). The height of the contractions at first increases, 

 but after a time decreases, and with a certain strength the muscle remains at 

 rest (Fig. 163; Nos. 11-18). If the strength of the shocks be raised still fur- 

 ther, contractions appear again, which at first are weak (Nos. 19, 20), but gradu- 

 ally become stronger until they finally may become supramaximal. With a 



