ELECTRO -PH YSIOLOG Y 



727 



indicating a current in the same direction as that of the polarizing 

 stream. This is really an action stream, due to the opening excita- 

 tion set up at the anode (p. 637). It is only obtained when the tissue 

 is living, and is far more strongly marked in the anodic than in the 

 kathodic region. 



Suppose that the nerve in Fig. 276 is stimulated by the opening 

 of the battery B, and that, immediately after, the nerve is connected 

 with the galvanometer G by the electrodes E, E t . Suppose, further, 

 that the shaded region near the anode remains more excited for a 

 short time than the rest of the nerve, and we have seen (p. 684) that 

 after the opening of a strong current there is a defect of conductivity, 

 especially in the neighbourhood of the anode, which^wouldftend to 



FIG. 276. DIAGRAM TO SHOW 

 DISTRIBUTION OF ' POSITIVE 

 POLARIZATION ' AFTER OPEN- 

 ING POLARIZING CURRENT. 



B, battery ; G, galvanometer. 

 The dark shading signifies that 

 the excitation to which the 

 current causing the positive 

 deflection after the opening of 

 the polarizing current is due is 

 greatest in the immediate neigh- 

 bourhood of the anode, and 

 fades away in the intrapolar 

 region. + indicates the anode 

 and - the kathode of the polar- 

 izing current. 



FIG. 277- HITTER'S TETANUS. 

 A strong voltaic current was 

 passed for some time through 

 the nerve of a muscle-nerve 

 preparation. On opening the 

 circuit, the muscle gave one 

 strong contraction, and then 

 entered into irregular tetanus, 

 which continued for four 

 minutes. (Only the first part 

 of the tracing is reproduced.) 



localize excitation. The portion of nerve at E being galvanometric- 

 ally negative to that at E x , an action current will pass through the 

 galvanometer from Ej to E, and through the nerve in the same 

 direction as the original stimulating stream. 



Under certain conditions a state of continuous excitation in the 

 anodic region of a nerve is shown by a tetanus of its muscle (Ritter's 

 tetanus, p. 636, and Fig. 277). 



Griitzner and Tigerstedt have put forward a different theory of 

 the break contraction. They say it is really a closing contraction 

 due to the closure of the negative polarization current through the 

 tissue itself, as soon as the polarizing current is opened. But while 

 stimulation does sometimes take place in this way, the contention 



