146 GENERAL PROPERTIES OF LIVING TISSUES 



nect the remaining pair of cups through a closed 

 short-circuiting key with the capillary electrom- 

 eter. Let the galvanic current flow some min- 

 utes through the nerve, then turn the rocker 

 towards the electrometer and open the short- 

 circuiting key. 



Note a movement of the meniscus in a direction 

 indicating that the former cathode is now posi- 

 tive to the former anode. 

 The nerve is polarized. 

 Positive Variation. 

 If the polarizing current 

 is strong and brief, the 

 Fi 40 negative polarization 



after-current will speed- 

 ily give place to a positive current, i. e. one in the 

 direction of the polarizing current. This positive 

 current is really an action current. When the 

 polarizing current is broken, the rise of irritabil- 

 ity at the anode stimulates points nearer the 

 anode more strongly than points farther away. 

 Points nearer the anode become, therefore, nega- 

 tive to points farther away, and a current flows 

 through the electrometer circuit from the less 

 negative to the more negative pole, and through 

 the nerve in the direction from anode to cath- 

 ode. This positive variation is seen only 'in 

 living nerves. 



