3] 



ELECTROTAXIS 



143 



rapidly for a moment, towards the opposite pole (anode), but 

 then quickly begin to redistribute themselves throughout the 

 water. This redistribution has occurred in about 20 seconds 



FIG. 35. Apparatus for studying electrotaxis of Paramecium. A rectangular trough, 

 whose ends are of clay and sides of wax, is built upon a glass plate. The current 

 is applied by means of brush electrodes. The direction of the migration of the 

 paramecia is indicated by the arrow. They move towards the kathode. (From 

 VERWORN, '95.) 



after the current is broken, and the time is independent of the 

 strength of the preexisting current. 



The movement of the Infusorian from one pole to the other 

 takes place along the lines of flow of the current. If the ter- 

 minals are two parallel plates, these lines are about parallel 

 (Fig. 35); if they are two points near the opposite sides of 



A B 



FIG. 36. Curves made by Paramecia in its galvanotactic response when pointed 

 electrodes are used in the drop of water. A, beginning of migration ; B, com- 

 plete aggregation. (From VERWORN, '95.) 



a water drop, the lines have the direction of the lines made 

 by iron filings scattered on a plate over the two poles of a 

 magnet (Fig. 36). 



Besides this path of general migration, the form of the path 

 followed by individuals varies with the current. Normally 

 Paramecium moves in a long spiral. As the current is in- 



