3] ELECTROTAXIS 141 



see the long flagellum which precedes in locomotion coming to 

 lie in the current and directed towards the kathode, so that the 

 animal migrates in that direction. The following explanation 

 of the observed fact that the flagellum becomes directed towards 

 the kathode has been offered by VERWORN ('89 b , p. 298). The 

 flagellum and the pole from which it arises constitute the most 

 sensitive end of the body. When the flagellum is stimulated 

 it beats violently, and since it is stimulated most when turned 

 towards the anode, it beats most violently when in this attitude. 

 A position 180 from this is one of comparative rest. In interme- 

 diate positions the degree of stimulation is intermediate. After 

 a few strokes the body will " naturally " come to assume and to 

 retain that position in which the flagellum is least stimulated. 

 More detailed still is our knowledge of electrotaxis among 



FIG. 33. Trachelomonas hispida, swimming towards the kathode ( ) upon closure 

 of the current. The arrow shows the direction of locomotion. (From VER- 

 WORN, '89.) 



the ciliate Infusoria. The authors who have worked upon 

 this group are chiefly VERWORX ('89* and '89 b ) and LUDLOFF 

 ('95). The work of the former shows that the phenomenon 

 of electrotaxis is exhibited by many species, especially Para- 

 mecium aurelia and P. bursaria, Stentor ccerulens and S. 

 polymorpha, Pleuronema chrysalis, Opalina ranarum, Bursaria 

 truncatella, Halteria grandinella and Stylonichia mytilus. 

 LUDLOFF employed only Paramecium, but studied it much 

 more completely, especially using various currents of known 

 relative intensity.* He found that the precision with which 



* LUDLOFF employed a trough with wax walls, clay ends, and glass bottom. 

 and used brush electrodes. The intensities of current given by him are the 

 readings of the galvanometer. The cross-section of the water mass in which 

 the Paramecia were, and over which the current spread itself, is not exactly 

 given, but was probably about 20 sq. mm. If we employ the unit of strength 

 recommended by HERMANN and MATTHIAS (p. 128), namely, 1 one-millionth of 



