GALVANOTROPISM 45 



While the locomotor mechanism of unicellular organ- 

 isms, like Paratncecia and Volvox, is as simple as that 

 of higher organisms, the locomotion of microorganisms 

 possessing only one flagellum, like Euglena, is more com- 

 plicated. It was generally assumed that the flagellum acted 

 like a single oar and that it was directed forward, but 

 this is not correct. It is shaped like a U and its free 

 end is directed backward; and Bancroft has emphasized 

 that it acts by the formation of a loop which moves like 

 a wave from the base of the flagellum to its free tip. The 

 same author discovered that Euglena are galvanotropic 

 when raised in acid media. On account of the asymmetry 

 of their locomotor apparatus they are compelled to swim 

 in a spiral, in most cases to the cathode, exceptionally to 

 the anode. Bancroft showed that the orientation of these 

 organisms by the galvanic current is identical with that 

 by light. 21 



All the phenomena of galvanotropism are, therefore, 

 reduced to changes in the tension of associated muscles 

 or contractile elements, as a consequence of which the 

 motion of the organism toward one pole is facilitated, 

 while the motion toward the opposite pole is rendered 

 difficult. Galvanotropism is, therefore, a form of forced 

 motions produced by the galvanic current instead of by 

 injury to the brain. 



There remains then the question of how a galvanic 

 current can bring about those changes which result in 

 the anelectrotonic and catelectrotonic condition mentioned 

 at the beginning. Currents can pass through tissues only 

 in the form of ions whose progress is blocked by mem- 

 branes which are more permeable for certain salts than 

 for others. Those salts which go through the membrane 

 carry the current through the tissue elements, those 



