INTERFERENCE OF EXCITATIONS 197 



accurate investigation of the mechanism of ciliary activity. The 

 galvanotactic swimming toward the cathode is explained by the 

 same principle as that applicable to all galvanotaxis.^ As a result 

 of the excitation produced by the anode, the cell body must 

 assume a position wherein the border cilia, which are of greatest 

 importance in swimming, are equally stimulated on both sides 

 of that part of the body directed toward the anode. It is only 

 in this position that forward swimming is possible, for as a result 

 of Mwsymmetrical excitation of the border cilia a turning must at 

 once occur, which automatically brings about a resumption of the 

 position of the long axis. The perioral cilia bring about the 

 screw-like movement around the axis during swimming. It fol- 

 lows that the freely swimming individuals must necessarily move 

 towards the cathode. In the case of the thigmotactically moving 

 individuals the activity of the border cilia is inhibited. The 

 perioral and the locomotion cilia bring about the assumption of 

 the position of the axis, above described. The perioral cilia dur- 

 ing movement bring about a turning of the body on the vertical 

 axis toward the side opposite that of the orifice and it follows 

 that the body can occupy only that axial position wherein the 

 perioral cilia are least excitated. This is, however, only the 

 case when the long axis of the body is transverse to the direction 

 of the current, and the perioral cilia are directed toward the 

 cathode, for stimulation arises from the anode. The reason why 

 the infusoria do not turn toward the anode from this transverse 

 position of the axis is to be found in the fact that the anterior 

 locomotion cilia are stimulated to a greater extent by the turning 

 toward the anode, and bring about a movement in the contrary 

 direction. The transverse position of the axis is thus the result 

 of an antagonistic action between the perioral and the anterior 

 locomotion cilia. It therefore follows that the characteristic 

 position, which is necessarily assumed by the thigmotactically 

 creeping individuals, is brought about by an interference action 

 between tactile and galvanic stimulation. 



These, then, are a few examples of the interference action of 

 various stimuli on the single cell. They show us in part fairly 



1 Max Verworn: "Allgemeine Physiologie." V Aufl. Jena 1909. 



