Jennings, Behavior of Paramecium, 469 



showed the opposite relation, and I can well believe that in 

 some cultures the majority may conduct themselves in this man- 

 ner, and that this was the case with the Paramecia observed by 

 the authors named. But certainly as a rule most of the organ- 

 isms swim against the current, not with it. The phenomena 

 may best be observed by placing Paramecia in a tube which is 

 narrowed in the middle and open at both ends. Only the cen- 

 tral part of the tube is filled with water, the two ends contain- 

 ing only air. Over the two ends are fitted rubber caps, such 

 as are used for medicine droppers (Fig. 10). By compressing 



Fig. 10. Tube for study of the reaction to water currents. See text. 



one of these caps the water is forced through the narrow part 

 of the tube with any desired velocity, and is always under com- 

 plete control. With a certain velocity of current most of the 

 animals are seen to become oriented and to swim against the 

 current. The tube must not be too narrow, since in this case 

 many of the individuals strike against the side of the tube, and 

 then no longer respond well to the current, the contact reaction 

 interfering with "rheotaxis" as well as with many other reac- 

 tions. In any case, many individuals show no orientation or 

 are oriented in the opposite direction, yet the phenomenon is 

 sufficiently general to show clearly that we have here a real re- 

 action of the organism. 



How is this reaction to water currents brought about ? If 

 we direct a fine current of water for a moment upon a Para- 

 mecium that is swimming quietly, we find that it gives the 

 "avoiding reaction" in a not very pronounced form. That is, 

 it stops, or begins to progress more slowly, and swerves more 

 strongly toward the aboral side, appearing thus to swing from 

 side to side, the anterior end really describing circles of consid- 

 erable size, as in Fig. 8. b. The effect of this current on the 

 animal is of course to change in some way the resistance it 



