THE BEHAVIOR OF INFUSORIA; PARAMECIUM 95 



faces the new cathode. It remains in this position till the current is 

 reversed anew. Thus, when in contact with a surface, Paramecia often 

 show a transverse orientation with reference to the electric current. At 

 times the animal while in this position moves forward along the surface 

 with which it is in contact, transversely to the current; on reversal of 

 the current it turns about and moves in the opposite direction. This 

 may often be observed if the Paramecia are 

 placed on a slide in a thin layer of water 

 through which the electric current is passed. 

 Many of them in swimming come against 

 the glass or the surface film of the water. 

 Thereupon they begin to move transversely 

 to the current, as just described. Mean- 

 while the free swimming specimens con- 

 tinue to pass toward the cathode. 



,,,. . .,, j.~ FIG. 67. Oblique position 



With a Stronger Current a Still different taken by Paramecium in contact with 



effect is produced. The Paramecia are a surface . when under the action of 



. the electric current. 



swimming forward in the slow, cramped 



manner that is characteristic for strong currents. On coming in con- 

 tact with the surface film or the glass, the animals at once begin to 

 move backward (toward the anode) instead of forward. This con- 

 tinues as long as the contact continues. On becoming free they swim 

 forward again. The reason for this behavior seems to be as follows : 

 In a strong electric current, as we know, the anterior cilia tend to drive 

 the animal backward, the posterior cilia forward (Fig. 62, b) ; the latter 

 prevail. The contact reaction, as we have seen, causes the cilia behind 

 the region of contact to cease movement. When swimming forward 

 under the conditions mentioned, the Paramecia usually come in con- 

 tact with the surface at the thickest part of the body, near the middle 

 of its length. Thereupon, owing to the contact reaction, the cilia be- 

 hind this spot, driving the animal forward, cease to beat, while the cilia 

 in front, driving it backward, continue their action. Hence, the 

 anterior cilia gain the upper hand and force the animal backward. 



Why does this contact stimulus thus interfere with the reaction to 

 other stimuli? There are two possible factors to be considered here, 

 one physical, the other physiological. The animal seems actually to 

 attach itself to solids, probably by a secretion of mucus. Such a secre- 

 tion is very evident in many infusoria, though it has not been demon- 

 strated in Paramecium. This attachment would, in a purely physical 

 way, impede the movements due to other stimuli. While it is possible 

 that this factor may play a small part in the matter, it is clear that it is 

 not the important or essential factor. If it were, we should see the cilia 



