REACTIONS OF INFUSORIA TO ELECTRIC CURRENT 157 



But Wallengren has shown that the effect of the current is in these in- 

 fusoria of essentially the same character as in others. Let us examine 

 briefly the facts as set forth by Wallengren (1902 and 1903). 



Spirostomum (Fig. 106) is a very long, slender infusorian, easily 

 bent in any direction, and very contractile. The peristomal cilia are 

 very large and numerous, extending from the anterior end along one 

 side to a point behind the middle. Whether striking forward or back- 

 ward, the beating of these 

 ciha is decidedly more effec- 

 tive than that of the cilia on 

 the opposite side of the 

 body. It is to this fact, 

 taken in connection with the 

 slenderness and suppleness 

 of the body, that most of 

 the peculiarities in the reac- 

 tion of Spirostomum to the 

 electric current are due. 



In a very weak current, 

 such as does not cause con- 

 traction of the body, Spiro- 

 stomum swims to the cath- 

 ode. The ciHa on the 

 anodic part of the body 

 strike backward, those in 

 the cathodic region forward, 

 just as happens in Para- 

 mecium. As a result, the 



animal takes a position with Fig. 106. — Diagrams iUustrating reaction of 

 anterior end directed to the Spirostomum to the electric current. A,B, D, and 

 . ■ IT T -^ after Wallengren (1903). 



cathode, in essentially the 



same manner as does Paramecium, — usually turning to the aboral side, 

 but in certain cases toward the oral side. When the anterior end is 

 directed toward the cathode, the cilia on the cathodic half of the body 

 are partly directed forward, but with the weak current most of them still 

 strike most strongly backward. Those of the anode half of course 

 strike backward, so that the general result is to drive the animal 

 forward to the cathode. Sometimes Spirostomum under these condi- 

 tions comes against the bottom or other soKd object ; it may then nearly 

 or quite cease to move forward. The facts thus far are quite parallel 

 to those observed in Paramecium. 



As the electric current is made stronger, the cilia on the cathodic 



