REACTIONS OF INFUSORIA TO ELECTRIC CURRENT 155 



Thus we can distinguish two factors in the turning produced by the 

 electric current. The first is a tendency to turn directly toward the 

 ■cathode, the second a tendency to turn toward a structurally defined 

 side, — usually the aboral side. The conflict of these tendencies when 

 the animal is in 6 c 



certain positions, 

 and their mutual 

 reenforcement in t" 

 other positions, 

 often give rise to _ ^. , ,, ,• - ^ ,.,.,.,, . 



, riG. 102. — Diagrams of the reaction of Colpidium to the electric 



pecuhar and com- current when in various positions. Based on the descriptions and 

 phcated phenom- ^^ures given by Pearl (1900). 



€na. Thus, in Colpidium, as described by Pearl (1900), we have the 

 following different methods of reacting to the electric current. (It 

 should be premised that Colpidium tends under ordinary conditions to 

 turn toward the aboral side.) 



(i) When the anterior end is directed approximately toward the 

 anode, or in any position in which the aboral side is nearest the cathode, 



Colpidium turns toward the 

 aboral side (Fig. 102, a, b), till 

 the anterior end is directed 

 _ toward the cathode. Both the 

 factors mentioned above coop- 

 erate to produce this result. 



(2) When the animal is 

 nearly transverse, or is ob- 

 lique, with the oral side next 

 to the cathode, it usually 

 s-wims slowly forward, and at 



Fig. ro3. — Diagram of one method by which ., • rrrarlTiallv tnrn<; 



Colpidium reacts to the electric current when transverse ^^^ ^ame time graQUaily tUmS 

 -with the oral side to the cathode. Constructed from toward the Oral side till it be- 

 data given by Pearl (1900). ^^^^^ oriented (Fig. I02, C-d). 



The two tendencies mentioned above oppose each other in this case, and 

 the first one overcomes the second* 



(3) But in other cases when the animal is in the position described 

 in the last paragraph (Fig. 103, a) it reacts in another way. It moves 

 forward, slowly turning toward the oral side (Fig. 103, a-b), then turns 

 on its long axis (b-c) (as happens in ordinary locomotion). This brings 

 the aboral side next to the cathode (c). Now the animal turns suddenly 

 toward the aboral side till the anterior end is directed toward the cathode 

 (Fig. 103, d). In this case, then, the two tendencies mentioned above 

 oppose each other till the revolution on the long axis occurs, then they 

 reenforce each other. 



