REACTIONS OF INFUSORIA TO ELECTRIC CURRENT 



155 



Fig. 102. — Diagrams of the reaction of Colpidium to the electric 

 current when in various positions. Based on the descriptions and 

 figures given by Pearl (1900). 



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 b c 



certain positions, a ,^ ^*<4,''^*° '--^ d 



and their mutual 

 reenforcement in 

 other positions, 

 often give rise to 

 peculiar and com- 

 plicated phenom- 

 ena. 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.) 



(1) 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 

 swims slowly forward, and at 



>lpid 1 reacts to the electric current when transverse the Same time gradually turns 

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

 data given bv Pearl (iqoo). • , i /-rp- „ j\ 



6 - vy comes oriented (rig. 102, c-a). 



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. 



Fig. 103. — Diagram of one method by which 



