and Laboratory Methods. 1511 



was led through unpolarisable, brush electrodes. The current was obtained 

 from a battery of small bichromate cells. 



The reactions of Opalina are first discussed. It was found that this form, 

 when in an alkalinated or neutralised medium, showed an "attraction" to (i. e., 

 formed a collection in) an acid test solution and a "repulsion" from an alkaline, 

 and, in response to the electrical stimulus, collected at the anode. If the salt 

 solution containing the organisms was acidified the reactions were reversed, col- 

 lections being formed in the alkaline test solution and at the kathode pole. The 

 reactions of Nyctotherus showed a still closer dependence on the chemical 

 reaction of the medium than did those of Opalina. In a strongly alkalinated 

 medium Nyctotherus collected in acids and at the anode pole. In a weakly 

 alkalinated medium these organisms collected in weakly acid test solutions and 

 were "repulsed" from strong acids and from alkalis of all strengths. In response 

 to the electric current collections were formed at the anode except in very strong 

 currents, when there was a transverse orientation. In a neutral medium there 

 was "repulsion" from both acids and alkaline test solutions and the electrotactic 

 reaction was transverse to the direction of the current. Passing to the reactions 

 in acid media, it was found that when in a weakly acid salt solution, the organ- 

 isms formed collections in weakly alkaline test solutions and at the kathode 

 pole. "Repulsion" occurred from strong alkalis and from acids of any strength. 

 With strong electric currents there occurred again the transverse orientation. 

 In a strongly acid medium collections were formed in alkaline test solutions and 

 at the kathode. Under all conditions except when in strongly alkalinated media 

 Balantidium elongatum collected in alkaline test solutions and at the kathode 

 pole. In strongly alkalinated saline, however, this form collected in weakly 

 acid test solutions and exhibited a diphasic reaction to strong solutions, being 

 first "attracted" to the acid and then in a short time passing over to the alkali. 

 In this strongly alkaline medium there was also a diphasic reaction to the cur- 

 rent. An immediate movement to the anode was replaced — after a time depend- 

 ent on the strength of the current — by motion towards and collection at the 

 kathode. Without going into the details of the individual cases it may be stated 

 that in the two other species studied, Balaiitidium entozoon and B. duodeui, 

 essentially similar reactions were found. In all cases there was a distinct paral- 

 lelism between the chemotaxis and the electrotaxis. 



The ciliary action in these responses was studied principally in Opalina and 

 Nyctotherus. Opalina reacts to repellent stimuli by a response like the "motor 

 reflex" of the free living infusoria as described by Jennings. This reaction 

 brings about its "repulsion" from alkalis. Its collections in acid solutions are, 

 however, the result of a different sort of a response. When the anterior end of 

 the organism comes in contact with a weak acid the ciliary waves change their 

 direction in such a way as to directly orient the body along the lines of diffusion. 

 The organism then swims toward the center of diffusion. This is probably the first 

 clear case recorded in the literature where an inf usorian becomes directly oriented 

 along the path of diffusion of ions, and forms collections in solutions as a result 

 of such a response. The orientation to the electric current is brought about 

 by a rotation as in the ordinary "motor reflex" until the anterior end is towards 



