108 



(in Fig. 55, 



hich is manifested by the retraction of the pseudo- 

 podia, and, if the stimulus lasts 

 long, by the destruction of the 

 protoplasm at the place where 

 the current enters. When 

 communication is broken, the 

 destructive process at the anode 

 immediately ceases, whilst, on 

 the other hand, a -transitory 

 contraction occurs at the sur- 

 face which is turned towards 

 the cathode. 



Perhaps even more interest- 

 ing and important than these 

 processes are the phenomena 

 produced by Galvanotrop- 

 ism, which have been observed 

 by Verworn in a number of 

 unicellular organisms (IV. 39, 

 40). 



Many organisms, in conse- 

 quence of the influence of the 

 constant current, are caused to move in certain fixed directions, 

 just as they move when stimulated by a ray of light (heliotropism). 

 " If a drop, containing as many Paramcecia aurelia as possible, is 

 placed upon a slide between two non-polarisable electrodes, and the 

 constant galvanic circuit is closed, it is seen that the Paramaecia 

 immediately leave the anode in a mass, and hurry in a dense 

 swarm to the cathode, where they collect in great numbers. 

 After a few seconds the rest of the drop becomes completely 

 free from Protista, whilst at the cathode there is a dense seething 

 crowd of them. Here they remain as long as the current persists. 

 When connection is broken, the whole swarm immediately forsakes 

 the cathode to swim back in the direction of the anode. How- 

 ever, they do not all collect at the anode, part of them re- 

 maining scattered about in the drop ; at first they do not come 

 near to the cathode, but after a time they gradually approach it, 

 until finally all the Protista are again evenly distributed through- 

 out the drop." 



If pointed electrodes are employed, the Paramcecia swarm 

 inwards to form a galvanic Hgure around the cathode (Fig. 56.4). 



FIG. 55. Actinostihasrium Eichhornii, 

 tween the poles of a constant current. A 

 short time after the closing of the current, 

 granular destruction of the protoplasm 

 commpnces at the anode (+). At the 

 cathode the pseudopodi* have become 

 normal again. (After Verworn, Tab. 1, 

 Fig. 2.) 



