GALVANOTAXIS 363 



accelerated or retarded by a direct or indirect action of the electric current 1 . 

 Since the orientation is unaltered so long as the current remains constant, it 

 is evidently due to the stimulus exercised by the current, and not to any 

 transitory shock-effect. Possibly, however, organisms may be found to 

 show orienting movements under the action of induction-shocks, and it has 

 still to be determined whether certain Bacteria and other organisms can 

 show a phobo-galvanic response. 



The conversion of positive into negative galvanotaxis produced by an 

 increase in the strength of the current is due to a reversal of the polar 

 orientation, just as in the reversal of phototaxis by increasing intensity 

 of light. In both cases the tropic stimulus so modifies the movement of 

 the cilia as to cause the organisms to turn in a particular direction, and 

 then to swim continually in this direction. This applies whether the 

 organism has a single flagellum, or a tuft of cilia at one end, or whether 

 it is covered all over by numerous similar or dissimilar cilia. According to 

 Ludloff 2 , the galvanotactic orientation of Paramaecium is correlated with 

 a dissimilar action upon the ciliary movement at the two ends. Similarly, 

 Wallengren 3 concludes that it is owing to the cilia on different regions of 

 the body being unequally affected that Opalina ranarum shows negative 

 instead of positive galvanotaxis when the current increases beyond a certain 

 intensity. Paramaecium aurelia swims hinder end first in a 0-4 to 

 0-7 per cent, solution of sodium chloride ; and, according to Loeb, this 

 causes the organism to show positive instead of negative galvanotaxis, 

 although the body is oriented in the same way as in water 4 . 



These observations leave it uncertain whether the cilia are directly 

 or indirectly affected 5 , nor do they give any insight of the mode of percep- 

 tion. Separate ciliated fragments of Infusoria move in the same way as the 

 intact organism, and in the case of Bursaria truncatella, show the same 

 galvanotactic responses 6 . Hence it appears that individual cilia and groups 

 of cilia have a considerable degree of independence, and are in themselves 

 individually responsive to galvanotropic stimuli. It is not, however, certain 

 whether the galvanotactic movement of Amoebae carried out by the 

 protrusion and retraction of pseudopodia is a physiological reaction or is 



1 Verworn, Pfliiger's Archiv f. Physiologic, 1889, Bd. XLVI, p. 280; Ludloff, I.e., p. 544; 

 Wallengren, 1. c., p. 369. 



a Ludloff, 1. c., p. 552. 



8 H. Wallengren, 1. c., pp. 375, 381. More varied results may be obtained when the organism 

 possesses dissimilar cilia which react differently. 



* J. J. Loeb, Pfliiger's Archiv f. Physiologic, 1897, Bd. LXVI, p. 352. Putter (1. c., p. 297) finds 

 that the backward movement ceases as the organisms become accommodated to the salt-solution. 



5 On the unequal sensitivity of dissimilar cilia cf. Verworn, Piitter, and Wallengren. E. Roesele 

 (Zeitschr. f. allgem. Physiologic, 1902, Bd. II, p. 164) states that the mouth opening near to the 

 basis of the cilia possesses the greatest sensitivity to induction-shocks and to mechanical stimuli in 

 Stentor and Vorticella. 



6 Verworn, 1889, 1. c., p. 293. 



