364 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



merely due to the fact that the polar electrolytic action of the electrical 

 current causes the surface-tension to be lowered on the side towards 

 which movement occurs, or raises it on the opposite side *. 



Theoretical. It seems probable that the first stage in perception is due 

 to the electrolytic decomposition, and the sorting of the ions set up by the 

 electrical current. If the organisms are impure water 2 , changes of this kind 

 can only go on internally, whereas in saline media all the conditions for 

 chemotropic stimulation will be produced. The protoplast may possibly 

 not be permeable to all ions, so that local accumulations of them might be 

 produced 3 . It is not, however, possible to say whether the separated anions 

 and kations may act like externally applied chemicals 4 , or whether the 

 partial or unequal dissociation at different points in the protoplast may act 

 as a tropic stimulus. 



Loeb 5 concludes that the galvanotropic stimulus is directly due to the 

 impact of the negative and positive ions on the organism as they travel 

 to anode and kathode. Loeb finds that the local action of acids and 

 alkalies produces similar deformations to those caused by electric currents, 

 but forgets that the stimulating action of a reagent does not necessarily 

 remain the same when it is applied in concentrated form. Furthermore, 

 Piitter 6 has shown that the action of a strong galvanic current is not the 

 same as that of acids and alkalies. 



SECTION 79. Cytotaxis. 



By negative cytotaxis is denoted the tendency of organisms or parts 

 of organisms to separate from each other, by positive cytotaxis their 

 tendency to approach 7 , but the terms give no direct indication of the 

 ways and means by which such phenomena are brought about. In some 

 cases tropic stimuli come into play, as when an excreted substance exerts 

 a chemotropic action, such as is shown during the attraction of certain 

 antherozoids to the ova. Individuals of the same species of Infusoria and 

 also of Bacteria may exert tropic stimuli on each other by means of their 

 excreta. The attraction of aerotactic Bacteria to an assimilating algal cell 



1 Cf. Verworn, Pfluger's Archiv f. Physiol., 1889, Bd. XLVl; Schenck, ibid., 1897, Bd - LXVI. 



2 [Practically an impossibility owing to exudation from the organisms. The resistance of pure 

 water is so high (3-4 x io 5 ohms, per c.c. at 11 C.) that a considerable increase of voltage would be 

 necessary, and the water would rapidly become overheated.] 



3 That electrolysis may cause the culture-fluid to become poisonous is well known. 



* Cf. Nernst, Nachricht. d. Ges. d. Wiss. zu Gottingen, 1899, p. 104 ; Ewart and Bayliss, Proc. 

 of the Royal Society, 1905, p. 63. 



5 Loeb, Pfluger's Archiv f. Physiol., 1897, Bd. LXV, p. 518. See also H. H. Dale, Centralbl. f. 

 Physiol., 1901, Bd. XV, p. 303. 



6 Putter, Archiv f. Anat. u. Physiol., Supplementband, 1900, p. 294. 



1 Roux, Archiv f. Entwickelungsmechanik, 1894, Bd. I, pp. 57, 200; Programm und Forschungs- 

 methoden d. Entwickelungsmechanik, 1897, p. io. 



