THE CELL 



the phenomenon is, therefore, only a secondary effect of the current. It 

 should be remarked further that neither weak acids nor electro-negative ions 

 exercise such an influence. 



Electrical stimuli like other stimuli exercise a directing influence on Loco- 

 motor movements. If a constant current be passed through a vessel in which 

 are frog tadpoles or fish embryos, the animals orient themselves with their 

 long axes in the direction of the current, and with the head directed toward 

 the cathode. They remain in this position as long as the current is closed; 

 when the current is reversed the animals turn as if by command (Her- 

 mann). 



Hermann explained this form of galvanotaxis by supposing the central 

 nervous system to be excited by the ascending current, but to be unaffected or 

 even paralyzed by the descending current, so that the larvae and embryos either 

 instinctively or reflexly take the position in which they are stimulated least. 

 Loeb on the contrary has made it quite probable by experiments on shrimps and 



Amblystoma larvae that the current 

 produces parallel changes of tension 

 and energy production in associated 

 groups of muscles, the result of which 

 is that the movement toward one pole 

 is facilitated, but movement toward 

 the opposite pole is impeded. Thus 

 with the shrimps the tension of the 

 flexors predominates on the side of 

 the anode, while the tension of the 

 extensors predominates on the side of 

 the cathode. With a current of me- 

 dium strength the animals always 

 move toward the anode; if when the 

 current is turned on the head end is 

 already near the anode, the change 

 in position is effected by a forward 

 movement ; if the tail end lies nearer 

 the anode, it is effected by a back- 

 ward movement. 



The following examples of gal- 

 vanotaxis may be mentioned. Cer- 

 tain echinoderms in their youngest 

 FIG. 34. Showing the effects of a constant cur- and oldest stages (f ree-swimming 

 rent on the shrimp Polaemonetes, when the gastrulae and the creeping* mature 

 current passes transversely through the ani- an i ma l s ) exhibit no galvanotaxis, 

 mal's body, after Loeb and Maxwell. The whi]e in the intermed i ate stages 

 legs on the side of the anode are strongly ,. . . , . , , . 



flexed, those on the side of the cathode are (free-swimming plutei and bipen- 

 strongly extended. naria) they exhibit very marked gal- 



vanotaxis, and wander to the cathode 



(Carlgren). The majority of ciliate Infusoria and Amoebae assemble at the 

 cathode, if an electric current is conducted through the vessel in which they are 

 contained. Many flagellate Infusoria show the opposite reaction by moving to 

 the anode. Finally, it has been observed that the ciliate Infusorian Spirostomum 

 places itself with its long axis at right angles to the current (Verworn). All 

 these differences find an explanation according to Wallengren in the general fact 



