THE VITAL PROPERTIES OF THE CELL 



109 



An appearance similar to that produced when iron filings are 

 attracted by a magnet is seen. " Under the circumstances," as 



A 



B 



Fig. 56. On completing the circnit of the constant current all the Paramcecia in a drop 

 of water swim within the curve of the electric current towards the negative pole (A), until 

 after a time they collect on the other side of the pole (B). (After Verworn IV. 40, Fig. 20.) 



Verworn remarks, " it may be observed that after all the 

 Paramcecia have wandered over to the negative pole, the largest 

 collection is formed behind, that is to say reckoning from the 

 positive pole on the other side of the negative pole, and that 

 only a few remain on this side of the pole (Fig. 56 B). When the 

 connection is broken the Protista swim back again, in the manner 

 described above, towards the positive pole, keeping at first, just as 

 before, well within the curve of the electric current, until gradually 

 the movement, and with it the division into groups, becomes ir- 

 regular as^ain." 



In the same manner, a number of other Ciliata (such as 

 Stentor, Colpoda, Halteria, Coleps, Urocentum) and Flagellata 

 (such as Trachelomonas, Peridinium) are galvanotropic. 



Amoeba?, react in a similar manner. At the first moment after 

 the circuit of the constant current has been completed a cessa- 

 tion of the streaming movements of the granules occurs ; very 

 soon, however, the hyaline pseudopodia are suddenly protruded 

 from the end which is turned towards the cathode, and, whilst 

 the remainder of the body substance flows in the same direction, 

 and keeps continually stretching out new pseudopodia, the Amoeba 

 creeps towards the cathode. When the current is reversed it is 

 seen that the granular streaming movements are also immediately 

 reversed, and the Amoeba commences to creep in the opposite 

 direction. 



The movement towards the cathode may be called negative 

 galvanotropism. As there exist both negative and positive 

 heliotropism and thermotropism, so we occasionally find isolated 



