ELECTROTAXIS 109 



Secure a culture of paramoecium by placing a handful of hay, 

 or decaying leaves, in a large glass jar filled with water from a 

 pond or ditch, standing in a room at ordinary temperatures for a 

 week. 



Build a square cell on an ordinary glass microscope slide. To 

 do this place two small strips of rubber or glass parallel with 

 the edges of the slide, and connect the two by similar strips made 

 of moulding clay, or small strips of burnt clay which will become 

 heavily saturated with water. Fill the shallow cell with the 

 culture fluid containing the organisms, place on the stage of a 

 microscope and examine with a lens of wide field, which will give 

 the general form of the paramoecia. Connect batteries of a voltage 

 of 10-15 with the non-polarizable electrodes and then touch the 

 brushes of the electrodes to the pieces of clay. This will send a 

 current directly through the culture fluid. Note the movement 

 of the paramoecia toward the kathode. Break the circuit and 

 note movements. Place a commutator in the circuit and reverse 

 the direction of the current while the electrodes are in contact 

 with the cell. 



Repeat with any motile organisms which may be procured. l 



1 Davenport, C. B. Electrotaxis. Exper. Morphology. Parti. 1897. 



