MOVEMENTS OF IRRITATIOX. 431 



from a galvanic battery* of several elements are connected with a 

 current reverser (commutator). From the commutator pass two 

 other wires, the ends of which are attached to unpolarisable 

 electrodes (see 63). In the course of one of these wires is inter- 

 calated a key. 



We now set up a microscope. On the stage is placed a watch- 

 glass charged with Paramecium-containing fluid. Even under low 

 powers we see the organisms in active movement, crossing the 

 fluid in all directions. If we introduce the electrodes into the 

 fluid and close the circuit, all the Paramecia, as if by command, 

 direct their anterior end towards the negative electrode and move 

 towards it. In a short time the fluid in the neighbourhood of the 

 anode is quite devoid of Paramecia ; they have all collected at the 

 kathode. If we break the circuit, the infusoria direct their 

 anterior end towards the anode ; they move towards it and collect 

 there, but the aggregation is not so complete as at the kathode on 

 making the circuit, since the organisms soon distribute them- 

 selves again uniformly throughout the fluid. 



The Paramecia having collected at the kathode on completion 

 of circuit, and the commutator being now reversed, the organisms 

 at once execute movements corresponding with the new conditions, 

 and they can be forced to turn round every moment by reversing 

 the commutator. In Euglena viridis no galvanotropic peculiarities 

 have so far been determined with certainty. 



1 See Strasburger, Wirkung der War me und des Lichts auf Schwdrm- 

 sporen, Jena, 1878, and Klebs, Unterjuchungen am dem botan. Inst. zu 

 Tiibingen, Bd. 1, H. 2. 



2 See Aderhold, Jenaitche Zeitschrift f. Naturwissenschaft, BJ. 22, and Jen- 

 sen, Archiv. f. d. ges. Physiologie, Bd. 53. 



3 See Sachs, Flora, 1876. 



4 See details in Pfeffer, Untersuchanyen aus dem botan. last, zu Tubingen, 

 Bd. 1, p. 450, and Bd. 2, p. 584. 



5 See Verworn, Pfliiger's Archiv f. d. ges. Physiologic, Bd. 45 and Bd. 46. 



170. Movements of Chlorophyll Bodies. 



The movements of the chlorophyll grains in plant-cells are 

 of great biological importance. We have here to do, as it would 

 appear, not with movements due to the chlorophyll grains them- 



* The current with which we work must be neither too weak nor too strong. 

 Strong currents kill the infusoria. 



