THE BEHAVIOR OF INFUSORIA; PARAMECIUM 



8i 



Fig. $g. — a. Curves followed by Paramecia when 

 pointed electrodes are used. B, Collection of Para- 

 mecia behind the cathode, when the electrodes are 

 placed close together. After Verworn (1899). 



new cathode. If the electrodes are small points, the Paramecia swim 

 in curves, such as are known to be formed by the current (Fig. 59). 

 If while all are moving 

 toward the cathode the cur- 

 rent is interrupted, the group 

 breaks up and the Paramecia 

 scatter in all directions. 



If the current is at first 

 very weak, the Paramecia do 

 not react sharply, only a few 

 of them swimming toward 

 the cathode. When the 

 strength of the current is increased, more of the animals react and the 

 movement is more rapid, till at a certain strength of current practically 

 all are swimming rapidly to the cathode. With a further increase in 

 the current, the rate of progression toward the cathode becomes slower. 

 As the increase continues, the rate of swimming decreases till progress 

 nearly or quite ceases. The animals now remain in position, with 

 anterior ends directed toward the cathode, but not moving in either 

 direction. Increasing the current still farther, the animals begin to 

 swim backward toward the anode. At this time each Paramecium 

 is seen to have become deformed, being short and thick. If the cur- 

 rent is farther increased, the animals burst at one end and go to pieces. 

 These remarkable phenomena were first observed by Verworn (1889 a). 



How is this striking behavior brought about? Why do the Para- 

 mecia first all go to the cathode, then in a stronger current stop, then 

 swim backward to the anode ? 



A. Reaction to Induction Shocks 



In attempting to answer these questions, it will be best to take up 

 first the reactions to single induction shocks. To observe the reactions 

 accurately, the Paramecia must be placed in some viscid but not inju- 

 rious substance, such as the jelly produced by allowing a few quince 

 •seeds to soak in a watch-glass of water containing the animals (Statke- 

 witsch, 1904 a). This makes the movements so slow that they can be 

 followed under the microscope. The reaction to induction shocks under 

 these conditions has been studied especially by Statkewitsch (1903). 

 When an induction shock is passed through a drop of such fluid con- 

 taining Paramecia, the animals are found to react especially at that 

 part o£ the body which is next the anode. Here the cilia are suddenly 

 reversed, striking forward instead of backward ; the ectosarc contracts 



