3] ELECTROTAXIS 14 



r 



intense at the kathode and is .also in opposite directions at the 

 two poles. This law is important, and may be thus formulated: 

 The current intensifies at the anode the backward movements and 

 at the kathode the forward movements of the cilia, and the latter 

 are more intensified than the former ; or, in other words, the 

 anode stimulation increases the effectiveness of the normal 

 stroke, the kathode stimulation diminishes the effectiveness of 

 the normal stroke, and the diminishing effect is the greater of 

 the two. 



On the basis of these observed facts, LUDLOFF has proposed 

 a theory which accounts for several of the electrotactic phe- 

 nomena in the Ciliata, especially the fact that with strong 

 currents there is a diminution in the rate of locomotion, and 

 that at a lower intensity the axis of the organism is placed in 

 the axis of the current, with its anterior end towards the 

 kathode. This theory may be stated as follows: In every com- 

 plete swing of a cilium two phases may be distinguished 

 the backward "stroke" and the forward "recovery." Nor- 

 mally the stroke is the more effective, otherwise forward loco- 

 motion would not occur. The excess in effectiveness of the 

 stroke may be designated by the quantity x. Let us assume a 

 Paramecium lying in the axis of the current with its anterior 

 end towards the kathode. Then the stimulus received at the 

 anode or hinder end increases the effectiveness of the stroke by 

 a quantity which we may designate m. Thus the excess 

 energy of the stroke over recovery is for these hinder cilia 

 x + m. The stimulus received at the kathode or anterior end 

 diminishes the effectiveness of the stroke by a quantity which 

 we may call n, which is larger than m. Here the excess energy 

 of stroke over recovery is x n. If at any intensity of cur- 

 rent n exceeds x, the anterior cilia will work to oppose the 

 forward motion of the individual, and when n x = x + m loco- 

 motion will not occur. Such a strength of current probably 

 occurred in the experiment given on p. 142, where locomotion 

 ceased at above 60 8. 



To account for orientation of the axis and its anterior 

 end, we have merely to apply the general law given above. 

 Let us suppose that we are observing a Paramecium lying in 

 the axis of a current of medium intensity, with its anterior 



