ioo PHYSIOLOGY OF STREAMING MOVEMENTS 



a reversal of the current reverses the points at which the respective stimuli 

 originate. It remains, however, to be seen whether prolonged weak 

 currents exercise any analogous effects. As a matter of fact, a current 

 weakened by the interposition of a resistance coil produces a much greater 

 effect when it passes through the long axis of an elongated cell than when 

 it traverses the cell transversely to its length, and to the direction of 

 streaming. Since, however, the total resistance to the current is nearly 

 the same in both cases, the same current traverses a greater length of the 

 cell in the first case, and is also more concentrated in amperes per unit 

 area. Hence the greater effect. If the current in the first case is restricted 

 by means of vaseline insulations to as short a length as possible of the cell, 

 approximately the same influence is produced as when it crosses the 

 cell transversely. Similarly in cells which are approximately cubical, 

 the effect produced by the current seems to have no relation to its direction 

 with regard to the plane of rotation. 



When a weak current has been acting for some time, irregular 

 variations in the rapidity of streaming often take place, and recur at more 

 or less regular intervals. Streaming may then be temporarily more 

 active in one region of the endoplasm than in another (rapid successive 

 observations), the change of tempo being rapidly propagated around the 

 cell, leaving the entire endoplasm temporarily rotating more actively. 

 Similarly when a period of retardation begins, the current may be at 

 first slower on one side of the cell or on one side of the indifferent line, 

 than on the other. These variations are usually shown in dying cells, 

 and do not seem to have any connexion with the direction of the current 

 which is causing them. 



Similarly the kinetic inertia even of slowly streaming endoplasm 

 is too great to allow a weak current in virtue of its (extremely feeble) 

 electro-magnetic properties to exercise any directive influence upon floating 

 paramagnetic or diamagnetic particles. A sudden shock or a strong 

 current temporarily or permanently deranges the motor-mechanism, 

 whereas prolonged weak currents influence the protoplasm as a whole, 

 and streaming only secondarily, whether they produce an acceleration 

 and subsequently a retardation, or retard streaming from the first. 



