ELECTRICAL AND ELECTRO-MAGNETIC THEORIES in 



hence the electrical potentials of the two surfaces also l differ. The 

 unceasing chemical action in the protoplasm can easily therefore maintain 

 currents circulating from one surface to the other according to the local 

 differences of potential and of conductivity. 



The theory that streaming is due to the repelling action of opposed 

 currents in ectoplasm and endoplasm necessitates the highly improbable 

 assumption of the existence of an insulating layer between them, and is 

 moreover contradicted by the fact that when streaming becomes very 

 active in Elodea, Vallisneria, only the merest film of ectoplasm may 

 remain adherent to the cell-wall. Hence it is useless to discuss what the 

 direction of these currents would need to be in regard to that of streaming. 



A greater degree of probability attaches to what may be termed the 

 electro-magnetic theory, which necessitates the assumption of either a 

 permanent polarity in the magnetic cellulose membrane or a temporary 

 one induced by the action of electric currents. A simple mode of showing 

 the production of motion in a fluid by electro-magnetic action, is to place 

 a box with a glass bottom on one pole of an electro- magnet and to pass 

 an electric current through the mercury and round the magnet as shown 

 in Fig. 14. The same current causes the mercury to move, and induces 

 strong polarity in the magnet. Similarly, the passage of a current through 

 the endoplasm at right angles to the direction of streaming would suffice 

 to produce and maintain movement in a particular direction. The 

 existence of such a current would necessitate a reverse one to complete 

 the circuit. This might take place inwardly or outwardly along the 

 indifferent line, and since the current would be in a closed internal 

 circuit, it would be difficult or impossible to detect without fatally injuring 

 the cell. Moreover, if the cell-membrane was a magnetic shell with its 

 inner and outer surface as poles, it would not exhibit any perceptible 

 polarity. This mode of propulsion, however, involves a corresponding back- 

 ward reaction upon the cell- wall, just as the magnet in Fig. 14 tends to revolve 

 in the opposite direction to the rotating mercury. We have already seen 

 that it is highly doubtful whether any such backward reaction is permanently 

 exercised upon the outer layers of the cell by the streaming endoplasm. 



It does not necessarily follow that an electric current passing longi- 

 tudinally through a cell should retard streaming in one direction and 

 accelerate it in the other, for the current is at right angles to the supposed 

 action current, and hence may not affect the propulsive mechanism. When 

 currents are passed through at right angles to the direction of streaming, 

 the latter is occasionally accelerated or retarded more on one side than on 

 the other, but this is more probably an electrolytic effect than the result 



1 Jt is possible that the greatest difference of potential exists between the cell-wall and cell-sap, 

 the protoplasm acting as the chemical medium separating them. 



