1 82 THE ORIGIN OF THE NERVOUS SYSTEM 



electrical factor which is adequate as the primary factor 

 in these processes. The point may be emphasized, 

 however, that according to the conception advanced 

 here the electrical factor is effective, not directly as 

 electrical but only through the changes in the physio- 

 logical state brought about by it and the localization of 

 those changes in relation to the electric currents. 



The direction of electrical polarization in a given cell 

 depends on the position of the poles of the polarizing 

 current, and it must be pointed out that with respect 

 to any particular source of current two opposite possi- 

 bilities exist, depending on the relation of the cell 

 concerned to the source. The situation as regards bio- 

 electric currents is not fundamentally different from 

 that in the galvanic cell. We call one pole of the cell 

 positive, the other negative, but it is a familiar fact 

 that the pole which is negative when the two poles are 

 connected by a conducting medium outside the cell is 

 positive with respect to the other pole inside the cell. 

 We commonly say that the current flows in opposite 

 directions inside and outside the galvanic cell. Similarly 

 in the case of bioelectric phenomena, if a particular 

 region of an organism is electronegative with respect to 

 another, when the two regions are connected by a con- 

 ducting medium, e.g., a wire, outside the protoplasm, it 

 must be electropositive internally, that is, through the 

 protoplasm, with respect to the other region. Here, as 

 in the galvanic cell, the directions of the current inside 

 and outside the tissue are opposite. As regards the 

 electric polarization of a cell by such a current, it is 

 evident that two opposed possibilities exist, according 

 as the cell lies in one or the other half of the circuit. 



