346 ELECTRO-PHYSIOLOGY CHAP. 



seat of electromotive energy, the first essential is to ascertain 

 its distribution of potential. How this can be effected with 

 the help of a homogeneous, leading- off circuit, i.e. one which 

 in itself, and by its application to the moist conductor, develops 

 no differences of potential on contact with the surface of 

 the electromotive conductor, has already been stated. It 

 remains to show how far conclusions may be drawn from the 

 distribution of surface potential as to the internal electrical 

 conditions. Starting with the consideration of a regular column 

 of fluid, in the centre of which, at any point of its axis, an 

 electromotive force is in action, the lines of current in the 

 plane of any longitudinal section may be represented by the 

 accompanying diagram (Fig. 108). 



c 



FIG. 108. Diagram of current distribution in a column of fluid. (Rosen thai.) 



If, e.g., (A) represents a small body composed of two different 

 metals in contact, the entire column will be traversed by lines 

 of current in the direction of the outgoing arrows, which 

 collectively form a series of planes (planes of current) lying 

 one within the other. Corresponding with the " fall of potential " 

 there will be, at each point of the path of current, a positive, or 

 negative, potential, and it is easy to conceive a second system of 

 lines or planes if each equi- potential point on the different lines 

 or curves of current (planes of current) is joined together, as 

 indicated by the dotted lines. These last curves, in which the 

 intensity of current diminishes in proportion with increasing 

 resistance as they approach the surface of the column are 

 known as curves of potential, or isoelectric curves, which again 

 form collectively a system of curved planes (planes of potential, 

 isoelectric planes), cutting the planes of current at right angles. 



