cox AND OTHERS: ELECTRIC TISSUE 



495 



note the internal resistance. The current in whatever circuits are 

 closed within the body of the fish is treated, somewhat arbitrarily, as 

 traversing a single path of resistance, R\ 



R' 



t 



i. 



fA/^W 



LVWvVWJ 



R 



Figure 6. Simple diagram for describing the impulse from the main organs of Electrophorus. 

 (From J. Gen. Physiol.) 



Let I, I, and /' denote the currents in r, R, and R', respectively. Since 

 the current i branches to form the currents / and /', it follows that: 



i = i + r. 



Let V denote the voltage measured by the oscillograph, connected at 

 p and q. This voltage may be reckoned in any of the three branches 

 of the network, and, thus, we obtain three expressions for V, as follows: 

 V = IR, V = I'R', V = E - ir. 



Eliminating i and /', among these four equations, we obtain two ex- 

 pressions for the external current / in terms of the voltage V: 



/ = 



I = -- V 



R ' r ' \r ' R' 



The first of these equations is used to find the current / from the 

 measured voltage V, by means of the known resistance R. The values 

 of / and V are plotted as in figure 5. The other equation is then used 

 to interpret the graph so obtained. If the resistances r and R' are 

 ohmic, they are constants in this equation, which is then a linear rela»- 

 tion between / and V, such as is actually found to exist. If, in this 

 equation, we let V = E, we find the corresponding value of / to be 

 —E/R\ If we suppose that E and R' have the same values at dif- 

 ferent instants during the discharge, this equation states that the 

 graphs for the different instants, when extrapolated to negative values 

 of /, will intersect at a point. The co-ordinates of this point, moreover, 

 will determine the values of E and R' . 



Actually, the lines shown in the figure, which are typical of those 

 obtained from measurements after the peak of the impulse has been 

 attained, do nearly meet in a point. The fact that the graphs of the 



