Origins of the Receptor Potential 67 



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Fig. 29. Current- voltage relations in an eccentric cell of the eye 

 of Limulus. The slope of each curve is equal to the electrical 

 resistance of the cell membrane in the immediate neighborhood 

 of the measuring electrode. This value changes when light of 

 different intensities is shone on the eye. Open circles represent 

 voltages obtained by different strengths of current at the various 

 levels of illumination. The small closed circles indicate parallel 

 relationships between impulse frequency and current. Abscissa : 

 current passed across the cell membrane, in amperes X io~*. 

 Ordinate: membrane potential (mV) and impulse frequency (n). 

 Inset An electrical model of the eccentric cell membrane. A 

 complete description is given in the text. (From Rushton,*" Figs. 

 4 and 4^.) 



