• - 



/ + 



•/B/t ?^' 



40 



30 



20 



10 



7 nA 



Fig. 21. (A) Intracellular records from an eccentric cell in the lateral 

 eye of Limulus. The three traces illustrate the response of the cell to 

 increasing strengths of current passed through the recording electrode. 

 (B) Impulse frequency plotted against stimulus intensity for (A) current 

 steps I sec. long, (B) trains of pulses of 7 msec, duration and recurring 

 at 40/sec., (C) trains of pulses of 7 msec, duration and recurring at 

 different frequencies. Ordinate and abscissa in (A) and (B) indicate 

 impulse frequency and current intensity, respectively. In (C) the ordinate 

 again indicates impulse ( = pulse) frequency; the abscissa indicates the 

 strength of current required to give a complete train of impulses. (A 

 from Fuortes,'^ Fig. 9.) 



51 



