206 



A. ARVANITAKI AND N. CHALAZONITIS 



Fig. 7. Graded subthresh- 

 old and threshold re- 

 sponses of the nerve cell 

 to monochromatic flashes. 



Highly photosensitive med- 

 ium sized nerve cell ( 1 80 |jl), 

 densely pigmented, initially 

 inactive in the dark, sub- 

 mitted to four monochro- 

 matic (579 mii.) flashes of 

 20 msec (signalled by the 

 vertical bars under the re- 

 cordings), of increasing in- 

 tensities, from top to bot- 

 tom: 0-8, 2, 4 and 8 :■; 

 10^ cal g mm 2 sec"i. 



The rate of the generator 

 potential, the frequency 

 and the number of the 

 spikes increase with the 

 intensity. The upper por- 

 tions of the spikes are not 

 seen. 



