MacNICHOL, WOLBARSHT, AND WAGNER 



807 



0.0 



1.2 



M ill 



1.7 



550m|u 



Fig. 9. \'ariation of ganglion cell response with change in intensity of stimulus. 

 0.5 sec stimulus repeated at 2-sec intervals. Log intensity of stimulus is in upper 

 right of each record. 0.0 log units = 1.7 ^aw/cm^ 



effect of a sudden release of inhibition. It is neither due to excitation 

 during darkness nor does it depend upon any pre-existing impulse ac- 

 tivity, whether it be spontaneous or in response to light. It may re- 

 semble the classic phenomena of "anodal break excitation" and "post- 

 inhibitoi7 reboimd." 



Whatever the mechanism of its production, it is evident that the 

 "oflE" response represents a definite kind of message carried by many 

 of the fibers of • the optic nerve. We do not yet understand its 

 significance. 



In the examples shown thus far, the "on" response has represented 

 a short-wavelength sensitive process and the "off" response one with 



