MacNICHOL, WOLBARSHT, AND WAGNER 



797 



in the region ol the second-order neurons with which the receptors 

 synapse. He showed that slow potential changes in response to flashes 

 of light could be obtained from localized regions in the isolated 

 retinas of fishes by means of ultra-micropipette electrodes. The intra- 

 retinal potentials were of two types and were quite different from any- 

 thing previously reported. One of these potentials, called by Svaeti- 

 chin the luminosity or "L" response, appeared abruptly when the 

 electrode reached a certain depth in the retina. The approach to this 

 region was usually signaled by the sudden appearance of a negative 

 resting potential of 25 to 35 mv and large negative going (hyper- 

 polarizing) electrical changes during illumination. This type of re- 

 sponse is shown in the upper record in Fig. 1, which shows the effects 

 of equal energy flashes of different wavelength. The "L" response 

 has subsequently been demonstrated in a wide variety of fishes (17, 



Fig. 1. Luminosity (L) response (top trace) and chromatic (C) response (bot- 

 tom trace, R-G) recorded from the retina of a marine fish (family Gerridae). The 

 flashes of light for stimulating the retina were obtained by rotating a wheel con- 

 taining 24 interference filters adjusted by means of neutral density films to give 

 a constant energy spectrum. The wavelength sweep was driven by a voltage ob- 

 tained from a potentiometer geared to the filter wheel. A full scan required ap- 

 proximately 15 seconds. From Svaetichin and MacNichol (25). 



