908 LIGHT AND LIFE 



combined to make a preliminary study of color vision in the gold- 

 fish, a happy choice because of its ubiquity and inexpensiveness. More 

 detailed studies have been made of two electrical potentials found in 

 isolated retinas of fishes by Svaetichin, a few years ago. These were 

 called the luminosity, or L, response and the chromaticity, or C, re- 

 sponse, and appeared a't characteristic depths when the microelectrodes 

 were inserted into the retina. Tomita has identified the former as 

 arising from the outer plexiform layer, which in fishes contains giant 

 cells arrayed horizontally, and the latter as arising from the bipolar 

 cells of the inner nuclear layer, or perhaps extracellularly within that 

 layer. The problem was to see whether either response was related 

 to color vision, and how the responses correlate with the discharges 

 of the ganglion cells. Micropipette electrodes were used to record the 

 L and C responses, and metal microelectrodes were used for the dis- 

 charges of the retinal ganglion cells. "On-off" discharge patterns were 

 found for most ganglion cells, just as in frog and other vertebrate 

 retinas. The "on-off" pattern exhibited striking wavelength de- 

 pendency. Some cells gave pure "on" responses in the short wave- 

 length end of the spectrum and pure "off" responses at the long 

 wavelength end. The shift from one to the other was sometimes very 

 sharp, occurring within a 10 m/x distance. Other cells exhibited the 

 reverse sort of pattern, short-wave "off" responses, long-wave "on" 

 responses. Assuming that this wavelength dependency of the ganglion 

 cell's discharge is related to the C response, these workers adjusted the 

 stimulus to give a constant level of response at each wavelength and 

 determined the threshold intensity at each wavelength. In general, 

 they found distinct and separate threshold levels for the "on" and 

 "off" responses, and the "off" discharge exerted a strong inhibition 

 on the other discharge. For example, in certain units the "on" dis- 

 charge occupied the shorter wavelength end of the spectrum, the 

 "off" discharge the longer wavelength end. In that case, the threshold 

 was much higher for the "off" discharge, and it inhibited the "on" 

 discharge. In other units there was a short-wave "oft" resjjonse with a 

 low threshold and a long-wave "on" response with a high threshold. 

 A third type of ganglion (ell was also found which gave both "on" 

 and "off" responses throughout the spectrum. 



The three types of sensitivity response curves from the goldfish 

 retina have been compared with the absorption curves of a number of 

 hypothetical jMgments through the use of a nomogram prepared by 

 Dartnall. The short wavelength inhibitory system, or short-wave 

 "off," system fits the characteristics of a visual iMgment with a maxi- 



