798 LIGHT AND LIFE 



19, 20, 30) and in the cat (3, 12, 20) . It is probably present in the 

 retinas of all vertebrates. 



The other type of intraretinal response, called the chromatic or 

 "C" response by Svaetichin, was obtained from a slightly more proxi- 

 mal region of the retina. It also appeared abruptly with the sudden 

 appearance of a resting potential. When the retina was illuminated 

 by flashes of light from the short-wave end of the spectrum, the 

 responses were negative and indistinguishable from the "L" type re- 

 sponses. As progressively longer wavelengths were used the responses 

 diminished in amplitude, until a neutral point was reached at which 

 no sustained response could be recorded. At longer wavelengths the 

 response became positive, or depolarizing. This kind of response 

 is shown in the lower record of Fig. 1. Stimulation at the neutral 

 point produced no sustained potential change. Only brief negative 

 and positive transients appeared at the beginning and end of a 

 flash. 



Not only was this type of response highly unusual, but it also 

 indicated a possible mechanism for color vision. Furthermore, it has 

 only been seen in certain shallow water fishes, some species of which 

 have been demonstrated to have color vision. [See Walls (38) for a 

 comprehensive review of behavioral studies on color vision in fishes.] 

 On the other hand, frogs and cats, which are the animals commonly 

 used for electrophysiological studies, appear to lack the chromatic re- 

 sponse and also have no demonstrable color vision. 



Svaetichin's experiments were repeated and confirmed in their main 

 features by several groups of Japanese workers (19, 20, 30). Svaeti- 

 chin (24) at first suggested that these responses were recorded di- 

 rectly from the receptors, in this case one or the other of a pair 

 of twin cones, and that the positive and negative potentials were the 

 result of the differential color sensitivities of the two cells comprising 

 the pair. Tomita (27) , on the other hand, stated that the potentials 

 arise in more proximal layers of the retina. Subsequently, investiga- 

 tion in which the tips of the electrodes were localized by means of 

 a dye-marking technique proved the correctness of Tomita's assertion 

 (16, 17,28). 



Fig. 2, opposite. Stnictmc of goldfisli retina (Cartnssius nurntu.<.). fonnalin-fixed. 

 Bodian silver-impregnated section of retina on right. Tracing illustrating main 

 (cll types in each layer at left. Abbreviations from top to bottom: P. L., pig- 

 ment layer; V.C.L., visual cell layer with cones shown; O.L.M., outer limiting mem- 

 brane; O.N.L., outer nuclear layer; O.P.L., outer plcxiform layer showing giant 

 horizontal cells (presumed origin of "L" response); I.N.L., inner nuclear layer 



