S‐potentials from colour units in the retina of fish (Cyprinidae)

S-potentials recorded from the excised tench retina left undisturbed in the optic cup show colour cells of the two types originally described by Svaetichin green' cones. The blue pigment has not been measured, but it probably corresponds with that found by Marks in ;blue' cones. However, the red pigment whose action spectrum we measured had its maximum at 680 nm, whereas the difference spectrum of Marks's red cone pigment peaked at 620 nm. The 620 nm cones excite the luminosity S-units but not the R/G units.5. In the range where only one type of cone is effective the relation between the light intensity, I(0), and V(0), the S-potential generated (both expressed in suitable units), is given by equation (1) p. 545. It is the relation that would be found if cone signals increased the conductance through a polarized ;S-membrane' in proportion to the flux of caught quanta.