The visual pigment of the conger eel

New methods of studying the spectral absorption of intact retinae are described. Using these methods the retina of Conger conger (L.) has been studied and the retinal spectral absorption curves are compared with those obtained on retinal extracts made with digitonin solution. The retina of the conger like that of deep-sea fish is golden in colour, its absorption curve being similar in shape to that of frog rhodopsin but with its maximum displaced about 16 $\text{m}\mu $ towards the blue end of the spectrum. The absorption curve of unbleached retinae is displaced about 4 $\text{m}\mu $ towards the red end of the spectrum from the absorption curve of unbleached retinal extract, but, when an estimated correction for possible yellow impurities in the extract is made, this displacement is only one of 2 $\text{m}\mu $. The change in optical denisty of the dark-adapted retina on bleaching with strong white light is $\text{0.6 at}$ $\lambda =484$ $\text{m}\mu $: this probably represents a retinal density for unbleached pigment of about 0.8. The visual pigment in the intact retina is approximately twice as effective as simple calculations based on extracts would predict. The absorption of light by the retina is dominated by the principal photosensitive pigment, whilst the screening of the rods, due to the absorption of light by the layers of retina lying between the rods and the internal limiting membrane, is trivial.