The Effect of Two Wave‐Lengths of Light upon the Same Retinal Element

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Abstract
Summary.: Well isolated elements picked out by the micro‐electrode technique from the dark adapted retina of the cat have been stimulated with one or two wave‐lengths of a spectrum and the discharge of spikes counted at ‘on’ and ‘off’.In many isolated elements the log intensity—spike frequency curves have been shown to run a different course for different wave‐lengths. When this is so two wave‐lengths can be shown to elicit different relative frequencies at ‘on’ and ‘off’ within a large range of variation in the energy ratio of the two wave‐lengths. The pure on‐elements and a considerable number of on/off‐elements do not have these properties; wave‐lengths equated for equal visual purple activation at one energy level then remain equated at all intensity levels.When two wave‐lengths, which can be differentiated by their relative spike frequencies at ‘on’ and ‘off’, are acting simultaneously on the same element it is generally found that either of the two is proponent and succeeds in maintaining its off/on‐ratio in the sum whilst the properties of the other one are suppressed.By making such comparisons in equal retinal visual purple units the contribution of visual purple stimulation can be kept constant for all wave‐lengths to be combined. By these means contributions from other types of receptors to the interaction patterns of two wave‐lengths can be distinguished.Several examples of interaction between the effects of two wave‐lengths upon the same element are given. They substantiate the conclusion that interaction can take place when one wavelength simultaneously stimulates two photochemical substances with ordinates overlapping the same spectral region.For the experiments support has been received from the Rocker‐feller Foundation and the Swedish Medical Research Council.