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WHEN the late Dr. R. J. Lythgoe, of University College, London, about 1935, took up research on visual purple--the photosensitive substance of the retinal rods-our knowledge in this field had advanced but little since the beginning of this century. To a large extent his own precise and well-planned work, partly carried out in fruitful collaboration with Dr. C. F. Goodeye as an expert on photochemistry, is responsible for the clarity that now makes it possible to write about this subject with feelings of satisfaction. As very few British physiologists have taken' an active experimental interest in the subject of vision, the work of Lythgoe has not received the recognition that it deserves, and so, perhaps, it is fitting that an appreciation should come from a colleague abroad. Though all Lythgoe's contributions to the problems of sight were stamped with the same hall-mark of quality, no better tribute can be paid to his memory than to indicate in a brief review the place and significance of his work on visual purple against the background of past and present contributions to the same subject-one particularly dear to him. I can only quote a selected number of papers in the list of references. From these papers and an earlier review (Granit, Documenta Ophthalm., 1, 7 ; 1938) those interested in the subject will easily find the rest of the references. Lythgoe's own summary (Brit. J. Ophthalm., 24, 21 ; 1940) is of particular interest as a final statement of his matured views on the subjects of visual purple and dark adaptation.

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GRANIT, R. VISUAL PURPLE. Nature 151, 631–632 (1943).

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