On the photochemistry of the retina and on visual purple / translated from the German of W. Kühne ; edited, with notes, by Michael Foster.

  • Kuhne, W, 1851-1930.
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: On the photochemistry of the retina and on visual purple / translated from the German of W. Kühne ; edited, with notes, by Michael Foster. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    ^ are scanty or absent. When these animals lose their visual ■purple they remain blind until the epithelium has furnished a fresh supply, while animals which are provided with cones con- tinue, under the same circumstances, to be able to see by means of a second more perfect visual apparatus which, in all proba- bility, is the sole organ of specific colour sensations—I mean , the cones. I have convinced myself^ that frogs, whose retinas had been so completely bleached by exposure to the sun that a reddish tinge did not return till they had been kept 30 minutes in the dark, could see thoroughly well, and I hope hereafter to give a satisfactory account of their ability under these circum- stances to distinguish colours. As far as our knowledge goes ' at present, it is extremely improbable that the visual purple has any share in colour vision, although of course it must be admitted that the visual purple and the rods (apart from the cones) enable us not only to see the spectrum, but also to per- ceive it as consisting of a series of various tints of grey, very much as it appears, in all probability, to the colour blind. Our results concerning the occurrence and relations of the visual purple are in such close accordance with M. Schultze's hypo- thesis of the significance of the cones and rods in reference to colour vision, that it is sufficient to refer to it in order to check at once all hopes of finding a correspondence between opto- graphic results and specific colour perceptions. If, however, we succeed, as in ordinary photography, in applying photographic developers to the red rods at the moment when the very first steps of the decolourisation of the visual purple have begun, we must in the end succeed in reproducing optographically any thing which we see as dark and light in indirect vision, if we could disentangle in the optogram the numerous after-images which in daily life are so completely woven together. It remains indeed as wonderful as before how it is that the inner limbs of the rods, by a chemical touch as it were, can feel such minute decomposition of the purple ; but that is, after all, nothing more wonderful than what is taking place in our olfactory cells every day of our lives. In spite of regeneration of the purple during life as after 1 Sec Appendix, note E.