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

  • Kühne, W. (Willy), 1837-1900
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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    being first brought on the filter by means of a fine pipette, the retina being left till last, when all the clear part has gone through. It will take about 24 hours until the last drop is filtered; if the mass has been shaken, it very often does not filter at all. It need hardly be stated that a miniature funnel with a very small filter must be used. I have myself taken the trouble to prove that all colour may be taken away entirely from the residue on the filtering by washing with colourless bile ; but I do not recommend this plan of increasing the purple by washing, because the slightly coloured wash-water is hardly worth collecting, while, on the other hand, the red saturated filter paper and the varnish-like homogeneous agglutinated retinas when removed from it can be employed for many im- portant experiments. The filtrated solution of the visual purple is perfectly clear and of a beautiful carmine red colour. At first I thought I perceived a somewhat blue fluorescence, but I have reason to suppose that in the first experiment in which I and others fancied we saw this, it was traces of the black epithelium pigment, whose appearance deceived us. In the light the solution became first orange, then yellow, finally colourless like water. The peculiar chamois colour which appears in the retina as it bleaches, often occurs in the purple solution but not so clearly. In direct sunlight the dissolved purple bleaches in a moment; in diffuse daylight with very varying rapidity, apparently dependent on the intensity of the light, being considerably longer during the afternoon, although our eyes at that time seemed to be quite as much, or even more affected by the light than in the morning or mid-day. This circumstance, which is well known to the photographer and not inexplicable, is also very perceptible in the bleaching of the purple while still in situ in the retina. Time and fitting material have up to this time failed me for going more fully into the chemical reactions of the visual purple1. Whoever considers the trouble of preparing the purple will not be surprised that ] first of all employed it in another direction, and any one who remembers the disadvantages which the presence of bile acid in