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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    inents, it might be thought that the period of photo-chemical rest thus occasioned, although short, in some way or other caused the return of the purple. This however is not the case, for if a divided eye be held up against the daylight for a period quite sufficient to bleach an isolated retina, and then, while the light is still falling on it, the retina be rapidly drawn out of the bulb, this will always be found to be at the first moment beautifully red. It is seen that my observations support those of Boll in this limited sense, that the retina may be bleached in living animals, after long continued exposure to direct sunlight; I may moreover add that frogs which had been left to themselves for several days, in a glass case, in a very sunny place, at the end of that time had colourless retinas. While I do not agree with Boll's experience of the effects of a moderately lighted chamber, we are at one as to the results of more intense illumination. If the photo-chemical processes which take place in the retina separated from the eye, are taken as representing those which are going on in the living eye, the visual purple may be conceived of as continually being destroyed by the act of seeing, and by some process or other being as continually renewed; and indeed Boll has expressed some such view as this. The oculist led by experience would immediately seek for the pro- cess of regeneration in the nourishment brought by the circu- lating blood; for this is a favourite way of accounting for most of these kinds of events. In the case in point, however, the matter is far less complicated. That which restores the visual purple is something nearer to hand, and cannot, in a frog's eye at all events, depend on the constant renewal of the blood, since an eye, when taken out and opened, exhibits the same apparent indifference to light as when connected with the whole body and the nutritive currents. If therefore we are correct in supposing the sensitive purple to be continually restored, the regeneration must proceed from something lying behind or on the rods, that is, from the retinal epithelium or from the choroid. Something must be there which either prevents the purple becoming lost, or re-creates