Remarks on colour-blindness and the tests to be adopted for its detection / by F.W. Edridge-Green.

  • Edridge-Green, F. W. (Frederick William), 1863-1953.
Date:
[1900]
Catalogue details

Licence: In copyright

Credit: Remarks on colour-blindness and the tests to be adopted for its detection / by F.W. Edridge-Green. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    could not be the visual substance because it was absent from the cones, and only cones were to be found in the fovea centralis, the region of most dis- tinct vision ; that it is entirely wanting in some animals which see very well; and lastly, that animals such as frogs, naturally possessing the pigment, continue to see very well when their visual purple has been abso- lutely bleached, as it may be by prolonged exposure of the eyes to strong light. I will deal with the last two objections first. The second objection may be answered by the view that there may be a similar substance present in the eye of these animals having the same function, but that to our eyes it is colourless. The third objection may be answered by compar- ing the retina with any secreting gland. Just as the mamma keeps secreting on stimulation, the pigment cells of the retina may be secreting sufficient of the visual purple for vision, but not sufficient for external recognition. We know that when the retina is stimu- lated by light the processes of the pigment cells are forced down amongst the rods as far as the external limiting membrane. The first objection of Kiihne is very important, but may be answered by the hypo- thesis which I have put forward, namely, that the cones are not sensitive to light but only to changes in the visual purple. I mean that they are not sensi- tive to light in the sense that they do not, when light falls upon them, convey any light sensation to the brain. They are sensitive to light in one way, namely, that when light falls upon them it causes the inner limbs to contract, but this change has been noted when light falls on the other eye or on the skin. This may be the means by which the visual purple is drawn out, and support is lent to this view by the fact that the following experiments can be best made with only one eye, and when no light is allowed to fall on any part of the body with the exception of