Lectures on the human eye in its normal and pathological conditions / by Adolf Alt.

  • Alt, Adolf.
Date:
1880
Catalogue details

Licence: Public Domain Mark

Credit: Lectures on the human eye in its normal and pathological conditions / by Adolf Alt. Source: Wellcome Collection.

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    optical transverse sections of the rods and cones, form a regu- lar mosaic. This shows, however, a different arrangement according to the region from which the specimen is taken. While in the region of the macula lutea every cone appears to be surrounded by a single ring of rods, the latter are more and more numerous and the cones farther apart from each other, the nearer they approach the periphery of the retina. Kuehne, Boll and others have recently found that during life the outer part of the rods has a purple hue, being satura- ted with the so-called retinal purple which is secreted from the pigmented epithelial layer. From the description given in the foregoing, the way in which the connection between the optic nerve and the rods and cones is established, is the following: The opti- cus fibres enter the ganglionic cells which send one or two peripheral offsets into the inner molecular layer, where they anastomose with the central offsets of the nuclei of the inner granular layer. The peripheral offsets of these enter the outer molecular layer from which the central offsets of the rods and cones (the rod-fibres and cone-fibres) are seen to emerge. As Merkel has proven, the peripheral fibres of the inner granules are in direct connection with the central off- sets of the cone-granules; the same has not yet been proven for the rods. We know therefore of a direct communication between the cones and the central organ, while the same is not yet established for the rods. It is certainly a very remarkable fact, that the so-called visual purple which by recent investigations has been ac- corded so important an influence in the act of vision, does not tint the cones, which are undoubtedly percipient organs, but renders the rods, which appear to be at least less im- portant for direct vision, purple. It would therefore appear that the physiological value of the visual purple has been overrated. The structure of the retina, as we have described it, is very materially altered in its peripheral parts, and in the region of the macula lutea. Near the ora serrata the nerve fibres, rods and cones gradually disappear, while the supporting tissue becomes