Abstract
The association of visual purple or rhodopsin with the visual function of the rods in dim or twilight vision as maintained in the duplicity theory of von Kries (Nagel, 1 Helmholtz, 2 Parsons, 3 and Hartridge 4 ) is generally regarded as well substantiated.
As to the genesis of this pigment, numerous ideas have been advanced, although it is generally held that it is a product of the epithelial pigment cell (Garten 5 and Kolmer 6 ).
In the present work on the gecko retina, which is cone-free, certain observations have been made which suggest that the outer segment of the rod may be more directly concerned in the production of this pigment.
When the retina is preserved in modified Held's fixative (v. Kolmer, op. cit.) and stained with iron haematoxylin and erythrosin, numerous droplets, which stain with a varying intensity from gray to black, are seen on and between the outer segments of the rods. In addition, a characteristic lamellar arrangement of deeply staining granular material in the outer segment of the rod is very evident. When stained sections of eyes which have been kept in darkness for twenty-four hours are studied microscopically, the droplets are found to he very numerous and the deeply stained granular material in the rod outer segment is greatly reduced in amount or is not to be seen at all. On the other hand, identically prepared sections of eyes that have been exposed to light for six hours not only show a great reduction in the number of droplets, but the granular striations in the rods are very compact and deeply stained. Intergrades between the two extreme conditions are also to be found and, within the same retina, whether light or dark adapted, there is a stiking correlation between the number of droplets present and the amount of granular material within the rod outer segment.
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