Little is known about the chemical nature of the visual purple, the chief light-sensitive substance in the retina. In the past the retina with its ten or more layers was generally extracted with a solution of digitonin or of sodium cholate to give a colloidal solution of visual purple which contained many other chemical substances naturally occurring in the tissue. The crude extract was then examined by optical methods to determine its photochemical properties. Recently the whole retina was extracted with solvents of lipids, and carotenoids were found. The controversial reports on the carotenoids gave only slight evidence of their chemical nature. It is questionable whether or not the lightsensitive substance and carotenoids come from the bacillary layer or the rest of the retina or from both.
This paper is a report on the attempt to isolate and to determine some of the chemical properties of purified visual purple.
KRAUSE AC. CHEMISTRY OF THE RETINA: IV. THE BACILLARY LAYER. Arch Ophthalmol. 1937;18(5):807–812. doi:10.1001/archopht.1937.00850110123011
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