1. Vitamin A has been found in the retinas and the combined pigment epithelia and choroid layers of frogs, pigs, sheep, and cattle. The vitamin was identified by (a) its specific absorption at 328 mµ; (b) the blue color yielded with antimony trichloride, associated with an absorption band at about 620 mµ; (c) anti-xerophthalmic and growth-promoting activity; and (d) quantitative relationships among the results of these three types of observation.
2. The mammalian retinas contain about 22γ, the frog retinas about 400γ, and the frog pigmented layers almost 2 mg. of vitamin A per gram of dry tissue.
3. With the possible exception of hepaxanthin, no other carotenoids were found in the mammalian tissues.