Abstract
1. 1. The preen glands ( glandula uropygialis) of ducks, geese, and chickens were examined for provitamin D content. No evidence for the occurrence of the provitamin was found. Therefore, the theory that birds obtain their vitamin D through preening no longer can be supported. 2. 2. A study of the distribution of provitamin D in the body of chickens revealed a high concentration in the sterols of the feet. 3. 3. A sample of provitamin D from chicken feet was converted by ultraviolet light into vitamin D. Biological evaluation of this vitamin indicated a high activity for chicks, approximately equal to the activity of vitamin D 3. It is, therefore, concluded that the natural provitamin D of birds is either 7-dehydrocholesterol or a sterol of very similar structure.
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