It was recognized, many years ago, that certain diseases were due to dietary deficiencies. In recent years considerable research has been directed toward the study of factors which influence the utilization of carotene and vitamin A. Vitamin A was one of the first substances discovered which would cause diseases due to a lack of it in foods. A deficiency of vitamin A results in a number of clinical symptoms j some of the symptoms due to a lack of vitamin A are loss of weight, decreased resistance to infection, and xerophthalmia.
The disease caused by a specific vitamin deficiency can usually be cured by administering substances containing the particular vitamin or provitamin. There are several provitamin A pigments (carotenoids) found in plants. The most active of these pigments, as a precursor for vitamin A, is B-carotene. The following structures of ^3-carotene and vitamin A are those established by Kuhn and Karrer (l)
