The earliest knowledge of the nutritional value of vitamin A stemmed from the recognition of the abnormal physiology which resulted from its absence. One of the first symptoms is night blindness. Its nutritional cure has been known for thousands of years. Eber's papyrus, written about 3,500 years ago, prescribed roast ox liver or the liver of black cocks to prevent night blindness. One thousand years later, Hippocrates also recommended the use of ox liver for the cure of night blindness. In 1956, I found that cock's liver was still prescribed by medicine men in Ruanda (central Africa) to treat young boys for night blindness and Bitot's spots.
However, it was not until the early part of the 20th century that experimental observations led to the discovery of vitamin A.1 Osborne and Mendel at Yale University and McCollum and Davis at the University of Wisconsin realized that a fat-soluble factor
Roels OA. Vitamin A Physiology. JAMA. 1970;214(6):1097-1102. doi:10.1001/jama.1970.03180060075015