Abstract
An attempt has been made in the present review to outline a few known facts about each fat soluble vitamin and to mention the most recent advances of general interest that have occurred since publication of the symposium on vitamins sponsored by the American Medical Association in 1939. No attempt has been made to delve into many of the details in this field; rather, data have been presented which it is hoped will be of value in orienting conceptions in a rapidly changing subject. VITAMIN A CHEMISTRY AND PHYSIOLOGY The chemistry and physiology of vitamin A and substances having vitamin A activity have been considered in some detail in previous reviews in The Journal.1 Evidence reveals that there exists, in addition to vitamin A, another compound which has been designated as vitamin A2. In chemical structure vitamin A1 is related closely to vitamin A2; biologically the