Since its discovery in the early part of this century, we have learned a great deal about vitamin A. Among other things, we now know that this once-mysterious compound is essential for normal growth and development, that it plays a central role in maintaining the body's skin and epithelial cells, and that it forms part of the two pigments needed by the retina to help the eye adjust to varying degrees of light. Yet, as late as 1907--when a young biochemist named Elmer McCollum arrived at the University of Wisconsin to take an instructor's post--very few scientists even suspected the existence of such compounds.

Scientists knew relatively little about nutritional needs in those days. True, in the 1880s a few researchers had already begun investigating the link between diet and certain diseases, such as beriberi. And by 1906, the English biochemist, Frederick Gowland Hopkins, was looking into...