The first demonstration of the existence of a vitamin and the full recognition of this fact are often attributed to the work of McCollum, who found that a sub stance in butterfat and cod-liver oil was necessary for growth and health of ani mals fed purified diets. It became obvious that an organic substance present in microconcentrations was vital to growth and reproduction of animals. Following the coining of the word vitamine by Funk, McCollum named this fat-soluble sub stance vitamin A. We can, therefore, state that vitamin A was certainly one of the first known vitamins, yet its function...