 Building on the work of Edward Mellanby, who had been inspired by the discovery of vitaminA by McCollum and Davis, McCollum fed animals with induced rickets cod liver oil that was heated and aerated so its vitamin A was destroyed.The oil could no longer cure night blindness but did cure rickets.After his rats recovered, he named the substance for the next free letter of the alphabet, vitamin D. Then they became convinced that sunshine and cod-liver oil both protected against rickets and tested this by carrying rats outside to the sunshine.