He initially believed the rats weren't eating enough of the grains to maintain their health so he investigated the addition of flavors to enhance their diet. He found when either butterfat or protein free milk were added the rats did significantly better. Further investigations discovered a fat soluble nutrient. To distinguish it from Casimir Funk's previously discovered 'vital amine' that prevented beri-beri, he established the letter designation for vitamins. He labeled his fat soluble vitamin "vitamin A" and called Funk's water soluble vitamin "vitamin B".
He discovered vitamin D while investigating cod liver oil and established its antirachtic properties. Find out what else occurred on this day in science history.