Abstract
The chemical study of vitamin A dates "back to the work of Hopkins. As early as 1906, he had determined and reported that, "no animal can live upon a mixture of pure protein, fat, and carbohydrate and even when the necessary inorganic material is carefully supplied, the animal still cannot flourish. The animal body is adjusted to live either upon plant tissue or other animals and these contain countless substances other than the proteins, carbohydrates, and fats." In his experiments, using rats as subjects, Hopkins found that the addition of small amounts of milk to diets otherwise composed of purified foodstuffs resulted in growth, and that this was due to an alcohol-soluble organic substance or substances in the milk. This alcohol-soluble organic substance is known today as vitamin A.