In addition to carbohydrates, proteins, and fats, our bodies need water, salts, and substances known as vitamins to grow and function properly. In 1931 Paul Karrer succeeded in extracting vitamin A from cod-liver oil and in determining its composition. Vitamin A is necessary for the body to grow, and one of its components is carotene, which is found in carrots and elsewhere. This was the first vitamin to undergo a mapping of its structure. In 1933 Karrer also determined the structure of vitamin B2, which made it possible to produce the vitamin by artificial means.