In the 1920s, scientists believed folate deficiency and anemia were the same condition. In 1931, researcher Lucy Wills made a key observation that led to the identification of folate as the nutrient required to prevent anemia during pregnancy. Wills demonstrated that anemia could be reversed with brewer's yeast. In the late 1930s, folate was identified as the corrective substance in brewer's yeast. It was first isolated via extraction from spinach leaves by Herschel K. Mitchell, Esmond E. Snell, and Roger J. Williams in 1941. The term "folic" is from the Latin word folium (which means leaf) because it was found in dark-green leafy vegetables. Historic names included L. casei factor, vitamin Bc after research done in chicks and vitamin M after research done in monkeys.