Dorothy Mary Crowfoot Hodgkin (1910 –1994) received the 1964 Nobel Prize for Chemistry for determining the structures of several biologically important compounds using X-ray crystallography. She is often referred to as a founder of the science of protein crystallography. Hodgkin and her mentor, J. D. Bernal, were the first to successfully apply X-ray diffraction to crystals of biological substances, beginning in 1934 with pepsin, an enzyme that breaks down proteins in the stomach. Hodgkin's contributions to crystallography included solving the structures of cholesterol, lactoglobulin (a protein found in milk), ferritin (a protein aiding in iron storage, found in the liver and spleen), tobacco mosaic virus, penicillin, vitamin B12, and insulin. She also developed methods for indexing and processing X-ray intensities.