Leopold Ruzicka (1887-1976) was awarded half the 1939 Nobel Prize in Chemistry for his work on polymethylenes and higher terpenes. Ruzicka's investigations of natural odorous compounds, begun in 1916, culminated in the discovery that muscone and civetone, molecules used in the perfume industry, contain rings of 15 and 17 carbon atoms, respectively. Before this discovery, rings with more than eight atoms had been unknown and were thought to be too unstable to exist. Ruzicka's discovery greatly expanded research on these compounds. He also showed that the carbon skeletons of terpenes and many other large organic molecules are made of multiple units of isoprene. In the mid-1930s, Ruzicka discovered the molecular structure of several male sex hormones, notably testosterone and androsterone, and subsequently synthesized them.