Leopold Ruzicka was a Swiss chemist, born in Yugoslavia, who shared the 1939 Nobel Prize in Chemistry with Adolf Buntenandt for his research into ring molecules and terpenes (hydrocarbons found in the essential oils of many plants). In 1916 Ruzicka began investigations into the active compounds in musk and civet, finding that they were ring structures consisting of 15 and 17 carbon atoms, respectively. This discovery had a profound effect on organic chemistry, as until that time rings with more than six atoms were thought to be too unstable to exist. In the 1930s he synthesized several male sex hormones, including testosterone, having previously discovered their molecular structure.