was at the root of many of society's problems. However, unlike Malthus, he believed that technology, particularly contraception, should be the main check to this growth. In 1880, he met Aletta Jacobs, the first female doctor in the Netherlands since the enlightenment, who helped him understand the biology of birth control. With Bernardus Hermanus Heldt and Jan Martinus Smit, he co-founded the (Neo-Malthusian League or NMB) on 2 November 1881. The society's aim was to reduce poverty by balancing family size with the available means for subsistence, with information on contraception a means to this end. He travelled extensively with his wife to promote these values, attending the 1904 International Council of Women and subsequently touring the United States shortly before his death. Personal life Gerritsen was a believer in free marriage and for many years declined marrying his life companion Aletta Jacobs. When they did marry in 1892 to legitimise their future children, she took the then radical step of retaining her maiden name. Their only child, born on 9 September 1893, died only one day old. Gerritsen died on 5 July 1905 from cancer. As it was at the time illegal in the Netherlands, he was cremated in Hamburg. Legacy Gerritsen's legacy has largely been overshadowed by his more famous wife. Originally intended for Amsterdam University Library, in 1903 his library of over 18,000 books and 13,000 pamphlets was sold to the John Crerar Library and shipped to Chicago for an undisclosed sum. Along with his wife's collection, it was subsequently expanded and purchased by the University of Kansas in 1954. The Gerritsen Collection has become an important resource for feminist researchers. Selected works Sole author Joint author References Citations Bibliography 1850 births 1905 deaths Members of the House of Representatives (Netherlands) Aldermen of Amsterdam Municipal councillors of Amersfoort People from Amersfoort