She was hired by plague specialist Professor J. J. van Loghem to work on a study of plague in ship- and harbour-rats for the ministry of health. In 1928 she became director of the laboratories of the GG and GD and formed a class on hygiene which she then taught. One of her early discoveries was a large group of women who were being treated for gonorrhea despite actually suffering from the minor infection vulvovaginitis, due to sloppy laboratory tests. Proper diagnosis enabled the women to return to work and avoid the embarrassment and social stigma of a sexually transmitted infection. In 1940 she was promoted by van Loghem to professor of microbiology of infectious diseases in Amsterdam with the speechZiektekiemen. The next year she spoke at an event celebrating his 25th anniversary as professor and in 1948 she took over his professorship of bacteriology, epidemiology and immunology. During the war years she participated in the artsenverzet. After male students were removed forcibly from one of her classes, she refused to teach until she was fired in 1944. In February 1945 she was arrested on suspicion of hiding illegal radio transmitters and was locked in the Oranjehotel until 6 May 1945. After her release she married her long-time lover, the playwright August Defresne on 22 June 1945. He had not been able to marry her before because his first wife would not grant him a divorce, and after 1934, she could not marry him because she would have to give up her work at the GG and GD due to the Algemeen Rijksambtenaren Reglement law of 1934 that stated a female government employee younger than 45 who married would be honorably discharged on the day of her wedding. Their relationship still needed to remain a secret, because co-habitation was considered the same as marriage under the ARAR. From 1937-1950 she was chairman of the Medical Women's International Association. From 1947-1951 she was on the Dutch National UNESCO committee. During a trip to the USA she was involved in discussions about biological warfare, to which she was opposed. From 1949-1953 she was chairman of the medical faculty. She refused a request by the ministry of war to build a biological warfare laboratory and spoke out about it in February 1958. Ruys died in Amsterdam.
Works
Publications by Ruys include:
De verwekker der rattenbeetziekten, PhD thesis, 1925
Wisselende opvatting over besmetting, 1928
De hygiëne van voeding, woning en kleeding, 1934
Ziektekiemen, 1940
Prof. dr. J.J. van Loghem, 1916-1941 : 25th Anniversary of the inauguration of van Loghem as a professor at the University of Amsterdam, 1941
Bacteriological and Epidemiological Data on Typhoid Fever in Amsterdam, 1948
The Diphtheria Epidemic in Amsterdam, 1949
Human, rights : the task before us. Les droits de l'homme : notre tache, 1951
Ali-esterase inhibitors and growth, 1953
Leerboek Microbiologie en Immunologie - Voor artsen en studenten in de geneeskunde., editor, 8 volume textbook, Uitg. N.V.A. Oosthoek, 1950
