Notably, a strain of diphtheria-causing bacteria that Williams isolated and cultivated was instrumental in producing an antitoxin to bring the disease under control.
Anna believed that the poor training of the doctor in attendance was partly to blame for the tragedy, and so she resolved to resign from her teaching position and retrain as a physician.
[2] Later that year Williams enrolled in the Woman's Medical College of the New York Infirmary, where she was taught by Elizabeth Blackwell[5] and Mary Putnam Jacobi.
[6] After graduating in 1891, Williams taught pathology and hygiene at her alma mater, and underwent further medical training in Vienna, Heidelberg, Leipzig, and Dresden.
"[3] In 1896 Williams traveled to the Pasteur Institute in Paris hoping to find a toxin for scarlet fever that could be used to develop an antitoxin, as she had done for diphtheria.
In 1905, Williams developed a new method for preparing and staining brain tissue to show the presence of Negri bodies, which gave results in minutes rather than days.
and, in collaboration with Josephine Baker's Division of Child Hygiene, developed a better diagnostic test for trachoma, a disease that was claiming the eyesight of many of the urban poor, particularly children.
After the war ended, Williams was one of the scientists of the front lines of research trying to combat the deadly 1918 pandemic of Spanish flu.
In 1905, the pair published their classic text Pathogenic Micro-organisms Including Bacteria and Protozoa: A Practical Manual for Students, Physicians and Health Officers which quickly became known simply as 'Park and Williams' by readers.
In her acceptance speech, she thanked the colleagues she had worked with over the years, including many of the women who were building careers in bacteriology alongside her or under her own mentorship at the Department of Health.
In 1934, despite an outpouring of support, Williams along with nearly a hundred other workers was made to step down from her position by New York City's mandatory retirement age of seventy.
[4] Upon her retirement, mayor Fiorello La Guardia accurately summed up Williams' career: she was, he said, "a scientist of international repute".