1935. Through her association and work at Hull House and living side by side with the poor residents of the community, Hamilton witnessed the effects that the dangerous trades had on workers' health through exposure to carbon monoxide and lead poisoning. As a result, she became increasingly interested in the problems the workers faced, especially occupational injuries and illnesses. The experience also caused Hamilton to begin considering how to merge her interests in medical science and social reform to improve the health of American workers. When the Woman's Medical School closed in 1902, Hamilton took a position as bacteriologist with the Memorial Institute for Infectious Diseases, working with Ludvig Hektoen. During this time, she also formed a friendship with bacteriologist Ruth Tunnicliffe. Hamilton investigated a typhoid epidemic in Chicago before focusing her research on the investigation of industrial diseases. Some of Hamilton's early research in this area included attempts to identify causes of typhoid and tuberculosis in the community surrounding Hull House. Her work on typhoid in 1902 led to the replacement of the chief sanitary inspector of the area by the Chicago Board of Health. The study of industrial medicine (work-related illnesses) had become increasingly important because the Industrial Revolution of the late nineteenth century had led to new dangers in the workplace. In 1907 Hamilton began exploring existing literature from abroad and noticed that industrial medicine was not being studied as much in America. She set out to change the situation and published her first article on the topic in 1908. Medical Investigator Hamilton began her long career in public health and workplace safety in 1910, when Illinois governor Charles S. Deneen appointed her as a medical investigator to the newly formed Illinois Commission on Occupational Diseases. Hamilton led the commission's investigations, which focused on industrial poisons such as lead and other toxins. She also authored the "Illinois Survey," the commission's report that documented its findings of industrial processes that exposed workers to lead poisoning and other illnesses. The commission's efforts resulted in the passage of the first workers' compensation laws in Illinois in 1911, in Indiana in 1915, and occupational disease laws in other states. The new laws required employers to take safety precautions to protect workers. By 1916 Hamilton had become America's leading authority on lead poisoning. For the next decade she investigated a range of issues for a variety of state and federal health committees.