Harvey Washington Wiley of the U.S. Department of Agriculture's Bureau of Chemistry was concerned about the unrestricted contents of food that Americans were buying. So when he sent out a call for volunteers, 12 young men, mostly poorly-paid clerks, answered the call. They must have been hungry, because they didn't run for the hills as soon as they found out what kind of six-month experiment they'd signed up for.
Wiley’s staff would put borax in their butter, milk, or coffee. Formaldehyde would lurk in their meats, copper sulfate and saltpeter in their fruit pies. Wiley would begin at low doses and then ratchet up the amount until one or more of the men complained of debilitating symptoms, like vomiting or dizziness. Those people would then be excused from the program until they felt well enough to resume. In the event a subject died or became seriously ill, he would waive the right to pursue legal remedy against the government.
The year was 1902. With funding and consent from Congress, Wiley was about to embark on an experiment he dubbed the “hygienic table trials,” but it was the Washington news media that came up with the nickname that would stick: They called his volunteers "the Poison Squad."
The results of those experiments led to the Pure Food and Drug Act and the Meat Inspection Act in 1906. The experiments lasted for five years, although the squad of volunteers changed. Read what those young men went through in the name of science and safety at mental_floss.