In the fall of 1932, the fliers began appearing around Macon County, Ala., promising “colored people” special treatment for “bad blood.”

“Free Blood Test; Free Treatment, By County Health Department and Government Doctors,” the black-and-white signs said. “YOU MAY FEEL WELL AND STILL HAVE BAD BLOOD. COME AND BRING ALL YOUR FAMILY.”

Hundreds of men — all Black and many of them poor — signed up. Some of the men thought they were being treated for rheumatism or bad stomachs. They were promised free meals, free physicals and free burial insurance.

What the signs never told them was they would become part of the “Tuskegee Study of Untreated Syphilis in the Negro Male,” a secret experiment conducted by the U.S. Public Health Service to study the progression of the deadly venereal disease — without treatment.

On July 26, 1972 — 50 years ago Tuesday — much of the public learned of the gruesome Tuskegee experiment when the New York Times ran an Associated Press story on its front page revealing that the men had deliberately been left untreated for 40 years. The revelation led to the end of the study, congressional hearings and a class-action lawsuit.

The study recruited 600 Black men, of whom 399 were diagnosed with syphilis and 201 were a control group without the disease. The researchers never obtained informed consent from the men and never told the men with syphilis that they were not being treated but were simply being watched until they died and their bodies were examined for ravages of the disease.

Charles Pollard, one of the last survivors, recalled that he heard that men were receiving free physicals at a local one-room schoolhouse, according to James H. Jones’s book “Bad Blood: The Tuskegee Syphilis Experiment.”