In 1932, the United States Public Health Service began the Tuskegee Study of Untreated Syphilis in the Negro Male, with 600 subjects, approximately two-thirds of whom had syphilis. The subjects were told only that they were being treated for “bad blood.” Approximately 100 died from the disease. It was later revealed that for research purposes, the men were denied drugs that could have saved them.

Upon closer inspection, the leaf her 2-year-old was attempting to put in his mouth in the middle of the playground on that lovely fall day was in fact a used tampon. She snatched it from him and Purelled both of their hands before rushing them back to their apartment on Dean. She put him in the bath and scrubbed, and by the time her husband found them, they were both crying.

“We have to leave New York,” she said after he put the baby to bed. “Let’s move back home.”

“There are tampons in Alabama,” he said, and then, “What’s the worst that could happen?”

It was the question they’d played out since graduate school, when her hypochondria had been all-consuming. Back then, leaning into her fears, describing them, had given her some comfort, but then they had Booker and suddenly the worst looked so much worse.

“He could get an S.T.D., and then we’d be the black parents at the hospital with a baby with an S.T.D., and the pediatrician would call social services, and they would take him away, and we’d end up in jail.”

“O.K.,” he said slowly. “That would be bad, but it’s statistically very, very unlikely. Would it make you feel better if we called the doctor?”

She shook her head. Her husband only used the word “statistically” when he wanted to avoid using the words “you’re crazy.” She knew that the doctor would just tell her to trust him, but she also knew that when the worst happens in this country, it often happens to them.

She comes by her hypochondria and iatrophobia honestly. When she was growing up in Alabama, people still talked about their grandfathers, fathers and brothers who had died of bad blood. That was the catchall term for syphilis, anemia and just about anything that ailed you. The 600 men who were enrolled in the Tuskegee Study were told they’d get free medical care. Instead, from 1932 to 1972, researchers watched as the men developed lesions on their mouths and genitals. Watched as their lymph nodes swelled, as their hair fell out. Watched as the disease moved into its final stage, leaving the men blind and demented, leaving them to die. All this when they knew a simple penicillin shot would cure them. All this because they wanted to see what would happen. For years afterward, her grandmother refused to go to the hospital. Even at 89, perpetually hunched over in the throes of an endless cough, she’d repeat, “Anything but the doctor.” Bad blood begets bad blood.

She’s more trusting than her grandmother, but she still has her moments. Like many women, she was nervous about giving birth. All the more so because she was doing it in New York City, where black women are 12 times as likely to die in childbirth as white women. And in that very statistic, the indelible impression of Tuskegee. The lingering, niggling feeling that she is never fully safe in a country where doctors and researchers had no qualms about watching dozens of black men die — slowly, brutally — simply because they could. When she held Booker in her arms for the first time and saw her grandmother’s nose on his perfect face, love and fear rose up in her. “What’s the worst that could happen?” her husband asks, and she can’t speak it — the worst. Instead, she tries to turn off the little voice in her head, the one that wants to know: How exactly do you cure bad blood?

Yaa Gyasi was born in Ghana, raised in Huntsville, Ala., and lives in Brooklyn. Her first novel, “Homegoing,” won the PEN/Hemingway Award and the National Book Critics Circle’s John Leonard Prize. Photo illustration by Jon Key. Syringe: Science Museum, London, via Wellcome Collection.