There’s a photo from the 1960s, of a young boy in California holding two shrunken human heads. The boy is the stepfather of writer Steven Lance, and the heads came from a family friend named Wilburn Ferguson. He had gotten them from an Amazonian tribe called the Shuar, who shriveled the heads of their enemies using a fluid derived from jungle plants. Ferguson, a nurse, former religious missionary, and lifelong dreamer who had moved his family to South American in the 1930s to pursue medical research in the Amazon, believed that the fluid could do something else—something life-giving. In his Atavist Magazine* feature “The Secret Formula,” Lance explains the root of Ferguson’s theory, which was shared by his devoted wife, Ruth:

Soldiers who fought the Shuar, according to stories Ferguson heard, might wake up one morning to find a stack of [heads] in their camp, shriveled but still recognizable as those of fallen comrades. It was powerful propaganda, a warning to steer clear. Head shrinking was “the most effective national defense ever devised,” Ferguson wrote.

He suspected that it might be much more than that…. “The thought occurred to me,” Ferguson recalled, “that perhaps the active ingredients of this process could be in some way adapted to shrink, or at least check, the wild growth of cancer cells.”

By that time, as Siddhartha Mukherjee explains in his 2010 book The Emperor of All Maladies: A Biography of Cancer, scourges like smallpox and tuberculosis were yielding to medical advances. “But of all diseases,” Mukherjee writes, “cancer had refused to fall into step in this march of progress.” Cancer is out-of-control division and growth of abnormal cells that can destroy healthy tissue and spread through the body. As Americans escaped other ailments and lived longer, more of them developed the disease. By 1926, it had become the nation’s second leading cause of death.

Long stigmatized and little understood, cancer now drew widespread attention. One senator proposed a $5 million reward for “information leading to the arrest of human cancer.” Americans dreamed of finding what Fortune called a “new principle of treatment.” The Fergusons were caught up in the zeitgeist. The thought inspired by the shriveled head was simple enough: If cancer killed by growing, shrinking was a way to fight it. For the Fergusons to test their theory, they needed access to whatever the Shuar were using on their enemies’ heads.

What followed was a saga spanning several decades and countries, and more disappointments than successes. Ferguson tried to prove his hypothesis, mustering evidence from lab experiments and patients (some consenting, others not). The scientific establishment rejected him. Yet today, more than 20 years after his death, he still has acolytes—people who told Lance that they believe Ferguson discovered something world-changing:

Ferguson wasn’t a snake-oil salesman or a con artist. Outlandish though some of his stories still seem, the details contained within them were consistent. The people I spoke to who knew Ferguson were struck by his sincerity. He could be stubborn and impractical, but as my stepdad recalled, Ferguson was always careful to point out that he hadn’t discovered a silver bullet, merely a promising treatment that needed more study. What he wanted most of all was a real scientific shot.

Ferguson was an outsider his whole life. Like a modern-day Don Quixote, he chased an impossible dream based more on faith than evidence. He wandered the wilderness seeking a miracle. The doctors and scientists who doubted him had every reason to. But what if they missed a bark or root of medical importance? What if Ferguson saw something they couldn’t? What if he was right?

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*The author of this post is the editor in chief of The Atavist, which is Longreads’ sister publication.