In the early 1920s, if you were a wealthy European man who felt your vigor was declining, you had options.
You could take the waters at a spa. You could try one of the many tonics available at pharmacies across the continent. You could modify your diet, reduce alcohol, get more fresh air.
Or you could travel to Paris, hand Serge Voronoff a considerable sum of money, and have him sew thin slices of chimpanzee or baboon testicle tissue directly into your own scrotum.
This was mainstream medicine for approximately a decade. Voronoff had a waiting list.
The Logic, Such As It Was
Serge Voronoff (1866–1951) was a Russian-born surgeon who had spent years working in Egypt, where he had observed the effects of castration on the eunuchs employed in the Egyptian court. He had seen, firsthand, that men without functional testes aged differently — became softer, less vigorous, less physically capable.
His conclusion, which seems reasonable given the state of endocrinology at the time, was that the testes produced something vital. His further conclusion — which is where things start going sideways — was that the solution to men feeling old and depleted was to give them more testicular tissue.
The problem with transplanting human testes was supply. Donors were rare, and the ethics of the whole enterprise were murky even then. Voronoff turned to our nearest biological relatives.
He began transplanting thin slivers of chimpanzee and baboon testicular tissue into human patients — specifically into the inner lining of the scrotum, where he believed they would establish a vascular connection and begin producing whatever vitality-giving substance the testes were thought to manufacture.
The patients reported remarkable results. They felt younger. More energetic. More sexual. Their hair seemed to grow back. Their libido returned. They slept better. They had more drive.
Voronoff published enthusiastically. His practice grew. He moved into larger premises. He attracted patients from around the world — wealthy businessmen, aristocrats, military officers, politicians. At the height of the craze, similar procedures were being performed across Europe and in the United States. An Icelandic surgeon named Jonas Sveinsson reportedly transplanted testis slices from a cash-strapped farmer to a wealthy Norwegian businessman in 1929, who then allegedly fathered three children with his 23-year-old wife. Sveinsson publicized this outcome with obvious pride.
The results, needless to say, were the placebo effect — operating at extraordinary scale.
What Was Actually Happening
The biology was not on Voronoff’s side.
Transplanted tissue from another species cannot survive long-term in a human host. The immune system identifies foreign tissue, mounts a rejection response, and destroys it. Any perceived benefits from the procedure would fade as the implanted tissue broke down — typically over weeks to months.
But the window before rejection was long enough for patients to report dramatic improvements. They felt better. The placebo effect in men who had paid substantial sums for a prestigious surgical procedure performed by a celebrated Paris surgeon was predictably powerful. When the benefits faded, patients often returned for repeat procedures, attributing the decline to natural aging rather than to the fundamental impossibility of what Voronoff was doing.
There was another problem the field didn’t understand until much later: even if the transplanted tissue had somehow survived and begun producing testosterone, injected or implanted testosterone in this form faces the same pharmacological obstacles Brown-Séquard had encountered. The hormone doesn’t survive in forms the body can use for long.
When the Music Stopped
The scientific community had been uncomfortable with Voronoff’s claims for years. In 1927, the Royal Society of Medicine in London sent an international committee to Algiers — where Voronoff had by then relocated after some scandals in Paris — to evaluate his work.
The committee’s conclusion was unambiguous: Voronoff’s claims were, in the words of the contemporary record, “all poppycock.”
This was not a subtle finding. The Royal Society of Medicine was not an organization given to extravagant language. “Poppycock” was about as direct a scientific repudiation as the era could produce.
Voronoff continued operating for several more years — patients didn’t stop wanting the procedure simply because a committee said it was ineffective — but the medical establishment had withdrawn its endorsement. His reputation began to erode. By the mid-1930s, when real testosterone had been isolated and synthesized in a laboratory, the transplantation era was effectively over.
Voronoff lived until 1951, long enough to watch the field he had helped define move completely beyond him. He died still believing in his work.
The Unwitting Contribution
Like Brown-Séquard before him, Voronoff’s lasting contribution was less scientific than motivational.
The spectacle of wealthy men paying large sums to have animal tissue surgically implanted in their bodies — and reporting genuine satisfaction with the results — made the case, loudly and expensively, that the male body wanted something the testes provided. The demand was real. The market was real. The question of what, exactly, testes produced that made men feel vital was real.
That question, by the 1930s, was being answered in laboratories by chemists rather than surgeons. They didn’t need monkey testes. They needed chemistry.
The Geography of Desperation
There’s a thread running through all of these stories — Berthold’s roosters, Brown-Séquard’s dog juice, Voronoff’s primate tissue — that deserves acknowledgment.
Every one of these experiments, legitimate or absurd, was driven by the same observation: men lose something as they age. Something that is connected to the testes. Something that affects energy, muscle, mood, libido, and vitality in ways that are unmistakable. That observation was correct. The hypothesis was correct. The biology was real.
The treatments didn’t work because science hadn’t yet found the molecule. But the problem the treatments were trying to solve? That was completely legitimate, and it was documented across three thousand years of human experience.
What’s Next
In the final post of Series 1, we meet the chemists who finally got the answer right — extracting testosterone from bull testes in Amsterdam and synthesizing it from cholesterol in Göttingen and Basel, all in the same remarkable year: 1935.
