Great moments in quackery.

Though to be fair, he did put his money where his mouth was. And, given the knowledge at the time, I guess you couldn't dismiss it as nuts until somebody ran the experiments.

Voronoff's hypothesis was this: hormones, like testosterone produced by the testes, would reverse aging by a process he called "rejuvenation." One of his first experiments used himself as a test subject. He injected ground up dog and guinea pig testicles under his own skin, but was disappointed when this did not result in any verifiable effect. He reasoned that living grafts of testicular tissue, rather than injections, would have a more dramatic and lasting rejuvenation effect.

This lead to cross-species glandular transplantation surgeries. His early experiments involved transplanting thyroid tissue into humans with a thyroid deficiency. He also began transplanting the testicles of executed criminals into rich old guys (as a treatment for senility and schizophrenia), but had to stop when the demand for the procedure far exceeding the supply of criminal testicles. At this point, Voronoff began using monkey testicles instead, and his first "monkey gland" to human transplant took place in June of 1920. [...]

A thin slice of testicle would be inserted into the recipient's scrotum, with the hope that it would fuse with the endogenous tissue. This...er...innovative approach was applauded by hundreds of the worlds leading surgeons at the International Congress of Surgeons in London in 1923. His work also delved into the transplantation of monkey ovaries into human women. [...] By the Great Depression over 500 men had received Voronoff's therapy, the demand becoming so high that he had to set up his own monkey farm to keep up.

As you might expect, Voronoff's work came up empty and he died in obscurity. Though there is a theory out there that his transplant studies were the vector through which HIV entered the human population.