By Michael Mosley
BBC Four's Medical Mavericks
The British Medical Journal recently asked people to vote for the greatest medical breakthrough of the last 160 years.
Fancy a cup full of these bacteria?
The shortlist included vaccines, X-rays, the discovery of the structure of DNA, sanitation - and anaesthesia.
There is no doubt the discovery of drugs capable of blocking pain is one of the greatest inventions of all time - it utterly transformed surgery from a barbaric and savage act of desperation into a life-saving science.
What few people realise, however, is that it came about largely through the work of people who carried out experiments on themselves.
Men like dentist Horace Wells who, to test the power of nitrous oxide, had one of his teeth extracted while inhaling the gas.
Or Dr William Morton who almost died testing ether on himself, but whose work led to the word "anaesthesia" (meaning "without feeling") being coined.
It is astonishing how many of the great medical breakthroughs, from vaccines to treatments for infectious disease, are the result of self-experimentation. And it is a tradition that is still alive today.
Infected with bacteria
In 1984 a young Australian, Dr Barry Marshall, did what many fellow doctors at the time saw as little more than a reckless publicity stunt.
He deliberately infected himself with a newly discovered strain of bacteria called Helicobacter pylori.
These bacteria had been discovered by a colleague, Robin Warren, in the stomachs of patients with ulcers.
Dr Marshall and Dr Warren were convinced that these bacteria were a significant cause of gastric bleeding and stomach ulcers. As Barry recalls, they met a lot of scepticism.
"It was obvious that most doctors didn't believe us," he said.
"You're wrong Dr Marshall, these bacteria are harmless and people with ulcers just catch the harmless bacteria - you're getting all excited about nothing."
Dr Marshall tried to infect animals with Helicobacter, without success.
So in the end he decided he had no option but to infect himself.
First he was gastroscoped; a fibre optic tube was passed down into his stomach and a biopsy of his stomach lining taken. It was normal. Next he asked a lab technician to help.
"Barry asked me to culture the bacteria, which I did. Smelt terrible, like swamp water. When I'd grown enough I gave him a ring," said technician Neil Noakes.
Dr Marshall was violently ill
"He came into the lab, I handed him the beaker and he knocked it back. Just skulled it down. Not the sort of thing you'd want to sip, I guess."
Swallowing several thousand million bacteria in one go made Barry almost as ill as he had expected.
"Within a few days I was in pain and started vomiting," he said.
"Every morning I woke first thing, at the crack of dawn, raced out to the bathroom and vomited into the toilet."
Ten days later he again had himself gastroscoped and another sample of his stomach lining taken.
"Sure enough I had very, very severe gastritis (inflammation of the stomach wall). Those bacteria were in my stomach by the millions.
"So I was very, very excited at that point because I had proved that the bacteria could infect a healthy person and cause damage in the stomach."
He treated himself with a complex regime of antibiotics and his symptoms eased. His experiment triggered research which has transformed millions of lives.
"At least 10 million people a year used to bleed from ulcers and most of those people don't have any trouble any more," Dr Marshall said.
"Something which people had spent decades and hundreds of millions of dollars studying is now very simple.
"Two guys in Perth, Western Australia, discovered the cause and the treatment and really that's the end of it."
In 2005 Barry Marshall and Robin Warren won the Nobel Prize for Medicine.
Barry did the experiment on himself because he didn't feel it was ethical to ask someone else to go first.
For similar reasons Professor David Pritchard and colleagues at Nottingham University recently infected themselves with hookworm.
They had discovered that hookworm produce chemicals that can calm the human immune system, reducing symptoms of allergic diseases like hay fever and asthma.
But before testing the worms on patients they needed to find out just how safe worm infestation is. So they volunteered themselves.
"We did it to show our commitment and because we felt it would only be appropriate to proceed once we had found a dose that was safe to try as part of a clinical trial."
At a time when the ethical basis of much medical research is increasingly under question it is rather wonderful to discover that scientists are still prepared to put their bodies on the line.
Michael Mosley presents Medical Mavericks on Wednesdays at 2100GMT on BBC Four from 7 February.