Ambroise Pare was a barber-surgeon
born in 1510, at the time when surgery was a low-status profession carried out by strong-handed menials. Pare worked for some time in a public hospital, then became a surgeon
in the French army.
At the time the severed blood vessels left by ampuation were typically sealed by burning the ends with a red hot iron. This was known as cautery. Pare invented a method of tying off these vessels with threads known as ligatures. Unfortunately, this wouldn't be very practical for a long time due to the problem of infection. Pare also designed quite sophisticated artificial legs.
As an army surgeon, Pare came up against a lot of gunshot wounds. These were a lot more likely to become infected than arrow or blade wounds because the gunshot carries dirty cloth into the wound. At the time it was thought the gunpowder poisoned the wound. The standard treatment for gunshot wounds was to pour boiling oil into them or apply the trusty old red hot iron. This may have worked in some cases, but tended to cause more harm than good.
During a battle, Pare ran out of hot oil. Faced with scores of patients with gunshot wounds, he had to think fast. He hastily put together a cool salve made from, among other things, egg yolks. He applied this to the wounds and then spent all night worrying about his actions - would the patients on which he had used the salve be badly effected by it? Maybe even dead? He hastened to the medical tent to see, and to his surprise the patients on which he'd used the salve were fairing a lot better than the others.
Because Pare was a lowly surgeon, many doctors didn't listen to his ideas. It took the support of the King of France, whom Pare was surgeon to, to get his ideas widely accepted.