The British Medical Journal is launching a competition to decided the greatest medical breakthrough.
Present-day medical experts are championing discoveries from the last 166 years.
Harry Burn, Chief Medical Officer for Scotland, is backing germ theory as the greatest medical milestone.
Germ theory says that infectious diseases are caused by the activity of micro-organisms within the body.
Germ theory explained common causes of death
It stems from the discovery by a Viennese doctor, Ignaz Semmelweis, in 1847, who realised a colleague had died from puerperal sepsis - blood poisoning - after cutting his finger while carrying out an autopsy on a woman who had died in childbirth.
Dr Semmelweis realised the disease was being carried on the hands of medical students to women in labour, and said medics should wash their hands before attending deliveries.
Deaths from puerperal sepsis among patients coming into contact with students fell from 12 to 2%.
His work influenced surgeon Joseph Lister in Glasgow, who introduced antisepsis to his practice by using carbolic acid solutions to dress wounds and who insisted surgical instruments - and surgeon's hands - should be washed in carbolic acid.
Although both Semmelweis and Lister faced resistance from their managers to their ideas, the germ theory did gain universal acceptance through work by Robert Koch and Louis Pasteur, as well as Alexander Fleming.
It meant that, compared to the end of the 19th century when infection caused around 30% of deaths, by 1980 deaths from infectious diseases in the US had fallen to 36 in every 100,000.
Dr Burns says: "Had the germ theory not emerged as an explanation for the common causes of death in the 19th century, it is hard to imagine that these major killers would have been overcome in any other way."
But he adds: "Perhaps the most depressing task that remains before us is to continually restate the lesson Semmelweis taught his medical students 160 years ago.
"Doctors and other healthcare workers are failing to wash their hands before contact with patients, and such failure is still costing lives.
"Resistance to the simple but lifesaving 19th century innovations remains alive and well in the 21st century."