The British Medical Journal is launching a competition to decide the greatest medical breakthrough.
John Snow developed this chloroform inhaler in the 1850s
Present-day medical experts are championing discoveries from the last 166 years - since the BMJ was launched - and the journal is asking for people to vote for their favourite.
The nominations range from antibiotics to the contraceptive pill and sanitation and computers.
The 15-strong shortlist was whittled down from 100 nominations from BMJ readers.
And leading modern doctors and scientists have championed each milestone.
The competition, which people can vote in over the next 10 days, is being held to mark the relaunch of the BMJ.
Editor Fiona Godlee said: "Any of these milestones would make a deserving winner.
"They have all made an enormous contribution to society and made a difference to millions of lives."
Click on each link to read about each milestone and to vote for the winner.
What do you think is the greatest medical milestone? You can send us your views using the link below: