When Edward Jenner arrived at St George's Hospital in 1770, the student found himself in the middle of a smallpox epidemic. Most of its victims, who were crammed four to a bed in candle-lit wards, died horrible deaths from the incurable disease.
Twenty-six years later, Jenner gave a child the first successful vaccination against smallpox.
A curious reminder of the breakthrough hangs in the University of London library at St George's - a red-brown cowhide with a white stripe from a rare-breed Gloucester that was known as Blossom.
In 1796, the animal passed cowpox - a bovine relative of smallpox - to a milkmaid, Sarah Nelmes, on a Gloucestershire farm. Jenner, who was then the local doctor, took material from a pustule on Nelmes's hand and smeared it in an incision in the hand of eight-year-old James Phipps. The boy then acquired immunity to the more deadly disease.
Jenner's family gave Blossom's hide to St George's in 1857 to commemorate its illustrious alumnus and to encourage future students.
Some people question the hide's authenticity, as the Gloucester Folk Museum also boasts a Jenner cowskin. The medical school, however, notes that more than one cow might have been involved in Jenner's painstaking trials.
As the medic himself noted: "I am at least six hours daily, with my pen bending over writing paper, till I am grown crooked as a cow's horn."