Edward Jenner was a physician in the eighteenth and nineteenth century who studied the disease known as cowpox. Traditional medical knowledge demonstrated that milkmaids who contracted the disease cowpox became immune to smallpox. On account of this information Jenner surmised that pus from cowpox blisters (such as shown in the pictures) could be used to inoculate against smallpox. Learn more about Jenner, vaccines, and immunology in this learning leaflet.