While still a medical student, Jenner noticed that milkmaids who had contracted a disease called cowpox, which caused blistering on cow’s udders, did not catch smallpox. Unlike smallpox, which caused severe skin eruptions and dangerous fevers in humans, cowpox led to few ill symptoms in these women. On May 14, 1796, Jenner took fluid from a cowpox blister and scratched it into the skin of James Phipps, an eight-year-old boy. A single blister rose up on the spot, but James soon recovered. On July 1, Jenner injected the boy again, this time with smallpox matter, and no disease developed. The vaccine was a success. Doctors all over Europe soon adopted Jenner’s innovative technique, leading to a drastic decline in new sufferers of the devastating disease