Building off contemporary folk wisdom, Englishman Edward Jenner tested vaccination against smallpox on various patients. Note the bovine observer at the door.

Courtesy Science Photo Library __1796: __Edward Jenner inoculates a boy with cowpox. After the lad recovers from the infection, Jenner inoculates him with smallpox, but the boy remains healthy. Vaccination is born.

Before Jenner, smallpox was a massive scourge and a leading cause of death, especially among children. Those whom it didn't kill it disfigured with pockmarked faces.

Some European families adopted the Turkish practice of inoculating their children with low doses of smallpox in hopes of building up their immunity to the disease. This was popularized in England by Lady Mary Wortley Montagu, who had her own child inoculated. The Royal family, freshly arrived from the Kingdom of Hanover in Germany, inoculated two of the Princess of Wales' children in 1723 to secure the succession. (Ironically, the Hanovers had come to the throne of Great Britain because so many Stuart and Orange heirs had succumbed to smallpox.) But the process was risky.

Jenner had heard the folk wisdom that milkmaids and others who contracted the mild and harmless cowpox through their proximity to cattle did not fall victim to the deadly smallpox. He inoculated his year-and-a-half-old son in 1789 with swine pox (a related pig disease) and then smallpox. The boy did not contract smallpox.

The dramatic 1796 experiment used fluid taken from a cowpox sore on milkmaid Sarah Nelmes. The experimental subject was 8-year-old James Phipps, who did not get smallpox despite Jenner's repeated attempts to infect him starting July 1. Ethicists debate whether such an experiment would be at all possible today.

Jenner carried out further experiments on patients and was likewise unable to infect them with smallpox if he had vaccinated them or they had contracted cowpox naturally. He published the results of 23 cases in a 1798 monograph, An inquiry into the causes and effects of the Variolae Vaccinae, a disease discovered in some of the western counties of England, particularly Gloucestershire, and known by the name of the cow-pox.

Jenner wrote several revisions of this work as he added cases, and other researchers soon replicated his work. He called the process vaccination after the Latin word for cow, vacca. He also introduced the word virus.

Vaccination caught on quickly, but more than a century passed before scientists isolated and understood the viruses involved. After a global vaccination campaign, the World Health Organization declared smallpox eradicated in 1979.

(Source: Thomas Cooper Library, University of South Carolina)

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