Edward Jenner's early 19th century experiments involved injecting several children (including his own son) with pus from cows suffering from cowpox. People at the time were horrified. However, during the first part of the 19th century, it became accepted that Jenner's methods provided protection against one of the most deadly diseases of the time.
Jenner was not the first to attempt inoculation. There is evidence of similar experiments being carried out in both India and China the century before.