Most people are familiar with the story of how vaccination was invented, but I'll give it a brief review before getting to the point of interest: in 1796, Dr. Edward Jenner conducted an experiment (which would have been highly illegal in modern times), by collecting pus from a cowpox pustule of a milkmaid, Sarah Nelms, and injecting it into a little boy, James Phipps. (No, the names don't matter, but I like character-driven plots).
At this time smallpox was a major public health problem, up to one in three children died from the disease. Cowpox, however, was common but nowhere near as deadly. After little Phipps was injected with the the Nelms pus, he developed a characteristic cowpox pustule, but was relatively no worse for the wear.
Six weeks later, Jenner exposed Phipps to smallpox in the same manner. Not only that, he was insistently exposed over a period of years (where were this kid's parents, and what were they thinking?), and yet he never contracted the highly virulent disease. Thus, it was proven that exposure to a virus can stimulate the immune systemto fight off similar viruses in the future, and vaccination was born.
This story is familiar to most people who have had an introductory biology class. What most people don't know, however, is the origin of not the concept of vaccination but the word itself.
Since the mechanism of immunity was not yet know, many people, including the French, ridiculed Jenner's idea. In stereotypically snooty fashion, they coined a mocking term for the procedure: "vaccination" is derived from vache, the French word for cow. If you translate it literally, the term roughly means "to be made into a cow."
I'm just as much of a book lover as a science lover and am fascinated by the evolution of both words and species, just thought that was an interesting item to add to Jenner's well-known story.