A WORD, PLEASE — vaccine

continuity: Next, Professor Aubrey Vellum, with the farm animal that's been hiding in your medical records all along.

the verdict: You roll up your sleeve, the nurse says 'just a little scratch,' and the vaccine is in before you've finished wincing. You get a sticker, maybe a lollipop, and nobody in that room is thinking about cows. They should be.

a word, please: Vaccine. A word, please.

the crack: Here's the secret: vaccine comes from vacca , the Latin word for 'cow.' It got there through an English doctor named Edward Jenner, who took some farmyard wisdom seriously. Dairy workers said that if you'd caught cowpox, a mild sore picked up from the cows you milked, you didn't catch smallpox, the great killer of the age. Jenner looked into it, and in seventeen ninety-eight he published what he'd found. He called cowpox variolae vaccinae , which simply means 'cow smallpox,' and our word was born inside that name. At first, vaccine meant just one thing: the matter from a cowpox sore, used to protect people.

the collision: So how did the cow wander into everything else? Enter Louis Pasteur, the great French scientist. By eighteen eighty-one he was making lab-grown protection against anthrax, and later rabies, diseases with nothing to do with cows at all. Yet in a speech in London that year, he proposed calling every such protection a vaccine, to honor Jenner. The world agreed, and the cow stayed. Now, you may hear that vaccine comes from vacare , 'to empty,' as if it empties the body of disease. It's a tidy story, and it isn't true. The real one has a cow in it, which is better. Today the newest shot in the shiniest clinic still carries a Latin cow in its name, standing quietly in every doctor's office for over two hundred years.

the glimmer: And here's the part I love most: one of the most lifesaving ideas people ever had began with farm workers noticing something about their own lives, and a doctor humble enough to listen.

the exit: That's the word. Next time you roll up your sleeve, give the cow a little nod.