It came from the first concoction made by Edward Jenner who was using pus from smallpox victims (cow is "vacca" in Latin.) to vaccinate against smallpox. He first took pus from cow udders from cows with cowpox and scratched other cows and added the pus to the open skin. Voila! No cowpox was created. It's pretty disgusting, but not half as disgusting as what they are putting into babies and everyone else right now: Poisons, fetal cells, and other horrific stuff.