I'm often reminded of the way the smallpox vaccine was discovered around 1800. An English doctor noticed that "milkmaids", working with cows on dairy farms, had clearer complexions than many others who got "cowpox". He made and demonstrated a vaccine made from a milkmaids sore on her hand which imparted her antibodies. And we had a vaccine for smallpox. The first vaccine.

I was working in the garden with one of  my young grandsons a few years ago when he asked me if I wanted a carrot. Saying yes he pulled two out of the cow-manure fertilized soil, shook them off,  handed me one and started eating the other. I said to him that maybe we should wash these off first? He said no, his mom (a family practice MD) had said they were good for you, right out of the garden bed, just like that.