Circa 1930s. Origin unknown. Use unknown.
You can find out more by reading Quack!: Tales of Medical Fraud from the Museum of Questionable Medical Devices, described by Orangedesperado: "Many items to consider with the original ads and copy. Don't forget the prostate warmer which worked with the heat of a light bulb and was helpful for stimulating the center of the 'male brain'."
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.