The recipe quoted above is a standard hangover cure, usually with some kind of alcohol for the hair of the dog. I believe in Jeeves's case it was a secret recipe--or is that just in the show?

I looked in "Kingsley Amis On Drink" The British novelist notes the time-honored Bloody Mary, and something called the Underberg: highly alcoholic bitters taken straight. He describes the effect thusly:
"The effect on one's insides, after a few seconds, is rather like that of throwing a cricket-ball into an empty bath, and the resulting mild convulsions and cries of shock are well worth witnessing. But thereafter a comforting glow supervenes, and very often a marked turn for the better."