When a person, after drinking too much, finds himself disordered next morning, the advice is, to take a hair of the same dog, or of the old dog. Quaere, upon what ground this notion is taken up? Is it from an opinion, that poisonous animals carry their own antidote, as the exungia viperina is good against the bite of a viper, and a bit of the liver of a mad dog was formerly thought to be a remedy for canine madness ? The drawing of blood from a witch was imagined to pre-vent the effects of her witchcraft, and seems to proceed upon the same principle. However, I leave it to your numerous correspondents to inform, whence the common advice above-mentioned could possibly originate, and upon what footing it stands.