E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Hair of the Dog that Bit You (A).
Simila similbus curantur. In Scotland it is a popular belief that a few hairs of the dog that bit you applied to the wound will prevent evil consequences. Applied to drinks, it means, if overnight you have indulged too freely, take a glass of the same wine next morning to soothe the nerves. If this dog do you bite, soon as out of your bed, take a hair of the tail in the morning.