I found this site when searching out the source of the phrase 'Three Sheets To The Wind"
THE PHRASE FINDER
I haven't been looking for long, but I already found some coolness.
To keep with the '3 sheets' theme, here is partial text from, and a link to Gary Martin's entry on 'Hair of the Dog':
"With most metaphorical phrases that have a literal origin, for example toe the line and on the warpath, the later figurative use doesn't become popular until the literal use has fallen out of use. 'The hair of the dog' is unusual in that the figurative version is recorded before any known examples of the literal meaning.
John Heywood, in his invaluable early text, A dialogue conteinyng the nomber in effect of all the prouerbes in the Englishe tongue, 1546, uses the phrase with a clear reference to drinking:
I pray thee let me and my fellow have
A hair of the dog that bit us last night -
And bitten were we both to the brain aright.
We saw each other drunk in the good ale glass.
Another useful text, Randle Cotgrave's A dictionarie of the French and English tongues, 1611, also records the 'drinking' version of the expression:
Our Ale-knights [habitual drinkers] often use this phrase, and say, Give us a haire of the dog that last bit us.
It isn't until the 18th century that the literal use of dogs' hair to cure bite wounds is recorded in print. Robert James alludes to the method in A Treatise on Canine Madness, 1760:..."