'Mat Hatter' -- from mercury or snakes?

Can any Dopers provide any evidence either way about the theory that “Mad as a Hatter” comes from mercury poisoned hatters? The theory is plausible (and repeated often enough), but the Snopes Urban Legend site (who I trust almost as much as Cecil) calls it an unlikely derivation
(at http://www.snopes2.com/spoons/fracture/hatter.htm

So any cites, references, or even reliable authorities either way? Ignorance awaits your stamping out!
(I’m doing an article on mercury; I’d love to get this definitively right)
Just to go over the situation briefly, here’s the pros and cons that I know of:

Pros: It’s a very plausible theory. Mercury is undoubtedly poisonous, and prolonged exposure will cause neurological damage (most obviously shaking and twitching, but there can be other symptoms, too). I don’t think there’s much dispute that hatmaking, in the 17th and 18th centuries, used mercury and hatmakers were exposed to enough to poison them. Another piece of support for the theory is the name “Danbury Shakes” which I’ve been told (any references for this, too would be appreciated) referred to the affliction of hatmakers in Danbury, CT (which was a center of the hat industry).

Cons: The Snopes article doesn’t so much refute the merucry theory as say that there’s no support for it. They mention some other possible derivations, such as Lewis Carroll satirizing a well-known businessman (this seems unlikely to me, as the Snopes article mentions a usage of the phrase from 1837), or coming from ‘mad as an adder’ (using the now-archaic meaning of ‘mad’ as ‘venomous’ I imagine also possibly sliding into the meaning of angry as well). This last derivation is the opinion of a source from 1901, so it’s not just a new idea, thought I don’t know what the support for it is.

I don’t know if I would call this a reliable source, but:

Where the phrase “Mad as a hatter” came from was a question on Who Wants To Be A Millionaire a few weeks ago. The answer was the mercury thing.

Hmm. This may be a good question for Cecil. I can’t find any definite proof off-hand. But here are some possible helpful links…

Agency for Toxic Substances and Disease Registry (a reliable source of info)

From a Google search…(I don’t know how reliable these are)

Some EPA-cited references on the subject of mercury poisoning (not sure if they specifically mention the mad hatter case or not)…

Fawer, R.F., U. DeRibaupierre, M.P. Guillemin, M. Berode and M. Lobe. 1983. Measurement of hand tremor induced by industrial exposure to metallic mercury. J. Ind. Med. 40: 204-208.

Piikivi, L. 1989. Cardiovascular reflexes and low long-term exposure to mercury vapor. Int. Arch. Occup. Environ. Health. 61: 391-395.

from niblink.com

I don’t know how reliable that particular source is, but it agrees with all of the things that I had heard in the past about “hatter’s shakes”

As much as I respect Snopes, I think they’re a little too skeptical on this one.

An important step on the road to turning your beaver pelt into a hat was carroting the fur. I quote from an excellent page on the fur trade:

(ellipse mine).

Huffing mercury fumes into the lungs would seem to be an ideal way to get it into the bloodstream pronto.

Lighthouses with large lenses (First or Second order, I think) used a tub of mercury
to float the lens, in order that it could rotate around its (pre-electric) light source. NESCSAUM (North East States and Eastern Canadian Provinces Mercury Study) says:

The Canadian Coast Guard, which is responsible for lighthouses and other navagation aids in Canadian waters, takes the mercury threat seriously, as there are still 60 manned lighthouses in Canada.

This Coast Guard Canada page has interesting information about the historic lighthouse I look after:

I have the original 1866 keeper’s log on my desk at the moment, by coincidence, and I can’t find any reference to sex with Mrs. Davies…

Evan Morris, in his Word Detective column, agrees that it’s from mad as a hatter. He doesn’t mention the “mad as an adder” theory at all.

From Brewer’s Dictionary of Phrase and Fable:

The earliest reference to “mad as a hatter” in the OED is 1837, but it doesn’t shed any light on the origin of the phrase. Under “hatters’ shakes” it has:

I realise that none of this advances either case.