A metallic pool sat in the palm of my hand, glittering silver. A slow waterfall of heavy silver ball bearings tumbled from the crease in my palm, bouncing and rolling crazily across my black desktop.
When I later found out how poisonous the metal named for the speedy Roman messenger god is, I was horrified. I'd played with the stuff, bouncing tiny beads of it between my fingertips.
Mercury's huge atoms can cause tremendous damage to living tissues, especially in the nervous system—hanging around for a long time like a particularly tenacious bull in a china shop.
Luckily for me, mercury is not terribly dangerous in its typical, metallic form. This is principally because, at body temperature, mercury is fairly stable. Metallic mercury does not thus readily absorb through skin or digestive system (although it is not 100% safe to ingest, as some minute quantities will likely enter the bloodstream).
Mercury salts or mercury vapor, on the other hand, are quite dangerous. In salts, mercury quickly absorbs into the body and in gaseous form the metal will enter the bloodstream with incredible speed. Mercury salts, such as acetate, sulfate and mercuric chloride, are common in certain industries and may sometimes enter food animals and plants through industrial pollution. The mercury ions thus present in the circulatory system are thus free to wreak havok wherever they may land. Mercury is a cumulative toxin, with very long residency time in the bloodstream and tissues, so that repeated exposure to even minute quantities can cause damage in the long term.
Historically, this was a big problem for hat makers, alchemists, metal smelters (particularly those who worked with lead and/or silver, two metals often found with mercury) and chemists.
Reworked and revised: 9/6/07
references:
Dr. Joseph F. Smith Medical Library online -http://www.chclibrary.org/micromed/00050500.html
Taber's Cyclopedic Medical Dictionary, 19th edition (FA Davis, Philadelphia, 1997).