Bad things come in small packages. On August 14, 1996, Karen Wetterhahn, a toxicologist and professor of chemistry at Dartmouth College, spilled a drop, a tiny speck, of dimethylmercury on her left hand. Wetterhahn, tall, thin, intense, was an expert on how toxic metals cause cancer once they penetrate cell membranes. When she spilled the poisonous droplet in her lab, she thought nothing of it; she was wearing latex gloves. What she didn't know killed her.

The dimethylmercury was volatile enough to penetrate the glove. Five months later Wetterhahn began stumbling into doors and slurring words. After three weeks in a hospital, she slipped into a coma.

"I went to see her, but it wasn't the kind of coma I'd expected," recalled