so then the argument was, well, the relationship between high lead and low iq is because there's a social class difference. but i mean, that's where the animal studies were very important, and because it demonstrated that that didn't explain it. these are the animals we've been using to study the effects of chronic lead treatment on behaviour in brain chemistry. there's a great deal of fighting among these animals, and they're very hard for experimenters to catch, which is another indication of reactivity and aggressiveness in them. a letter written by sir henry yellowlees, the government's chief medical advisor, has been leaked