As 750 scientists and animal-genetics researchers prepare to gather in Minneapolis on July 23-27, city police are canceling vacations days, beefing-up crowd control training and supporting a new city law to make wearing a gas mask a misdemeanor for everyone except police, fire and medical emergency officials. Law enforcement agents point to threatening e-mails from anti-choice activists (protesting genetically engineered food) who threaten to disrupt the meeting in much the same way they disrupted the World Trade Organization in Seattle last year.