If Bubonic plague and yellow fever sound foreign to Canadians, a large share of the credit is due to Canada's oldest federal health activity -- National Health and Welfare's Quarantine Service, whose medical officers stand guard to keep Canada free from infectious disease. Working from reports of the World Health Organization, "Q-Men" in stations on both coasts chart every new outbreak of disease. All vessels from these areas must be inspected by a quarantine officer before docking. If necessary, passengers and crew are inoculated or removed to shore stations for treatment, and the ship fumigated. In addition, the service assures care for foreign crewmen. Despite its remarkable record, the "Q" service is known little by inland citizens. Like the good health it ensures, it is hardly noticeable -- as long as it's there.