Now & then.
D000552:Ambulances / Q000266:history; D004631:Emergency Medical Service Communication Systems / Q000266:history; D004632:Emergency Medical Services / Q000266:history* / Q000639:trends; D004864:Equipment and Supplies; D049673:History, 20th Century; D017053:Infection Control / Q000266:history; D009936:Organizational Innovation; D014187:Transportation of Patients / Q000266:history; D014481:United States