History of emergency medical services in the United States.
D000063:Accidents, Traffic; D000488:Allied Health Personnel / Q000193:education; D000552:Ambulances / Q000592:standards; D003422:Critical Care; D003695:Delivery of Health Care; D004632:Emergency Medical Services / Q000266:history*; D004636:Emergency Service, Hospital / Q000592:standards; D005380:Financing, Government; D006281:Health Occupations / Q000193:education; D049673:History, 20th Century; D007878:Legislation as Topic; D011845:Radio; D013689:Telephone; D014187:Transportation of Patients; D014481:United States