Columbia subject headings:
Harvard subject headings:
Health insurance--United States--History--20th century.
Industrial hygiene--United States--History--20th century.
Labor unions and health insurance--United States--History--20th century.
National health insurance--United States--History--20th century.
Princeton subject headings:
Health insurance--United States--History--20th century.
Labor unions and health insurance--United States--History--20th century.
National health insurance--United States--History--20th century.