Columbia subject headings:
Amazon River Valley--Description and travel.
Amazon River Valley--Social conditions.
Rubber industry and trade--Amazon River Valley.
Harvard subject headings:
Amazon River Valley--Description and travel.
Amazon River Valley--Economic conditions.
Amazon River Valley--Social conditions.
Ecology--Amazon River Valley.
Rubber industry and trade--Amazon River Valley.
Princeton subject headings:
Amazon River Valley--Description and travel.
Amazon River Valley--Economic conditions.
Amazon River Valley--Social conditions.
Ecology--Amazon River Valley.
Rubber industry and trade--Amazon River Valley.