Columbia subject headings:
Harvard subject headings:
Rubber industry and trade--Brazil--History--20th century.
Rubber industry workers--Amazon River Region--History--20th century.
Rubber industry workers--Brazil--Diaries.
Yungjohann, John C. (John Christian), -1930--Diaries.
Princeton subject headings:
Amazonas (Brazil)--Description and travel.
Hevea--Brazil--Amazonas.
Rubber tappers--Brazil--Amazonas--Diaries.
Yungjohann, John C. (John Christian), -1930--Diaries.