Columbia subject headings:
Chicle industry--Mexico--Campeche.
Chicle--Mexico--Campeche.
Mayas--Mexico--Campeche--Economic conditions.
Harvard subject headings:
Chicle industry--Mexico--Campeche.
Mayas--Employment--Mexico--Campeche.
Mayas--Mexico--Campeche--Economic conditions.
Mexico--Economic conditions.
Mexico--Social conditions.
Princeton subject headings: