Barretto, M.P. 1963. Diagncsis of chronic amebiasis. II. Comparative study of the efficiency of the zinc sulfate centrifugal-floatation technic, in successive stool specimens and of the examination of purged stools, used either separately or in combination. Revista do Instituto de Medicina Tropical de São Paulo. 5, 1 (Feb. 1963), 1–11.