Adobe walls and straw-thatched roofs of inhabited dwellings in a subtropical area treated with DDT in May 1945 still show evidence of residual action of the preparation 29 months afterwards, in October 1947. DDT can be recovered in significant quantities from the treated surfaces by quantitative chemical methods.
The International Health Division of The Rockefeller Foundation. Calle Viena 26, Mexico, D. F.
Laboratorio de Química, Instituto de Salubridad y Enfermedades Tropicales, México, D. F.
United States Department of Agriculture, Agricultural Research Administration, Bureau of Entomology and Plant Quarantine, Orlando, Florida.