Homeland security.

• Position: Dichlorodiphenyl trichloroethane (DDT - Brief Article - Illustration

This photograph, taken on July 8, 1945, shows an insecticide-spraying machine being tested publicly for the first time. The figure on this beach on Long Island, New York, has been enveloped in a fog of dichlorodiphenyl trichloroethane, or DDT.

In the postwar era, chemistry seemed to be on the verge of overcoming some of our oldest enemies: the insects that destroy our crops and infect us with diseases like malaria, which is transmitted by mosquitoes. Ten years after this photo was taken, DDT became the principal tool of the WHO Global Malaria Eradication Program. In the late 1960s, after the spraying of untold tons of DDT, the program was abandoned as unworkable. Today, malaria infects between 300 million and 500 million people every year, and kills between 1 and 3 million, most of them pregnant women and...