Much of what the Pentagon knows about the effects of bacterial attacks on cities came from ... secret tests conducted on San Francisco and other American cities from the 1940s through the 1960s, experts say. In the 1950s, Army researchers dispersed Serratia on Panama City, Fla., and Key West, Fla., with no known illnesses resulting. They also released fluorescent compounds over Minnesota and other Midwestern states to see how far they would spread in the atmosphere. The particles of zinc-cadmium-sulfide -- now a known cancer-causing agent -- were detected more than 1,000 miles away in New York state, the Army told the Senate hearings. In New York, military researchers in 1966 spread Bacillus subtilis variant Niger, also believed to be harmless, in the subway system by dropping lightbulbs filled with the bacteria onto tracks in stations in midtown Manhattan. The bacteria were carried for miles throughout the subway system. The Army kept the biological-warfare tests secret until word of them was leaked to the press in the 1970s. Between 1949 and 1969 ... open-air tests of biological agents were conducted 239 times, according to the Army's testimony in 1977 before the Senate's subcommittee on health. In 80 of those experiments, the Army said it used live bacteria that its researchers at the time thought were harmless. Several medical experts have since claimed that an untold number of people may have gotten sick as a result of the germ tests. These researchers say even benign agents can mutate into unpredictable pathogens once exposed to the elements.