The Homeland Security Department last month released what they said was nontoxic gas into New York’s Grand Central Station to trace how chemicals might flow through the terminal in a terrorist attack. We speak with biological and chemical terrorism expert Leonard Cole, who asks what this “nontoxic gas” actually was. He wrote a book about how–in the 1950s and 1960s, U.S. government scientists ran a series of tests to determine how easy it would be to expose large numbers of people to a lethal bacteria. [includes rush transcript]

In the aftermath of the London bombings, the U.S. Government raised the terrorist threat level to Orange, or “High.” The alert was particularly applied to the nation’s trains and subway systems. Although far less money has been spent on security measures for public transportation than for the airline industry, experts say subways and trains may be particularly vulnerable to chemical and biological attacks. Late last month, the Homeland Security Department released what they said was nontoxic gas into New York’s Grand Central Station to trace how chemicals might flow through the terminal in a terrorist attack.

But some government simulations of chemical and biological attacks in the past have been somewhat different.

In the 1950s and sixties, scientists from the Fort Detrick biological weapons program ran a series of tests to determine how easy it would be to expose large numbers of people to a lethal bacteria. Containers of nontoxic bacteria were planted in the New York subway, bacteria was secretly pumped into the Pentagon ventilation system and clouds of bacteria were released in San Francisco. And germs that were meant to sicken but not kill humans were tested on conscientious objectors in the military.

• Leonard Cole, an Adjunct Professor of Political Science at Rutgers-Newark in New Jersey. An expert in biological and chemical terrorism, Cole is also the author of “The Eleventh Plague, The Politics of Chemical and Biological Warfare,” and “The Anthrax Letters: A Medical Detective Story.”