He is a cheerful old farmer who jokes as he serves rice cakes made by his wife, and then he switches easily to explaining what it is like to cut open a 30-year-old man who is tied naked to a bed and dissect him alive, without anesthetic. The old man, who insisted on anonymity, explained the reason for the vivisection. The Chinese prisoner had been deliberately infected with the plague as part of a research project ... to develop plague bombs for use in World War II. After infecting him, the researchers decided to cut him open to see what the disease does to a man's inside. No anesthetic was used, he said, out of concern that it might have an effect on the results. That research program was one of the great secrets of Japan during and after World War II: a vast project to develop weapons of biological warfare, including plague, anthrax, cholera and a dozen other pathogens. Unit 731 of the Japanese Imperial Army conducted research by experimenting on humans and by field testing" plague bombs ... to see whether they could start plague outbreaks. They could. At least 3,000 people ... were killed in the medical experiments; none survived. The research was kept secret after the end of the war in part because the United States Army granted immunity from war crimes prosecution to the doctors in exchange for their data. Japanese and American documents show that the United States helped cover up the human experimentation. Instead of putting the ringleaders on trial, it gave them stipends.