Long ago humans discovered that certain animals and plants were capable of causing severe illness or death if anyone consumed them. Some were clever enough to extract liquids from these poisonous plants and tip their arrows with the poison before hunting. It was inevitable that these natural poisons would be used on the battlefield. In 600 b.c. Greek soldiers fighting against Greeks from another city became mysteriously ill after drinking water that their enemies had poisoned with rotting animal carcasses. In the 1400s, Tartars captured a town by catapulting the bodies of plague victims over the walled city. In eighteenth-century North America, British military leaders sent blankets containing smallpox germs to Indian camps in the hopes of causing outbreaks of the dreaded disease. The twentieth century has seen an increase in the sophistication of biological warfare. During World War I, the Germans were accused of inoculating...