Bubonic plague infection causes tiny blood vessels in the feet and toes to clog up and cut off circulation. Without blood, the flesh dies and turns black (called "gangrene"). This is why in the Middle Ages bubonic plague was called "the Black Death."
Bubonic Plague Pictures: Foot Gangrene Photos of Bubonic Plague Infections and Transmission
From Mary Kugler, R.N., former About.com Guide
About.com Health's Disease and Condition content is reviewed by our Medical Review Board
Foot gangrene caused by bubonic plague
Photo courtesy of the CDCMore About Bubonic Plague
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