Dysaethesia Aethiopica

Dysaethesia Aethiopica was a term to describe a mental illness which was believed to be why Afro-American slaves were lazy.
American physician Samuel A. Cartwright described the condition in 1851. Today, dysaethesia aethiopica is considered an example of pseudoscience. Many people think it is an example of scientific racism. 
Cartwright wrote that the illness caused people to break and mishandle everything they touched. They walked about as if they were in a daze, or half asleep. They often argued with people in charge and caused disturbances. They did not feel pain, and did not react when physically punished. It affected people who did not have white (or European) people to look after them.