overseers were seldom prosecuted under these laws. No slave could give testimony in the courts. According to Adalberto Aguirre's research, 1,161 slaves were executed in the United States between the 1790s and 1850s. Quick executions of innocent slaves as well as suspects typically followed any attempted slave rebellions, as white militias overreacted with widespread killings that expressed their fears of rebellions, or suspected rebellions. Although most slaves had lives that were very restricted in terms of their movements and agency, exceptions existed to virtually every generalization; for instance, there were also slaves who had considerable freedom in their daily lives: slaves allowed to rent out their labor and who might live independently of their master in cities, slaves who employed white workers, and slave doctors who treated upper-class white patients. After 1820, in response to the inability to import new slaves from Africa and in part to abolitionist criticism, some slaveholders improved the living conditions of their slaves, to encourage them to be productive and to try to prevent escapes. It was part of a paternalistic approach in the antebellum era that was encouraged by ministers trying to use Christianity to improve the treatment of slaves. Slaveholders published articles in Southern agricultural journals to share best practices in treatment and management of slaves; they intended to show that their system was better than the living conditions of northern industrial workers. Medical care for slaves was limited in terms of the medical knowledge available to anyone. It was generally provided by other slaves or by slaveholders' family members, although sometimes "plantation physicians", like J. Marion Sims, were called by the owners to protect their investment by treating sick slaves. Many slaves possessed medical skills needed to tend to each other, and used folk remedies brought from Africa. They also developed new remedies based on American plants and herbs. An estimated nine percent of slaves were disabled due to a physical, sensory, psychological, neurological, or developmental condition. However, slaves were often described as disabled if they were unable to work or bear a child, and were often subjected to harsh treatment as a result. According to Andrew Fede, an owner could be held criminally liable for killing a slave only if the slave he killed was "completely submissive and under the master's absolute control". For example, in 1791 the North Carolina General Assembly defined the willful killing of a slave as criminal