Slave owners used these falsified scientific differences to justify what they were doing. Due to the belief that African Americans had less kidney secretion and altered glands, "this greater degree of sweating makes them more tolerant of heat and less tolerant of cold than whites" (Jefferson 763). Jefferson believed that glands were modified in African Americans that allowed them to be more tolerant of heat, which reiterated the fact that they were expected to work outside in the fields. If society believed that they were accustomed to working in the fields, this allowed them to feel justified in what they did to the slaves. Jefferson said that African Americans are genetically engineered to sleep less: "They seem to need less sleep." A Negro, after the hard work of the day, will be induced by the slightest entertainment to sit until midnight or later, knowing that he must go out at first dawn in the morning” (764). Jefferson's assertion that slaves actually needed less sleep allowed him to view their long hours in the field as acceptable, because he believed they did not tire as easily. The scientific facts on which Jefferson based his claims were blatantly falsified, but society was quick to believe what he said.