Rush claims that both racial difference and disease are produced by bodies that are out of balance with their environment. He says that all bodies are healthiest in a temperate environment, as opposed to tropical or tundra, and describes Blackness as a "form of leprosy that ate away at the universal humanity below the skin." He claims that heat, diet, and a "deficiency of labor" created African cultures and that Blackness can be passed on like any other "disease."