Working on frogs and extrapolating to humans, Malpighi demonstrated the structure of the lungs, previously thought to be a homogeneous mass of flesh, and he offered an explanation for how air and blood mixed in the lungs. Malpighi also used the microscope for his studies of the skin, kidneys, and liver. For example, after he dissected the body of a black man, Malpighi made some groundbreaking headway into the origin of black skin. He found that the black pigment was associated with a layer of mucus just beneath the skin.