In his Notes on the State of Virginia, Jefferson argues that there are "real distinctions which nature has made" between white and Black people. This perceived distinction will be repeatedly used to assert the value of labor for Black people in supporting an increase in their lung capacity. Black lung capacity has also been written about in this time period by white colonizers of African nations who observed Indigenous African swimmers, divers, and fishermen. Jefferson writes: "This greater degree of transpiration renders them more tolerant of heat, and less so of cold, than the whites. Perhaps too a difference of structure in the pulmonary apparatus, which a late ingenious experimentalist has discovered to be the principal regulator of animal heat, may have disabled them from extricating, in the act of inspiration, so much of that fluid from the outer air, or obliged them in expiration, to part with more of it."