In A Treatise on Tropical Disease and the West Indies, Mosley notes differences in how Black people display pain during surgical operations in comparison with white people. This "scientific paper" will be used to "prove" that Black people feel less pain than white people–a belief system that persists in contemporary medicine.

Mosley writes: "The Locked-Jaw appears to be disease entirely of irritability. Negroes, who are most subject to it, whatever the cause may be, are void of sensibility to a surprising degree. They are not subject to nervous diseases. They sleep sound in every disease; nor does any mental disturbance ever keep them awake. They bear surgical operations much better than white people: and what would be the cause of unsupportable pain to a white man, a Negro would almost disregard."