By the definition accepted in the United States, any person with even a small amount of Negro Blood... is a Negro. Logically, it would be exactly as justifiable to say that any person with even a small amount of white blood is white. Why do they say one rather than the other? Because the former classification suits the convenience of those making the classification. Society, in short, regards as true those systems that produce the desired results. Science seeks only the most generally useful systems of classification; these it regards for the time being, until more useful classifications are invented, as true.
