How the old wives tales of 1930s racism sometimes, surprisingly, turn out to be the literal truth

Until 1950, blood transfusions in the United States were segregated along racial lines. By the 1970s, this was considered shocking and racist; blood is blood and the ethnicity of the donor is or no conceivable relevance from a clinical perspective. It now appears that there really is a difference between white peoples blood and that from black people.