The search for a reliable and reproducible means to distinguish bloods of humans and animals was critically important for clinical medicine (especially the practice of blood transfusion), but also important for forensic purposes, and for establishing paternity and maternity. But the ability to distinguish the bloods of individuals advanced other social goals, especially the elusive, if long sought after, desire for racial purity in populations. This article considers how the popular dissemination of human blood types challenged traditional understanding of identity and difference, and some of the ways in which new information about an individual's blood type could be mobilized in the interests of the state, as a means of disaster planning, and as a method to limit dysgenic offspring' by preventing the marriages of blood-incompatible couples.
