„Helen, by Maria Edgeworth”. www.gutenberg.org. Приступљено 2020-09-15. „One in particular, from Spain, of high rank and birth, of the sangre azul, the blue blood, who have the privilege of the silken cord if they should come to be hanged.”
„The annual register. v.51 1809.”. HathiTrust (на језику: енглески). стр. 813. Приступљено 2020-09-15. „The nobility of Valencia..are, by themselves, divided into three classes, blue blood, red blood, and yellow blood. Blue blood is confined to families who have been made grandees.”