Blood blood clotting in a transparent container. When blood is drawn in a glass container and left undisturbed for about an hour, four different layers can be seen. A dark clot forms at the bottom (the "black bile"). Above the clot is a layer of red blood cells (the "blood"). Above this is a whitish layer of white blood cells (the "phlegm"). The top layer is clear yellow serum (the "yellow bile"). The ABO blood group system was discovered in the year 1900 by Karl Landsteiner. Jan Janský is credited with the first classification of blood into the four types (A,
Blood, toil, tears, and sweat are "It [poetry] is forged slowly and painfully, link by link, with blood and sweat and tears" (Lord Alfred Douglas, 1919), "Blood, sweat, and tear-wrung millions" (Lord Byron, 1823), and "...mollifie/ It with thy teares, or sweat, or blood" (John Donne, 1611). In Latin, Cicero and Livy had used the phrase "sweat and blood". "We are in the preliminary stage of one of the greatest battles in history... That we are in action at many points—in Norway and in Holland—, that we have to be prepared in the Mediterranean. That the air battle is continuous, and that many preparations have