Blood typing. Multi-well sample tray of blood for use in a histocompatibility test to see if a transplant would be successful. This blood has been taken from the umbilical cord and placenta of a pregnant woman. Histocompatibility is used by the body's immune system to recognise its own cells. The most important proteins in this recog- nition system are Human Leukocyte Antigens (HLA). Transplanted tissue which has marked HLA differ- ences from that of the recipient will be attacked by that person's immune system. Blood from the placenta and umbilical cord is less likely to be rejected by a recipient than normal blood. Photographed at the Milan Cord Blood Bank, Italy.