Blood sample. Centrifuged sample of blood in a test tube, in this case blood taken from the umb- ilical cord that joins a foetus to its mother. Umbilical blood may be used to treat leukaemia and other disorders of the immune system. The orange fluid on top is serum which consists of water, salts, glucose, & proteins. The red matter beneath the serum is mainly blood cells. Centrifuges separate the cells and serum by spinning the sample at a high speed. Umbilical cord blood is useful because it contains a high number of stem cells which divide to form healthy new cells, and is less likely to be rejected by the new host. Photographed at the Milan Cord Blood Bank, Italy.