MODEL RELEASED. Mechanical blood harvesting. Nurse rehydrating a patient who is attached to a machine (centre right) that is harvesting stem cells from his blood. Blood from one arm passes through the apheresis machine and returns to the other arm. The machine uses a centrifuge to rapidly spin the blood. Components of different weight separate out, allowing needed parts to be harvested. This method allows more collection of blood parts than in normal processing. The patient has Hodgkin's disease, a cancer of the lymph nodes. Treatments, like radiotherapy, will destroy many white blood cells in the lymph nodes, requiring replacement by stem cells that develop into new blood cells.