MARK THOMAS / SCIENCE PHOTO LIBRARY MARK THOMAS / SCIENCE PHOTO LIBRARY
Taking blood. Nurse removing a cannula from the arm of an elderly patient after taking a blood sample. A cannula is a combination of a hollow needle with a tube inside. The needle enables the tube to be inserted into a patient's vein. Once inserted, the needle is removed leaving the tube in place. This allows blood to be taken from the vein more easily. Photographed at the West Middlesex University Hospital, London, UK.
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