Bags of blood from the National Blood Service containing different blood groups - A, B, AB and O - on display in the Wellcome Wing of the Science Museum, London. 'Inside you, there is another you - your immune system. Its tiny agents watchfully patrol your body, distinguishing what's yours from what's not. That's how your body protects you from disease. Doctors identify your blood type by looking for a specific combination of molecules on the surface of your red blood cells. These molecules are called blood antigens.'
© Science Museum / Science & Society Picture Library