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  • Getting past the guards

    The Economist - 12/02/2011

    BY ACCIDENT and by design, human bodies are hard to break into. They are surrounded by defensive walls (the skin, the lining of the gut, the barrier between the bloodstream and the brain), patrolled by sentries (the cells and antibodies of the immune system) and filled with mazes, such as the intricate network of blood capillaries that connects the arteries to the veins, delivering food and oxygen to cells as it does so.