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Basically because your skin has several layers to it (see link, below), and the layer that has the blood vessels capable of bleeding in it is further down than a superficial scrape would affect.
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<span>Clostridium perfringens and Salmonella</span>
True, a vast, flat, treeless Arctic region of Europe, Asia, and North America in which the subsoil is permanently frozen.
Different enzymes have specific active sites which can only catalyze one <span>substrate. Enzyme-substrate complexes are produced only when the substrate fits into the active site :)</span>