The first signs that young blood could blunt the ravages of aging came more than 60 years ago when a team at Cornell University — using a somewhat ghoulish procedure devised a century earlier and used to study wound healing — sutured together two rats so that they would share a common circulatory system. After old and young rats were joined for many months, the bones of both animals became similar in weight, volume and density, thus helping to ward off the bone brittleness that typically accompanies old age.
Some 15 years later, researchers at the University of California performed their own old–young rat pairing experiments. As they reported in 1972, older partners in this arrangement lived around 10 to 20 percent longer than control rats paired to other old animals.
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