Two teams of scientists published studies on Sunday showing that blood from young mice reverses aging in old mice, rejuvenating their muscles and brains. As ghoulish as the research may sound, experts said that it could lead to treatments for disorders like Alzheimer’s disease and heart disease. “I am extremely excited,” said Rudolph Tanzi, a professor of neurology at Harvard Medical School, who was not involved in the research. “These findings could be a game changer.” The research builds on centuries of speculation that the blood of young people contains substances that might rejuvenate older adults. In the 1950s, Clive...