Doctors Try to Help Body Grow its Own Bypasses By LAURAN NEERGAARD    WASHINGTON (AP) -- Peter Cummins lay still as doctors administered 20 injections into the 81-year-old's calves and thighs, hoping the genetic experiment will spur new blood vessels to grow around his clogged leg arteries.    The experiment at the National Institutes of Health marks a resurgence in attempts to get the body to grow its own bypasses, at first in the legs and, if that works, perhaps later in the heart...