Most of us think of ourselves as people who go out of our way to do the right thing, especially if it helps those less fortunate than ourselves.  We donate to charities; we volunteer our time; we tell our friends about worthy causes.  Nevertheless I was surprised to find that I had forgotten about a much-needed gift that most of us can give:  blood.  A few weeks ago I was embarrassed to find out it had been six months since my last bloo...