Boston Marathon blasts: runners donate blood

Amid the horror of the Boston Marathon blasts, NBC Sports Network is reporting stories of great bravery.

They took to Twitter, writing: "Reports of Marathon Runners that crossed finish line and continued to run to Mass General Hospital to give blood to victims #PrayforBoston"

President Barack Obama summed it up in his reaction, saying: "On days like this, there are no Republicans or Democrats, we are united as Americans."