blood volume we have when you lie down. >> it's experimental. the team is doing studies with high school hockey and football players to test safety. others say ultimate safety snlt goiisn't going to come from devs but from technique and rule chang changes. an op-ed was written saying "don't let kids play football." that's the message millions are going to hear when they watch "concussion." dr. sanjay gupta, cnn, new york. >> thank you so much. coming up next, we are continuing to monitor breaking news out of chicago. li live. pictures right now where protesters are gathering. you see them right there. at times blocking access to stores in the city's very busy shopping district. they are walking down the magnificent file. we'll get an update.