"Discover the main systems of our amazing human body with this new series of books! The blood that flows through your body constantly brings food and oxygen to your muscles, organs, and bones and carries away waste. And it is all powered by that magnificent muscle, your heart. Did you know that your heart beats about 100,000 times a day? Or that the blood in your body travels a total of 12,000 miles daily? That's more than four times the width of...