The blood brings oxygen to the body cells<span> and takes away their carbon dioxide. The blood that travels </span>back<span> to the </span>heart<span> and </span>lungs<span> is </span>dark red<span>. It has picked up carbon dioxide from the </span>body cells<span>, and it has left most of its oxygen with the cells.
</span><span>http://lsa.colorado.edu/essence/texts/lungs.html
</span>
