The blood does even more than carry food and oxygen to every part of our bodies. Its work is so important that the heart has to keep pumping it day in and day out without ever stopping to rest.
A person who weighs 100 pounds has about four quarts of blood. Bigger people have more. Smaller people have less.
A drop of blood looks like a drop of red ink. But it is much, much more complicated. The liquid part of our blood is not red. Blood looks red because it has many tiny red cells in it. Red cells are far too small to be seen without a microscope. It would take thousands of thern to make a row an inch long. Everyone has billions of red cells in his blood.
The chief work of the red cells is to carry oxygen. They gather it in the lungs and take it to all the other cells of the body.
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