You can see that blood, so necessary for life, is not a simple thing. Many different substances have their special work and importance.

Although the red cells are by far more numerous in the blood and give blood its color, the white blood cells have a critical role, too. The white blood cells are called leukocytes.

The most common leucocytes are granular cells. These cells pass in and out of the blood to the spot where germs or injured tissue have collected Some of these cells, called neutrophiles, take bacteria into themselves and destroy them. They also give off substances which digest and soften dead tissue and form pus.

Other white cells in the blood are called lymphocytes. The lymphocytes often increase in numbers in a part of the body where infection has continued for more than a short time. This is a part of the body’s process for fighting infections, so you can see their job is quite important.

Still other white blood cells are the monocytes. These cells, together with other cells in the tissues, have the ability to take up pieces of dead material. They can also surround material such as dirt, and keep it from coming in contact with healthy tissue cells.

By the way, even though white blood cells are so necessary to the body, too many of them are not good either. When too many white blood cells are formed, and they do not grow into the healthy, active cells that are needed, the condition is called leukemia, or cancer of the blood.

So the blood is like a chemical formula in which there has to be just the right amount of each substance red cells, white cells, proteins, salts carbohydrates, fats, and so on.