I t's called the river of life, the five or six quarts of blood that stream through the 60,000 tortuous miles of arteries, veins, and capillaries.

Blood contains many elements with specific functions—red cells to transport oxygen from the lungs to body tissues, white cells to fight off disease, and tiny elements called platelets to help form clots and repair tears in the blood vessel wall. All float freely in an intricate complex of liquid proteins and metals known as plasma .

Because of the blood's extreme importance to life, any injury to it—or to the grand network of channels through which it flows—may have the most serious consequences. The troubles that beset the circulation may be grouped conveniently into two categories: diseases of the blood and diseases of the blood vessels.

Diseases of the Blood

D iseases of the blood include disorders that affect the blood elements directly (as in the case of hemophilia , where a deficiency in clotting proteins is at fault) as well as abnormalities in the various organs involved in maintaining proper blood balance (i.e., spleen, liver and bone marrow). The various ills designated and described below are arranged according to the blood component most affected (i.e., clotting proteins, red blood cells, and white blood cells).