Not only does phagocytosis allow us to remove minute, potentially deadly body invaders, but it also is important in the maintenance of healthy tissues. Without this mechanism, harmful materials would accumulate and interfere with the body’s ability to function. A good example is the macrophages (white blood cells in the tissues) of the human spleen and liver, which dispose of more than 10,000,000,000 old (aged) blood cells a day!