Scott Haltzman, age 10, of Allentown, Pennsylvania, for his question:

How do  fingernails grow?

Each nail has a root that keeps growing new material to make it longer. You might expect the root to be at the tip, because this is where the nail gets longer  ¬or so it seems. Actually, the root is at the opposite end of the nail, farthest from the fingertip. The new material it adds keeps pushing the whole nail forward and the tip grows longer, or so it seems.

The root that keeps growing new nail material is called the matrix. Actually, this matrix is a special little pocket of skin made of extra small cells. It has ex¬tra tiny nerves and extra tiny blood vessels. But it can build special skin cells and pack them together to make nail material. The nail material has no living nerves or blood vessels. There is no pain when we cut or shape the tips. But the matrix root is very sensitive. And if it is badly damaged, the nail material it grows may be twisted out of shape.