Larry Wells, age 9, of Visalia, California, for his question:

How long are all the blood vessels in the body?

The blood vessels in the body come in assorted widths and lengths. Some of the thick ones run most of the way up and down your arms and legs. Some of the thinnest ones are so short that you would need about 50 of them to measure one inch. These little capillary blood vessels are finer than the hairs on your head. All the blood vessels, large and small, are linked together is a branching network that spreads through almost every part of your body. The blood they carry never stops flowing, day or night, as long as you live.

Naturally a person cannot remove all his blood vessels and stretch them out in a long line. But experts can figure just about how long that line should be. They can estimate the total length of the large and small blood vessels in the body of a grown man. The line, they figure, would be longer than 50,000 miles. This is long enough to stretch more than twice around the world's wide equator.