THE THING ABOUT LIFE IS THAT ONE DAY YOU'LL BE DEAD, by David Shields, Knopf, 231 pages, $23.95.

David Shields is a writer, editor and English professor at the University of Washington. In this delightful and entertaining book, he ponders the nature of mortality, from birth and adolescence through middle age to old age. He calls it a "blend of biological fact, family anecdote, philosophical speculation, cultural history and criticism and quotations from a wide range of writers and thinkers."

Shields is 51 and his father is 97, yet it is the younger Shields who is feeling old. He thinks his father is one of these rare people who is so "alive" that he not only lives a longer life, but a richer life. It both pleases him and irritates him, almost as if it were competitive.

His father, he writes, "is cussedly, maddeningly alive and interesting."

During his meditation, Shields throws out some terribly interesting factual material about life, such as the claim that "infants sleep 20 hours a day, 1-year-olds sleep 13 hours a day, a teenager sleeps 9 hours, a 40-year-old sleeps seven hours, and people 65 and older sleep five hours ...

"By age 65, an unbroken night of sleep is rare; 20 percent of the night consists of lying awake. As I constantly have to remind my now light-sleeping father, people ages 73-92 awake, on average, 21 times a night owing to disordered breathing."

Shortly before his father's 97th birthday, the son asked him what he had learned over such a long life, and his reply was, "The secret of a long, healthy life is to exercise every day even if it's only for 30 minutes, and don't let anything deter you from it."

When the son said he really had meant what life had taught him, not how to live long, and his father shrugged and said, "There's one comforting thing about the aging process: I'll never have to do it again."

Then he said, "On balance, the world is a much better place than it was in Brooklyn, New York, in 1910." Then he regretted not getting his degree from CCNY or his master's in journalism from Columbia — and possibly becoming a sports columnist for the New York Times.

After that, there were tears.

The younger Shields remembers his father working as an umpire for the industrial league, i.e., Machinists v. the Accountants. "But they played with a hardball, they played for blood, their wives cheered like enraged schoolgirls." The first time he saw him umpire was a game between Denny's Restaurant and Safeway Market.

"He was the only umpire working the game," writes Shields, "so on balls hit to the outfield he'd run down the foul line to make sure the ball had been caught, and on balls hit to the infield he'd run to first base to be in position to decide. He signaled safe by spreading his arms and flapping them, as if readying for flight. He signaled out by jerking his thumb, and the entire right side of his body, down. Between innings he juggled three baseballs."

Young Shields has never been very athletic, but he was very proud of his father's work on the baseball diamond.

In the mid-'50s, comedian Danny Kaye played the Hollywood Bowl and Shields' father, Milt, and his wife went to see him. At intermission, Kaye asked how many people had attended P.S. 149, and about 10 people raised their hands. But only Milt Shields said he remembered the P.S. 149 fight song, so he and Kaye sang it together with enthusiasm.

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